An experimental model of heat storage in working firefighters.

OBJECTIVE: Develop experimental models to study uncompensable heat stress (UCHS) in working firefighters (FFs).

METHODS: FFs ingested core temperature (Tc) capsules prior to performing sequential tasks in 40 degrees C and personal protective ensemble (PPE), or 18 degrees C and no PPE. Both trials were conducted in an environmental chamber with FFs using self-contained breathing apparatus (SCBA).

RESULTS: FFs exercising in heat and PPE reproduced UCHS conditions. For every FF in both trials for whom the capsules worked, Tc was elevated, and Tc(max) occurred after completion of study protocol. Trials with PPE resulted in a mean maximum temperature of 38.94 degrees C (+/-0.37 degrees C); Tc(max) reached 40.4 degrees C. Without PPE, maximum Tc averaged 37.79 degrees C (+/-0.07 degrees C). Heat storage values ranged from 131 to 1205 kJ, averaging 578 kJ (+/-151.47 kJ) with PPE and 210.83 kJ (+/-21.77 kJ) without PPE.

CONCLUSIONS: An experimental model has been developed that simulates the initial phases of an interior fire attack to study the physiology of UCHS in FF. The hot environment and PPE increase maximum Tc and heat storage over that due to the exertion required to perform the tasks and may decrease time to volitional fatigue. This model will permit controlled studies to optimize work-rest cycles, rehab conditions, and physical conditioning of FFs.