Covering Your Back

Sept. 1, 1999
Understanding the choices, benefits and limitations of chemical protective clothing can save your skin -- and your life.

Dr. Jim Zeigler would like to clear up the misconception many people have that chemical protective clothing protects the wearer from hazards.

"There are no red 'S's on these garments," says Zeigler, a research associate with the DuPont Nonwoven Division, in explaining what he calls the Superman Syndrome. "What protects you is your training: how well you have identified the hazards and how well you have engineered your process," he continues. "The clothing is really that last line of defense when all else fails and everything is going wrong. You don't want to make it the only thing that's between you and the hazard."

Dr. Neil Langerman, president of Advanced Chemical Safety, compares chemical protective clothing (CPC) to a suit of armor that, while it may be perfect, is useless if the soldier inside does not know what to do. "It's part of a total package of risk control. OSHA 1910.132 requires ... a personal protective equipment assessment for just this reason." In fact, the OSHA standard decrees that employers retrain employees who do not wear personal protective clothing properly. Education is critical to successfully deploying CPC, but it's part of a larger continuum of preplanning, anticipating possible hazards and being deliberative, rather than reactive, to chemical challenges.

Employees who resist using CPC or who use it improperly may resent being told what to do or may feel encumbered by the clothing and the rules. Zeigler suggests the problem results from failure to properly educate users about the hazard and the risks, to instill a value for protective precautions and to involve them in selecting CPC. "You haven't built the value of it in them and trained them that there is a hazard present and that they need to wear it or put themselves at risk," he says. "You have to be careful not to make employees fearful, yet build confidence that, while the chemicals are hazardous, they can work safely with them."

Choosing CPC

For maximum protection, several factors should guide selection of CPC:

  • Nature of the hazard, both type of chemical and form;
  • Length of exposure;
  • Chemical resistance of the CPC ( i.e., its permeation and penetration resistance rates); and
  • Comfort.

The first step is to refer to the current Material Safety Data Sheets and technical data sheets provided by the chemical supplier as a guide to the level of protection required.

The American Society for Testing and Materials (ASTM) clearly defines the standards by which the chemical resistance of protective clothing must be measured. The critical measurements are the permeation and penetration resistance rates.

"Permeation" is the diffusion of chemical molecules from the outer surface to the inner surface of the CPC fabric. Langerman warns that all CPC leaks, so it's important to know how much of the chemical leaks through the fabric in the space of a minute, (i.e., the permeation rate).

ASTM F739 covers continuous contact with the chemical throughout the test period; ASTM F1383 covers intermittent contact during the test period.

"Penetration resistance" is based on breakthrough (i.e., how long it takes for the chemical to appear on the inside surface of the garment) and the amount of permeation that can be measured on a unit of the area of material per unit of time.

Todd R. Carroll, senior engineer, Research and Development, Kappler Protective Apparel and Fabrics, says that penetration is a valuable gauge of chemicals that do not present a significant skin threat, because penetrating chemicals may not be visible, yet can permeate at dangerous concentrations. Chemical resistance information is typically only available for the fabric, so consider the expected performance of the closure and interfaces, such as gloves and cuffs, when selecting garments. Also, because the ASTM F903 test only covers a 60-minute period, the supplier should be contacted if the garment will be used for a longer period.

"Chemical resistance information should be matched to the toxicity of the chemical being handled, the exposure scenario and the exposure duration," he says. "My approach is to analyze my scenario, using the 'REC' principle." This is:

Recognize the chemical hazard. "This allows you to reference chemical data that describes the expected performance of the fabric," Carroll says. "Match the duration of the work to the expected chemical resistance."

Evaluate the need to assess your exposure scenario, work, and toxicity of the chemical and physical hazards present. Effective evaluation tells the end user what style of garment is needed to provide the necessary level of protection. Look at the seam type (i.e., served, bound, ultra-sonic, tapped, glued) and garment configuration (i.e., coverall, splash suit, encapsulating, gas-tight) you will need.

Control concerns purchasing and using the garments selected. Training on the limitation of the protective items is critical to the field performance of any protective device.

Chemical protective garments also are tested for the amount of time required for the chemical to pass through the fabric and are rated according to the number of hours that maximum protection is afforded. To minimize risk, garments should be discarded and replaced before they reach the recommended maximum exposure time. This can be costly, so consider tradeoffs among the factors governing selection of CPC.

For example, low permeation and penetration resistance rates of a fabric might make it desirable in a particular situation, but that one-time protection must balance against its cost, its comfort and flexibility, the form and concentration of the chemical and the total exposure time. If the exposure were minimal, the garment cumbersome or uncomfortable, or the cost prohibitive, it might be prudent to consider a garment with higher penetration resistance and permeation rates.

According to Carroll, chemicals attack protective clothing through degradation, which is a physical breakdown of the fabric, such as discoloration, swelling or puckering that reduce its physical properties.

"Users should be aware of any visual change in their protective clothing and retreat if signs of degradation become apparent. They could indicate that other chemicals are present that were not expected, or that the garment is actually not protective against the chemicals present," he says. "Degradation should be discussed during the control portion of the selection process when users are being training on the expected field performance of the selected garments."

Heat and Comfort

In considering the protection level of CPC fabrics, Zeigler warns buyers to investigate and reason through the claims. He cites moisture vapor transfer rate (MVTR) claims for microporous fabrics as an example.

MVTR measures the rate at which the moisture passes through the fabric. Because evaporation of perspiration cools the body, the higher the MVTR, the cooler the garment will be, according to

theory. DuPont commissioned three studies of MVTR at Florida State University by a pioneer in the field of heat stress management.

When the body no longer can release more heat than it produces, the core temperature rises, leading to heat stress. "We found that using this measurement of moisture vapor transfer rate does not explain the performance of CPC garments on people," he says. "What explains their performance is the ability of air to flow through the garment and that also relates to chemical permeability.

"When you get down to a monolithic barrier, such as a total film coating, you dont have airflow or permeation, but you also don"t have evaporation. That's why putting on a totally encapsulated suit is stressful in terms of heat stress in cold and hot temperatures."

Heat stress occurs with all chemical protective clothing, Zeigler observes. This can be dealt with by ventilating the garment with supplied air or incorporating cooling within the garment with encapsulated frozen gel or water, by hydrating the wearer and monitoring carefully the amount of time he wears the garment, and by clothing selection. Two-piece garments allow more air movement than coveralls.

Carroll suggests checking the air permeability of fabric by holding it against your mouth and attempting to blow through it. If you can, the fabric will see the benefit of air permeability during use. If you can't, the pressure drops experienced within a garment during normal use will not allow air flow through the material, and comfort will be affected.

He adds that microporous fabrics operate on the "critical path" theory (i.e., a web of very small holes). Droplets of chemicals cannot pass through the fabric pores, because of their size. Water vapor and chemical molecules can, however, because they are smaller. In other words, warns Carroll, if you can measure air flow through a fabric, you should not expect any real liquid holdout.

Perm-selective membranes have a high moisture vapor transfer rate and a highly selective permeability to most chemicals, Zeigler says, providing a balance between porosity and protection. The material retains heat, putting a greater thermal burden on the wearer than spun fabrics, though less than microporous films.

Another consideration is the environment in which the garment is to be worn. At very low temperatures, material brittleness is important; at very high temperatures, material structural integrity is of greater importance.

Examine carefully any studies performed on the garments you're considering, as well as the reputation and history of the manufacturer.

Let your employees wear the garments in work situations and listen to their comments on performance, comfort, fit, flexibility and durability, because protection is compromised when the clothing is stressed.

"Workers wearing the equipment should be trained to be constantly aware of any change in the situation," Carroll says. "These include identifying additional chemicals not considered initially, encountering chemicals that have mixed that were not thought to have been mixed, large changes in environmental conditions, visual signs of degradation on clothing items, any signs of exposure or encountering hazards that might require other protective clothing."

Specifiers also should reconsider the garments, as fabric technology and garment design change from year to year. Among trends in chemical protective equipment are hybrid garments that protect the wearer from multiple chemical hazards and fabrics with selective permeability.

Carroll suggests, "Specifiers routinely reassess their selection by reviewing the trade journals, as well as manufacturers" catalogues and Web sites. Under 29CFR1910.132, OSHA requires that new hazard analyses be performed as conditions in the workplace change."

Decontamination Issues

The purpose of CPC is to protect the skin, lungs and body systems from contamination by chemicals, whether solid, liquid, mist or dust, by creating a barrier to immediate and future contact. Thus, using CPC includes developing decontamination strategies to protect the wearer when he removes it.

While CPC decontamination generally comes down to washing the garment or disposing of it, Langerman suggests that decontamination may not be necessary in daily practice. "For example, the gloves a gasoline tanker driver wears do not really need to be cleaned after filling a station tank. They probably weren't contaminated. If they were, the gasoline would evaporate." Lab coats and clean- room clothing can be sent for cleaning, he adds, and rain suits probably don't need cleaning unless they are visibly contaminated.

The problem with reusing contaminated CPC is removing the suit, storing it and putting it on again without exposing the wearer to contamination. "There are times when chemical suits can be reused, but you have to have control of the situation and know what your hazards are, the level of exposure and that the suit has been properly decontaminated," Zeigler says. "A misconception of CPC is that it"s just there for on-the-job, but it's also for off-the-job. That"s why knowing how to put it on and take it off is often as important as how well you wear it."

A big concern is the use of decontamination solution, Zeigler adds. "People presume that those decontamination solutions work with all chemicals, and they don't. The things used for decontamination are not real pleasant chemicals because they actually can damage other materials."

Decontamination measures should be appropriate to the situation; otherwise, it could spread contamination or cause recontamination. Blowing off CPC allows it to be inhaled or contaminate surfaces on which it settles. Using too heavy a mist or spray can force the chemical through the garment. Rinsing gloves in a sink, then washing the hands (an accepted practice) without first decontaminating the faucet handles can spread risk. On the other hand, Langerman warns, "Workers will not follow a rigorous decontamination protocol unless they perceive a real hazard or risk."

Perhaps the most important aspect of getting maximum value from your investment in chemical protective clothing is summarized by Langerman: "Remember, all PPE leaks, it is just a question of how much. As I see it, the biggest mistake is to put excess faith in the PPE and not follow good chemical hygiene."

That means being proactive and minimizing the risk of contact with hazardous chemicals. Zeigler recommends using the process safety management philosophy as your guide, asking: What kinds of things could go wrong? Am I prepared to deal with that? Do I have a contingency plan? How you will deal with threats of fire and explosion? Have you crossed that threshold where you have a flammable or explosive situation? Does everyone know what the hazards and issues are? Do you have a defined and drilled set of procedures to deal with the most likely circumstances? Do you have a clear path for evacuation? Who must you call and who might be involved if you have an accident? "Those are things that you resolve up front and drill on until everyone is aware of them," he says.

"Chemical protective clothing should be deployed when there has been a hazard assessment performed and the hazard cannot be controlled by other means. Even if you have engineered the hazard out, you may still want to wear CPC as insurance," Zeigler advises. "It's not an on-off switch kind of issue. It's a continuum."

Voice your opinion!

To join the conversation, and become an exclusive member of EHS Today, create an account today!