Effects of Air Gaps on Heat Loss through Firefighter Turnout Composites with Different Moisture Barrier Components

Heat stress is a significant concern to firefighter health and is largely affected by the heat release properties of protective clothing. Air gaps exist in multi-layer firefighter clothing and have a great impact on body heat dissipation. In this study, the effect of air gap size on heat loss through firefighter turnout composites in different ambient environments was explored with a specially designed hotplate system. Three firefighter turnout composites with different moisture barriers were tested in mild (25 °C) and hot environments (35 and 45 °C). Study findings showed the air layer’s thermal insulation and evaporative resistance increased up to a critical air gap size of about 15 millimeters when tested in mild condition due to the occurrence of natural convection. When tested in hot environments, the insulation and evaporative resistance of air gap kept increasing. The most significant finding was that air gaps together with ambient conditions affected the amount of moisture absorption inside moisture barriers, which further influenced the evaporative resistance and evaporative heat loss of firefighter composites containing bi-component moisture barriers. In contrast, for fabric composites with microporous moisture barrier, their evaporative resistance was relatively independent of air gap size and ambient conditions. The results from this study are useful for the modeling of heat transfer through firefighter clothing and are of great importance for the design of firefighter composites.