Heat stress in protective clothing

Protective clothing keeps hazardous substances away from the body, but it also keeps heat in. For a rescuer wearing breathing apparatus and a chemical protective suit, heat is often the factor that limits working time — sometimes more than the air supply. Heat illness can develop within minutes of hard work and is preventable with planning.

Why the body overheats

The body produces heat with every movement: carrying a breathing apparatus, climbing ladders or moving a casualty multiplies the heat output several times over. Normally this heat is lost to the surroundings, mainly by the evaporation of sweat. Protective clothing interrupts this: the less permeable to air and water vapour it is, the less sweat can evaporate. Sweat soaks the underclothing, core temperature rises, the heart beats faster to carry blood both to the muscles and to the skin, and the body loses water and salt.

The total load comes from three sources: the environment (air temperature, humidity, radiant heat from fire or hot plant), the work rate and the clothing. A cool day does not make a gas-tight suit safe.

Encapsulating suits

Gas-tight chemical protective suits worn over breathing apparatus are the most demanding case. Practically no sweat evaporates through the suit material, so almost all the heat produced stays inside. Visors fog, fine movements become difficult and the wearer may not notice how hot they are getting. Working times in such suits are short — often well under the duration of the air cylinder — and a decontamination period must be added before the suit can be removed.

Measuring the environment

The WBGT index (wet bulb globe temperature), described in ISO 7243, combines air temperature, humidity, air movement and radiant heat into one value used to screen for heat stress. It is a useful planning tool for work in ordinary or lightly protective clothing, and clothing adjustment values are used for heavier ensembles. For fully encapsulating suits, measurements of air temperature and radiant heat give an indication of the environment, but the wearer's own condition is the deciding factor.

Work and rest

Plan short work periods and longer rest periods as the load increases; rotate teams instead of extending one team's time.
Keep a fully equipped standby team ready — a heat-exhausted wearer needs rescue just like one who is out of air.
Allow time for doffing and decontamination in the plan; the wearer is still under heat load during decontamination.
Schedule heavy work for the cooler part of the day when possible, and provide shade or a cool rest area close to the exit.

Acclimatisation and fitness

People who are not used to working in heat are at much higher risk. NIOSH recommends that new workers start with no more than 20 % of the usual exposure on the first day and increase it gradually. Acclimatisation fades after a period away from hot work. Good aerobic fitness, adequate sleep and avoiding alcohol the day before all improve tolerance. Recent illness — especially with fever, diarrhoea or vomiting — and some medicines reduce it.

Hydration

Drink before, during and after work, not only when thirsty. For moderate work in heat, NIOSH recommends about 1 cup (roughly 250 ml) of cool water every 15–20 minutes, with electrolyte drinks during prolonged sweating over several hours. Wearers in breathing apparatus cannot drink during an entry, so they must start well hydrated and drink at every break. Very large amounts of plain water alone can also be harmful; follow the organisation's medical guidance.

Cooling

After leaving the hazard zone and completing decontamination, the wearer removes the suit, opens or removes other layers and rests in shade or a cool area. Cooling the forearms and hands in cool water is a simple and effective method. Cooling vests worn under the suit can extend safe working time, but they add weight and must be compatible with the suit and breathing apparatus.

Signs of heat illness

Condition	Typical signs	Action
Heat rash, cramps	Skin rash; painful muscle cramps	Rest in a cool place, fluids with salts
Heat exhaustion	Heavy sweating, weakness, headache, dizziness, nausea, rapid pulse	Stop work, remove clothing, cool, fluids, medical check
Heat stroke	Confusion, unusual behaviour, collapse, seizures; skin may be hot and dry or still sweating	Medical emergency: call for help, cool immediately and aggressively

Confusion and strange behaviour in a wearer are a warning sign in themselves: the person affected is often the last to notice.

Rehabilitation at the scene

Fire and rescue services organise rehabilitation of crews at longer incidents: a rest area out of the hazard and out of the sun or cold, fluids and food, cooling, and a medical check before crews return to work. In the United States, the requirements formerly in NFPA 1584 (rehabilitation during emergency operations and training) are now part of the consolidated NFPA 1580 (2025 edition) on occupational health and wellness. In Europe, national bodies such as INRS in France and DGUV in Germany publish guidance on work in heat.