Physiological strain and countermeasures with firefighting.

Protective clothing is integral to the task of firefighting, but at the same time can increase physiological strain and impair work capacity. Encapsulation of the head and the high thermal resistance and/or low water vapor permeability of the clothing ensemble impede evaporative heat dissipation, thus elevating the rate of heat storage and creating a state of uncompensable heat stress (UHS). In addition, the additional weight from carrying a supplemental air supply and the greater respiratory work of breathing through a regulator can create a negative spiral of thermal hyperpnea from greater respiratory demands and metabolic heat production. The elevated respiratory demands also increase cardiac strain and potentially the risk for myocardial events. Tolerance time during UHS is determined by three factors: the core temperature at the beginning of the heat stress exposure, the core temperature that can be tolerated before exhaustion or collapse ensues, and the rate of increase in core temperature from the beginning to end of the heat stress exposure. Protective clothing is often employed in highly dynamic environments, making portability, longevity and integration with the task requirements and clothing critical design characteristics for countermeasures. To date, most countermeasures have been relatively indirect in nature, primarily with alterations in work scheduling along with physiological manipulations such as cooling manipulations during recovery periods. Advances are required in materials science to develop lighter and less restrictive protective equipment, concurrent with cooling strategies that target specific regions or which can be effectively implemented during exercise.