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Welcome to e-Bulletin #4

Welcome to the 4th edition of the Heat Stress e-Bulletin from Thermal Hyperformance. We aim to provide you with a monthly overview of what's happening in the heat stress space, without taking ourselves too seriously. We strive to maximise the health, safety and performance of workers exposed to hot conditions, and trust this information assists you in that endeavour.

Beverage Temperature and Rehydration

Questions regarding fluid temperature and rehydration have been raised in 16 of the 19 toolbox/pre-shift education sessions delivered in the past month, a pattern consistent with previous months and years. Workers almost exclusively report being advised by OHS teams or co-workers to consume tepid fluids post shift or when dehydrated during shift, to promote rapid rehydration. When asked why chilled fluids are not recommended for rehydration, workers generally report that absorption is delayed until cold fluids attain a temperature similar to that of the body. Presumably this would be due to delayed delivery of fluid from the gut to the intestines, otherwise known as gastric emptying or GE.

The search for the source of this workplace advice revealed a host of health/wellness articles and blogs discussing the topic, some for and some against cold fluids but all providing nothing more than anecdotal evidence supporting their viewpoint. Research examining the effect of temperature on GE report mixed results. While some researchers found no GE effect for temperature, the advice provided to workers may be based upon observations of lower GE immediately following consumption of a cold (4°C) as opposed to thermoneutral (37°C) meal (Sun et al., 1988), or cold beverage (Bateman et al., 1982). Importantly, the reported GE delay was both modest in magnitude and duration (<5 minutes). If temperature was a key regulator of GE, the rapid warming of fluids upon ingestion (Shi et al., 2000), particularly where workers have elevated core temperature, would act to minimise any GE difference between cold and tepid fluids. Those who use thermosensitive pills may observe this response when individuals consume cold fluids prior to the pill passing the pyloric sphincter.

In light of rapid rewarming of ingested fluids, and in the context of gastric volume and beverage energy density as the key factors influencing GE, cool beverages are thought to have little effect on GE (Leiper et al., 2015). Furthermore, given that cool beverages result in greater consumption than warm fluids following exercise (Boulze et al., 1983; Khamnei et al., 2011), higher ad libitum fluid consumption would contribute to offsetting any temperature effect on GE. Hence, advising workers to avoid cold fluids appears to be a misinterpretation of the research. A more appropriate message for workers may be to consume fluids at the temperature they prefer. In doing so, temperature based palatability would be maximised and increase the likelihood of workers maintaining restoring fluid balance. 

Lastly, despite 'provision of cool drinking water' being the most common method of occupational heat stress prevention (Xiang et al., 2015) (more on this survey in future e-Bulletins), there remains some confusion in the hydration messaging to workers. By resisting the urge to cherry pick information to consider research evidence as a whole, the unacceptable level of pseudoscience in workplace hydration can be remedied.


  • Bateman DN. Effects of meal temperature and volume on the emptying of liquid from the human stomach. J Physiol. 1982; 331:461-7.
  • Boulze D, Montastruc P, Cabanac M. Water intake, pleasure and water temperature in humans. Physiol Behav. 1983; 30(1):97-102.
  • Khamnei S, Hosseinlou A, Zamanlu M. Water temperature, voluntary drinking and fluid balance in dehydrated taekwondo athletes. J Sports Sci Med. 2011; 10(4):718-24. 
  • Leiper JB. Fate of ingested fluids: factors affecting gastric emptying and intestinal absorption of beverages in humans. Nutr Rev. 2015; 73 Suppl 2:57-72.
  • Shi X, Bartoli W, Horn M, Murray R. Gastric emptying of cold beverages in humans: effect of transportable carbohydrates. Int J Sport Nutr Exerc Metab. 2000; 10(4):394-403.
  • Sun WM, Houghton LA, Read NW, Grundy DG, Johnson AG. Effect of meal temperature on gastric emptying of liquids in man. Gut. 1988; 29(3):302-5.
  • Xiang J, Hansen A, Pisaniello D, Bi P. Perceptions of Workplace Heat Exposure and Controls among Occupational Hygienists and Relevant Specialists in Australia. PLoS One. 2015; 10(8):e0135040.

Emergency Cooling in Remote Settings

Providing appropriate care for hyperthermic workers in remote regions is challenging, as medical facilities may be several hours away. The cool first, transport second rule is particularly relevant here, but how can effective cooling be achieved in these resource limited settings?

Part of the heat stress management curriculum we deliver to remote medical staff and workers relates to the practicalities of decreasing core temperature, including by water immersion. While 'safe' naturally occurring bodies of water across Northern Australia are rare, a small water reservoir for cooling can be created with a tarp (see image below). A paper published last month from the University of Connecticut examined tarp assisted water (9°C) immersion against passive rest in the heat (Hosokawa et al., 2016). Not surprisingly, tarp cooling resulted in a substantially faster decline of core temperature (0.17°C/min) than passive rest (0.04°C/min). In fact, 9°C tarp cooling ranks favourably against more traditional immersion studies (see review of Brearley and Walker, 2015).

Cold water may be difficult to source in remote settings, so temperate water is a more accessible alternative. While temperate water will result in slower cooling rates of 0.05-0.10°C (Brearley and Walker, in development; Taylor et al., 2008), it remains a worthwhile alternative to passive cooling. Through use of a tarp, water immersion can be a practical solution and should be considered as an emergency cooling strategy for remote workers.


  • Brearley M, Walker A. An Evaluation of Cooling Modalities in Hot and Humid Occupational Settings. Paper in development.
  • Brearley M, Walker A. Water immersion for post incident cooling of firefighters; a review of practical fire ground cooling modalities. Extrem Physiol Med. 2015; 4:15.
  • Hosokawa Y, Adams WM, Belval LN, Vandermark LW, Casa DJ. Tarp-Assisted Cooling as a Method of Whole-Body Cooling in Hyperthermic Individuals. Ann Emerg Med. 2016 Nov 4. 
  • Taylor NA, Caldwell JN, Van den Heuvel AM, Patterson MJ. To cool, but not too cool: that is the question--immersion cooling for hyperthermia. Med Sci Sports Exerc. 2008; 40(11):1962-9. 

Climate Forecast, December - February

The Bureau of Meteorology predict NSW and QLD to experience above average day and night temperatures through the summer period, in contrast to the September - November forecast (e-Bulletin #1). Workers in QLD have already experienced such conditions, enduring heatwave conditions last week. Conditions across northern Australia are expected to continue the pattern of the past 15 months, with warmer than normal temperatures

December to February
Chance of above median minimum temperature
December to February
Chance of above median maximum temperature

Latest Research Article

The following paper was published yesterday and available here (for those with access rights).

M Brearley, I Norton, D Rush, M Hutton, S Smith, L Ward, H Fuentes (2016). Influence of Chronic Heat Acclimatisation on Occupational Thermal Strain in Tropical Field Conditions. Journal of Occupational & Environmental Medicine 58(12), 1250-1256.

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 male urban search and rescue personnel had physiological and perceptual responses compared during the initial 4 hour 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.

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