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Ergonomics Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/terg20
Physiological responses to simulated firefighter exercise protocols in varying environments ab
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Gavin P. Horn , Richard M. Kesler , Robert W. Motl , Elizabeth T. Hsiao-Wecksler , Rachel E. c
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Klaren , Ipek Ensari , Matthew N. Petrucci , Bo Fernhall & Karl S. Rosengren a
Fire Service Institute, University of Illinois, Urbana-Champaign, IL, USA
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Department of Mechanical Science and Engineering, University of Illinois, UrbanaChampaign, IL, USA c
Department of Kinesiology and Community Health, University of Illinois, UrbanaChampaign, IL, USA
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Neuroscience Program, University of Illinois, Urbana-Champaign, IL, USA
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Department of Kinesiology and Nutrition, University of Illinois, Chicago, IL, USA
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Department of Psychology, University of Wisconsin, Madison, WI, USA Published online: 19 Jan 2015.
To cite this article: Gavin P. Horn, Richard M. Kesler, Robert W. Motl, Elizabeth T. Hsiao-Wecksler, Rachel E. Klaren, Ipek Ensari, Matthew N. Petrucci, Bo Fernhall & Karl S. Rosengren (2015): Physiological responses to simulated firefighter exercise protocols in varying environments, Ergonomics, DOI: 10.1080/00140139.2014.997806 To link to this article: http://dx.doi.org/10.1080/00140139.2014.997806
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Ergonomics, 2015 http://dx.doi.org/10.1080/00140139.2014.997806
Physiological responses to simulated firefighter exercise protocols in varying environments Gavin P. Horna,b*, Richard M. Keslera, Robert W. Motlc, Elizabeth T. Hsiao-Weckslerb, Rachel E. Klarenc, Ipek Ensaric, Matthew N. Petruccid, Bo Fernhalle and Karl S. Rosengrenf a Fire Service Institute, University of Illinois, Urbana-Champaign, IL, USA; bDepartment of Mechanical Science and Engineering, University of Illinois, Urbana-Champaign, IL, USA; cDepartment of Kinesiology and Community Health, University of Illinois, UrbanaChampaign, IL, USA; dNeuroscience Program, University of Illinois, Urbana-Champaign, IL, USA; eDepartment of Kinesiology and Nutrition, University of Illinois, Chicago, IL, USA; fDepartment of Psychology, University of Wisconsin, Madison, WI, USA
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(Received 30 June 2014; accepted 2 December 2014) For decades, research to quantify the effects of firefighting activities and personal protective equipment on physiology and biomechanics has been conducted in a variety of testing environments. It is unknown if these different environments provide similar information and comparable responses. A novel Firefighting Activities Station, which simulates four common fireground tasks, is presented for use with an environmental chamber in a controlled laboratory setting. Nineteen firefighters completed three different exercise protocols following common research practices. Simulated firefighting activities conducted in an environmental chamber or live-fire structures elicited similar physiological responses (max heart rate: 190.1 vs 188.0 bpm, core temperature response: 0.0478C/min vs 0.0438C/min) and accelerometry counts. However, the response to a treadmill protocol commonly used in laboratory settings resulted in significantly lower heart rate (178.4 vs 188.0 bpm), core temperature response (0.0378C/min vs 0.0438C/min) and physical activity counts compared with firefighting activities in the burn building. Practitioner Summary: We introduce a new approach for simulating realistic firefighting activities in a controlled laboratory environment for ergonomics assessment of fire service equipment and personnel. Physiological responses to this proposed protocol more closely replicate those from live-fire activities than a traditional treadmill protocol and are simple to replicate and standardise. Keywords: firefighting; test protocol; core temperature; heart rate; heat stress
1.
Introduction
While fighting a fire, heat stress and the resulting elevation in body temperature and heart rate have a myriad of effects on the body, including hastening the onset of muscular fatigue, promoting dehydration, increasing cardiovascular strain and interfering with cognitive function (Rowell 1974; Horn et al. 2011). To study the effects of firefighting personal protective equipment (PPE) and activities on physiology and biomechanics, research has been conducted in a variety of testing environments. Some studies have tracked individual firefighters while on duty (e.g. Sothmann et al. 1992) or studied work in firefighting PPE in thermoneutral conditions (e.g. Louhevaara et al. 1995). Others have utilised training drills in a live-fire burn structure to simulate fireground activities (e.g. Manning and Griggs 1983; Romet and Frim 1987; Colburn et al. 2011; Burgess et al. 2012; Horn et al. 2013). Many research groups have commonly used a treadmill protocol in a temperaturecontrolled room (e.g. Selkirk and McLellan 2004; Selkirk, McLellan, and Wong 2006; Kong et al. 2010; Hostler et al. 2010a, 2010b; Gallagher et al. 2012). Historically, studies at the Illinois Fire Service Institute (IFSI) have utilised controlled tasks that simulate firefighting activities in a live-fire burn structure (e.g. Smith and Petruzzello 1998; Smith et al. 2011; Park et al. 2011; Horn et al. 2011), and we have demonstrated that the heart rate and core temperature responses from these simulated activities are similar to those reported during typical live-fire firefighter training drills (Horn et al. 2013). Although studies that collect data from firefighters during actual fire events provide the most realistic firefighting conditions, these studies are limited due to the lack of control and variability across events. Using live-fire training structures increases the ability to control the situation, obtain more accurate measurements during and immediately after firefighting activities and increases the repeatability of the testing environment. However, significant variation in environmental conditions in these studies must be acknowledged and many in-situ data collection instruments cannot withstand the radiant heat and smoke during live-fire activities, thus limiting measurement possibilities. Furthermore, livefire testing is costly to conduct (financial, personnel, safety) and is not generally feasible for most academic research institutions. In contrast, an environmentally controlled (temperature/humidity) room provides the ability to accurately and reliably specify test conditions, allows significantly expanded in-situ data collection capabilities and has lower operational
*Corresponding author. Email: [email protected] q 2015 Taylor & Francis
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expense. However, these environmentally controlled chambers are typically limited in their ability to replicate the fireground due to space constraints, typically relying on treadmill or stairmill protocols. To our knowledge, there are no reports comparing data collected from firefighters conducting typical ‘simulated firefighting activities’ in live-fire and environmental chambers. A National Institute for Occupational Safety and Health report has called for the establishment of a standard protocol for physiological testing, arguing that it is difficult to make comparisons between different heat stress studies due to the various protocols employed (Barker 2005). Furthermore, firefighting PPE is currently not evaluated with a standard ergonomic test, even though the need for such a standard test is apparent. Coca et al. (2010) further argue for the need for ensemble-level studies to understand the effect of PPE on a firefighter in a more holistic manner. A standard ‘work’ cycle can be utilised to compare the effects of different PPE ergonomics on the firefighter in a realistic and repeatable manner (Coca et al. 2010). It remains difficult to compare results from previous studies investigating the effect of simulated firefighting activity due to the varying protocols that have been used. Furthermore, it is apparent that in order to study the effects of metabolic stress and fatigue on firefighting populations, the simulated activities must provide a valid surrogate for the metabolic stress induced by realistic firefighting tasks, yet there are no comparisons currently available in the literature. The purpose of this study was to examine the effect of different firefighter exercise protocols on metabolic stress and physiological responses with the goal of providing insights to help inform standards for experimental protocols designed to assess the impact of a variety of factors on firefighting activities.
2. Methods 2.1. Participants Twenty-four adult career and volunteer firefighters from the State of Illinois with no self-reported health issues or orthopaedic or neuromuscular problems were recruited to participate in this study. Subjects completed a health history inventory and a physical activity readiness questionnaire (Thomas, Reading, and Shephard 1992) prior to testing. Based on these assessments, all participants were determined to be eligible for physical activity. Participants provided informed written consent indicating that they understood and voluntarily accepted the risks and benefits of participation. This study was approved by the University of Illinois Institutional Review Board.
2.2. Firefighter exercise protocols All firefighters participated in the same three exercise protocols proposed to potentially replicate work levels experienced on the fireground: (1) walking on a treadmill in an environmental chamber (ECTM, 478C, 30% humidity), (2) simulated firefighting tasks in an environmental chamber (ECFF, 478C, 30% humidity) and (3) simulated firefighting tasks in a burn building with live-fire (BBFF, on average 1358C at 30 cm from ceiling, 858C at 120 cm from the floor, 308C at 30 cm above the floor, very low humidity). Upon entering the environmental chamber or burn building, subjects were acclimatised to the environments for five minutes prior to beginning any activity. For the treadmill protocol, subjects walked at 4.5 km/h at a 2.5% incline for 14 minutes following the initial five-minute rest period. This rate and incline have been commonly used to study firefighters (e.g. Selkirk and McLellan 2004; Selkirk, McLellan, and Wong 2006; Kong et al. 2010; Hostler et al. 2010a, 2010b; Gallagher et al. 2012), though in this case, the ambient temperature was higher than that previously reported (typically # 358C) and the exposure time was relatively shorter to match the exposure of the firefighting task scenarios. The simulated firefighting scenarios used in this study (burn building firefighting [BBFF], environmental chamber firefighting [ECFF]) were developed from the legacy live-fire activities that have been conducted at IFSI for several decades (e.g. Smith and Petruzzello 1998; Horn et al. 2011; Park et al. 2011; Smith et al. 2011). Whereas many of these studies incorporated slightly different activities and operational timeframes, they all typically included several different stations that simulated activities common on the fireground such as moving through a structure (climbing stairs, crawling while searching a room), getting water to the fire (advancing a hoseline) and looking for hidden fire (pulling down the ceiling or chopping a block). The simulated firefighting scenario labelled ‘BBFF’ in this study was adopted from these legacy protocols and comprised four activities completed in a two-minute work-rest cycle, where a single activity (climbing stairs, moving a hoseline, searching a room, pulling down the ceiling) is performed for two straight minutes, followed by a twominute rest period. After the two minutes of rest, the next activity is carried out for two minutes before the next provided rest period. In order to replicate these activities in a controlled environmental chamber for the ‘ECFF’ protocol, the research team designed and built a compact Firefighting Activities Station (FAS) that would fit within a typical laboratory-sized environmental chamber (2.9 £ 3.4 £ 2.7m3). A model of the structure of the room can be seen in Figure 1, and photographic images of its use are shown in Figure 2.
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Figure 1. (a) Three-dimensional sketches of the Firefighting Activities Station (FAS) while situated within a 2.9 £ 3.4 £ 2.7 m3 environmental chamber (dimensions are in metres). The FAS can be rapidly reconfigured within a few seconds to provide the following simulated firefighting activities: (b) Stair climb; (c) Hose advance; (d) Search; (e) Overhaul task. The triangular section in the corner of the room provides a target for consistent movements on the hose advance and overhaul task.
Complete drawings and three-dimensional model files for the FAS are available for distribution through the corresponding author, and summaries are provided as supplemental data for this manuscript online. The activities consisted of: (1) a stair climb in which the subject climbed to the second step on a three-step staircase (1.2-m wide, 18- cm rise, 28- cm run), touched both feet to the second step, then stepped backward down to ground level; (2) a simulated hose advance, in
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Figure 2.
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Simulated firefighting activities performed in the FAS: (a) Stair climb; (b) Hose advance; (c) Search; (d) Overhaul task.
which a section of hose was fixed to the low pulley (0.3 m from floor) from a modified gym exercise machine (PLA200X, Powerline) with 9.1 kg resistance during movement; (3) a simulated search, which included crawling around the perimeter of the room on hands and knees, performing hand movements to locate victims and exits; and (4) a simulated overhaul task in which a pike pole was attached to the high pulley (2.3 m from the floor) from the modified gym exercise machine that required pulling a weight of 9.1 kg from overhead. During the hose and overhaul tasks, one repetition was counted as beginning with the weight stack at rest, touching the end of the tool (either hose or pole) to a target located 1.8 m (70 in) from the first stair edge, and returning the weight stack to the resting position. This weight and distance were selected based on experience with past protocols similar to ‘BBFF’, and after several pilot trials indicated they provided the typical range of motion encountered during these activities for individuals of various different body types. Subjects performed these tasks with a self-selected technique, as long as they completed the full movement of the tool. Firefighters were instructed to perform all activities at a self-selected pace that simulated their effort on a fireground and were allowed to modify their technique at any time throughout the activity. While two-minute rest periods were scheduled after each two-minute activity period, firefighters were allowed to rest during the instructed activity period if they felt overly fatigued or if this replicated their activity/technique on the fireground. Throughout each simulated firefighting exercise protocol, two trained staff members remained with the subject completing the activities; one to count number of repetitions and monitor heart rate with a local monitor and the other to act as a safety escort, demonstrating each activity during the rest periods and ensuring the participant completed each in a safe manner. For both activities conducted in the environmental chamber, overhead fluorescent lights were illuminated throughout the trial. In the burn building, ambient lighting was provided by the fire set and hand-held flashlights carried by the safety escort. For each individual participant, attempts were made to administer all three exercise protocols at roughly the same time of day (average test time within 1.7 ^ 1.5 hours) to control for any effects of circadian rhythms. However, in a few instances, this was not possible due to scheduling conflicts.
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2.3. Protocol This study used a counterbalanced design to investigate the effects of different simulated firefighter exercise protocols on maximal values and changes in heart rate, core temperature, self-perceived conditions and accelerometry counts. Participants were initially assigned to one of the three protocols outlined in the previous section: environmental chamber treadmill (ECTM), ECFF and BBFF. Subsequent trials were presented to the participants in a counterbalanced order with at least 24 hours of rest in between each condition. A schematic of the general study protocol is shown in Figure 3. At least 24 hours prior to their first test session, preliminary assessments were obtained, including anthropomorphic data collection (height, weight, chest depth, leg length) and acclimatisation with the FAS instrument and assigned firefighting PPE. On the same day, all subjects completed a graded maximal exercise test following a modified Gerkin treadmill protocol (NFPA 2013) to volitional fatigue in order to identify the subject’s maximum oxygen uptake (VO2max). Firefighters wore an open-circuit spirometry system (K4b2, Cosmed Srl, Rome, Italy) during the maximal exercise test, which was terminated by volitional fatigue, thus providing a measure of the firefighter’s maximum oxygen uptake. Participants received a core temperature pill that they were instructed to ingest 6– 12 hours prior to data collection. Prior to completing each of the three exercise protocols, participants were instrumented with a physiological status monitor (Equivital, Phillips Respironics, Andover, MD, USA) to measure heart rate and record data from the core temperature pill. Accelerometers (ActiGraph, Pensacola, FL, USA) for measuring movement of limbs and the core based on activity counts were attached using a Velcro strap on the right side of the firefighters’ bodies located at the wrist, ankle and hip. All subjects then donned full National Fire Protection Association (NFPA) 1971 compliant structural firefighting PPE provided for the study (Globe Manufacturing, Pittsfield, NH, USA) and a 45-minute self-contained breathing apparatus (SCBA; Firehawk M7, MSA Co., Cranberry Township, PA, USA) air pack. Subjects breathed through the SCBA system (in burn building, Firehawk M7) or portable open-circuit spirometry system worn on the firefighter’s chest (in environmental chamber; K4b2, Cosmed Srl, Rome, Italy) during all physical activity tasks. Throughout the simulated firefighting activity, subject’s core temperature, heart rate and activity counts were recorded. Furthermore, core temperature and heart rate were continuously monitored throughout the entire data collection protocol to determine the maximum change in temperature. This maximum commonly occurs several minutes after the end of firefighting activities (Horn et al. 2013). In order to determine firefighter self-perceptions of their physical conditions before and at the end of the exercise protocols, several self-response measures were collected. These included the perception of respiratory distress (breathing scale), perception of thermal sensation (Thermal Sensation Scale), overall well-being (feeling scale) and perception of exertion (perceived exertion). Perception of respiratory distress was assessed using the seven-point scale developed by Morgan and Raven (1985). Odd numbers on the scale are anchored with descriptions (e.g. ‘My breathing is okay right now’, ‘I can’t breathe’, etc.). Perception of thermal sensation ranging from ‘unbearably cold’ (0.0) to ‘unbearably hot’ (8.0) were assessed using the rating scale developed by Young (1987). Firefighters rated how they were feeling using the feeling scale developed by Hardy and Rejeski (1989). For this 11-point scale, anchors are provided at 0 (neutral) and at odd integers ranging from 2 5 (very bad) to þ 5 (very good). Finally, a rating of perceived exertion (RPE) was recorded immediately after the activity was completed using the 15-point, 6-20 Borg scale (Borg 1998). To complete this assessment, firefighters were asked to rate how hard they were working during the activity on a scale that ranges between 6 (‘no exertion at all’) and 20 (‘maximal exertion’). Subjects verbally responded to the questions for each scale, which was verified and recorded by an investigator. Immediately before and after simulated firefighting activities, several biomechanics measurements were conducted to quantify gait performance, functional balance and situational awareness. Pre- and post-activity measurements were obtained in a room adjacent to the training area to facilitate data collection in a timely manner after completion of the activity. These activities affect core temperature changes, so values are reported during intervals associated with the
Figure 3.
Experimental protocol for a firefighter test subject during all proposed studies.
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14 minutes of simulated firefighting activities (using subscript FF) and over the entire test session (using subscript Tot). Upon completion of these post assessments, firefighters doffed their PPE and rested for at least 10 minutes or until their core temperature began to return to baseline levels. The measures obtained during each exercise protocol included the maximum heart rate achieved (HRmax), the average heart rate during the activity (HRave), the maximum core temperature measured during the exercise protocol (TcoMax,FF), the change in core temperature during exercise (DTcoMax,FF), the maximum core temperature measured during the test session (TcoMax,Tot), the change in core temperature from beginning to end of the test session (DTcoMax,Tot) and the vector magnitude of the three-dimensional acceleration counts measured at the firefighters hip (Accel_Hip), ankle (Accel_Ankle) and wrist (Accel_Wrist). Accelerometer data were parsed for each of the four 2-minute activity periods during the simulated firefighting activity drills. During these drills, the number of cycles that each subject completed on the stairs, hose advance and overhaul tasks as well as distance travelled on the search were recorded along with the maximum heart rate achieved during each of these cycles. Data from the breathing scale, feeling scale and thermal sensations scale were obtained immediately before and after completing an exercise protocol (pre- and post-firefighting), while RPE was only collected post-firefighting. 2.4.
Analytical methods
The heart rate, core temperature and accelerometry reported for the three exercise protocols (ECTM, ECFF, BBFF) were analysed independently using repeated measures analysis of variance (ANOVA) to determine differences between each exercise protocol. The four self-perception variables reported before and after the three exercise protocols were analysed independently using repeated measures ANOVA to determine differences between each exercise protocol and changes with time (i.e. difference between pre- and post-activity). Where significant main effects are determined by the ANOVA, data reported for individual exercise protocols were studied using a post hoc paired t-test. Finally, the cycle counts and maximum heart rate encountered during each of the four work cycles in the ECFF and BBFF conditions was analysed independently using paired t-test. Statistical significance was set at p # 0.05. 3.
Results
Twenty-four firefighters completed the entire study protocol in a counterbalanced fashion. However, during five subjects’ trials, in at least one condition the core temperature measurement was affected by water consumed by the participant prior to reaching a maximum temperature after completion of the activities, indicating that the core temperature pill had not left the stomach before beginning the study. All data from these subjects were removed, therefore we report results from the remaining 19 individual participants (18 male, 1 female). Table 1 includes descriptive statistics from these firefighters. Participants were between 19 and 43 years old and ranged from normal body mass index (21.0 kg/m2) to obese (35.3 kg/m2). Maximum oxygen uptake ranged from 28.6 mL·kg21·min21 to 58.3 mL·kg21·min21, with five of the subjects unable to reach the NFPA and International Association of Fire Fighters/International Association of Fire Chiefs Joint Labor Management Wellness-Fitness Initiative (WFI) recommended minimum of 42 mL·kg21·min21 (NFPA 2013; IAFF 2014). During the maximal exercise test, subjects achieved on average 99% of their age-predicted maximum heart rate (220-age). For all heart rate and core temperature measurements made during the three trials (Table 2), the ECTM condition resulted in the smallest response to the exercise protocol, while the ECFF condition typically resulted in the largest. Maximum heart rate measured during the ECTM activity was significantly smaller than ECFF ( p , 0.001) and BBFF ( p ¼ 0.003), and a lower average heart rate was measured in ECTM compared to ECFF ( p ¼ 0.028). The average heart rate achieved during the ECFF trials was larger than the BBFF trials ( p ¼ 0.028). The maximum core temperature measured immediately after firefighting activities was significantly larger in the BBFF condition compared to the ECTM ( p ¼ 0.040), Table 1.
Descriptive statistics for the firefighter subjects (n ¼ 19).
Age (years) Height (m) Weight (kg) BMI (kg/m2) VO2max (ml/kg/min) HRpeak (bpm)
Mean (SD)
Range
27.8 (6.9) 1.81 (0.07) 89.5 (14.2) 27.2 (3.5) 45.0 (7.8) 190.7 (10.5)
19 – 43 1.69 – 1.93 62.0 – 114.5 21.0 – 35.3 28.6 – 58.3 178– 210
Note: BMI, body mass index; VO2max, maximal oxygen consumption achieved on the graded exercise test; HRpeak, peak heart rate achieved on the graded exercise test.
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Table 2. Mean (SD) heart rate, core temperature, and vector magnitude accelerometer data from each exercise protocol condition (n ¼ 19).
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HRmax (bpm) HRave (bpm) TcoMax,FF (oC) DTco,FF (oC) TcoMax,Tot (oC) DTco,Tot (oC) Acel_Hipd Acel_Ankled Acel_Wristd
Environmental chamber treadmill (ECTM)a
Environmental chamber firefighting (ECFF)b
Burn building firefighting (BBFF)c
178.4 (14.1)b,c 151.5 (19.3)b 37.98 (0.31)c 0.52 (0.17)b 38.52 (0.33) 1.25 (0.26) 4906 (1404)b,c 13,239 (4329)b,c 6691 (4022)b,c
190.1 (11.1)a 159.7 (12.3)a,c 38.14 (0.34) 0.66 (0.22)a 38.72 (0.43) 1.42 (0.36) 16,691 (2346)a 26,749 (5890)a 32,630 (6130)a
188.0 (13.2)a 155.6 (13.1)b 38.20 (0.29)a 0.60 (0.21) 38.73 (0.42) 1.36 (0.29) 14,299 (4426)a 24,751 (8868)a 30,400 (9477)a
Note: Superscripts indicate a significant difference (p , 0.05) from the specified condition; *HRmax, maximum heart rate; HRave, average heart rate; Tco, max,FF, maximum core temperature during simulated firefighting activities; DTco,FF, change in core temperature during simulated firefighting activities; Tco, max,Tot, maximum core temperature achieved during study; DTco,Tot, change in core temperature during study protocol; Acel_Hip, hip accelerometer counts; Acel_Ankle, ankle accelerometer counts; Acel_Wrist, wrist accelerometer counts. d n ¼ 15.
whereas the change in core temperature pre- to post-simulated firefighting activity was significantly larger for ECFF than ECTM ( p ¼ 0.021). For all accelerometry data, the vector magnitude counts were significantly lower in the ECTM trials compared to either of the simulated firefighting trials ( p , 0.001) and no differences were measured between the two firefighting activity trials (i.e. ECFF and BBFF). Perceptual measures on the other hand indicated that the firefighters felt significantly more affected by the ECFF condition than the other simulated firefighting activities (Table 3). Prior to firefighting, participants indicated feeling between ‘Good’ and ‘Very Good’ (, 4.1), were relatively comfortable (, 4.2) and had no issues with breathing (, 1.2), though they did report slightly more difficulty breathing prior to the BBFF condition than the ECTM ( p ¼ 0.021). However, post-firefighting, firefighters reported significantly lower scores in the ECFF condition than in the ECTM and BBFF conditions on the breathing scale ( p ¼ 0.004, p ¼ 0.025), feeling scale ( p , 0.001, p , 0.001) and thermal sensations scale ( p ¼ 0.001, p ¼ 0.002). Furthermore, firefighters rated their perceived exertion level much higher for ECFF than BBFF ( p ¼ 0.022) and ECTM ( p , 0.001), while BBFF trials also resulted in significantly higher perceived exertion than ECTM ( p , 0.001). Identical activities were conducted in the ECFF and BBFF trials that enable comparison of the work completed in each trial regardless of environmental condition (Table 4). The number of stairs climbed and hose advance cycles completed in the ECFF condition were significantly higher than the BBFF ( p ¼ 0.047, p ¼ 0.015, respectively). Accelerometry data indicated that vector magnitude counts in the ECFF condition were not significantly different than the BBFF condition (Table 5). As expected, accelerometry counts in the stairs were much higher for the ankles than the wrist and hip locations, whereas the hose advance and overhaul tasks resulted in much higher movement of the wrist accelerometers and the search task resulted in nearly identical counts for the arms and legs. 4.
Discussion
The most important outcome from this study is that similar physiological responses and activity counts were measured during simulated firefighting activities in a controlled environmental chamber (ECFF condition) as in a live-fire burn Table 3.
Mean (SD) perceptual measures from each exercise protocol condition (n ¼ 19).
Breathing scale Feeling scale Thermal sensations RPE
Pre Post Pre Post Pre Post Post
Environmental chamber treadmill (ECTM)a
Environmental chamber firefighting (ECFF)b
Burn building firefighting (BBFF)c
1.11 (0.32)c 3.37 (1.12)b 4.05 (0.97) 1.11 (2.13)b 4.24 (0.39) 5.87 (0.76)b 13.8 (2.4)b,c
1.16 (0.37) 4.16 (0.69)a,c 4.11 (0.94) 2 0.37 (2.17)a,c 4.34 (0.47) 6.47 (0.51)a,c 17.1 (1.5)a,c
1.37 (0.68)a 3.68 (0.82)b 4.26 (0.81) 1.32 (2.33)b 4.05 (0.60) 5.84 (0.71)b 16.3 (1.6)a,b
Note: Superscripts indicate a significant difference (p , 0.05) from the specified condition.
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Table 4. Mean (SD) work cycles, distance, and maximum heart rate recorded from each of the four stations conducted in the firefighting condition (n ¼ 19).* Environmental chamber firefighting (ECFF) Stairs Hose advance Search Overhaul
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a
Cycles (#) Max heart rate Cycles(#) Max heart rate Distance (ft) Max heart rate Cycles(#) Max heart rate
Burn building firefighting (BBFF)
a
33.9 (7.1)a 162.7 (14.3) 45.8 (9.9)a 177.6 (11.3) 92.4 (29.9) 181.4 (13.6) 52.5 (11.3) 184.7 (12.9)
36.0 (6.1) 166.0 (13.2) 50.8 (13.4)a 180.2 (10.6) 97.5 (32.1) 183.6 (11.7) 50.9 (12.6) 187.3 (12.6)
(bpm) (bpm) (bpm) (bpm)
Indicates a significant difference (p , 0.05) between conditions.
Table 5. Mean (SD) vector magnitude acceleration counts from each of the four stations conducted in the firefighting condition (n ¼ 16). Environmental chamber firefighting (ECFF) Stairs Hose advance Search Overhaul
Acel_Hip Acel_Ankle Acel_Wrist Acel_Hip Acel_Ankle Acel_Wrist Acel_Hip Acel_Ankle Acel_Wrist Acel_Hip Acel_Ankle Acel_Wrist
4691 (881) 10,046 (3160) 5343 (1143) 3832 (1542) 3608 (1707) 7637 (1317) 5489 (1452) 10,870 (3549) 10,559 (3203) 3055 (1257) 3873 (1409) 9553 (2530)
Burn building firefighting (BBFF) 4133 9085 4737 3356 2041 7307 4703 10,627 9705 2472 3608 9124
(1321) (3894) (1327) (1658) (1518) (2306) (1719) (4425) (3620) (1090) (1707) (3366)
Note: Acel_Hip, hip accelerometer counts; Acel_Ankle, ankle accelerometer counts; Acel_Wrist, wrist accelerometer counts.
structure (BBFF condition). Average heart rates were slightly higher in the chamber, which is attributed to a larger amount of work completed during these trials. This result is likely due, in part, to greater visibility within the chamber provided by the overhead lights compared to the flashlight and firelight in the BBFF condition. Additionally, significant differences in physiological responses were obtained in the treadmill protocol compared to the firefighting activities in terms of maximum and average heart rate, core temperature response to the activities and total accelerometry counts. However, firefighters perceived a significantly higher exertion level as well as had more negative affect, felt hotter and had more difficulty breathing in the ECFF condition than the other conditions studied here. The increasingly negative feelings and heart rate may be attributed to the heavier exertion in this condition combined with breathing warm moist air in the environmental chamber as compared to regulated air from an SCBA. Simulated firefighting activities in a live-fire burn structures have historically provided a controlled means of stressing firefighters in a manner that results in similar physiological strain as fireground activities (Romet and Frim 1987; Horn et al. 2013). However, these live-fire structures are not commonly available to academic research programmes due to their specialised nature, cost and required safety precautions. Laboratory environmental chambers cannot reproduce the high temperatures, radiant heat flux conditions or the psychological effects of the flame and smoke seen in live-fire burn buildings. However, our results indicate that using the FAS in an environmental chamber within a lab setting can induce similar physiological responses as a live-burn scenario. This provides evidence that activities in a relatively small and costefficient chamber can be used as a viable substitute for activities performed in a live-fire scenario. Whereas the differences are small and there may be limited clinical relevance of this finding, the average heart rates were higher throughout the ECFF protocol compared to the BBFF protocol and firefighters perceived an increased exertion level and more negative self-perceptions of their physical condition; these results accurately reflect that firefighters completed more work through the ECFF protocol as measured via accelerometry and total work counts during the activities. Firefighters reported during informal feedback that they were less confident of their movements in the BBFF protocol due to the limited visibility within the burn structure. However, in the ECFF protocol, lights within the chamber were on throughout, allowing more accurate and confident movements, which likely resulted in the completion of more work.
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We suggest that this protocol might more accurately reflect fireground conditions if the chamber lights were turned off and flashlights were used to illuminate the objects, targets and pathway as was done in the BBFF protocol. Furthermore, firefighters reported discomfort in breathing warm moist air from the chamber in ECFF condition, but not in the other conditions. The more negative affect and ratings of post-exercise breathing and thermal conditions as well as higher heart rates in the ECFF condition are partially attributed to this concern. The ECFF condition could provide a higher fidelity simulation of the live-fire conditions if subjects were breathing through their SCBA while conducting activities in the chamber. The approach proposed by Kesler et al. (2014) would allow portable collection of metabolic data while breathing through a firefighting SCBA and may reduce the negative feelings reported here. This difference between inhaled air conditions introduces some controlled variability in the design and is acknowledged as a limitation of this study. However, important metabolic data were collected from the two environmental chamber tasks and will be reported elsewhere. While largely similar physiological responses were measured between the ECFF and BBFF protocols, the heart rate and core temperature responses and accelerometer counts during the common treadmill protocol in the environmental chamber (ECTM) were significantly reduced compared to the simulated firefighting activities trials. Treadmill protocols are frequently utilised in academic settings when studying physiological responses of firefighters, and it is common to have participants work for a much longer period of time – often multiple cylinders of air – in order to achieve a similar increase in heart rate and core temperature commonly encountered in live-fire scenarios that would require one cylinder of air or less (Selkirk and McLellan 2004; Hostler et al. 2010b). Furthermore, the ECTM protocol does not replicate the typical fireground activities particularly closely, nor does it stress the different muscle groups commonly employed on the fireground as seen by the significantly reduced movement of accelerometers at each location, particularly the hip and wrist. The thermal conditions (478C) used during this treadmill protocol were significantly hotter than those typically reported in literature (# 358C) (Selkirk and McLellan 2004; Hostler et al. 2010b). We chose to utilise this temperature as it is near the upper limit of common commercial environmental chambers as well as laboratory tools used in different parts of the study. While lower than the temperature within the burn structure, this higher environmental chamber temperature is more likely to replicate the common working environment that firefighters encounter in a structure fire (excluding operations where the firefighter is in the fire room or the occurrence of extreme events which are relatively uncommon in actual operation). The increase in core temperature during the ECTM protocol was approximately 0.0378C/min, which is significantly higher than the temperature change rate reported by Selkirk and McLellan (2004) when working at the same treadmill speed and incline (‘Medium level’) at 358C (maximum temperature studied). Interestingly this value is nearly as high as the rate of rise working at the ‘High level’ at 358C (0.0398C/min) (Selkirk and McLellan 2004). These core temperature change rates are significantly smaller than those measured in the ECFF activities (0.0478C/min; in thermal conditions identical to the ECTM protocol) and the BBFF activities (0.0438C/min; in live-fire conditions). Compared to core temperature change rates measured during repeated bouts of live-fire training activities, these rates from ECFF and BBFF activities correspond very well with the maximum rate measured during latter work cycles (0.0488C/min) (Horn et al. 2013). 5.
Conclusions
Nineteen firefighters completed three different exercise protocols to simulate physiological responses common during firefighting activities that were conducted in both a controlled environmental chamber and live-fire training facility. The most significant outcome of this study is that the protocol utilising a newly proposed FAS within a laboratory grade environmental chamber (ECFF) introduced here elicited similar physiological responses as the simulated firefighting activities conducted in a live-fire structure under very different thermal conditions (BBFF). This result provides confidence in the ability of laboratory-based studies to replicate more realistic live-fire scenarios in terms of physiological response of the participants. By comparison, the response to a treadmill protocol commonly used in laboratory settings (ECTM) resulted in significantly reduced heart rate, core temperature and activity counts compared with the BBFF protocol. These data can be used to inform researchers and policy-makers of the effect of different protocols on SCBA or PPE human factors assessment. Disclosure statement There are no conflicts of interest regarding this work.
Funding This work was supported by the Department of Homeland Security Fire Prevention and Safety Program [grant #EMW-2010-FP-01606].
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References Barker, Roger. 2005. A Review of Gaps and Limitations in Test Methods for First Responder Protective Clothing and Equipment. NIOSH contract number 254-2004-M-0594. Borg, Gunnar. 1998. Perceived Exertion and Painscales. Champaign, IL: Human Kinetics. Burgess, J. L., M. D. Duncan, C. Hu, S. R. Littau, D. Caseman, M. Kurzius-Spencer, G. Davis-Gorman, and P. F. McDonagh. 2012. “Acute Cardiovascular Effects of Firefighting and Active Cooling during Rehabilitation.” Journal of Occupational and Environmental Medicine 54 (11): 1413– 1420. Coca, A., W. J. Williams, R. J. Roberge, and J. B. Powell. 2010. “Effects of Fire Fighter Protective Ensembles on Mobility and Performance.” Applied Ergonomics 41 (4): 636– 641. Colburn, D., J. Suyama, S. E. Reis, J. L. Morley, F. L. Goss, Y. Chen, C. G. Moore, and D. A. Hostler. 2011. “A Comparison of Cooling Techniques in Firefighters after a Live Burn Evolution.” Prehospital Emergency Care 15 (2): 226– 232. Gallagher, M. Jr., R. J. Robertson, F. L. Goss, E. F. Nagle-Stilley, M. A. Schafer, J. Suyama, and D. Hostler. 2012. “Development of a Perceptual Hyperthermia Index to Evaluate Heat Strain during Treadmill Exercise.” European Journal of Applied Physiology 112 (6): 2025– 2034. Hardy, C. J., and W. J. Rejeski. 1989. “Not What, but How One Feels: The Measurement of Affect during Exercise.” Journal of Sport and Exercise Psychology 11 (3): 304– 317. Horn, G. P., S. Blevins, B. Fernhall, and D. L. Smith. 2013. “Core Temperature and Heart Rate Response to Repeated Bouts of Firefighting Activities.” Ergonomics 56 (9): 1465– 1473. Horn, G. P., S. Gutzmer, C. A. Fahs, S. J. Petruzzello, E. Goldstein, G. C. Fahey, B. Fernhall, and D. L. Smith. 2011. “Physiological Recovery from Firefighting Activities in Rehabilitation and Beyond.” Prehospital Emergency Care 15 (2): 214– 225. Hostler, D., J. C. Bednez, S. Kerin, S. E. Reis, P. W. Kong, J. Morley, M. Gallagher, and J. Suyama. 2010a. “Comparison of Rehydration Regimens for Rehabilitation of Firefighter Performing Heavy Exercise in Thermal Protective Clothing: A Report from the Fireground Rehab Evaluation (FIRE) Trial.” Prehospital Emergency Care 14 (2): 194– 201. Hostler, D., S. E. Reis, J. C. Bednez, S. Kerin, and J. Suyama. 2010b. “Comparison of Active Cooling Devices with Passive Cooling for Rehabilitation of Firefighter Performing Exercise in Thermal Protective Clothing: A Report from the Fireground Rehab Evaluation (FIRE) Trial.” Prehospital Emergency Care 14 (3): 300–309. IAFF (International Association of Firefighters). 2014. Health, Safety & Medicine. WFI Fitness Assessments, Appendix A. Accessed June 10, 2014. www.iaff.org/hs/PDF/Appendix_A_Final.pdf Kesler, R. M., E. Hsiao-Wecksler, R. W. Motl, and G. Horn. 2014. “A Modified SCBA Facepiece for Accurate Metabolic Data Collection from Firefighters.” 7th World Congress of Biomechanics, Boston, MA. Kong, P. W., G. Beauchamp, J. Suyama, and D. Hostler. 2010. “Effect of Fatigue and Hypohydration on Gait Characteristics during Treadmill Exercise in the Heat while Wearing Firefighter Thermal Protective Clothing.” Gait and Posture 31 (2): 284– 288. Louhevaara, V., R. Ilmarinen, B. Griefahn, C. Kunemund, and H. Makinen. 1995. “Maximal Physical Work Performance with European Standard Based Fire-Protective Clothing System and Equipment in Relation to Individual Characteristics.” European Journal of Applied Physiology 71 (2– 3): 223– 229. Manning, J. E., and T. R. Griggs. 1983. “Heart Rates in Fire Fighters Using Light and Heavy Breathing Equipment: Similar Near Maximal Exertion in Response to Multiple Work Load Conditions.” Journal of Occupational Medicine 25 (3): 215– 218. Morgan, W. P., and P. B. Raven. 1985. “Prediction of Distress for Individuals Wearing Industrial Respirators.” American Industrial Hygiene Association Journal 46 (7): 363– 368. NFPA (National Fire Protection Association). 2013. NFPA 1582: Standard on Comprehensive Occupational Medical Program for Fire Departments. Quincy, MA: National Fire Protection Association. Park, K., K. S. Rosengren, G. P. Horn, D. L. Smith, and E. T. Hsiao-Wecksler. 2011. “Assessing Gait Changes in Firefighters Due to Fatigue and Protective Clothing.” Safety Science 49 (5): 719– 726. Romet, T. T., and J. Frim. 1987. “Physiological Responses to Fire Fighting Activities.” European Journal of Applied Physiology 56 (6): 633– 638. Rowell, L. B. 1974. “Human Cardiovascular Adjustments to Exercise and Thermall Stress.” Physiological Reviews 54 (1): 75 – 159. Selkirk, G. A., and T. M. McLellan. 2004. “Physical Work Limits for Toronto Firefighters in Warm Environments.” Journal of Occupational and Environmental Hygiene 1 (4): 199– 212. Selkirk, G. A., T. M. McLellan, and J. Wong. 2006. “The Impact of Various Rehydration Volumes for Firefighters Wearing Protective Clothing in Warm Environments.” Ergonomics 49 (4): 418– 433. Smith, D. L., and S. J. Petruzzello. 1998. “Selected Physiological and Psychological Responses to Live-Fire Drills in Different Configurations of Firefighting Gear.” Ergonomics 41 (8): 1141– 1154. Smith, D. L., S. J. Petruzzello, E. Goldstein, U. Ahmad, K. Tangella, G. G. Freund, and G. P. Horn. 2011. “Effect of Live-Fire Training Drills on Platelet Number and Function.” Prehospital Emergency Care 15 (2): 233– 237. Sothmann, M., K. Saupe, D. Jasenhof, and J. Blaney. 1992. “Heart Rate Responses of Fire-Fighters to Actual Emergencies.” Journal of Occupational and Environmental Medicine 34 (8): 797– 800. Thomas, S., J. Reading, and R. J. Shephard. 1992. “Revision of the Physical Activity Readiness Questionnaire (PAR-Q).” Canadian Journal of Sport Sciences 17 (4): 338– 345. Young, A. A. 1987. “Thermal Sensations during Simultaneous Warming and Cooling at the Forearm: A Human Psychophysical Study.” Journal of Thermal Biology 12 (4): 243 –247.
Ergonomics Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/terg20
Physiological responses to simulated firefighter exercise protocols in varying environments ab
a
c
b
Gavin P. Horn , Richard M. Kesler , Robert W. Motl , Elizabeth T. Hsiao-Wecksler , Rachel E. c
c
d
e
f
Klaren , Ipek Ensari , Matthew N. Petrucci , Bo Fernhall & Karl S. Rosengren a
Fire Service Institute, University of Illinois, Urbana-Champaign, IL, USA
b
Department of Mechanical Science and Engineering, University of Illinois, UrbanaChampaign, IL, USA c
Department of Kinesiology and Community Health, University of Illinois, UrbanaChampaign, IL, USA
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d
Neuroscience Program, University of Illinois, Urbana-Champaign, IL, USA
e
Department of Kinesiology and Nutrition, University of Illinois, Chicago, IL, USA
f
Department of Psychology, University of Wisconsin, Madison, WI, USA Published online: 19 Jan 2015.
To cite this article: Gavin P. Horn, Richard M. Kesler, Robert W. Motl, Elizabeth T. Hsiao-Wecksler, Rachel E. Klaren, Ipek Ensari, Matthew N. Petrucci, Bo Fernhall & Karl S. Rosengren (2015): Physiological responses to simulated firefighter exercise protocols in varying environments, Ergonomics, DOI: 10.1080/00140139.2014.997806 To link to this article: http://dx.doi.org/10.1080/00140139.2014.997806
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Ergonomics, 2015 http://dx.doi.org/10.1080/00140139.2014.997806
Physiological responses to simulated firefighter exercise protocols in varying environments Gavin P. Horna,b*, Richard M. Keslera, Robert W. Motlc, Elizabeth T. Hsiao-Weckslerb, Rachel E. Klarenc, Ipek Ensaric, Matthew N. Petruccid, Bo Fernhalle and Karl S. Rosengrenf a Fire Service Institute, University of Illinois, Urbana-Champaign, IL, USA; bDepartment of Mechanical Science and Engineering, University of Illinois, Urbana-Champaign, IL, USA; cDepartment of Kinesiology and Community Health, University of Illinois, UrbanaChampaign, IL, USA; dNeuroscience Program, University of Illinois, Urbana-Champaign, IL, USA; eDepartment of Kinesiology and Nutrition, University of Illinois, Chicago, IL, USA; fDepartment of Psychology, University of Wisconsin, Madison, WI, USA
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(Received 30 June 2014; accepted 2 December 2014) For decades, research to quantify the effects of firefighting activities and personal protective equipment on physiology and biomechanics has been conducted in a variety of testing environments. It is unknown if these different environments provide similar information and comparable responses. A novel Firefighting Activities Station, which simulates four common fireground tasks, is presented for use with an environmental chamber in a controlled laboratory setting. Nineteen firefighters completed three different exercise protocols following common research practices. Simulated firefighting activities conducted in an environmental chamber or live-fire structures elicited similar physiological responses (max heart rate: 190.1 vs 188.0 bpm, core temperature response: 0.0478C/min vs 0.0438C/min) and accelerometry counts. However, the response to a treadmill protocol commonly used in laboratory settings resulted in significantly lower heart rate (178.4 vs 188.0 bpm), core temperature response (0.0378C/min vs 0.0438C/min) and physical activity counts compared with firefighting activities in the burn building. Practitioner Summary: We introduce a new approach for simulating realistic firefighting activities in a controlled laboratory environment for ergonomics assessment of fire service equipment and personnel. Physiological responses to this proposed protocol more closely replicate those from live-fire activities than a traditional treadmill protocol and are simple to replicate and standardise. Keywords: firefighting; test protocol; core temperature; heart rate; heat stress
1.
Introduction
While fighting a fire, heat stress and the resulting elevation in body temperature and heart rate have a myriad of effects on the body, including hastening the onset of muscular fatigue, promoting dehydration, increasing cardiovascular strain and interfering with cognitive function (Rowell 1974; Horn et al. 2011). To study the effects of firefighting personal protective equipment (PPE) and activities on physiology and biomechanics, research has been conducted in a variety of testing environments. Some studies have tracked individual firefighters while on duty (e.g. Sothmann et al. 1992) or studied work in firefighting PPE in thermoneutral conditions (e.g. Louhevaara et al. 1995). Others have utilised training drills in a live-fire burn structure to simulate fireground activities (e.g. Manning and Griggs 1983; Romet and Frim 1987; Colburn et al. 2011; Burgess et al. 2012; Horn et al. 2013). Many research groups have commonly used a treadmill protocol in a temperaturecontrolled room (e.g. Selkirk and McLellan 2004; Selkirk, McLellan, and Wong 2006; Kong et al. 2010; Hostler et al. 2010a, 2010b; Gallagher et al. 2012). Historically, studies at the Illinois Fire Service Institute (IFSI) have utilised controlled tasks that simulate firefighting activities in a live-fire burn structure (e.g. Smith and Petruzzello 1998; Smith et al. 2011; Park et al. 2011; Horn et al. 2011), and we have demonstrated that the heart rate and core temperature responses from these simulated activities are similar to those reported during typical live-fire firefighter training drills (Horn et al. 2013). Although studies that collect data from firefighters during actual fire events provide the most realistic firefighting conditions, these studies are limited due to the lack of control and variability across events. Using live-fire training structures increases the ability to control the situation, obtain more accurate measurements during and immediately after firefighting activities and increases the repeatability of the testing environment. However, significant variation in environmental conditions in these studies must be acknowledged and many in-situ data collection instruments cannot withstand the radiant heat and smoke during live-fire activities, thus limiting measurement possibilities. Furthermore, livefire testing is costly to conduct (financial, personnel, safety) and is not generally feasible for most academic research institutions. In contrast, an environmentally controlled (temperature/humidity) room provides the ability to accurately and reliably specify test conditions, allows significantly expanded in-situ data collection capabilities and has lower operational
*Corresponding author. Email: [email protected] q 2015 Taylor & Francis
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expense. However, these environmentally controlled chambers are typically limited in their ability to replicate the fireground due to space constraints, typically relying on treadmill or stairmill protocols. To our knowledge, there are no reports comparing data collected from firefighters conducting typical ‘simulated firefighting activities’ in live-fire and environmental chambers. A National Institute for Occupational Safety and Health report has called for the establishment of a standard protocol for physiological testing, arguing that it is difficult to make comparisons between different heat stress studies due to the various protocols employed (Barker 2005). Furthermore, firefighting PPE is currently not evaluated with a standard ergonomic test, even though the need for such a standard test is apparent. Coca et al. (2010) further argue for the need for ensemble-level studies to understand the effect of PPE on a firefighter in a more holistic manner. A standard ‘work’ cycle can be utilised to compare the effects of different PPE ergonomics on the firefighter in a realistic and repeatable manner (Coca et al. 2010). It remains difficult to compare results from previous studies investigating the effect of simulated firefighting activity due to the varying protocols that have been used. Furthermore, it is apparent that in order to study the effects of metabolic stress and fatigue on firefighting populations, the simulated activities must provide a valid surrogate for the metabolic stress induced by realistic firefighting tasks, yet there are no comparisons currently available in the literature. The purpose of this study was to examine the effect of different firefighter exercise protocols on metabolic stress and physiological responses with the goal of providing insights to help inform standards for experimental protocols designed to assess the impact of a variety of factors on firefighting activities.
2. Methods 2.1. Participants Twenty-four adult career and volunteer firefighters from the State of Illinois with no self-reported health issues or orthopaedic or neuromuscular problems were recruited to participate in this study. Subjects completed a health history inventory and a physical activity readiness questionnaire (Thomas, Reading, and Shephard 1992) prior to testing. Based on these assessments, all participants were determined to be eligible for physical activity. Participants provided informed written consent indicating that they understood and voluntarily accepted the risks and benefits of participation. This study was approved by the University of Illinois Institutional Review Board.
2.2. Firefighter exercise protocols All firefighters participated in the same three exercise protocols proposed to potentially replicate work levels experienced on the fireground: (1) walking on a treadmill in an environmental chamber (ECTM, 478C, 30% humidity), (2) simulated firefighting tasks in an environmental chamber (ECFF, 478C, 30% humidity) and (3) simulated firefighting tasks in a burn building with live-fire (BBFF, on average 1358C at 30 cm from ceiling, 858C at 120 cm from the floor, 308C at 30 cm above the floor, very low humidity). Upon entering the environmental chamber or burn building, subjects were acclimatised to the environments for five minutes prior to beginning any activity. For the treadmill protocol, subjects walked at 4.5 km/h at a 2.5% incline for 14 minutes following the initial five-minute rest period. This rate and incline have been commonly used to study firefighters (e.g. Selkirk and McLellan 2004; Selkirk, McLellan, and Wong 2006; Kong et al. 2010; Hostler et al. 2010a, 2010b; Gallagher et al. 2012), though in this case, the ambient temperature was higher than that previously reported (typically # 358C) and the exposure time was relatively shorter to match the exposure of the firefighting task scenarios. The simulated firefighting scenarios used in this study (burn building firefighting [BBFF], environmental chamber firefighting [ECFF]) were developed from the legacy live-fire activities that have been conducted at IFSI for several decades (e.g. Smith and Petruzzello 1998; Horn et al. 2011; Park et al. 2011; Smith et al. 2011). Whereas many of these studies incorporated slightly different activities and operational timeframes, they all typically included several different stations that simulated activities common on the fireground such as moving through a structure (climbing stairs, crawling while searching a room), getting water to the fire (advancing a hoseline) and looking for hidden fire (pulling down the ceiling or chopping a block). The simulated firefighting scenario labelled ‘BBFF’ in this study was adopted from these legacy protocols and comprised four activities completed in a two-minute work-rest cycle, where a single activity (climbing stairs, moving a hoseline, searching a room, pulling down the ceiling) is performed for two straight minutes, followed by a twominute rest period. After the two minutes of rest, the next activity is carried out for two minutes before the next provided rest period. In order to replicate these activities in a controlled environmental chamber for the ‘ECFF’ protocol, the research team designed and built a compact Firefighting Activities Station (FAS) that would fit within a typical laboratory-sized environmental chamber (2.9 £ 3.4 £ 2.7m3). A model of the structure of the room can be seen in Figure 1, and photographic images of its use are shown in Figure 2.
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Figure 1. (a) Three-dimensional sketches of the Firefighting Activities Station (FAS) while situated within a 2.9 £ 3.4 £ 2.7 m3 environmental chamber (dimensions are in metres). The FAS can be rapidly reconfigured within a few seconds to provide the following simulated firefighting activities: (b) Stair climb; (c) Hose advance; (d) Search; (e) Overhaul task. The triangular section in the corner of the room provides a target for consistent movements on the hose advance and overhaul task.
Complete drawings and three-dimensional model files for the FAS are available for distribution through the corresponding author, and summaries are provided as supplemental data for this manuscript online. The activities consisted of: (1) a stair climb in which the subject climbed to the second step on a three-step staircase (1.2-m wide, 18- cm rise, 28- cm run), touched both feet to the second step, then stepped backward down to ground level; (2) a simulated hose advance, in
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Simulated firefighting activities performed in the FAS: (a) Stair climb; (b) Hose advance; (c) Search; (d) Overhaul task.
which a section of hose was fixed to the low pulley (0.3 m from floor) from a modified gym exercise machine (PLA200X, Powerline) with 9.1 kg resistance during movement; (3) a simulated search, which included crawling around the perimeter of the room on hands and knees, performing hand movements to locate victims and exits; and (4) a simulated overhaul task in which a pike pole was attached to the high pulley (2.3 m from the floor) from the modified gym exercise machine that required pulling a weight of 9.1 kg from overhead. During the hose and overhaul tasks, one repetition was counted as beginning with the weight stack at rest, touching the end of the tool (either hose or pole) to a target located 1.8 m (70 in) from the first stair edge, and returning the weight stack to the resting position. This weight and distance were selected based on experience with past protocols similar to ‘BBFF’, and after several pilot trials indicated they provided the typical range of motion encountered during these activities for individuals of various different body types. Subjects performed these tasks with a self-selected technique, as long as they completed the full movement of the tool. Firefighters were instructed to perform all activities at a self-selected pace that simulated their effort on a fireground and were allowed to modify their technique at any time throughout the activity. While two-minute rest periods were scheduled after each two-minute activity period, firefighters were allowed to rest during the instructed activity period if they felt overly fatigued or if this replicated their activity/technique on the fireground. Throughout each simulated firefighting exercise protocol, two trained staff members remained with the subject completing the activities; one to count number of repetitions and monitor heart rate with a local monitor and the other to act as a safety escort, demonstrating each activity during the rest periods and ensuring the participant completed each in a safe manner. For both activities conducted in the environmental chamber, overhead fluorescent lights were illuminated throughout the trial. In the burn building, ambient lighting was provided by the fire set and hand-held flashlights carried by the safety escort. For each individual participant, attempts were made to administer all three exercise protocols at roughly the same time of day (average test time within 1.7 ^ 1.5 hours) to control for any effects of circadian rhythms. However, in a few instances, this was not possible due to scheduling conflicts.
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2.3. Protocol This study used a counterbalanced design to investigate the effects of different simulated firefighter exercise protocols on maximal values and changes in heart rate, core temperature, self-perceived conditions and accelerometry counts. Participants were initially assigned to one of the three protocols outlined in the previous section: environmental chamber treadmill (ECTM), ECFF and BBFF. Subsequent trials were presented to the participants in a counterbalanced order with at least 24 hours of rest in between each condition. A schematic of the general study protocol is shown in Figure 3. At least 24 hours prior to their first test session, preliminary assessments were obtained, including anthropomorphic data collection (height, weight, chest depth, leg length) and acclimatisation with the FAS instrument and assigned firefighting PPE. On the same day, all subjects completed a graded maximal exercise test following a modified Gerkin treadmill protocol (NFPA 2013) to volitional fatigue in order to identify the subject’s maximum oxygen uptake (VO2max). Firefighters wore an open-circuit spirometry system (K4b2, Cosmed Srl, Rome, Italy) during the maximal exercise test, which was terminated by volitional fatigue, thus providing a measure of the firefighter’s maximum oxygen uptake. Participants received a core temperature pill that they were instructed to ingest 6– 12 hours prior to data collection. Prior to completing each of the three exercise protocols, participants were instrumented with a physiological status monitor (Equivital, Phillips Respironics, Andover, MD, USA) to measure heart rate and record data from the core temperature pill. Accelerometers (ActiGraph, Pensacola, FL, USA) for measuring movement of limbs and the core based on activity counts were attached using a Velcro strap on the right side of the firefighters’ bodies located at the wrist, ankle and hip. All subjects then donned full National Fire Protection Association (NFPA) 1971 compliant structural firefighting PPE provided for the study (Globe Manufacturing, Pittsfield, NH, USA) and a 45-minute self-contained breathing apparatus (SCBA; Firehawk M7, MSA Co., Cranberry Township, PA, USA) air pack. Subjects breathed through the SCBA system (in burn building, Firehawk M7) or portable open-circuit spirometry system worn on the firefighter’s chest (in environmental chamber; K4b2, Cosmed Srl, Rome, Italy) during all physical activity tasks. Throughout the simulated firefighting activity, subject’s core temperature, heart rate and activity counts were recorded. Furthermore, core temperature and heart rate were continuously monitored throughout the entire data collection protocol to determine the maximum change in temperature. This maximum commonly occurs several minutes after the end of firefighting activities (Horn et al. 2013). In order to determine firefighter self-perceptions of their physical conditions before and at the end of the exercise protocols, several self-response measures were collected. These included the perception of respiratory distress (breathing scale), perception of thermal sensation (Thermal Sensation Scale), overall well-being (feeling scale) and perception of exertion (perceived exertion). Perception of respiratory distress was assessed using the seven-point scale developed by Morgan and Raven (1985). Odd numbers on the scale are anchored with descriptions (e.g. ‘My breathing is okay right now’, ‘I can’t breathe’, etc.). Perception of thermal sensation ranging from ‘unbearably cold’ (0.0) to ‘unbearably hot’ (8.0) were assessed using the rating scale developed by Young (1987). Firefighters rated how they were feeling using the feeling scale developed by Hardy and Rejeski (1989). For this 11-point scale, anchors are provided at 0 (neutral) and at odd integers ranging from 2 5 (very bad) to þ 5 (very good). Finally, a rating of perceived exertion (RPE) was recorded immediately after the activity was completed using the 15-point, 6-20 Borg scale (Borg 1998). To complete this assessment, firefighters were asked to rate how hard they were working during the activity on a scale that ranges between 6 (‘no exertion at all’) and 20 (‘maximal exertion’). Subjects verbally responded to the questions for each scale, which was verified and recorded by an investigator. Immediately before and after simulated firefighting activities, several biomechanics measurements were conducted to quantify gait performance, functional balance and situational awareness. Pre- and post-activity measurements were obtained in a room adjacent to the training area to facilitate data collection in a timely manner after completion of the activity. These activities affect core temperature changes, so values are reported during intervals associated with the
Figure 3.
Experimental protocol for a firefighter test subject during all proposed studies.
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14 minutes of simulated firefighting activities (using subscript FF) and over the entire test session (using subscript Tot). Upon completion of these post assessments, firefighters doffed their PPE and rested for at least 10 minutes or until their core temperature began to return to baseline levels. The measures obtained during each exercise protocol included the maximum heart rate achieved (HRmax), the average heart rate during the activity (HRave), the maximum core temperature measured during the exercise protocol (TcoMax,FF), the change in core temperature during exercise (DTcoMax,FF), the maximum core temperature measured during the test session (TcoMax,Tot), the change in core temperature from beginning to end of the test session (DTcoMax,Tot) and the vector magnitude of the three-dimensional acceleration counts measured at the firefighters hip (Accel_Hip), ankle (Accel_Ankle) and wrist (Accel_Wrist). Accelerometer data were parsed for each of the four 2-minute activity periods during the simulated firefighting activity drills. During these drills, the number of cycles that each subject completed on the stairs, hose advance and overhaul tasks as well as distance travelled on the search were recorded along with the maximum heart rate achieved during each of these cycles. Data from the breathing scale, feeling scale and thermal sensations scale were obtained immediately before and after completing an exercise protocol (pre- and post-firefighting), while RPE was only collected post-firefighting. 2.4.
Analytical methods
The heart rate, core temperature and accelerometry reported for the three exercise protocols (ECTM, ECFF, BBFF) were analysed independently using repeated measures analysis of variance (ANOVA) to determine differences between each exercise protocol. The four self-perception variables reported before and after the three exercise protocols were analysed independently using repeated measures ANOVA to determine differences between each exercise protocol and changes with time (i.e. difference between pre- and post-activity). Where significant main effects are determined by the ANOVA, data reported for individual exercise protocols were studied using a post hoc paired t-test. Finally, the cycle counts and maximum heart rate encountered during each of the four work cycles in the ECFF and BBFF conditions was analysed independently using paired t-test. Statistical significance was set at p # 0.05. 3.
Results
Twenty-four firefighters completed the entire study protocol in a counterbalanced fashion. However, during five subjects’ trials, in at least one condition the core temperature measurement was affected by water consumed by the participant prior to reaching a maximum temperature after completion of the activities, indicating that the core temperature pill had not left the stomach before beginning the study. All data from these subjects were removed, therefore we report results from the remaining 19 individual participants (18 male, 1 female). Table 1 includes descriptive statistics from these firefighters. Participants were between 19 and 43 years old and ranged from normal body mass index (21.0 kg/m2) to obese (35.3 kg/m2). Maximum oxygen uptake ranged from 28.6 mL·kg21·min21 to 58.3 mL·kg21·min21, with five of the subjects unable to reach the NFPA and International Association of Fire Fighters/International Association of Fire Chiefs Joint Labor Management Wellness-Fitness Initiative (WFI) recommended minimum of 42 mL·kg21·min21 (NFPA 2013; IAFF 2014). During the maximal exercise test, subjects achieved on average 99% of their age-predicted maximum heart rate (220-age). For all heart rate and core temperature measurements made during the three trials (Table 2), the ECTM condition resulted in the smallest response to the exercise protocol, while the ECFF condition typically resulted in the largest. Maximum heart rate measured during the ECTM activity was significantly smaller than ECFF ( p , 0.001) and BBFF ( p ¼ 0.003), and a lower average heart rate was measured in ECTM compared to ECFF ( p ¼ 0.028). The average heart rate achieved during the ECFF trials was larger than the BBFF trials ( p ¼ 0.028). The maximum core temperature measured immediately after firefighting activities was significantly larger in the BBFF condition compared to the ECTM ( p ¼ 0.040), Table 1.
Descriptive statistics for the firefighter subjects (n ¼ 19).
Age (years) Height (m) Weight (kg) BMI (kg/m2) VO2max (ml/kg/min) HRpeak (bpm)
Mean (SD)
Range
27.8 (6.9) 1.81 (0.07) 89.5 (14.2) 27.2 (3.5) 45.0 (7.8) 190.7 (10.5)
19 – 43 1.69 – 1.93 62.0 – 114.5 21.0 – 35.3 28.6 – 58.3 178– 210
Note: BMI, body mass index; VO2max, maximal oxygen consumption achieved on the graded exercise test; HRpeak, peak heart rate achieved on the graded exercise test.
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Table 2. Mean (SD) heart rate, core temperature, and vector magnitude accelerometer data from each exercise protocol condition (n ¼ 19).
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HRmax (bpm) HRave (bpm) TcoMax,FF (oC) DTco,FF (oC) TcoMax,Tot (oC) DTco,Tot (oC) Acel_Hipd Acel_Ankled Acel_Wristd
Environmental chamber treadmill (ECTM)a
Environmental chamber firefighting (ECFF)b
Burn building firefighting (BBFF)c
178.4 (14.1)b,c 151.5 (19.3)b 37.98 (0.31)c 0.52 (0.17)b 38.52 (0.33) 1.25 (0.26) 4906 (1404)b,c 13,239 (4329)b,c 6691 (4022)b,c
190.1 (11.1)a 159.7 (12.3)a,c 38.14 (0.34) 0.66 (0.22)a 38.72 (0.43) 1.42 (0.36) 16,691 (2346)a 26,749 (5890)a 32,630 (6130)a
188.0 (13.2)a 155.6 (13.1)b 38.20 (0.29)a 0.60 (0.21) 38.73 (0.42) 1.36 (0.29) 14,299 (4426)a 24,751 (8868)a 30,400 (9477)a
Note: Superscripts indicate a significant difference (p , 0.05) from the specified condition; *HRmax, maximum heart rate; HRave, average heart rate; Tco, max,FF, maximum core temperature during simulated firefighting activities; DTco,FF, change in core temperature during simulated firefighting activities; Tco, max,Tot, maximum core temperature achieved during study; DTco,Tot, change in core temperature during study protocol; Acel_Hip, hip accelerometer counts; Acel_Ankle, ankle accelerometer counts; Acel_Wrist, wrist accelerometer counts. d n ¼ 15.
whereas the change in core temperature pre- to post-simulated firefighting activity was significantly larger for ECFF than ECTM ( p ¼ 0.021). For all accelerometry data, the vector magnitude counts were significantly lower in the ECTM trials compared to either of the simulated firefighting trials ( p , 0.001) and no differences were measured between the two firefighting activity trials (i.e. ECFF and BBFF). Perceptual measures on the other hand indicated that the firefighters felt significantly more affected by the ECFF condition than the other simulated firefighting activities (Table 3). Prior to firefighting, participants indicated feeling between ‘Good’ and ‘Very Good’ (, 4.1), were relatively comfortable (, 4.2) and had no issues with breathing (, 1.2), though they did report slightly more difficulty breathing prior to the BBFF condition than the ECTM ( p ¼ 0.021). However, post-firefighting, firefighters reported significantly lower scores in the ECFF condition than in the ECTM and BBFF conditions on the breathing scale ( p ¼ 0.004, p ¼ 0.025), feeling scale ( p , 0.001, p , 0.001) and thermal sensations scale ( p ¼ 0.001, p ¼ 0.002). Furthermore, firefighters rated their perceived exertion level much higher for ECFF than BBFF ( p ¼ 0.022) and ECTM ( p , 0.001), while BBFF trials also resulted in significantly higher perceived exertion than ECTM ( p , 0.001). Identical activities were conducted in the ECFF and BBFF trials that enable comparison of the work completed in each trial regardless of environmental condition (Table 4). The number of stairs climbed and hose advance cycles completed in the ECFF condition were significantly higher than the BBFF ( p ¼ 0.047, p ¼ 0.015, respectively). Accelerometry data indicated that vector magnitude counts in the ECFF condition were not significantly different than the BBFF condition (Table 5). As expected, accelerometry counts in the stairs were much higher for the ankles than the wrist and hip locations, whereas the hose advance and overhaul tasks resulted in much higher movement of the wrist accelerometers and the search task resulted in nearly identical counts for the arms and legs. 4.
Discussion
The most important outcome from this study is that similar physiological responses and activity counts were measured during simulated firefighting activities in a controlled environmental chamber (ECFF condition) as in a live-fire burn Table 3.
Mean (SD) perceptual measures from each exercise protocol condition (n ¼ 19).
Breathing scale Feeling scale Thermal sensations RPE
Pre Post Pre Post Pre Post Post
Environmental chamber treadmill (ECTM)a
Environmental chamber firefighting (ECFF)b
Burn building firefighting (BBFF)c
1.11 (0.32)c 3.37 (1.12)b 4.05 (0.97) 1.11 (2.13)b 4.24 (0.39) 5.87 (0.76)b 13.8 (2.4)b,c
1.16 (0.37) 4.16 (0.69)a,c 4.11 (0.94) 2 0.37 (2.17)a,c 4.34 (0.47) 6.47 (0.51)a,c 17.1 (1.5)a,c
1.37 (0.68)a 3.68 (0.82)b 4.26 (0.81) 1.32 (2.33)b 4.05 (0.60) 5.84 (0.71)b 16.3 (1.6)a,b
Note: Superscripts indicate a significant difference (p , 0.05) from the specified condition.
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Table 4. Mean (SD) work cycles, distance, and maximum heart rate recorded from each of the four stations conducted in the firefighting condition (n ¼ 19).* Environmental chamber firefighting (ECFF) Stairs Hose advance Search Overhaul
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a
Cycles (#) Max heart rate Cycles(#) Max heart rate Distance (ft) Max heart rate Cycles(#) Max heart rate
Burn building firefighting (BBFF)
a
33.9 (7.1)a 162.7 (14.3) 45.8 (9.9)a 177.6 (11.3) 92.4 (29.9) 181.4 (13.6) 52.5 (11.3) 184.7 (12.9)
36.0 (6.1) 166.0 (13.2) 50.8 (13.4)a 180.2 (10.6) 97.5 (32.1) 183.6 (11.7) 50.9 (12.6) 187.3 (12.6)
(bpm) (bpm) (bpm) (bpm)
Indicates a significant difference (p , 0.05) between conditions.
Table 5. Mean (SD) vector magnitude acceleration counts from each of the four stations conducted in the firefighting condition (n ¼ 16). Environmental chamber firefighting (ECFF) Stairs Hose advance Search Overhaul
Acel_Hip Acel_Ankle Acel_Wrist Acel_Hip Acel_Ankle Acel_Wrist Acel_Hip Acel_Ankle Acel_Wrist Acel_Hip Acel_Ankle Acel_Wrist
4691 (881) 10,046 (3160) 5343 (1143) 3832 (1542) 3608 (1707) 7637 (1317) 5489 (1452) 10,870 (3549) 10,559 (3203) 3055 (1257) 3873 (1409) 9553 (2530)
Burn building firefighting (BBFF) 4133 9085 4737 3356 2041 7307 4703 10,627 9705 2472 3608 9124
(1321) (3894) (1327) (1658) (1518) (2306) (1719) (4425) (3620) (1090) (1707) (3366)
Note: Acel_Hip, hip accelerometer counts; Acel_Ankle, ankle accelerometer counts; Acel_Wrist, wrist accelerometer counts.
structure (BBFF condition). Average heart rates were slightly higher in the chamber, which is attributed to a larger amount of work completed during these trials. This result is likely due, in part, to greater visibility within the chamber provided by the overhead lights compared to the flashlight and firelight in the BBFF condition. Additionally, significant differences in physiological responses were obtained in the treadmill protocol compared to the firefighting activities in terms of maximum and average heart rate, core temperature response to the activities and total accelerometry counts. However, firefighters perceived a significantly higher exertion level as well as had more negative affect, felt hotter and had more difficulty breathing in the ECFF condition than the other conditions studied here. The increasingly negative feelings and heart rate may be attributed to the heavier exertion in this condition combined with breathing warm moist air in the environmental chamber as compared to regulated air from an SCBA. Simulated firefighting activities in a live-fire burn structures have historically provided a controlled means of stressing firefighters in a manner that results in similar physiological strain as fireground activities (Romet and Frim 1987; Horn et al. 2013). However, these live-fire structures are not commonly available to academic research programmes due to their specialised nature, cost and required safety precautions. Laboratory environmental chambers cannot reproduce the high temperatures, radiant heat flux conditions or the psychological effects of the flame and smoke seen in live-fire burn buildings. However, our results indicate that using the FAS in an environmental chamber within a lab setting can induce similar physiological responses as a live-burn scenario. This provides evidence that activities in a relatively small and costefficient chamber can be used as a viable substitute for activities performed in a live-fire scenario. Whereas the differences are small and there may be limited clinical relevance of this finding, the average heart rates were higher throughout the ECFF protocol compared to the BBFF protocol and firefighters perceived an increased exertion level and more negative self-perceptions of their physical condition; these results accurately reflect that firefighters completed more work through the ECFF protocol as measured via accelerometry and total work counts during the activities. Firefighters reported during informal feedback that they were less confident of their movements in the BBFF protocol due to the limited visibility within the burn structure. However, in the ECFF protocol, lights within the chamber were on throughout, allowing more accurate and confident movements, which likely resulted in the completion of more work.
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We suggest that this protocol might more accurately reflect fireground conditions if the chamber lights were turned off and flashlights were used to illuminate the objects, targets and pathway as was done in the BBFF protocol. Furthermore, firefighters reported discomfort in breathing warm moist air from the chamber in ECFF condition, but not in the other conditions. The more negative affect and ratings of post-exercise breathing and thermal conditions as well as higher heart rates in the ECFF condition are partially attributed to this concern. The ECFF condition could provide a higher fidelity simulation of the live-fire conditions if subjects were breathing through their SCBA while conducting activities in the chamber. The approach proposed by Kesler et al. (2014) would allow portable collection of metabolic data while breathing through a firefighting SCBA and may reduce the negative feelings reported here. This difference between inhaled air conditions introduces some controlled variability in the design and is acknowledged as a limitation of this study. However, important metabolic data were collected from the two environmental chamber tasks and will be reported elsewhere. While largely similar physiological responses were measured between the ECFF and BBFF protocols, the heart rate and core temperature responses and accelerometer counts during the common treadmill protocol in the environmental chamber (ECTM) were significantly reduced compared to the simulated firefighting activities trials. Treadmill protocols are frequently utilised in academic settings when studying physiological responses of firefighters, and it is common to have participants work for a much longer period of time – often multiple cylinders of air – in order to achieve a similar increase in heart rate and core temperature commonly encountered in live-fire scenarios that would require one cylinder of air or less (Selkirk and McLellan 2004; Hostler et al. 2010b). Furthermore, the ECTM protocol does not replicate the typical fireground activities particularly closely, nor does it stress the different muscle groups commonly employed on the fireground as seen by the significantly reduced movement of accelerometers at each location, particularly the hip and wrist. The thermal conditions (478C) used during this treadmill protocol were significantly hotter than those typically reported in literature (# 358C) (Selkirk and McLellan 2004; Hostler et al. 2010b). We chose to utilise this temperature as it is near the upper limit of common commercial environmental chambers as well as laboratory tools used in different parts of the study. While lower than the temperature within the burn structure, this higher environmental chamber temperature is more likely to replicate the common working environment that firefighters encounter in a structure fire (excluding operations where the firefighter is in the fire room or the occurrence of extreme events which are relatively uncommon in actual operation). The increase in core temperature during the ECTM protocol was approximately 0.0378C/min, which is significantly higher than the temperature change rate reported by Selkirk and McLellan (2004) when working at the same treadmill speed and incline (‘Medium level’) at 358C (maximum temperature studied). Interestingly this value is nearly as high as the rate of rise working at the ‘High level’ at 358C (0.0398C/min) (Selkirk and McLellan 2004). These core temperature change rates are significantly smaller than those measured in the ECFF activities (0.0478C/min; in thermal conditions identical to the ECTM protocol) and the BBFF activities (0.0438C/min; in live-fire conditions). Compared to core temperature change rates measured during repeated bouts of live-fire training activities, these rates from ECFF and BBFF activities correspond very well with the maximum rate measured during latter work cycles (0.0488C/min) (Horn et al. 2013). 5.
Conclusions
Nineteen firefighters completed three different exercise protocols to simulate physiological responses common during firefighting activities that were conducted in both a controlled environmental chamber and live-fire training facility. The most significant outcome of this study is that the protocol utilising a newly proposed FAS within a laboratory grade environmental chamber (ECFF) introduced here elicited similar physiological responses as the simulated firefighting activities conducted in a live-fire structure under very different thermal conditions (BBFF). This result provides confidence in the ability of laboratory-based studies to replicate more realistic live-fire scenarios in terms of physiological response of the participants. By comparison, the response to a treadmill protocol commonly used in laboratory settings (ECTM) resulted in significantly reduced heart rate, core temperature and activity counts compared with the BBFF protocol. These data can be used to inform researchers and policy-makers of the effect of different protocols on SCBA or PPE human factors assessment. Disclosure statement There are no conflicts of interest regarding this work.
Funding This work was supported by the Department of Homeland Security Fire Prevention and Safety Program [grant #EMW-2010-FP-01606].
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