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Heat Stress: Risk Factors

Workers should be aware of the many factors that can impact the risk of heat illness.

Risk Factors

A worker might be affected by many risk factors at the same time.

thermometer held in the sunEnvironment

High temperatures, especially if paired with high humidity, pose large risks for heat illness. High humidity makes sweating less effective at cooling the body. Dripping sweat does not evaporate as well. Direct sun exposure, lack of wind or breeze, and proximity to radiant heat sources such as engines or other hot equipment can also increase risk.

Pills being poured out of a prescription bottleMedications

Heat tolerance can be affected by medications taken for

  • cold, allergies, and congestion
  • muscle spasms
  • blood pressure
  • urine production (diuretics)
  • high blood pressure (beta blockers)
  • diarrhea
  • dizziness/vertigo
  • psychosis
  • depression

Two underground mine workersActivities

High exertion, overworking (not enough rest breaks), or repeated strenuous days in the heat increase the risk for heat illness. Highly-motivated workers attempting to push through discomfort from heat strain can also be at increased risk.

construction worker wiping off sweatNo Acclimatization

New employees or experienced employees returning from time away will not be acclimatized to heat. Acclimatized workers may also be at risk for heat illness following a sudden change in worksite temperature such as heat waves or mining in a new area, or from increases in activity level.

miner drinking waterDehydration

Not drinking enough water increases the risk of heat illness. Drink 1 cup (8 ounces) of water every 15-20 minutes while working in the heat.

arm and blood pressure cuffHealth Conditions

A number of conditions can affect heat tolerance, including:
•  Short-term illnesses, such as diarrhea, vomiting, or respiratory infections
•  Chronic conditions, such as diabetes and heart disease
•  Being overweight or obese
•  Poor physical fitness

ambulance workers attending to a patientPrior Heat Illness

A prior heat injury or illness increases the risk of having a future heat injury or illness.

Other factors

•  Alcohol use in the past 24 hours
•  Non-breathable clothing or personal protective equipment, such as respirators, water/chemical resistant outer wear, or other required protective equipment—all of these can increase the effective working temperature for workers.
•  Age over 60


Points to Remember

Acclimatization is critical
       Lack of acclimatization is a major factor in heat-related deaths on the job

Hydration is critical
Dehydration greatly increases the risk of heat illness

A recent illness can temporarily lower your heat tolerance

Be aware of other personal risk factors for heat illness
       Prior heat illness
       Certain medications
       Certain health conditions
       Alcohol use within 24 hours of working in heat

Case Study: Heat Illness and Medication Use

A 27-year-old employee with two years’ mining experience was coming to the end of a 12-hour shift at a mill in Arizona when he experienced muscle cramps and vomiting from dehydration. Although he did not lose consciousness, he missed two days of work due to the incident. The employee had been taking medication for high blood pressure.

Lessons Learned

Young, healthy, and experienced – anyone can get heat illness! This incident may have been related to the employee’s high blood pressure medication. Multiple factors together, such as certain medications, a recent illness, or repeated strenuous days in the heat, can increase the risk for heat illness.