Heat Stress

The term heat stress is used to describe a number of heat-related illnesses that occur when the body is not able to maintain a normal temperature.

Heat-related disorders include heat stroke, heat exhaustion, heat cramps, and heat rashes. Heat stress can occur in both indoor and outdoor work settings. Indoor operations involving high air temperatures, radiant heat sources, heavy lifting and other strenuous physical activities, and direct physical contact with hot objects increase the potential for heat stress. Outdoor work during the hot summer months, especially activities that require workers to wear semipermeable or impermeable protective clothing also increases the likelihood of heat stress. Individuals vary in their susceptibility to heat stress.

Environmental factors that may increase the risk of experiencing heat stress include:
• High temperatures and humidity • Exposure to indoor sources of heat (ovens, furnaces) • Direct sunlight • Limited airflow or air movement • Wearing personal protective equipment (PPE) • Heavy clothing • Heavy workload

Personal factors that may contribute to an individual experiencing heat stress include:
• Level of physical fitness • Opportunity to acclimate to conditions • Age • Dehydration • Obesity • Alcohol or drug use • Infection or illness • Sunburn • Certain medications 
• Pregnancy • Previous heat-related illness • Chronic disease

Regulatory Citation
• 29 USC 654 — Duties of employers and employees (including Pub. L. 91–596 “OSH Act of 1970” §5(a)(1), the “General Duty Clause”)
• 29 CFR 1910.120 — Hazardous waste operations and emergency response (HAZWOPER)

All employers must take the necessary steps to mitigate a known hazard. If excessive heat is a recognized hazard, the employer must address it. Wearing PPE puts workers at hazardous waste sites or responding to emergency situations at greater risk of heat stress. Paragraph 1910.120(g)(5)(x) requires employers to address the potential for heat stress in a written personal protective equipment program which is part of the employer's safety and health program and also part of the site-specific safety and health plan.

Key Definitions
• Acclimatization means exposing the employee to the hot environment for progressively longer periods to allow the body to adapt.
• Administrative controls mean reducing specific job hazards through changes in work procedures (e.g., written safety policies, schedule changes, training, and supervision).
• Conduction means the heat exchange between the heat and a surface.
• Convection means the exchange between the skin surface and the surrounding air.
• Engineering controls means reducing or eliminating specific job hazards through the use of or substitution of machinery or equipment (e.g., ventilation, air cooling, fans, shielding, and insulation).
• Fluid replacement means providing cool water to employees and encouraging them to drink small amounts frequently.

Summary of Requirements
Although OSHA does not have a standard that specifically addresses employee exposures to extreme heat, the agency does encourage employers to take steps to prevent heat-related illnesses. OSHA inspectors do conduct heat inspections and do issue General Duty Clause citations when heat hazards are present. Steps employers should take when employees are exposed to heat include:

Protect indoor workers from heat stress

  • Engineering controls include cooling the air with fans, shielding, proper ventilation, insulation, and air conditioning. Heat reduction also occurs by using power assists and reducing the physical demands placed on employees.
  • Administrative controls and work practices include training employees to avoid heat stress, educating them on the dangers of using alcohol and drugs (even over-the-counter medications) and acclimatizing workers to the heat.

Protect outdoor workers from heat stress
Outdoor workers are at an increased risk of experiencing heat-related illnesses during the hot summer months when sweating alone may not be enough to cool the body. To prevent heat-related illnesses and fatalities, employers should remind employees to:

  • Drink water every 15 minutes, even if they are not thirsty.
  • Keep an eye on fellow workers.
  • Rest in the shade to cool down.
  • Wear a hat and light-colored clothing.
  • Learn the signs of heat illness and what to do in an emergency.
  • Take it easy during the first days of work in the heat to acclimatize.

Monitor workers for signs of heat stress
To monitor workers, measure:

  • Heart rate. Count the radial pulse during a 30-second period as early as possible in the rest period.
  • If the heart rate exceeds 110 beats per minute at the beginning of the rest period, shorten the next work cycle by one-third and keep the rest period the same.
  • If the heart rate still exceeds 110 beats per minute at the next rest period, shorten the following work cycle by one-third.
  • Oral temperature. Use a clinical thermometer (3 minutes under the tongue) or a similar device to measure the oral temperature at the end of the work period (before drinking).
  • If oral temperature exceeds 99.6°F (37.6°C), shorten the next work cycle by one-third without changing the rest period.
  • If oral temperature still exceeds 99.6°F (37.6°C) at the beginning of the next rest period, shorten the following work cycle by one-third.
  • Do not permit a worker to wear a semi-permeable or impermeable garment when his/her oral temperature exceeds 100.6°F (38.1°C).
  • Body water loss. Measure weight on a scale accurate to 0.25 lb at the beginning and end of each workday to see if enough fluids are being taken to prevent dehydration. Weights should be taken while the employee wears similar clothing or, ideally, no clothing. The body water loss should not exceed 1.5 percent total body weight loss in a workday.
  • Initially, the frequency of physiological monitoring depends on the air temperature adjusted for solar radiation and the level of physical work. The length of the work cycle will be governed by the frequency of the required physiological monitoring.

Train workers to recognize the signs of heat stress in themselves and their coworkers and what to do in an emergency:

Heatstroke. Heatstroke is a life-threatening condition that occurs when the body is no longer able to regulate temperature through sweating. Symptoms include confusion, loss of consciousness, convulsions, hot, dry skin, and extremely high body temperature. First aid includes calling 911, moving the affected worker to a cool, dry area, and aggressive attempts to lower body temperature through the removal of outer clothing and wetting the skin. The worker needs immediate medical attention. Do not leave the worker unattended.

Heat exhaustion. This condition requires prompt first-aid treatment to prevent it from becoming more serious. Symptoms include clammy skin, nausea, headache, dizziness, weakness, thirst, muscle cramps, and fainting. First aid treatment includes moving the employee to a cooler area, removing outer clothing, and giving cool fluids to drink.

Heat cramps. Heat cramps are painful muscle cramps that occur after sweating and inadequate fluid intake. Symptoms are involuntary muscle spasms and excessive sweating. First aid includes moving the employee to a cool area and providing fluids to drink, especially electrolyte-replacing liquids such as sports drinks. The affected employee should gently stretch the cramped muscle(s).

Heat fatigue. Heat fatigue occurs when workers have had a chance to adapt to the hot working environment. Symptoms include trouble concentrating and working. First aid involves moving the worker to a cooler area and rest.

Heat rash. Heat rash, also known as prickly heat, appears as itchy red bumps on the skin. First aid includes rinsing the affected area with cool water and thoroughly drying the skin.

Photo by Thomas Kinto on Unsplash 

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