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Influence of Chronic Heat Acclimatization on Occupational Thermal Strain in Tropical Field Conditions

Brearley, Matt B. PhD; Norton, Ian MB, BAO; Rush, Daryl; Hutton, Michael; Smith, Steve MLM; Ward, Linda MAppSci; Fuentes, Hector MB, BS

Journal of Occupational and Environmental Medicine: December 2016 - Volume 58 - Issue 12 - p 1250–1256
doi: 10.1097/JOM.0000000000000902
Original Articles

Objective: To examine whether non-heat acclimatized (NHA) emergency responders endure greater physiological and perceptual strain than heat acclimatized (HA) counterparts in tropical field settings.

Methods: Eight HA and eight NHA men urban search and rescue personnel had physiological and perceptual responses compared during the initial 4 hours shift of a simulated disaster in tropical conditions (ambient temperature 34.0 °C, 48% relative humidity, wet bulb globe temperature [WBGT] 31.4 °C).

Results: From the 90th minute through to end of shift, HA (38.5 °C) sustained a significantly higher gastrointestinal temperature than NHA (38.1 °C) (mean difference 0.4 ± 0.2 °C, 95% confidence interval [CI] 0.2 to 0.7 °C, P = 0.005) despite comparable heart rate (P = 0.30), respiratory rate (P = 0.88), and axilla skin temperature (P = 0.47). Overall, perception of body temperature was similar between cohorts (P = 0.87).

Conclusions: The apparent tolerance of greater physiological strain by HA responders occurred in the absence of perceptual differences.

National Critical Care and Trauma Response Centre, Level 8 Royal Darwin Hospital (Dr Brearley), Tiwi, NT, Australia; World Health Organisation (Dr Norton), Geneva, Switzerland; Queensland Fire and Emergency Services (Mr Rush, Mr Smith), Cannon Hill, Queensland; Northern Territory Fire and Rescue Service (Mr Hutton), Darwin, Northern Territory; Menzies School of Health Research (Ms Ward), Tiwi, Northern Territory; Princess Alexandra Hospital (Dr Fuentes), Woolloongabba, Queensland, Australia.

Address correspondence to: Matt B. Brearley, PhD, National Critical Care and Trauma Response Centre, Level 8 Royal Darwin Hospital, Rocklands Drive, Tiwi 0810, Australia (

This project was funded by a Trauma and Disaster Management (TRADIM) research grant.

The authors were funded by their respective employers and have no conflict of interest to declare.

Copyright © 2016 by the American College of Occupational and Environmental Medicine