Aims: To assess the physiological and perceptual responses of fire fighters to a simulated protracted incident in tropical conditions, and to compare the effectiveness of four cooling methods.
Methods: 60 fire fighters participated in a simulated structural firefighting exercise that consisted of furniture removal, tunnel crawling and sandbag filling while wearing structural firefighting attire in field conditions (mean outdoor wet-bulb globe temperature of 29.4°C) for 30 minutes, followed by removal of the firefighting ensemble for 30 minutes of cooling; repeated 3 times. Fire fighters were assigned to a cooling cohort (1 Shade; 2 Crushed Ice Ingestion; 3 Water Immersion; 4 Misting Fan) matched for body mass index (BMI). During the cooling phase, cohort 1 rested quietly in the shade, cohort 2 ingested 7.5mL.kg-1 body mass of crushed ice, cohort 3 were immersed in 25°C water and cohort 4 were seated in front of a misting fan. All 4 groups had ad libitum access to water and/or a carbohydrate/electrolyte beverage. An ingestible telemetry pill permitted measurement of core temperature throughout the exercise, while tympanic temperature, heart rate, blood pressure, subjective thermal sensation and thermal discomfort ratings were recorded periodically throughout the cooling phase.
Results: Overall, pre-exercise core temperature averaged 37.4°C and rose 1.1°C to average 38.5°C following the initial work phase of the exercise, with 5 participants exceeding a core temperature of 39.0°C. Mean core temperature of the water immersion group decreased to average 0.1°C below pre-exercise readings, whereas the shade, crushed ice and misting fan groups averaged 0.3–0.4°C above rest at the cessation of the initial cooling bout. A similar pattern continued throughout the exercise, with the water immersion cohort demonstrating lower mean core temperature following the 2nd work phase (0.5–0.7°C), 2nd cooling phase (0.3–0.6°C) and final work bout (0.3–0.4°C) than the other groups. Thermal sensation was perceived as warm to hot following the initial work bout for all cohorts. 10 minutes of resting in the shade or ice ingestion resulted in thermal sensation improving to slightly warm to warm, whereas the water immersion and misting fan group’s thermal sensation improved to slightly cool to cool. After 30 minutes of cooling, the ice ingestion and shade groups felt neutral to slightly warm with the water immersion and misting fan group’s maintaining their cool to slightly cool ratings. A similar pattern was repeated across the 2nd and 3rd cooling bouts.
Conclusions: This investigation confirms that physical activity while wearing structural firefighting attire in a tropical environment promotes rapid heat storage. Temperate water immersion is more effective in lowering core temperature than shade, crushed ice ingestion or use of a misting fan during rest periods. For protracted incidents, a rehabilitation centre with medical support, hydration and cooling inclusive of temperate water immersion is recommended.