Working in the Heat

Although hot work environments are common, they are not insignificant.  In some areas of the world, workers face extreme heat almost all year.  Hot conditions can also exist in confined spaces, boiler rooms, engine rooms and when workers wear protective clothing.

While heat is indicated directly by a thermometer, a more complete picture includes air temperature, radiant heat sources, air speed, humidity, direct contact with hot objects and heat created by strenuous physical activities.

Worker variables to consider include age, weight, physical fitness, extent of acclimatization, metabolism, alcohol or drug use, and medical conditions. Prior heat injury and worker clothing can also worsen heat conditions.

The only way the body cools itself is by getting rid of excess heat through sweating. When sweating can’t occur, the body stores heat which causes the body core temperature to rise and the heart rate to increase.  A person overly taxed by heat may experience fainting (HEAT SYNCOPE) and/or HEAT CRAMPS.  Heat cramps can occur in the legs and arms as well as in the abdomen.  If left uncorrected, the condition will progress to HEAT EXHAUSTION where the body temperature continues to rise and the victim may experience inability to concentrate; irritability; weakness; giddiness; nausea or vomiting; fainting; headache; dizziness; and perhaps lack of thirst.  People suffering from heat exhaustion may be too confused to recognize their own danger.

The last stage of heat exposure is HEAT STROKE—a true medical emergency.  A person suffering heat stroke will die unless removed from the heat, cooled and treated.  The primary signs and symptoms of heat stroke are confusion; irrational behavior; loss of consciousness; convulsions; a lack of sweating (usually); hot, dry skin; and high body temperature.

HEAT RASH and HEAT FATIGUE are the most common problems in hot work environments.  Heat rash or prickly heat is red skin papules usually appearing in areas where clothing is restrictive and skin is persistently wetted by unevaporated sweat.  While the affected areas may become infected if not treated, most heat rashes disappear after exposure stops. HEAT FATIGUE is usually due to lack of acclimatization and training.  Heat fatigue can result in impaired performance of skilled sensory motor, mental, or vigilance jobs.

Precautions: A successful heat stress prevention program includes training, monitoring, workplace evaluation and exposure controls. Workers need to be acclimated or used to working in hot conditions because to a certain extent the human body can adapt to heat.  Conversely, workers not acclimated and thrust into hot environments are less able to physically cope.

New workers and workers returning from vacation or other breaks from the heat require special attention until re-acclimated.

Basic worker training should include information on the signs and symptoms of heat illnesses, prevention and first aid treatment.

Supervisory training should include basic worker training plus work load assessment; establishing cool/rest periods; and heat stress monitoring. The effect of protective clothing, if worn, should be discussed. All workers need to understand the importance of maintaining fluid and electrolyte balance.

Engineering controls may include general ventilation; shade; spot cooling; local exhaust ventilation at points of high heat production; and heat shielding.  Administrative controls may include reducing physical effort and taking adequate rest breaks in a cool area.  When possible, work should be scheduled around peak heat periods.  Water and electrolyte replacement drinks should be available and cooling vests or other protective clothing may be necessary.  Worker fitness should be initially and regularly evaluated.