HEALTH AT WORK

Workplace Safety

Heat Illness at Work: How to Spot It Before It Becomes an Emergency

20 October 2026 · Health at Work · AI-assisted draft

Photo: Yaroslav Shuraev / Pexels

Every year, workers collapse on construction sites, in commercial laundries, on farm fields and inside bakeries. The cause is not always obvious in the moment - a worker who seemed fine an hour ago is now confused, barely standing, with skin that feels dangerously dry and hot. Heat illness moves fast, and the window between early warning signs and a life-threatening emergency can be as short as twenty minutes. Yet in most workplaces, the response plan amounts to 'offer water and a break' - a strategy that fails precisely when conditions are severe enough to matter.

This article explains what heat illness actually does to the body, which workers and tasks carry the highest risk, how to recognise the progression from mild heat stress to heatstroke before it becomes irreversible, and what employers must put in place to prevent it. The controls exist. The barrier is almost always the assumption that heat is an inconvenience rather than a hazard.

What Heat Does to the Body: The Physiology Behind the Emergency

The human body maintains a core temperature of around 37 degrees Celsius through a continuous process of heat dissipation - primarily sweating and the dilation of blood vessels near the skin surface. When the environment is hot, humid, or both, these mechanisms come under pressure. Sweating becomes less effective when air humidity is high, because sweat cannot evaporate efficiently. Radiant heat from furnaces, ovens, foundry equipment or direct sunlight adds a load the body did not evolve to shed quickly.

As core temperature rises, the body diverts blood from internal organs toward the skin in an attempt to cool down. Heart rate increases. If fluid losses from sweating are not replaced, blood volume falls. At around 38 to 39 degrees Celsius, a worker begins to experience heat exhaustion: heavy sweating, weakness, pale or clammy skin, nausea, headache, muscle cramps and a feeling of faintness. This is the stage at which most workers should stop and recover - and where most employers either miss the signals or dismiss them.

If work continues past this point, core temperature can climb above 40 degrees Celsius. At this threshold the body's thermoregulatory system begins to fail. Heatstroke is characterised by hot, dry or minimally sweating skin, rapid and strong pulse, confusion, slurred speech, loss of coordination and, in severe cases, loss of consciousness and seizure. Heatstroke is a medical emergency. Without immediate cooling and hospital treatment, it can cause permanent organ damage or death. The critical distinction for any supervisor or co-worker to understand is this: a confused worker in a hot environment is not 'just tired' - they need emergency intervention now.

Who Is Most at Risk: Jobs, Tasks and Individual Factors

Outdoor workers under direct sun carry high risk, but heat illness is equally common indoors where ventilation is poor and process heat is high. The workplaces that generate the most cases include commercial kitchens and bakeries, laundries and dry-cleaning premises, foundries and metal casting facilities, glass manufacturing, construction sites during warm seasons, agricultural work including harvesting and irrigation, warehouses and distribution centres without air handling, and boiler rooms and utilities maintenance.

Tasks that combine physical exertion with heat exposure are the most dangerous. A worker lifting and stacking in a warm warehouse generates internal metabolic heat on top of the ambient load. A road worker laying tarmac on a sunny day faces radiant heat from both above and below. The combination of high air temperature, high humidity, radiant heat, physical work rate and heavy or impermeable protective clothing is additive - each factor makes the others worse.

Certain individual characteristics increase vulnerability significantly. Workers who are new to the job and have not yet acclimatised are at substantially higher risk during their first week or two of hot work than experienced colleagues doing the same task. Older workers, those with cardiovascular conditions, diabetes or kidney disease, workers who are overweight, and those taking certain medications - including diuretics, antihistamines and some blood pressure medicines - lose heat less efficiently. Workers who have experienced heatstroke previously are also at elevated risk of recurrence. These factors do not mean a worker cannot do the job; they mean the job must be managed more carefully for them.

Early Warning Signs Supervisors and Co-Workers Must Recognise

The earliest signs of heat stress are easy to miss or to attribute to something else. Watch for a worker who becomes quieter than usual, who stops interacting normally, who begins making small errors on tasks they normally perform without thought. Physical signs at this stage include heavy sweating, flushed face, complaints of headache or feeling sick, and muscle cramps - especially in the legs and abdomen. Thirst is a lagging indicator: a worker who reports feeling thirsty is already measurably dehydrated.

As heat exhaustion develops, the worker may appear pale rather than flushed as blood pressure drops. They may feel faint when standing, and their skin may feel cool and clammy despite the ambient heat. At this stage the correct response is to move the worker to a cool place, encourage slow sipping of cool water or an electrolyte drink, remove excess clothing and apply cool wet cloths to the neck, armpits and groin. Most workers recover fully within thirty minutes with this treatment, but anyone who does not improve - or who deteriorates - needs emergency medical care.

The shift to heatstroke is indicated by confusion, agitation or unusual behaviour, a change in the level of consciousness, skin that is very hot and dry, and a rapid pulse. A worker showing these signs must not be left alone. Call for emergency help immediately while beginning active cooling - immersion in cool water if possible, or covering with ice packs to the neck, armpits and groin while awaiting the emergency services. Do not give fluids by mouth to a person who is confused or unconscious.

Employer Duties: What Occupational Health Regulations Require

Under typical occupational health regulations in most jurisdictions, employers have a duty to assess the risks posed by thermal environments and to implement controls proportionate to those risks. This duty does not wait for a heatwave. It applies wherever process heat, physical work rate, protective clothing or seasonal conditions create a foreseeable risk of heat illness.

A suitable risk assessment for heat must identify which tasks and locations generate the highest heat burden, consider individual vulnerability factors among the workforce, specify the controls to be applied and the thresholds that trigger additional action, and define an emergency response procedure. The assessment should be reviewed whenever working conditions change - a new production process, a different shift pattern, a stretch of unusually hot weather - not only at the start of each year.

Employers must also ensure that workers are acclimatised before being exposed to full heat loads. New starters and workers returning after a break of more than a week should be introduced to hot work gradually over a period of seven to fourteen days, starting at around fifty percent of the normal heat exposure and increasing incrementally. This single measure reduces heat illness rates among new workers substantially, yet it is frequently overlooked because it requires planning workloads in advance.

Practical Controls: What Works and What Does Not

The hierarchy of controls applies to heat as it does to any other hazard. Engineering controls come first and are the most reliable. These include mechanical ventilation and air cooling in enclosed workspaces, local exhaust ventilation to capture process heat at source rather than letting it mix into the general atmosphere, insulating hot surfaces and pipes, and scheduling hot process work for cooler parts of the day or night shift where operationally possible.

Work-rest schedules are the most practical administrative control for outdoor and process environments where engineering solutions have limits. The principle is straightforward: as the heat index rises, the proportion of time a worker spends actively working in the heat should fall, and the proportion of time resting in a cool location should increase. The rest location must actually be cooler - a shaded area in direct sun is better than nothing but is not the same as a mechanically cooled rest room.

Fluid replacement deserves more precise guidance than 'drink plenty of water'. Workers doing heavy physical work in heat can lose one to two litres of sweat per hour. They should be drinking approximately 250 millilitres of cool water every fifteen to twenty minutes throughout the shift, not waiting until they feel thirsty. Drinks containing electrolytes are preferable for workers on shifts longer than two hours, as plain water alone does not replace the sodium and potassium lost in sweat, and over-consumption of plain water in these conditions carries its own risks.

Clothing and PPE deserve honest assessment. Impermeable chemical protective suits can raise the effective heat burden dramatically, even in moderate ambient temperatures. Where the hazard allows it, breathable alternatives should be chosen. Cooling vests containing phase-change material or ice pockets provide meaningful benefit for workers who must wear heavy protective clothing and have access to a rest area where vests can be re-cooled.

The weakest controls are awareness posters and voluntary self-reporting. Workers under heat stress often lack the cognitive clarity to recognise their own condition. Buddy systems - where co-workers are explicitly assigned to observe each other for signs of heat illness - are more reliable than self-assessment in hot environments.

What a Worker Should Do If They Are Already Affected

A worker who experiences headache, nausea, muscle cramps or feeling faint during hot work should stop immediately, tell a supervisor or colleague, move to a cooler place and begin drinking cool water slowly. They should not attempt to push through the symptoms. Doing so increases both the severity of the episode and the risk that a manageable case of heat exhaustion progresses to a potentially fatal heatstroke.

Workers who have experienced a significant heat illness episode - particularly heatstroke - should be assessed by an occupational health professional before returning to hot work. Heatstroke can impair the body's ability to regulate temperature for weeks or months afterward, meaning the same exposure that a colleague tolerates safely may cause rapid relapse. An occupational health assessment can establish a graduated return-to-work plan and identify any underlying health factors that need to be addressed.

What Employers and Workers Commonly Get Wrong

The most widespread misconception is that heat illness is only a risk during exceptional weather events. In reality, workers in commercial kitchens, foundries and laundries face heat loads that would constitute a heatwave outdoors - every single shift, year-round. Process industries must manage heat as a permanent feature of the working environment, not a seasonal concern.

A second common error is equating 'providing water' with 'managing heat risk'. Access to water is necessary but not sufficient. It does not address work rate, ventilation, acclimatisation or the individual health factors that make certain workers more vulnerable. A full risk assessment and a set of proportionate controls are required.

Third, supervisors often lack the confidence to remove a worker from a hot environment over the worker's own objection. A worker who insists they are fine but shows signs of confusion, poor coordination or uncharacteristic behaviour in a hot environment should be treated as someone whose judgement is already impaired by heat. Supervisors must be empowered - and trained - to act on observable signs rather than self-reported wellness.

Health at Work supports employers in assessing thermal risk, designing acclimatisation programmes, training supervisors to recognise and respond to heat illness, and developing emergency heat response protocols. Heat is a hazard that announces itself plainly in the environment. The employers and workers who treat it seriously prevent emergencies that are entirely predictable and entirely preventable.