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Testing Requirements for Moisture Barriers

By Jeffrey O. and Grace G. Stull 

Laboratory testing is conducted on materials used in the construction of firefighter protective clothing to ascertain that they will perform as needed to provide minimum protection under actual fireground conditions. In many cases, these tests are not designed to mimic the types of exposures that firefighters experience. Rather, they provide a reproducible assessment of clothing and materials, which will rank their performance consistent with observations for how clothing performs in the field. For moisture barriers, this is true for nearly all of the tests that apply this layer. The tests rigorously evaluate how moisture barriers keep liquids from reaching the clothing interior, but certain limitations apply.

All laboratory tests are performed on new materials. The tests in the NFPA 1971 Standard attempt to simulate use and care by repeatedly washing material samples and exposing these samples to low level heat exposures. It is believed that the mechanical action of the samples inside a washing machine and dryer also help to simulate some wear and tear on garments, although it is generally understood that these preconditions do not replace the full range of exposure effects sustained during garment use and care.

Shower testing is similarly performed using washed garments. This washing can remove some of the water repellent finishes placed on shell materials and affects overall garment liquid holdout, but only new garments are tested.

In reality, garments are exposed to a range of conditions that vary with the location, department, and activities of the individual firefighter. It is impossible to simulate all of these conditions in testing firefighter protective clothing and clothing materials. This inability for creating tests that totally reproduce fireground conditions begs the question of how firefighters remain assured that their moisture barrier layers continue to perform in holding out liquids. The answer lies in the fact that very strict tests are used in the laboratory while field performance is judged using easier tests. Thus, the laboratory barrier tests required by the NFPA 1971 assume that some degradation take place. Field tests set in NFPA 1851 for the selection, care, and maintenance of the garment are more subjective and involve lesser demands on barrier performance but still demonstrate whether the garments keep liquids out.

The latest edition of NFPA 1851 provides four separate evaluations that permit assessment of the moisture barrier after its use in the field:

Light Evaluation
In the "Light Evaluation" test, liner integrity lining is checked by placing the liner (moisture barrier and thermal barrier) over a light table and examining the appearance of the lining; bright areas show possible defects in the moisture barrier or areas of the thermal barrier that have thinned. This evaluation is required as part of an annual inspection and can only show gross defects in a moisture barrier/thermal liner system.

Leakage Evaluation
The "Leakage Evaluation," also called the "puddle test," involves an alcohol-water mixture, which is made with 1 part isopropanol (rubbing alcohol) and 6 parts tap water; the mixture is poured onto the selected cupped areas of the moisture barrier side of the lining to evaluate its integrity; the thermal barrier side of the lining is then viewed after 3 minutes to determine if it shows any signs of wetness, which would indicate there are leaks in the moisture barrier. At a minimum, the front and back body panels of each protective garment element are evaluated using three different moisture barrier material areas and three different moisture barrier areas with a seam. NFPA 1851 specifies testing of the following liner areas:
• Broadest part of the shoulders
• Back waist area of the coat
• Knees
• Crotch area
• Seat area

While the test can be awkward to perform, it will show places of penetration if there are holes in the moisture barrier or lifted tape in seams. Any discovered leakage is cause for repair or consideration of barrier replacement, depending on the extent of damage. This test is also part of the annual Advanced Inspection requirements for moisture barriers, required by NFPA 1851.

Complete Liner Inspection
The "Complete Liner Inspection" is a detailed examination of the garment lining system where the liner system is opened to expose all internal surfaces for inspection and testing. Liners are inspected for:
• Loss of seam integrity
• Broken or missing stitches
• Loose or missing moisture barrier seam tape
• Moisture barrier delamination as evidenced by separation of film from substrate fabric, flaking, or powdering
• Material physical integrity
• UV or chemical degradation as evidenced by discoloration, significant changes in material texture, loss of material strength,
• Loss of liner material
• Shifting of liner material
• Physical damage to all layers and each side of the individual layers

Complete liner inspections are applied to garments after three years of service (after two years for garments that are part of ensembles with the CBRN option), and then annually thereafter. This inspection can only subjectively evaluate the appearance of the moisture barrier, but the inspection of the film side can show damage that would otherwise go undetected.

Water Penetration Barrier Evaluation
In the "Water Penetration Barrier Evaluation," which is part of the Complete Liner Inspection, a hydrostatic tester is used to evaluate the integrity of selected portions of the barrier layer. The tester applies water pressure to the substrate side of the moisture barrier and if the moisture barrier is damaged, leaks appear on the film side of the barrier. This evaluation is applied to the same areas as described for the leakage evaluation above. The test constitutes the most precise evaluation of the moisture barrier and is fully capable of discerning holes in the moisture barrier layer.

All of these evaluations are capable of showing problems with the moisture barrier which can lead to the unwanted inward penetration of liquids. In many cases, these problems will be obvious, particularly if there is a hole in the moisture barrier cause by a puncture or tear from some outside source (such as a sharp pointed object). In other cases, the damage may be less discernable as the damage can be caused by repeated rubbing in a particular area, as a result of equipment such as the straps of the firefighter’s SCBA, a harness, or a tool belt. Still there are other circumstances where there is no visible damage and yet a pinhole in the barrier is discovered by the hydrostatic test during the complete liner inspection.

When a field evaluation does show damage, the department is required to determine whether the damage can be repaired or if the liner must be replaced (or the garment retired). The increasing field inspection of moisture barriers is causing further attention to liquid barrier issues. In the last part of this article series we will show how both laboratory testing and field evaluations translate into expectations for protection of firefighters in the field.

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