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Welcome to e-Bulletin #5

Welcome to the 5th 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. This late January edition will be followed by e-Bulletin #6 in mid February. We strive to maximise the health, safety and performance of workers exposed to hot conditions, and trust this information assists you in that endeavour.

Northern Australia Heat Stress Research

It is well known that Northern Australia experiences hot and seasonally humid conditions. The region is sometimes referred to as the 'Monsoonal North', owing to the monsoonal rains that tend to occur from January to March. In contrast, the limited rain and high temperatures during the 'build up' season (October-December) pose a thermoregulatory challenge to residents, particularly those routinely exposed to the elements such as workers. Yet, little is known of how these workers experience and manage heat stress during the build up. To address this gap, an electronic survey was launched last week for workers to document their subjective responses to working and managing heat stress during the 2016 build up.

The survey is part of Sarah Guajardo's CDU Honours research of which we are a collaborator. If you are interested in contributing to this research, please click the link below to request more information. Note that the survey closes February 17, and participation is limited to those that worked in the region depicted below for at least part of the October, November and December 2016, including FIFO workers. 

Request more information
Australia's Monsoonal North Region.
Source -

Solar Radiation and Heat Stress

A feature of the 2016/17 summer has been sustained heatwave periods for eastern Australia and periodic heatwaves elsewhere. Heatwaves are multifactorial but generally coincide with extended periods of sunlight (visible solar radiation), exposing workers to both heat and solar radiation. During these periods, statements and questions from workers related to heat stress and sun exposure are very common. So what are the thermoregulatory implications of working in direct sunlight?

A common response to working in the sun is the sensation of a hotter body temperature. Thermal sensation is the product of both internal and skin temperatures, so uniform body temperature changes are not required to alter thermal sensation. Higher skin temperatures result from sunlight exposure during exercise (Nielsen et al., 1988; Omani et al., 2016), and likely explain the perceived increase in body temperature, as less effect is observed for core temperature during short work periods. Cutaneous vasodilation of irradiated skin could lower central blood volume to result in a higher heart rate for a given workload (Nielsen et al., 1988), but this is not universally reported. The higher skin temperatures and resultant thermal sensation are likely to drive behaviour modifications, the most basic being to seek shade. In warm to hot conditions, resting in the shade during breaks is a common practice, resulting in a modest but more rapid core temperature decline than when exposed to sun (DeMartini et al., 2011).

In terms of performance, a constant moderate workload in 30C and 50%RH with 800W/m2 solar radiation results in volitiona
l fatigue occurring in approximately half the time compared to when no solar radiation is imposed. To provide context, Darwin, Northern Territory (latitude ~12.5 degrees S) experiences mean October early afternoon solar radiation of 829W/m2, that is considered oppressive.  








Mean (SD) time to exhaustion at 70% maximal aerobic power in 30C, 50% and varied solar radiation (Data reproduced from Otani et al., 2016). 


  • DeMartini JK, Ranalli GF, Casa DJ, Lopez RM, Ganio MS, Stearns RL, McDermott BP, Armstrong LE, Maresh CM. Comparison of body cooling methods on physiological and perceptual measures of mildly hyperthermic athletes. J Strength Cond Res. 2011;25(8): 2065-74. 
  • Nielsen B, Kassow K, Aschengreen FE. Heat balance during exercise in the sun. Eur J Appl Physiol Occup Physiol. 1988;58(1-2): 189-96.
  • Otani H, Kaya M, Tamaki A, Watson P, Maughan RJ. Effects of solar radiation on endurance exercise capacity in a hot environment. Eur J Appl Physiol. 2016 116(4): 769-79. 

Heat Stroke Fatality

The maximum temperature anomaly figure for the week ending January 17 (provided by BoM) demonstrates the heatwave conditions experienced by NSW and Southern QLD of late. With high day and night time temperatures impacting a large proportion of Australians, there has been a lot of media coverage devoted to heat stress. Amongst these reports was the tragic tale of a heat stroke fatality on the Sunshine Coast of SE QLD. While verified information is limited, media reports state that a 30 year old male was riding trails on a quad bike and separated from his friend to stop for a rest break. Upon his friend returning an unspecified time later, the rider was found in need of emergency medical care. Paramedics attended to the victim (reported core temperature of 42C), but he passed away at the scene.  

While less is known of quad bike riding, trail bike riding or motocross (MotoX) is a strenuous activity that can elicit extreme physiological responses. During a round of the Australian MotoX Championships contested in mild conditions (25C maximum temperature), one riders core temperature increased at a rate of ~0.1C/min across the 30 minute race. For the final 7 minutes of the race, the riders core temperature was greater than 40C, accompanied by a marked decrease in performance (3rd to 12th), and apparent health upon finishing the race. Immediate post race immersion in 22C water was applied to lower the riders core temperature, accompanied by rehydration and observation until normothermia was restored. While this case was from a professional setting, there are many anecdotal reports of recreational rides undertaken in hot weather resulting in heat stress. Given that the rides are undertaken remote from medical care, in warm to hot conditions we recommend vehicles located at a base/central point contain emergency cooling in the form of an esky with ice, fluids and towels or similar to provide rapid cooling should a heat related illness develop. Such equipment would permit rapid cooling while medical assistance is in transit to the scene. 

Lastly, it's great to see the financial support for the victims family provided by the community. As of time of writing, in excess of $100k has been raised via GoFundMe.  

Difference between maximum temperature of week ending 17 January 2017 and long term mean.
Source - Bureau of Meteorolgy
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