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MSHA News Release No. 98-0730
Mine Safety and Health Administration
Contact: Amy Louviere
Phone: (703) 235-1452

Thursday, July 30, 1998

MSHA Urges Miners to Stay Cool

With summer temperatures continuing at high levels throughout much of the nation, the Mine Safety and Health Administration (MSHA) is urging all surface and underground miners to avoid prolonged exposure to excessive heat.

In mining, as in other industries, exposure of workers to excessively hot conditions can cause problems including heat stroke, heat exhaustion, heat cramps and heat rash. In addition, symptoms associated with excessive exposure to heat can adversely affect a miner's capacity to work safely,especially in regard to dexterity and coordination, the ability to remain alert during lengthy and monotonous tasks, and the ability to make quick decisions.

"Miners are exposed to so many potential health and safety hazards, they cannot afford to lose their edge on the job," said J. Davitt McAteer, assistant labor secretary for mine safety and health. "Intense heat takes its toll -- both physically and mentally. Consequently, mine operators need to moderate the heat in work areas and to minimize workers' time in hot places. One solution might be to schedule the most physically grueling activities during the coolest parts of the day."

In surface mines and mills, the primary heat sources include the sun, machines, dryers and kilns. Wall-rock, which is the rock immediately adjoining mineral deposits, is the primary source of heat in underground mines. In addition, powered equipment that is operated underground -- diesel engines, electric motors and compressed air equipment -- greatly contribute to the heat load of a mine.

Deep underground metal and non-metal mining operations, prevalent in the western United States, are some of the hotter work sites for miners because of the unusually high heat flow from the earth. The average temperature range for underground mineral mines may vary from 77 to 92 degrees; rock temperature may run as hot as 120 or 130 degrees. As the depth of mining increases for the development of new sources of minerals, more and more miners may be exposed to hotter levels of the earth's crust.

Generally speaking, work site temperatures, humidity and air movement can be controlled to lower the heat load and to provide tolerable work conditions in hot mines. Mine planning, ventilation and air conditioning may reduce the heat stress to acceptable levels. At a point, however, these control measures can fail to prevent the temperature rise in a worker's body core, and proper work practices that include frequent breaks may be the only heat-stress control measure.

Heat stroke is the most serious health problem associated with work in hot environments. It occurs when the body's temperature regulatory system fails. A heat stroke victim may become mentally confused, delirious or unconscious as the skin becomes hot, dry, red or spotted. A person with signs or symptoms of heat stroke requires immediate hospitalization to lower the body temperature.

Heat exhaustion is caused by the loss of large amounts of fluid and electrolytes. A worker suffering from heat exhaustion experiences extreme weakness or fatigue, giddiness, nausea or headache. The skin becomes clammy and moist, and the complexion becomes pale or flushed. Rest in a cool place and an ample supply of water or commercially available liquids containing electrolytes are usually all that is needed for a complete recovery.

Heat cramps are painful spasms of the muscles that occur among those who sweat profusely, drink large quantities of water, and do not adequately replace the body's electrolyte loss. Relief comes with the replenishment of electrolytes.

Heat rash, also known as prickly heat, is likely to occur in hot, humid environments where sweat is not easily removed from the skin by evaporation and the skin remains wet most of the time. The sweat ducts become plugged and a skin rash soon appears. Loose garments and good personal hygiene are the best preventative.