Best practices
Heat stress at work: prevention under OSHA’s 2026 heat emphasis programme
Why heat illness is preventable yet still fatal, what OSHA’s April 2026 directive signals, and the controls that protect indoor and outdoor workers.
General information only, not medical or legal advice.
Heat is one of the oldest occupational hazards and one of the most preventable. OSHA notes that Although illness from exposure to heat is preventable, every year, thousands become sick from occupational heat exposure, and some cases are fatal.1 With hotter seasons and more indoor processes running at high temperatures, heat has moved from a summer reminder to a year-round programme element.
The 2026 regulatory signal
OSHA’s heat page highlights its enforcement focus: the National Emphasis Program – Outdoor and Indoor Heat-Related Hazards.1 under OSHA Directive CPL 03-00-024, (April 10, 2026).1 National emphasis programmes direct inspection resources to specific hazards; for employers, the practical message is that inspectors will ask to see a heat plan, evidence of acclimatisation and access to water, rest and shade.
Who is at risk
OSHA lists the occupational risk factors as heavy physical activity, warm or hot environmental conditions, lack of acclimatization, and wearing clothing that holds in body heat.1 Importantly, Hazardous heat exposure can occur indoors or outdoors, and can occur during any season if the conditions are right, not only during heat waves.1
The industries where workers have suffered heat illness include outdoor sectors such as agriculture, roofing and package delivery, and indoor sectors such as bakeries, laundries, foundries, warehousing and Manufacturing with hot local heat sources, like furnaces (e.g., paper products or concrete)1.
How heat harms the body
The body needs to get rid of its extra heat (a process called heat dissipation) to stay at a healthy temperature, particularly during physical activity.1 Heat dissipation happens naturally through sweating and increased blood flow to the skin.1 When it fails, the internal body temperature keeps rising and the worker may experience symptoms that include thirst, irritability, a rash, cramping, heat exhaustion, or heat stroke.1
Heat illness is a spectrum of disorders due to increased body temperature.2 At the severe end, Heat stroke is the most severe heat-related illness and requires immediate medical attention.1 OSHA describes its warning signs as mental dysfunction such as unconsciousness, confusion, disorientation, or slurred speech.1 Heat exhaustion Can be a precursor of heatstroke; the symptoms include heavy sweating, rapid breathing and a fast, weak pulse.2
A prevention programme that works
Acclimatisation
Lack of acclimatisation is a named risk factor, and clinical sources list gradual adjustment to heat, and sufficient fluids and electrolytes2 among preventive measures. Build a written schedule that increases exposure gradually for new starters and for workers returning from leave.
Reduce the heat load
Workers cool down more rapidly if the external (environmental) heat and physical activity (metabolic heat) are reduced.1 That points to controls at both ends: shade, ventilation, spot cooling, reflective shielding and insulation of hot surfaces on the environmental side; mechanical aids, scheduling heavy tasks for cooler hours and job rotation on the metabolic side.
Water, rest, shade
Make cool drinking water easy to reach, schedule rest breaks that increase with the heat index, and provide shaded or cooled rest areas. Supervisors should have authority to pause work.
Clothing and PPE
Because clothing that holds in body heat is a risk factor, review PPE choices for heat burden. General advice is to wear loose-fitting clothing in the heat.2 Where impermeable protective clothing is required, use cooling vests and shorter work-rest cycles.
Training and buddy systems
Workers and supervisors should recognise early symptoms and know they are allowed to stop. A buddy system helps because confusion is a symptom of heat stroke, so the affected worker may not self-report.
Emergency response
Heat stroke requires immediate medical attention. Every site should have a plan for rapid cooling, a way to call emergency services with an accurate location, and drills.
Watch: preventing heat illness
Technology in heat programmes
Several tools are now common: weather and heat-index apps that trigger work-rest schedules, wearable sensors that estimate physiological strain, and digital checklists that record water, rest and shade provision. These support — but do not replace — supervision and an organisational culture where stopping work is acceptable.
Indoor heat: the overlooked half
Indoor heat often lacks the visible cues of a heat wave. Foundries, kitchens, boiler rooms and warehouses can exceed safe conditions year-round. Engineering controls — ventilation, insulation, shielding and air-conditioned rest areas — are the most reliable controls in these settings because the heat source is constant.
Writing your heat plan
A written plan makes responsibilities clear and gives inspectors evidence. It should name who monitors conditions and how often; the triggers that change work-rest schedules; the acclimatisation schedule; where water, shade and cooled rest areas are; what training workers and supervisors receive; and the emergency response for suspected heat stroke, including cooling methods and how to direct emergency services to the location.
Review the plan before each warm season and after any heat-related incident or near miss. Include indoor areas in the review, because their heat sources do not follow the weather forecast. Consult workers on practical issues such as the distance to water and whether rest areas are actually cool enough to be used.
Supervisors make the difference
Heat illness can progress quickly, and the person affected may be the last to notice because confusion is itself a symptom. That is why supervisors and co-workers are central to any plan. Train them to recognise early signs such as heavy sweating, cramps, dizziness or unusual behaviour, to move the person to a cooler area, and to call for medical help when signs of heat stroke appear. A buddy system, where workers check on each other at set intervals, is a simple administrative control that works on large and small sites alike.
Supervisors also control the work pace. Allowing extra breaks, rescheduling heavy tasks to cooler hours and rotating crews are decisions that need authority on the day, not only a policy on paper.
Hazardous heat exposure can occur indoors or outdoors, and can occur during any season if the conditions are right, not only during heat waves.1
Key takeaways
- OSHA’s heat National Emphasis Program directive is dated April 10, 2026; expect heat plans to be examined.
- Risk factors are heavy activity, hot conditions, lack of acclimatisation and heat-retaining clothing.
- Heat stroke is a medical emergency signalled by confusion or slurred speech.
- Acclimatisation, water-rest-shade, engineering controls and trained supervisors form the core programme.
Frequently asked questions
What are the main risk factors for occupational heat illness?
OSHA lists heavy physical activity, warm or hot environmental conditions, lack of acclimatization, and clothing that holds in body heat. Personal risk factors also play a role.
Can heat illness happen indoors?
Yes. OSHA notes hazardous heat can occur indoors or outdoors and in any season. Bakeries, laundries, foundries, boiler rooms, warehouses and manufacturing with furnaces are examples.
What are the warning signs of heat stroke?
Mental dysfunction such as unconsciousness, confusion, disorientation or slurred speech. Heat stroke is a medical emergency requiring immediate attention.
What is acclimatisation?
Gradual adjustment to working in heat over several days, which allows the body to cope better. New and returning workers are most at risk without it.
What is the 2026 OSHA heat directive?
OSHA Directive CPL 03-00-024, dated April 10, 2026, sets out the National Emphasis Program for outdoor and indoor heat-related hazards, directing inspection attention to heat.
Sources
Every factual statement marked with a number links to the source below. Sources were retrieved on 23 October 2026; check the publisher for later revisions.
- Heat — Working in Outdoor and Indoor Heat Environments (OSHA) osha.gov
- Heat illness (Wikipedia) en.wikipedia.org
