HEAT STRESS IN THE TRAINING ENVIRONMENT
BY DAVID F. CLARK, F.F., M.Ed.; DENISE L. SMITH, Ph.D.; STEVEN J. PETRUZZELLO, Ph.D.; AND BRADLEY G. BONE, F.F., R.N.
Since 1992, the University of Illinois Fire Service Institute, in conjunction with the University of Illinois Department of Kinesiology and the Department of Physical Education and Dance at Skidmore College in New York, has been investigating the problems of heat stress induced by firefighting tasks and compounded by turnout gear. The initial laboratory-based study, reported in the November 1994 and February 1996 issues of Fire Engineering, showed that firefighters experienced significantly greater cardiovascular, respiratory, and thermoregulatory stress and greater perceived exertion during standardized submaximal treadmill walking when wearing NFPA 1500 full encapsulation turnout gear than when wearing the hip boot and coat ensemble. Also, with full encapsulation, the distress took longer to abate after the work period was over. Firefighting involves strenuous physical activity that often is performed under hot and hostile conditions and results in substantial strain on the firefighter. The strain is a result of the combination of heavy physical work and extreme thermal stress. The physical work is imposed by a variety of equipment that must be manipulated (e.g., hoses, axes, ladders), the nature of the tasks performed (e.g., chopping, dragging), and the heavy and bulky protective equipment (i.e., turnout gear) and breathing apparatus that must be worn. The thermal stress results from a combination of the heat radiating from the fire and an increase in metabolic heat trapped around the firefighter`s body by the insulative properties of the protective clothing.
Previous studies have reported physiological and psychological responses of individuals wearing protective clothing during exercise in thermoneutral environments and/or in climate chambers.1,2,3 Despite the near-universal agreement that firefighting imposes significant physical and psychological stress, there is little or no research available regarding the physiological and psychological effects of firefighting drills in simulated firefighting conditions.
We felt that the physiological and psychological responses to firefighting training drills would be of interest because of the information they could provide regarding firefighter performance during actual firefighting activities. The purpose of this study, therefore, was to investigate selected physiological and psychological responses of firefighters to firefighting tasks in a concrete burn building containing controlled live fires.
METHOD
Fifteen male career and volunteer firefighters (age: 30.3 ± 6.0 years; weight: 85.4 ± 9.5 kg; height: 180.6 ± 1.1 cm) who were attending a breathing apparatus specialist course at the University of Illinois Fire Service Institute participated in the study.4
Measurements of heart rate were obtained from a wireless heart rate monitor (Polar Vantage XLT, Model 145900; Port Washington, New York) worn by the subjects, tympanic membrane temperatures were recorded using a FirstTempT infrared thermometer (Genius Model 3000A, Sherwood IMS, Inc., Carlsbad, California), and blood lactate levels were determined from blood samples obtained via a finger stick and analyzed by a blood lactate analyzer (YSI; 2300 STAT; Yellow Springs, Ohio).
Psychological measurements were also obtained. Ratings of perceived exertion, a judgment made by the firefighter of how hard he was working on the task, perceptions of respiration, perceptions of thermal sensations, and a measure of how subjects were feeling, were collected.
Testing Procedures
The firefighters performed two firefighting tasks (advancing a charged 134-inch hoseline and chopping on a wood block located four feet above the ground) for eight minutes each while inside the concrete burn building. A measurement station was set up on the first floor and the firefighting tasks were performed on the second floor, where three controlled fires were located. Ambient temperatures on the second floor ranged from 76.7 to 93.37C (l70.1 to 199.97F). Outside temperatures varied from 1.1 to 8.97C (34.0 to 48.07F). Subjects were tested individually; each test began at the measurement station.
Preliminary measurements were taken. Then for the first task, each firefighter was instructed to advance the 134-inch hoseline up an exterior fire escape and continue advancing the line inside to various locations on the second floor, as directed by an instructor waiting there. He did not attack the fires. After maneuvering the hose from room to room for eight minutes, the firefighter left the hose and descended the interior stairs for the second measurement period. Here, approximately one minute elapsed while measurements were obtained and the subject`s air tank was replaced.
The firefighter was then instructed to ascend the exterior fire escape and enter the second floor to perform the chopping task for eight minutes. Following this task, the firefighter again descended the interior stairs for the third and final measurements.
RESULTS
Physiological Variables
The average heart rate was 182.3 bmin-1 at the end of the second task. The heart rate after the first task was significantly higher than the pre-exercise rate. The rate after chopping was likewise significantly higher than after hose handling, indicating that heart rate continued to rise during the second eight minutes. The same pattern held true for tympanic temperatures. A tympanic membrane temperature (Rtym) of 40.17C (104.17F) was recorded at the completion of the second task. The fact that heart rate and tympanic temperature were so elevated after only eight minutes and continued to climb is of concern, since firefighters often must work for extended periods of time. Blood lactate was significantly higher after the first eight minutes but did not increase further during the second task. The blood lactate value suggests that the firefighters did exceed the onset of blood lactate accumulation (OBLA), indicating that they were working above 60 percent of their maximal oxygen consumption. Heart rate, temperature, and blood lactate data for the three measurement periods are shown in Figure 1.
Psychological Variables
Consistent with measurements of heat rate and temperature, greater distress was evident following the second task than the first. Perceptions of respiration, thermal sensations, and perceived exertion all increased from the hose drag task to the wood chopping task. Taken together, these data mirror the physiological strain experienced by the firefighters and indicate that they experienced a significant increase in psychological distress over the course of performing the firefighting tasks used in this study. The psychological responses are shown in Figure 2.
DISCUSSION
The present study was conducted to describe firefighters` physiological and psychological responses to completing, in full turnout gear, training tasks that closely resemble tasks that would be performed in an actual firefighting situation.
The heart rate data from this study suggest that firefighters achieve near maximal heart rates when involved in firefighting activities. These data are consistent with other studies. It is relevant to note that heart rates and tympanic membrane temperatures were quite high at the completion of only eight minutes of work and continued to rise during the second eight-minute task. This is likely the result of increased thermal stress caused by a combination of the heat load of the building and the metabolic heat produced by the heavy physical work. This is likely compounded by the body`s inability to cool itself normally because of the full encapsulation from the turnout gear.
More work needs to be done to describe the psychological response to firefighting and thermal stress. Few investigations have considered firefighters` psychological responses to firefighting tasks in a thermal environment. Some work has examined subjective ratings to varying intensities of physical work in different protective clothing ensembles, but this hasn`t been done in environments typically encountered by firefighters.
CONCLUSIONS
In summary, the combination of physical exertion in protective turnout gear and high thermal load leads to near maximal heart rates and significantly elevated tympanic temperatures after only 16 minutes of firefighting activities. The blood lactate data suggest that firefighters are working above OBLA but rely predominately on aerobic metabolism to support firefighting activities in the heat. This finding provides additional evidence to argue for high fitness levels for firefighters. Finally, the psychological data mirrored the greater physiological strain of performing firefighting tasks in a hot environment while wearing full turnout gear. n
This work was supported by the University of Illinois Research Board, a Collaborative Research Grant from Skidmore College, and the Fire Service Institute at the University of Illinois. The authors wish to thank all those who were involved in the completion of the study for their cooperation.
References
1. Duncan, H.W., G.W. Gardner, R.J. Barnard. “Physiological responses of men working in firefighting equipment in the heat,” Ergonomics; 1979:22, 521-527.
2. Sköldström, B. “Physiological responses of firefighters to workload and thermal stress,” Ergonomics; 1987:30, 1589-1597.
3. White, M.K., T.K. Hodous, “Reduced work tolerance associated with wearing protective clothing and respirators,” American Industrial Hygiene Association Journal; 1987:49, 523-530.
4. Smith D.L., S.J. Petruzzello, J.M. Kramer, J.E. Misner, “Physiological, psychophysical, and psychological responses of firefighters to firefighting training drills,” Aviation, Space, and Environmental Medicine; 1996:67, 1063-1068.
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Figure 1. Average physiological responses to the training drills (heart rate, top; tympanic temperature, middle; blood lactate, bottom). * indicates significant elevations from pre-task. ** indicates significant elevations from pre-task and from eight minutes. Figure 2. Average psychological responses to the training drills (perceptions of respiration, top; thermal sensations, middle; perceived exertion, bottom). * indicates significant elevations from the hose drag task to the wood chopping task.
DAVID F. CLARK, F.F., M.Ed., is a staff instructor at the University of Illinois Fire Service Institute in Champaign, Illinois.
DENISE L. SMITH, Ph.D., is an associate professor in the Department of Physical Education and Dance, Skidmore College, Saratoga Springs, New York, and a visiting professor at the University of Illinois Fire Service Institute in Champaign, Illinois.
STEVEN J. PETRUZZELLO, Ph.D., is an assistant professor in the Department of Kinesiology, University of Illinois at Urbana-Champaign, Urbana, Illinois.
BRADLEY G. BONE, F.F., R.N., is a field staff instructor at the University of Illinois Fire Service Institute in Champaign, Illinois.
