Indoor Heat in Plants & Buildings

Heat illness isn't only an outdoor problem. Workers in foundries, bakeries, commercial kitchens, laundries, boiler rooms, warehouses, greenhouses, factories and unconditioned attics face hot, humid air for entire shifts. Without sun, heat can still build up from machines, ovens, steam and trapped warm air, and workers may not realize how much stress they are under.

• Plant & Factory Workers
• Kitchen & Laundry Staff
• Warehouse Workers
• Maintenance Crews
• Supervisors

Sources of indoor heat

• Process heat: furnaces, ovens, kilns, boilers, steam lines, dryers and molten metal. See Ovens & Furnaces and Steam Systems.
• Hot weather heating buildings with metal roofs, no insulation and poor ventilation.
• Humidity from steam, wet processes and poor airflow, which prevents sweat from cooling the body.
• Equipment heat from motors, compressors and lights.
• Hot work and protective clothing, which trap heat. See Cooling PPE.
• Heavy physical work that raises body heat.

Signs of heat illness

• Heat cramps: painful muscle spasms.
• Heat exhaustion: heavy sweating, weakness, headache, dizziness, nausea, pale clammy skin and a fast pulse. Move to a cool place, give water and cool the person.
• Heat stroke (an emergency): confusion, slurred speech, fainting, seizures, very high body temperature and hot, dry or sweaty skin. Call 911, cool the person quickly with water or ice, and don't leave them. See Heat Illness.
• Watch coworkers. People with heat illness often don't recognize it themselves.

Rules and standards

• There has been no final federal OSHA heat standard for indoor or outdoor work as of this writing, although OSHA has proposed a rule and has an emphasis program on heat. Check for updates. See OSHA Emphasis Programs.
• OSHA can cite employers under the General Duty Clause for failing to protect workers from recognized heat hazards. Some states have specific heat standards that cover indoor work.
• NIOSH recommends heat stress programs, acclimatization and monitoring based on wet-bulb globe temperature (WBGT). See Heat Index & WBGT and Heat Acclimatization.

Controls

• Engineering controls first: air conditioning or spot cooling, ventilation, fans, reflective barriers and insulation on hot surfaces, shields, exhaust at heat sources and dehumidification.
• Administrative controls: acclimatize new and returning workers gradually (about 20 percent of the load on day one, building up over 1 to 2 weeks), schedule hot jobs for cooler times, rotate jobs, and provide rest breaks in a cool area.
• Water: drink about a cup (8 ounces) every 15 to 20 minutes in hot work, even if not thirsty. Provide cool water close by. Electrolyte drinks may help with heavy sweating; avoid excess caffeine and energy drinks.
• Use cooling vests, fans, misting and light clothing where possible, and loose breathable clothes.
• Monitor temperature and humidity with WBGT readings, and pay attention to people with risk factors such as age, obesity, medicines, previous heat illness or illness.
• Have an emergency plan, trained first aid, and a buddy system. Don't send someone with heat symptoms back to work.

Indoor heat checklist

• We identified hot areas and measured heat and humidity
• Fans, ventilation or cooling are in use, and hot surfaces are shielded
• New workers are acclimatized and rest breaks are in a cool area
• Cool water is nearby and I drink regularly
• Everyone knows the signs of heat illness and to call 911 for heat stroke

Last updated: October 8, 2026