Preventing Heat Stress Disorders

Heat

A worker's ability to do the job is affected by working in a hot environment: strength declines and the onset of fatigue comes sooner than it would otherwise. Constant heat can also impair a worker's mental alertness, often increasing the possibility of an accident.

Moreover, constant heat can lead to serious health effects such as heat rash, heat cramps, heat exhaustion, and heat stroke.

How Our Bodies Cope with Heat Exposure

No matter how hot the surrounding air becomes, the human body must always maintain its internal temperature of 98.6 degrees F. When we are in a hot work environment, the body first begins to get rid of excess heat by dilating the small blood vessels of the skin. Excess body heat can then be transferred to the surface mostly by evaporation of sweat (the heat is transferred to the sweat and water vapor from evaporating sweat takes the heat energy away from the skin). The rise in the skin temperature stimulates sweating even before there is a rise in the overall body temperature.

 

Health Effects

• Heat Rash (prickly heat). Excessive sweating can plug up sweat ducts and cause an inflammation or rash. This rash sometimes affects the body's ability to sweat and to cool itself, and therefore can lead to more serious problems, such as heat cramps or heat stroke (see below).
• Heat Cramps. Prolonged sweating with inadequate replacement of salt can lead to muscle spasms-usually in arms, legs, and abdomen.

• Heat Exhaustion (heat fainting), due to dehydration or low blood pressure from physical exertion. Results in headache, tiredness, nausea, dizziness, clammy skin, heavy sweating and, sometimes, fainting.
• Heat Stroke. Sometimes sweat suppression and increased storage of body heat lead to high body temperature (106 degrees F) which causes extreme stress. Symptoms include hot, dry skin, mental confusion, and, if serious enough, convulsions, and eventually coma.

Measuring Heat Stress

There are four basic factors affecting the amount of heat stress we receive from working in a hot area:

• Air temperature
• Humidity
• Radiant Heat (direct heat radiating from an object such as an oven or even the sun)
• Air Velocity

There is a way to evaluate the contributing effects of these four factors and determine the amount of heat stress you receive. The measurement is called the Wet Bulb Globe Temperature (WBGT). If you think heat is a problem in your workplace, you may want to measure the WBGT. Finding out what the WBGT is can give you ways to control heat exposure. Instruments that quickly measure the WBGT can be purchased by your company.

Another alternative is having the union call NIOSH (National Institute for Occupational Safety and Health). Also the employer can contact the OSHA consultation service to come in and do a free evaluation.

How to Beat the Heat

There are essentially two ways to reduce heat stress: through engineering controls and/or good work practices.

Engineering controls are the best way to go because they actually reduce or eliminate the factors responsible for the heat stress (e.g. hot air temperature, high humidity, radiant heat, and lack of air velocity). Examples of ways to deal with each factor are listed below:

• Air Temperature:
  • Use air conditioning.
  • Workers should take frequent breaks from the hot environment to allow their bodies to recover from the demands of the heat. A break area should be maintained at approximately 77 degrees F (or 25 degrees C). This temperature may feel too cold to workers who enter from an extremely hot environment; however, at this temperature a worker's heart rate and body temperature will fall quickly to the point of recovery from heat stress.
• Humidity:

• Use local exhaust ventilation at the sources in the process where humidity is generated.
• Enclose processes that give off humidity.
• Use dehumidifiers.
  
  
• Radiant Heat
  • Use insulation to contain the heat of hot
    machinery (ovens, dryers, etc.). Some types of insulation
    include fiber- glass, polished metal reflectors and metal screens.
    
    
• Air Velocity:
  • Use portable fans or roof fans that move air
    through the work area.
  • Use local exhaust ventilation at the sources
    where heat is generated.

 

Click here for details on Good Work Practices