Health hazard evaluation report: HETA-2000-0066-2892, United States Air Force Davis-Monthan Air Force Base, Tucson, Arizona.
The National Institute for Occupational Safety and Health (NIOSH) received a health hazard evaluation (HHE) request from the management of the United States Air Force Institute for Environmental, Safety, and Occupational Risk Analysis (AFIERA), Brooks Air Force Base (AFB), San Antonio, Texas. The request indicated that Air Force recruits employed as aircraft fuel systems inspection and repair workers at Davis-Monthan AFB, Tucson, Arizona, were exposed to heat stress, jet fuel, and jet fuel vapors in confined spaces (aircraft fuel tanks). The employees reported experiencing dizziness, lethargy, skin irritation, and a 'jet-fuel taste' during and long after exposure to jet fuel. The requesters asked NIOSH to evaluate the heat stress aspects of the employee complaints and make recommendations to prevent heat illness among the employees. The evaluation was part of an on-going collaborative study of Air Force employees' acute exposure to jet fuel (JP-8), and the other concerns were addressed by this larger study. Data were collected April 10-14, 2000. Individual and task-specific metabolic rates were estimated, and wet bulb globe temperatures (WBGTs) were measured. Heat strain monitoring included core body temperature (CBT) and heart rate measurements on 25 participants and pre- and post-shift body weight measurements on 12 participants. The sampling results were compared to the NIOSH recommended action limits and recommended exposure limits (RALs/RELs) and the American Conference of Governmental Industrial Hygienists (ACGIH®) Threshold Limit Values (TLVs®). NIOSH and ACGIH assess heat stress using sliding scale limits based on environmental and metabolic heat loads. In addition, ACGIH provides physiological heat strain limits useful for those wearing impermeable personal protective equipment (PPE) and in situations of excess heat stress. For individuals with normal cardiac performance, ACGIH recommends that sustained (over several minutes) heart rate should remain below 180 beats per minute (bpm) minus age (in years), maximum CBT should remain below 100.4 F for unselected, unacclimatized personnel (101.3 F for medically selected, acclimatized personnel), recovery heart rate at one minute after a peak work effort should be below 110 bpm, and there should be no symptoms of sudden and severe fatigue, nausea, dizziness, or lightheadedness. The results of the evaluation indicated that all of the participants were acclimatized to their work environment and that none were exposed to heat stress conditions in excess of the screening criteria. However, 5 of 25 participants (20%) experienced heat strain signs (CBT and/or HR in excess of the ACGIH criteria). In addition, 2 of 12 participants (17%) had greater than 1.5% body weight loss over their shifts indicating they were at greater risk of developing a heat-related illness. Seven participants (58%) developed mild dehydration (any body weight loss of 1.5% or less) during their job activities. Overall, body weight changes ranged from -2.3% to +0.6%, with a median percent body weight change of -0.3%. Because of the work environment, the potential for heat strain increases as temperatures rise during the spring and summer. This factor and the study results justify continuing to include personnel in the Davis-Monthan AFB heat stress management program. In addition, participants were not aware of having developed heat strain, indicating a need for a physiological self-monitoring program to be added to the heat stress program. During our evaluation, health hazards from environmental conditions and overwork did not exist for fuel cell maintenance and other workers. However, hazardous environmental conditions can exist during spring and summer, and 20% of participants developed heat strain as indicated by the physiological monitoring results (CBT and heart rate levels in excess of occupational criteria). Also, of the 12 participants who were weighed pre- and post-shift, 9 developed at least mild dehydration and 2 were dehydrated. Davis-Monthan AFB has a formal heat stress program and a system for reporting heat-related illnesses. Recommendations are made to implement physiological (heat strain) monitoring, to develop an acclimatization schedule, and to take WBGT measurements in or around immediate work areas at least hourly during the hottest parts of the shift and hottest months of the year.