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.

Read more in Part 2