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Chapter 31 - Personal Protection-test

OVERVIEW AND PHILOSOPHY OF PERSONAL PROTECTION

Robert F. Herrick

The entire topic of personal protection must be considered in the context of control methods for preventing occupational injuries and diseases. This article presents a detailed technical discussion of the types of personal protection which are available, the hazards for which their use may be indicated and the criteria for selecting appropriate protective equipment. Where they are applicable, the approvals, certifications and standards which exist for protective devices and equipment are summarized. In using this information, it is essential to be constantly mindful that personal protection should be considered the method of last resort in reducing the risks found in the workplace. In the hierarchy of methods which may be used to control workplace hazards, personal protection is not the method of first choice. In fact, it is to be used only when the possible engineering controls which reduce the hazard (by methods such as isolation, enclosure, ventilation, substitution, or other process changes), and administrative controls (such as reducing work time at risk for exposure) have been implemented to the extent feasible. There are cases, however, where personal protection is necessary, whether as a short-term or a long-term control, to reduce occupational disease and injury risks. When such use is necessary, personal protective equipment and devices must be used as part of a comprehensive programme which includes full evaluation of the hazards, correct selection and fitting of the equipment, training and education for the people who use the equipment, maintenance and repair to keep the equipment in good working order and overall management and worker commitment to the success of the protection programme.

Elements of a Personal Protection Programme

The apparent simplicity of some personal protective equipment can result in a gross underestimation of the amount of effort and expense required to effectively use this equipment. While some devices are relatively simple, such as gloves and protective footwear, other equipment such as respirators can actually be very complex. The factors which make effective personal protection difficult to achieve are inherent in any method which relies upon modification of human behaviour to reduce risk, rather than on protection which is built into the process at the source of the hazard. Regardless of the particular type of protective equipment being considered, there is a set of elements which must be included in a personal protection programme.

Hazard evaluation

If personal protection is to be an effective answer to a problem of occupational risk, the nature of the risk itself and its relationship to the overall work environment must be fully understood. While this may seem so obvious that it barely needs to be mentioned, the apparent simplicity of many protective devices can present a strong temptation to short cut this evaluation step. The consequences of providing protective devices and equipment which are not suitable to the hazards and the overall work environment range from reluctance or refusal to wear inappropriate equipment, to impaired job performance, to risk of worker injury and death. In order to achieve a proper match between the risk and the protective measure, it is necessary to know the composition and magnitude (concentration) of the hazards (including chemical, physical or biological agents), the length of time for which the device will be expected to perform at a known level of protection, and the nature of the physical activity which may be performed while the equipment is in use. This preliminary evaluation of the hazards is an essential diagnostic step which must be accomplished before moving on to selecting the appropriate protection.

Selection

The selection step is dictated in part by the information obtained in hazard evaluation, matched with the performance data for the protective measure being considered for use and the level of exposure which will remain after the personal protective measure is in place. In addition to these performance-based factors, there are guidelines and standards of practice in selecting equipment, particularly for respiratory protection. The selection criteria for respiratory protection have been formalized in publications such as Respirator Decision Logic from the National Institute for Occupational Safety and Health (NIOSH) in the United States. The same sort of logic can be applied to selecting other types of protective equipment and devices, based upon the nature and magnitude of the hazard, the degree of protection provided by the device or equipment, and the quantity or concentration of the hazardous agent which will remain and be considered acceptable while the protective devices are in use. In selecting protective devices and equipment, it is important to recognize that they are not intended to reduce risks and exposures to zero. Manufacturers of devices such as respirators and hearing protectors supply data on the performance of their equipment, such as protection and attenuation factors. By combining three essential pieces of information—namely, the nature and magnitude of the hazard, the degree of protection provided, and the acceptable level of exposure and risk while the protection is in use—equipment and devices can be selected to adequately protect workers.

Fitting

Any protective device must be properly fitted if it is to provide the degree of protection for which it was designed. In addition to the performance of a protective device, proper fit is also an important factor in the acceptance of the equipment and the motivation of people to actually use it. Protection which is ill-fitting or uncomfortable is unlikely to be used as intended. In the worst case, poorly fitted equipment such as clothing and gloves can actually create a hazard when working around machinery. Manufacturers of protective equipment and devices offer a range of sizes and designs of these products, and workers should be provided with protection which fits properly to accomplish its intended purpose.

In the case of respiratory protection, specific requirements for fitting are included in standards such as the United States Occupational Safety and Health Administration’s respiratory protection standards. The principles of assuring proper fit apply over the full range of protective equipment and devices, regardless of whether they are required by a specific standard.

Training and education

Because the nature of protective devices requires modification of human behaviour to isolate the worker from the work environment (rather than to isolate the source of a hazard from the environment), personal protection programmes are unlikely to succeed unless they include comprehensive worker education and training. By comparison, a system (such as local exhaust ventilation) which controls exposure at the source may operate effectively without direct worker involvement. Personal protection, however, requires full participation and commitment by the people who use it and from the management which provides it.

Those responsible for the management and operation of a personal protection programme must be trained in the selection of the proper equipment, in assuring that it is correctly fitted to the people who use it, in the nature of the hazards the equipment is intended to protect against, and the consequences of poor performance or equipment failure. They must also know how to repair, maintain, and clean the equipment, as well as to recognize damage and wear which occurs during its use.

People who use protective equipment and devices must understand the need for the protection, the reasons it is being used in place of (or in addition to) other control methods, and the benefits they will derive from its use. The consequences of unprotected exposure should be clearly explained, as well as the ways users can recognize that the equipment is not functioning properly. Users must be trained in methods of inspecting, fitting, wearing, maintaining, and cleaning protective equipment, and they must also be aware of the limitations of the equipment, particularly in emergency situations.

Maintenance and repair

The costs of equipment maintenance and repair must be fully and realistically assessed in designing any personal protection programme. Protective devices are subject to gradual degradation in performance through normal use, as well as catastrophic failures in extreme conditions such as emergencies. In considering the costs and benefits of using personal protection as a means of hazard control it is very important to recognize that the costs of initiating a programme represent only a fraction of the total expense of operating the programme over time. Equipment maintenance, repair, and replacement must be considered as fixed costs of operating a programme, as they are essential to maintaining the effectiveness of protection. These programme considerations should include such basic decisions as whether single use (disposable) or reusable protective devices should be used, and in the case of reusable devices, the length of service which can be expected before replacement must be reasonably estimated. These decisions may be very clearly defined, as in cases where gloves or respirators are usable only once and are discarded, but in many cases a careful judgement must be made as to the efficacy of reusing protective suits or gloves which have been contaminated by previous use. The decision to discard an expensive protective device rather than risk worker exposure as a result of degraded protection, or contamination of the protective device itself must be made very carefully. Programmes of equipment maintenance and repair must be designed to include mechanisms for making decisions such as these.

Summary

Protective equipment and devices are essential parts of a hazard control strategy. They can be used effectively, provided their appropriate place in the hierarchy of controls is recognized. The use of protective equipment and devices must be supported by a personal protection programme, which assures that the protection actually performs as intended in conditions of use, and that the people who have to wear it can use it effectively in their work activities.

EYE AND FACE PROTECTORS

Kikuzi Kimura

Eye and face protection includes safety spectacles, goggles, face shields and similar items used to protect against flying particles and foreign bodies, corrosive chemicals, fumes, lasers and radiation. Often, the whole face may need protection against radiation or mechanical, thermal or chemical hazards. Sometimes a face shield may be adequate also for protecting the eyes, but often specific eye protection is necessary, either separately or as a complement to the face protection.

A wide range of occupations require eye and face protectors: hazards include flying particles, fumes or corrosive solids, liquids or vapours in polishing, grinding, cutting, blasting, crushing, galvanizing or various chemical operations; against intensive light as in laser operations; and against ultraviolet or infrared radiation in welding or furnace operations. Of the many types of eye and face protection available, there is a correct type for each hazard. Whole-face protection is preferred for certain severe risks. As needed, hood or helmet type face protectors and face shields are used. Spectacles or goggles may be used for specific eye protection.

The two basic problems in wearing eye and face protectors are (1) how to provide effective protection which is acceptable for wearing over long hours of work without undue discomfort, and (2) the unpopularity of eye and face protection due to restriction of vision. The wearer’s peripheral vision is limited by the side frames; the nose bridge may disturb binocular vision; and misting is a constant problem. Particularly in hot climates or in hot work, additional coverings of the face may become intolerable and may be discarded. Short-term, intermittent operations also create problems as workers may be forgetful and disinclined to use protection. First consideration should always be given to the improvement of the working environment rather than to the possible need for personal protection. Before or in conjunction with the use of eye and face protection, consideration must be given to guarding of machines and tools (including interlocking guards), removal of fumes and dust by exhaust ventilation, screening of sources of heat or radiation, and screening of points from which particles may be ejected, such as abrasive grinders or lathes. When the eyes and face can be protected by the use of transparent screens or partitions of appropriate size and quality, for example, these alternatives are to be preferred to the use of personal eye protection.

There are six basic types of eye and face protection:

1.     spectacle type, either with or without side shields (figure 31.1)

Figure 31.1 Common types of spectacles for eye protection with or without sideshield

2.     eye cup (goggle) type (figure 31.2)

Figure 31.2 Examples of goggle-type eye protectors

3.     face shield type, covering eye sockets and the central portion of the face (figure 31.3)

Figure 31.3 Face shield type protectors for hot work

4.     helmet type with shielding of the whole front of the face (figure 31.4)

Figure 31.4 Protectors for welders

5.     hand-held shield type (see figure 31.4)

6.     hood type, including the diver’s helmet type covering the head completely (see figure 31.4)

There are goggles that may be worn over corrective spectacles. It is often better for the hardened lenses of such goggles to be fitted under the guidance of an ophthalmic specialist.

Protection against Specific Hazards

Traumatic and chemical injuries. Face shields or eye protectors are used against flying  particles, fumes, dust and chemical hazards. Common types are spectacles (often with side shields), goggles, plastic eye shields and face shields. The helmet type is used when injury risks are expected from various directions. The hood type and the diver’s helmet type are used in sand- and shot-blasting. Transparent plastics of various sorts, hardened glass or a wire screen may be used for protection against certain foreign bodies. Eye cup goggles with plastic or glass lenses or plastic eye shields as well as a diver’s helmet type shield or face shields made of plastic are used for protection against chemicals.

Materials commonly used include polycarbonates, acrylic resins or fibre-based plastics. Polycarbonates are effective against impacts but may not be suitable against corrosives. Acrylic protectors are weaker against impacts but suitable for protection from chemical hazards. Fibre-based plastics have the advantage of adding anti-misting coating. This anti-misting coating also prevents electrostatic effects. Thus such plastic protectors may be used not only in physically light work or chemical handling but also in modern clean-room work.

Thermal radiation. Face shields or eye protectors against infrared radiation are used mainly in furnace operations and other hot work involving exposure to high-temperature radiation sources. Protection is usually necessary at the same time against sparks or flying hot objects. Face protectors of the helmet type and the face shield type are mainly used. Various materials are used, including metal wire meshes, punched aluminium plates or similar metal plates, aluminized plastic shields or plastic shields with gold layer coatings. A face shield made of wire mesh can reduce thermal radiation by 30 to 50%. Aluminized plastic shields give good protection from radiant heat. Some examples of face shields against thermal radiation are given in figure 31.3 .

Welding. Goggles, helmets or shields that give maximum eye protection for each welding and cutting process should be worn by operators, welders and their helpers. Effective protection is needed not only against intensive light and radiation but also against impacts upon the face, head and neck. Fibreglass-reinforced plastic or nylon protectors are effective but rather expensive. Vulcanized fibres are commonly used as shield material. As shown in figure 31.4 , both helmet type protectors and hand-held shields are used to protect the eyes and face at the same time. Requirements for correct filter lenses to be used in various welding and cutting operations are described below.

Wide spectral bands. Welding and cutting processes or furnaces emit radiations in the ultraviolet, visible and infrared bands of the spectrum, which are all able to produce harmful effects upon the eyes. Spectacle type or goggle type protectors similar to those shown in figure 31.1 and figure 31.2 as well as welders' protection such as those shown in figure 31.4  can be used. In welding operations, helmet type protection and hand-shield type protectors are generally used, sometimes in conjunction with spectacles or goggles. It should be noted that protection is necessary also for the welder’s assistant.

Transmittance and tolerances in transmittance of various shades of filter lenses and filter plates of eye protection against high-intensity light are shown in table 31.1. Guides for selecting correct filter lenses in terms of the scales of protection are given in table 31.2, table 31.3, table 31.4, table 31.5 and table 31.6 .

Table 31.1 Transmittance requirements (ISO 4850-1979)

Scale number

Maximum transmittance in the ultraviolet spectrum

Luminous transmittance

Maximum mean transmittance in the infrared spectrum

 

t λ

τV

τNIR

τMIR

 

313 nm%

365 nm%

maximum%

minimum%

Near IR 1,300 to 780 nm%

Mid. IR 2,000 to 1,300 nm %

1.2

0.0003

50

100

74.4

37

37

1.4

0.0003

35

74.4

58.1

33

33

1.7

0.0003

22

58.1

43.2

26

26

2.0

0.0003

14

43.2

29.1

21

13

2.5

0.0003

6.4

29.1

17.8

15

9.6

3

0.0003

2.8

17.8

8.5

12

8.5

4

0.0003

0.95

8.5

3.2

6.4

5.4

5

0.0003

0.30

3.2

1.2

3.2

3.2

6

0.0003

0.10

1.2

0.44

1.7

1.9

7

0.0003

0.037

0.44

0.16

0.81

1.2

8

0.0003

0.013

0.16

0.061

0.43

0.68

9

0.0003

0.0045

0.061

0.023

0.20

0.39

10

0.0003

0.0016

0.023

0.0085

0.10

0.25

11

Value less than or equal to transmittance permitted for 365 nm

0.00060

0.0085

0.0032

0.050

0.15

12

 

0.00020

0.0032

0.0012

0.027

0.096

13

 

0.000076

0.0012

0.00044

0.014

0.060

14

 

0.000027

0.00044

0.00016

0.007

0.04

15

 

0.0000094

0.00016

0.000061

0.003

0.02

16

 

0.0000034

0.000061

0.000029

0.003

0.02

Taken from ISO 4850:1979 and reproduced with the permission of the International Organization for  Standardization (ISO). These standards can be obtained from any ISO member or from the ISO  Central Secretariat, Case postale 56, 1211 Geneva 20, Switzerland. Copyright remains with ISO.

Table 31.2 Scales1 of protection to be used for gas-welding and braze-welding

Work to be carried out

l = flow rate of acetylene, in litres per hour

 

l ≤ 70

70 < l ≤ 200

200 < l ≤ 800

l > 800

Welding and braze-welding  of heavy metals

4

5

6

7

Welding with emittive  fluxes (notably light alloys)

4a

5a

6a

7a

1 According to the conditions of use, the next greater or the next smaller scale can be used.

Taken from ISO 4850:1979 and reproduced with the permission of the International Organization  for Standardization (ISO). These standards can be obtained from any ISO member or from the ISO  Central Secretariat, Case postale 56, 1211 Geneva 20, Switzerland. Copyright remains with ISO

Table 31.3 Scales1 of protection to be used for oxygen cutting

Work to be carried out

Flow rate of oxygen, in litres per hour

 

900 to 2,000

2,000 to 4,000

4,000 to 8,000

Oxygen cutting

5

6

7

1 According to the conditions of use, the next greater or the next smaller scale can be used.

NOTE: 900 to 2,000 and 2,000 to 8,000 litres of oxygen per hour, correspond fairly closely to the  use of cutting nozzles diameters of 1 to 1.5 and 2 mm respectively.

Taken from ISO 4850:1979 and reproduced with the permission of the International Organization  for Standardization (ISO). These standards can be obtained from any ISO member or from the ISO  Central Secretariat, Case postale 56, 1211 Geneva 20, Switzerland. Copyright remains with ISO.

Table 31.4 Scales1 of protection to be used for plasma arc cutting

Work to be carried out

l = Current, in amperes

 

l ≤ 150

150 < l ≤ 250

250 < l ≤ 400

Thermal cutting

11

12

13

1 According to the conditions of use, the next greater or the next smaller scale can be used.

Taken from ISO 4850:1979 and reproduced with the permission of the International Organization  for Standardization (ISO). These standards can be obtained from any ISO member or from the ISO  Central Secretariat, Case postale 56, 1211 Geneva 20, Switzerland. Copyright remains with ISO.

Table 31.5 Scales1 of protection to be used for electric arc welding or arc gouging.

1 According to the conditions of use, the next greater or the next smaller scale can be used.

2 The expression "heavy metals" applies to steels, alloy steels, copper and its alloys, etc.

NOTE: The hatched areas correspond to the ranges where the welding operations are not usually used in the current practice of manual welding.

Source: ISO 4850.

Table 31.6 Scales1 of protection to be used for plasma direct arc welding.

1 According to the conditions of use, the next greater or the next smaller scale can be used.

The hatched areas correspond to the ranges where the welding operations are not usually used in the current practice of manual welding.

Source: ISO 4850.

A new development is the use of filter plates made of welded crystal surfaces which increase their protective shade as soon as the welding arc starts. The time for this nearly instantaneous shade increase can be as short as 0.1 ms. The good visibility through the plates in non-welding situations can encourage their use.

Laser beams. No one type of filter offers protection from all laser wavelengths. Different kinds of lasers vary in wavelength, and there are lasers that produce beams of various wavelengths or those whose beams change their wavelengths by passing through optical systems. Consequently, laser-using firms should not depend solely on laser protectors to protect an employee’s eyes from laser burns. Nevertheless, laser operators do frequently need eye protection. Both spectacles and goggles are available; they have shapes similar to those shown in figure 31.1 and figure 31.2 . Each kind of eyewear has maximum attenuation at a specific laser wavelength. Protection falls off rapidly at other wavelengths. It is essential to select the correct eyewear appropriate for the kind of laser, its wavelength and optical density. The eyewear is to provide protection from reflections and scattered lights and the utmost precautions are necessary to foresee and avoid harmful radiation exposure.

With the use of eye and face protectors, due attention must be paid to greater comfort and efficiency. It is important that the protectors be fitted and adjusted by a person who has received some training in this task. Each worker should have the exclusive use of his or her own protector, while communal provision for cleaning and demisting may well be made in larger works. Comfort is particularly important in helmet and hood type protectors as they may become almost intolerably hot during use. Air lines can be fitted to prevent this. Where the risks of the work process allow, some personal choice among different types of protection is psychologically desirable.

The protectors should be examined regularly to ensure that they are in good condition. Care should be taken that they give adequate protection at all times even with the use of corrective vision devices.

FOOT AND LEG PROTECTION

Toyohiko Miura

Injuries to the foot and leg are common to many industries. The dropping of a heavy object may injure the foot, particularly the toes, in any workplace, especially among workers in the heavier industries such as mining, metal manufacture, engineering and building and construction work. Burns of the lower limbs from the molten metals, sparks or corrosive chemicals occur frequently in foundries, iron- and steelworks, chemical plants and so on. Dermatitis or eczema may be caused by a variety of acidic, alkaline and many other agents. The foot may also suffer physical injury caused by striking it against an object or by stepping on sharp protrusions such as can occur in the construction industry.

Improvements in the work environment have made the simple puncturing and laceration of the worker’s foot by protruding floor nails and other sharp hazards less common, but accidents from working on damp or wet floors still occur, particularly when wearing unsuitable foot wear.

Types of Protection.

The type of foot and leg protection should be related to the risk. In some light industries, it may be sufficient hat workers wear well-made ordinary shoes. Many women, for example will wear footwear that is comfortable to them, such as sandals or old slippers, or footwear with very high or worn-down heels. This practice should be discouraged because such footwear can cause an accident.

Sometimes a protective shoe or clog is adequate, and sometimes a boot or leggings will be required (see figure 31.5, figure 31.6 and figure 31.7). The height to which the footwear covers the ankle, knee or thigh depends on the hazard, although comfort and mobility will also have to be considered. Thus shoes and gaiters may in some circumstances be preferable to high boots.

Figure 31.5 Safety shoes

Figure 31.6 Heat protective boots

Figure 31.7 Safety sneakers

Protective shoes and boots may be made from leather, rubber, synthetic rubber or plastic and may be fabricated by sewing, vulcanizing or moulding. Since the toes are most vulnerable to impact injuries, a steel toe cap is the essential feature of protective footwear wherever such hazards exist. For comfort the toe cap must be reasonably thin and light, and carbon tool steel is therefore used for this purpose. These safety toe caps may be incorporated into many types of boots and shoes. In some trades where falling objects present a particular risk, metal instep guards may be fitted over protective shoes.

Rubber or synthetic outer soles with various tread patterns are used to minimize or prevent the risk of slipping: this is especially important where floors are likely to be wet or slippery. The material of the sole appears to be of more importance than the tread pattern and should have a high coefficient of friction. Reinforced, puncture-proof soles are necessary in such places as construction sites; metallic insoles can also be inserted into various types of footwear that lack this protection.

Where an electrical hazard exists, shoes should be either entirely stitched or cemented, or directly vulcanized in order to avoid the need for nails or any other electrically conductive fasteners. Where static electricity may be present, protective shoes should have electrically conductive rubber outer soles to allow static electricity to leak from the bottom of the shoes.

Footwear with a dual purpose has now come into common use: these are shoes or boots that have both anti-electrostatic properties mentioned above together with the ability to protect the wearer from receiving an electrical shock when in contact with a low-voltage electrical source. In the latter case, the electrical resistance between the insole and the outer sole must be controlled in order to provide this protection between a given voltage range.

In the past, “safety and durability” were the only considerations. Now, worker comfort has also been taken into account, so that lightness, comfort and even attractiveness in protective shoes are sought-after qualities. The “safety sneaker” is one example of this kind of footwear. Design and colour may come to play a part in the use of footwear as an emblem of corporate identity, a matter that receives special attention in countries like Japan, to name only one.

Synthetic rubber boots offer useful protection from chemical injuries: the material should show not more than 10% reduction in tensile strength or elongation after immersion in a 20% solution of hydrochloric acid for 48 hours at room temperature.

Especially in environments where molten metals or chemical burns are a major hazard, it is important that shoes or boots should be without tongues and that the fastenings should be pulled over the top of the boot and not tucked inside.

Rubber or metallic spats, gaiters or leggings may be used to protect the leg above the shoe line, especially from risks of burns. Protective knee pads may be necessary, especially where work involves kneeling, for example in some foundry moulding. Aluminized heat-protective shoes, boots or leggings will be necessary near sources of intense heat.

Use and Maintenance

All protective footwear should be kept clean and dry when not in use and should be replaced as soon as necessary. In places where the same rubber boots are used by several people, regular arrangements for disinfection between each use should be made to prevent the spread of foot infections. A danger of foot mycosis exists that arises from the use of too tight and too heavy types of boots or shoes.

The success of any protective footwear depends upon its acceptability, a reality that is now widely recognized in the far greater attention that is now paid to styling. Comfort is a prerequisite and the shoes should be as light as is consistent with their purpose: shoes weighing more than two kilogram per pair should be avoided.

Sometimes foot and leg safety protection is required by law to be provided by the employers. Where the employers are interested in progressive programmes and not just meeting legal obligations, concerned companies often find it very effective to provide some arrangement for easy purchase at the place of work. And if protective wear can be offered at wholesale price, or arrangements for convenient extended payment terms are made available, workers may be more willing and able to purchase and use better equipment. In this way, the type of protection obtained and worn can be better controlled. Many conventions and regulations, however, do consider supplying workers with work clothing and protective equipment to be the employer’s obligation.

HEAD PROTECTION

Isabelle Balty and Alain Mayer

Head Injuries

Head injuries are fairly common in industry and account for 3 to 6% of all industrial injuries in industrialized countries. They are often severe and result in an average lost time of about three weeks. The injuries sustained are generally the result of blows caused by the impact of angular objects such as tools or bolts falling from a height of several metres; in other cases, workers may strike their heads in a fall to a floor or suffer a collision between some fixed object and their heads.

A number of different types of injury have been recorded:

·     perforation of the skull resulting from the application of an excessive force to a very localized area, as for example in the case of direct contact with a pointed or sharp-edged object

·     fracture of the skull or of the cervical vertebrae occurring when an excessive force is applied on a larger area, stressing the skull beyond the limits of its elasticity or compressing the cervical portion of the spine

·     brain lesions without fracture of the skull resulting from the brain being displaced suddenly within the skull, which may lead to contusion, concussion, haemorrhage of the brain or circulatory problems.

Understanding the physical parameters that account for these various types of injury is difficult, although of fundamental importance, and there is considerable disagreement in the extensive literature published on this subject. Some specialists consider that the force involved is the principal factor to be considered, while others claim that it is a matter of energy, or of the quantity of movement; further opinions relate the brain injury to acceleration, to acceleration rate, or to a specific shock index such as HIC, GSI, WSTC. In most cases, each one of these factors is likely to be involved to a greater or lesser extent. It may be concluded that our knowledge of the mechanisms of shocks to the head is still only partial and controversial. The shock tolerance of the head is determined by means of experimentation on cadavers or on animals, and it is not easy to extrapolate these values to a living human subject.

On the basis of the results of analyses of accidents sustained by building workers wearing safety helmets, however, it seems that head injuries due to shocks occur when the quantity of energy involved in the shock is in excess of about 100 J.

Other types of injuries are less frequent but should not be overlooked. They include burns resulting from splashes of hot or corrosive liquids or molten material, or electrical shocks resulting from accidental contact of the head with exposed conductive parts.

Safety Helmets

The chief purpose of a safety helmet is to protect the head of the wearer against hazards, mechanical shocks. It may in addition provide protection against other for example, mechanical, thermal and electrical.

A safety helmet should fulfil the following requirements in order to reduce the harmful effects of shocks to the head:

1.     It should limit the pressure applied to the skull by spreading the load over the largest possible surface. This is achieved by providing a sufficiently large harness that closely match various skull shapes, together with a hard shell strong enough to prevent the head from coming into direct contact with accidentally falling objects and to provide protection if the wearer’s head should hit a hard surface (figure 31.8). The shell must therefore resist deformation and perforation.

Figure 31.8 Example of essential elements of safety helmet construction

2.     It should deflect falling objects by having a suitably smooth and rounded shape. A helmet with protruding ridges tends to arrest falling objects rather than to deflect them and thus retain slightly more kinetic energy than helmets which are perfectly smooth.

3.     It should dissipate and disperse the energy that may be transmitted to it in such a way that the energy is not passed totally to the head and neck. This is achieved by means of the harness, which must be securely fixed to the hard shell so that it can absorb a shock without being detached from the shell. The harness must also be flexible enough to undergo deformation under impact without touching the inside surface of the shell. This deformation, which absorbs most of the energy of a shock, is limited by the minimum amount of clearance between the hard shell and the skull and by the maximum elongation of the harness before it breaks. Thus the rigidity or stiffness of the harness should be the result of a compromise between the maximum amount of energy that it is designed to absorb and the progressive rate at which the shock is to be allowed to be transmitted to the head.

Other requirements may apply to helmets used for particular tasks. These include protection against splashes of molten metal in the iron and steel industry and protection against electrical shock by direct contact in the case of helmets used by electrical technicians.

Materials used in the manufacture of helmets and harnesses should retain their protective qualities over a long period of time and under all foreseeable climatic conditions, including sun, rain, heat, bela-freezing temperature, and so on. Helmets should also have a fairly good resistance to flame and should not break if dropped onto a hard surface from a height of a few metres.

Performance Tests

ISO International Standard No. 3873-1977 was published in 1977 as a result of the work of the subcommittee dealing especially with “industrial safety helmets”. This standard, approved by practically all the member states of the ISO, sets out the essential features required of a safety helmet together with the related testing methods. These tests may be divided into two groups (see table 31.7), namely:

1.     obligatory tests, to be applied to all types of helmets for whatever use they may be intended: shock-absorbing capacity, resistance to perforation and resistance to flame

2.     optional tests, intended to be applied to safety helmets designed for special groups of users: dielectric strength, resistance to lateral deformation and resistance to low temperature.

Table 31.7 Safety helmets: testing requirements of ISO Standard 3873-1977

Characteristic

Description

Criteria

Obligatory tests

Absorption of shocks

A hemispherical mass of 5 kg is allowed to fall from a height of  1 m and the force transmitted by the helmet to fixed false (dummy) head is measured.

The maximum force measured should not exceed 500 daN.

 

The test is repeated on a helmet at temperatures of -10°, +50°C and under wet conditions.,

 

Resistance to penetration

The helmet is struck within a zone of 100 mm in diameter on its uppermost point using a conical punch weighing 3 kg and a tip angle of 60°.

The tip of the punch must not come into contact with the false (dummy) head.

 

Test to be performed under the conditions which gave the worst results in the shock test.,

 

Resistance to flame

The helmet is exposed for 10 s to a Bunsen burner flame of 10 mm in diameter using propane.

The outer shell should not continue to burn more than 5 s after it has been withdrawn from the flame.

Optional tests

Dielectric strength

The helmet is filled with a solution of NaCl and is itself immersed in a bath of the same solution. The electric leakage under an applied voltage of 1200 V, 50 Hz is measured.

The leakage current should not be greater than 1.2 mA.

Lateral rigidity

The helmet is placed sideways between two parallel plates and subjected to a compressive pressure of 430 N

The deformation under load should not exceed 40 mm, and the permanent deformation should not be more than 15 mm.

Low-temperature test

The helmet is subject to the shock and penetration tests at a temperature of -20°C.

The helmet must fulfil the foregoing requirements for these two tests.

The resistance to ageing of the plastic materials used in the manufacture of helmets is not specified in ISO No. 3873-1977. Such a specification should be required for helmets made out of plastic materials. A simple test consists in exposing the helmets to a high-pressure, quartz-envelope 450 watt xenon lamp over a period of 400 hours at a distance of 15 cm, followed by a check to ensure that the helmet can still withstand the appropriate penetration test.

It is recommended that helmets intended for use in the iron and steel industry be subjected to a test for resistance to splashes of molten metal. A quick way of carrying out this test is to allow 300 grams of molten metal at 1,300°C to drop onto the top of a helmet and to check that none has passed through to the interior.

The European Standard EN 397 adopted in 1995 specifies requirements and test methods for these two important characteristics.

Selection of a Safety Helmet

The ideal helmet providing protection and perfect comfort in every situation has yet to be designed. Protection and comfort are indeed often conflicting requirements. As regards protection, in selecting a helmet, the hazards against which protection is required and the conditions under which the helmet will be used must be considered with specific attention to the characteristics of the available safety products.

General considerations

It is advisable to choose helmets complying with the recommendations of ISO Standard No. 3873 (or its equivalent). The European Standard EN 397-1993 is used as a reference for the certification of helmets in application of the 89/686/EEC directive: equipment undergoing such certification, as is the case with almost all personal protective equipment, is submitted to a mandatory third party certification before being put onto the European market. In any case, helmets should meet the following requirements:

1.     A good safety helmet for general use should have a strong shell able to resist deformation or puncture (in the case of plastics, the shell wall should be not less than 2 mm in thickness), a harness fixed in such a way as to ensure that there is always a minimum clearance of 40 to 50 mm between its upper side and the shell, and an adjustable headband fitted to the cradle to ensure a close and stable fit (see figure 31.8).

2.     The best protection against perforation is provided by helmets made of thermoplastic materials (polycarbonates, ABS, polyethylene and polycarbonate–glass fibre) and fitted with a good harness. Helmets made of light metal alloys do not stand up well to puncture by pointed or sharp-edged objects.

3.     Helmets with protruding parts inside the shell should not be used, as these may cause serious injuries in the case of a sideways blow; they should be fitted with a lateral protective padding that must be neither flammable nor subject to melting under the effect of heat. A padding made of fairly rigid and flame resistant foam, 10 to 15 mm thick and at least 4 cm wide will serve this purpose.

4.     Helmets made of polyethylene, polypropylene or ABS tend to lose their mechanical strength under the effects of heat, cold and particularly heavy exposure to sunlight or ultraviolet (UV) radiation. If such helmets are regularly used in the open air or near UV sources like welding stations, they should be replaced at least every three years. Under such conditions, it is recommended that polycarbonate, polyester or polycarbonate–glass fibre helmets be used, as these have a better resistance to ageing. In any case, any evidence of discoloration, cracks, shredding of fibres or of creaking when the helmet is twisted, should cause the helmet to be discarded.

5.     Any helmet that has been submitted to a heavy blow, even if there are no evident signs of damage, should be discarded.

Special considerations

Helmets made of light alloys or having a brim along the sides should not be used in workplaces where there is a hazard of molten metal splashes. In such cases, the use of polyester–glass fibre, phenol textile, polycarbonate–glass fibre or polycarbonate helmets is recommended.

Where there is a hazard of contact with exposed conductive parts, only helmets made of thermoplastic material should be used. They should not have ventilation holes and no metal parts such as rivets should appear on the outside of the shell.

Helmets for persons working overhead, particularly steel framework erectors, should be provided with chin straps. The straps should be about 20 mm in width and should be such that the helmet is held firmly in place at all times.

Helmets made largely of polyethene are not recommended for use at high temperatures. In such cases, polycarbonate, polycarbonate–glass fibre, phenol textile, or polyester–glass fibre helmets are more suitable. The harness should be made of woven fabric. Where there is no hazard of contact with exposed conductive parts, ventilation holes in the helmet shell may be provided.

Situations where there is a crushing hazard call for helmets made of glass–fibre reinforced polyester or polycarbonate having a rim with a width of not less than 15 mm.

Comfort considerations

In addition to safety, consideration should also be given to the physiological aspects of comfort for the wearer.

The helmet should be as light as possible, certainly not more than 400 grams in weight. Its harness should be flexible and permeable to liquid and should not irritate or injure the wearer; for this reason, harnesses of woven fabric are to be preferred to those made of polyethene. A full or half leather sweatband should be incorporated not only in order to provide sweat absorption but also to reduce skin irritation; it should be replaced several times during the life of the helmet for hygienic reasons. To ensure better thermal comfort, the shell should be of a light colour and have ventilation holes with a surface range of 150 to 450 mm2. Careful adjustment of the helmet to fit the wearer is necessary in order to ensure its stability and to prevent its slipping and reducing the field of vision. Various helmet shapes are available, the most common being the “cap” shape with a peak and a brim around the sides; for work in quarries and on demolition sites, the “hat” type of helmet with a wider brim provides better protection. A “skull-cap” shaped helmet without a peak or a brim is particularly suitable for persons working overhead as this pattern precludes a possible loss of balance caused by the peak or brim coming into contact with joists or girders among which the worker may have to move.

Accessories and Other Protective Headgear

Helmets may be fitted with eye or face shields made of plastic material, metallic mesh or optical filters; hearing protectors, chin straps and nape straps to keep the helmet firmly in position; and woollen neck protectors or hoods against wind or cold (figure 31.9). For use in mines and underground quarries, attachments for a headlamp and a cable holder are fitted.

Figure 31.9 Example of safety helmet with chin strap (a), optical filter (b) and woolen neck protector against wind and cold (c).

Other types of protective headgear include those designed for protection against dirt, dust, scratches and bumps. Sometimes known as “bump caps,” these are made of light plastic material or linen. For persons working near machine tools such as drills, lathes, spooling machines and so forth, where there is a risk of the hair being caught, linen caps with a net, peaked hair nets or even scarves or turbans may be used, provided that they have no exposed loose ends.

Hygiene and Maintenance

All protective headgear should be cleaned and checked regularly. If splits or cracks appear, or if a helmet shows signs of ageing or deterioration of the harness, the helmet should be discarded. Cleaning and disinfection are particularly important if the wearer sweats excessively or if more than one person share the same headgear.

Substances adhering to a helmet such as chalk, cement, glue or resin may be removed mechanically or by using an appropriate solvent that does not attack the shell material. Warm water with a detergent may be used with a hard brush.

For disinfecting headgear, articles should be dipped into a suitable disinfecting solution such as a 5% formalin solution or a sodium hypochlorite solution.

HEARING PROTECTION

John R. Franks and Elliott H. Berger

Hearing Protectors

No one knows when people first discovered that covering the ears with the flats of the hands or plugging up the ear canals with one’s fingers was effective in reducing the level of unwanted sound—noise—but the basic technique has been in use for generations as the last line of defence against loud sound. Unfortunately, this level of technology precludes the use of most others. Hearing protectors, an obvious solution to the problem, are a form of noise control in that they block the path of the noise from the source to the ear. They come in various forms, as depicted in figure 31.10 .

Figure 31.10 Examples of different types of hearing protectors

An earplug is a device worn in the external ear canal. Premolded earplugs are available in one or more standard sizes intended to fit into the ear canals of most people. A formable, user-molded earplug is made of a pliable material that is shaped by the wearer to fit into the ear canal to form an acoustic seal. A custom-molded earplug is individually made to fit the particular ear of the wearer. Earplugs can be made from vinyl, silicone, elastomer formulations, cotton and wax, spun glass wool, and slow-recovery closed-cell foam.

A semi-insert earplug, also called an ear-canal cap, is worn against the opening of the external ear canal: the effect is similar to plugging one’s ear canal with a fingertip. Semi-insert devices are manufactured in one size and are designed to fit most ears. This sort of device is held in place by a lightweight headband with mild tension.

An earmuff is a device composed of a headband and two circumaural cups that are usually made of plastic. The headband may be made of metal or plastic. The circumaural ear cup completely encloses the outer ear and seals against the side of the head with a cushion. The cushion may be made of foam or it may be filled with fluid. Most earmuffs have a lining inside the ear cup to absorb the sound that is transmitted through the shell of the ear cup in order to improve the attenuation above approximately 2,000 Hz. Some earmuffs are designed so that the headband may be worn over the head, behind the neck or under the chin, although the amount of protection they afford may be different for each headband position. Other earmuffs are designed to fit on “hard hats.” These may offer less protection because the hard-hat attachment makes it more difficult to adjust the earmuff and they do not fit as wide a range of head sizes as do those with headbands.

In the United States there are 53 manufacturers and distributors of hearing protectors who, as of July 1994, sold 86 models of earplugs, 138 models of earmuffs, and 17 models of semi-insert hearing protectors. In spite of the diversity of hearing protectors, foam earplugs designed for one-time use account for more than half of the hearing protectors in use in the United States.

Last line of defence

The most effective way to avoid noise-induced hearing loss is to stay out of hazardous noise areas. In many work settings it is possible to redesign the manufacturing process so that operators work in enclosed, sound-attenuating control rooms. The noise is reduced in these control rooms to the point where it is not hazardous and where speech communication is not impaired. The next most effective way to avoid noise-induced hearing loss is to reduce the noise at the source so that it is no longer hazardous. This is often done by designing quiet equipment or retrofitting noise control devices to existing equipment.

When it is not possible to avoid the noise or to reduce the noise at the source, hearing protection becomes the last resort. As the last line of defence, having no backup, its effectiveness can often be abridged.

One of the ways to diminish the effectiveness of hearing protectors is to use them less than 100% of the time. Figure 31.11  shows what happens. Eventually, no matter how much protection is afforded by design, protection is reduced as percent of wearing time decreases. Wearers who remove an earplug or lift an earmuff to talk with fellow workers in noisy environments can severely reduce the amount of protection they receive.

Figure 31.11 Decrease in effective protection as time of non-use during an 8-hour day increases  (based on 3-dB exchange rate)

The Rating Systems and How to Use Them

There are many ways to rate hearing protectors. The most common methods are the single-number systems such as the Noise Reduction Rating (NRR) (EPA 1979) used in the United States and the Single Number Rating (SNR), used in Europe (ISO 1994). Another European rating method is the HML (ISO 1994) that uses three numbers to rate protectors. Finally, there are methods based on the attenuation of the hearing protectors for each of the octave bands, called the long or octave-band method in the United States and the assumed protection value method in Europe (ISO 1994).

All of these methods use the real-ear attenuation at threshold values of the hearing protectors as determined in laboratories according to relevant standards. In the United States, attenuation testing is done in accordance with ANSI S3.19, Method for the Measurement of Real-Ear Protection of Hearing Protectors and Physical Attenuation of Earmuffs (ANSI 1974). Although this standard has been replaced by a newer one (ANSI 1984), the US Environmental Protection Agency (EPA) controls the NRR on hearing protector labels and requires the older standard to be used. In Europe attenuation testing is done in accordance with ISO 4869-1 (ISO 1990).

In general, the laboratory methods require that sound-field hearing thresholds be determined both with the protectors fitted and with the ears open. In the United States the hearing protector must be fitted by the experimenter, while in Europe the subject, assisted by the experimenter, performs this task. The difference between the protectors-fitted and ears-open sound field thresholds is the real-ear attenuation at threshold. Data are collected for a group of subjects, presently ten in the United States with three trials each and 16 in Europe with one trial each. The average attenuation and associated standard deviations are calculated for each octave band tested.

For purposes of discussion, the NRR method and the long method are described and illustrated in table 31.8 .

Table 31.8 Example calculation of the Noise Reduction Rating (NRR) of a hearing protector

Procedure:

1. Tabulate the sound pressure levels of pink noise, arbitrarily set for simplicity of computation  to a level of 100 dB in each octave band.

2. Tabulate the adjustments for the C-weighting scale at each octave-band centre frequency.

3. Add lines 1 and 2 to obtain the C-weighted octave-band levels and logarithmically combine  the C-weighted octave-band levels to determine the C-weighted sound pressure level.

4. Tabulate the adjustments for the A-weighting scale at each octave-band centre frequency.

5. Add line 1 and line 4 to obtain the A-weighted octave-band levels.

6. Tabulate the attenuation provided by the device.

7. Tabulate the standard deviations of attenuation (times 2) provided by the device.

8. Subtract the values of the mean attenuations (step 6) and add the values of the standard  deviations times 2 (step 7) to the A-weighted values (step 5) to obtain the estimated A-weighted  octave-band sound levels under the device as it was fitted and tested in the laboratory. Combine  the A-weighted octave-band levels logarithmically to obtain the A-weighted sound level effective  when the device is worn.

9. Subtract the A-weighted sound pressure level (step 8) and a 3-dB safety factor from the  C-weighted sound pressure level (step 3) to obtain the NRR.

Steps

Octave-band center frequency in Hz

 

125

250

500

1000

2000

4000

8000

dBX

1. Assumed octave-band level of noise

100.0

100.0

100.0

100.0

100.0

100.0

100.0

 

2. C-weighting correction

-0.2

0.0

0.0

0.0

-0.2

-0.8

-3.0

 

3. C-weighted octave-band levels

99.8

100.0

100.0

100.0

99.8

99.2

97.0

107.9 dBC

4. A-weighting correction

-16.1

-8.6

-3.2

0.0

+1.2

+1.0

-1.1

 

5. A-weighted octave-band levels

83.9

91.4

96.8

100.0

101.2

101.0

98.9

 

6. Attenuation of hearing protector

27.4

26.6

27.5

27.0

32.0

46.01

44.22

 

7. Standard deviation × 2

7.8

8.4

9.4

6.8

8.8

7.33

12.84

 

8. Estimated protected A-weighted octave band levels

64.3

73.2

78.7

79.8

78.0

62.3

67.5

84.2 dBA

9. NRR = 107.9 - 84.2 - 3 = 20.7 (Step 3 - Step 8 - 3 db5)

               

1 Mean attenuation at 3000 and 4000 Hz.

2 Mean attenuation at 6000 and 8000 Hz.

3 Sum of standard deviations at 3000 and 4000 Hz.

4 Sum of standard deviations at 6000 and 8000 Hz.

5 The 3-dB correction factor is intended to account for spectrum uncertainty in that the noise in which  the hearing protector is to be worn may deviate from the pink-noise spectrum used to calculate the NRR.

The NRR may be used to determine the protected noise level, that is, the effective A-weighted sound pressure level at the ear, by subtracting it from the C-weighted environmental noise level. Thus, if the C-weighted environmental noise level was 100 dBC and the NRR for the protector was 21 dB, the protected noise level would be 79 dBA (100–21 = 79). If only the A-weighted environmental noise level is known, a 7-dB correction is used (Franks, Themann and Sherris 1995). So, if the A-weighted noise level was 103 dBA, the protected noise level would be 89 dBA (103–[21-7] = 89).

The long method requires that the octave-band environmental noise levels be known; there is no shortcut. Many modern sound level meters can simultaneously measure octave-band, C-weighted and A-weighted environmental noise levels. However, no dosimeters currently provide octave-band data. Calculation by the long method is described below and shown in table 31.9 .

Table 31.9 Example of the long method for computing the A-weighted noise reduction  for a hearing protector in a known environmental noise

Procedure:

1. Tabulate the measured octave-band levels of the environmental noise.

2. Tabulate the adjustments for A-weighting at each octave-band centre frequency.

3. Add the results of steps 1 and 2 to obtain the A-weighted octave-band levels. Combine the  A-weighted octave-band levels logarithmically to obtain the A-weighted environmental noise level.

4. Tabulate the attenuation provided by the device for each octave band.

5. Tabulate the standard deviations of attenuation (times 2) provided by the device for each octave  band.

6. Obtain the A-weighted octave-band levels under the protector by subtracting the mean attenuation  (step 4) from the A-weighted octave-band levels (step 3),  and adding the standard deviation of the  attenuations times 2 (step 5). The A-weighted octave band levels are combined logarithmically to  obtain the A-weighted  sound level effective when the hearing protector is worn. The estimated  A-weighted noise reduction in a given environment is calculated by subtracting the  A-weighted  sound level under the protector from the A-weighted environmental noise level (the result of step  3 minus that of step 6).

Steps

Octave-band center frequency in Hz

 

125

250

500

1000

2000

4000

8000

dBA

1. Measured octave-band levels of noise

85.0

87.0

90.0

90.0

85.0

82.0

80.0

 

2. A-weighting correction

-16.1

-8.6

-3.2

0.0

+1.2

+1.0

-1.1

 

3. A-weighted octave-band levels

68.9

78.4

86.8

90.0

86.2

83.0

78.9

93.5

4. Attenuation of hearing protector

27.4

26.6

27.5

27.0

32.0

46.01

44.22

 

5. Standard deviation × 2

7.8

8.4

9.4

6.8

8.8

7.33

12.84

 

6. Estimated protected  A-weighted octave-band levels.  (Step 3 - Step 4 + Step 5)

49.3

60.2

68.7

69.8

63.0

44.3

47.5

73.0

1 Mean attenuation at 3000 and 4000 Hz.

2 Mean attenuation at 6000 and 8000 Hz.

3 Sum of standard deviations at 3000 and 4000 Hz.

4 Sum of standard deviations at 6000 and 8000 Hz.

The subtractive standard deviation corrections in the long method and in the NRR computations are intended to use the laboratory variability measurements to adjust the estimates of protection to correspond to values expected for most of the users (98% with a 2-standard-deviation correction or 84% if a 1-standard-deviation correction is used) who wear the hearing protector under conditions identical to those involved in the testing. The appropriateness of this adjustment is, of course, heavily dependent upon the validity of the laboratory-estimated standard deviations.

Comparison of the long method and the NRR

The long method and the NRR computations may be compared by subtracting the NRR (20.7) from the C-weighted sound pressure level for the spectrum in table 31.9  (95.2 dBC) to predict the effective level when the hearing protector is worn, namely 74.5 dBA. This compares favourably to the value of 73.0 dBA derived from the long method in table 31.9 . Part of the disparity between the two estimates is due to the use of the approximate 3 dB spectral safety factor incorporated in line 9 of table 31.8 . The spectral safety factor is intended to account for errors arising from the use of an assumed noise instead of an actual noise. Depending upon the slope of the spectrum and the shape of the attenuation curve of the hearing protector, the differences between the two methods may be greater than that shown in this example.

Reliability of test data

It is unfortunate that the attenuation values and their standard deviations as obtained in laboratories in the United States, and to a lesser extent in Europe, are not representative of those obtained by everyday wearers. Berger, Franks and Lindgren (1996) reviewed 22 real-world studies of hearing protectors and found that US laboratory values reported on the EPA-required label overestimated protection from 140 to almost 2000%. The overestimation was greatest for earplugs and least for earmuffs. Since 1987, the US Occupational Safety and Health Administration has recommended that the NRR be derated by 50% before calculations are made of noise levels under the hearing protector. In 1995, the US National Institute for Occupational Safety and Health (NIOSH) recommended that the NRR for earmuffs be derated by 25% that the NRR for formable earplugs be derated by 50% and that the NRR for premolded earplugs and semi inserts be derated by 70% before calculations of noise levels under the hearing protector are made (Rosenstock 1995).

Intra- and inter-laboratory variability

Another consideration, but of less impact than the real-world issues noted above, is within-laboratory validity and variability, as well as differences between facilities. Inter-laboratory variability can be substantial (Berger, Kerivan and Mintz 1982), affecting both the octave-band values and the computed NRRs, both in terms of absolute computations as well as rank ordering. Therefore, even rank ordering of hearing protectors based on attenuation values is best done at present only for data from a single laboratory.

Important Points for Selecting Protection

When a hearing protector is selected, there are several important points to be considered (Berger 1988). Foremost is that the protector will be adequate for the environmental noise in which it will be worn. The Hearing Conservation Amendment to the OSHA Noise Standard (1983) recommends that the noise level under the hearing protector be 85 dB or less. NIOSH has recommended that the noise level under the hearing protector be no higher than 82 dBA, so that risk of noise-induced hearing loss is minimal (Rosenstock 1995).

Second, the protector should not be overprotective. If the protected exposure level is more than 15 dB below the desired level, the hearing protector has too much attenuation and the wearer is considered to be overprotected, resulting in the wearer’s feeling isolated from the environment (BSI 1994). It may be difficult to hear speech and warning signals and wearers will temporarily either remove the protector when they need to communicate (as mentioned above) and verify warning signals or they will modify the protector to reduce its attenuation. In either case, the protection will usually be reduced to the point that hearing loss is no longer being prevented.

At present, accurate determination of protected noise levels is difficult since reported attenuations and standard deviations, along with their resultant NRRs, are inflated. However, using the derating factors recommended by the NIOSH should improve accuracy of such a determination in the short run.

Comfort is a critical issue. No hearing protector can be as comfortable as not wearing one at all. Covering or occluding the ears produces many unnatural sensations. These range from a change in the sound of one’s own voice due to the “occlusion effect” (see below), to a feeling of fullness of the ears or pressure on the head. Use of earmuffs or earplugs in hot environments may be uncomfortable because of the increase in perspiration. It will take time for wearers to get used to the sensations caused by hearing protectors and to some of the discomfort. However, when wearers experience such types of discomfort as headache from headband pressure or pain in the ear canals from earplug insertion, they should be fitted with alternative devices.

If earmuffs or reusable earplugs are used, a means to keep them clean should be provided. For earmuffs, wearers should have easy access to replaceable components such as ear cushions and ear cup liners. Wearers of disposable earplugs should have ready access to a fresh supply. If one intends to have earplugs reused, wearers should have access to earplug cleaning facilities. Wearers of custom-molded earplugs should have facilities to keep the earplugs clean and access to new earplugs when they have become damaged or worn out.

The average American worker is exposed to 2.7 occupational hazards each and every day (Luz et al. 1991). These hazards may require the use of other protective equipment such as “hard hats,” eye protection and respirators. It is important that any hearing protector selected be compatible with other safety equipment that is required. The NIOSH Compendium of Hearing Protective Devices (Franks, Themann and Sherris 1995) has tables that, among other things, list the compatibility of each hearing protector with other safety equipment.

The Occlusion Effect

The occlusion effect describes the increase in the efficiency with which bone-conducted sound is transmitted to the ear at frequencies below 2,000 Hz when the ear canal is sealed with a finger or an earplug, or is covered by an earmuff. The magnitude of the occlusion effect depends upon how the ear is occluded. The maximum occlusion effect occurs when the entrance to the ear canal is blocked. Earmuffs with large ear cups and earplugs that are deeply inserted cause less of an occlusion effect (Berger 1988). The occlusion effect often causes hearing protector wearers to object to wearing protection because they dislike the sound of their voices—louder, booming and muffled.

Communication Effects

Because of the occlusion effect that most hearing protectors cause, one’s own voice tends to sound louder—since the hearing protectors reduce the level of environmental noise, the voice sounds much louder than when the ears are open. To adjust for the increased loudness of one’s own speech, most wearers tend to lower their voice levels substantially, speaking more softly. Lowering the voice in a noisy environment where the listener is also wearing hearing protection contributes to the difficulty of communicating. Furthermore, even without an occlusion effect, most speakers raise their voice levels by only 5 to 6 dB for every 10 dB increase in environmental noise level (the Lombard effect). Thus, the combination of lowered voice level because of the use of hearing protection combined with inadequate elevation of voice level to make up for environmental noise has severe consequences on the ability of hearing-protector wearers to hear and understand each other in noise.

The Operation of Hearing Protectors

Earmuffs

The basic function of earmuffs is to cover the outer ear with a cup that forms a noise-attenuating acoustic seal. The styles of the ear cup and the earmuff’s cushions as well as the tension provided by the headband determine, for the most part, how well the earmuff attenuates environmental noise. Figure 31.12 displays both an example of a well-fitted earmuff with a good seal all around the outer ear as well as an example of an earmuff with a leak underneath the cushion. The chart in figure 31.12  shows that while the tight-fitting earmuff has good attenuation at all frequencies, the one with a leak provides practically no low-frequency attenuation. Most earmuffs will provide attenuation approaching bone conduction, approximately 40 dB, for frequencies from 2,000 Hz and greater. The low-frequency attenuation properties of a tightly fitting earmuff are determined by design features and materials that include ear cup volume, the area of the ear cup opening, headband force and mass.

Figure 31.12 Well-fitted and poorly fitted earmuffs and their attenuation consequences

Earplugs

Figure 31.13  displays an example of a well-fitted, fully inserted foam earplug (about 60% of it extends into the ear canal) and an example of a poorly fitted, shallowly inserted foam earplug that just caps the ear canal entrance. The well-fitted earplug has good attenuation at all frequencies. The poorly fitted foam earplug has substantially less attenuation. The foam earplug, when fitted properly, can provide attenuation approaching bone conduction at many frequencies. In high-level noise, the differences in attenuation between a well-fitted and a poorly fitted foam earplug can be sufficient to either prevent or permit noise-induced hearing loss.

Figure 31.13 A well-fitted and a poorly fitted foam earplug and the attenuation consequences

Figure 31.14  displays a well-fitted and poorly fitted premolded earplug. In general, premolded earplugs do not provide the same degree of attenuation as properly fitted foam earplugs or earmuffs. However, the well-fitted premolded earplug provides adequate attenuation for most industrial noises. The poorly fitted premolded earplug provides substantially less, and no attenuation at 250 and 500 Hz. It has been observed that for some wearers, there is actually gain at these frequencies, meaning that the protected noise level is actually higher than the environmental noise level, putting the wearer at more risk of developing noise-induced hearing loss than if the protector were not worn at all.

Figure 31.14 A well-fitted and a poorly fitted premolded earplug

Dual hearing protection

For some environmental noises, especially when daily equivalent exposures exceed about 105 dBA, a single hearing protector may be insufficient. In such situations wearers can use both earmuffs and earplugs in combination to achieve about 3 to 10 dB of extra protection, limited primarily by the bone conduction of the head of the wearer. Attenuation changes very little when different earmuffs are used with the same earplug, but changes greatly when different earplugs are used with the same earmuff. For dual protection, the choice of the earplug is critical for attenuation below 2,000 Hz, but at and above 2,000 Hz essentially all earmuff/earplug combinations provide attenuation approximately equal to the skull’s bone-conduction pathways.

Interference from glasses and head-worn personal protective equipment

Safety glasses, or other devices such as respirators that interfere with the earmuff’s circumaural seal, can degrade earmuff attenuation. For example, eye wear can reduce attenuation in individual octave bands by 3 to 7 dB.

Flat-response devices

A flat-attenuation earmuff or earplug is one that provides approximately equal attenuation for frequencies from 100 to 8,000 Hz. These devices maintain the same frequency response as the unoccluded ear, providing undistorted audition of signals (Berger 1991). A normal earmuff or earplug may sound as if the treble of the signal has been turned down, in addition to the overall lowering of the sound level. The flat-attenuation earmuff or earplug will sound as if only the volume has been reduced since its attenuation characteristics are “tuned” by the use of resonators, dampers and diaphragms. Flat-attenuation characteristics can be important for wearers having high-frequency hearing loss, for those for whom understanding speech while being protected is important, or for those for whom having high-quality sound is important, such as musicians. Flat attenuation devices are available as earmuffs and earplugs. One drawback of the flat-attenuation devices is that they don’t provide as much attenuation as conventional earmuffs and earplugs.

Passive amplitude-sensitive devices

A passive amplitude-sensitive hearing protector has no electronics and is designed to allow voice communications during quiet periods and provide little attenuation at low noise levels with protection increasing as the noise level increases. These devices contain orifices, valves, or diaphragms intended to produce this nonlinear attenuation, typically beginning once sound levels exceed 120 dB sound pressure levels (SPL). At sound levels below 120 dB SPL, orifice and valve-type devices typically act as vented earmolds, providing as much as 25 dB of attenuation at the higher frequencies, but very little attenuation at and below 1,000 Hz. Few occupational and recreational activities, other than shooting competitions (especially in outdoor environments), are appropriate if this type of hearing protector is expected to be truly effective in preventing noise-induced hearing loss.

Active amplitude-sensitive devices

An active amplitude-sensitive hearing protector has electronics and design goals similar to a passive amplitude-sensitive protector. These systems employ a microphone placed on the exterior of the ear cup or ported to the lateral surface of the earplug. The electronic circuit is designed to provide less and less amplification, or in some cases to completely shut down, as the environmental noise level increases. At the levels of normal conversational speech, these devices provide unity gain, (the loudness of speech is the same as if the protector wasn’t worn), or even a small amount of amplification. The goal is to keep the sound level under the earmuff or earplug to less than a 85 dBA diffuse-field equivalent. Some of the units built into earmuffs have a channel for each ear, thus allowing some level of localization to be maintained. Others have only one microphone. The fidelity (naturalness) of these systems varies among manufacturers. Because of the electronics package built into the ear cup which is necessary to have an active level-dependent system, these devices provide about four to six decibels less attenuation in their passive state, electronics turned off, than similar earmuffs without the electronics.

Active noise reduction

Active noise reduction, while an old concept, is a relatively new development for hearing protectors. Some units work by capturing the sound inside the ear cup, inverting its phase, and retransmitting the inverted noise into the ear cup to cancel the incoming sound. Other units work by capturing sound outside the ear cup, modifying its spectrum to account for the attenuation of the ear cup, and inserting the inverted noise into the ear cup, effectively using the electronics as a timing device so that the electrically inverted sound arrives in the ear cup at the same time as the noise transmitted through the ear cup. Active noise reduction is limited to the reduction of low-frequency noises below 1,000 Hz, with a maximum attenuation of 20 to 25 dB occurring at or below 300 Hz.

However, a portion of the attenuation provided by the active noise reduction system simply offsets the reduction in attenuation of the earmuffs that is caused by the inclusion in the ear cup of the very electronics which are required to effect the active noise reductions. At present these devices cost 10 to 50 times that of passive earmuffs or earplugs. If the electronics fail, the wearer may be inadequately protected and could experience more noise under the ear cup than if the electronics were simply shut off. As active noise cancellation devices become more popular, costs should diminish and their applicability may become more widespread.

The Best Hearing Protector

The best hearing protector is the one that the wearer will use willingly, 100% of the time. It is estimated that approximately 90% of noise-exposed workers in the manufacturing sector in the United States are exposed to noise levels of less than 95 dBA (Franks 1988). They need between 13 and 15 dB of attenuation to provide them with adequate protection. There are a wide array of hearing protectors that can provide sufficient attenuation. Finding the one that each worker will wear willingly 100% of the time is the challenge.

PROTECTIVE CLOTHING

S.Zack Mansdorf

Hazards

There are several general categories of bodily hazards for which specialized clothing can provide protection. These general categories include chemical, physical and biological hazards. Table 31.10  summarizes these.

Table 31.10 Examples of dermal hazard categories

Hazard

Examples

Chemical

Dermal toxins

Systemic toxins

Corrosives

Allergens

Physical

Thermal hazards (hot/cold) 

Vibration

Radiation

Trauma producing

Biological

Human pathogens

Animal pathogens

Environmental pathogens

Chemical hazards

Protective clothing is a commonly used control to reduce worker exposures to potentially toxic or hazardous chemicals when other controls are not feasible. Many chemicals pose more than one hazard (for example, a substance such as benzene is both toxic and flammable). For chemical hazards, there are at least three key considerations that need attention. These are (1) the potential toxic effects of exposure, (2) likely routes of entry, and (3) the exposure potentials associated with the work assignment. Of the three aspects, toxicity of the material is the most important. Some substances simply present a cleanliness problem (e.g., oil and grease) while other chemicals (e.g., contact with liquid hydrogen cyanide) could present a situation which is immediately dangerous to life and health (IDLH). Specifically, the toxicity or hazardousness of the substance by the dermal route of entry is the critical factor. Other adverse effects of skin contact, besides toxicity, include corrosion, promotion of cancer of the skin and physical trauma such as burns and cuts.

An example of a chemical whose toxicity is greatest by the dermal route is nicotine, which has excellent skin permeability but is not generally an inhalation hazard (except when self-administered). This is only one of many instances where the dermal route offers a much more significant hazard than the other routes of entry. As suggested above, there are many substances that are not generally toxic but are hazardous to the skin because of their corrosive nature or other properties. In fact, some chemicals and materials can offer an even greater acute risk through skin absorption than the most dreaded systemic carcinogens. For example, a single unprotected skin exposure to hydrofluoric acid (above 70% concentration) can be fatal. In this case, as little as a 5% surface burn typically results in death from the effects of the fluoride ion. Another example of a dermal hazard—though not an acute one—is the promotion of skin cancer by substances such as coal tars. An example of a material which has high human toxicity but little skin toxicity is inorganic lead. In this case the concern is contamination of the body or clothing, which could later lead to ingestion or inhalation, since the solid will not permeate intact skin.

Once an evaluation of the routes of entry and toxicity of the materials has been completed, an assessment of the likelihood of exposure needs to be carried out. For example, do workers have enough contact with a given chemical to become visibly wet or is exposure unlikely and protective clothing intended to act simply as a redundant control measure? For situations where the material is deadly although the likelihood of contact is remote, the worker must obviously be provided with the highest level of protection available. For situations where the exposure itself represents a very minimal risk (e.g., a nurse handling 20% isopropyl alcohol in water), the level of protection does not need to be fail-safe. This selection logic is essentially based on an estimate of the adverse effects of the material combined with an estimate of the likelihood of exposure.

The chemical resistance properties of barriers

Research showing the diffusion of solvents and other chemicals through “liquid-proof” protective clothing barriers has been published from the 1980s to the 1990s. For example, in a standard research test, acetone is applied to neoprene rubber (of typical glove thickness). After direct acetone contact on the normal outside surface, the solvent can normally be detected on the inside surface (the skin side) within 30 minutes, although in small quantities. This movement of a chemical through a protective clothing barrier is called permeation. The permeation process consists of the diffusion of chemicals on a molecular level through the protective clothing. Permeation occurs in three steps: absorption of the chemical at the barrier surface, diffusion through the barrier, and desorption of the chemical on the normal inside surface of the barrier. The time elapsed from the initial contact of the chemical on the outside surface until detection on the inside surface is called the breakthrough time. The permeation rate is the steady-state rate of movement of the chemical through the barrier after equilibrium is reached.

Most current testing of permeation resistance extends over periods of up to eight hours, reflecting normal work shifts. However, these tests are conducted under conditions of direct liquid or gaseous contact that typically do not exist in the work environment. Some would therefore argue that there is a significant “safety factor” built into the test. Countering this assumption are the facts that the permeation test is static while the work environment is dynamic (involving flexing of materials or pressures generated from gripping or other movement) and that there may exist prior physical damage to the glove or garment. Given the lack of published skin permeability and dermal toxicity data, the approach taken by most safety and health professionals is to select the barrier with no breakthrough for the duration of the job or task (usually eight hours), which is essentially a no-dose concept. This is an appropriately conservative approach; however, it is important to note that there is no protective barrier currently available which provides permeation resistance to all chemicals. For situations where the breakthrough times are short, the safety and health professional should select the barriers with the best performance (i.e., with the lowest permeation rate) while considering other control and maintenance measures as well (such as the need for regular clothing changes).

Aside from the permeation process just described, there are two other chemical resistance properties of concern to the safety and health professional. These are degradation and penetration. Degradation is a deleterious change in one or more of the physical properties of a protective material caused by contact with a chemical. For example, the polymer polyvinyl alcohol (PVA) is a very good barrier to most organic solvents, but is degraded by water. Latex rubber, which is widely used for medical gloves, is of course water resistant, but is readily soluble in such solvents as toluene and hexane: it would be plainly ineffective for protection against these chemicals. Secondly, latex allergies can cause severe reactions in some people.

Penetration is the flow of a chemical through pinholes, cuts or other imperfections in protective clothing on a nonmolecular level. Even the best protective barriers will be rendered ineffective if punctured or torn. Penetration protection is important when the exposure is unlikely or infrequent and the toxicity or hazard is minimal. Penetration is usually a concern for garments used in splash protection.

Several guides have been published listing chemical resistance data (many are also available in an electronic format). In addition to these guides, most manufacturers in the industrially developed countries also publish current chemical and physical resistance data for their products.

Physical hazards

As noted in table 31.10 , physical hazards include thermal conditions, vibration, radiation and trauma as all having the potential to affect the skin adversely. Thermal hazards include the adverse effects of extreme cold and heat on the skin. The protective attributes of clothing with respect to these hazards is related to its degree of insulation, whereas protective clothing for flash fire and electric flashover requires flame resistance properties.

Specialized clothing can provide limited protection from some forms of both ionizing and non-ionizing radiation. In general, the effectiveness of clothing that protects against ionizing radiation is based on the principle of shielding (as with lead-lined aprons and gloves), whereas clothing employed against non-ionizing radiation, such as microwave, is based on grounding or isolation. Excessive vibration can have several adverse effects on body parts, primarily the hands. Mining (involving hand-held drills) and road repair (for which pneumatic hammers or chisels are used), for example, are occupations where excessive hand vibration can lead to bone degeneration and loss of circulation in the hands. Trauma to the skin from physical hazards (cuts, abrasions, etc.) is common to many occupations, with construction and meat cutting as two examples. Specialized clothing (including gloves) are now available which are cut-resistant and are used in applications such as meat cutting and forestry (using chain saws). These are based either on inherent cut-resistance or the presence of enough fibre mass to clog moving parts (e.g., chain saws).

Biological hazards

Biological hazards include infection due to agents and disease common to humans and animals, and the work environment. Biological hazards common to humans have received great attention with the increasing spread of blood-borne AIDS and hepatitis. Hence, occupations which might involve exposure to blood or body fluids usually require some type of liquid-resistant garment and gloves. Diseases transmitted from animals through handling (e.g., anthrax) have a long history of recognition and require protective measures similar to those used for handling the kind of blood-borne pathogens that affect humans. Work environments that can present a hazard due to biological agents include clinical and microbiological laboratories as well as other special work environments.

Types of Protection

Protective clothing in a generic sense includes all elements of a protective ensemble (e.g., garments, gloves and boots). Thus, protective clothing can include everything from a finger cot providing protection against paper cuts to a fully encapsulating suit with a self-contained breathing apparatus used for an emergency response to a hazardous chemical spill.

Protective clothing can be made of natural materials (e.g., cotton, wool and leather), man-made fibres (e.g., nylon) or various polymers (e.g., plastics and rubbers such as butyl rubber, polyvinyl chloride, and chlorinated polyethylene). Materials which are woven, stitched or are otherwise porous (not resistant to liquid penetration or permeation) should not be used in situations where protection against a liquid or gas is required. Specially treated or inherently non-flammable porous fabrics and materials are commonly used for flash fire and electric arc (flashover) protection (e.g., in the petrochemical industry) but usually do not provide protection from any regular heat exposure. It should be noted here that fire-fighting requires specialized clothing that provides flame (burning) resistance, a water barrier and thermal insulation (protection from high temperatures). Some special applications also require infrared (IR) protection by use of aluminized overcovers (e.g., fighting petroleum fuel fires). Table 31.11  summarizes typical physical, chemical, and biological performance requirements and common protective materials used for hazard protection.

Table 31.11 Common physical, chemical and biological performance requirements

Hazard

Performance characteristic required

Common protective clothing materials

Thermal

Insulation value

Heavy cotton or other natural fabrics

Fire

Insulation and flame resistance

Aluminized gloves; flame resistent treated gloves; aramid fibre and other special fabrics

Mechanical abrasion

Abrasion resistence; tensile strength

Heavy fabrics; leather

Cuts and punctures

Cut resistance

Metal mesh; aromatic polyamide fiber and other special fabrics

Chemical/toxicological

Permeation resistance

Polymeric and elastomeric materials; (including latex)

Biological

“Fluid-proof”; (puncture resistant)

 

Radiological

Usually water resistance or particle resistance (for radionuclides)

 

Protective clothing configurations vary greatly depending on the intended use. However, normal components are analogous to personal clothing (i.e., trousers, jacket, hood, boots and gloves) for most physical hazards. Special-use items for applications such as flame resistance in those industries involving the processing of molten metals can include chaps, armlets, and aprons constructed of both treated and untreated natural and synthetic fibres and materials (one historical example would be woven asbestos). Chemical protective clothing can be more specialized in terms of construction, as shown in figure 31.15 and figure 31.16 .

Figure 31.15 A worker wearing gloves and a chemically protective garment pouring chemical

Figure 31.16 Two workers in differing configurations of chemical protective clothing

Chemically protective gloves are usually available in a wide variety of polymers and combinations; some cotton gloves, for example, are coated by the polymer of interest (by means of a dipping process). (See figure 31.17).

Figure 31.17 Various types of chemically resistant gloves

Some of the new foil and multilaminate “gloves” are only two-dimensional (flat)—and hence have some ergonomic constraints, but are highly chemical resistant. These gloves typically work best when a form-fitting outer polymer glove is worn over the top of the inner flat glove (this technique is called double gloving) to conform the inner glove to the shape of the hands. Polymer gloves are available in a wide variety of thicknesses ranging from very light weight (<2 mm) to heavy weight (>5 mm) with and without inner liners or substrates (called scrims). Gloves are also commonly available in a variety of lengths ranging from approximately 30 centimetres for hand protection to gauntlets of approximately 80 centimetres, extending from the worker’s shoulder to the tip of the hand. The correct choice of length depends on the extent of protection required; however, the length should normally be sufficient to extend at least to the worker’s wrists so as to prevent drainage into the glove. (See figure 31.18).

Figure 31.18 Natural-fibre gloves; also illustrates sufficient length for wrist protection

Boots are available in a wide variety of lengths ranging from hip length to those that cover only the bottom of the foot. Chemical protective boots are available in only a limited number of polymers since they require a high degree of abrasion resistance. Common polymers and rubbers used in chemically resistant boot construction include PVC, butyl rubber and neoprene rubber. Specially constructed laminated boots using other polymers can also be obtained but are quite expensive and in limited supply internationally at the present time.

Chemical protective garments can be obtained as a one-piece fully encapsulating (gas-tight) garment with attached gloves and boots or as multiple components (e.g., trousers, jacket, hoods, etc.). Some protective materials used for construction of ensembles will have multiple layers or laminas. Layered materials are generally required for polymers that do not have good enough inherent physical integrity and abrasion resistance properties to permit manufacture and use as a garment or glove (e.g., butyl rubber versus Teflon®). Common support fabrics are nylon, polyester, aramides and fibreglass. These substrates are coated or laminated by polymers such as polyvinyl chloride (PVC), Teflon®, polyurethane and polyethylene.

Over the last decade there has been an enormous growth in the use of nonwoven polyethene and microporous materials for disposable suit construction. These spun-bonded suits, sometimes incorrectly called “paper suits,” are made using a special process whereby the fibres are bonded together rather than woven. These protective garments are low in cost and very light in weight. Uncoated microporous materials (called “breathable” because they allow some water vapour transmission and hence are less heat stressful) and spun-bonded garments have good applications as protection against particulates but are not normally chemical-or liquid-resistant. Spun-bonded garments are also available with various coatings such as polyethylene and Saranex®. Depending on the coating characteristics, these garments can offer good chemical resistance to most common substances.

Approval, Certification and Standards

The availability, construction, and design of protective clothing varies greatly throughout the world. As might be expected, approval schemes, standards and certifications also vary. Nevertheless, there are similar voluntary standards for performance throughout the United States (e.g., American Society for Testing and Materials—ASTM—standards), Europe (European Committee for Standardization—CEN—standards), and for some parts of Asia (local standards such as in Japan). The development of worldwide performance standards has begun through the International Organization for Standardization Technical Committee 94 for Personal Safety-Protective Clothing and Equipment. Many of the standards and test methods to measure performance developed by this group were based on either CEN standards or those from other countries such as the United States through the ASTM.

In the United States, Mexico, and most of Canada, no certification or approvals are required for most protective clothing. Exceptions exist for special applications such as pesticide applicators clothing (governed by pesticide labelling requirements). Nevertheless, there are many organizations that issue voluntary standards, such as the previously mentioned ASTM, the National Fire Protection Association (NFPA) in the United States and the Canadian Standards Organization (CSO) in Canada. These voluntary standards do significantly affect the marketing and sale of protective clothing and hence act much like mandated standards.

In Europe, the manufacturing of personal protective equipment is regulated under the European Community Directive 89/686/EEC. This directive both defines which products fall within the scope of the directive and classifies them into different categories. For categories of protective equipment where the risk is not minimal and where the user cannot readily identify the hazard easily, the protective equipment must meet standards of quality and manufacture detailed in the directive.

No protective equipment products may be sold within the European Community unless they have the CE (European Community) mark. Testing and quality assurance requirements must be followed to receive the CE mark.

Individual Capabilities and Needs

In all but a few cases, the addition of protective clothing and equipment will decrease productivity and increase worker discomfort. It may also lead to decreased quality, since error rates increase with the use of protective clothing. For chemical protective and some fire-resistant clothing there are some general guidelines that need to be considered concerning the inherent conflicts between worker comfort, efficiency and protection. First, the thicker the barrier the better (increases the time to breakthrough or provides greater thermal insulation); however, the thicker the barrier the more it will decrease ease of movement and user comfort. Thicker barriers also increase the potential for heat stress. Second, barriers which have excellent chemical resistance tend to increase the level of worker discomfort and heat stress because the barrier normally will also act as a barrier to water vapour transmission (i.e., perspiration). Third, the higher the overall protection of the clothing, the more time a given task will take to accomplish and the greater the chance of errors. There are also a few tasks where the use of protective clothing could increase certain classes of risk (e.g., around moving machinery, where the risk of heat stress is greater than the chemical hazard). While this situation is rare, it must be considered.

Other issues relate to the physical limitations imposed by using protective clothing. For example, a worker issued a thick pair of gloves will not be able to perform tasks easily that require a high degree of dexterity and repetitive motions. As another example, a spray painter in a totally encapsulating suit will usually not be able to look to the side, up or down, since typically the respirator and suit visor restrict the field of vision in these suit configurations. These are only some examples of the ergonomic restrictions associated with wearing protective clothing and equipment.

The work situation must always be considered in the selection of the protective clothing for the job. The optimum solution is to select the minimum level of protective clothing and equipment that is necessary to do the job safely.

Education and Training

Adequate education and training for users of protective clothing is essential. Training and education should include:

·     the nature and extent of the hazards

·     the conditions under which protective clothing should be worn

·     what protective clothing is necessary

·     the use and limitations of the protective clothing to be assigned

·     how to inspect, don, doff, adjust and wear the protective clothing properly

·     decontamination procedures, if necessary

·     signs and symptoms of overexposure or clothing failure

·     first aid and emergency procedures

·     the proper storage, useful life, care and disposal of protective clothing.

This training should incorporate at least all of the elements listed above and any other pertinent information that has not already been provided to the worker through other programmes. For those topical areas already provided to the worker, a refresher summary should still be provided for the clothing user. For example, if the signs and symptoms of overexposure have already been indicated to the workers as part of their training for working with chemicals, symptoms that are a result of significant dermal exposures versus inhalation should be reemphasized. Finally, the workers should have an opportunity to try out the protective clothing for a particular job before a final selection is made.

Knowledge of the hazard and of the limitations of the protective clothing not only reduces the risk to the worker but also provides the health and safety professional with a worker capable of providing feedback on the effectiveness of the protective equipment.

Maintenance

The proper storage, inspection, cleaning and repair of protective clothing is important to the overall protection provided by the products to the wearer.

Some protective clothing will have storage limitations such as a prescribed shelf life or required protection from UV radiation (e.g., sunlight, welding flash, etc.), ozone, moisture, temperature extremes or prevention of product folding. For example, natural rubber products usually call for all of the precautionary measures just listed. As another example, many of the encapsulating polymer suits can be damaged if folded rather than allowed to hang upright. The manufacturer or distributor should be consulted for any storage limitations their products may have.

Inspection of protective clothing should be performed by the user on a frequent basis (e.g., with each use). Inspection by co-workers is another technique which may be used to involve wearers in ensuring the integrity of the protective clothing they have to use. As a management policy, it is also advisable to require supervisors to inspect protective clothing (at appropriate intervals) that is used on a routine basis. Inspection criteria will depend on the intended use of the protective item; however, it would normally include examination for tears, holes, imperfections and degradation. As one example of an inspection technique, polymer gloves used for protection against liquids should be blown up with air to check for integrity against leaks.

Cleaning of protective clothing for reuse must be performed with care. Natural fabrics can be cleaned by normal washing methods if they are not contaminated with toxic materials. Cleaning procedures suitable for synthetic fibres and materials are commonly limited. For example, some products treated for flame resistance will lose their effectiveness if not properly cleaned. Clothing used for protection against chemicals which are not water-soluble often cannot be decontaminated by washing with simple soap or detergent and water. Tests performed on pesticide applicators’ clothing indicate that normal washing procedures are not effective for many pesticides. Dry cleaning is not recommended at all since it is often ineffective and can degrade or contaminate the product. It is important to consult the manufacturer or distributor of the clothing before attempting cleaning procedures that are not specifically known to be safe and workable.

Most protective clothing is not repairable. Repairs can be made on some few items such as fully encapsulating polymer suits. However, the manufacturer should be consulted for the proper repair procedures.

Use and Misuse

Use. First and foremost, the selection and proper use of protective clothing should be based on an assessment of the hazards involved in the task for which the protection is required. In light of the assessment, an accurate definition of the performance requirements and the ergonomic constraints of the job can be determined. Finally, a selection that balances worker protection, ease of use and cost can be made.

A more formal approach would be to develop a written model programme, a method that would reduce the chance of error, increase worker protection and establish a consistent approach to the selection and use of protective clothing. A model programme could contain the following elements:

1.     an organization scheme and administrative plan

2.     a risk assessment methodology

3.     an evaluation of other control options to protect the worker

4.     performance criteria for the protective clothing

5.     selection criteria and procedures to determine the optimum choice

6.     purchasing specifications for the protective clothing

7.     a validation plan for the selection made

8.     decontamination and reuse criteria, as applicable

9.     a user training programme

10.     an auditing plan to assure that procedures are consistently followed.

Misuse. There are several examples of misuse of protective clothing that can commonly be seen in industry. Misuse is usually the result of a lack of understanding of the limitations of protective clothing on the part of management, of the workers, or of both. A clear example of bad practice is the use of nonflame-resistant protective clothing for workers who handle flammable solvents or who work in situations where open flames, burning coals or molten metals are present. Protective clothing made of polymeric materials such as polyethylene may support combustion and can actually melt into the skin, causing an even more severe burn.

A second common example is the reuse of protective clothing (including gloves) where the chemical has contaminated the inside of the protective clothing so that the worker increases his or her exposure on each subsequent use. One frequently sees another variation of this problem when workers use natural-fibre gloves (e.g., leather or cotton) or their own personal shoes to work with liquid chemicals. If chemicals are spilled on the natural fibres, they will be retained for long periods of time and migrate to the skin itself. Yet another variation of this problem is taking contaminated work clothing home for cleaning. This can result in the exposure of an entire family to harmful chemicals, a common problem because the work clothing is usually cleaned with the other articles of clothing of the family. Since many chemicals are not water-soluble, they can be spread to other articles of clothing simply by mechanical action. Several cases of this spread of contaminants have been noted, especially in industries which manufacture pesticides or process heavy metals (e.g., poisoning families of workers handling mercury and lead). These are only a few of the more prominent examples of the misuse of protective clothing. These problems can be overcome by simply understanding the proper use and limitations of the protective clothing. This information should be readily available from the manufacturer and health and safety experts.

RESPIRATORY PROTECTION

Thomas J. Nelson

In some industries, air contaminated with potentially harmful dusts, fumes, mists, vapours or gases may cause harm to the workers. The control of exposure to these materials is important to decrease the risk of occupational diseases caused by breathing the contaminated air. The best method to control exposure is to minimize workplace contamination. This can be accomplished by using engineering control measures (e.g., by enclosure or confinement of the operation, by general and local ventilation and substitution of less toxic materials). When effective engineering controls are not feasible, or while they are being implemented or evaluated, respirators can be used to protect the health of the worker. For respirators to work as anticipated, an appropriate and well-planned respirator programme is necessary.

Respiratory Hazards

Hazards to the respiratory system can be in the form of air contaminants or due to a lack of sufficient oxygen. The particulates, gases or vapours that constitute air contaminants may be associated with different activities (see table 31.12 ).

Table 31.12 Material hazards associated with particular activities

Type of hazard

Typical sources or activities

Examples

Dusts

Sewing, grinding, sanding, chipping, sand blasting

Wood dust, coal, silica dust

Fumes

Welding, brazing, smelting

Lead, zinc, iron oxide fumes

Mists

Spray painting, metal plating, machining

Paint mists, oil mists

Fibers

Insulation, friction products

Asbestos, fiber glass

Gases

Welding, combustion engines, water treatment

Ozone, carbon dioxide, carbon monoxide, chlorine

Vapours

Degreasing, painting, cleaning products

Methylene chloride, toluene, mineral spirits

Oxygen is a normal component of the environment that is necessary to sustain life. Physiologically speaking, oxygen deficiency is a reduction in the availability of oxygen to the body’s tissues. It may be caused by the reduction in the percentage of oxygen in the air or by the reduction in the partial pressure of oxygen. (The partial pressure of a gas equals the fractional concentration of the gas in question times the total atmospheric pressure.) The most common form of oxygen deficiency in working environments occurs when the percentage of oxygen is reduced because it is displaced by another gas in a confined space.

Types of Respirators

Respirators are categorized by the type of cover offered for the respiratory system (inlet covering) and by the mechanism used to protect the wearer from the contaminant or from oxygen deficiency. The mechanism is either air purification or supplied air.

Inlet coverings

The “inlets” to the respiratory system are the nose and the mouth. For a respirator to work, these must be sealed by a cover that will in some way isolate the person’s respiratory system from hazards in the respirable environment while simultaneously permitting the intake of sufficient oxygen. The types of coverings that are used may be either tight or loose.

Tight-fitting coverings may take the form of a quarter mask, a half mask, a full facepiece, or a mouth bit. A quarter mask covers both the nose and the mouth. The sealing surface extends from the bridge of the nose to below the lips (a quarter of the face). A half facepiece forms a seal from the bridge of the nose to underneath the chin (half the face). The seal of a full facepiece extends from above the eyes (but below the hair line) to underneath the chin (covering the full face).

With a respirator employing a mouth bit, the mechanism for covering the respiratory system inlets is slightly different. The person bites onto a rubber bit that is attached to the respirator and uses a nose clip to seal the nose. Thus both of the respiratory system inlets are sealed. Mouth bit type respirators are a special type that are used only in situations that call for escape from a hazardous atmosphere. They will not be discussed further in this chapter, since their use is so specialized.

The quarter, half or full-face types of coverings can be used with either an air-purifying or supplied-air type of respirator. The mouth bit type exists only as an air-purifying type.

Loose-fitting inlet coverings, as suggested by their name, do not rely on a sealing surface to protect the worker’s respiratory system. Rather they cover the face, head, or head and shoulders, providing a safe environment. Also included in this group are suits that cover the entire body. (Suits do not include garments that are worn solely to protect the skin, such as splash suits.) Since they do not seal to the face, loose-fitting inlet coverings operate only in systems that provide a flow of air. The flow of air must be greater than the air required for breathing to prevent the contaminant outside the respirator from leaking to the inside.

Air-purifying respirators

An air-purifying respirator causes ambient air to be passed through an air-purifying element that removes the contaminants. Air is passed through the air-purifying element by means of the breathing action (negative pressure respirators) or by a blower (powered air-purifying respirators, or PAPRs).

The type of air-purifying element will determine which contaminants are removed. Filters of varying efficiencies are used to remove aerosols. The choice of filter will depend on the properties of the aerosol; normally, particle size is the most important characteristic. Chemical cartridges are filled with a material that is specifically chosen to absorb or react with the vapour or gaseous contaminant.

Supplied-air respirators

Atmosphere-supplying respirators are a class of respirators that supply a respirable atmosphere independent of the workplace atmosphere. One type is commonly called an air-line respirator and operates in one of three modes: demand, continuous flow or pressure demand. Respirators operating in demand and pressure-demand modes can be equipped with either a half-face or a full facepiece inlet covering. The continuous-flow type can also be equipped with a helmet/hood or a loose-fitting facepiece.

A second type of atmosphere-supplying respirator, called a self-contained breathing apparatus (SCBA), is equipped with a self-contained air supply. It may be used for escape only or for entry into and escape from a hazardous atmosphere. The air is supplied from a compressed-air cylinder or by a chemical reaction.

Some supplied-air respirators are equipped with a small supplemental air bottle. The air bottle provides the person using the respirator with the ability to escape if the main air supply fails.

Combination units

Some specialized respirators may be made to operate both in a supplied-air mode and in an air-purifying mode. They are called combination units.

Respiratory Protection Programmes

For a respirator to function as intended, a minimal respirator programme needs to be developed. Regardless of the type of respirator used, the number of people involved and the complexity of the respirator use, there are basic considerations that need to be included in every programme. For simple programmes, adequate requirements may be minimal. For larger programmes, one may have to prepare for a complex undertaking.

By way of illustration, consider the need of keeping records of fit testing of equipment. For a one- or two-person programme, the date of last fit test, the respirator fit tested and the procedure could be kept on a simple card, while for a large programme with hundreds of users, a computerized database with a system to track those persons who are due for fit testing may be required.

The requirements for a successful programme are described in the following six sections.

1. Programme administration

The responsibility for the respirator programme should be assigned to a single person, called the programme administrator. A single person is assigned this task so that management clearly understands who is responsible. Just as important, this person is given the status necessary to make decisions and run the programme.

The programme administrator should have sufficient knowledge of respiratory protection to supervise the respirator programme in a safe and effective manner. The programme administrator’s responsibilities include the monitoring of respiratory hazards, maintaining records and conducting programme evaluations.

2. Written operating procedures

Written procedures are used to document the programme so that each participant knows what needs to be done, who is responsible for the activity and how it is to be carried out. The procedure document should include a statement of the goals of the programme. This statement would make it clear that the management of the company is responsible for the health of the workers and the implementation of the respirator programme. A written document setting forth the essential procedures of a respirator programme should cover the following functions:

·     respirator selection

·     maintenance, inspection and repair

·     training of employees, supervisors and the person issuing the respirators

·     fit testing

·     administrative activities including purchasing, inventory control and record keeping

·     monitoring of hazards

·     monitoring of respirator use

·     medical evaluation

·     the provision of emergency-use respirators

·     programme evaluation.

3. Training

Training is an important part of a respirator programme. The supervisor of the people using respirators, the users themselves and the people who issue respirators to the users all need to be trained. The supervisor needs to know enough about the respirator being used and why it is being used so that he or she will be able to monitor for proper usage: in effect, the person issuing the respirator to the user needs enough training to be sure that the correct respirator is handed out.

The workers who use respirators need to be given training and periodic retraining. The training should include explanations and discussions of the following:

1.     the nature of the respiratory hazard and possible health effects if the respirator is not used properly

2.     the reason a particular type of respirator was selected

3.     how the respirator works and its limitations

4.     how to put the respirator on and check that it is working and adjusted properly

5.     how to maintain, inspect and store the respirator

6.     a respirator fit test for negative pressure respirators.

4. Respirator maintenance

Respirator maintenance includes regular cleaning, inspection for damage, and replacement of worn parts. The manufacturer of the respirator is the best source of information on how to perform cleaning, inspection, repair and maintenance.

Respirators need to be cleaned and sanitized periodically. If a respirator is to be used by more than a single person, it should be cleaned and sanitized before being worn by others. Respirators intended for emergency use should be cleaned and sanitized after each use. This procedure should not be neglected, since there may be special needs to keep the respirator functioning properly. This may include controlled temperatures for cleaning solutions to prevent damage to the device’s elastomers. Furthermore, some parts may need to be cleaned carefully or in a special manner to avoid damage. The manufacturer of the respirator will provide a suggested procedure.

After cleaning and sanitizing, each respirator needs to be inspected to determine if it is in proper working condition, if it needs replacement of parts or repairs, or if it should be discarded. The user should be sufficiently trained and familiar with the respirator in order to be able to inspect the respirator immediately prior to each use in order to ensure that it is in proper working condition.

Respirators that are stored for emergency use need to be periodically inspected. A frequency of once each month is suggested. Once an emergency use respirator is used, it needs to be cleaned and inspected prior to re-use or storage.

In general, inspection will include a check for tightness of connections; for the condition of the respiratory inlet covering, head harness, valves, connecting tubes, harness assemblies, hoses, filters, cartridges, canisters, end of service life indicator, electrical components and shelf life date; and for the proper function of regulators, alarms and other warning systems.

Particular care needs to be given in the inspection of the elastomers and plastic parts commonly found on this equipment. Rubber or other elastomeric parts can be inspected for pliability and signs of deterioration by stretching and bending the material, looking for signs of cracking or wear. Inhalation and exhalation valves are generally thin and easily damaged. One should also look for the build-up of soaps or other cleaning materials on the sealing surfaces of valve seats. Damage or build-up can cause undue leakage through the valve. Plastic parts need to be inspected for damage, such as having stripped or broken threads on a cartridge, for example.

Air and oxygen cylinders should be inspected to determine that they are fully charged according to the manufacturer’s instructions. Some cylinders require periodic inspection to make sure the metal itself is not damaged or rusting. This might include periodic hydrostatic testing of the integrity of the cylinder.

Parts that are found to be defective need to be replaced by stock supplied by the manufacturer itself. Some parts may look very similar to another manufacturer’s, but may perform differently in the respirator itself. Anyone making repairs should to be trained in proper respirator maintenance and assembly.

For supplied-air and self-contained equipment, a higher level of training is required. Reducing or admission valves, regulators and alarms should be adjusted or repaired only by the respirator manufacturer or by a technician trained by the manufacturer.

Respirators that do not meet applicable inspection criteria should be immediately removed from service and repaired or replaced.

Respirators need to be properly stored. Damage can occur if they are not protected from physical and chemical agents such as vibration, sunlight, heat, extreme cold, excessive moisture or damaging chemicals. The elastomers used in the facepiece can be easily damaged if not protected. Respirators should not be stored in such places as lockers and tool boxes unless they are protected from contamination and damage.

5. Medical evaluations

Respirators may affect the health of the person using the equipment because of added stress on the pulmonary system. It is recommended that a physician evaluate each respirator user to determine that he or she can wear a respirator without difficulty. It is up to the physician to determine what will constitute a medical evaluation. A physician may or may not require a physical examination as part of the health assessment.

To perform this task the physician must be given information on the type of respirator being used and the type and length of work the worker will be performing while using the respirator. For most respirators, a normal healthy individual will not be affected by respirator wear, especially in the case of the lightweight air-purifying types.

Someone expected to use an SCBA under emergency conditions will need a more careful evaluation. The weight of the SCBA by itself adds considerably to the amount of work that must be performed.

6. Approved respirators

Many governments have systems to test and approve the performance of respirators for use in their jurisdictions. In such cases, an approved respirator should be used since the fact of its approval indicates that the respirator has met some minimum requirement for performance. If no formal approval is required by the government, any validly approved respirator is likely to provide better assurance that it will perform as intended when compared to a respirator that has gone through no special approval testing whatsoever.

Problems Affecting Respirator Programmes

There are several areas of respirator use that may lead to difficulties in managing a respirator programme. These are the wearing of facial hair and the compatibility of glasses and other protective equipment with the respirator being worn.

Facial hair

Facial hair can present a problem in managing a respirator programme. Some workers like to wear beards for cosmetic reasons. Others experience difficulty shaving, suffering from a medical condition where the facial hairs curl and grow into the skin after shaving. When a person inhales, negative pressure is built up inside the respirator, and if the seal to the face is not tight, contaminants can leak inside. This applies to both air-purifying and supplied-air respirators. The issue is how to be fair, to allow people to wear facial hair, yet to be protective of their health.

There are several research studies that demonstrate that facial hair in the sealing surface of a tight-fitting respirator leads to excessive leakage. Studies have also shown that in connection with facial hair the amount of leakage varies so widely that it is not possible to test whether workers may receive adequate protection even if their respirators were measured for fit. This means that a worker with facial hair wearing a tight-fitting respirator may not be sufficiently protected.

The first step in the solution of this problem is to determine if a loose-fitting respirator can be used. For each type of tight-fitting respirator—except for self contained breathing apparatus and combination escape/air-line respirators—a loose-fitting device is available that will provide comparable protection.

Another alternative is to find another job for the worker which does not require the use of a respirator. The final action that can be taken is to require the worker to shave. For most people who have difficulty shaving, a medical solution can be found that would allow them to shave and wear a respirator.

Eyeglasses and other protective equipment

Some workers need to wear eyeglasses in order to see adequately and in some industrial environments, safety glasses or goggles have to be worn to protect the eyes from flying objects. With a half-mask respirator, eyeglasses or goggles can interfere with the fit of the respirator at the point where it is seated on the bridge of the nose. With a full facepiece, the temple bars of a pair of eyeglasses would create an opening in the sealing surface of the respirator, causing leakage.

Solutions to these difficulties run as follows. For half-mask respirators, a fit test is first carried out, during which the worker should wear any glasses, goggles or other protective equipment that may interfere the respirator’s function. The fit test is used to demonstrate that eyeglasses or other equipment will not interfere with the function of the respirator.

For full-facepiece respirators, the options are to use contact lenses or special eyeglasses that mount inside the facepiece—most manufacturers supply a special spectacles kit for this purpose. At times, it has been thought that contact lenses should not be used with respirators, but research has shown that workers can use contact lenses with respirators without any difficulty.

Suggested Procedure for Respirator Selection

Selecting a respirator involves analysing how the respirator will be used and understanding the limitations of each specific type. General considerations include what the worker will be doing, how the respirator will be used, where the work is located and any limitations a respirator may have on work, as shown schematically in figure 31.19 .

Figure 31.19 Guide to Respirator Selection

Worker activity and worker location in a hazardous area need to be considered in selecting the proper respirator (for example, whether the worker is in the hazardous area continuously or intermittently during the work shift and whether the work rate is light, medium or heavy). For continuous use and heavy work a lightweight respirator would be preferred.

Environmental conditions and level of effort required of the respirator wearer may affect respirator service life. For example, extreme physical exertion can cause the user to deplete the air supply in a SCBA such that its service life is reduced by half or more.

The period of time that a respirator must be worn is an important factor that has to be taken into account in selecting a respirator. Consideration should be given to the type of task—routine, nonroutine, emergency, or rescue work—that the respirator will be called upon to perform.

The location of the hazardous area with respect to a safe area having respirable air must be considered in selecting a respirator. Such knowledge will permit planning for the escape of workers if an emergency occurs, for the entry of workers to perform maintenance duties and for rescue operations. If there is a long distance to breathable air or if the worker needs to be able to walk around obstacles or climb steps or ladders, then a supplied-air respirator would not be a good choice.

If the potential for an oxygen-deficient environment exists, measure the oxygen content of the relevant work space. The class of respirator, air-purifying or supplied-air, that can be used will depend on the partial pressure of oxygen. Because air-purifying respirators only purify the air, sufficient oxygen must be present in the surrounding atmosphere to support life in the first place.

Respirator selection involves reviewing each operation to ascertain what dangers may be present (hazard determination) and to select the type or class of respirators that can offer adequate protection.

Hazard Determination Steps

In order to determine the properties of the contaminants that may be present in the workplace, one should consult the key source for this information, namely, the supplier of the material. Many suppliers provide their customers with a material safety data sheet (MSDS) which reports the identity of the materials in a product and supplies information on exposure limits and toxicity as well.

One should determine whether there is a published exposure limit such as a threshold limit value (TLV), permissible exposure limit (PEL), maximum acceptable concentration, (MAK), or any other available exposure limit or estimate of toxicity for the contaminants. It ought to be ascertained whether a value for the immediately dangerous to life or health (IDLH) concentration for the contaminant is available. Each respirator has some use limitation based on the level of exposure. A limit of some sort is needed to determine whether the respirator will provide sufficient protection.

Steps should be taken to discover if there is a legally mandated health standard for the given contaminant (as there is for lead or asbestos). If so, there may be specific respirators required that will help narrow the selection process.

The physical state of the contaminant is an important characteristic. If an aerosol, its particle size should be determined or estimated. The vapour pressure of an aerosol is also significant at the maximum expected temperature of the work environment.

One should determine whether the contaminant present can be absorbed through the skin, produce skin sensitization or be irritating or corrosive to the eyes or skin. It should also be found for a gaseous or vapour contaminant if a known odour, taste or irritation concentration exists.

Once the identity of the contaminant is known, its concentration needs to be determined. This is normally done by collecting the material on a sample medium with subsequent analysis by a laboratory. Sometimes the assessment can be accomplished by estimating exposures, as described below.

Estimating Exposure

Sampling is not always required in hazard determination. Exposures can be estimated by examining data relating to similar tasks or by calculation by means of a model. Models or judgment can be used to estimate the likely maximum exposure and this estimate can be used to select a respirator. (The most basic models suitable to such a purpose is the evaporation model, a given amount of material is either assumed or allowed to evaporate into an air space, its vapour concentration found, and an exposure estimated. Adjustments can be made for dilution effects or ventilation.)

Other possible sources of exposure information are articles in journals or trade publications which present exposure data for various industries. Trade associations and data collected in hygiene programmes for similar processes are also useful for this purpose.

Taking protective action based on estimated exposure involves making a judgement based on experience vis-à-vis the type of exposure. For example, air monitoring data of previous tasks will not be useful in the event of the first occurrence of a sudden break in a delivery line. The possibility of such accidental releases must be anticipated in the first place before the need of a respirator can be decided, and the specific type of respirator chosen can then be made on the basis of the estimated likely concentration and nature of the contaminant. For example, for a process involving toluene at room temperatures, a safety device that offers no more protection than a continuous-flow air line need be chosen, since the concentration of toluene would not be expected to exceed its IDLH level of 2,000 ppm. However, in the case of a break in a sulphur dioxide line, a more effective device—say, an air-supplied respirator with an escape bottle—would be called for, since a leak of this sort could quite readily result in an ambient concentration of contaminant above the IDLH level of 20 ppm. In the next section, respirator selection will be examined in further detail.

Specific Respirator Selection Steps

If one is unable to determine what potentially hazardous contaminant may be present, the atmosphere is considered immediately dangerous to life or health. An SCBA or air line with an escape bottle is then required. Similarly, if no exposure limit or guideline is available and estimates of the toxicity cannot be made, the atmosphere is considered IDLH and an SCBA is required. (See the discussion below on the subject of IDLH atmospheres.)

Some countries have very specific standards governing respirators that can be used in given situations for specific chemicals. If a specific standard exists for a contaminant, the legal requirements must be followed.

For an oxygen-deficient atmosphere, the type of respirator selected depends on the partial pressure and concentration of oxygen and the concentration of the other contaminants that may be present.

Hazard ratio and assigned protection factor

The measured or estimated concentration of a contaminant is divided by its exposure limit or guideline to obtain its hazard ratio. With respect to this contaminant, a respirator is selected that has an assigned protection factor (APF) greater than the value of the hazard ratio (the assigned protection factor is the estimated performance level of a respirator). In many countries, a half mask is assigned an APF of ten. It is assumed that the concentration inside the respirator will be reduced by a factor of ten, that is, the APF of the respirator.

The assigned protection factor can be found in any existent regulations on respirator use or in the American National Standard for Respiratory Protection (ANSI Z88.2 1992). ANSI APFs are listed in table 31.13 .

Table 31.13 Assigned protection factors from ANSI Z88 2 (1992)

Type of respirator

Respiratory inlet covering

 

Half mask1

Full facepiece

Helmet/hood

Loose-fitting facepiece

Air-Purifying

10

100

 

 

Atmosphere-supplying

SCBA (demand-type)2

10

100

 

 

Airline(demand-type)

10

100

 

 

Powered air-purifying

50

10003

10003

25

Atmosphere-supplying air-line type

Pressure-fed demand type

50

1000

-

-

Continuous Flow

50

1000

1000

25

Self-contained breathing apparatus

Positive pressure (demand open/closed circuit)

-

4

-

-

1 Includes one-quarter mask, disposable half masks and half masks with elastomeric facepieces.

2 Demand SCBA shall not be used for emergency situations such as fire fighting.

3 Protection factors listed are for high efficiency filters and sorbents (cartridges and canisters). With dust filters an assigned protection factor of 100 is to be used due to the limitations of the filter.

4 Although positive pressure respirators are currently regarded as providing the highest level of  respiratory protection, a limited number of recent simulated workplace studies concluded that all  users may not achieve protection factors of 10,000. Based on this limited data, a definitive assigned  protection factor could not be listed for positive pressure SCBAs. For emergency planning purposes  where hazardous concentrations can be estimated, an assigned protection factor of no higher than  10,000 should be used.

Note: Assigned protection factors are not applicable for escape respirators. For combination respirators, e.g., air-line respirators equipped with an air-purifying filter, the mode of operation in use will dictate the assigned protection factor to be applied.

Source: ANSI Z88.2 1992.

For example, for a styrene exposure (exposure limit of 50 ppm) with all of the measured data at the worksite less than 150 ppm, the hazard ratio is 3 (that is, 150 ¸ 50 = 3). Selection of a half-mask respirator with an assigned protection factor of 10 will assure that most unmeasured data will be well below the assigned limit.

In some cases where “worst-case” sampling is done or only a few data are collected, judgement must be used to decide if enough data have been collected for an acceptably reliable assessment of exposure levels. For example, if two samples were collected for a short-term task that represents the “worst-case” for that task and both samples were less than two times the exposure limit (a hazard ratio of 2), a half-mask respirator (with an APF of 10) would likely be an appropriate choice and certainly a continuous-flow full facepiece respirator (with an APF of 1,000) would be sufficiently protective. The contaminant’s concentration must also be less than the maximum-use concentration of the cartridge/canister: this latter information is available from the manufacturer of the respirator.

Aerosols, gases and vapours

If the contaminant is an aerosol, a filter will have to be used; the choice of filter will depend on the efficiency of the filter for the particle. The literature provided by the manufacturer will provide guidance on the appropriate filter to use. For example, if the contaminant is a paint, lacquer or enamel, a filter designed specifically for paint mists may be used. Other special filters are designed for fumes or dust particles that are larger than usual.

For gases and vapours, adequate notice of cartridge failure is necessary. Odour, taste or irritation are used as indicators that the contaminant has “broken through” the cartridge. Therefore, the concentration at which the odour, taste or irritation is noted must be less than the exposure limit. If the contaminant is a gas or vapour that has poor warning properties, the use of an atmosphere-supplying respirator is generally recommended.

However, atmosphere-supplying respirators sometimes cannot be used because of the lack of an air supply or because of the need for worker mobility. In this case, air-purifying devices may be used, but it is necessary that it be equipped with an indicator signalling the end of the device’s service life so that the user will be given adequate warning prior to contaminant breakthrough. Another alternative is to use a cartridge change schedule. The change schedule is based on cartridge service data, expected concentration, pattern of use and duration of exposure.

Respirator selection for emergency or IDLH conditions

As noted above, IDLH conditions are presumed to exist when the concentration of a contaminant is not known. Furthermore, it is prudent to consider any confined space containing less than 20.9% oxygen as an immediate danger to life or health. Confined spaces present unique hazards. Lack of oxygen in confined spaces is the cause of numerous deaths and serious injuries. Any reduction in the percentage of oxygen present is proof, at a minimum, that the confined space is not adequately ventilated.

Respirators for use under IDLH conditions at normal atmospheric pressure include either a positive-pressure SCBA alone or a combination of a supplied-air respirator with an escape bottle. When respirators are worn under IDLH conditions, at least one standby person must be present in a safe area. The standby person needs to have the proper equipment available to assist the wearer of the respirator in case of difficulty. Communications have to be maintained between the standby person and the wearer. While working in the IDLH atmosphere, the wearer needs to be equipped with a safety harness and safety lines to permit his or her removal to a safe area, if necessary.

Oxygen-deficient atmospheres

Strictly speaking, oxygen deficiency is a matter only of its partial pressure in a given atmosphere. Oxygen deficiency can be caused by a reduction in the percentage of oxygen in the atmosphere or by reduced pressure, or both reduced concentration and pressure. At high altitudes, reduced total atmospheric pressure can lead to very low oxygen pressure.

Humans need a partial oxygen pressure of approximately 95 mm Hg (torr) to survive. The exact pressure will vary among people depending on their health and acclimatization to reduced oxygen pressure. This pressure, 95 mm Hg, is equivalent to 12.5% oxygen at sea level or 21% oxygen at an altitude of 4,270 meters. Such an atmosphere may adversely affect either the person with reduced tolerance to reduced oxygen levels or the unacclimatized person performing work requiring a high degree of mental acuity or heavy stress.

To prevent adverse effects, supplied-air respirators should be provided at higher oxygen partial pressures, for example, about 120 mm Hg or 16% oxygen content at sea level. A physician should be involved in any decisions where people will be required to work in reduced-oxygen atmospheres. There may be legally mandated levels of oxygen percent or partial pressure that require supplied-air respirators at different levels than these broadly general guidelines suggest.

Suggested Procedures for Fit Testing

Each person assigned a tight-fitting negative-pressure respirator needs to be fit tested periodically. Each face is different, and a specific respirator may not fit a given person’s face. Poor fit would allow contaminated air to leak into the respirator, lowering the amount of protection the respirator provides. A fit test needs to be repeated periodically and must be carried out whenever a person has a condition that may interfere with facepiece sealing, e.g., significant scarring in the area of the face seal, dental changes, or reconstructive or cosmetic surgery. Fit testing has to be done while the subject is wearing protective equipment such as spectacles, goggles, a face shield or a welding helmet that will be worn during work activities and could interfere with respirator fit. The respirator should be configured as it will be used, that is, with a chin canister or cartridge.

Fit test procedures

Respirator fit testing is conducted to determine if a particular model and size of mask fits an individual’s face. Before the test is made, the subject should be oriented on the respirator’s proper use and donning, and the test’s purpose and procedures should be explained. The person being tested should understand that the he or she is being asked to select the respirator that provides the most comfortable fit. Each respirator represents a different size and shape and, if fit properly and used properly, will provide adequate protection.

No one size or model of respirator will fit all types of faces. Different sizes and models will accommodate a broader range of facial types. Therefore, an appropriate number of sizes and models should be available from which a satisfactory respirator can be selected.

The person being tested should be instructed to hold each facepiece up to the face and eliminate those which obviously do not give a comfortable fit. Normally, selection will begin with a half mask, and if a good fit cannot be found, the person will need to test a full facepiece respirator. (A small percentage of users will not be able to wear any half mask.)

The subject should conduct a negative- or positive-pressure fit check according to the instructions provided by the manufacturer before the test is begun. The subject is now ready for fit testing by one of the methods listed below. Other fit test methods are available, including quantitative fit test methods which use instruments to measure leakage into the respirator. The fit test methods, which are outlined in the boxes here, are qualitative and do not require expensive test equipment. These are (1) the isoamyl acetate (IAA) protocol and (2) the saccharin solution aerosol protocol.

Test exercises. During the fit test, the wearer should carry out a number of exercises in order to verify that the respirator will allow him or her to perform a set of basic and necessary actions. The following six exercises are recommended: standing still, breathing normally, breathing deeply, moving the head from side to side, moving the head up and down, and speaking. (See figure 31.20 and figure 31.21).

Figure 31.20 Isoamyl acetate quantitive fit-test method

Odour Threshold Screening

1. Three one-litre glass jars with metal lids (e.g., ordinary canning jars) are required. (Note some manufacturers sell a fit test kit with all the parts and solutions necessary to perform this test.)

2. Odour-free water (e.g., distilled or spring water) at approximately 25°C should be used for the solutions.

3. The isoamyl acetate (IAA) (also known as isopentyl acetate) stock solution is prepared by adding 1 ml of pure IAA to 800 ml of odour-free water in a one-litre jar and shaking for 30 seconds. This solution should be prepared afresh at least weekly.

4. The odour test solution is prepared in a second jar by placing. 0.4 ml of the stock solution into 500 ml of odour-free water by means of a clean dropper or pipette. Shake for 30 seconds and allow to stand for two to three minutes so that the IAA concentration above the liquid may reach equilibrium. This solution may be used for only one day.

5. A test blank is prepared in a third jar by adding 500 ml of odour-free water.

6. The screening test should be conducted in a room separate from the room used for actual fit testing. The two rooms should be independently and efficiently ventilated—they should not be connected to a recirculating ventilation system.

7. The odour test and test blank jars should be labelled by some means for identification.

8. The person being tested should be instructed to make sure the covers are on tight, and then to shake each bottle. Next, unscrewing the lid of each bottle, the person sniffs at the mouth of the bottle and indicates which bottle smells like bananas.

9. The mixtures used in the IAA odour detection test should be prepared in an area separate from that in which the test is performed,in order to prevent olfactory fatigue in the person being tested.

10. If the person is unable correctly to identify the jar containing the odour test solution, the IAA QLFT may not be used.

Fit Test

1. The fit test chamber should be substantially similar to a clear 55-gallon drum liner suspended inverted over a two-foot diameter frame, so that the top of chamber is about six inches above the person’s head. A small hook should be attached to the inside top center of the chamber.

2. Each respirator used for the fitting and fit testing should be equipped with organic vapour cartridges or in some other way should offer protection against organic vapours. The cartridges or masks should be changed at least weekly.

3. After selecting, donning and properly adjusting a respirator, the subject being tested should wear it to the fit test room. This room should be separate from the room used for odour threshold screening and respirator selection, and should be well ventilated, as by an exhaust fan or lab hood, to prevent general room contamination.

4. A copy of the test exercises should be taped to the inside of the test chamber.

5. Upon entering the test chamber, the subject should be given a 6 inch by 5 inch piece of paper towel or other porous, absorbent single-ply material, folded in half and wetted with 0.75 ml of pure IAA. The towel is hung on the hook at the top of the chamber.

6. Allow two minutes for the IAA test concentration to be reached before starting the fit test exercises. This would be an appropriate time to talk with the subject, to explain the fit test, the importance of cooperation, the purpose for the head exercises or to demonstrate some of the exercises.

7. Each exercise should be performed for 30 seconds to one minute.

8. If at any time during the test, the subject detects the banana-like odour of IAA, he or she should quickly exit from the test chamber and leave the test area to avoid olfactory fatigue.

9. Upon returning to the selection room, the subject should remove the respirator, repeat the odour sensitivity test, select and put on another respirator, return to the test chamber, etc. The process continues until a respirator that fits well has been found. Should the odour sensitivity test be failed, the person should wait about five minutes before retesting. Odour sensitivity will usually have returned by this time.

10. When a respirator is found that passes the test, its efficiency should be demonstrated for the person by having him or her break the face seal and take a breath before exiting the chamber.

11. Persons who have successfully passed this fit test may be assigned a device with protection factors no higher than 10.

Figure 31.21 Sacharin aerosol quantitive fit-test method

Taste Threshold Screening

1. A test enclosure is used that is approximately 30 cm in diameter by 35 cm tall whose front portion (at least) is transparent. It should allow free movement of the head when a respirator is worn. (Note that some manufacturers sell a fit test kit with all the parts and solutions necessary to perform this test.)

2. The test enclosure should have a three-quarter inch hole in front of the test subject's nose and mouth area to accommodate the nebulizer nozzle.

3. The entire screening and testing procedure should be explained to the person prior to the conduct of the screening test.

4. The subject should place the test enclosure over his or her head. For the threshold screening test, the subject should breathe through the open mouth.

5. Using a DeVilbiss Model 40 inhalation medication nebulizer or equivalent, the test conductor should spray the threshold check solution into the enclosure. This nebulizer should be clearly marked to distinguish it from the fit test solution nebulizer (below).

6. The threshold check solution consists of 0.83 grams of sodium saccharin (USP) in water. It is prepared by placing 1 ml of the fit test solution (see below) in 100 ml of water.

7. To produce the aerosol, the nebulizer bulb is firmly squeezed so that it collapses completely and then released and allowed to expand fully.

8. Ten squeezes of the bulb are repeated rapidly so as to direct the saccharin aerosol into the enclosure and the subject is asked whether the saccharin can be tasted. Correct use of the nebulizer should result in the delivery of approimately 1 ml of liquid for each ten squeezes.

9. If the first response is negative, ten more squeezes are repeated rapidly and the person is again asked whether the saccharin is tasted.

10. If the second response is negative, ten more squeezes are repeated rapidly and the subject is again asked whether the saccharin can be tasted.Sorry

11. The test conductor will take note of the number of squeezes required to elicit a taste response (10, 20 or 30).

12. If the saccharin is not tasted after 30 squeezes, the subject may not perform the saccharin fit test.

13. If a taste response is elicited, the subject should be asked to take note of the taste for reference in the fit test.

Fit Test

1. The fit test uses the same enclosure described above.

2. Respirators to be tested should be selected as described above. The respirator should be equipped with a particulate filter.

3. Each subject should wear his or her respirator for several minutes before starting the fit test.

4. The subject should put on the enclosure while wearing the respirator selected.

5. The subject may not eat, drink (except plain water) or chew gum for 15 minutes before the test begins.

6. A second DeVilbiss Model 40 inhalation medication nebulizer or equivalent is used to spray the fit test solution into the enclosure. This nebulizer should be clearly marked to distinguish it from the screening test solution nebulizer.

7. The fit test solution is prepared by adding 83 grams of sodium saccharin to 100 ml of warm water.

8. As before, the subject should breathe through the open mouth.

9.The nebulizer is inserted into the hole in the front of the enclosure and the fit test solution is sprayed into the enclosure using the same technique as for the taste threshold screening and the same number of squeezes required to elicit a taste response in the screening (10, 20 or30).

10. After generation of the aerosol the subject should be instructed to perform the test exercises listed above.

11. Every 30 seconds, the aerosol concentration should be replenished using one-half the number of squeezes as initially (5, 10 or 15).

12. The subject should indicate to the test conductor if at any time during the fit test the taste of saccharin isdetected.

13. If the saccharin is detected the fit is deemed unsatisfactory and a different respirator should be tried.

14. Subjects who have successfully passed this fit test may be assigned devices with protection factors no higher than 10.

REFERENCES 

American Industrial Hygiene Association (AIHA). 1991. Respiratory Protection: A Manual and Guideline. Fairfax, Va: AIHA.

American National Standards Institute (ANSI). 1974. Method for the Measurement of Real-Ear Protection of Hearing Protectors and Physical Attenuation of Earmuffs. Document No. S3.19-1974 (ASA Std 1-1975). New York: ANSI.

—. 1984. Method for the Measurement of Real-Ear Attenuation of Hearing Protectors. Document No. S12.6-1984 (ASA STD55-1984). New York: ANSI.

—. 1989. Practice for Occupational and Educational Eye and Face Protection. Document No. ANSI Z 87.1-1989. New York: ANSI.

—. 1992. American National Standard for Respiratory Protection. Document No. ANSI Z 88.2. New York: ANSI.

Berger, EH. 1988. Hearing protectors - Specifications, fitting, use and performance. In Hearing Conservation in Industry, Schools and the Military, edited by DM Lipscomb. Boston: College-Hill Press.

—. 1991. Flat-response, moderate-attenuation and level-dependent HPDs: How they work, and what they can do for you. Spectrum 8 Suppl. 1:17.

Berger, EH, JR Franks, and F Lindgren. 1996. International review of field studies of hearing protector attenuation. In Proceedings of the Fifth International Symposium: Effects of Noise On Hearing, edited by A Axelsson, H Borchgrevink, L Hellstrom, RP Hamernik, D Henderson, and RJ Salvi. New York: Thieme Medical.

Berger, EH, JE Kerivan, and F Mintz. 1982. Inter-laboratory variability in the measurement of hearing protector attenuation. J Sound Vibrat 16(1):14-19.

British Standards Institute (BSI). 1994. Hearing Protectors - Recommendations for Selection, Use, Care and Maintenance - Guidance Document. Document No. BSI EN 458:1994. London: BSI.

Bureau of Labour Statistics. 1980. Work Injury Report - An Administrative Report On Accidents Involving Foot Injuries. Washington, DC: Bureau of Labour Statistics, Department of Labour.

European Committee for Standardization (CEN). 1993. Industrial Safety Helmets. European Standard EN 397-1993. Brussels: CEN.

European Economic Community (EEC). 1989. Directive 89/686/EEC On the Approximation of the Laws of the Member States Relating to Personal Protective Equipment. Luxembourg: EEC.

European Standard (EN). 1995. Specification for welding filters with switchable luminous transmittance and welding filters with dual luminous transmittance. Final draft ref. no. pr EN 379: 1993E.

Federal Register. 1979. Noise Labeling Requirements for Hearing Protectors. Fed. regist. 44 (190), 40 CFR, part 211: 56130-56147. Washington, DC: GPO.

—. 1983. Occupational Noise Exposure: Hearing Conservation Amendment: Final Rule. Fed regist.. 48 (46): 9738-9785. Washington, DC: GPO.

—. 1994. Respiratory Protection. Fed regist. Title 29, Part 1910, Subpart 134. Washington, DC: GPO.

Franks, JR. 1988. Number of workers exposed to occupational noise. Sem Hearing 9(4):287-298, edited by W. Melnick.

Franks, JR, CL Themann, and C Sherris. 1995. The NIOSH Compendium of Hearing Protection Devices. Publication no. 95-105. Cincinnati, Ohio: NIOSH.

International Organization for Standardization (ISO). 1977. Industrial Safety Helmets. ISO 3873. Geneva: ISO.

—. 1979. Personal Eye-Protectors for Welding and Related Techniques - Filters - Utilization and Transmittance Requirement. International Standard ISO 4850. Geneva: ISO.

—. 1981. Personal Eye-Protectors – Filters and Eye-Protectors against Laser Radiation. ISO 6161-1981. Geneva: ISO.

—. 1990. Acoustics -Hearing Protectors -Part 1: Subjective Method for the Measurement of Sound Attenuation. ISO 4869-1:1990(E).Geneva: ISO.

—. 1994. Acoustics -Hearing Protectors -Part 2: Estimation of Effective A-Weighted Sound Pressure Levels When Hearing Protectors Are Worn. ISO 4869-2:1994(E). Geneva: ISO.

Luz, J, S Melamed, T Najenson, N Bar, and MS Green. 1991. The structured ergonomic stress level (E-S-L) index as a predictor of accident and sick leave among male industrial employees. In Proceedings of the ICCEF 90 Conference, edited by L Fechter. Baltimore: ICCEF.

Marsh, JL. 1984. Evaluation of saccharin qualitative fitting test for respirators. Am Ind Hyg Assoc J 45(6):371-376.

Miura, T. 1978. Shoes and Foot Hygiene (in Japanese). Tokyo: Bunka Publishing Bureau.

—. 1983. Eye and face protection. In Encyclopaedia of Occupational Health and Safety, 3rd edition. Geneva: ILO.

National Institute for Occupational Safety and Health (NIOSH). 1987. NIOSH Respirator Decision Logic. Cincinnati, Ohio: NIOSH, Division of Standards Development and Technology Transfer.

National Safety Council. N.d. Safety Hats, Data Sheet 1-561 Rev 87. Chicago: National Safety Council.

Nelson, TJ, OT Skredtvedt, JL Loschiavo, and SW Dixon. 1984. Development of an improved qualitative fit test using isoamyl acetate. J Int Soc Respir Prot 2(2):225-248.

Nixon, CW and EH Berger. 1991. Hearing protection devices. In Handbook of Acoustical Measurements and Noise Control, edited by CM Harris. New York: McGraw-Hill.

Pritchard, JA. 1976. A Guide to Industrial Respiratory Protection. Cincinnati, Ohio: NIOSH.

Rosenstock, LR. 1995. Letter of March 13, 1995 from L. Rosenstock, Director, National Institute for Occupational Safety and Health, to James R. Petrie, Committee Chairperson, Mine Safety and Health Administration, US Department of Labour.

Scalone, AA, RD Davidson, and DT Brown. 1977. Development of Test Methods and Procedures for Foot Protection. Cincinnati, Ohio: NIOSH.

OTHER RELEVANT READINGS 

Head protection at work. 1986. J Occup Acc 8(3):157-236.

Mayer, A, S Salsi, and JP Grosdemange. 1974. Industrial safety helmets. Result of tests, principal manufacturing details, criteria for selection (in French). Notes Sci Tech 14.