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 1, figure 2 and figure 3). 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 1. Safety shoes

Figure 2. Heat protective boots

Figure 3. 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.

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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 1). The shell must therefore resist deformation and perforation.
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.

Figure 1. Example of essential elements of safety helmet construction

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 1), 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 1. Safety helmets: testing requirements of ISO Standard 3873-1977

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 1).
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 2). For use in mines and underground quarries, attachments for a headlamp and a cable holder are fitted.

Figure 2. 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.

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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 1.

Figure 1. 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 2 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 2. 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 1.

Table 1. 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.

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 2.

Table 2. 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).

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 2 (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 2. 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 1. 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 3 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 3 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 3. Well-fitted and poorly fitted earmuffs and their attenuation consequences

Earplugs

Figure 4 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 4. A well-fitted and a poorly fitted foam earplug and the attenuation consequences

Figure 5 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 5. 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.

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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 1 summarizes these.

Table 1. Examples of dermal hazard categories

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 1, 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 2 summarizes typical physical, chemical, and biological performance requirements and common protective materials used for hazard protection.

Table 2. Common physical, chemical and biological performance requirements

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 1 and figure 2.

Figure 1. A worker wearing gloves and a chemically protective garment pouring chemical

Figure 2. 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 3). 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 4).

Figure 3. Various types of chemically resistant gloves

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Figure 4. 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. 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.

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