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Understanding the Heat Equation

The heat equation is a simple way to determine the circumstances under which the human body’s cooling system could fail, and when employees exerting themselves physically in the heat could be at risk of heat illness.

Any environment that combines high temperature, high humidity, and physical exertion-whether work or sport-is a prime source of heat-related illness.

How the Body Cools Itself

The body has a natural cooling system that is used to protect internal organs-particularly the brain-from increases in temperature. When blood temperature exceeds 98.6° Fahrenheit, your heart rate increases and your blood circulates closer to the surface of the skin. This allows heat to
transfer out of the blood and into the cooler environment outside the body. But this heat transfer is only effective if the temperature outside the body is less than inside.

If your body can’t lose enough heat by transferring heat out of the bloodstream, your brain will signal the sweat glands to start sending fluids to the surface of the skin. Once the sweat reaches the surface of the skin, the sweat will be evaporated off the skin by the hot, dry environment outside the body. The body’s heat will dissipate with the evaporated sweat.

But when the humidity is high as well as the temperature, the body’s natural cooling system isn’t very effective. High heat prevents cooling through heat transfer out of the bloodstream, and high humidity prevents sweat from evaporating. The result can be heat-related illness.

Health Effects—Heat Disorders

Heat stroke, 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. Signs include: mental confusion, delirium, loss of consciousness, convulsions or coma; a body temperature of 106 degrees Fahrenheit or higher; and hot dry skin which may be red, mottled or bluish. Victims of heat stroke will die unless treated promptly. While medical help should be called, the victim must be removed immediately to a cool area and his/her clothing soaked with cool water. He/she should be fanned vigorously to increase cooling. Prompt first aid can prevent permanent injury to the brain and other vital organs.

Heat exhaustion develops as a result of loss of fluid through sweating when a worker has failed to drink enough fluids or take in enough salt, or both. The worker with heat exhaustion still sweats, but experiences extreme weakness or fatigue, giddiness, nausea, or headache. The skin is clammy and moist, the complexion pale or flushed, and the body temperature normal or slightly higher. Treatment is usually simple: the victim should rest in a cool place and drink salted liquids. Salt tablets are not recommended. Severe cases involving victims who vomit or lose consciousness may require longer treatment under medical supervision.

Heat cramps, painful spasms of the bone muscles, are caused when workers drink large quantities of water but fail to replace their bodies’ salt loss. 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 salted liqids by mouth or saline solutions intravenously for quicker relief, if medically determined to be required.

Fainting may be a problem for the worker unacclimatized to a hot environment who simply stands still in the heat. Victims usually recover quickly after a brief period of lying down. Moving around, rather that standing still, will usually reduce the possibility of fainting.

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 and impairs a worker’s performance or even results in temporary total disability. It can be prevented by showering, resting in a cool place, and allowing the skin to dry.

Dealing With Hot Work Environments

If you are responsible for monitoring workers in a high heat environment- indoors or out- you need to be aware of measures that should be taken to prevent employees from overheating. You also need to be aware that no matter how prepared you might be, or how well you train workers about the dangers of hot environments, there will always be those that seek shortcuts, or disregard precautions. How well or how poorly an individual reacts to heat stress is dependent on personal characteristics such as age, weight, fitness, medical condition, and acclimatization. Persons with heart or circulatory diseases or those who are on “low salt” diets, for example, are at high risk for heat related illnesses.

Vigilance of supervisors and managers is critical in ensuring that preventative policies and procedures are observed, as well as identifying danger signals that indicate a worker in distress.

There are general guidelines to assist in establishing work plans for a hot environment, but it is unwise to establish a “one-size-fits-all” policy. Each environment is different. Procedures that work in the morning may not be as applicable in the afternoon. Changing environmental conditions such as cloud coverage, wind (or lack thereof), humidity- all play a role in determining how much exposure workers can safely tolerate. Indoor conditions can also change across the course of a shift due to changing humidity levels, outside temperatures, or influences from other work processes occurring nearby.

Tomorrow we will look at Engineering and Administrative controls that can be used to mitigate the possibility of heat illnesses in the workplace.

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Categories: Health, Safety, Training
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