This chapter involves protecting human beings who enter environments that contain hazards such as radiation, chemical or biological contamination, and electric shock. Because many of the same principles are involved in protecting people and products from human contamination, it also includes a discussion of clothing for personnel who work in medical facilities or cleanrooms.
Four significant types of environmental threats from which individuals in a variety of work and life situations need to be protected are chemical, biological, radiological, and nuclear hazards, generally referred to as CBRN. While these hazards can occur in any of the three states of matter (solid, liquid, or gas), some of the most hazardous to humans often occur in a combination of those states as aerosols. Aerosols are tiny particles of solids or liquids suspended in a gas. They include dusts, sprays, smoke, and mists. Because they are airborne, they can lead to more widespread transmission of hazards than, for example, a solid, which would need to be contacted by each individual. Dusts, often referred to as suspended particulate matter, can distribute fibers such as asbestos; chemical hazards such as oily chemical agents and pesticides; and radioactive material or biohazards such as molds and spores over a relatively large area.
The size of particles in the environment or suspended in aerosols can be of major concern to protective clothing designers as they choose appropriate materials and configure designs. The way in which particles behave is also a factor. Since particles are often irregularly shaped, the term aerodynamic diameter is used to describe particle size. Aerodynamic diameter is the equivalent diameter of a sphere with a specific density that would move at the same rate as the particle being described. Most aerosols contain particles of many different sizes, so specifications for protection often include the maximum number of particles of each size that is acceptable for protection to be considered sufficient.
Examples of chemical substances from which humans need protection include pesticides, industrial byproducts, or chemical warfare agents. Because many of these hazards involve not only solids, liquids, and gases but also mixed phases such as aerosols, they thus require attention to their solid, liquid, and gaseous components for proper protection. Many substances in this category are grouped together under what are labeled toxic industrial chemicals (TICs). The U.S. Occupational Safety and Health Administration (OSHA) states that TICs “can be chemical hazards (e.g., carcinogens, reproductive hazards, corrosives, or agents that affect the lungs or blood) or physical hazards (e.g., flammable, combustible, explosive, or reactive)” (OSHA, “Toxic Industrial”). Of primary importance is that materials used for protection must not be damaged or defeated by the chemicals involved.
Biological hazards involve living organisms that can reproduce in supportive environments. These include bacteria, viruses, and infectious wastes of many kinds. They are particularly dangerous because even minute amounts can debilitate a community once they have entered just one “host” and subsequently been passed to others while they continue to grow. In the face of epidemics, as the public becomes increasingly concerned about contagious diseases such as hepatitis, Ebola, or various forms of flu, clothing that provides protection from biological hazards has been of special interest in health care fields.
Radiation hazards may result from the accidental release of radioactive material from a nuclear power plant or the explosion of an atomic bomb. Some of the substances in this category, such as the radioactive materials in a so-called “dirty bomb”, are among the hazards referred to as toxic industrial materials (TIMs). Radiation hazards in the workplace may involve either ionizing or nonionizing radiation. (See Energy Basics 7.2.)
In addition to CBRN hazards, many work situations contain dangers from electric shock or potential fire hazards from static electricity. Static electricity generated by personnel, and especially by the clothing they wear, also can damage products being manufactured.
Designers need to be aware of the ways in which each of these hazards is propelled toward the body and protective clothing. It is also important to understand the pathways by which these hazards reach the body and how they affect human health. These two topics will be discussed next. The remainder of the chapter is organized around the basics of each of these hazards: the effect of each hazard on the human body, the types of materials used for protection, and the factors that are important for clothing designers to consider in designing protection.
The danger of intrusion of a substance begins when some force attracts or moves hazardous substances toward the body or the surface of a protective garment. Thus, one of the keys to protection lies in eliminating the attraction of hazards to the area being protected and increasing their acceleration away from the area.
Airflow provides much of the impetus required to move substances toward, away from, or around the body and protective clothing. For example, when a surgeon bends an elbow in a surgical gown, that movement pushes air in the sleeve toward a localized area and may force bacteria or blood through interstices in a gown made of woven fabric. Movement in clothing may also create the kind of bellows effect discussed in Chapter 5. It propels organisms from the inside of a garment through the nearest garment openings into the air outside. Other movements, as well as inhalation can create a negative pressure that draws organisms into garments or into the respiratory tract.
The kinetic energy of moving air is often utilized in protective clothing. People who work with nerve gas or unknown disease-bearing agents generally wear a positive pressure (inflated) garment. (See Figure 7.1 and also Case Study 2.1 in Chapter 2.) Air fed into the suit is vented outward so that if a leak should occur, the air flowing out would propel dangerous substances away from the body.
Isolation clothing and transport equipment for people with infectious diseases use negative pressure to protect people around the wearer. (See Figure 7.2.) Thus, if a break occurs in an isolation garment, any organisms would be pulled into the garment rather than pushed out toward a noninfected person.
Air-flow techniques may be designed into the circulation systems in rooms to direct the flow of particles in the environment and thus reduce the need for protective clothing. In an operating room, for example, a surgeon may stand on the downwind side of the operating table so that any infectious particles are accelerated away from the patient. Airflow techniques are also used to direct radioactive gases and particles away from workers in uranium mines.
Airflow alone may not be effective in directing particle movement if some other attractive force is present. Static electricity, for example, may cause electrically charged particles to accelerate rapidly toward an area having an opposite charge, even opposing airflow. That is why antistatic finishes are so important in many medical and industrial garments. If particles are accelerating toward a protective garment, then the size, shape, and elasticity of the particle become critical considerations in determining the types of protective materials needed. All of the factors that affect larger-scale impacts discussed in Chapter 6 also affect these smaller-scale interactions. In addition to mass and velocity, compressibility and surface roughness of the particles need to be considered. If protection from a specific particle is to be provided, not only will these factors need to be determined, but the ways in which particles may be changed after the initial collision must also be anticipated.
Hazardous substances may reach and eventually harm the body by four different routes. The first is by direct contact. The substance can be touched or spilled on the skin. Substances that enter the body in this manner are termed percutaneous (through the skin) threats. A droplet of moisture containing the organism of a disease, for example, may be propelled through the air toward a healthy individual by means of a sneeze or cough, or it may be left on items that the infected individual has touched. Direct contact may also occur through an open wound or exposed mucous membranes, such as those surrounding the eye.
Various areas of the body may be affected by contact with the same chemical, biological, or radioactive substance in different ways. Figure 7.3 shows, for example, the degree to which different areas of the body can absorb the pesticide, parathion. While the palm of the hand absorbs only about 2 percent of the parathion that contacts it, the scrotum may absorb as much as 100 percent. Biological organisms in particular may be very system-specific in terms of their route into the body and the way in which they harm the body. The military has developed a model called the Body Region Hazard Analysis (BRHA) that is used to convert measures of exposure at 20 different locations on the body into a value that indicates the relative protection offered by items of chemical protective clothing (Standing Committee, 1997). This analysis takes into account both the exposure to chemical/biological hazards and the relative sensitivity of each body area.
Second, damage may result from breathing in hazardous substances that are vaporized or suspended in the air. Hazards like pesticides, coal dust, or disease-bearing microorganisms may destroy the lining of the lungs or may move through the lungs into the bloodstream or the central nervous system where they can effect changes. Air containing radioactive particles may be breathed in and cause cell damage throughout the body. OSHA states that if TICs enter the body through the lungs, poisoning occurs more quickly “because of the ability of the agent to rapidly diffuse throughout the body” (OSHA “Toxic Industrial Chemicals”).
Third, hazardous substances may be ingested either directly or by ingesting contaminated food, drink, or drugs. As with airborne hazards, these may affect the digestive system directly or move through it to the circulatory or nervous system.
Fourth, a hazardous substance may be injected into the body. The substance may be a hazardous chemical or a biological organism deposited on a contaminated needle, or a toxin may be injected through the bite of an animal or insect.
Much of the protective clothing on the market today has been designed to cope with the first two pathways into the body and these will be the focus of this chapter. However, it is worth noting that although clothing and respirators are primarily designed to prevent hazards from touching the skin or being inhaled, many CBRN protective ensembles must totally enclose the body in order to be effective. Therefore, such activities as safe eating and drinking must be provided for in the design of the ensemble. In addition, because even minute amounts of toxins can be lethal, CBRN protective ensembles must be designed to avoid any puncture.
It should also be noted that since radiation is a form of electromagnetic energy that travels through space without the involvement of physical matter, radioactively contaminated material and other forms of radiation in the environment may affect body cells without actually entering the body via any of the routes discussed above.
Although chemical and biological hazards involve different substances, the ensembles used to protect the body from them are similar, and thus many clothing ensembles are designated as providing chemical/biological (CB) protection.
Impermeable materials appropriate for protection from CB hazards are generally films or sheets. (See Chapter 3.) They share many of the qualities of waterproof materials discussed in Chapter 3, but they must also have the characteristic of being non-reactive chemically with the hazardous substances in a specific environment. Films or sheets of polyvinyl chloride (PVC) polypropylene, polyurethane, polyethylene, and natural rubber are among those that provide CB protection. These differ in density (which eventually affects the weight of a garment), resistance to cracking, flexibility, tensile strength, and performance in extremes of temperatures. The relative cost of these materials may influence a designer’s choice of a material for a specific garment, particularly for a disposable item. In cases where films are not thought to have sufficient tensile strength, they may be bonded or laminated to a strong, thin fabric such as woven nylon. It is important for both designers and users to understand diffusion, which is a major concern for impermeable materials. (See Energy Basics 7.1.) To defeat a wider range of chemicals, several layers of different films may be laminated together into a single thin film.
Woven fabrics may also be made impermeable with coatings. One material that is frequently used for chemical protection is butyl-coated nylon. “Butyl” refers to butyl rubber, a synthetic rubber that resists a variety of chemicals and is impenetrable to gases. Because butyl rubber is highly elastic, has excellent elastic recovery, and resists sunlight, ozone, and other factors that accelerate aging, butyl-coated nylon does not suffer the amount of cracking and leakage commonly associated with coated fabrics. In addition, the nylon backing increases the strength and puncture resistance of the system. Neoprene and other synthetic rubbers may also be used in some industrial situations.
It is important that the materials chosen for CB garments have relatively smooth surfaces. This characteristic is essential if particles or drops of moisture are to be prevented from lodging in the fabric surface and making decontamination difficult.
In addition to a fabric’s resistance to toxic substances, one of the most important characteristics of an impermeable material for CB protection is the ease with which it can be made into clothing. Because stitching creates holes in clothing, garment parts must be joined by means of heat-sealing methods. (These methods are discussed in Chapter 9.) Some manufacturers sew garments in the normal fashion and then fuse a strip of thermoplastic suit material over each seam to fill in the needle holes (Figure 7.4). Barrier zippers such as those shown in Figures 9.25 and 9.26 may be used, or if a suit is disposable, a heat-sealing process may be used to close a suit once it is donned, and the suit is then merely slashed to allow exit. (See Figure 9.47.)
The characteristic resistance to chemicals of many of these materials makes them resistant to many adhesives and some may be resistant to specific heat sealing techniques as well. Therefore, it is extremely important that the possibilities for construction processes be explored as fabrics are being evaluated for their resistance to particular hazardous substances.
Selectively permeable membranes (SPMs) used for CB garments need to be carefully chosen so that protection is provided for all of the hazards in the environment. Information on the structure and function of SPMs can be found in Chapter 3 under “Permselective Treatments.”
Permeable materials may be worn for emergency or splash protection to provide a more comfortable, breathable garment for constant wear that can be removed quickly before chemicals completely penetrate the material. Sometimes material thickness is used to add to the necessary breakthrough time, or water-repellency may be used to discourage moisture that contains bacteria or other particles from being wicked through clothing. A surgeon’s gown, for example, may be made water repellent or waterproof in the areas most likely to come into contact with moisture. Thus, the gown in Figure 7.5 has a fluid-resistant section from midchest to knees and from wrist to elbow to prevent a fabric soaked with fluid (from the surgeon’s perspiration or the patient’s blood) from transferring bacteria through the garment to the sterile operating field.
Although one might think that tight weaves of cotton or of synthetic fibers (which do not absorb much moisture) might provide a good barrier to liquids, it has been shown that they may actually increase the penetration of liquids and sprays (Marer 2000, 165). This is particularly true with synthetics because the long, smooth, tightly packed fibers promote wicking and this capillary action encourages the rapid transport of liquids, especially those in droplet or aerosol form, from one face of a fabric to the other. Other studies have found that as the temperature of some liquids rise, their permeability rate increases, with some liquids being more significantly affected than others (Cao 2007).
The type of clothing needed to protect the body from CB hazards depends upon the hazards in the environment and the activity of the wearer. Sufficient protection may be provided by a face mask and rubber gloves or may require a totally encapsulating suit with a positive pressure backup system. Some of the most difficult problems for clothing designers arise in trying to isolate the body totally from CB hazards. Thus, many CB-protective garments are among the most innovative functional clothing designs.
In addition to providing basic protection, CB garments must meet many of the same criteria as everyday clothing. Ideally, they should (1) not interfere with the movement needed to do a specific job; (2) allow the wearer the maximum possible use of the senses of touch, hearing, and sight; (3) allow or provide for adequate relief from heat stress; and (4) if reusable, be easily cleanable. Both reusable and disposable garments need to be designed in a way that allows wearers to doff them without risking contamination. Because many items of CB protection are expensive, companies may own only a limited number of items. This means that adjustability may be a prime consideration in garment design since one suit may have to fit people of a variety of sizes and shapes.
If separate items (e.g., a jacket, pants, and hood) are being designed, the interfaces between them are particularly critical. Attention needs to be paid to providing wide overlaps so the pieces do not separate during movement. Garment edges need to be kept close to the body. For example, to keep a jacket hem close to the pants, some jackets have a strap that passes from back to front between the legs that can be secured at the front and adjusted to pull the jacket hem against the pants. Other jackets may have an inner elasticized “skirt” to hug the jacket to the pants below the waist. Restraint straps that pass under the arms may also be used to keep the lower edge of separate hoods close to the jacket. If equipment, such as that containing air supply, is to be worn over the garment, the location of garment overlaps may need to be planned so that the equipment helps secure garment edges but does not interfere with movement.
If protection is needed for a liquid hazard, once the proper liquid-protective material has been selected, a designer needs to develop garment features that will prevent liquids that run off the garment surface from penetrating the garment. This is usually done by paying close attention to overlaps and relating them to typical body positions for the worker. For example, the ensemble shown for a greenhouse worker spraying pesticides in Figure 7.6 has overlaps planned to accommodate the direction of liquid flow. Since the hands are generally up holding the hose, gloves overlap the sleeves to minimize liquid flow that might occur into the sleeve cuff if the gloves were tucked in. The neckline opening is lapped from front to back because of the direction in which the spray would be striking the body. The jacket provides a wide overlap and runoff area over the pants as do the pants over the boots. If the hands were held down at the sides, and water was being sprayed from above the body, it would make more sense to place the sleeve of the garment over the glove or to develop a secure connection that prevented penetration from any direction.
Exhaust valves or crack valves are usually placed in positive pressure suits to avoid an accidental bursting or blowout. Crack valves open when a predetermined level of pressure builds up, allowing a one-way escape of air from the suit. Exhaust valves or other openings of this type are often protected under some sort of splash cover (Figure 7.7) to prevent liquid from running down into vents and being accidentally propelled through them. Note that the opening of the splash cover is placed at the bottom so that gravity can assist in keeping liquids from entering the area.
In addition to understanding the user, activity, and environment before beginning to design CB clothing, designers need to be aware of government regulations in this area. For most activities in which hazards are present, there are recommendations or even mandates regulating what people in those situations must wear. Even if clothing is not mandated to be worn, many items of protective clothing must pass certain regulations in order to be manufactured or imported into specific countries. Having a thorough knowledge of these regulations is critical before beginning design work.
A number of groups and government agencies have researched hazards and the health risks with exposure to CB agents and proposed systems for classifying the levels of CB protection needed. Two types of classification systems for CB protective clothing will be discussed here—one for industry and one for the military.
The U.S. Environmental Protection Agency (EPA) has developed recommendations for personal protective equipment (PPE) for pesticide application. (EPA, “Personal Protective”). The International Organization for Standardization (ISO) and the American Society for Testing and Materials (ASTM) are also currently developing performance standards for pesticide applicators that will designate categories of protective clothing for three different levels of risk (NASDA “PPE for Pesticide”). There are also regulations for exposure to biological hazards such as bloodborne pathogens (OSHA “Occupational Exposure”).
The Occupational Safety and Health Administration has designated levels of personal protective equipment needed for work involving hazardous waste and for first responders who are at risk (OSHA “General Description”). These are used as guidelines for people who work in agriculture with pesticides as well as for those who work with chemicals in industrial situations. An example of a suit that could be worn for Level A protection can be found in Figure 7.11. It is to be used when the highest level of respiratory, skin, and eye protection is needed. It involves complete coverage with a totally encapsulating suit, a self-contained breathing apparatus (SCBA), and chemically resistant gloves and boots. A disposable protective suit may be worn over this ensemble to help with decontamination.
Level B is to be used when the highest level of respiratory protection is required but a lesser degree of skin coverage is needed. It involves the use of hooded, chemically resistant clothing for the areas in which the chemical hazards are most likely to contact the body (e.g., coveralls or an apron); a positive pressure, full-facepiece SCBA; chemically resistant gloves and boots; and a hard hat (Figure 7.8). A face shield is optional.
Level C guidelines are to be followed when specifics about respiratory hazards are known and criteria for protection with respirators can be set at a level lower than for Level B. The criteria for skin protection is similar to that for Level B. Level C protection typically involves the use of a filtered breathing system such as a gas mask with a sorbent canister, chemically resistant clothing that covers the most likely areas of contact with the chemical, and chemically resistant gloves and boots (see Figure 7.8C). A face shield is optional.
Level D protection is basically a work uniform with no respiratory or skin protection for what OSHA terms “nuisance contamination only.” It involves the use of coveralls and chemically resistant steel toe and shank boots (see Figure 7.8D). Items such as safety glasses or goggles, gloves, face shields, and hard hats are optional.
Military groups categorize degrees of CB protection using MOPP (Mission Oriented Protective Posture) levels. Each level is planned for a specific situation, from readiness when there is the threat of a chemical/biological warfare attack to the levels needed during and postattack. Figure 7.9 illustrates the gear worn by the U.S. Army for each of the MOPP levels. The protective gear includes a CB overgarment that is designed to be worn over the regular uniform, CB protective overboots and gloves, and a mask that filters out CB agents. The mask is accompanied by a hood that is either separate or part of the overgarment. The overgarment is breathable and employs carbon to filter toxins so that they do not reach the suit interior. (See the discussion of selectively permeable treatments in Chapter 3.) The overboots and gloves are impermeable and typically made of natural rubber or neoprene.
For each level, there is a prescribed set of items to be accessible within a certain period of time, a set of items to be carried, and a set of items to be worn. In MOPP 0, a protective mask is carried and a suit, gloves, and overboots need to be readily available. In MOPP 1, a CB attack is considered possible. For this level, a CB protective overgarment is worn over the regular uniform and a protective mask, overboots, and gloves are carried. In MOPP 2, an attack is likely. For this level, the overgarment and overboots are worn, and the mask and gloves are carried. In MOPP 3, there is an airborne threat but no percutaneous threat, so the overgarment is worn completely closed; the boots, mask, and hood are worn; and the gloves are carried. MOPP 4 is used for the highest level of threat, and all items are worn.
Probably the most familiar full-enclosure suits are the hazmat (hazardous material) suits seen on workers cleaning up toxic spills or contaminated facilities. These are impermeable garments worn with some sort of breathing apparatus so that the wearer is completely isolated from the environment. Impermeable suits are generally used when there is a need for the additional protection of positive pressure and/or when air for suit inflation can be provided without a significant energy cost to the wearer.
For some situations, fully encapsulating suits may also be made of selectively permeable membranes. Most chemical warfare garments worn by soldiers in the field, for example, use SPMs because of the heat stress that would be caused by wearing a totally enclosed impermeable system for long periods of time. SPM systems have also been designed for first responders who might need to be prepared for the threat of chemical spills or “dirty bombs.” Full-enclosure systems all require some sort of respirator for the provision of breathable air. Impermeable suits also need some way to cool the body as heat builds up inside the suit. This is often provided by circulating air. In positive pressure suits, the air used to inflate the suit may also be circulated and used to remove built-up heat and moisture.
Care must also be taken to consider features that allow safe donning and doffing. Often, the outer face of a garment cannot be touched during doffing. Managing this may involve adding features to both clothing and dressing facilities. Special benches may be provided or hooks hanging from ceilings and loops on an upper garment aid in keeping one-piece garments from dragging on the floor during donning and doffing. It is important for a designer to understand the decontamination procedures used for a specific situation because this may determine the order in which garments can be doffed and the features needed to ensure safe doffing.
There are two basic situations for which fully encapsulating suits are designed. In the first, individuals cannot be hooked up to clean air for breathing and cooling, so a self-contained system for those functions must be worn on the body. Some suits used with self-contained systems are designed to be worn under a backpack that contains the breathing/cooling system, whereas others are designed to be worn over the system. The multilayered impermeable garment in Figure 7.10 is worn with an exterior backpack that provides breathing and ventilating air. The suit in Figure 7.11 was designed to be worn over a specific type of air-supply backpack so that the breathing system is protected as well. It is important to know and understand the specifications for the breathing/cooling system that will be in use before beginning to design. It is also critical to know if the suit has to be designed to interface with several types or different brands of equipment, each of which may have different shapes and different features.
The other situation for which CB suits are designed is for a laboratory or for working near a facility where there is a life-support system to which the wearer can be attached by way of an umbilical cord (Figures 7.12 and 7.13). Air for breathing as well as cooling or warming may be fed into the suit as shown in Figure 7.12. This constant air supply also gives the suit positive pressure, lifting it off the body so air can circulate close to the skin surface.
The features of a suit and a breathing device must be designed to work together. Breathing systems should be carefully designed and placed so that they do not create stress points or cause suit puncture. In addition, the suit must allow access to air supply devices in emergencies, and users need to be able to monitor air supply and leave an area before air runs out. Figure 7.11 shows a zipper to the side of the center front for emergency access and a clear vinyl window above it over the air supply gauge. It should be noted that many systems use audible alarms to indicate this since in some environments, vision may be obscured by smoke, and the like.
Backpack straps or other additional equipment worn over many full-enclosure suits may crush air spaces needed for both ventilation and the protective benefits of positive pressure. Therefore, many full-enclosure systems contain spacers as part of an air-cooled undergarment system. These keep the suit materials from collapsing and shutting off airflow. A schematic diagram of a typical undergarment system is shown in Figure 7.14.
If an umbilical cord is not used, there are two types of air delivery systems worn with CB suits: self-contained units or filter systems. Self-contained units either circulate breathing air or provide oxygen on a demand basis (the wearer draws in oxygen with each inhalation in a closely fitted mask). Filter systems merely detoxify air in the environment to make it breathable. Self-contained units are heavy because of the weight of the pressurized tanks needed to carry oxygen. However, the lighter filter systems may not provide sufficient breathing air in some toxic or flame environments where an oxygen deficiency exists.
Various methods are used to direct and circulate air around a CB suit for ventilation. Some suits are fitted with a network of plastic tubing that is laced through keepers or loops on the inner suit surface. These deliver ventilation throughout the garment to areas where airflow may be cut off as the body moves. This is especially important for the extremities. In some places, the tubes feed air into baffles that prevent air from blowing directly on the eyes or other sensitive areas. For example, the ventilation system of the suit shown in Figure 7.12 has a nylon coil sole in the boot that directs air to the underside of the foot, an area normally cut off from airflow, but does not allow the air to blow out directly and tickle the foot.
Both the clarity and range of vision are important for many activities for which full-enclosure suits are worn. The suits shown in Figures 7.10, 7.12, and 7.16B, in particular, have totally clear head coverings that allow a full range of side-to-side vision. The clear rigid helmet in Figure 7.16B can be rotated so that if scratches interfere with vision, a clean visual area can be moved into place. Often, clear helmets and hoods will be made of specially treated materials that do not fog up when the wearer breathes. Some of the air supplied to the suit may also be directed onto the face shield to provide fresh air for breathing and to prevent the wearer’s breath from fogging the viewing area. Air flowing into a hood or helmet for vision provides the additional function of moving the carbon dioxide exhaled by the wearer away so that it does not cause ill effects when continually rebreathed. It should also be noted that since airflow within a head covering often creates a fairly high level of noise, various methods of baffling sound from this air supply may need to be incorporated into the system.
The relationship between hoods and respirators is a particularly important part of designing full-enclosure garments. Clear panels for vision need to be kept in front of the face as a wearer moves. Because many respirators are considerably heavier in front, they are generally fitted with tight, rubberized straps that hug the head to hold the facepiece in place. If respirators are worn over the hood, the tight straps of the respirator hold the facepiece of a hood in place. If respirators are worn under the suit, the suit design needs to be carefully examined in the hood area to be certain that the hood accommodates them and that any facepiece on the respirator lines up with the facepiece on the hood, particularly when the head turns. The type of clear plastic hoods or helmets shown in Figures 7.10, 7.12, and 7.16B go a long way toward solving visibility problems. Better visibility may also be achieved by tethering the hood in some fashion to the facepiece or support straps on the respirator.
Providing continuous coverage between head and face covers, gloves, and boots and the main body of the suit poses particularly difficult problems for designers. The gaps between these body segments have been handled in a variety of ways. Head coverings and bootie-type foot coverings are generally sealed permanently to the suit or, in some cases, may be cut in one continuous piece with the suit. Although this keeps coverage continuous, it may create problems with durability and sizing. Because of the great amount of wear on the soles of the feet and the possibility of stepping on something that might puncture the suit, steel toe and shank boots are usually worn over bootie extensions of the suit. These outer boots also help control ballooning in the leg area of positive pressure suits and provide a sizing feature by restricting the excess length and width of the suit leg so that it does not trip the wearer or interfere with movement. (See Figure 7.16A.)
Even though gloves may occasionally be permanently sealed to a suit, the stiffness of suit materials, the importance of individual glove sizing, and the wear on gloves make it more likely that they will be joined to each suit with some airtight mechanism. Two different systems for sealing a glove to the sleeve are shown in Figure 7.15. Figure 7.15A shows the sleeve of a suit with rigid wrist rings permanently attached at the sleeve cuff. These have a bead or ridge on each edge. Rubber gloves are stretched over each wrist ring, and then a rubber ring, much like a garter or a thick rubber band, is placed over the top of the assembly to form an airtight seal. This same sealing mechanism can also be used for boots.
Figure 7.15B shows a so-called bayonet system that employs rigid rings on both sleeve and glove. The two are joined together by inserting one into the other and twisting until it snaps in place, in much the same manner as a bayonet is attached to a rifle, or a special lens is attached to a camera. The rigid ring that is the male portion of the connector may be permanently glued to the sleeve or force-fit with a ring inside the sleeve. Because gloves generally have a shorter life, the rigid connector on the glove is generally clamped onto the glove rather than permanently attached. Some similar systems employ more cone-shaped rigid connectors rather than rings. Others may snap into one another with a force fit rather than twisting in place.
The connection of a helmet or hood to the rest of a full-enclosure garment is a difficult one to achieve. In items such as a space suit, the connection with separate segments of the suit can be made with locking rings. (See Figure 9.27.) In lower-tech and disposable suits, such as hazmat suits, head coverings are generally permanently sealed to the suit. One challenge, then, is to develop a fastening system that allows access into the suit, since a seam that runs directly up the center front and over the face area would interfere with vision. Some suits use a rear entry design; others use long, diagonal closures. (See Figure 7.16A.) Another approach is shown in Figure 7.16B, with a zipper that runs over the shoulders on either side of the helmet, looping around below the helmet in back. Regardless of the garment opening, if a rigid helmet is sealed to the suit, the neck opening of the helmet must be large enough for the head as well as any respirator or communication equipment being worn to pass through, and the opening must be long enough to allow the suit to be pulled up and over the head.
Often, suits designed for work in an outdoor environment must have additional protection from extreme thermal conditions or other environmental hazards. The ability to rescue an injured worker may also be important. The suit shown in Figure 7.13 has special safety loops near the wrist area to allow the attachment of lifelines for rescue in an emergency.
Much attention must be paid to durability issues for full-enclosure suits. It might be more accurate to say that CB suits that totally enclose the body are engineered rather than designed. Designers and engineers must work together, since each applied stress on a particular garment area can affect multiple areas of the garment and must be considered with all other stresses in the course of design decisions. The stresses on both fabrics and garment forms become considerably more complex for a total-enclosure suit with positive pressure. Although the optimal internal air pressure can be calculated for a static geometric form made of any given material, it is not so easily calculated for a garment. Movement may change suit volume or cause localized increases in pressure. For example, when a worker bends at the waist in a positive pressure CB suit, air inside the suit is pushed down toward the crotch, and the pressure there is increased. Unfortunately, this is also an area where several seams come together so it may already be a weak seam location. Reinforcements in areas such as this, where pressure builds up, can help ensure that the suit will not burst as the wearer moves.
Since larger sizes of the same design involve increased volume and thus increased pressures, a specific design cannot be merely graded up to a larger size. Mathematical calculations have to be made to determine the specific stresses for this larger volume and the suit must be redesigned or additional reinforcements must be built in to accommodate them.
There are also practical and psychological considerations for those wearing total-enclosure suits for long periods of time. It is a time-consuming and sometimes costly process to don and doff suits, so once a suit is donned, it is advantageous to keep an individual in it as long as possible. One of the major issues that needs to be considered for long-term wearing of full-enclosure suits is toileting (i.e., waste removal). A unique system of waste management was developed in a design research study using MOPP gear (Cardello et al. 1991). The designers for that project placed a zippered expansion panel in the underarm seam of a one-piece MOPP 4 garment in the torso and upper arm areas and another in the crotch area. These functioned in much the same way as an expansion panel on a suitcase. When the zippers were open, they revealed panels of CB protective material so there was no break in protection. The extra width allowed a wearer to retract his or her arms from the sleeves and into the suit. With the panel at the crotch also open, this allowed the operation of a waste removal system for both urine and fecal matter. A two-way air lock pocket system then was used to pass the bags of waste out of the suit. The excess material in the panels could then be zipped closed so that excess suit bulk would not interfere with mobility. In combination with a safe nutrient delivery system, this suit allowed soldiers in the study to remain encapsulated for 54.5 hours, more than doubling the previous duration record.
Potential radiation hazards are present in many different situations in daily life and in work settings. Radiation is used for the inspection of goods; the sterilization of food; the production of plastics and rubbers; and the elimination of static electricity in the film, printing, and textile industries. It is present in the paint used for luminous dials and in research equipment such as electron microscopes. It exists in uranium mines as well as nuclear power plants and X-ray facilities.
In general, the major radiation hazards that occur in industry are controlled by shielding the radiation source with lead or concrete rather than by clothing the worker. Inspection of products is often carried out by remote control in an isolated room shielded by lead walls. Warning devices are used to indicate leakage of radiation into a work area. When workers must move in and out of a potentially radioactive area, each may wear a dosimeter, which measures the amount of radiation to which the wearer has been exposed. These devices range from clip-on badges to rings to wristwatches to devices that can be plugged into a smartphone. When a worker approaches the maximum allowable dose, he or she is simply removed from an area where radiation is present for a specific period of time.
In order to develop radiation protective clothing, designers must first understand the hazard and the type of exposure each work situation presents and be aware of the role clothing can play in protection. For example, nuclear reactors require a concrete wall approximately 10 feet (3.05 m) thick to prevent the escape of some of the high-speed particles that may be emitted. It is inconceivable that any material suitable for clothing could provide this protection. Clothing can, however, protect workers from other forms of radiation and from radioactive substances carried in dust, oil, and grease in areas where repair and maintenance jobs have to be carried out. Clothing and respirators keep these substances from being deposited on the skin surface or carried into the body through the lungs.
There are a variety of radiation hazards in the environment, some of which are present in daily life and some that occur in special situations or in specific work environments. Energy Basics 3.1 provided a basic discussion of atoms, protons, neutrons, electrons, and nuclear energy. Chapter 5 presented some basics of radiation from the standpoint of heat. (See Energy Basics 5.1 for a basic discussion of radiation.) Although radiant thermal energy in moderate amounts does not pose a threat to the body, other forms of radiation can be more hazardous. This chapter will discuss methods of protecting the body from the potential hazards of ionizing and nonionizing forms of radiation (Energy Basics 7.2), including information about radioactivity, X-rays, and microwaves. Understanding the basics of ionizing radiation will provide a foundation for developing protective garments for people such as nuclear power plant workers and for hospital workers and patients exposed to X-rays. Understanding the basics of nonionizing radiation will help designers decide on the necessity of providing protective clothing for many modern day objects such as microwave ovens and cell phones.
When an atom contains more than 83 protons in its nucleus, its neutrons have difficulty holding the nucleus together. The nuclei of these so-called heavier atoms may begin to come apart or decay, releasing kinetic or electromagnetic energy in the process (Energy Basics 7.3). Atoms that spontaneously emit particles from their nuclei are termed radioactive. When the nucleus of a radioactive atom comes apart, the resulting nuclei each have only a portion of the protons of the original nucleus. Each lighter nucleus is electrically charged and picks up electrons to form atoms of new, lighter elements. Eventually these atoms may disintegrate to the point that their nuclei contain less than 83 protons and lose their radioactivity.
X-radiation is a type of ionizing radiation that has an extremely short wavelength. It can pass through materials that would ordinarily reflect or absorb visible light. X-radiation is one of the more commonly experienced radiation hazards.
The most widely known X-rays are those that are used in hospitals and doctors’ offices. The images (commonly called X-rays, but more properly called radiographs) that subsequently appear on the film show the degree to which various body parts absorb or reflect X-radiation. Lighter areas show body tissues that are denser or have more electrons (a higher atomic number) and that therefore scatter and absorb more X-rays. Darker areas are less dense body tissues that allow X-rays to pass through. Thicker tissue masses scatter and absorb X-rays more than thinner ones, and diseased tissues often absorb X-rays differently than normal tissues do. Consequently, radiographs may be used to make visible any breaks in bones or cancerous masses inside the body.
In the laboratory, X-rays are produced by bombarding a metal target with a stream of high-speed electrons (Figure 7.17). As they impact the metal, the electrons are stopped and their kinetic energy is transformed into heat and X-rays. The more rapidly the electrons are moving when they hit the target, the shorter the wavelength and the more penetrating the X-radiation that is produced. Planning for appropriate protection therefore requires precise knowledge of the wavelength of X-rays emitted by equipment.
A complicating factor in controlling X-rays is that they do not continue in a forward path indefinitely. As they strike atoms in various materials, they may scatter in different directions (Figure 7.18). In order to prevent this, the X-ray beam may be made narrower or a material with a high atomic number, such as lead, may be placed behind the item being X-rayed, so that the rays that pass through are absorbed rather than scattered back through the item.
Establishing guidelines for body tolerance to radiation is a complex task because radiation not only takes many forms (light, X-rays, microwaves, and so on), but it is also measured and described in many ways. Human exposure to radiation is usually expressed by the unit, the rem (roentgen-equivalent-mammal) or the millirem (1/1000th of a rem). The rem takes into account both the dose of radiation received and its relative biological effectiveness.
Radiation is everywhere in the environment. The U.S. Nuclear Regulatory Commission (USNRC) states that the average annual radiation dose per person in the United States is 620 millirem (USNRC “Doses in Our”). A typical chest X-ray subjects the body to between 0.05 and 0.3 rem. The USNRC has established limits on the amount of ionizing radiation exposure permitted for workers in facilities licensed by them. It sets limits for whole body exposure, with special limits for the lens of the eye and higher limits for the skin of the extremities (USNRC “Occupational”). Special limits have been set for the entire gestation period for pregnant workers (USNRC “Dose Equivalent”). It should be noted that focused rays used for localized exposure, as is done with radiation therapy for cancer, may greatly exceed the dosage limits for workers with no fatal effects. Researchers have found that shielding the head, the spinal column, and the blood-forming organs increases tolerance for the presumed fatal doses of radiation.
The tremendous increase in the use of electronic equipment such as cell phones in everyday life has prompted much debate about the safety needs of workers exposed to nonionizing radiation such as RF energy and other radiation in the microwave frequency range. It is clear that microwaves can warm living tissues, and that heat alone can sometimes present a hazard. Thus at higher levels, such as in its use in a microwave oven, the heat could clearly present health problems. However, at the lower levels required for the use of a cell phone, most scientists do not believe the heat generated by nonionizing radiation will produce particularly hazardous effects on the body. It should be noted that this varies with the area of the body being heated— the scrotum and the eyes are particularly vulnerable to RF heat.
Scientists do not always agree whether both high- and low-level RF energy produces nonthermal effects as well. There have been many reports of serious medical problems experienced by military personnel who work with radar equipment and people in communities in the path of power lines or radio transmitters often claim that they have a higher than average incidence of cancer. One of the difficulties of drawing conclusions about health hazards posed by electronic items that emit nonionizing radiation is that there are so many variables that need to be explored. The National Cancer Institute states that although cell phones emit radio-frequency (nonionizing) energy that can be absorbed in body tissues closest to where they are being held, the amount absorbed depends on the time of use, the location of the antenna and its distance from the user, the technology used by the phone and the distance of the user from cell phone towers. They state that “Studies thus far have not shown a consistent link between cellphone use and cancers of the brain, nerves, or other tissues of the head or neck. More research is needed because cell phone technology and how people use cell phones have been changing rapidly” (National Cancer Institute “Cell Phones”).
One early and very fascinating account of the long-range effects of microwaves is contained in a study of the U.S. Embassy in Moscow (U.S. Senate Committee 1979) in which medical tests on the personnel and their families living in the embassy are detailed. These studies were conducted following an extended period during which it was determined that a low-level beam of microwave radiation was being directed at the building, presumably as part of an effort to spy.
Because radiation takes so many forms and is present in many aspects of individuals’ personal and work lives, clothing that protects from radiation takes many forms. Three types will be explored here: garments for nuclear power plant workers; X-ray-protective garments, and protection for people exposed to microwaves.
Three factors that are reviewed when determining measures to take for personal protection of workers in nuclear power plants are time, distance, and shielding. As the time of exposure to sources of radiation increases, a greater number of particles will strike the body. The distance of the body from a source of radiation affects the intensity with which the particles strike as well as the number of particles that impact a body. Shielding the individual from radiation involves the isolation of the radiation source or the individual with appropriate materials and enclosures.
The purpose of most protective gear for nuclear power plant workers is to keep radioactively contaminated particles from being deposited on clothing or the body. Ensembles generally take the form of a respirator and a fully encapsulating coverall with integrated or overlapping gloves, boots and hood. Figure 7.19 shows two typical ensembles. Anticontamination suits such as those shown are made of various materials—from impermeable vinyl to bonded paper-like materials such as Tyvek® to closely woven materials made of cotton. Most of these garments are baggy, relatively nonfitted designs that provide complete coverage while allowing as much mobility and safe movement as possible for many different figure types. Elastic at the wrists, ankles, and sometimes the waist keep garment segments in place. Necklines are often elasticized under overlapping hoods so that they will be close to the body. Great care is taken to ensure that no skin is exposed between garment parts. Rubber gloves are usually worn overlapping wristbands or wrist elastic. Foot protection may be integrated into the coverall or separate shoe covers may be worn. Because of the hard wear on fabric shoe soles, rubber or vinyl boots are usually worn over booties or shoe covers.
A separate hood may be used to allow freer movement of the head from side to side. Hoods that are designed to be used with an external respirator have a closely fitted face opening. Suits that have an air supply provision or an interior respirator can have a less closely fitted hood with a clear vinyl head or face area. The hood design in Figure 7.20 allows 3608 visibility.
Any reusable protective clothing that is worn around radiation hazards must go through rigorous decontamination and laundering to ensure that radioactive particles have been totally removed before the garment is worn again. Therefore, the garments chosen for power plant workers are often disposable. While they present the problem of contaminated waste, disposable materials reduce the cost and difficulty of laundering contaminated garments and creating contaminated wash water. Whether disposable or reusable, the fabrics in these garments serve as a type of filter, presenting a barrier to prevent dust, grease, and other substances in the environment that contain radioactive particles from settling on workers’ clothing. Where liquids are present in the work area, these materials may have waterproof or water-resistant finishes or be composed of laminates of several thin layers of materials.
Figure 7.21 shows a method used by many workers who wear disposable coveralls to fit them closely to the body. To save on cost and inventory, some companies buy suits in one or two larger sizes, and workers do their own custom fitting in the dressing room by wrapping out extra length and width with tape.
The protection required by workers exposed to X-rays is quite different from that required by nuclear power plant workers. X-ray equipment is shielded as much as possible. Technicians often stand outside the X-ray room or behind a lead shield as they work. However, in some situations such as with infants, where technicians may need to help locate the body parts to be X-rayed, or fluoroscopy (where continuous X-ray images are made visible on a screen as the patient moves), a technician may have to work near the X-ray source, and in those instances clothing provides a logical answer to protection. The person being X-rayed may also need to have body parts other than those being X-rayed shielded, and many of those shielding items involve clothing.
Elements that provide a shield from X-rays are high-density ones such as lead, antimony, and tungsten. The material that has been most commonly used in X-ray protective clothing is lead-impregnated vinyl. This material is generally made of lead powder mixed with vinyl and extruded and formed into sheeting. Leaded glass may also be used for visibility when protection is needed for the eyes. Raheel discusses the use of melt spun fibers of lead metal for shielding mats and reports that they are flexible and easy to cut and sew. “Thus, it is suitable for making work clothing (vests) for nuclear power station workers or x-ray shielding aprons” (1994, 3). It is also possible to provide equal protection from X-rays using antimony rather than lead in protective materials. Antimony is considerably lighter than lead but about four times as costly, so its use in clothing has not been as widespread. Because of concerns about possible health hazards of lead, several tungsten-filled high-density thermoplastic composites have also been developed for X-ray protection. Polymer compounds have also been used for radiation protection, often fused with several layers of other kinds of protective materials (e.g., those for chemical threats) in a composite fabric.
The protection offered by many radiation protective materials is expressed in millimeters of lead equivalency. This is the amount of protection that would be offered by a specific thickness of lead if it were substituted for the fabric. For example, many materials used in garments are designated as offering “0.5 mm protection.” This means that they provide the same protection as a sheet of lead 0.5 mm thick. The millimeter equivalency protection needed in a particular setting depends on the particular hazard and the state laws in effect. The specific requirements for a setting must be determined by a physicist or an environmental health and safety specialist. Materials may need to be tested to determine that their lead equivalency protection is maintained. Manufacturers caution that garment protection levels can be affected, for example, if a garment is folded or draped over corners. Many provide a special hanger with each garment they sell.
Many states still require lead aprons with specific lead equivalencies to be placed on dental patients prior to X-rays, although the scattering of rays is increasingly less likely with modern dental X-ray equipment. Most X-ray bibs cover the chest and torso area. The model shown in Figure 7.22 also covers the throat and neck since exposure of the thyroid gland to X-rays is of major concern. The weight of the leaded material and a Velcro attachment at the neckline keep the bib in place on the body. Some models are backed by a textured material such as an open-cell foam between the bib and the body so that friction helps hold it in place. When X-rays are taken, for example, of a broken bone, some type of leaded garment or blanket may be placed over the rest of the body, particularly over the reproductive organs. Such a covering prevents any rays that might scatter from the X-ray site from reaching specific areas of the body.
The major problems in designing X-ray protective garments are due to the heavy weight of leaded materials and, often, their imbalance on the body. Coverage that provides maximum protection with minimum material is the ideal. X-ray technicians generally wear a leaded apron that protects the front chest and torso, the areas most directly exposed to the X-rays that may scatter from the equipment (Figure 7.23). Although front-closure as well as front-wrap aprons are available, they tend to gape along the front opening and have the extra weight of a full back piece and the front overlap areas (Figure 7.24A). Separate wrap skirts and vests are available (Figure 7.24B) and while the total weight of these is greater than an apron, these items allow some of the weight of the leaded protection normally carried by the shoulders to be transferred to the hips.
When the need for protection occurs primarily on the front of the body, the imbalance of weight has been handled in a number of ways. One manufacturer has developed a stretch back panel from waist to shoulder blades to help increase conformity of their full aprons to the back of the body. Other aprons contain wide straps that wrap around the body and secure with hook-and-loop fasteners so that size and contour can be greatly varied.
Other strap designs are used to secure the open-back type of apron shown in Figure 7.25. Since any backstraps must counterbalance a considerable amount of weight from the front of the garment, they must not only be strong but also be attached to the garment in such a way that they do not tear away from it under the strain. Figure 7.25A shows strong, reinforced straps that are riveted through the apron back at several points. Adjustable straps can then be looped through them. Figure 7.25B shows an apron that has been placed in a fabric cover that extends to form the back of the garment as well. The back portion of the cover extends into straps, which are wrapped around and tied for proper fit in the front. Because the straps are part of the back—there are no seams or attachment points for them—this design helps keep the straps from separating from the garment.
There is great concern for eye and thyroid protection for both X-ray technicians and patients. Although collars and other head-protective devices may succeed in protecting the thyroid gland, they may fail to protect the eyes. Leaded eyeglasses are available as are leaded acrylic face shields.
Since X-rays can scatter, the rule of thumb used for protecting openings in a garment is that each opening must be backed with a protective piece one and a half times the width of the opening. This means that if there is an air space at the waistline 1/8 inch (0.32 cm) deep between the skirt and the hem of the vest shown in Figure 7.24B, a minimum of 3/16 inch (0.487cm) overlap would be required to remain at all times to provide protection from scattering rays. Because many areas of the body expand during movement, the overlap in many areas would actually need to be much wider to be certain protection was maintained.
Leaded vinyl garments are extremely hot. Although X-rays are generally taken during a brief period of time, the technician may wear an apron continuously because the intervals between patients are too brief to disrobe. The design in Figure 7.26 was developed to deal with this problem. The front flap, which is fastened with Velcro, can be dropped to provide momentary ventilation and then quickly returned to place when needed. The neckline of this design also provides extra protection for the thyroid gland.
Because of the many X-ray procedures used, a wide variety of accessories are available both for the technician and for the patient. Figure 7.27 shows some of these items: gloves, diapers, gonad shields, collars, and apronettes. Many of these items are now being incorporated in garments such as panties or bras that make donning the leaded panels easier and keep them in place more effectively.
Basic shielding materials are often coated or enclosed in other materials to make them more attractive in clothing. The many colors and textures as well as the printed materials seen in X-ray protective clothing are the result of either enveloping the leaded apron in a decorative outer fabric covering or coating them with vinyls or similar waterproof coatings that can be easily sponge-cleaned and thus used by many people.
Microwave protection has existed in industry and for the military for some time and a number of companies have begun to produce fashion items to shield the body from microwaves in the home or office. Originally marketed for pregnant women, these consumer garments are now available for both sexes, particularly for individuals who spend long hours at a computer. Garments may be made using a fine stainless steel mesh or knitted metal-coated yarns, among the most prevalent being nylon coated with silver.
Garments that shield from electromagnetic radiation can also be used for security. Some credit cards, garment security tags, and other devices use Radio Frequency Identification (RFID) chips to store information so that it can be read back by a reader without requiring power. RFID technologies rely on radio waves as both communication and power: the reader sends out a radio signal, which the chip uses as power to return a short communication to the reader. Because some chips will respond to any reader, it is possible in some cases to lift information from RFID chips a person may be wearing or carrying by putting a reader in proximity to the chip. However, radio waves can be reflected, as can many other forms of radiation. The same metallic layer in a garment that can shield the body from microwaves or other forms of electromagnetic radiation can also shield an RFID chip from the radio waves produced by a reader.
There are many situations in which clothing is used as a filter to keep hazardous particles in the air, in dust, or in liquid and oily substances away from the body. In other situations, it may be important to keep oils, skin particles, and hair from dropping off the body and contaminating the environment. Before choosing filtration materials, it is important to understand the nature of the particles a garment needs to exclude. A filter may be as simple as mosquito netting or as complex as a chemically protective fabric for workers cleaning up a toxic waste spill. This next section looks at the structure of filters and discusses two examples of the ways in which they can provide protection for or from people.
Although solid films or coated materials offer protection from small particles, they may not always provide the most satisfactory clothing solution. In many situations, garments made of these impermeable materials are too hot and cumbersome and really provide more protection than is needed. Therefore, a good number of materials used in protective clothing and equipment serve as filters to strain out hazardous particles, yet allow air or water to pass through.
Filters for face masks or respirators are made of webs of many types of materials, depending on the end use. A typical surgeon’s mask such as the one shown in Figure 7.28 may be made of several layers of tightly woven cotton and polyester or of disposable filtration materials. Some of the most commonly used filtration materials for solid particles as well as liquids and gases are disposable webs such as Tyvek.
Disposable webs are commonly used for full garments as well. Because of the problem of decontaminating and laundering garments that have been exposed to bacteria, chemicals, pesticides, or radioactive particles, disposable protective clothing has become popular in many fields. At the same time, concerns about the disposal methods for these materials and the condition of landfills has raised concerns about their safe and efficient disposal.
A more sophisticated filter structure must be used in the presence of sprays or vaporized liquids. A respirator for a spray painter, for example (Figure 7.29), may contain a filter composed of fibers such as glass or a nonreactive plastic material. Much attention has been given to the health hazards introduced by the filtration materials themselves. It is important to know that materials used as filters will not degrade or decompose into hazardous particles that can irritate or injure the skin surface or enter the body by being inhaled.
All of the materials just described are part of what are termed mechanical filters that trap particles by having interstices that are too small for particles to pass through. Chemical filters work like the SPMs discussed earlier in this chapter and in Chapter 3. They bind toxic gases and other substances chemically. Specially treated (activated) carbon, for example, is able to adsorb gas molecules into its open sites or pores.
The effectiveness of a filter depends not only on choosing appropriate materials (See Design Strategies 7.1) but also on how well those materials are used in a design. Tight areas in garments may create pressure points that can force particles through a filtration material. Loose areas in masks or respirators may create large gaps that allow particles to pass around filtration materials. Thus, the most reliable tests for the efficiency of filters come after filtration materials have been incorporated into garments and equipment that meet specific needs of workers.
Although asbestos has been used since prehistoric times and health problems due to its use have been suspected for centuries (Ashdown 1989), the Environmental Protection Agency first banned its use in the United States in 1978. By that time, because of the wide use of asbestos as an insulation material for construction of buildings and ships since the 1930s, hundreds of thousands of public and commercial buildings contained asbestos that needed to be removed for public safety. This spawned an expanding industry of workers trained in asbestos abatement (the reduction or removal of asbestos from existing structures).
Asbestos causes disease primarily because its fibers are inhaled and subsequently lodge in the lungs. Once there, since they cannot be expelled or absorbed, they trigger a reaction that causes chronic scarring of the lung tissue known as asbestosis. This reduces the ability of the lungs to use oxygen and results in a reduced life expectancy. Although the vast majority of asbestos-related disease is due to inhaled fibers with no evidence that the fibers can travel through the skin, asbestos abatement workers must wear both a respirator and protective clothing. This is because regular work clothing might attract fibers that could be carried away from the work site and later inhaled when the worker is not wearing a respirator, or carried into the family laundry to provide hazards to others.
Asbestos abatement takes place in a sealed area. Workers totally isolate themselves and the asbestos-containing area by sealing it off with double layers of heavy plastic and providing a single entrance/exit through a series of airlocks. The airlocks serve as areas to don protective clothing on the way in and shed contaminated clothing to become progressively cleaner as a worker moves outward. Air is constantly pumped out of the work area through a high-efficiency particulate air (HEPA) filter. This collects fibers so that only clean air emerges and creates a negative pressure so that no fibers are accidentally propelled to the outer environment. The HEPA filter and all materials used in the work area, including contaminated protective clothing, are surrounded by plastic and either disposed of as hazardous waste or kept totally contained until they can be placed within the next sealed work area.
The basic ensemble worn by an asbestos abatement worker includes a respirator, a coverall with a hood and foot coverings (both preferably attached to the coverall), rubber gloves, and boots. Because of the difficulty and cost of decontamination, most coveralls used for work with asbestos are disposable and closely resemble the ensemble shown in Figure 7.19 for nuclear power plant workers.
The process of asbestos removal creates specific clothing needs. Because asbestos is generally located in the ceilings or the wrapping of overhead pipes, workers need great range of movement. They need to be free to reach overhead, climb ladders, and bend or kneel down to shovel up removed debris that has fallen to the floor during the process. Because many types of asbestos are wet down with a surfactant to facilitate removal, the environment and the worker are often wet and this places additional demands on a protective garment. The enclosed nature of the removal site and the totally encompassing ensemble both create a very warm environment. When added to the physical effort the job requires, the worker will sweat profusely. The wetting of disposable garment materials from both sides and the strain placed on garments by movement extremes leads to a situation in which protective clothing is easily torn. Snagging on equipment and other items in the work area adds to the incidence of coverall tears. For these reasons, the basic disposable material needs to be strong and water resistant. The materials used are usually a spunbonded polyethylene or polypropylene and the basic material is sometimes coated with a breathable, waterproof finish.
Several options have been posed for improving the design of coveralls for asbestos abatement. Ashdown (1989) proposed contouring of the pattern for disposable coveralls so that they more closely mimic the working position of the abatement worker and adding a cut-on underarm gusset to facilitate arm movement. These changes are discussed in Chapter 2 and a diagram of suggested pattern changes is shown in Figure 2.43. Developments continue to be made in the area of materials that have sufficient strength, especially when wet.
A cleanroom is defined by the International Standards Organization as a “room in which the concentration of airborne particles is controlled and which is constructed and used in a manner to minimize the introduction, generation, and retention of particles inside the room and in which other relevant parameters, e.g., temperature, humidity, and pressure, are controlled as necessary” (Whyte 2010, 1). Typical contaminants that are controlled within a cleanroom include dust, human skin particles, hair, lint, bacteria, cigarette smoke, and dirt. Cleanrooms are used to manufacture items such as sterile supplies, pharmaceutical products, microchips, and precision instruments. Although there are many similarities between the types of protection needed for asbestos abatement and work in a cleanroom, they involve opposite problems. In asbestos removal, the focus is on protecting the wearer from hazards. In the cleanroom, the focus is on protecting the items being produced from human contamination. The situation is similar to that in the operating room, where surgical gowns and gloves protect a patient from any contamination from medical personnel. However, some cleanrooms actually exceed the cleanliness of operating rooms.
Cleanrooms are designated in terms of classes that are determined by the maximum number of a specific size of particle that will be allowed in the room. Both the U.S. government and the International Standards Organization have cleanroom classification standards.
Assuring a contamination-free room generally involves five steps. First, air entering the room is filtered to remove contaminants. This is accomplished with the HEPA filter described for asbestos removal, except that in this case it filters air entering the room. Second, particles that enter the room on workers (e.g., lint from clothing) or are generated in the manufacturing process need to be removed from the room through a constant process of air exchange. The placement of entrance and exit air grills establishes a pattern of airflow. Most cleanrooms use what is called laminar airflow in which air moves in layers (i.e., at a uniform velocity along parallel flow lines), either from an entrance point in the ceiling to a removal grid in the floor or from one wall of the cleanroom to the opposite wall (Austin and Timmerman 1965).
Third, every precaution must be taken to limit the production of particles within the room. Nonlinting fabrics and nonchipping wall and floor surfaces should be used. Even pencils and paper are prohibited because of the particles that might be produced during their use. Static-generating materials may cause particles to cling to surfaces where they can be knocked off into the production area.
Fourth, the products need to be protected from the settling of particles. Workstations and people interrupt airflow and serve as areas of deposit for particles. Laminar flow helps maintain airflow and cleanrooms are generally set up so that production moves from the area nearest the air exit to the cleanest areas that are nearest the air inlet.
Fifth, personnel and materials brought into the room need to be thoroughly cleaned. Austin and Timmerman state that personnel are the “single greatest cause of contamination. They leave a trail of particulate and gaseous contamination behind them” (1965, 77). To minimize this trail, workers must don garments that cover every body area but the eyes, wear no makeup or skin lotions that might contaminate the cleanroom, and enter the room through a series of airlocks that contain air showers. Many cleanrooms use a tacky mat at the entrance to the last airlock to clean any remaining particles off of the shoes before donning cleanroom shoe covers.
The preceding review of the principles of cleanrooms should net the designer a list of criteria for cleanroom clothing. An ensemble must provide total containment to prevent contamination of the room from skin particles, hair, and other contaminants from the body. The fabrics used for the ensemble must either be impermeable or serve as filters that maintain the class level of the cleanroom. All materials and fastening devices must be lint-free and they should not generate static electricity. Design forms must be as simple and flat as possible. Any details such as gathers, stitching ridges, etc. provide areas for particles to lodge.
Figure 7.30 illustrates two typical cleanroom ensembles. The ensemble shown in Figure 7.30A consists of a one-piece loosely fitted coverall, a hood, a snap-in mask, gloves, and booties. The ensemble shown in Figure 7.30B is comprised of separate pants and coat, short booties and gloves. Both disposable and launderable materials are used for these types of designs. When disposable materials are used, they are sometimes combined with a microporous film that provides waterproofing with breathability. Reusable clothing is more practical in this situation than it is for asbestos removal because there are no hazardous particles involved, so decontamination is not an environmental or health issue. Reusable clothing is generally made of polyester continuous filament fibers, often with the addition of an antistatic treatment or the incorporation of a grid or stripes of metallic or other electrically conducting threads. These ensure that there is no static buildup on the garment that might attract particles, which could then be brushed onto a work surface. Fabrics are woven rather than knitted to control pore size and reduce surface texture. All seams in the garment must be either heat sealed (see Chapter 9) or flat felled (i.e., double stitched like jeans so that all raw edges—even those inside the suit—are completely covered). Zippers with a covering flap are used at the front of coveralls for donning. Fitting adjustments are usually made with gripper snaps because hook-and-loop tape, buttons and buttonholes, and other types of fasteners often have too much potential to generate and collect particles.
The coverall designs in Figure 7.30 illustrate the emphasis placed on simplicity in design features. Belts, pockets, flaps, and other design features are discouraged, and in some cleanroom classes, prohibited. In some classes of cleanrooms, it may be permissible to have limited gathers, belting, and other design features, on the back of the garment where it is less likely to be knocked off onto the production area during work.
The ensembles shown in Figure 7.30 contain several potential problems for containment. The primary area of concern is the face. The hood often does not fit properly around the face. Employees are also able to remove the face mask and tend to do so even though it is not allowed because the mask and hood are so hot and uncomfortable. This exposes the area most problematic for contamination. A number of cleanroom professionals have expressed the belief that the one-piece coverall may also contribute to contamination because the only exit route for air inside the suit is through the neckline. Some firms select long coats and pants because the pumping action of the arms during work moved air to the point of least resistance, the hem of the coat, and toward the air outlet grille in the floor. By contrast, movement that forces air out of the neckline of a coverall would dump contaminants on the work area. This is but one example of the many situations that call for a designer to carefully examine both the nature of airflow in the environment and the activity of workers to determine the best design solution.
Restrictions on design features limit methods that can be used to achieve fit and this often results in restrictions of mobility. Thermal comfort can also be a problem, particularly in the hood area, although it may be minimized by the fact that cleanroom temperatures can be lowered to accommodate workers and often is lowered for the sake of products being manufactured.
Donning and doffing are considerations as well. Both ensembles shown in Figure 7.30 are easy to don and doff, but the coverall has the potential to be contaminated during donning because the whole upper garment drags on the floor as the lower garment is donned.
Aesthetics presents an additional problem. Ashdown found that, in part because asbestos abatement workers were almost exclusively male and worked completely hidden from view by others, they had no concerns about the visual appearance of their clothing. Loker found quite the opposite in her survey of cleanroom personnel. They did complain about the lack of visual appeal of their garments, from their overall “bunny suit” silhouette to the lack of versatility and opportunity for individual expression. Because of the restrictions on design features, it is difficult to introduce individual details and more body-conforming designs. A range of colors of cleanroom materials are available, however, and have potential for introducing more visual interest than the traditional white.
The basics of electricity were covered in Chapter 4. (See especially Energy Basics 4.1.) Three concepts are important to an understanding of electrically protective clothing: current, voltage, and resistance. Electrical current is expressed in amperes (the rate at which an electrical charge moves through a circuit). Current cannot travel through an electric circuit unless there is enough voltage (the difference in electrical potential from one end of a conducting wire to the other). Chapter 5 noted that heat flows from hot to cold and that the rate of flow of heat depends on the difference in temperature between two objects. Electricity behaves in much the same way. When there is a highly negative charge on one end of a wire and a highly positive charge on the other end, there is a greater difference in potential (voltage) and thus a greater rate of flow of electricity. As was discussed in Energy Basics 4.1, some materials offer more resistance (measured in ohms) to this flow of electricity than others. In addition, temperature may affect the resistance of a specific material.
The combination of a strong current and a high resistance may produce great amounts of heat. This makes sense if you think of this action as an inelastic collision in which free electrons often bump into fixed particles, increasing their rate of vibration. This heat is put to good use in toasters, irons, or electric heaters. In items such as clothing, however, excess heat can cause burns to skin or textile materials. Heat-producing components must be appropriately insulated from the body. Electric wires and cords are designed to have a specific amount of resistance, handle a specific potential difference, and carry a specific load of current. If these limits are exceeded, the heat and electrical current could destroy the insulation surrounding the cord (by melting it or by forcing loose the electrons of the material) and could cause both fire and electric shock.
Electric shock occurs when too much electric current passes through the body and stimulates the body’s electrons to excessive vibration. Since current only flows through a closed circuit, it is clear that electric shock occurs when the body completes a circuit. A difference in electrical potential between one area of the body and another come about when a hand, for example, touches a high-voltage wire while the feet are touching the ground, which has low electrical potential. Current then flows from the hand through the body to the feet and the ground.
Electric current passing through the body affects the nervous system. If the current is great enough to affect the nerves that control breathing and the heartbeat, electric shock may lead to electrocution. An AC current as low as 0.05 amperes or a DC current of 0.5 amperes can be fatal. These levels may sound very small, but it is important to bear in mind that the body acts as a significant resistor in an electrical circuit. The amount of resistance introduced by the body depends on a number of factors, such as what part of the body is in contact, whether the skin is dry or wet with sweat (and thus high in salt content and highly conductive) or whether it is immersed in water, which readily conducts the current. It also depends on whether the point of contact of the body has been insulated with an electrically resistant garment such as a rubber glove.
Workers who repair electrical lines or work around electric shock hazards make good use of both equipment and clothing to prevent body injury. The power lines near electrical lineworkers are generally draped with insulating blankets to reduce potential sources of shock (Figure 7.31). Workers wear insulating garments on body areas most likely to contact shock hazards. In addition, they may use nonconductive tools called hot sticks to work on potentially dangerous electrical lines. Safety belts and other equipment that connect them to the work area are made of nonconductive materials such as filament nylon.
The material most commonly used for protective clothing is thick rubber. Rubber and many other materials used for protection from electrical hazards are termed dielectric. Dielectric materials are insulators that work by storing energy rather than blocking its flow. The protection provided by a rubber garment depends on the weight, thickness, and purity of the rubber used. Electrical lineworkers wear thick, insulating rubber gloves and sleeves over their work clothing (Figure 7.32). They may also wear thick-soled rubber boots so that the other end of the circuit, the feet, can be insulated from low electrical potential areas such as the ground. This is so that electric current will not be drawn through the body so readily. This approach to electric shock prevention is particularly useful when the environment is wet, since water increases the ease of electrical conduction. Dielectric hard hats made of plastics such as polyethylene are also worn.
Glove design is critical to both protection and a worker’s ability to do a job. In the United States, the Occupational Safety and Health Administration defines classes of gloves that provide safe protection for various levels of voltage (OSHA, “Personal Protective”). Gloves carry a color-coded tag for each classification level. Lower classes might be used for someone working with electric meters; higher ones would be used for work on utility poles. For example, Class 0 gloves must provide protection for up to about 1,500 volts; Class 4 gloves must provide protection for up to 54,000 volts. OSHA regulations also specify tests that gloves must pass before, and every six months after, first use. It is also recommended that rubber gloves be inflated to inspect them for leakage after each wearing to ensure that they can still be counted on for maximum protection.
To aid in visual inspection, gloves are generally made in two colors. A base layer of protection is laid down in one color of rubber and then the glove is dipped in successive layers of another color. When the base color can be seen through outer surface, it indicates that protection is compromised and the glove needs to be replaced. Manufacturers give precise care and storage instructions, cautioning users not to fold protective items to prevent even the smallest crack from developing and destroying insulation.
Gloves worn by electrical workers are formed in the working position and should be fire-resistant if, in the jobs workers perform, they are at risk of being exposed to electric arc or other fire hazards. Many gloves are also treated so that they are protected from damage by ozone or ultraviolet rays. Liners may be worn under the gloves to absorb sweat in hotter weather or to provide additional insulation from colder weather. Because of the ease with which rubber is snagged or cut by wood or metal in the work area, protective gloves made of leather are often worn over them (Figure 7.32).
Sleeves made of the same rubber extend from the wrists up over the shoulders to provide additional protection (Figure 7.33). The sleeves attach to one another across the front chest and back shoulder blade area. (See also Figure 7.31.) Many are molded into a working position. Workers are cautioned to wear clothing that is closely fitted with no loose edges that might catch on the work environment. This clothing should be made of inherently flame-resistant fibers such as Nomex®, modacrylic, or carbon or of a cotton treated with a flame resistant (FR) finish because of the danger of sparks that might ignite synthetic materials and cause them to melt to the skin. These cautions also extend to fasteners and trim on garments as well as rain or cold weather gear worn over work clothing.
Many utility workers wear regular work boots because contact with electric current occurs normally in the hand, arm, and shoulder area. However, firefighters, emergency personnel, and others who may work around fallen high-voltage lines in wet conditions generally wear heavy rubber boots that have been tested to protect the wearer from electrical hazards (OSHA “Foot Protection”).
Static electricity occurs when an object has excess electrons or excess protons. Electrons jump from a negatively charged object (one that has extra electrons) to a positively charged object (one that lacks electrons). Static electricity can be the result of friction, that is, the rubbing off of electrons from the surface of a material that has relatively loosely attached electrons. Thus, it may be experienced by shuffling across a thick carpet in rubber-soled shoes. Since electrons are easily knocked off the carpet (especially if it is made of wool or nylon) but not easily knocked off the rubber, extra electrons build up on the shoes, giving them a negative charge. This type of contact charge through friction is called the triboelectric effect. If the body then touches a good conductor such as a metal surface or even a seated person who has not built up as negative a charge, these extra electrons jump from the body and create an electric spark that is experienced as a mild shock. The triboelectric series is a list of materials in order of the polarity of their charge. Materials nearer each other on the list are less likely to exchange a static charge when they touch.
Static electricity creates problems in a variety of workplaces. First, the sparks created when static electricity is transferred may initiate a fire or explosion, especially in environments where fuel is plentiful. Therefore, in a spacecraft or in hospital areas where the oxygen content in the air is high, in operating rooms where anesthetic gases are present, or in mines where combustible gases may be released during the mining process, care is taken to avoid static electricity in all aspects of the environment, including clothing.
Second, even small amounts of static electricity built up on the surface of a fabric may cause it to attract dust or other particles in the environment. In operating rooms, bacteria must be kept from the sterile field of the operating table. Static electricity on a surgeon’s gown could attract nonsterile particles from the rest of the room, and these particles could inadvertently be knocked onto the patient. In nuclear power plants, static buildup on workers’ clothing may cause the clothing to attract radioactive dust, grease, or other particles in the plant and make decontamination difficult. Static electricity has become an expensive problem in a number of industries, most notably those involving microchips. A worker who releases a slight static charge—even one not perceived by the worker—in the process of touching a microchip, can erase the entire contents of the microchip.
There are several methods of dealing with problems created by static electricity. First, it is possible to reduce the potential for static buildup by introducing humidity into the air of the environment. This approach can also be applied to fibers and fabrics (i.e., they can be given finishes that help them attract any moisture in the air). This helps a fabric avoid the buildup of static charge on its surface.
Another approach is to incorporate highly conductive fibers in fabrics. These fabrics are made by incorporating a conductive material such as carbon, silver, or stainless steel (1) within a polymer such as polyester as part of the dope forming an extruded fiber; (2) as part of a bicomponent fiber; (3) in a core-spun yarn; (4) as particles integrated into the surface of a base fiber; or (5) as a fiber or fabric coating (Alluniforms, ‘Clean room fabric’; Kirsten, 2013). A typical material for cleanroom clothing, for example, consists of a polyester fabric with a grid or stripes of carbon/polyester fibers. One blend for static protection where volatile fuels are present combines Nomex and carbon (Euclid Vidaro “Cleanroom”).
Garments made with conductive fibers are often called ESD (electrostatic discharge) garments. Their purpose is to shield sensitive devices by helping electrons transfer easily from a garment surface to the atmosphere or move through a grounding strap on the wrist that is connected to the work table (Figure 7.34). This approach of incorporating conductive fibers in garments may be a more long-lasting and effective one because of the lack of durability of some antistatic finishes.
Static-dissipating garments such as the lab coats shown in Figure 7.34 have features such as an extended coattail and long sleeves. These garment features ensure contact with the grounded chair and work table, respectively, so that any static charge that might build up can be conducted away from the work surface. Workers may also wear static-dissipating shoe covers or straps.
A number of occupations and recreational activities require protection from blades, sharp tools, or punctures due to a variety of hazards (e.g., animal teeth). In general, the materials used to protect the body from these hazards are similar to those described in Chapter 6 for ballistics protection. Aramids (e.g., Kevlar), steel-reinforced fibers, ultra-high molecular weight polyethylene, and stainless steel meshes are perhaps the most widely used materials for cut resistance. For protection from cuts and punctures, however, these base materials have been formed in rather innovative ways to create unique fabrics that are specifically engineered to meet the needs of end users such as loggers, meat packers, and recreational divers.
Materials used solely for cut resistance differ from ballistics materials in that they generally do not have to provide impact protection; they simply need to resist being cut. Therefore, knit structures can be used, resulting in items such as functional, mobile gloves for meat cutters, who need protection primarily on the hands and lower arms. (See Figure 7.35A.) Similar gloves may be used under a surgeon’s rubber glove to provide cut protection from the scalpel. A unique application of high-strength fibers can be seen in the development of loggers’ chaps, which are used to protect legs from accidental contact with a chainsaw. (See Design Solutions 3.1.)
Another structure for cut protection is a chain link material made of stainless steel. Figure 7.35B shows a meat cutter’s glove made of this material. Figure 7.35C shows a unique application of the material in these chain link gloves to a puncture-resistant end use. The material was made into a full length suit to protect divers from sharks. The chain link is worn over a 1/4 inch (0.64 cm) thick neoprene foam diving suit. The nature of sharks’ teeth, which have sharp points but quickly widen, allows them to sink only slightly into the mesh before the small diameter of the metal link prevents their penetration. Because the foam suit provides a stand-off from the diver’s skin surface, damage to the diver is prevented. While the material is relatively heavy, this is not an issue for the diver underwater, especially with the buoyancy of the foam suit. The use of this rigid material in this flexible fabric formation is uniquely suited to meet the user’s needs in this particular situation. The provision of standoff may be a critical factor in other situations where protection from punctures is needed. Mosquito netting and the meshes used on items such as beekeeping hats contain openings that are small enough to exclude the creatures but not necessarily their stingers. These materials must be used in a way that provides space between them and the skin surface.
Cut resistance is far more easily provided than protection from punctures. Metal chain link fabric such as that used in meat cutters’ gloves could be used as a flexible layer in a ballistics vest that would add protection from knife penetration but not necessarily from ice picks. SuperFabric® is a composite material made of a cut-resistant fabric substrate with tiny “armor plates” applied to the surface. The armor plates are made from a hard resin, and are shaped in a geometric pattern like hexagonal tile (Figure 7.36). The resin is not flexible and would create a rigid (but very durable) shell if coated continuously onto the fabric. However, printed as tiny dots, the resin can resist cuts and abrasions while allowing the material to flex and breathe. Because none of the spaces between dots line up, even a knife edge will rest on top of the dots rather than cutting into the fabric.
Needles, nails, and other thin, sharp pointed objects such as ice picks, however, are more problematic. In the past, the only way to prevent punctures was with the incorporation of a solid, rigid plate. Many solid shields are seen in accessory items, for example, the solid steel soles and toe caps in boots for firefighters that protect their feet from puncture by nails, glass, and other sharp objects. Puncture-resistant plates in clothing are generally inserted into pockets in clothing items over body areas most exposed to threats or most vital to life.
In recent years, a number of composite materials and puncture-resistant coatings have been developed and applied to items such as gloves. Often, a puncture-resistant composite material is applied only to the palm of a knit glove, protecting the area most likely to come into contact with, for example, an AIDS-contaminated needle, while leaving the rest of the glove freely mobile.
Situations where flame or hot materials or surfaces are present pose several types of hazards. First, much of the danger to individuals comes as a result of exposure to the radiant energy produced by the heat source. Air temperature, although a lesser hazard, also poses a threat in some fire situations that can degrade many materials. In addition, in industrial work where molten metal may fall on clothing or in firefighting where a flaming portion of a building structure may fall on a firefighter, protection from conduction and ignition is critical. The fabrics planned specifically for fire and flame hazards, then, must be both flame and ignition resistant (i.e., they should remain intact—not tear, shrink, or melt—when confronted with flame and should not support combustion). They should also be nonconductive and able to reflect radiant energy.
The ability of a fabric to resist heat conduction is as important as its ability to resist flames. Anyone who has baked a potato knows that although the foil does not burn, it still conducts sufficient heat to bake the potato. Nomex aramid, PBI, and novaloid all provide significant resistance to conduction of heat. Conduction of heat is also prevented in many ensembles by the use of thick, nonconductive, air-filled layers. (See, for example, Figure 5.37.) The heat protection provided by a series of fabric layers can be tested using a standard test method in which a flame is placed below the outermost layer and a heat sensor above the innermost layer of a system. The rating of each system is expressed as its thermal protective performance (TPP) (NFPA, “NFPA 1971: Standard”).
One of the most difficult problems facing designers of clothing for molten metal hazards is that more heat-resistant fibers are less likely to degrade and, thus, less likely to shed the molten metal. When the metal sticks to a garment, there is more potential for the heat of the metal splashed onto the suit to eventually work its way through to the skin layer of the worker, even if the fabric does not degrade. Thus, some manufacturers favor flame-resistant fibers that are engineered to shed molten metal over aramids and aluminized leathers and the like, to which molten metal tends to stick.
Molten metal protective clothing presents an excellent example of how the material in several chapters of this book need to be read and understood to solve a specific clothing design problem. As with other protective clothing situations, using the techniques in Chapter 1 to gain an understanding the precise nature of the hazard, the worker’s environment and activity and the needs and wants of the user will aid greatly in making appropriate design decisions. Information about flame-resistance and flameproofing has already been presented in Chapter 3. (See “Flameproof and Flame-Resistant Fibers” and “Coatings.”) The theory on which high heat resistant materials are based has also been covered in Chapter 5. (See “Fabric Surfaces and Radiant Energy,” “Blocking Radiant Heat Gain,” and the case study “Keeping Cool: Ensembles for Firefighting.”) Protection from radiant energy at very high temperatures (such as those found in front of furnaces in many industrial situations or in airport fires where high-temperature flames are produced as airplane fuels burn) is best provided by aluminized materials. These are discussed in Chapter 5 under the heading of “Aluminized Fabrics.” In addition, since condensation of steam releases a tremendous amount of heat, in some situations it will be important to prevent this condensation from taking place on the skin or in a layer of the garment too close to the skin surface. (See Chapter 5, “Wind, Water, and Temperature Extremes.”)
The situations that involve flame and molten metal are so varied that a different approach may be needed for each. In some situations, a protective apron and long gloves may be sufficient. In others, a full suit such as the fire entry suit shown in Figure 5.37 must be worn. Design details that may provide places for molten metal to lodge must be eliminated in some situations; flame-resistant fasteners and thread may be a necessity in others.
Because of the bulk of materials and the full body coverage needed, many of the provisions for mobility discussed in Chapter 2 will apply to the design of clothing for molten metals. Of particular importance is the designer’s attention to other equipment, such as breathing apparatus that must be worn with these ensembles. Some of the provisions needed for these are discussed earlier in this chapter under the heading of “Fully Encapsulated CB Protection.”
While each of the hazards in this chapter has been discussed separately, most industrial, military, first-responder, and medical environments will probably contain combinations of several of these hazards. In addition, most activities that require protective clothing will demand that designers have a thorough understanding of mobility, thermal balance, and many additional factors discussed in other chapters. Integrating all of these issues effectively poses some of the greatest challenges to clothing designers.