Mining Health Hazard Evaluation Report 78-101-100, Field Study of Heat Stress at a Surface Coal Mine, Man, West Virginia

摘要

The level of heat stress was evaluated using two Bendix Electronic Wet Bulb Globe Temperature (WBGT) instruments, two Standard WBGT Set-ups and three Botsballs (WGT). Four types of vehicles were surveyed: (1) 50-ton Kenworth coal truck, (2) 40-ton Cline coal truck, (3) D9 earthmover, and (4) 50 ton 773 Caterpillar rock truck. From a previous NIOSH investigation under similar conditions, a metabolic heat production level of 153 kilocalories per hour (Kcal/hr) was determined for a D9 earthmover operator. This is the value used to determine WBGT Threshold Limit Values (TLVs) and work rest cycles. A Kenworth coal truck, earthmover, and rock truck were studied on July 21, 1978. On both days a WBGT station was set up in the area of operation of an earthmover. Figures 1, 2 and 3 show the dry-bulb temperatures measured for both days. The maximum daily temperature was reached between 3 and 4 p.m. on July 21, 1978. Hourly WBGT time weighted averages were calculated and plotted in Figures 4 and 5. The TLV for continuous work of this type is 88 degrees fahrenheit for workers used to doing this type work in similar conditions (acclimatized). This level was exceeded in the vehicle cab on July 20 by the earthmover and on July 21 by the earthmover and rock truck.