Google ‘heat-related illness’ and you’re likely to see an identical spectrum of illness cited on each website: heat stroke, heat exhaustion, heat syncope, heat cramp and heat rash (listed in order of seriousness). Interactions with heat-exposed workers over the past 10 years have identified a disconnect between this spectrum and the self-reported symptoms as a result of prolonged occupational heat exposure, a view supported by heat stress survey data. For example, from a broad range of outdoor workers based in Northern Australia, fatigue, headache and irritability were frequently reported on a daily or weekly basis during the October to December (harshest three months for thermoregulation) (Carter et al., 2020).
We define a heat hangover as the moderate negative physiological and perceptual side effects of excess heat exposure (Brearley, 2016), mimicking alcoholic hangover symptoms and onset. While fatigue, headache and nausea are shared symptoms of a heat hangover and heat exhaustion (Howe and Boden, 2007), additional symptoms of dizziness (Glazer, 2005), profuse sweating (Howe and Bowden, 2007) and hyperventilation (Carter et al., 2005) differentiate heat exhaustion.
The workplace consequences of heat hangovers are yet to be fully understood, with the impact of heat-related symptoms on vigilance, concentration, decision making and execution of physical skills are areas of interest. Negative impact on these factors may explain the prevalence of workplace accidents in the hottest months of the year (Xiang et al., 2015).
We are working on identifying the contributing factors. At this stage, it appears that heat hangovers develop due to a worker exceeding their individual heat exposure threshold. We quantify heat exposure as the area under a worker’s core temperature curve, with the blue and green curves of the figure below depicting two workers across a 12-hour shift. Note that the curve of Worker B (Blue) reaching 39.1ºC at ~300 minutes resulting in his immediate cooling and redeployment to a less heat exposed role for the remainder of the shift. This strategy assisted in keeping his core temperature relatively low for the second half of shift whereas the core temperature of Worker A (Green) remained elevated during this period. Overall, heat exposure based upon the core temperature curve was ~37% higher for Worker A, likely contributing to his heat hangover symptoms at the conclusion of the shift.
Brearley M (2016). Preliminary evidence of a heat hangover, a new heat illness classification for occupational settings? Proceedings of Science of Sport, Exercise and Physical Activity in the Tropics, Townsville.
Brearley M, Harrington P, Field E, Oppermann E, Lee D (submitted). Impact of hot and humid work conditions on perceived heat stress symptoms and management strategies.
Carter S, Field E, Oppermann E, Brearley M (2020). The impact of perceived heat stress symptoms on work-related tasks and social factors: A Cross-Sectional Survey of Australia’s Monsoonal North. Applied Ergonomics. 82:102918 Carter R 3rd, Cheuvront SN, Williams JO, Kolka MA, Stephenson LA, Sawka MN, Amoroso PJ. (2005) Epidemiology of hospitalizations and deaths from heat illness in soldiers. Medicine and Science in Sports and Exercise. 37(8): 1338-44
Glazer JL (2005). Management of heatstroke and heat exhaustion. American Family Physician. 71(11): 2133-40 Howe AS, Boden BP (2007). Heat-related illness in athletes. American Journal of Sports Medicine 35(8): 1384-95 Xiang J, Hansen A, Pisaniello D, Bi P (2015). Extreme heat and occupational heat illnesses in South Australia, 2001-2010. Occupational and Environmental Medicine 72(8): 580-86