U.S. Department of Labor
Occupational Safety & Health Administration

THREAT OF NO SWEAT

The rate at which people sweat is determined not only by genetics, but by hydration, state of acclimation, and aerobic fitness.

Hydration is the simplest to explain: You can't sweat if your body doesn't have enough water. The fire service the world over knows that to maintain normal body function, fluid must be replaced as soon as possible. It's also well known that by the time you experience thirst, you are probably already dehydrated. That's when potential functional capacity will be significantly reduced.

Acclimation is a physiological adaptation that the human body makes with repeated exposures to heat stress during exercise; it increases our rate of sweat production, shortens the time it takes for sweating response to start and conserves sodium. Some of the best-acclimated firefighters are breathing apparatus training officers because they're repeatedly exposed to heat during fire training.

Regular and sustained aerobic exercise can elicit a similar response. Firefighters who maintain an adequate level of fitness will have reduced cardiovascular strain and lower core temperature for the same level of heat stress. Fit firefighters also tend to have reduced levels of body fat, which means that they don't have to carry around extra non-functional weight. In other words, less energy will be required by a fit person to do the same job as a less-fit person. Body fat also is a very good insulator and will compromise the body's ability to lose heat.

Of course, it doesn't matter how hydrated, how acclimated or how fit a person is — if the sweat cannot evaporate, then thermo-regulation will be compromised. It's therefore essential that firefighters are aware of the signs and symptoms of heat stress so that it can be identified early and the appropriate measures taken.

At the first sign of any of these symptoms, firefighters should notify the officer in charge, who will take appropriate action, which can include:

• Instituting work/rest cycles.
• Keeping cool and avoiding radiant heat.
• Drinking small amounts of appropriate fluids.
• Avoiding coffee, tea and alcoholic beverages.
• Using water spray bottles, damp towels and misting fans.
• Ice packs are not recommended.

www.osha.gov

U.S. Department of Labor
Program Highlights

Fact Sheet No. OSHA 95-16

Many workers spend some part of their working day in a hot environment. Workers in foundries, laundries, construction projects, and bakeries -- to name a few industries -- often face hot conditions which pose special hazards to safety and health.

HEAT STRESS CAUSES BODY REACTIONS

Four environmental factors affect the amount of stress a worker faces in a hot work area: temperature, humidity, radiant heat (such as from the sun or a furnace) and air velocity. Perhaps most important to the level of stress an individual faces are personal characteristics such as age, weight, fitness, medical condition and acclimatization to the heat.

The body reacts to high external temperature by circulating blood to the skin which increases skin temperature and allows the body to give off its excess heat through the skin. However, if the muscles are being used for physical labor, less blood is available to flow to the skin and release the heat.

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

Of course there are many steps a person might choose to take to reduce the risk of heat stress, such as moving to a cooler place, reducing the work pace or load, or removing or loosening some clothing.

But the body cannot dispose of excess heat, it will store it. When this happens, the body's core temperature rises and the heart rate increases. As the body continues to store heat, the individual begins to lose concentration and has difficulty focusing on a task, may become irritable or sick and often loses the desire to drink. The next stage is most often fainting and death is possible if the person is not removed from the heat stress.

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 (1) mental confusion, delirium, loss of consciousness, convulsions or coma; (2) a body temperature of 106 degrees F or higher; and (3) hot dry skin which may be red, mottled, or bluish. Victims of heat stroke will die unless treated promptly. While awaiting medical help, the victim must be removed to a cool area and his or her clothing soaked with cool water. He or she should be fanned vigorously to increase cooling. Prompt first aid can prevent permanent injury to the brain and other vital organs.

Heat exhaustion results from 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 an electrolyte solution (a beverage used by athletes to quickly restore potassium, calcium, and magnesium salts). Severe cases involving victims who vomit or lose consciousness may require longer treatment under medical supervision.

Heat cramps, painful spasms of the 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 liquids by mouth or saline solutions intravenously for quicker relief, if medically determined to be required.

PREVENTING HEAT STRESS

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

1. A variety of engineering controls including general ventilation and spot cooling by local exhaust ventilation at points of high heat production may be helpful. Shielding is required as protection from radiant heat sources. Evaporative cooling and mechanical refrigeration are other ways to reduce heat. Cooling fans can also reduce heat in hot conditions. Eliminating steam leaks 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.

2. Work practices such as providing plenty of drinking water -- as much as a quart per worker per hour -- at the workplace can help reduce the risk of heat disorders. Training first aid workers to recognize and treat heat stress disorders and making the names of trained staff known to all workers is essential. 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 greater risk.

3. 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 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.

4. 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 5-day period of acclimatization. This period should begin with 50 percent of the normal workload and time exposure the first day and gradually building up to 100 percent on the fifth day.

5. Employee education is vital so that workers are aware of the need to replace fluids and salt lost through sweat and can recognize dehydration, exhaustion, fainting, heat cramps, salt deficiency, heat exhaustion, and heat stroke as heat disorders. Workers should also be informed of the importance of daily weighing before and after work to avoid dehydration.

MORE INFORMATION

A 15-page booklet, Working in Hot Environments, is available free from National Institute for Occupational Safety and Health Publications, 4676 Columbia Parkway, Cincinnati, Ohio 45226; telephone (513) 533-8287.

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