PHYSIOLOGICAL RESPONSES TO WORKING IN BUNKER GEAR: A COMPARATIVE STUDY
Editor’s note: Research that was the basis for this paper was conducted in June, 1992. 1990 NFPA statistics cited herein were the most recent available when the study was conducted.
In 1975, legislation mandated the initiation of “Project FIRES” to develop a garment that would provide firefighters with greater protection from burns. Fully encapsulated gear, termed “NFPA 1500″ or “bunker” gear, resulted from this project. This gear is currently used by many municipal fire departments.
As of 1990, burns accounted for four percent of all volunteer firefighting deaths, six percent of all career deaths, and nine percent of all (volunteer and career) fireground injuries.’ (Editor’s note: The National Fire Protection Association reported that burns accounted for 3.6 percent of all volunteer firefighting deaths. 18.2 percent of all career firefighting deaths, and 7.8 percent of all firefighting deaths nationwide for the year 1993. In 1992, 9.8 percent of fireground injuries resulted from burns.) Although the gear may have played a role in reducing the percentage of deaths/injuries from bums, it also may have exacerbated a problem that has continued to plague firefighters and, thus, equipment manufacturers—heat stress. This paper does not presume to answer the question. Which gear is best for a firefighter? Its purpose is to add information crucial to this ongoing and important debate. Our focus was to investigate the cardiovascular and thermoregulatory responses of firefighters while performing physical work in firefighting turnout gear.
THE HEAT-STRESS FACTOR
Ideally, firefighters want gear that not only provides optimal thermal protection but also adds little to the cardiovascular/thermoregulatory stress when fighting fires. Currently, heart attacks account for approximately 36 percent of on-duty fire deaths, w hereas bums account for about five percent of firefighter deaths.’ (Editor’s note: NFPA data indicate that heart attacks accounted for 50.6 percent of all on-duty firefighter deaths in 1993. Of the 34 fireground deaths in 1993. 52.9 percent were due to heart attacks.)
In light of the relatively low number of deaths due to bums and the steady and much greater incidence of heart attacks, it seems reasonable to ask an important question: Is the new NFPA 1500 gear inadvertently exacerbating heat stress in exchange for greater protection from burns? It can be argued that most of the deaths due to heart attack and stroke are related to heat stress and physical exertion—that is, competing demands arise from the need to provide adequate blood flow to the metabolically active muscles and to the periphery in an attempt to cool the body, thus overwhelming the cardiovascular system. In 1990, all heart attack deaths of on-duty firefighters were due to stress and overexertion. (Editor’s note: 95 percent of 1993 firefighter deaths from heart attacks were due to stress or overexertion. according to the NFPA.)
The cause of the extreme physical response to w’ork in firefighting gear has been addressed by Faff and Tutak? These authors purport that the physical strain induced by the use of the protective equipment during exercise in an environmental chamber can be attributed mainly to the heat stress connected within the very humid microclimate generated inside the suit; the turnout gear retains the heat generated by the body. As a result, the firefighter’s cardiovascular response is altered: A competition ensues between the muscles that need an adequate amount of blood to support the metabolically active muscle and the body’s heat-dissipating mechanisms, which require increased skin blood flow to rid the body of excess heat. The NFPA 1500 gear, the authors say. limits evaporative cooling by acting as a second skin.
The 1500 gear, therefore, affects the thermal gradient between the environment and the skin by increasing the number of air layers. As a result, a greater amount of heat is stored next to the body, preventing further heat loss from the skin. As heat builds up. the heart attempts to pump more blood to the surface. This increases not only the body’s heart rate but the workload of the heart as well.
Although it is known that firefighting gear contributes to the firefighter’s workload by adding bulk and weight and decreasing the body’s cooling capacity, little work has been done to quantify firefighters’ physiological response to different configurations of firefighting gear.
STUDY PROTOCOL
To quantify the differences in physiological stress due to increased heat production and added heat retention of firefighting gear, we studied 16 firelighters under laboratory conditions. Each firefighter performed a standard amount of work; subjects walked on a motor-driven treadmill at a constant speed and elevation (3.5 km/hr ‘ at I0% grade) for 15 minutes in three different clothing configurations. On separate days, subjects wore (a) “station blues,” (b) a hipboot configuration of firefighting gear typically worn prior to the 1987 proposal of the NFPA 1500 standard, and (c) the current “NFPA 1500 standard” gear.
The hip-boot configuration consisted of three-quarter hip boots, full-length turnout coat (8.5-oz. Nomex® shell with neoprene vapor barrier and batt liner), helmet, and gloves. The NFPA 1500 standard gear consisted of bunker boots, bunker pants, turnout coat (8.5-oz. PBI® shell with GoreTex® barrier and quilted liner), Nomex® hood with full gauntlet, helmet, and gloves. A self-contained breathing apparatus (SCBA) and a facepiece were worn without the respirator for the hip-boot and NFPA 1500 testing conditions. The facepiece was modified to allow for the collection and analysis of expired air. The order of testing was randomly assigned. The mean weights of the turnout gear for the hip-boot and the NFPA 1500 clothing configurations were 20.18 kg and 20.17 kg, respectively.
TEST RESULTS
We found that the subjects’ heart rate, rectal temperature, mean skin temperature, and oxygen consumption were significantly greater when walking in the NFPA 1500 standard ensemble than when walking in station blues or the hip-boot configuration. During the last minute of exercise, heart rate averaged 15.7 beats/m in. higher in the 1500 clothing than in the hip-boot configuration (174.5 vs. 158 beat.s/m in.’) and 50.1 beat s/m in. higher than in the station blues (124.4 beats/m in.’), despite the fact that a standard exercise workload was used for all three conditions.
Rectal temperature was consistently higher when subjects walked in the 1500 gear than in the hip-boot configuration or the station blues. Perhaps the most noteworthy aspect of the temperature data is that rectal temperature continued to increase during the recovery time in the 1500 gear tests [reaching a peak of 38.2°C (100.86°F) after 10 minutes of passive recovery], whereas it plateaued in the hip-boot configuration. This has important implications for the work-rest cycles of firefighters.
Heart rate response during pre-exercise rest, submaximal exercise, and post-exerose recovery in different clothing configurations. Means and standard error of the estimate.
Rectal temperature response during pre-exercise rest, submaximal exercise, and post-exercise recovery in different clothing configurations. Means and standard error of the estimate.
Mean skin temperature response during pre-exercise rest, submaximal exercise, and post-exercise recovery in different clothing configurations Means and standard error of the estimate
Oxygen consumption response during pre-exercise rest, submaximal exercise, and post-exercise recovery in different clothing configurations. Means and standard error of the estimate.
Mean skin temperatures also were greater in the 1500 gear than in the hip-boot configuration.
The subjects achieved a steady-state oxygen consumption, which reflects the amount of energy expended during a task, while walking in the station blues. Oxygen consumption was slightly but significantly higher for the 1500 gear than for the hipboot configuration.
These data suggest that the firefighters experienced significantly greater cardiovascular and thermoregulatory stress during a standard activity when that activity was performed in the 1500 standard gear than when wearing the hip-boot ensemble. The difference in physiological responses to the gear, despite an absolute load, may be explained in terms of the insulative properties of the NFPA suit, which decreases the body’s ability to dissipate heat due to additional encapsulation of the legs (bunker pants) and head (Nomex® hood). This causes the heart to work harder, presumably in an attempt to pump more blood to the skin. This is supported by the subject’s higher rectal temperatures seen during the NFPA 1500 condition. It is also possible that the NFPA 1500 gear (specifically the bunker pants) is more cumbersome and thereby decreased the mechanical efficiency of the individual when performing a physical task. This would increase the metabolic cost of the work and add to the thermal and cardiovascular load of the task. This is supported by the higher oxygen consumption levels of the subjects seen during the NFPA 1500 condition compared with the hip-boot condition.
In summary, the results of our study suggest that the NFPA 1500 standard firefighting gear imposes greater physiological stress on the body than either the hip-boot configuration or the station blues while performing a physical task at an absolute workload in ambient temperature. Additional research is needed to determine (a) if greater physiological responses would be apparent in a hot and hostile environment; (b) if physiological responses would be different if subjects selected their own work rale, as opposed to having an investigator dictate work rate: and (c) whether the extra protection from burns is outweighed by the potentially greater likelihood of cardiac events (i.e., myocardial infarction) and/or heatrelated injuries (i.e., heat stroke, heat exhaustion).
In light of the significance of the decision regarding which gear is to be worn by a department, we believe greater efforts should be made to obtain relevant scientific information. Clearly, more work is necessary before we can say definitively which gear provides the greatest thermal protection and imposes the least cardiovascular stress on the firefighter.
Endnotes
- A.E. Washburn, P.R. LeBlanc. R.I-. Fahey. 1991. “Report on Firefighter Fatalities,” NFPA Journal, July/Aug.,52.
- M.J. Karter. P.R. LeBlanc. 1991. ”U.S. Firefighter Injuries—1990.” NFPA Journal. Nov./Dec..43.
- Washburn.
- Ibid.
- J. Faff. T. Tutak. 1989, “Physiological responses to working with fire fighting equipment in the heat in relation to subjective fatigue,” Ergonomics, 32(6), 629-638.
- D.L. Smith, S.J. Petruz/.ello. J.M. Kramer, et al. “Selected Physiological and Psychobiological Responses to Physical Activity in Different Configuratons of Firefighting Gear,” Ergonomics, in press.
