A comparison of cooling techniques in firefighters after a live burn evolution

Abstract

Objective: We compared the use of two active cooling devices with passive cooling in a moderate-temperature (≈ 22 °C) environment on heart rate (HR) and core temperature (T(c)) recovery when applied to firefighters following 20 minutes of fire suppression.

Methods: Firefighters (23 men, two women) performed 20 minutes of fire suppression at a live-fire evolution. Immediately following the evolution, the subjects removed their thermal protective clothing and were randomized to receive forearm immersion (FI), ice water perfused cooling vest (CV), or passive (P) cooling in an air-conditioned medical trailer for 30 minutes. Heart rate and deep gastric temperature were monitored every 5 minutes during recovery.

Results: A single 20-minute bout of fire suppression resulted in near-maximal mean ± standard deviation HR (175 ± 13 b min(-1), P; 172 ± 20 b·min(-1), FI; 177 ± 12 b·min(-1), CV) when compared with baseline (p < 0.001), a rapid and substantial rise in T(c) (38.2° ± 0.7°, P; 38.3° ± 0.4°, FI; 38.3° ± 0.3°, CV) compared with baseline (p < 0.001), and body mass lost from sweating of nearly 1 kilogram. Cooling rates (°C·min) differed (p = 0.036) by device, with FI (0.05 ± 0.04) providing higher rates than P (0.03 ± 0.02) or CV (0.03 ± 0.04), although differences over 30 minutes were small and recovery of body temperature was incomplete in all groups.

Conclusions: During 30 minutes of recovery following a 20-minute bout of fire suppression in a training academy setting, there is a slightly higher cooling rate for FI and no apparent benefit to CV when compared with P cooling in a moderate temperature environment.

Figure 1

Heart rate and T_c recovery during a 30-minute rehab period following fire suppression for passive (solid line), forearm immersion (dashed line) and liquid perfused vest (dotted line) cooling. The predicted equations for the HR recovery by device are VEST: Predicted heart rate = 139.07 − 4.543 * Minute + 0.091 * Minute², CHAIR: Predicted heart rate = 127.90 − 4.543 * Minute + 0.091 * Minute², PASSIVE: Predicted heart rate = 132.68 − 4.543 * Minute + 0.091 * Minute² The predicted equations for the T_c by device are VEST: Predicted T_c = 38.463 − 0.023 * Minute, CHAIR: Predicted T_c = 38.804 − 0.048 * Minute, PASSIVE: Predicted T_c = 38.427 − 0.021 * Minute.

Figure 2

Survival analysis of HR recovery during a 30-minute rehab period following fire suppression for the criterion of HR < 100 and HR < 80 stratified by cooling device (Panels A, C) and subjects aerobic fitness (Panels B, D).

Figure 3

Survival analysis of T_c recovery during a 30-minute rehab period following fire suppression stratified by cooling device.