Effects of environmental temperature and humidity on evaporative heat loss through firefighter suit materials made with semi-permeable and microporous moisture barriers

Abstract

The goal of this research was to understand how firefighter protective suits perform in different operational environments. This study used a sweating guarded hotplate to examine the effect of environmental temperature (20–45°C) and relative humidity (25–85% RH) on evaporative heat loss through firefighter turnout materials. Four firefighter turnout composites containing three different bi-component (semi-permeable) and one microporous moisture barriers were selected. The results showed that the evaporative resistance of microporous moisture barrier systems was independent of environmental testing conditions. However, absorbed moisture strongly affected evaporative heat loss through semi-permeable moisture barriers coated with a layer of nonporous hydrophilic polymer. Moisture absorption in mild environment (20–25°C) tests, or when testing at high humidity (>85% RH), significantly increased water vapor transmission in semi-permeable turnout systems. It was also found that environmental conditions used in the total heat loss (THL) test (25°C and 65% RH) produced moisture condensation in bi-component barrier systems, making them appear more breathable than could be expected when worn in hotter environments. Regression models successfully qualified the relationships between moisture uptake levels in semi-permeable barrier systems and evaporative resistance and THL. These findings reveal the limitations in relying on THL, the heat strain index currently called for by the NFPA 1971 Standard for Structural Firefighter personal protective equipment, and supports the need to measure turnout evaporative resistance at 35°C (Ret), in addition to THL at 25°C.

Effects of Outer Shell Fabric Color, Smoke Contamination, and Washing on Heat Loss through Turnout Suit Systems

“…When tested in standard nonisothermal ambient conditions of temperature and humidity without incident solar radiation, turnout composites gained weight because of moisture condensation. 6 We also found that under no radiation, the moisture content inside the moisture barriers and thermal liners was similar, but higher than that of the outer shells (p < 0.05). A similar phenomenon was reported by He et al 42 A possible reason for the higher water absorption in the thermal liner is that the thermal liner was closer to the water-saturated hotplate surface, which would have resulted in a more humid microenvironment.…”

“…The drying effect caused by radiation would decrease the performance of turnout systems with bi-component moisture barriers. 6…”

“…[3][4][5] It was also reported that the performance of bi-component moisture barriers depends on user environments. 6 Bi-component moisture barriers contain microporous membrane coated with solid hydrophilic film. When used in hot, dry conditions, the evaporative resistance of bi-component moisture barriers increases dramatically due to lower moisture absorption.…”

“…When used in hot, dry conditions, the evaporative resistance of bi-component moisture barriers increases dramatically due to lower moisture absorption. 6 The thermal liner is the thickest component and provides the most insulation. 7 A thinner thermal liner with a breathable moisture barrier could result in a higher heat loss value.…”

Thermally stable poly(urethane‐imide)s with enhanced hydrophilicity for waterproof‐breathable textile coatings

“…These films are not porous and are hence water impermeable 1,5 . In this latter scenario, the breathability is attributed to the molecular absorption‐diffusion‐desorption mechanism, which in turn is driven by the temperature and humidity gradient 6–8 . Hydrophilic polymers generally possess polar groups such as hydroxyl (OH), amino (NH 2 ), carboxyl (COOH), or ether (O) linkages which can form hydrogen bonds with water 9,10 .…”