Heat Stress
Quick answer
Heat stress is the strain placed on the body when it cannot cool itself effectively in hot conditions. It is the underlying condition that, if unmanaged, leads to heat exhaustion or heat stroke. Managing heat stress is a matter of controlling the four levers every employer has: water, rest, shade and workload.
What heat stress is
Heat stress is the physiological load on a worker's body from a combination of environmental heat, physical exertion, humidity, sun exposure and clothing or PPE that traps heat. It is not a single symptom — it is a state.
Managed well, heat stress produces nothing more than discomfort. Managed poorly, it produces heat cramps, heat exhaustion and heat stroke, along with the near-invisible costs: slower work, more mistakes, more accidents, more sick days.
Why it matters for productivity as well as safety
Heat stress reduces cognitive performance and reaction time long before it produces obvious illness. Studies consistently show that productivity drops sharply above 27–30°C, and error rates on manual and cognitive tasks climb with them.
For an employer, this means heat stress is not only a safety issue — it is an operational one. The same interventions that prevent heat illness also protect output, quality and customer service on hot days.
The four levers you actually control
Water: cool drinking water within easy reach, plus a rule that people drink before they feel thirsty. Rest: scheduled paid breaks in a genuinely cooler location as heat index rises. Shade or cool space: not just 'somewhere out of the sun', but somewhere the body can actually recover. Workload: heavier tasks scheduled earlier, lighter or indoor tasks reserved for peak heat.
Common mistakes
Assuming indoor workers are safe
Kitchens, warehouses and delivery vans routinely exceed the thresholds where heat stress becomes dangerous.
Leaving breaks to personal discretion
'Take a break if you need one' is not a plan. Scheduled paid breaks at defined heat-index triggers are.
Frequently asked questions
- Is heat stress the same as heat exhaustion?
- No. Heat stress is the underlying strain on the body. Heat exhaustion is one of the illnesses that heat stress can produce if it isn't managed.