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Performance and Limits of Moisture Barriers


Firefighters expect their protective clothing to keep them dry and free from contamination. This expectation derives from the fact that a principal layer used in the construction of garments, gloves and footwear is a barrier layer that is dedicated to keeping liquid out.  

This expectation is tempered by the fact that even though clothing uses a moisture barrier in its construction, openings can still let outside liquid enter. In the case of gloves and footwear, certain liquid exposure conditions and orientations of the firefighter may enable liquid — usually water — to enter through the top of the boot or in through the cuff or gauntlet of the glove. While these forms of liquid entry are physically possible, they are not common because garments are generally designed with appropriate interfaces that have large overlapping areas or special designs that direct liquid from entering gloves and boots.

For example, pant legs generally extend anywhere from 6 to 10 inches down over the top of the boot. The only way for water to penetrate this interface region is if the firefighter has his or her leg parallel to the ground where there is standing water.

Likewise for the gloves, manufacturers have designed water wells into the ends of coat sleeves to direct water from running inside the coat arm and into the glove. These clothing features are not liquid-proof as the average firefighter knows.

NFPA 1971
The same perspective exists for garments. The moisture barrier is continuous over the body where the outer shell material appears. NFPA 1971, which governs the design and performance requirements for this clothing, dictates that the liner must extend to within a specified distance of the clothing hems. For both coats and pants, the principal openings occur elsewhere.

For coats, principal openings include the front closure that extends down the middle, the collar area, the bottom hem, and the sleeve ends. Liquid can enter inside the coat through any of these areas. Since the implementation of the overall liquid integrity ("shower") test, manufacturers have been very diligent about the design of the coat front closure.

After this test became mandatory in the 1997 revision of NFPA 1971, most garment closures were radically redesigned to include moisture barrier in the storm flap and interior edges of the closure to limit liquid penetration. Depending upon the garment design, taping seams in other parts of the garments, such as where the collar joins the garment, also became a necessary practice.

Pants have fewer liquid entry points, mainly the front fly, the waist area, and the pant leg ends. Coat overlap on the pants helps to remedy any liquid infiltration up into the coat or in though the waistband of the pants. Nevertheless, liquid in large enough quantities can enter through these areas when the orientation of the firefighter allows or even assists penetration. Firefighters acknowledge that these areas of clothing can easily be avenues of liquid penetration.

Under some circumstances it is possible for liquid penetration to occur through the moisture barrier material itself. Given the very stringent requirements for the barrier layer to be tested against different liquids, moisture barriers are fairly robust in keeping out liquids. Still, any physical or thermal damage to the film layer of the moisture barrier or loosening of tape at seams can provide definite locations for liquid penetration.

Physical damage
Thermal or physical damage to the barriers are generally obvious, but other pathways, namely interface areas, may seem to offer a more plausible route for the liquid to follow.

It is often difficult to rationalize leakage resulting from pinholes in the moisture barrier, which are discovered during hydrostatic testing of the moisture barrier in firefighter clothing. The pinholes are often not discernible from a visual examination, but when water is applied under pressure during the hydrostatic test, liquid is observed to penetrate. With increased testing of liners, by departments that have adopted NFPA 1851 for care and maintenance of firefighter protective clothing, organizations are finding a larger number of pinholes in clothing.

Firefighters must realize that clothing must be properly maintained through inspection and repair.
Not all pinholes correspond to areas of wear on the garment where damage might be expected to occur, such as under SCBA shoulder or waist straps. In the case of a pinhole leak, liquid must saturate the outer shell, pass through the hole, soak the thermal barrier, and then manifest in sufficient quantity to wet the skin or underclothing in order to be detected in the field.

This process could occur with water pressurized in a hose stream and even from the pressure created by kneeling. It would be unlikely for liquid to pass through pinholes if relatively smaller volumes are involved as might be the case for contaminated blood or body fluids or contact with chemical substances. . Nevertheless, NFPA 1851 indicates that any area of observed water penetration during the hydrostatic test is a failure because a breach in the barrier film does permit an avenue for potentially hazardous liquid to pass.

What does all this mean? Well, the above discussion points out that clothing is required to be designed and tested to keep liquids out. These liquids may be hot water, chemical contaminates, or blood and body fluids encountered in rescue events. When properly worn and maintained, clothing will keep these liquids out under most ordinary circumstances. But just as firefighter protective clothing cannot protect the firefighter from burn injuries under all thermal exposure conditions, limitation exists for liquid protection.

Liquid entry
There are circumstances that overwhelm or defeat the liquid protection capabilities of the clothing — large volumes of liquid and/or certain orientations of the firefighter — that work to allow liquid entry. As we pointed out earlier, these circumstances can be made worse when clothing interfaces aren’t properly used (e.g., deploying the collar in its intended upward position) or when clothing wear and tear damages the moisture barrier and its seams.

Fire departments wrestle with decisions for extensively investigating the condition of the moisture barrier because it imparts greater responsibility for ensuring that the clothing is delivering the intended liquid protection. Pinholes are failures of the moisture barrier, but their significance is hard to understand if the presented pathway for liquid contact is not straightforward. While pinholes are easily patched, it is possible that an overabundance of pinholes, even in relatively new clothing, could be a precursor to larger failures in the moisture barrier. The NFPA 1971 specified moisture barrier tests are much more rigorous than the field tests described in Part two of this series and these differences can be interpreted as a realization that some degradation of liquid protection is normal and will take place.

Ultimately, the moisture barrier is a critical component of firefighter protective clothing. Its integrity is a key factor for keeping harmful liquids away from the firefighter. Yet, liquid protection is based not only on the use of a moisture barrier but a clothing design that limits liquid passage through closures and other openings. Trained firefighters expect that their clothing will protect them from liquids; however, this training should also explain that there are limitations for liquid protection, just as there are limitations in protection against any hazard.

Firefighters must realize that clothing must be properly maintained through inspection and repair, and they must also anticipate that certain exposures can overwhelm their clothing's protective capabilities. It is not certain that the protective clothing industry has completely addressed this capability to all firefighters' satisfaction. Nevertheless, most firefighters will agree that liquid protection is an important attribute of protective clothing that is most definitely worth having.

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