Many fire service clothing manufacturers promote their liquid-protection capabilities by certifying their products to NFPA 1992, which covers liquid splash-protective garments for hazardous material emergencies. Protective clothing primarily intended for structural firefighting or technical rescue often carries additional certifications for NFPA 1992 compliance.
In general, liquid protection means that the protective clothing prevents the penetration of liquids through the clothing limiting contact of the liquid with the wearer’s skin or underclothing. Liquids can include water, particularly hot water, water with contaminants, liquid chemicals, blood, or body fluids.
All forms of barrier clothing are generally designed to keep at least one type of liquid from getting through the clothing. For example, clothing that is designed for blood borne pathogen protection, is intended to prevent wearer exposure to the pathogens associated with infected blood or body fluids.
The performance of garments and other types of clothing against liquids is based both on the product materials and its design. Both aspects of product performance are equally important for showing whether clothing holds out liquids.
Material performance
Material performance is the demonstration that the material system or layers prevent any visible penetration of liquids. This is normally ascertained through putting a sample of the material in a test cell, which holds the material in place while liquid is put in contact with the normal external side of the material.
Most often, pressure is applied behind the liquid for a set duration and intensity, while the other material side (representing the interior of the clothing) is observed for signs of penetration. The pressure applied and the time of exposure varies with the different forms of liquid tests, but the general principal of testing remains the same — liquid is either seen to come through the material or not.
Consequently, many test results are reported as either pass or fail. In some cases, the pressure or time of failure may also be reported. Materials showing passing results are those that do not let any liquid come through the material.
It is not a foregone conclusion that any continuous material will pass penetration testing. For the most part, materials must have some type of film or coating to show acceptable barrier performance.
Textiles and leather are porous and while they may be coated or treated with special finishes to retard different liquids, with enough pressure or time, liquids will generally penetrate these materials. There are also certain types of plastic films that are designed to be micro-porous, meaning that the holes or pathways through these materials are microscopic in size.
Moreover, the pathways themselves may be very small and indirect, twisting and turning in different directions. In order for liquids to find these pathways, very high levels of pressure must be applied and some liquids may or may not penetrate depending on the characteristics of the liquid.
Surface tension
The controlling factor is the liquid’s surface tension — a measure of the energy between a liquid and surface. Liquids with a high surface tension, like water and water-based liquids, require more pressure to facilitate penetration.
The higher the surface tension, the less ability there is for the liquid to spread out over the surface. It is illustrated by water beading on a waxed surface, like the finish on a car hood.
Yet, add some detergent (a surfactant) to the water and the water will no longer bead. Liquids with low surface tension tend to be better penetrating liquids. Many chemicals, like alcohol and petrochemical solvents, have low surface tensions as do blood and some body fluids.
Breaching material
The only other ways for a liquid to get through a material is by either degrading the material or by permeation. Degradation occurs when the chemical causes deterioration of the film, which in turn, creates small holes and penetration pathways.
The ability for the liquid to cause degradation depends on the nature of both the chemical and the material. Some chemicals can be harsh and will soften and cause other changes that lessen the material’s barrier characteristics. It simply depends on how the chemical interacts with the material.
Fortunately, most industry materials are designed to withstand the effects of multiple chemicals, but since there are so many possible chemicals that can be encountered, all materials are susceptible to at least some chemicals.
Permeation is the other way that a chemical or liquid can get through a material, but this process occurs on a sub-microscopic level. Here chemical molecules pass through the material and come out the other side as a vapor.
This is the same process that happens for material that is breathable, only in that case, the chemical that is passing through is water or water vapor. Needless to say, the amounts of liquid that pass through in this manner are generally very small and cannot be perceived.
However, permeation does become significant if the liquid is highly hazardous and is toxic by skin contact and absorption. Also, permeation can be at high enough rates to show visible liquid on the interior garment surface.
Protecting seams
The most obvious pathways for penetration are seams. The holes made by needles in sewing pieces of material together are easily penetrated by most liquids if those seams are not taped or sealed.
Some barrier material may be joined without sewing by heat-sealing the surfaces of the material together. In either approach, the seam may take on the same performance as the base material.
The exception is that some liquids may affect the tape different than the film. Some tapes rely on glue or adhesive, which can be attacked or dissolved by the chemical making this construction less effective for holding out certain liquids.
Clothing design
By their very nature, all clothing has openings. Of particular significance is the interface between clothing items. The design of these areas is important in affecting whether liquids will enter or not.
For example, it may seem obvious that liquids could enter a glove through the gauntlet or wristlet area, but if the end of the glove is covered up by interface with a coat sleeve, then the ability of liquid to penetrate that portion of the clothing is affected.
Similarly, how coats and pants close and the manner in which clothing items overlap all make the garments that much more resistant to liquid penetration. These openings are actually the more likely penetration pathways for liquid into the garment than are the material or its seams.
NFPA 1992 was developed specifically to address liquid splash protection for first responders and applies the test principles of both material and seam resistance to liquid penetration in addition to assessments of overall garment integrity, including the interfaces, when complete clothing ensembles are certified.
Where it differs with other standards is that the battery of chemicals is more general. The current list of test chemicals includes acetone, dimethylformamide, ethyl acetate, sodium hydroxide, sulfuric acid, and toluene.
This list includes chemicals that do not easily evaporate or are not skin toxic or carcinogenic in their vapor form. They are chemicals that would be concerns for liquid contact in industrial situations.
Generally, materials that do well against these chemicals will also perform well against other chemicals, yet there are many exceptions.
NFPA 1992 does not involve washing garments prior to testing as may occur for most fire service clothing; however, the testing involves repeated flexing and some abrasion on the material to simulate wear and tear on the product as might be experienced in use. Nevertheless, the ability of these preconditions to represent actual use has not been established.
NFPA 1992 also involves the evaluation of seams for liquid penetration using two chemicals — isopropanol (a very good penetrant) and concentrated sulfuric acid. In addition, whole garments or clothing items are evaluated for overall liquid integrity through a shower-type test.
Garment and clothing items that pass NFPA 1992 demonstrate a high level of liquid hold performance, but this does not mean that liquid contact will not occur. There are many chemicals that can cause degradation of the materials or seams, or permeation at very high levels.
Moreover, there are many circumstances in which garment closures and interface areas may permit the penetration of liquids given the orientation and activity of the wearer combined with the respective volume and characteristics of the liquid.
Certainly, where possible, first responders are trained to avoid unknown liquid pools or sources.
The added benefit of NFPA 1992 is that clothing that may demonstrate protection to ordinary fireground liquids or infectious liquids, provides protection against a broader range of liquid chemicals.
