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Welcome to the 2nd 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, from the latest research to interesting media articles, all without taking ourselves too seriously. We strive to maximise the health, safety and performance of workers exposed to hot conditions, we trust this information assists you in that endeavour. 

Cooling Refuge

Cooling is an important part of heat stress mitigation, and can be achieved through a variety of means. We have assisted with the design and implementation of semi-permanent cooling refuges/stations on construction and mining sites, that are well suited to a large workforce at a fixed location. But what options exist for smaller, mobile work teams?

Logisticians from Australia's disaster and emergency medical response team, the National Critical Care and Trauma Response Centre, constructed a large medical facility (~28 tonnes of equipment) for verification by the World Health Organisation. Construction was undertaken over several days in oppressive conditions, with maximal temperatures higher than 36C and WBGT greater than 34C for most of the build. A key feature of the facility is a 5.7x5.7m (663m3) cooling refuge. The logisticians converted a standard shelter by the addition of insulation and 2 air conditioners run by a generator to maintain conditions at a dry 22C. Uses during deployment include night shift sleeping quarters during the heat of the day, or to intermittently cool day shift workers.

An example of the refuge's cooling power is presented by the graph below. The worker attained a core temperature of 39.1C prior to a 30 min rest break in the cooling refuge. Core temperature dropped by 0.6C, 1.3C and 1.6C following 10, 20 and 30 minutes of cooling, respectively, returning core temperature to near resting value. The alternative would have been resting in 36C shade, drastically limiting cooling and subsequent work potential. We will profile an alternative approach to delivering cooling in the field in Novembers e-Bulletin.

External View
Internal View

NFL Fans at Risk of Heat Stress 

Shortly after the initial e-Bulletin was distributed, the NFL season commenced. The heat stress risk to NFL players is widely acknowledged during their summer pre-season, especially during periods of two training sessions per day in full uniform. Early season games are also known for their warmer weather and potential for heat related harm. This is particularly relevant for hot and humid climates such as NE Florida, home to the Jacksonville Jaguars. During their opening round loss to Green Bay at home, on field temperatures were anecdotally reported to have reached 45C. Conditions within the crowd appear to have been very hot as will, with over 80% of the 123 emergency calls taken from fans at the game being heat related, causing 35 transportations to hospital. This is a timely reminder for those spectators that partake in the Australian summer of sport. Ensure you have access to cooling, shade, adequate fluids, appropriate clothing including a hat plus sunscreen. An esky containing ice for consumption of slushies and/or to dip towels in ice cold water are simple but effective means for fans for lower body temperature when exposed to hot weather in the stands.

Benefits of Worker Heat Acclimatisation 

During late September, one of the three papers we had accepted for publication described the physiological responses of heat and non-heat acclimatised disaster responders during a 24hr deployment to tropical conditions. The key finding of this research was that following similar physiological responses during the initial stages of shift, heat acclimatised (HA) workers sustained a higher core temperature during self paced work in hot and humid conditions (34C, 48% RH). This result seems to challenge laboratory based research identifying less physiological strain, including lower core temperatures once athletes become HA. The key difference between research settings is that workload was not fixed in our project, allowing workers to determine their own pace. It's likely that upon attaining a mean core temperature of ~38.1C, the NHA workers regulated their workload to limit further body heat storage. The comparable thermal sensation (hot) and thermal discomfort (uncomfortable) during shift supports this claim, being symbolic of both groups regulating their work output according to how hot they felt.

The similar perception of body temperature despite the HA groups higher core temperature may be explained by greater exposure to hot working conditions. The two-fold effect of such exposure would not only promote regular elevations of core temperature to develop and maintain heat acclimatisation status (physiological adaptation), but also provide opportunities to refine pacing strategies in the heat (behavioural adaptation). The research has implications for employers of workers with varying heat acclimatisation status, such as FIFO work sites. The take home message is that NHA workers commencing their panel in hot and humid conditions following an extended absence are likely to choose a lower workload until they adapt to the new environment. Employers need to factor this into their planning. Alternatively, a fixed workload setting such as working to a deadline would result in greater body heat storage and overall physiological strain of NHA workers, increasing their risk of heat related illness until adapted to conditions.

This research was a collaboration between the National Critical Care and Trauma Response Centre, NT Fire and Rescue Service, QLD Fire and Emergency Services, World Health Organisation, Menzies School of Health Research and Princess Alexandra Hospital.


Brearley M, Norton I, Rush D, Hutton M, Smith S, Ward L, Fuentes H. Influence of chronic heat acclimatisation on occupational thermal strain in tropical field conditions. Journal of Occupational and Environmental Medicine. In Press. 

Spiralling Climate

Dr Joe Costello of Portsmouth University recently shared an animated representation of global temperature from 1850-2016, termed a climate spiral. The spiral is an effective means of representing change of time, based upon the HadCRUT4 global temperature dataset courtesy of the University of East Anglia and UK Met Office. The spiral is constantly being updated, to see the latest version, click hereThe change in 50 year intervals is provided below.

Driving Under the Influence (of Dehydration)

As an invited speaker of the Science of Sport, Exercise and Physical Activity in the Tropics, Associate Professor Ian Stewart of Queensland University of Technology presented on the topic of 'Assessing hydration status in occupational athletes: challenges faced and lessons learnt'. One of the studies profiled by Ian examined the effect of fluid restriction on a 2 hour monotonous driving task (available here). The Loughborough University researchers found that a 1.1% body mass deficit resulted in approximately twice the number of driver errors. Interestingly, the decrease in driving performance with dehydration was similar to that reported for driving with a blood alcohol level of 0.08. To provide context, a 1.1% body mass deficit is ~880mls for an 80kg worker.

What is the mechanism of impairment? Could a small decrease in total body water produce a physiological impairment to account for the additional errors? We know that when drivers had restricted access to fluid, their perceived alertness and ability to concentrate were both negatively impacted. If a ~1% body mass deficit was sufficient to impact concentration in field settings, workers exposed to hot (and humid) conditions would routinely be at a greater risk of injury due to minor dehydration, without factoring in any heat related deficits. In fact, a 1% body mass deficit would be considered well within the limit value on many worksites exposed to heat. For now, this research highlights that small physiological changes may manifest in negative outcomes for workers. Clearly additional studies are required to determine the independent and combined effects of dehydration and heat exposure in work settings, and we look forward to contributing to this space in 2017.

Watson P, Whale A, Mears SA, Ratner LA, Maughan R. Mild hypohydration increases the frequency of driver errors during a prolonged, monotonous driving task. Physiology & Behavior 147:313–318, 2015

Upcoming Events

Dili Marathon, October 8-10, Dili, Timor Leste. AusMAT Team Leader and managing runner heat stress.

App Development/Stakeholder Meeting, October 18, Hobart.

Heat Stress Research Partnership Meetings, October 19-21, Darwin. Hosted by the Northern Institute, Charles Darwin University. Attendees include James Cook University, Menzies School of Health Research and RMIT.

Heads of Workplace Safety Authorities Annual Forum, October 25-26, Sydney. Invited speaker presenting Heat stress management: moving beyond minimum compliance to best practice.

Heat Stress Research Meeting, October 27, Canberra.

In between these engagements over the coming month, we are working with clients from mining, utilities, construction, transportation and environmental monitoring fields to mitigate heat stress. 


For more information on what we are up to, click here.

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