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.

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.