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Managing heat stress and working in hot environments



When working in hot environments body temperature may rise, and the body responds by sweating.  As the sweat evaporates it cools the body.  If the process does not work several heat related illnesses may occur.  Water is key to this process; by providing adequate blood volume to transfer heat outward and perspiration to cool the body.

Other factors are as follows:

  • Humidity which may inhibit evaporation of sweat.
  • Inadequate water intake.
  • High ambient air temperature or radiant heat from blast furnaces, or sunshine.
  • Various protective clothing that may add to the heat load of the employee.

Heat Related Illnesses

Heat rash

  • Symptoms
    Sweat duct becomes blocked and sweat accumulates in the gland.  Heat rash is uncomfortable and can lead to more serious disorders due to lack of sweating. 
  • First Aid
    Apply drying lotion and powder.
  • Prevention
    Regular bathing - keeps skin dry and clean.

Fainting

  • Symptoms
    Common among workers not acclimated to working in hot environments.  Caused by blood pooling in lower extremities.
  • First Aid
    Remove employee to cooler area and lay down briefly, recovery is prompt and complete.
  • Prevention
    Proper acclimatization and avoid standing erect for extended periods of time, move around.

Heat Cramps

  • Symptoms
    Painful spasms of the muscles used during or after work.  Caused by excessive loss of salt from sweating.
  • First Aid
    Consumption of electrolyte replacement beverage.
  • Prevention
    Adequate salt intake during meals, no need for salt tablets - normal diet has ample salt.
    Begin drinking replenishing fluids 1-2 hours before beginning work in hot environment.

Heat Exhaustion

  • Symptoms
    Fatigue, nausea, headache, rapid heart rate and moist clammy skin.  Can progress to heat stroke.
  • First Aid
    Rest in cool area and drink fluids.
    Severe cases may require intravenous fluids.
  • Prevention
    Acclimatization of worker, and drinking ample water during work.

Heat Stroke

  • Symptoms
    Elevated body temperature, unconsciousness or convulsions, lack of sweating and possible vomiting and  diarrhea.
  • First Aid
    • A medical emergency that requires professional medical treatment.
    • Move patient to cool area, bath in cool water or cover in cool water soaked towels. 
    • Remove outer clothing and treat for shock.
    • Give no oral liquid if convulsing or unconscious.

Warning: Pregnant women, especially in the first trimester, are at increased risk for birth defects if body temperature is evaluated for extended periods of time.  Consult a physician.

Administrative Controls

Adequate fluid intake

Drink ample fluids throughout the day.

  • Best: plain cool (50-60 oF) water.
  • Avoid: alcohol, caffeinated beverages such as tea and coffee, which are diuretics, and excessive carbohydrates such as soda and fruit juice which can inhibit water uptake.
    • Increase rest periods throughout the day.
    • Job rotation for high exposure jobs.
    • Schedule hot work for cooler periods in the day.
    • Employee and supervisor training on heat related issues.

To encourage workers to drink water it should be readily accessible and kept clean and cool.

Acclimatize workers

Acclimatized worker will have increased ability to work in heat and be more resilient to the stress.  The process takes 4-7 days and there is a substantial loss when workers leave the work routine for one week or more and must be reacclimatized. 

Medical evaluation

A physician can help identify high risk groups that are more susceptible to heat stress.  Screen for the following:

  • Physically fit - poor muscle conditioning and obesity limit heat dissipation.
  • Medications taken by employees may adversely affect thermoregulation.  Employees should notify their supervisor of medications they are taking.

Engineering Controls

Fans can be used to increase circulation and increase evaporation of sweat. 

  • If air temperature is greater than 95 oF then fans should not be used, they will actually heat worker.  Average skin temperature is 95 oF in this case the air temperature must be reduced with auxiliary cooling methods.
  • Shields and barriers to protect worker from direct radiant heat source.

Personal Protective Clothing

  • Air cooled or water cooled garments.
  • Air supplied hoods and suits can be adapted to provide cooled air.
  • Wetted head bands and other overgarments.

Measurement of Heat Stress

Heat stress is measured using the Wet Bulb Globe Thermometer (WBGT).  The ACGIH has TLVs to assist in interpreting these measurements that establish a work rest routine appropriate for the type of work being done.

Evaluation strategy

  • Identify the work type
  • Determine current work/rest regimen
  • Collect WBGT data
  • Use WBGT index to evaluate
  • Make necessary adjustments

Summary

  • Educate
  • Identify workers at risk
  • Monitor environment and make adjustments
  • Provide PPE, water, rest and first aid as required.

In a changing work environment, the best approach is good employee education and management controls.

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