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MSHA News Release No. 2000-0825
Mine Safety and Health Administration
Contact: Amy Louviere
Phone: (703) 235-1452 

 Released Friday, August 25, 2000

MSHA Urges Miners to Keep Cool

   With summer in full swing and temperatures in the West at record-setting highs, the U.S. Department of Labor's Mine Safety and Health Administration (MSHA) is urging all surface and underground miners to avoid prolonged exposure to extreme heat. Over the past five years, about 150 miners have suffered from heat-related illnesses where they required time off, medical treatment or hospitalization.

   In mining, as in other industries, workers exposed to excessively hot conditions can suffer from a variety of heat-related disorders, from the relatively mild heat rash to life-threatening heat stroke. Miners most likely to succumb to heat stress are those not acclimatized to the high temperature, have had a previous heat-related illness, take certain medication, are over 45 or in poor physical condition.

   In surface mines and mills, the primary heat sources include the sun, machines, dryers and kilns. In underground mines, rock that adjoins mineral deposits is a primary source of heat. Furthermore, diesel engines, electric motors and compressed air equipment operated underground 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 Fahrenheit; 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.

   Depending upon the severity of exposure, symptoms of heat stress may range from clammy skin to muscle spasms, dizziness, nausea, abnormally high body temperatures, disorientation and convulsions. In even the most minor cases, heat can adversely affect a miner's capacity to work safely, cause loss of dexterity and coordination, and hamper his ability to make quick decisions.

To prevent heat stress, MSHA recommends the following:

   For further information about heat stress, visit MSHA's web site at