Evaluation of heat stress, heat strain, and rhabdomyolysis in park employees
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Evaluation of heat stress, heat strain, and rhabdomyolysis in park employees

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      The Health Hazard Evaluation Program received a request from the safety manager at a national park in California. The safety manager asked NIOSH to evaluate park employees working in extreme heat, review the park's current and proposed heat stress management policies, and recommend ways to prevent heat-related illnesses. The park covers 3.4 million acres with elevations ranging from 282 feet below sea level to 11,049 feet above sea level. July is the hottest month in the park, when average daily temperatures are 88°F-116°F. The park had a stargazing program that discouraged night-time activities (including maintenance work) requiring the use of artificial lighting. Park maintenance activities were scheduled as funding became available without regard to the season. In July 2013 we (1) measured core body temperature and heart rate in nine employees on 4 days; (2) analyzed employees' blood for markers of muscle breakdown and dehydration; (3) asked employees about their work history, medical history, and health symptoms; (4) measured temperature and humidity; (5) asked about symptoms of heat-related illness and muscle breakdown; and (6) reviewed the park's current and proposed heat stress policies and records of work-related injuries and illnesses. We found environmental conditions above limits for heat stress at work. Employees performed moderate to heavy tasks in elevated wet bulb globe temperatures (WBGT) conditions for longer periods of time than are recommended by NIOSH. One employee had a core body temperature over our defined heat strain criteria and several employees had sustained maximum heart rates consistent with heat strain. No employees were dehydrated or had significant muscle breakdown at work. The park had a heat stress policy, but it did not follow NIOSH heat stress recommendations for work and rest times. Additionally, employees did not follow the policy "buddy system." We recommended park managers (1) schedule strenuous outdoor work during cooler months, at night, or early in the morning; (2) reduce the amount of time employees work in extremely hot weather; (3) form a work group of employees, the safety manager, and a physician medical advisor to develop standard operating procedures for self-monitoring when working in the heat; (4) train employees on how to recognize early signs and symptoms of heat-related illness, and (5) revise the heat stress policy to include work/rest periods based on NIOSH WBGT and workload changes. We recommended the employees follow the heat stress policy, carry a radio, use the buddy system, learn the signs and symptoms of heat strain, drink plenty of fluids, take rest breaks as needed, and tell your supervisor immediately if you have symptoms of heat-related illness or if you note these symptoms in a coworker. NIOSHTIC No. 20044660
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