Firefighters undergo high level of heat stress during training and operation (Photo credit: Singapore Civil Defence Force).


by Department of Physiology

As the world begins to grapple with the uncomfortable reality of climate change, some of us find solace in the belief that its effects are confined to the polar regions of the globe. Its relevance has never appealed to an urban and tropical population that has either been conditioned to 35 degree Celsius (°C) or fortified within a false reality of an air-conditioned world. Until now.

In January this year, Channel News Asia televised an episode as part of its “Why It Matters” programme, explaining why Singapore is heating up twice as fast as the rest of the world.1 It turns out that the effect of global warming is amplified in urban environments, where heat-absorbing materials such as concrete roads have paved over the naturally dense, heat-regulating tropical landscape. This is also known as the Urban Heat Island effect, and by 2100, Singapore’s ambient temperature is projected to reach a maximum of 35 to 37°C. While a mere 0.25 degree increase per decade hardly triggers an alarm, Associate Professor Jason Lee with the Department of Physiology at the NUS Yong Loo Lin School of Medicine explained that with our island’s high humidity that limits our body’s ability to dissipate heat, Singaporeans should be concerned. As efficient as the human body is at dissipating heat, or thermoregulation, the margin for error is very thin, and can be lethal. 


Assoc. Prof. Lee is a subject matter expert in thermal physiology, having spent 12 years at the DSO National Laboratories as the Lead Physiologist and directed the Human Performance Programme. A key outcome of his research was the formulation of a holistic heat management system. This is achieved through profiling the associated heat strain in humans under various settings, formulating and evaluating heat mitigation strategies (physical conditioning regimes, heat acclimatisation, pre-activity cooling, work-rest cycles and hydration) and finally transiting them into policies such as training directives, training safety regulations and lesson plans. 


In the light of recent heat-related injuries, the Ministry of Defence (MINDEF) established an external Review Panel on Heat Injury Management in 2018, of which Assoc. Prof. Lee is one of the panellists, to strengthen their approach to safeguard soldiers’ safety. In particular, best international practices were reviewed and incorporated into our training system. “Fluid intake, long assumed as the single most important mitigation strategy to cope with heat, has minimal impact on attenuating heat strain during exercise. Instead, more emphasis should be placed on increasing one’s capacity to regulate heat. This can be achieved through better aerobic fitness, as well as progressive heat acclimatisation,” Assoc. Prof. Lee noted, as supported by his review meta-analysis. 2-3 


Assoc Prof Jason Lee (third from right) and members of the WSHC Heat Stress Guideline Workgroup (Photo credit: Work Safety and Health Council).


The debilitating effects of heat stress extend beyond the military. Assoc. Prof. Lee has been working with the Ministry of Home Affairs (MHA) to improve the performance and safety of our frontline officers. Specifically with the Singapore Civil Defence Force (SCDF), Assoc. Prof. Lee will co-organise the inaugural First Responders Safety and Performance Symposium in November 2019 in hope to gain insights on how to innovate their training, personal protective equipment as well as protecting the long-term occupational health of their emergency responders. 4 


Even if it does not mean death for most people, health and work productivity will likely be compromised. Almost 300,000 workers, or 13.6 per cent of our labour force is employed in the construction and logistics industries, where workers are exposed to the heat.5 The Workplace Health and Safety (WSH) Council, recognising the vast implications of poor heat stress management, has recently established a Review of Heat Stress Guideline Workgroup, chaired by Assoc. Prof. Lee, to revise the guidelines on managing heat stress in the workplace. An increase in ambient temperature will inevitably result in productivity losses in these sectors of the economy and potentially increases health risk, including heat induced accidents.


Working with a grant from the Global Asia Institute’s NUS Initiative to Improve Health in Asia, Assoc. Prof. Lee leads studies on the effects of environmental heat in Singapore and the region. The research, in a nutshell, aims to identify and quantify impacts of heat on health and work productivity due to climate change and to evaluate the impact of thermal stress on human cognitive performance. There is hope that the results will justify and incentivise the use of better heat management strategies.


Internationally, Assoc. Prof. Lee chairs the Scientific Committee on Thermal Factors at the International Commission on Occupational Health.6 The committee lends their expertise to wider organisations such as the World Meteorological Organisation (WMO) and World Health Organisation (WHO) in co-authoring a report that is due in 2020 on providing evidencedbased recommendations to occupational and health professionals responsible for workers operating in the heat (indoor and outdoor). The goal is to encourage more scientists and practitioners to participate in this area of research so that the world will be better equipped to cope with a warmer climate.7 Together with researchers at the N.1 Institute for Health at NUS, Assoc. Prof. Lee seeks to uncover individuals’ tolerance to heat stress. While personalising heat management for every individual may not be feasible in every context, understanding individuals’ responses to an absolute heat stress can allow stratification and therefore optimisation of work productivity and health.



1. Why It Matters: Killer Heat, Channel NewsAsia. January 2019. 


2. Alhadad, S.B., Tan, P.M.S., Lee, J.K.W. (2019). Efficacy of heat mitigation strategies on core temperature and endurance exercise: a meta-analysis. Frontiers in Physiology, 10 (71): 1-27. 


3. Drinking water not the best way to cool body, study finds. The Straits Times. 19 March 2019..


4. First Responders Safety and Performance Symposium. first-responders-safety-andperformance- symposium-2019


5. Singapore in Figures 2018, Department of Statistics Singapore. files/publications/reference/sif2018. pdf


6. International Commission on Occupational Health Scientific Committee on Thermal Factors


7. Kjellstrom, T., Lemke, B., Lee, J.K.W. (2019). WORKPLACE HEAT: an increasing threat to occupational health and productivity. American Journal of Industrial Medicine (In Press).