Quick Answer
The signs of heat exhaustion are heavy sweating, dizziness, headache, nausea, muscle cramps, weakness, unusual tiredness, confusion, irritability and poor concentration. In a workplace setting, any combination of these symptoms during hot conditions should stop the task, move the person to a cooler place, provide water and monitoring, and — if symptoms don't quickly improve or if confusion, loss of coordination or very hot skin appear — result in an immediate call to emergency services.
Why it matters
Heat exhaustion rarely announces itself. A supervisor who recognises the early signs — a normally sharp employee going quiet, a mistake that isn't like them, a slight unsteadiness on the stairs — is the single most important line of defence against a serious heat incident at work.
For a small business, the cost of missing those early signs is disproportionate. A single serious heat incident can mean an ambulance call, a temporary closure, an insurance claim, a regulator visit and lasting harm to a valued team member. The same investment — a few minutes of supervisor training and a written plan — prevents almost all of it.
Detailed guide
Understanding heat exhaustion
Heat exhaustion is a heat-related illness that occurs when the body loses too much water and salt through sweating and can no longer regulate its own core temperature effectively. It typically develops gradually — over minutes or hours — in workers exposed to hot or humid conditions, indoors or outdoors.
It is not the same as simply 'feeling hot'. Heat exhaustion is a physiological event: blood pressure drops, the heart works harder, judgement and coordination deteriorate, and the person becomes unable to work safely. Without action, it can progress to heat stroke — a life-threatening medical emergency.
Recognising heat exhaustion early is a supervisor skill, not a specialist skill. Any employer with heat-exposed workers — including indoor workers in kitchens, warehouses, laundries and delivery vans — should ensure every supervisor knows the warning signs and knows the first three actions to take.
Early warning signs
The following symptoms are the classic early signs of heat exhaustion at work. They rarely appear all at once — usually two or three at a time — and they are easy to miss if a supervisor isn't specifically looking for them. Any combination of these on a hot day should trigger a break and a check-in, not a 'push through'.
Heavy sweating that continues even during rest. Dizziness or feeling faint when standing up or moving. Headache that starts or worsens during the shift. Nausea, sometimes with vomiting. Muscle cramps, especially in the legs and abdomen. General weakness or a sudden drop in stamina. Unusual tiredness, disproportionate to the workload. Confusion, difficulty following instructions or answering simple questions. Irritability that isn't typical of the person. Poor concentration and small, uncharacteristic mistakes.
Every one of these becomes more dangerous inside a workplace than at home. A slightly disoriented person on a ladder, on a hot roof, on a warehouse forklift or near a hot fryer is not a mild concern — it is the moment to stop the task.
Heat exhaustion vs heat stroke
Heat exhaustion and heat stroke are different points on the same scale, and knowing which one you're looking at determines what you do next. The single most important distinction: heat exhaustion is a serious warning sign that requires immediate rest and cooling; heat stroke is a life-threatening medical emergency that requires an immediate call to emergency services.
Heat exhaustion
Heavy sweating. Skin cool, pale or clammy. Fast, weak pulse. Nausea or vomiting. Muscle cramps. Tiredness and weakness. Headache. Dizziness. The person is usually still able to think clearly and answer questions.
Heat stroke — call emergency services immediately
Very high body temperature (typically above 40°C / 104°F). Hot, red skin, which may be dry or damp. Rapid, strong pulse. Throbbing headache. Confusion, altered mental state, slurred speech, seizures, or loss of consciousness. Nausea and vomiting.
The rule of thumb: if the person is confused, unable to answer simple questions, unsteady, has very hot skin or has lost consciousness — treat it as heat stroke, call emergency services immediately, and begin aggressive cooling while you wait.
What to do immediately
When you see warning signs, the response is simple, structured and — critically — the same every time. This is why it needs to be written down and known by every supervisor before the first hot day of the year.
Stop the task and move the employee into shade, air-conditioning or the coolest available space. Remove excess clothing, PPE and anything that traps heat. Give small sips of cool drinking water if the person is fully alert and not nauseous. Cool the skin with wet towels, a fan, or cold water on wrists, neck and forearms. Stay with the employee and continue to monitor them — do not send them to rest alone. Reassess every few minutes. If confusion, loss of coordination, very hot skin, chest pain, seizures or loss of consciousness appear at any point, call emergency services immediately.
Who is most at risk
Heat illness risk is not evenly distributed. Certain workplaces, roles and personal factors carry substantially higher risk, and a supervisor who understands them can plan the day accordingly.
Workplaces that consistently exceed the thresholds where heat exhaustion becomes likely: warehouses and distribution centres, manufacturing floors, commercial kitchens, laundries, construction sites, agriculture and landscaping, roofing and outdoor trades, delivery drivers in cabs without effective air-conditioning.
People at elevated personal risk on any hot day: new hires in their first two weeks (unacclimatised), employees returning from a week or more away, temporary workers, older workers, pregnant workers, employees with cardiovascular or metabolic conditions, employees on medications that affect hydration, and anyone required to wear PPE that traps heat.
Common employer mistakes
Most workplace heat incidents follow the same handful of avoidable assumptions. Naming them is the first step to removing them from your workplace culture.
"They'll be fine." Heat exhaustion is a physiological event, not a matter of willpower. A worker who is showing warning signs is not fine — and asking them to prove it usually ends badly.
"They just need more water." Water helps, but the body also needs to stop working, cool down and rest. Handing someone a bottle and asking them to carry on is not a response plan.
"They've worked here for years." Long-tenured workers still lose acclimatisation after a week off, still get older, and still have days where they aren't at 100%. Experience is not immunity.
"They'll cool down later." Heat illness gets worse without intervention, not better. A worker who is unwell at 2pm will almost certainly be worse by 5pm if nothing changes.
"We've never had this happen." Every workplace that eventually experiences a serious heat incident could truthfully say this the day before. First incidents are, by definition, first incidents.
Preventing heat exhaustion
Prevention is the boring, cheap, effective part of heat safety. The interventions below are well established, low cost and quick to put in place — and together they eliminate the majority of workplace heat incidents.
Water: cool drinking water within easy reach of every work area, and a rule that people drink before they feel thirsty. Rest: scheduled paid breaks in a genuinely cooler space, escalating with heat index. Shade: not just 'somewhere out of the sun', but somewhere the body can actually recover. Airflow: fans, ventilation and cross-drafts, especially in indoor heat-source areas. Acclimatisation: a written schedule for new hires and returning workers over their first 1–2 weeks. Heat monitoring: check the actual heat index at the work area, not the office thermostat. Supervisor awareness: brief supervisors specifically on early warning signs at the start of every hot stretch. Shift planning: schedule heavier and hotter tasks earlier in the day and rotate through cooler tasks where possible.
The first hour after a heat incident
Even a mild heat exhaustion incident is a leading indicator that the day's plan is not working. The first hour after an incident is when a diligent employer prevents a second one on the same shift.
Ensure the affected employee is stable, comfortable and being monitored — do not send them home alone. Document what happened: time, temperature and heat index, task being performed, symptoms observed, actions taken and outcomes. Notify management and, where applicable, the safety representative. Review conditions on the shift: is the heat index worse than expected, is the water station still stocked, are supervisors circulating? Adjust the rest of the day's plan: shorten cycles, add breaks, move tasks indoors, send non-essential workers home early. Communicate the change to the whole team so they know why and what is expected. Review the underlying plan the following day — an incident, even a mild one, is a signal that some part of the plan needs to change.
Workplace heat exhaustion response checklist
Actionable steps employers can implement immediately.
- Stop the task and move the affected employee into shade or air-conditioning.
- Remove excess clothing and any PPE that traps heat.
- Give small sips of cool drinking water if the person is fully alert.
- Cool the skin with wet towels, a fan or cool water on wrists, neck and forearms.
- Stay with the employee and monitor breathing, alertness and skin temperature.
- If confusion, loss of coordination, very hot skin, chest pain or unconsciousness appear, call emergency services immediately.
- Document the incident: time, symptoms, environment, actions taken and outcome.
- Adjust the remainder of the shift: shorter cycles, additional breaks, workload changes.
- Notify management and the safety representative before end of shift.
- Review the plan the following day and update supervisor training if needed.
Common mistakes
Assuming heat exhaustion only happens outdoors
Kitchens, warehouses, laundries and delivery vans regularly reach conditions where heat exhaustion is a real risk — often without the visual cues that prompt action outdoors.
Leaving the response to individual judgement
A written response plan that every supervisor knows removes the decision-making burden at exactly the moment when decision-making is hardest.
Treating warning signs as personal weakness
Heat exhaustion is a physiological event. Comments about 'toughening up' delay the response that protects both the worker and the business.
Sending an affected worker home unsupervised
A person with heat exhaustion should not drive themselves home. They should be supervised until fully recovered or handed over to a family member or medical professional.
Skipping documentation because 'they're okay now'
Every incident is a data point. Without documentation, patterns and near-misses cannot be spotted before they become serious.
Frequently asked questions
- What is the first sign of heat exhaustion?
- Heavy sweating combined with tiredness, headache, dizziness or nausea is usually the first sign. A previously energetic employee going quiet, or making small uncharacteristic mistakes, is often the earliest supervisor-visible signal.
- Can someone recover quickly from heat exhaustion?
- Yes — with immediate rest, cooling and hydration, mild heat exhaustion often resolves within 30 to 60 minutes. However, the person should not return to hot work on the same shift, and their workload should be lighter the following day.
- How is heat exhaustion different from heat stroke?
- Heat exhaustion involves heavy sweating, tiredness, dizziness and clear thinking. Heat stroke involves confusion, loss of coordination, very hot skin (sometimes with no sweating) and can involve loss of consciousness. Heat stroke is a medical emergency — call emergency services immediately.
- Can indoor workers suffer heat exhaustion?
- Yes. Commercial kitchens, laundries, warehouses, manufacturing floors and delivery vans routinely reach conditions where heat exhaustion is a real risk — often without the visual cues that prompt action outdoors.
- Should employees continue working after heat exhaustion?
- Not the same day. The safe default is rest, hydration and monitoring for the remainder of the shift, and a lighter workload the following day. If any symptoms persisted or the person felt confused at any point, they should be assessed by a medical professional before returning to hot work.
Author
WorkplaceReady Editorial Team
WorkplaceReady publishes practical, OSHA-aligned guidance on workplace heat safety, risk assessment, and emergency response — written for the people responsible for keeping workers safe.