Weather, work and the person

The same thermometer reading can be safe for one person and dangerous for another. Heat strain is where the weather, the work and the person meet.

Effects depend on exposure, task and the person. That is why a single heat alert cannot protect everyone in the same way, and why plans can ask who is doing what, in what, and after what kind of night.

1. The weather. Air temperature is only the start. Humidity stops sweat from cooling the body, sun and hot surfaces add radiant heat, still air removes less of it, and a hot night leaves no time to recover. Conditions at a workplace or under a roof can be worse than the nearest weather station shows.

Evidence: Monitors at 24 indoor and outdoor workplaces in Singapore found workers could face more heat stress than nearby national weather stations reported.

2. The work. Heavy work makes heat inside the body. Protective clothing, gowns and masks hold it in. Long shifts, fixed hours and no shade or water break let it build. The same weather is a different risk for a desk worker, a builder and a nurse in protective gear.

Evidence: In a laboratory trial of 18 men doing treadmill work and virtual-reality welding and plank-walking at height, humid heat raised core temperature and unsteadied balance, though task speed and accuracy held up.

3. The person. Older bodies sweat less and feel thirst later. Heart, kidney and lung disease, diabetes and pregnancy add strain, and some medicines reduce the body’s ability to lose heat. A body that did not cool down overnight starts the next day already behind.

Evidence: Thinking held up at modest heat strain: 28 adults whose core temperature reached about 38.5 °C showed no loss of executive function or risk-taking. At 39.5 °C, in a separate study of 11 adults, executive function did fall.

Three groups heat plans often miss

People on long-term medicines. Some medicines for long-term conditions can reduce sweating or blood flow to the skin. Never stop or change a medicine because of the heat: ask a doctor, nurse or pharmacist, and plan water, shade and check-in calls.

Health workers in protective gear. Staff in gowns, gloves and masks carry heat they cannot shed. Plan cool rest rooms, water, shorter rotations in full gear, and cooling for the clinic itself.

Workers in hot factories and sheds. At three garment factories in Phnom Penh, workers reporting heat symptoms rose from 68% to 88% in the hot months, by their own reports. Measure heat where people work, cool roofs and walls, and add air flow, water and breaks.

Six questions for your heat action plan

Which groups work indoors in hot sheds, kitchens or factories, and does the plan measure heat where they work?
Who does heavy work, or works in sun or near hot surfaces, through the hottest hours?
Who wears protective clothing that holds heat in, including health workers?
Can people rest, drink and reach shade without losing pay?
Who is older, ill, pregnant or on long-term medicines, and who checks on them?
Do people get a cool night to recover, and does the warning count hot nights?

Sources

NUS Project HeatSafe, 2024. medicine.nus.edu.sg/wp-content/uploads/2024/03/PRESS-RELEASE_Project-HeatSafe-18MAR2024-FOR-IMMEDIATE-RELEASE.pdf
Tan et al., Medicine & Science in Sports & Exercise, 2025. heathealth.info/resources/physical-work-in-humid-heat-impairs-postural-balance-during-simulated-construction-tasks-at-height
Modest strain study of 28 adults, PubMed Central. pmc.ncbi.nlm.nih.gov/articles/PMC12804366
Tan et al., Journal of Sport and Health Science, 2024. doi.org/10.1016/j.jshs.2023.09.001
Wee and Lee, Pharmacological Reviews (summary by NUS Medicine, 2023). medicine.nus.edu.sg/news/medications-for-chronic-diseases-affect-the-bodys-ability-to-regulate-body-temperature-keep-cool
Yang et al., BMC Nursing, 2024. doi.org/10.1186/s12912-024-01770-x
Chea et al., BMC Public Health, 2025. bmcpublichealth.biomedcentral.com/articles/10.1186/s12889-025-22787-0