by Lars Aamoth, CSP
Manager, Operations

Throughout the summer season in recent years, temperatures routinely were forecast to approach and reach record high temperatures.  Heat stress may be thought of as a summertime safety issue, however it is present indoors year-round due to environmental ambient conditions caused by heat sources from process equipment in certain industries.

What are heat related illnesses and why should your company be concerned?  Heat stress is when the body cannot reduce the internal temperature by dissipating heat quickly enough.  This may lead to a rise in internal body temperature and associated symptoms.  Heat stress symptoms include heavy sweating, muscle cramps, headache, rapid pulse, nausea, dizziness, irritability and thirst.  Heat stroke occurs when the body is no longer capable of controlling its temperature.  Heat stroke is a medical emergency and medical attention is required immediately.  Symptoms of heat stroke include rapid temperature rise, hot dry skin, reduced or no sweating, rapid pulse, confusion, loss of consciousness, seizures and vomiting. 

There are additional risk factors that may contribute to heat related illnesses.  These risk factors include employees older than 65 years of age, lack of physical fitness, dehydration, use of certain medications, and workers not acclimated to the work environment, among others.  New workers will need one to two weeks to acclimatize to the environmental conditions.  The Centers for Disease Control and Prevention (CDC) recommends an acclimatization schedule of 20% exposure on day one and then no more than an additional 20% each additional day.  Donning certain types of Personal Protective Equipment (PPE) may also add to an individual worker’s heat stress.  PPE may restrict the body’s natural cooling mechanisms, including sweat evaporation and holding excess heat inside. 

An employee exhibiting signs of heat stress should be moved to a cool area, remove unnecessary clothing and PPE, cool the worker with cold compresses, encourage small sips of water and provide medical attention.  If an employee is exhibiting signs of heat stroke, dial 911 immediately.  First-aid for heat stroke includes moving employees to a cool area, removing unnecessary clothing and PPE, cooling the worker quickly with cold compresses on neck, armpits and groin, wetting the skin, provide circulating air and staying with the employee until medical help arrives.  Heat stroke is a medical emergency and if left untreated can lead to permanent disability or death. 

Heat related illnesses are preventable, and employers should develop a heat related illness protection program incorporated into their broader health and safety program.  Engineering controls should be utilized to reduce employees’ exposure to excessive heat and to increase evaporative cooling.   Administrative controls can also be utilized, including worker rotations and frequent breaks, to reduce the likelihood of heart-related illness.  Employees should be encouraged to drink plenty of fluids to stay hydrated and reduce consumption of fluids like sodas and energy drinks that can lead to fluid loss. 

Assessments of job tasks at risk for heat related illness can be conducted utilizing a Wet Bulb Globe Temperature (WBGT) meter which measures humidity, air movement, radiant heat and temperature.  Measurements should be collected at least hourly, during the hottest parts of the day and hottest months of the year.  Other factors include a clothing adjustment factor and metabolic work rate.  Upon completion of the assessment, the employer can determine an Action Level (AL) and Threshold Limit Value (TLV) based upon the American Conference of Governmental Industrial Hygienist (ACGIH) recommended values.  When limits approach or exceed the AL or TLV, engineering and administrative controls should be utilized to reduce employee exposure to acceptable values.

In accordance with OSHA’s heat stress guide, monitoring can be conducted by checking hear rate, recover heart rate, oral temperature or extent of body water loss.  To check the heart rate, count pulse for 30 seconds at the beginning of the rest period. If the heart rate exceeds 110 beats per minute, shorten the next work period by one third and maintain the same rest period.

The recovery heart rate can be checked by comparing the pulse rate taken at 30 seconds (P1) with the pulse rate taken at 2.5 minutes (P3) after the rest break starts. The two pulse rates can be interpreted using the following criteria.

Monitor workers who are at risk of heat stress, such as those wearing semi-permeable or impermeable clothing when the temperature exceeds 70°F, while working at high metabolic loads (greater than 500 kcal/hour). Personal monitoring can be done by checking the heart rate, recovery heart rate, oral temperature or extent of body water loss.

Heart Rate Recovery PatternP3Difference Between P1 and P3
Satisfactory Recovery<90
High Recovery
(Conditions may require further study)
No Recovery
(May indicate too much stress)

Check oral temperature with a clinical thermometer after work, but before the employee drinks water. If the oral temperature taken under the tongue exceeds 37.6°C, shorten the next work cycle by one third.

Measure body water loss by weighing the worker on a scale at the beginning and end of each workday. The worker’s weight loss should not exceed 1.5% of total body weight in a workday. If a weight loss exceeding this amount is observed, fluid intake should increase.

As the summer heat has just arrived, the risk of heat related illness will be with us for several months ahead and also year-round in certain facilities.  Employers should determine the job positions at risk, develop a heat related illness program and ensure their employees are protected through engineering controls, administrative controls or a combination of both.  Heat related illnesses are preventable and proper planning should be utilized to ensure the safety of all employees at your facility or job site.

How We Can Help
The EI Group, Inc. is well versed in safeguarding employees from heat related illnesses. Should you require an assessment or have other industrial hygiene concerns, please contact Lars Aamoth, CSP at (864) 423-5991 or [email protected].