Heat Stress

Work operations involving high temperatures, radiant heat sources, high humidity, direct physical contact with hot objects, or strenuous physical activities have a high potential for inducing heat stress in employees engaged in such operations. These activities are often conducted in areas such as steam tunnels; power plants; pipe chases; some mechanical rooms; outdoor construction activities; particularly on roofs; and outdoor construction activities that require the use of protective clothing.

Age, weight, degree of physical fitness, degree of acclimatization, metabolism, use of alcohol or drugs and a variety of medical conditions all affect a person’s sensitivity to heat. Even the type of clothing worn must be considered. In addition, the measurement of a hot environment involves more than just measuring the ambient air temperature -- radiant heat, air movement, and relative humidity are all factors that must be determined.

Heat Stress - any set of environmental and work load conditions which places excessive demands on the normal regulation of body temperature. When heat stress causes an imbalance between body heat gain and body heat loss, this can result in heat strain.

Heat Strain - a physiological reaction to environmental heat stress. Depending on individual tolerance and specific environmental conditions, heat strain can manifest itself in a variety of heat disorders, including heat cramps, heat exhaustion, heat syncope, heat stroke, and rashes.

When should a Heat Stress program be implemented?

The incidence of heat stress is the result of a variety of factors. Factors to be evaluated when considering the need for a Heat Stress Program include the following:

Ambient temperature
Relative humidity
Work location and air movement for cooling
Type of work required - the metabolic heat generated during heavy, moderate or light work
Required work clothing and safety equipment - impermeable work clothing increases the potential for heat stress
Employee symptoms and/or complaints
Employee conditioning and/or acclimatization

NIOSH (1986) states that a good heat stress training program should include at least the following components:

Knowledge of the hazards of heat stress;
Recognition of predisposing factors, danger signs, and symptoms;
Awareness of first-aid procedures for, and the potential health effects of, heat stroke;
Employee responsibilities in avoiding heat stress;
Dangers of using drugs, including therapeutic ones, and alcohol in hot work environments;
Use of protective clothing and equipment; and
Purpose and coverage of environmental and medical surveillance programs and the advantages of worker participation in such programs.
Hot jobs should be scheduled for the cooler part of the day, and routine maintenance and repair work in hot areas should be scheduled for the cooler seasons of the year.

Heat Stress Control Measures

A number of options are available for controlling heat exposures.

Engineering Controls

Controls such as ventilation, air cooling, fans, shielding, and insulation.

Where feasible, eliminate steam leaks and shut down hot machinery and equipment.

Administrative Controls

Workers should be allowed to take frequent rest breaks in a cooler environment. The higher the heat stress conditions, the longer the rest period should be. The supervisor and worker(s) should agree on a reasonable work schedule that minimizes the duration of heat exposure to the extent possible. Rotation of workers may be one feasible alternative.

Protective Clothing

If working outside, wear loose fitting, light colored, porous clothing which allows free air circulation over the body. Wear a well ventilated broad brimmed hat. If working inside, wear as little clothing as necessary.

Work Practices

Cool water (50-60 degrees F) or any cool liquid (except alcoholic beverages) should be made available to workers to encourage them to drink small amounts frequently, e.g., one cup every 20 minutes. An ample supply of liquids should be placed close to the work area. Although some commercial replacement drinks contain salt, this is not necessary for acclimatized individuals because most people add enough salt to their diets.

In some situations, a buddy system (no less than two employees) may be appropriate so the employees can observe each other for early signs of heat strain. Establish a means of communication so that employees can call for assistance or medical emergency when necessary.

Training

Heat stress training is the key to good work practices for both employees and supervisory personnel. All employees need to understand the reasons for using appropriate work practices to prevent heat stress and ensure a successful program.