A series of different material systems representing potential reinforced knee areas of firefighter protective garments were subjected to both conductive and radiant heat resistance testing. Conductive heat resistance testing of prepared garment knee samples was based on ASTM Test Method for Thermal Protective Performance of Materials for Protective Clothing for Hot Surface Contact (F 1060), and included repeated exposures to the same area of the sample seprated by wash/dry cycles to simulate use and wear of garments. Other knee samples were tested in accordance with ASTM Test Method for Radiant Protective Performance of Flame Resistant Clothing Materials (F 1939) at radiant heat fluxes of 8.4 and 84 kW/m2 representing ordinary and emergency fire ground conditions. For both types of testing, samples were tested under both dry and wet conditions. Time-to-pain and time-to-burn were measured in both series of tests using established calorimeter-based temperature thresholds.
While greater thickness and additional material layers generally provided increased thermal insulation, the results of this testing show that the composition of the knee reinforcement layers has a significant effect on protective performance. In addition, the condition of the tested specimens whether wet or dry, as well as the previous exposure history, also had a significant impact of burn threshold times. For example, under dry conditions, a knee reinforcement consisting of a Hypalon® rubber-coated material and two layers of a batt-type material showed 130% longer threshold times (to burn injury) than a similar reinforcement with leather. However, the same reinforcements tested wet exhibited 110% longer burn threshold times for the leather reinforcement. Differences in knee reinforcement performance are attributed to heat sink effects of the denser materials and the amount of water in the material system. The results show that the amount of protection will vary with the amount of water, the level of heat flux, and the composition of the knee reinforcement.