Heat Stress in Motorsports - Lessening the Effect on the Wearer by Selection of Fire Suit Materials and Construction

Heat Stress is the result of the body's inability to maintain a stable core temperature when subjected to a heat load. This occurs when the sum of the environmental heat load and the metabolic heat load exceeds the body's capacity for heat dissipation. Failure to dissipate the heat load results in increase in core temperature and the development of heat illness. This is a recognized problem in closed cockpit race cars and can lead to severe illness and even death. The Body's primary thermoregulatory pathway is sudation (the process of sweating and evaporative heat loss). Research, sponsored by Stand 21, has been carried out to study the effect of the “fire suit” on this process and to improve the breathe ability and performance in providing an environment for evaporative heat loss. The evaporative resistance and permeability index of the fabric define the comfort of the suit as experienced by the wearer. Air permeability of the material and the moisture vapor transmission rate are the key factors in the ability of the suit to “breathe” and dissipate heat through evaporation of sweat. Fabrics meeting the same standard of thermal protection (SFI3.2A level 5) but with different breathe ability index (ISO11092) were evaluated. Tests were conducted on five volunteers in a constant temperature environment of 60°C and 40% relative humidity while generating 160W/m² during exercise. Subjects were also tested with and without forced air cooling helmets. Parameters measured included blood pressure, heart rate, core temperature, skin temperature and skin water vapor pressure and dehydration. Three suit types were tested. The “fire suit” constructed based on the study of the fabric properties optimized for promoting evaporative heat loss demonstrated superiority in that the rise in core temperature to levels associated with heat stress was reduced by 40%. The heart rate, core temperature and skin water vapor pressure also increased more slowly.