Water Hydrating While Hard Working. Body Hydrating Concept Photo.

Heat Stress – Reducing Employee Risk

As working environment temperatures increase due to the season or other factors, heat-related risks can be effectively reduced for employees working inside or outside using a combination of controls and knowledge. What do you need to know to protect your employees?

  • The level of heat stress exposure at your facility
  • The human body’s response to heat stress
  • Steps that can be taken to prevent heat-related illnesses

Let’s briefly review each of these topics to help reduce the risk of heat stress for your employees.


Being aware of heat-related environmental conditions is the first step in prevention.

Ambient temperature alone is often not the complete picture, especially when working in a setting where the climate isn’t controlled, like when working outdoors. Four environmental factors affect the amount of heat stress a worker faces in a hot work area: ambient temperature, humidity, radiant heat (such as from the sun or a furnace) and air velocity. Tools for monitoring heat stress levels are available for indoor and outdoor environments. The heat index provided by the National Weather Service (NWS) indicates the “real feel” of the temperature outside using a combination of temperature and humidity factors. A Wet Bulb Global Temperature (WBGT) is recorded using a dedicated instrument and is a combination of temperature, wind/air velocity, solar/infrared radiation and humidity, and can be measured outdoors or indoors.

There’s an app for that! A heat stress mobile phone app developed by OSHA and NIOSH is available for employees working outdoors that will display a real-time heat index and heat-related stress risk factor by zip code or phone location. Evaluating the risk is always the first step in hazard prevention.


The human body responds to the stress of excess heat in various ways as it continuously works to maintain the core body temperature within a couple of degrees of the average “normal” of 98.6°F. When the body’s ability to self-regulate its core temperature fails and it continues to rise uncontrolled, serious consequences, including death, are possible.  Equally important to the environmental factors are personal characteristics such as age, weight, fitness, medical condition and acclimatization to the heat.

The body reacts to high external temperatures by increasing the heart rate and shunting blood to the skin which increases skin temperature and allows the body to give off its excess heat via convection and to a lesser degree, conduction. The effectiveness of this cooling is dependent on the immediate environment, the physical characteristics of the person and the manual labor they are performing.

Sweating is another means the body uses to maintain a stable internal body temperature in the face of heat.  Sweating is only effective if the humidity level is low enough to permit evaporation and if the fluids and salts lost are adequately replaced.

If the body cannot dispose of excess heat, it will store it.  When this happens, the body’s core temperature rises, and heat-related illnesses will manifest.


Heat Rash

Heat rash, also known as prickly heat, may occur in hot and humid environments where sweat is not easily removed from the surface of the skin by evaporation.  When extensive or complicated by infection, heat rash can be so uncomfortable that it inhibits sleep, can impede a worker’s performance, and can even result in temporary total disability.  It can be prevented by resting in a cool place and allowing the skin to dry.

Heat Cramps

Heat cramps – painful spasms of the muscles – are caused by not drinking enough fluids or failing to replace electrolytes lost via sweating.  Tired muscles – those used for performing the work – are usually the ones most susceptible to cramps.  Cramps may occur during or after working hours and may be relieved by taking liquids by mouth or saline solutions intravenously if severe and medically determined to be required.

Heat Exhaustion

Heat exhaustion results from an excess of retained heat in the body and loss of fluids and electrolytes through sweating. The worker with heat exhaustion still sweats but experiences other symptoms, including:

  • extreme weakness or fatigue
  • giddiness
  • nausea and/or headache
  • skin is clammy and moist
  • complexion pale or flushed
  • core body temperature is frequently slightly elevated

Treatment involves allowing the victim to rest in a cool place and drink water or an electrolyte solution (a beverage used by athletes to quickly restore potassium, calcium, and magnesium salts).  Severe cases involving victims who lose consciousness necessitate a 911/EMS call. If treatment is not provided, heat exhaustion may progress quickly to life-threatening heatstroke.


Heatstroke, the most serious health problem for workers in hot environments, is caused by the failure of the body’s internal mechanism to regulate its core temperature.  Sweating stops and the body can no longer rid itself of excess heat.

Symptoms of heatstroke include:

  • mental confusion, delirium, loss of consciousness, convulsions or coma
  • a body temperature of 106°F or higher
  • hot dry skin, which may be red, mottled or bluish

Victims of heatstroke necessitate a 911/EMS call and may die if not treated promptly.  While awaiting the arrival of EMS, the victim must be moved to a cool and/or shaded area with his/her outer clothing and boots loosened or removed. If possible, wet down the body and fan vigorously to increase cooling.  Apply cold packs to armpits and groin if available. Prompt first aid can prevent permanent injury to the brain and other vital organs.


Most heat-related health problems can be prevented or the risk of developing them reduced. Following a few basic precautions should lessen heat stress risk.

A variety of engineering controls may be helpful, including general ventilation and spot cooling by local exhaust ventilation at points of high heat production. For example, shielding is required as protection from radiant heat sources while evaporative cooling and mechanical refrigeration are other methods to reduce heat; eliminating steam leaks and proper maintenance of equipment will also help.  Equipment modifications, the use of power tools to reduce manual labor and personal cooling devices, or protective clothing are other ways to reduce the hazards of heat exposure for workers.

Work practices, such as providing plenty of drinking water (as much as a quart per worker per hour), sports drinks and even popsicles in a breakroom freezer can help reduce the risk of heat disorders. Employers should also consider an individual worker’s physical condition when determining his or her fitness for working in hot environments.  Older workers, obese workers and personnel on some types of medication are at a greater risk.

Alternating work and rest periods with longer rest periods in a cool area can help workers avoid heat stress.  If possible, heavy work should be scheduled during the cooler parts of the day, and appropriate protective clothing should be provided.  Supervisors should be trained to detect early signs of heat stress and should permit workers to interrupt their work if they are extremely uncomfortable.

Acclimatization to the heat through short exposures followed by longer periods of work in the hot environment can reduce heat stress.  New employees and workers returning from an absence of two weeks or more should have a 5-day period of acclimatization.  This period should begin with 50 percent of the normal workload and time exposure the first day, and gradually begin building up to 100 percent on the 5th day.

Training is vital so that employees are aware of the hazards, risk factors including hydration level (urine color chart), early warning signs, symptoms of heat-related illnesses, first-aid treatments and when to call 911. Training first-aid workers to recognize and treat heat stress disorders and making the names of trained staff known to all workers is also recommended.

Following these recommendations can prevent heat-related illness in your workplace. For more information on preventing heat-related illness in the workplace, visit the OSHA website at https://www.osha.gov/SLTC/heatstress/ or contact US Compliance.

U.S. Compliance provides safety, health and environmental services to hundreds of facilities in the manufacturing and general industry sector across the country and can help you develop an effective Heat Stress Prevention Program.

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