Firefighter feedback during active cooling: a useful tool for heat stress management?

Monitoring an individual's thermic state in the workplace requires reliable feedback of their core temperature. However, core temperature measurement technology is expensive, invasive and often impractical in operational environments, warranting investigation of surrogate measures which could be used to predict core temperature. This study examines an alternative measure of an individual's thermic state, thermal sensation, which presents a more manageable and practical solution for Australian firefighters operating on the fireground. Across three environmental conditions (cold, warm, hot & humid), 49 Australian volunteer firefighters performed a 20-min fire suppression activity, immediately followed by 20 min of active cooling using hand and forearm immersion techniques. Core temperature (Tc) and thermal sensation (TS) were measured across the rehabilitation period at five minute intervals. Despite the decline in Tc and TS throughout the rehabilitation period, there was little similarity in the magnitude or rate of decline between each measure in any of the ambient conditions. Moderate to strong correlations existed between Tc and TS in the cool (0.41, p<0.05) and hot & humid (0.57, p<0.05) conditions, however this was resultant in strong correlation during the earlier stages of rehabilitation (first five minutes), which were not evident in the latter stages. Linear regression revealed TS to be a poor predictor of Tc in all conditions (SEE=0.45-0.54°C) with a strong trend for TS to over-predict Tc (77-80% of the time). There is minimal evidence to suggest that ratings of thermal sensation, which represent a psychophysical assessment of an individual's thermal comfort, are an accurate reflection of the response of an individual's core temperature. Ratings of thermal sensation can be highly variable amongst individuals, likely moderated by local skin temperature. In account of these findings, fire managers require a more reliable source of information to guide decisions of heat stress management.

[1]  T. McLellan,et al.  Active Versus Passive Cooling During Work in Warm Environments While Wearing Firefighting Protective Clothing , 2004, Journal of occupational and environmental hygiene.

[2]  Gunnar Borg,et al.  Subjective Effort in Relation to Physical Performance and Working Capacity , 1978 .

[3]  M. Bushnell,et al.  Effect of Ambient Temperature on Human Pain and Temperature Perception , 2000, Anesthesiology.

[4]  Ye Yao,et al.  Experimental study on physiological responses and thermal comfort under various ambient temperatures , 2008, Physiology & Behavior.

[5]  Daniel S. Moran,et al.  Hand immersion in cold water alleviating physiological strain and increasing tolerance to uncompensable heat stress , 2008, European Journal of Applied Physiology.

[6]  Yan Liu,et al.  Validity and Reliability of Multiparameter Physiological Measurements Recorded by the Equivital Lifemonitor During Activities of Various Intensities , 2013, Journal of occupational and environmental hygiene.

[7]  Paul Webb,et al.  Human heat balance during postexercise recovery: separating metabolic and nonthermal effects. , 2008, American journal of physiology. Regulatory, integrative and comparative physiology.

[8]  Y Heled,et al.  [Core body temperature monitoring using the telemetric pill]. , 2003, Harefuah.

[9]  Hui Zhang,et al.  Partial- and whole-body thermal sensation and comfort— Part I: Uniform environmental conditions , 2006 .

[10]  E Simon,et al.  Central and peripheral thermal control of effectors in homeothermic temperature regulation. , 1986, Physiological reviews.

[11]  David A Jones,et al.  The effects of face cooling during hyperthermic exercise in man: evidence for an integrated thermal, neuroendocrine and behavioural response , 2007, Experimental physiology.

[12]  Cooling hyperthermic firefighters by immersing forearms and hands in 10 degrees C and 20 degrees C water. , 2007, Aviation, space, and environmental medicine.

[13]  Anthony Walker,et al.  The ageing Australian firefighter: an argument for age-based recruitment and fitness standards for urban fire services , 2014, Ergonomics.

[14]  N. Kondo,et al.  The physiology of acute heat exposure, with implications for human performance in the heat , 2008 .

[15]  David W. DeGroot,et al.  Extremity cooling for heat stress mitigation in military and occupational settings , 2013 .

[16]  Cooling Hyperthermic Firefighters by Immersing Forearms and Hands in 10°C and 20°C Water , 2007 .

[17]  Christian F. Bulcao,et al.  Relative contribution of core and cutaneous temperatures to thermal comfort and autonomic responses in humans. , 1999, Journal of applied physiology.

[18]  Chinmei Chou,et al.  Physiological and subjective responses to cooling devices on firefighting protective clothing , 2008, European Journal of Applied Physiology.

[19]  S. Mccabe,et al.  Patient and injury characteristics in the development of cold sensitivity of the hand: a prospective cohort study. , 1999, The Journal of hand surgery.

[20]  R. Hwang,et al.  Effects of temperature steps on human skin physiology and thermal sensation response , 2011 .

[21]  J. Glazer,et al.  Management of heatstroke and heat exhaustion. , 2005, American family physician.

[22]  Gavin P. Horn,et al.  Core temperature and heart rate response to repeated bouts of firefighting activities , 2013, Ergonomics.

[23]  Roald Bahr,et al.  Effect of Exercise Intensity, Duration and Mode on Post-Exercise Oxygen Consumption , 2003, Sports medicine.

[24]  P. Capodaglio.  The use of subjective rating of exertion in Ergonomics. , 2002, Giornale italiano di medicina del lavoro ed ergonomia.

[25]  T Reilly,et al.  A practical cooling strategy for reducing the physiological strain associated with firefighting activity in the heat , 2009, Ergonomics.

[26]  C. L. Lim,et al.  The ingestible telemetric body core temperature sensor: a review of validity and exercise applications , 2006, British Journal of Sports Medicine.

[27]  K B Pandolf,et al.  Cooling different body surfaces during upper and lower body exercise. , 1987, Journal of applied physiology.

[28]  K B Pandolf,et al.  Influence of Local and Central Factors in Dominating Rated Perceived Exertion during Physical Work , 1978, Perceptual and motor skills.

[29]  James M. Carter,et al.  Strategies to combat heat strain during and after firefighting , 2007 .

[30]  Charlie Huizenga,et al.  Skin and core temperature response to partial- and whole-body heating and cooling , 2004 .

[31]  J. Macdermid,et al.  Immersion in Cold-Water Evaluation (ICE) and Self-reported Cold Intolerance are Reliable but Unrelated Measures , 2008, Hand.

[32]  L. Armstrong,et al.  Cold Water Immersion: The Gold Standard for Exertional Heatstroke Treatment , 2007, Exercise and sport sciences reviews.

[33]  G. Norman.  Likert scales, levels of measurement and the “laws” of statistics , 2010, Advances in health sciences education : theory and practice.

[34]  F. Jensen,et al.  Influence of body temperature on the development of fatigue during prolonged exercise in the heat. , 1999, Journal of applied physiology.

[35]  David Nichols,et al.  Fighting fatigue whilst fighting bushfire : an overview of factors contributing to firefighter fatigue during bushfire suppression , 2007 .

[36]  Hui Zhang,et al.  Observations of upper-extremity skin temperature and corresponding overall-body thermal sensations and comfort , 2007 .