Thermal Stress Guidelines
In the northeastern part of the United States we typically encounter hot temperatures between the months of June and September. On some days outside temperatures can approach 100.0 Fahrenheit (F). On days in which the relative humidity is high the outside environment can be an undesirable place to be. If your job entails vigorous activity in a hot climate, heat stress can be a major occupational hazard.
Fortunately, the human body is pretty efficient at keeping our body temperatures constant. In order to maintain our body temperatures at a constant temperature, the body must release the heat. This is carried out through blood circulation and sweating. Once your body temperature reaches 98.6F, your heart begins to pump more blood through the circulatory system. Blood vessels expand and allow more blood flow to the skin surface where the excess heat can be released through the skin.
If this process is not enough to cool the body, your brain tells your sweat glands in the skin to release large quantities of sweat onto the skin surface. As the sweat evaporates it cools the skin by eliminating heat from the body. In environments with high humidities this process is hindered because the evaporative process is decreased and it is harder for the body to cool itself.
The problems resulting from this situation can range from being uncomfortable to death. With so much blood being pumped to the skin it is hard for the body to maintain its normal functions. Increased body temperature and physical discomfort promote irritability, anger, and other emotional states, that can cause workers to bypass safety procedures or to lose concentration while performing hazardous job functions.
There are many occupations that require workers to be in hot and humid environments. Outdoor jobs may include; construction, roofing, groundskeeping, or farming. Hot indoor occupations can include; bakery and restaurant kitchen workers, brick firing and ceramic processes, foundries, mines, boiler rooms, laundries, and glass manufacturing to name a few.
The following is a description of the potential harmful effects of heat (listed from the most dangerous to the least) courtesy of the Occupational Safety and Health Administration (OSHA)
Heat stroke occurs when the body's system of temperature regulation fails and body temperature rises to critical levels. This condition is caused by a combination of highly variable factors, and its occurrence is difficult to predict. Heat stroke is a medical emergency. The primary signs and symptoms of heat stroke are confusion; irrational behavior; loss of consciousness; convulsions; a lack of sweating (usually); hot, dry skin; and an abnormally high body temperature, e.g., a rectal temperature of 41°C (105.8°F). If body temperature is too high, it causes death. The elevated metabolic temperatures caused by a combination of workload and environmental heat load, both of which contribute to heat stroke, are also highly variable and difficult to predict.
If a worker shows signs of possible heat stroke, professional medical treatment should be obtained immediately. The worker should be placed in a shady area and the outer clothing should be removed. The worker's skin should be wetted and air movement around the worker should be increased to improve evaporative cooling until professional methods of cooling are initiated and the seriousness of the condition can be assessed. Fluids should be replaced as soon as possible. The medical outcome of an episode of heat stroke depends on the victim's physical fitness and the timing and effectiveness of first aid treatment.
Morningside campus employees should call x99 (on campus) or 212)854-5555 (off campus) immediately if he/she suspects that an employee is experiencing heat stroke.
Regardless of the worker's protests, no employee suspected of being ill from heat stroke should be sent home or left unattended unless a physician has specifically approved such an order.
The signs and symptoms of heat exhaustion are headache, nausea, vertigo, weakness, thirst, and giddiness. Fortunately, this condition responds readily to prompt treatment. Heat exhaustion should not be dismissed lightly, however, for several reasons. One is that the fainting associated with heat exhaustion can be dangerous because the victim may be operating machinery or controlling an operation that should not be left unattended; moreover, the victim may be injured when he or she faints. Also, the signs and symptoms seen in heat exhaustion are similar to those of heat stroke, a medical emergency.
Workers suffering from heat exhaustion should be removed from the hot environment and given fluid replacement. They should also be encouraged to get adequate rest.
Heat Cramps are usually caused by performing hard physical labor in a hot environment. These cramps have been attributed to an electrolyte imbalance caused by sweating. It is important to understand that cramps can be caused by both too much and too little salt. Cramps appear to be caused by the lack of water replenishment. Because sweat is a hypotonic solution (±0.3% NaCl), excess salt can build up in the body if the water lost through sweating is not replaced. Thirst cannot be relied on as a guide to the need for water; instead, water must be taken every 15 to 20 minutes in hot environments.
Under extreme conditions, such as working for 6 to 8 hours in heavy protective gear, a loss of sodium may occur. Recent studies have shown that drinking commercially available carbohydrate-electrolyte replacement liquids is effective in minimizing physiological disturbances during recovery.
Heat Collapse ("Fainting"). In heat collapse, the brain does not receive enough oxygen because blood pools in the extremities. As a result, the exposed individual may lose consciousness. This reaction is similar to that of heat exhaustion and does not affect the body's heat balance. However, the onset of heat collapse is rapid and unpredictable.
To prevent heat collapse, the worker should gradually become acclimatized to the hot environment.
As sweating increases, these papules give rise to a prickling sensation. Prickly heat occurs in skin that is persistently wetted by unevaporated sweat, and heat rash papules may become infected if they are not treated. In most cases, heat rashes will disappear when the affected individual returns to a cool environment.
A factor that predisposes an individual to heat fatigue is lack of acclimatization. The use of a program of acclimatization and training for work in hot environments is advisable. The signs and symptoms of heat fatigue include impaired performance of skilled sensorimotor, mental, or vigilance jobs. There is no treatment for heat fatigue except to remove the heat stress before a more serious heat-related condition develops.
Courtesy of the National Institute of Occupational Safety and Health NIOSH.
One of the best ways to reduce heat stress is to minimize heat in the workplace. However, there are some work environments where heat production is difficult to control, such as when furnaces or sources of steam or water are present in the work area or when the workplace itself is outdoors and exposed to varying warm weather conditions.
Humans are, to a large extent, capable of adjusting to the heat. This adjustment to heat, under normal circumstances, usually takes about 5 to 7 days, during which time the body will undergo a series of changes that will make continued exposure to heat more endurable.
On the first day of work in a hot environment, the body temperature, pulse rate, and general discomfort will be higher. With each succeeding daily exposure, all of these responses will gradually decrease, while the sweat rate will increase. When the body becomes acclimated to the heat, the worker will find it possible to perform work with less strain and distress.
Gradual exposure to heat gives the body time to become accustomed to higher environmental temperatures. Heat disorders in general are more likely to occur among workers who have not been given time to adjust to working in the heat or among workers who have been away from hot environments and who have gotten accustomed to lower temperatures. Hot weather conditions of the summer are likely to affect the worker who is not acclimatized to heat. Likewise, workers who return to work after a leisurely vacation or extended illness may be affected by the heat in the work environment. Whenever such circumstances occur, the worker should be gradually reacclimatized to the hot environment.
In the course of a day's work in the heat, a worker may produce as much as 2 to 3 gallons of sweat. Because so many heat disorders involve excessive dehydration of the body, it is essential that water intake during the workday be about equal to the amount of sweat produced. Most workers exposed to hot conditions drink less fluids than needed because of an insufficient thirst drive. A worker, therefore, should not depend on thirst to signal when and how much to drink. Instead, the worker should drink 5 to 7 ounces of fluids every 15 to 20 minutes to replenish the necessary fluids in the body. There is no optimum temperature of drinking water, but most people tend not to drink warm or very cold fluids as readily as they will cool ones.
Whatever the temperature of the water, it must be palatable and readily available to the worker. Individual drinking cups should be provided--never use a common drinking cup.
Heat acclimatized workers lose much less salt in their sweat than do workers who are not adjusted to the heat. The average American diet contains sufficient salt for acclimatized workers even when sweat production is high. If, for some reason, salt replacement is required, the best way to compensate for the loss is to add a little extra salt to the food. Salt tablets should not be used.
- Drink a lot of cool water all day, before you feel thirsty. Every 15 minutes, you may need a cup of water (5 to 7 ounces).
- Keep taking rest breaks. Rest in a cool, shady spot. Use fans.
- Wear light-colored clothing, made of cotton.
- Work in the shade.
- For heavy work in hot areas, take turns with other workers, so some can rest.
- If you travel to a warm area for a new job, you need time for your body to get used to the heat. Be extra careful the first 2 weeks on the job.
- If you work in protective clothing, you need more rest breaks. You may also need to check your temperature and heart rate.
Unfortunately, from time to time, the air-conditioning units servicing the Morningside Campus buildings breakdown. For employees who work indoors, this situation can be an uncomfortable experience. If the air conditioning unit in your work area is not functioning properly, your Area Manager should be notified. Your supervisor can contact your building area manager and place a request to the University's HVAC shop to make the necessary repairs to your unit.
While the HVAC system is being repaired supervisors should allow employees to take breaks in cool areas. In addition, there should be an adequate supply of drinking water available.
The EH&RS office possesses instrumentation that can measure ambient temperatures, relative humidity, and heat stress. Work/rest regimens can be provided to employees who must work outdoors on hot days (ex. grounds staff), in hot indoor environments (ex. boiler room mechanics), or in protective clothing. The EH&S office utilizes the guidelines set forth by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (ASHRAE) and the American Conference of Governmental Industrial Hygienists (ACGIH) when assessing the conditions associated with working in environments with elevated temperatures and relative humidities.
ASHRAE recommends that indoor office temperatures during the summer months should be between 73F to 79F with a relative humidity between 40 to 60 percent. If indoor temperatures and/or relative humidities rise above these recommended ranges, your supervisor should notify your area manager who can arrange for an investigation into the situation.
If you have a job that requires you to work in a hot environment, and you have questions regarding heat stress, please contact the EH&S office.