The purpose of chemical protective clothing is to protect the wearer from direct skin contact with hazardous substances in their various forms. Worldwide, there are about 8 million hazardous substances in use, according to a National Research Council estimate.
Sadly, we know far too little about the effects on human beings resulting from skin contact with most of these substances. Therefore, it is absolutely essential to establish an optimal level of protection for the wearers of chemical protective clothing.
Chemical protective suits are available in many different designs and materials. The key determinant in the choice of CPC must be the protective factor that is to be provided to the wearer based on the use to which the suit is to be put.
In many instances, the choice of type of protective clothing is based on previous practices, often due to lack of regulations or even guidelines from any health authority relating to the use of such clothing. The available budget for protective clothing can also be an important factor.
In this article, I will compare international standards for chemical protective suits, which are considered to provide the highest possible level of protection. These suits are usually referred to as "A" level suits. They should provide protection against all hazardous chemicals or other materials in whatever form they may arise -- liquid, gas, vapor or solid.
America vs. Europe
Currently there are two major internationally recognized standards available. These are the American standard NFPA 1991 (1994 edition) and the joint European standard EN 943, although the European standard at this time is still only a preliminary document.
The American NFPA 1991 (1994 edition) standard is, in my opinion, the better of the two. It is more user-friendly with distinct documentation and clearly defined minimum requirements. The structure of the European EN 943 standard is more complex. It offers a number of options for different classes of the minimum requirements which are not easy to interpret unless you are a qualified expert on the subject. I can well imagine that the reason for this is that the European standard has been drawn up, discussed, negotiated, compromised and agreed upon among all 15 member countries of the European Union.
I would now like to draw some comparisons between these two standards.
Abrasion Prior to Chemical Resistance Test
The American NFPA 1991 (1994 edition) standard stipulates the abrasion of suits to simulate wear and tear in service prior to the suits being tested for resistance to chemicals and other hazardous substances.
The European EN 943 standard contains no such stipulation relating to abrasion prior to chemical resistance tests.
Conclusion: The American standard recognizes the fact that a chemical protective suit is not only exposed to contact with hazardous and aggressive substances but also to wear and tear during its service.
Chemical-Permeation Resistance Test
The chemical resistance protection factor is established by means of what is knows as the permeation test. This is a test that is clearly stipulated in both the American NFPA and the European EN standards.
The stringent American standard stipulates a maximum detection level or permeation rate of only 0.1 g/cm2 per minute during a test period with a minimum duration of 60 minutes.
The European standard allows a maximum detection level or permeation rate of 1.0 g/cm2 per minute - 10 times more than its American counterpart - during a test with a duration of only 10 minutes. In the case of emergency teams, the test period is increased to 30 minutes. One sixth or one half of the American norm.
Conclusion: It is my opinion that our meager knowledge of the effects of contacts between human skin and hazardous substances has been given much more consideration by the North American standards committee than by its European colleagues.
Duration of the Test
The minimum duration of the chemical resistance or permeation test stipulated in the American standard, as already stated, is 60 minutes. However, if no breakthrough or other failure has occurred within this period of 60 minutes, the test must continue for a further period of up to 180 minutes or until such a breakthrough or failure has occurred.
The European standard states that if the test period of 10 minutes is applied for its chemical resistance/permeation test and has been passed successfully, i.e. without any breakthrough or failure within the stipulated 10 minutes, no more, no less, then the suit is approved. Thus, no "tolerances" are established, nor is any information gained as to exactly when breakthrough or any other failure may occur in the suit being tested.
Conclusion: A type approval protocol according to the American NFPA 1991 (1994 edition) standard offers significantly more qualified, more valuable, more useful and more important information to the user than its European counterpart.
A factor limiting the value of the permeation or chemical resistance test results under both the American and European standards is that the tests need only be carried out at one fixed temperature.
The temperature stipulated under the American standard is +25 degrees Centigrade (+77 F) and for Europe it is +20 degrees Centigrade (+68 F).
Conclusion: A hazardous or aggressive substance is generally much more aggressive at a high temperature than at a low one. Under the rules of the NFPA standard, the chemical resistance test is not only carried out on a suit that has been exposed to simulated wear and tear, but the suit also is exposed to chemicals at a higher temperature. That means these chemicals are more aggressive. There is no doubt that the American chemical resistance test is far more stringent than its European counterpart and its results, once again, of much greater value.
The American standard stipulates a more severe flame test than the European. The American standard requires a suit to be in contact with flames for a longer period. Further, the European standard offers various options for different classes of flame tests and requirements.
Conclusion: The existence of a number of different "look alike" options in the European standard requirements could easily lead to misinterpretation and misjudgments when selecting this type of protective equipment.
NFPA Has Superior Standard
Although the European standard EN 943 has been developed after the American NFPA 1991 (1994 edition), its requirements, except for the pressure leakage test, are not nearly as stringent. We can draw the general conclusion that chemical protective clothing which has been tested and type-approved according to the American NFPA 1991 (1994 edition) standard offers better protection to the wearer against chemicals and other hazardous substances than a corresponding suit tested and type-approved for civil use according to the standards applied in Europe today.
Moreover, a type approval in accordance with the American standard NFPA 1991 (1994 edition) is not a one-time event. It is subject to annual audits by the relevant authority. These annual tests may not only cover a variety of key product features in a sample of suits; they extend all the way back to the supplier's manufacturing procedures and quality assurance.
Confined Space Entries
Standards and type approval procedures establish the best possible foundations for evaluating and selecting new personal protective equipment and chemical protective clothing. However, sometimes these standards bring limitations and some can actually create problems.
A typical case could be entries into confined spaces, difficult access and narrow entries, where a gas and vapor-tight chemical protective suit is required.
Currently it is only possible to obtain a type approval certificate according to the NFPA 1991 (1994 edition) standard for suits of so-called totally encapsulated type where the self-contained breathing apparatus is carried inside the suit and is protected by it. Such a suit becomes rather large in volume and may prevent safe entry into a confined space and even jeopardize the safety of the wearer. The "big suit" design undoubtedly runs a greater risk of being punctured during work.
Currently the market does offer nonencapsulated suits with the breathing apparatus on the outside of gas and vapor-tight chemical protective suits. These are clearly better for use in confined space entries than the bulky totally encapsulated suits.
The American NFPA 1991 (1994 edition) standard currently makes it impossible to obtain type approval for a nonencapsulated vapor and gas-tight suit even if the suit is made of approved and certified materials. The main reason for this is that the market simply does not offer any SCBA units that have been additionally tested and certified to conform with the American NFPA 1991 (1994 edition) standard.
The European EN 943 standard which is structured in a completely different way and is not as stringent as its American counterpart, does provide for certification of nonencapsulated gas, vapor and chemical protective suits.
Disposable Or Limited Use Suits?
Advanced limited use or disposable protective suits are today based on very thin barrier films or foils laminated together. These films or foils, in their turn, are usually laminated to highly porous substrates which have relatively poor tensile strength properties. In some rare cases, the films are laminated to a strong, flexible fabric, forming a solid unit. The materials for suits of the limited use or disposable type are available with either a single coating on the outside or coatings on both the inside and outside.
The ultra thin films which are used are naturally very sensitive to mechanical stresses and abrasion and also to flames and heat. Any mechanical damage such as scratches or cracks is virtually impossible to detect visually without the aid of special instruments.
These difficulties in detecting any possible damage to the barrier laminate make it extremely difficult for the user to decide if it is safe to reuse a suit of limited use type even if it has not been exposed to any hazardous substances during the intervening period.
According to the NFPA 1991 (1994 edition) standard, an additional outer protective cover, often referred to as a flash cover, must be worn over a certified garment of disposable or limited use type in order to protect the sensitive material of the garment against abrasions, etc., and, in addition, to provide extra protection to the wearer against flames and chemicals that cause high temperatures by thermal reactions.
This additional flash cover is a necessity for the disposable or limited use type of suits, in order to be able to pass the pre-abrasion conditioning phase which is mandatory under the NFPA 1991 (1994 edition) standard and which precedes the actual chemical permeation resistance test, as has already been described.
Can We Rely Upon Standard Test Methods ?
Can we really trust the standard methods of testing suits to establish their degrees of resistance to permeation and breakthrough by hazardous substances if these methods are applied to disposable or limited use suits or garment materials ?
Generally, the answer is "Yes." However, questions have been raised as to whether the permeation test procedures used reflect real world situations. This applies particularly to tests of the materials used in the manufacture of disposable and limited use suits as these materials incorporate a highly porous and relatively thick substrate.
The discussions center around the fact that the test methods described in both the American and the European standards fail to stipulate that the edges of garment samples undergoing tests must be sealed. The question is, "Does this highly porous substrate allow any molecules of the chemical substance being used to test the garment to disappear during the detection process?" If the edges are not sealed, some molecules could actually escape via the substrate, getting away through the unsealed edges and thus escaping detection. The results of this test would then be misleadingly positive due to samples that leak.
Does Limited Use Mean Limited Protection ?
The term limited use suit tends to give a wrong impression. A better term perhaps would be disposable or advanced disposable suit. This would be more correct since this type of chemical protective clothing is made from disposable garment materials.
Evaluation -- An Important Task
The complexity of the different standards and types of applications requires a profound and comprehensive evaluation process before a decision is made on the selection of your next generation of chemical protective clothing. Even the word clothing in this concept is perhaps slightly inadequate. The decision will not be about a piece of clothing. It will be about a life support system -- the employee's last link in his chain of protective equipment. And someone's life could depend on it. Each and every one of us must take responsibility for ensuring that the right choice is made.
John F. Eklund is senior sales and product manager for Trelleborg Protective Products AB, Ystad, Sweden. He can be reached by e-mail at [email protected]