The Physiological Effects of Heat Stress

Adverse effects of elevated body temperature

Hyperthermia is a situation in which the actual body temperature is higher than your body’s “basal metabolism”, which is when the body is at idle.  It can occur as a response to heat exposure if you cannot get rid of the heat that you are absorbing from the environment as well as the heat you are producing yourself. Your body attempts to return its temperature to the “basal metabolism” set point.

There are several health problems that can develop if your body is not able to deal effectively with Hyperthermia. 

• An extended elevated body temperature will eventually result in tissue damage, much like the situation when a mother has a child with a 105° fever. 

• People that experience heat stress also develop aggressive behavior.  In a factory situation, this can lead to other serious problems in the workplace, especially with other workers who are also starting to feel the effects of the heat.

• Recklessness is another symptom that develops.  The affected worker no longer has the same level of patience that he or she usually exhibits, and cannot deal as effectively with small problems.  This leads to unnecessary accidents, which in turn, can create some far-reaching problems.

• Performance also slows down.  The body begins to compensate for its immediate problem of too much heat when the brain receives the heated blood. As body temperature rises, the brain sends out instructions to decrease the muscle tone.  Individuals may feel tired and listless, and not able to work as well.  Not only does production suffer as a result, but also the individual feels more of the burden of work.  It becomes increasingly harder to perform their regular tasks.

The health problems that result from heat stress can be serious. They include:

Heat Stroke, which is, by far, the most serious. 1700 people in the U.S. died of heat-related causes during one year. The mortality rate where individuals do not know how to handle this medical emergency can be upwards of 50%.  It’s that serious.

• Heat Syncope, which is fainting from exposure to heat. 

• Another is Heat Edema, which usually happens a day or two after the individual enters into a hot environment.  Heat Edema is the result of the body not able to dump the salt and water it is ingesting, and usually shows up as ankle swelling.

• Heat Cramps is another problem, which is a result of not enough salt. 

• Another major health problem is Heat Exhaustion.  In this case there is no sensation of thirst – usually because they have been drinking water already, but not enough.  The person exhibits headaches, nausea, vomiting, weakness, and anxiety.

We have a constant input of heat into our bodies and if we’re going to stay healthy, we have to have a constant output.  If we don’t have this output, we develop heat injuries.

Working in the heat

When you are working in the heat, there will be increased blood.  Exercising muscles require more blood, and, when you exercise, your muscles heat the blood.  The heated blood reaches the brain and tells the hypothalamus to cause skin vessel dilation and sweating. Heat loss then happens through the mechanisms of direct convection heat transfer from the body to the environment and from the evaporation of moisture from the skin.

As a rule, there is not enough blood volume to supply all the little skin vessels and capillaries in order to attempt to dissipate the heat loss.  The solution is to take in fluids to increase the volume.  Often, however, this is not enough.

The average individual may lose one to two liters of fluid without much decrease in performance.  When you become more dehydrated, however, your blood volume decreases and you cannot get rid of the heat load fast enough.  You just don’t have enough blood volume to supply the skin vessels for sweat production.  As a result, the body temperature begins to rise disproportionately as you become more dehydrated.

 Getting Rid of Heat

People who perform hard, physical work have two basic problems.

First is the amount of heat that their bodies produce because they are working.  Second, they are going to absorb heat out of the environment.  Heat lost from the person must equal the heat gained from the environment along with the heat the body produces from work. The problem is to maintain the heat balance of the worker. 

Basal metabolism, when you are not doing any work, produces 65 to 85 kilocalories/hr (like idling a car).  If you are just sitting at rest, the rate of rise form basal metabolism you normally produce per hour, will be about 2°F/hr.  If you work hard, you raise your body temperature at a rate of 9°F per hour.  Doing heavy labor will generate up to 570 calories per hour. Outside heat is added to that, i.e., sunshine alone adds 150 kc/hr.  There’s only so much a worker can handle before he must find some way to get rid of that extra heat. You can not stay in that environment very long.  You must get rid of the body heat build-up.

The physiologic mechanism for eliminating heat is through the evaporation of water, the evaporation of sweat.  Sweating is called upon when the physical means are no longer capable of eliminating heat, and our insensible water loss can’t keep up with production in the body.  Evaporation, or sweating, accounts for roughly 22% of the total heat loss from the body.  You can lose one kilocalorie for each 1.7 cc of sweat.

To handle a lot of heat requires the intake of a lot of fluids.  The stimulus for thirst as a rule is not enough to replace the body water loss.  Those of you who work in factories know that you must almost force workers to drink enough water.  Compound that problem with the fact that when air temperature exceeds 80°F, the body does not effectively lose heat by convection, or the evaporative cooling of the skin.  One actually begins to gain heat from the environment.

Summary

Simplified, work environments that are hot will create serious health problems for workers.  That, in turn, will also create economic loss for the company.  Relying on the human body to compensate is not enough.  Hoping that the workers will take necessary precautions is not enough, either.  Care and good planning is absolutely necessary to prevent the types of multiple problems that heat can create.  There are several approaches that can be taken, and all of them should be taken into consideration. 

 We offer one solution with our Magic Cool Bandannas.  These bandannas give an external source of moisture to create an evaporation cooling process right at the most vulnerable point.  They can’t cool the air, but they can cool the blood and the spinal column.   This product is not designed with an “R” factor in mind to retain coolness.  Rather it enhances the same powerful evaporative process the body already employs.  It also applies that cooling process right where it will be most effective, on the neck.

It is not the only solution to beat the heat, but is certainly one of the most cost effective, easily employed, and directly applied that there is.

Most of the information found in this article can be found in a publication produced by the American Society of Safety Engineers called “Heat Stress and Heat Disorders”.  This publication and other materials on this subject can be obtained from: 

                Wichita Chapter, American Society of Safety Engineers
                 PO Box 603, Wichita, KS  67201-0603