Temperature Induced Stress - Heat Exposure

Part 2 of 2


T.R. Consulting, Inc.

February 2003 Safety Article

Written and compiled by:

Tony Rieck




T.R. Consulting, Inc. regularly publishes safety and environmentally related articles on our website at http://www.trconsultinggroup.com/safety/archive.html. These articles are a free service provided by T.R. Consulting, Inc. to all interested parties in order to promote safety and environmental awareness.  T.R. Consulting, Inc. also provides safety training information and services.  Information about our safety training programs can be accessed at http://www.trconsultinggroup.com/safety/.


This month’s article is the second of a two part series discussing temperature induced stress.  To access the first part of this series about cold stress, go to http://www.trconsultinggroup.com/safety/jan2003.html.



Heat Stress


Exposure to warm temperatures for extended periods of time can lead to heat stress.  Many factors contribute to the level of stress experienced by an individual including:  ambient temperature, humidity, intensity of the task(s) being performed, the need to wear chemically protective suits, acclimatization, body salt balance, fluid intake, obesity, age, and cardiovascular fitness level.  Heat stress has four forms:


*        Heat Rash

*        Heat Cramps

*        Heat Exhaustion

*        Heat Stroke


These are not sequential steps.  While heat exhaustion is a precursor of heat stroke, an individual can become heat exhausted without ever experiencing either heat rash or heat cramps.



The Body’s Cooling Mechanisms


The body has two main mechanisms for cooling itself.  The main way that the body cools itself is through the evaporation of perspiration.  Glands excrete sweat onto the surface of the skin.  When the sweat evaporates into the ambient air, the body experiences evaporative cooling as the air carries away the heat.  The second way that the body cools itself is through pumping blood from the body’s core near the surface of the skin.  The body’s core temperature is approximately 98.6 degrees Fahrenheit.  If the blood encounters skin temperatures in excess of the core body temperature, the excess heat is absorbed by the blood (which also works to raise the core body temperature).





Humidity – Dry air will more readily cause the evaporation of the perspiration as it forms on the surface of the skin.  The more humid the weather, the closer the air is to its saturation point.  Thus, higher humidity results in less effective evaporation of perspiration and a lesser degree of cooling effectiveness.


Chemical Suits – Chemical suits are used to prevent contaminants in the atmosphere and surrounding environs from contacting the skin.  In order to prevent harmful contact, the suit is less than permeable.  As the risk posed by exposure to the chemical grows, the protective suits worn must be less permeable.  Thus, unlike every day outer garments that “breathe” and allow the evaporation of perspiration, chemical suits limit or, in some cases, virtually eliminate the body’s ability to cool through evaporation of sweat.  In high levels of skin protection, it is not uncommon to have heat stress related problems at temperatures as low as 75 degrees Fahrenheit.  Sweat that is produced tends to roll off the limbs and collect in gloves and boots, providing little, if any, benefit.  Wearing a garment under the chemical suit which will hold the sweat against the skin (such as thermal underwear) allows the wearer to experience significant cooling upon removal of the chemical suit, causes the highest possible rate of evaporative cooling to occur while wearing the protective suit, and can prevent burns and irritation caused by hot suit materials contacting bare skin.


Personal Factors – Obese individuals are more susceptible to heat stress because they have a higher body mass to skin surface ratio.  This means that each area of skin must work harder to cool the body.  Cardiovascular fitness allows an individual to perform more work before tiring.  Older individuals are more prone to heat stress as their bodies become less capable of compensating for temperature variations.  Also, individuals who are accustomed to warm climates and temperatures will be less bothered by the heat.


Diet-Related Factors – The body needs salt (body salt, not table salt) in order to sweat.  Sports drinks contain salts that closely resemble body salts that aid in the absorption of ingested liquids and promote evaporative cooling.  Alcoholic beverage intake (excessive) causes the body to dehydrate, reducing the body’s tolerance for heat.  Heat stress is, in general, the result of excessive fluid loss with inadequate fluid intake.  Therefore, regular ingestion of liquids serves to increase an individuals tolerance of the heat.  Caution should be exercised where beverages containing caffeine are concerned.  Caffeine is a diuretic with the potential to cause dehydration.  Recent studies, however, indicate that smaller amounts of caffeine contained in soft drinks may not be problematic and that the ingestion of liquids contained in these drinks more than balances out the effects of the caffeine.


Attitude – One of the biggest factors that contribute to the prevalence of heat stress in the workplace is a “macho” or competitive attitude that some workers exhibit.  While it appears to be acceptable to complain about cold temperatures and to take measures to compensate for exposure to the cold, some workers do not complain about the heat for fear that they might be viewed as “slackers” or less capable and productive workers than those who are less affected by the heat.  In the end, a greater disruption of the work on a site is caused by tending to someone who becomes heat exhausted (or worse, suffers heat stroke) than is caused by occasional rest periods and breaks for fluid intake.


Use of Cooling Devices A variety of cooling devices are available to enhance the body’s ability to tolerate heat.  Cooling gel-packs that are kept in coolers are available that can be inserted into specially designed vests and wrist bands.  Bandanas are available that, when twisted, provide a cooling effect.  Vortex cooling systems can be placed in the lines of air supplied respirators to cool the air.  The use of commonly available cooling devices can greatly extend an individuals ability to work in the heat.



Heat Rash


Heat rash, also commonly referred to as prickly heat, is a rash that is associated with profuse sweating.  Common sites for this type of irritation are the waist, armpits, and insides of the elbows.  While heat rash is not a serious injury requiring prompt medical attention, the distraction caused by the resultant discomfort can cause inattention by workers and a higher propensity for accidental injury.  Because the skin is broken, there is an increased ability for chemicals to permeate the skin.


Symptoms of Exposure


The skin is mildly inflamed with numerous tiny, red, itchy spots.  The outline of the rash is well-defined and is accompanied by aggravating, prickly sensations.




Calamine lotion and bath powder can relieve the pain.  Cool showers without soap will relieve the itching.  Preventative steps include wearing clean, starch-free clothing that has a loose fit.  Loose fitting clothes aid in the evaporation of sweat.


Heat Cramps


When the body loses excessive salt due to profuse sweating, painful spasms of the muscles can result.  This is especially true when a worker is performing tasks involving strenuous physical activity.  Heat cramps can occur by itself or as a symptom of heat exhaustion.  Heat cramps, when not indicative of heat exhaustion, does not require prompt medical attention, but should be viewed as a warning that the sufferer should be removed from the heat and re-hydrated.  When heat cramps are a symptom of heat exhaustion, medical treatment should be sought due to the risks of heat stroke.


Symptoms of Exposure


Painful spasms of the muscles usually located in the extremities following a period of profuse sweating.




Heat cramps can be prevented by maintaining the body’s salt balance.  Electrolytic fluids, such as sports drinks, can be used to maintain sufficient salt balance.  Sports drinks may be inadequate to treat heat cramps and liquids containing higher levels of electrolytes (such as Pedialyte or generic equivalent) or a salt solution (~1/4 teaspoon/pint) should be administered.


Heat Exhaustion


Heat exhaustion should be treated as a serious injury, because, if left untreated, heat exhaustion can develop into heat stroke, a life-threatening condition.  Heat exhaustion is a fatigue-like condition brought about by a combination of dehydration, salt loss and inefficient or insufficient cooling by evaporation of sweat.


Symptoms of Exposure


Symptoms of heat exhaustion include: fatigue, dizziness, nausea, and headache.  Heat exhaustion may be accompanied by heat cramps and the sufferer may vomit or faint.  Someone who is heat exhausted will usually be perspiring profusely with pale, clammy skin.  Other signs of heat exhaustion are shallow, fast breathing and a weak, rapid pulse. 




Unconscious victims must get prompt medical attention.  Conscious victims should be moved to a cool place where they can lie down with their feet elevated.  Electrolytic fluids (such as Pedialyte or generic equivalent) or a salt solution (~1/4 teaspoon/pint) should be administered slowly (sips).  Due to the potential for heat stroke, medical attention should be sought.



Heat Stroke


Heat stroke is a life-threatening condition.  The body becomes dangerously overheated when it’s heat regulating mechanisms break down.  The body core temperature can rise to 107 degrees Fahrenheit and beyond.  Unless treated, heat stroke victims will lapse into a coma and then die.


Symptoms of Exposure


Heat stroke is preceded by heat exhaustion.  The skin becomes hot, dry and red as sweating either ceases or diminishes markedly.  The pulse is rapid and faint.  Breathing is shallow.  The victims core body temperature will rise rapidly and dramatically.  Unconsciousness is followed by death.




Seek medical attention immediately (as soon as possible).  Victim should be moved to a cool, shady place.  Remove the victim’s clothing and cover with a thin, wet cloth (such as a sheet).  Fan the victim while keeping the covering wet to cool the victim until the victim’s skin feels cool to the touch.  If conscious, electrolytes (such as Pedialyte or generic equivalent) or a salt solution (~1/4 teaspoon/pint) may be administered.  The degree of recovery that can be expected is time dependant.  Victim’s receiving early treatment usually recover completely.




Monitoring Heat Stress


Especially when workers are required to wear high levels of personal protective equipment, it is important to monitor the degree of heat stress exposure.  Several methods are used.  Combining methods provides the most reliable assessment.  Methods currently used include:  radial pulse monitoring, body water loss measurement and measurement of the core body temperature.  By using these assessment measures in combination with good preventative practices, heat stress can often be treated prior to the onset of symptoms of overexposure.  



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