214 OSHA describes five types of heat disorders: Heat fatigue impairs performance of skilled sensorimotor, mental, or vigilant jobs. Treatment for heat fatigue is to remove the individual from the heat source. Heat rash, often called prickly heat, is the most common problem in hot work environments. Prickly heat is man- ifested as red papules on the skin and usually appears in areas where clothing is restrictive. As sweating in- creases, these papules give rise to a prickling sensation. Prickly heat occurs in skin that is persistently wetted by unevaporated sweat. In most cases, heat rashes will disappear when the affected individual returns to a cooler environment. Heat cramps* are sharp pains in the muscles that may occur alone or with one of the other heat stress disorders. In the workplace, heat cramps usually are caused by performing hard physical labor in a hot environment. Heat exhaustion* occurs when the body’s thermoregulatory system becomes overloaded and eventually fails. Heat exhaustion occurs when an individual performs strenuous activity in a hot environment for an extended pe- riod without consuming enough water, sodium, or both to replace what is lost to sweating. Heatstroke* occurs when the body’s temperature regulation system fails and the temperature rises to critical lev- els above 104°F (40°C). This condition is caused by a combination of highly variable factors, and its occurrence is difficult to predict. Heatstroke is considered a medical emergency. * A separate guideline follows for each of these conditions (see Guidelines 109A, 109B, and 109C). The American Conference of Governmental Industrial Hygienists has adopted threshold limit values for heat stress conditions designed to prevent the core temperature of workers from exceeding 100°F (38°C) (see the following table) (Adelakun, Schwartz, and Blias, 1999 American Conference of Governmental Industrial Hygienists, 2006). Threshold limit values for heat exposure establish work-rest regimens ranging from 25 percent to 75 percent rest during each hour based on wet-bulb globe temperature index, clothing, and workload (Adelakun et al., 1999). The wet-bulb temperature index is a heat stress indicator that measures the effects of temperature, humidity, and radiant energy using a wet-bulb globe temperature meter (Aerographer/Meteorology, 2006). Currently, the wet-bulb globe temperature index is the most common technique used to measure environmental factors that correlate with deep (core) body temperature and other physiologic responses to heat (U.S. Department of Labor, 2006). Permissible Heat Exposure Threshold Limit Values* Work–Rest Regimen Light Moderate Heavy Continuous work 30.0°C (86°F) 26.7°C (80°F) 25.0°C (77°F) 75% Work, 25% rest, each hour 30.6°C (87°F) 28.0°C (82°F) 25.9°C (78°F) 50% Work, 50% rest, each hour 31.4°C (89°F) 29.4°C (85°F) 27.9°C (82°F) 25% Work, 75% rest, each hour 32.2°C (90°F) 31.1°C (88°F) 30.0°C (86°F) *Temperatures are according to the wet-bulb globe temperature (WBGT) index. These threshold limit values are based on the assumption that nearly all acclimatized, fully clothed workers with adequate water and salt intake should function effectively under the given working conditions without exceeding a core body temperature of 38∞C (100.4∞F). They are also based on the assumption that the WBGT of the resting place is the same as or close to that of the workplace. Where the WBGT of the work area is different from that of the rest area, a time-weighted average should be used (the American Conference of Governmental Industrial Hygienists 1992–1993 Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices should be consulted). Source: From the U.S. Department of Labor. (2006). OSHA technical manual on heat stress. Retrieved December 6, 2006, from www.osha.gov/dts/osta/otm/tm_ii/otm_iii_4.html. It is important that management and workers recognize the symptoms of heat-related stress and illnesses and know to seek treatment. OSHA has developed a heat stress card that employees will find useful. Guideline continues on next page