The thermal ergonomics of firefighting reviewed

Applied Ergonomics 41 (2010) 161–172

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The thermal ergonomics of firefighting reviewed David Barr*, Warren Gregson, Thomas Reilly Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Henry Cotton Campus, Webster Street, Liverpool L3 2ET, United Kingdom

a r t i c l e i n f o

a b s t r a c t

Article history: Received 1 December 2008 Accepted 12 July 2009

The occupation of firefighting is one that has repeatedly attracted the research interests of ergonomics. Among the activities encountered are attention to live fires, performing search and rescue of victims, and dealing with emergencies. The scientific literature is reviewed to highlight the investigative models used to contribute to the knowledge base about the ergonomics of firefighting, in particular to establish the multi-variate demands of the job and the attributes and capabilities of operators to cope with these demands. The job requires individuals to be competent in aerobic and anaerobic power and capacity, muscle strength, and have an appropriate body composition. It is still difficult to set down thresholds for values in all the areas in concert. Physiological demands are reflected in metabolic, circulatory, and thermoregulatory responses and hydration status, whilst psychological strain can be partially reflected in heart rate and endocrine measures. Research models have comprised of studying live fires, but more commonly in simulations in training facilities or treadmills and other ergometers. Wearing protective clothing adds to the physiological burden, raising oxygen consumption and body temperature, and reducing the time to fatigue. More sophisticated models of cognitive function compatible with decisionmaking in a fire-fighting context need to be developed. Recovery methods following a fire-fighting event have focused on accelerating the restoration towards homeostasis. The effectiveness of different recovery strategies is considered, ranging from passive cooling and wearing of cooling jackets to immersions in cold water and combinations of methods. Rehydration is also relevant in securing the safety of firefighters prior to returning for the next event in their work shift. Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved.

Keywords: Firefighter Physical demands Physiological responses Recovery strategies

1. Introduction Firefighting is an occupation characterised by prolonged periods of low-intensity work and occasional bouts of moderate to highintensity efforts (Bos et al., 2004; Scott, 1988). In some instances, firefighters may also perform strenuous work for periods of an unpredictable duration under conditions of high environmental heat strain (Romet and Frim, 1987; Rossi, 2003; Smith et al. 1997, 2001). The tasks associated with firefighting place high physical demands upon those engaged. Carrying equipment, operating in protective clothing, and dealing with the tasks in hand entail a large outlay of energy expenditure (Bilzon et al., 2001; Gledhill and Jamnik, 1992; Lemon and Hermiston, 1977; von Heimburg et al., 2006). In order to complete such tasks successfully the firefighters must possess certain physiological characteristics. Successful completion of fire-fighting activities requires high levels of contribution from both aerobic and anaerobic energy systems (Bilzon et al., 2001; Gledhill and Jamnik, 1992) and is associated

* Corresponding author. E-mail address: [email protected] (D. Barr).

with high levels of muscular strength and endurance. In an occupational setting such as firefighting, protective clothing is required to shield the individual from hazards (e.g. fires and chemical substances) that may be encountered during work. The protective clothing worn by firefighters is typically heavy, thick with multiple layers, and also encapsulates the head. The reduced water-vapour permeability across the clothing layers also limits the rate of evaporative heat exchange with the environmental conditions increasing the degree of physiological strain (Cheung et al., 2000; Nunneley, 1989). The combined effects of strenuous exercise, protective clothing, and high ambient temperatures under which firefighters are frequently required to operate may lead to high levels of cardiovascular and thermoregulatory strain. Such physiological alterations are frequently associated with decrements in work capacity (Hancock and Vasmatzidis, 2003) and heat-induced exhaustion (Cheung et al., 2000). In this review we will summarise the available literature on the physical demands of fire-fighting activities and the physical attributes required for successful performance of such tasks. The physiological responses during fire-fighting simulations, the metabolic effects of protective clothing, and its impact on heat production and heat loss will also be described. The final section

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will focus on research into interventions for reducing the physiological strain. 2. Physiological profile of the firefighter The tasks associated with fire suppression and search and rescue activities impose a high physical burden on those engaged. Carrying equipment, operating in protective clothing, and dealing with the prevailing tasks entail a large outlay of energy expenditure. Given that firefighters are exposed to such stressors regularly, it is important that they possess certain physiological characteristics to allow for rapid and successful execution of fire-fighting activities. High levels of aerobic fitness, in combination with muscular strength and endurance in both the upper and lower body, flexibility, and a favourable body composition, are essential for meeting the demands associated with firefighting, maintaining the health and safety of the firefighter, and preserving public safety. Ability to perform such tasks quickly and effectively may lessen the amount of casualties and human suffering, and significantly reduce financial loss. 2.1. Aerobic fitness Tasks such as search and rescue of victims, climbing ladders and stairs, and charging a hose when performed in full fire-fighting protective clothing and self-contained breathing apparatus can have an energy cost corresponding to 80–100% of a firefighter’s _ VO 2max (Lemon and Hermiston, 1977; O’Connell et al., 1986; Bilzon et al., 2001; von Heimburg et al., 2006; Holmer and Gahved, 2007; Elsner and Kolkhorst, 2008). The findings from these studies have led to a variety of recommendations for aerobic power levels that provide an adequate safety margin for firefighters when performing fire-fighting activities. Maximal oxygen uptake values of firefighters from various countries are shown in Table 1. With no standard test for assessing _ VO 2max it is difficult to draw comparisons between brigades as a number of studies from many different countries have reported _ VO 2max values with some measured during maximal exercise tests and others estimated using submaximal exercise protocols, multistage fitness test or even a questionnaire, and in some cases no

_ indication of how VO 2max was assessed. The studies in Table 1 indicate that firefighters have a mean aerobic power ranging from 39.6 to 61 ml$kg 1$min 1; with some individual values ranging from 31.5 to 73.3 ml$kg 1$min 1. The firefighters at the lower end of the scale would not be able to perform successful execution of fire-fighting activities. Elsner and Kilkhorst (2008) shied away from prescribing a definite threshold for firefighters whilst emphasising its importance, _ reporting that those firefighters with the lower levels for VO 2max tended to complete a simulation that averaged 11.65  2.21 min _ more slowly than counterparts with higher levels of VO 2max . Moreover, the latter group members were able to operate at a higher _ proportion of VO 2max than the former group. In a study by Sothmann et al. (1990), seven from a group of 32 firefighters voluntarily quit a protocol involving fire-fighting activities due to excessive fatigue; _ five of the firefighters had VO 2max values between 26 and _ 33.5 ml$kg 1$min 1 and the remaining two had VO 2max values below 35 ml$kg 1$min 1. As a result of these findings the authors proposed an aerobic power value of 33.5 ml$kg 1$min 1 as the minimum acceptable level for performing fire-fighting activities. Another important finding from this study was that performance time of the fire-fighting simulation increased with advancing age _ even when subjects were matched for VO 2max. This finding and the fact that both cross-sectional and longitudinal studies have indicated a decline in maximal aerobic power at a rate of around 5 ml$kg 1$min 1 per decade after the age of 30 years in both endurance-trained and untrained individuals (Buskirk and Hodgson, 1987; Wilson and Tanaka, 2000) and firefighters (Kilbom, 1980; Saupe et al., 1991) have implications for firefighters of advancing age, as the required demands for successful completion of fire-fighting activities remain the same regardless of age. In a study of UK firefighters, Scott et al. (1988) reported that over 93% of firefighters rated themselves as having average or aboveaverage fitness levels compared to the general population. The _ 2max of the firefighters in this study was mean VO 43.7 ml$kg 1$min 1. Peate et al. (2002) also reported a lack of association between self-perception and actual aerobic fitness in US firefighters. From a group of firefighters in this study who rated _ themselves as having high fitness levels, 29% had a VO 2max value

Table 1 Summary of studies reporting aerobic capacity for firefighters. Author/year Davis et al., 1982 Skoldstrom, 1987 Faff and Tutak, 1989 Gahved and Holmer, 1989

Origin

USA Sweden Poland Sweden volunteer and professional firefighters Ilmarinen et al., 1997 Finish firefighting instructors Smith and Petruzzello, 1998 USA Carter et al., 1999 Canada Weafer, 1999 UK Petro-chemical plant fire response group Budd, 2001 Australian bush firefighters Hooper et al., 2001 U.K Bilzon et al., 2001 UK Royal Navy firefighters Peate et al., 2002 USA Clark et al., 2002 USA Eglin et al., 2004 UK firefighting instructors McLellan and Selkirk, 2004 Canada Eglin et al., 2004 UK firefighting instructors Smith et al., 2005 USA Selkirk et al., 2004 Canada von Heimburg et al., 2006 Norway Ilmarinen et al., 2004 Finland Carter et al., 2007 UK Barr et al., 2008 UK Firefighters Barr et al., 2009 UK Firefighters

Number

Age/range

V_ O2max /range

100 males 8 males 18 males 2 x 12 males

33.1  7.6/21–57 35  4/30–42 29  7 V, 33  5/ P, 34  3

39.6  6.42 Balke Treadmill protocol 49  7/45–54 Astrand protocol 41.4  8.8 Cycle ergometer V, 47  7.2/P,47.5  5.7

8 males 10 males 12 males 14 males

38 (31–44) 34.5  5/ 28-42 31.8  6.7 28.5  1.8

51.6/ 46-60 44.8  4.7/37–53 61  3.9 48.75  4.96

Not stated Estimated from 1.5 mile run Cycle ergometer Bruce Protocol Treadmill

28 males 21 males,1 female 34 males, 15 females 96 males, 5 females 168 males 13 males 24 males 10 males 11 males 15 males 14 males 12 males 10 males 12 males 9 males

26 /18–45 35  8/21–54 26  7 m/26  6 32  8/20–58 33.5  8.6/18–58 37.5  3.3 39  0.7 38.2  4.8 31.8  6/24–38 41  1 38  9/26–54 32.1/26–46 33.3  4.2 40.63  7.9/28.2–49.8 41.92  6.7/28.2–52

47/31–63 43.7  6/34.3–57.8 54.6  5 m/43  8.1 f 41.8  8 44.6  5/31.5–58 43.1  7.7 51.2  1 42.4  7.5 43.4  5.7/35–54 45.7  1.4 53  5/41–63 46.9  9.5/33.4–73.3 50.9  7.0 43.54  3.92/50.5 43.32  5.4/33.4–51.13

Not stated Stepping exercises test Treadmill V_ O

Method

2max

Bruce Protocol Treadmill Bruce Protocol Treadmill Submaximal step test Treadmill V_ O2max test Predicted (Astrand et al 2003 Estimated from 1.5 mile run Treadmill V_ O2max test Graded treadmill test Not stated Treadmill V_ O2max test Bruce Protocol Treadmill Bruce Protocol Treadmill

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between 22 and 37 ml$kg 1$min 1. These studies highlight the limitations of self-reported subjective fitness levels when compared to formal objective assessments. 2.2. Anaerobic fitness Studies have indicated that fire-fighting activities require high levels of contribution from the anaerobic energy system of around 40% of total energy expenditure (Lemon and Hermiston, 1977; Weafer, 1999; Bilzon et al., 2001). Blood lactate concentrations of up to 13.1 mmol$l 1 have been reported during fire-fighting simulations (Lemon and Hermiston, 1977; Gledhill and Jamnik, 1992; Smith et al., 1996; von Heimburg et al., 2006; Holmer and Gavhed, 2007), which can lead to the onset of fatigue, the extent of which depend on the fitness of a firefighter (Bilzon et al., 2001). The anaerobic threshold occurs at a higher percentage of maximal aerobic power in individuals with greater aerobic power (Ready and Quinney, 1982). As a result of this adaptation, a greater percentage of energy is derived from aerobic processes during firefighting activities of high intensity (Lemon and Hermiston, 1977; Bilzon et al., 2001). This capability is an advantage in that the recovery period following high-intensity efforts is shortened. Data for the anaerobic capacity of firefighters are limited, and the test protocols used to measure anaerobic capacity have not been validated. Nevertheless, a strong correlation between anaerobic capacity and performance of fire-fighting activities has been reported in male firefighters. Rhea et al. (2004) reported superior performance of fire-fighting activities that included hose pull, victim drag, stair climb, and equipment hoist in firefighters who performed better at a 400-m sprint. The anaerobic power of incumbent female firefighters was measured using the Wingate Anaerobic Test by Findley et al. (2002) who reported that female firefighters possessed anaerobic power levels similar to that of the general female population. The authors concluded that female firefighters might not possess the necessary properties within their skeletal muscle to perform the high-intensity work associated with firefighting. 2.3. Muscular strength Activities associated with firefighting such as carrying ladders and using heavy manual/hydraulic tools have been rated by firefighters to be the most demanding and frequently encountered tasks in terms of muscular strength and endurance, utilizing both upper and lower body musculature (Lusa et al., 1994). A high level of muscular strength is not only an important attribute for successful performance of fire-fighting tasks but also may serve to reduce the incidence of injury (Wilson et al., 2005). The relationship between muscular strength and fire-fighting activity using both single and multiple strength measurements is well documented. Davis et al. (1982), Williford et al. (1999), Bilzon et al. (2001), and Rhea et al. (2004) used isometric hand grip as a measure of strength, which is strongly correlated with upperbody strength and lean body mass (Leyk et al., 2007). These four studies reported strong relationships with fire-fighting activities which require both muscular strength and endurance such as forcible entry, hoisting of a hose, chopping tasks, and victim rescue. Sothmann et al. (2004) employed a test battery of field measures consisting of a hose drag/high-rise pack carry, arm lift, and arm endurance exercise. These test battery items combined significantly to predict performance time in fire-suppression activities. The authors concluded that use of this test battery would identify 82% and 72% of successful and unsuccessful performers, respectively. Similar findings were reported by Henderson et al. (2007) who noted that a high level of composite strength (bench press, ‘‘lat pull

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down’’, and grips strength) was a good predictor of fire-fighting performance time. Both Sothmann et al. (2004) and Henderson et al. (2006) advocated the use of simple field measures of muscular strength for the determination of successful fire-fighting performance. Nevertheless, the use of dynamic performance tests and isokinetic assessments could generate additional insights although their contributions have not been adequately assessed in this area. As strength is directly related to muscle cross-sectional area, the above findings suggest that individuals with low muscle mass, in particular women, may struggle to perform fire-fighting activities as the relative contribution is greater compared to larger individuals. 2.4. Body composition Excess body fat impacts on a firefighters’ performance in a number of ways. During exposure to hot environmental conditions, body fat acts as an insulator and hinders heat dissipation, thereby contributing to a greater rise in core temperature (McLellan, 1998). Excess body fat acts as a dead weight when performing locomotive work against gravity (Reilly, 1996), impacting on activities such as ladder and stair climbing (Willford et al., 1999). Excess body fat is also associated with low levels of cardiorespiratory fitness, which along with being overweight, is a risk factor for cardiovascular morbidities. One of the leading causes of in-line deaths of firefighters is myocardial infarction (Kales et al., 2003). Autopsies have shown underlying atherosclerosis in firefighters to be the major contributing factor in these myocardial infarctions (Kales et al., 2003). Significant correlations have been reported between percentage body fat and simulated fire-fighting performance. Willford et al. (1999) reported strong relationships between both percentage body fat and fat-free weight with performance of fire-fighting activities which included: stair climbing, hose hoist, forcible entry, advancing a hose, and victim rescue. The strongest relationship reported was between percent body fat and stair climbing, those with the highest fat values performing more slowly. Lyons et al. (2005) reported significant correlations between percentage body fat and both metabolic rate and heart rate during treadmill walking when wearing heavy fire-fighting protective clothing. Individuals with greater fat mass may therefore display a greater metabolic rate and a resultant increase in heat storage during fire-fighting activities relative to leaner individuals. Despite the above information, various authors have reported firefighters to be overweight and obese. Scott et al. (1988) reported that over 50% were overweight, with differences ranging from 3.6 to 12.1 kg. An increase in the prevalence of obesity with advancing age in firefighters was found by Soteriades et al. (2005) in a study performed over 5 years in which a 4-fold increase in firefighters with a body mass index (BMI) of over 40 was reported. Obese firefighters in this study were more likely to possess other risk factors for cardiovascular disease, such as hypertension and an unfavourable lipid profile. Clark et al. (2002) studied a group of US firefighters and reported that despite the firefighters meeting the requirements for maximal oxygen uptake (44 ml$kg 1$min 1), 60% were overweight and 32% were morbidly obese according to the BMI. However, due to the fact that firefighters tend to play sports such as rugby and soccer and also engage in resistance training, activities which increase skeletal muscle mass, the use the BMI must be applied with caution in this population as it tends to overestimate in people with high muscularity (Going and Davis, 2001; Reilly and Sutton, 2008). This was found to be the case in a study by Barr et al. (2008) who used dual-energy X-ray absorptiometry to assess body composition and reported that a group of 30 firefighters with a mean age of 41 and a BMI of 28 had a total

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body fat of 20%, which is within the healthy range for males of that age (World Health Organisation, 2000). 3. Physical demands of fire-fighting activity Firefighting is an occupation that imposes high physical demands on the operator when engaging in activities such as ladder and stair climbing, victim rescue, and equipment transportation. The physical demands associated with firefighting which result in near and maximal heart rate and require contributions from both aerobic and anaerobic energy systems are the result of the intrinsic metabolic and physical demands of various tasks combined with extrinsic stressors such as clothing and equipment (Bilzon et al., 2001). The metabolic demands of fire-fighting activities have been investigated in the absence of environmental stressors under both laboratory and field conditions. Routine station activities including equipment maintenance, cleaning and administration duties, hydrant inspection, fire _ prevention, and topography average w20% of a firefighters VO 2max (Scott et al., 1988). Activities which require the transportation of ones own mass against gravity while wearing full fire-fighter protective clothing, along with self-contained breathing apparatus in addition to moving heavy equipment required for firefighting, have been found to yield the greatest levels of energy expenditure. These findings have been reported during civilian (Lemon and Hermiston, 1977; O’Connell et al., 1986; Gledhill and Jamnik, 1992; von Heimburg et al., 2006; Holmer and Gavhed, 2007), naval (Bilzon et al., 2001), and industrial (Weafer, 1999) fire-fighting activities. The metabolic demands of civilian fire-fighting activities performed under field conditions are well documented. Gledhill and Jamnik (1992) investigated activities including carrying equipment upstairs in a high-rise building, rescuing victims, and forcible entry*. The most metabolically demanding activity was carrying a halligen tool* up high-rise stairs, resulting in a mean oxygen uptake of 44 ml$kg–1 min 1 and a heart rate response of 163 beats$min 1. Activities such as forcible entry and dragging a 90-kg manikin casualty utilised an oxygen uptake of 30.5 and 20 ml$kg–1 min 1, respectively. The highest heart rate (181 beats$min 1) value was reported during a pitched roof ventilation* task which only required an oxygen uptake of 28 ml$kg–1 min 1, suggesting a high anaerobic contribution during this task, probably due to the fact that activities such as this are more reliant on upper body musculature. Lemon and Hermiston (1977) investigated the physical demands of firefighters in protective clothing, but without self-contained breathing apparatus performed four tasks, namely: aerial ladder climb, victim rescue, hose dragging, and ladder raise. The design of this study allowed for individual quantification of each task as they were performed separately. The data indicated that all four tasks were of similar intensity; firefighters were working at w70% 1 _ VO 2max , 10 METS, and using around 12 kcal min . Those fire1 1 _ were able to fighters with a VO 2max greater than 40 ml$kg– min perform a greater percentage of each task aerobically compared to 1 1 _ firefighters with a VO 2max less than 40 ml$kg– min , who were more reliant on anaerobic processes. Holmer and Gahved (2007) quantified the metabolic cost of ‘simulated work tasks’ performed on a test ground. In total, five activities were performed twice. These activities included walking/ running on a flat ground, climbing three flights of stairs, and descending four flights of stairs into a basement. The average completion time of the activity was w22 min. The whole exercise elicited an oxygen uptake of 2.75 l$min 1 (33.9 ml$kg–1 min 1). The highest oxygen uptake value was observed during stair climbing of 3.55 l$min 1 (43.8 ml$kg–1 min 1). In this study, firefighters who had a high aerobic fitness were able to complete the

fire-fighting simulation in the shortest time period. O’Connell et al. (1986) reported that a minimal value of 2.7 l min 1 (39 ml kg 1 min 1) was required to complete 5 min of stair climbing on a stairtreadmill ergometer at a rate of 60 steps min 1 in full personal protective clothing incorporating self-contained breathing apparatus. During this activity the firefighters were working at 80.3%, _ 94%, and 87.8% of their maximum VO 2max , heart rate, and power output (watts), respectively. Rescue of victims from multi-storey buildings is a part of firefighting; during emergency situations it is unsafe to use lifts. Therefore, during victim rescue, firefighters must engage in activities such as stair climbing prior to performing rescue work. von Heimburg et al. (2006) documented the energy cost of victim rescue from a hospital with firefighters wearing full personal protective ensemble incorporating self-contained breathing apparatus (SCBA). During this field-based study firefighters climbed six floors up a staircase (a vertical assent of 20.5 m) while carrying a 10-m fire hose, an axe, and a flashlight (total weight including PPE and SCBA 37 kg). Once at the top of the stairs, the firefighter rescued six patients, by dragging them individually along the floor on a ‘rescue mat’, covering a total distance of 162 m. Mean oxygen uptake, heart rate, and blood lactate at the top of the stairs measured 2.8 l$min 1 (44 ml$kg–1 min 1, 88% maximum), 167  13 beats min 1 (83% of maximum), and 6.8 mmol l 1, respectively. The greatest oxygen uptake value of 3.7 l$min 1 was recorded during the patient rescue. The entire operation took w5 min to finish, and on completion mean heart rate and blood lactate were 182 beats min 1 and 13 mmol$l 1, respectively. Firefighting in industrial settings entails performing tasks specific in nature to that industry that are not encountered during civilian firefighting. Tasks such as forcible entry, ladder raising, and ceiling overhauls are very rarely or never performed during a chemical plant fire. The physical demands of firefighting in a petrochemical plant were examined by Weafer (1999). Information gathered from senior officers led to the identification of five essential tasks requiring stamina that are commonly encountered and performed by a single firefighter under emergency conditions in a petrochemical plant. These tasks were pulling a trailer (mass 210 kg) over a gravel surface, opening and closing a stiff valve, ascending and descending a vertical 10-m ladder, running out hose reels, followed by hoisting a hose up a 10-m structure using a rope line. The energy expenditure of these tasks was then quantified in 1 1 _ a group of firefighters (mean VO 2peak of 48.75 ml$kg– min ). The mean oxygen uptake and heart rate required across all the tasks was 40.14 ml$kg–1 min 1 and 171 beats$min 1, respectively. Pulling the trailer elicited the greatest metabolic response of 46.38 ml$kg–1 min 1 and 174 beats$min 1, respectively. Firefighting on board, a ship also requires the performance of tasks that are specific only to shipboard fire suppression activities. For example, activities such as drum carrying are essential to get liquid foam to fire-fighting teams working in below-deck engine rooms. Bilzon et al. (2001) quantified the metabolic demands of _ a range of shipboard fire-fighting tasks in male (VO 2max 1 1 _ 52.6 ml kgd1 min 1) and female (VO 43 ml kg min ) Royal 2max Navy fire-fighting personnel. Firefighters completed five 4-min tasks that are performed during shipboard firefighting; these tasks consisted of boundary cooling*, drum carry, extinguisher carry, hose run, and ladder climb while wearing a full fire-fighter ensemble incorporating SCBA. Each task was performed at a workrate endorsed as a ‘minimal acceptable standard’. The greatest heart rate responses in the males were observed during the drumcarrying task (88% of maximum heart rate) and the lowest during the boundary-cooling task (77% of maximum heart rate). The boundary cooling was the least demanding activity eliciting _ a metabolic demand of 44% and 55% VO 2max in males and females,

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respectively. The most demanding exercise was the ‘drum carrying’ _ 2max in requiring a peak metabolic demand of 82% and 78% VO males and females, respectively. The data from the above studies indicate that firefighting is a physically challenging occupation requiring high levels of an individual’s physical capacity. This work associated with such tasks result in high levels of metabolic heat production, due to the inefficiency of the body to get rid of heat and the impermeability of the protective clothing to dissipate heat. This will result in heat storage and increases in core temperature. The data from the above studies indicate that firefighting is a physically challenging occupation requiring high levels of an individual’s physical capacity. This observation demonstrates the need for firefighters to possess both high levels of muscular and aerobic fitness, and as the job itself is not enough to help firefighters maintain adequate levels of fitness, training programmes and allocated time should be made available for firefighters during ‘stand down’ time. 4. Thermal environments encountered by firefighters The environmental conditions encountered by firefighters impose heat strain through a combination of high ambient temperatures and radiant heat flux. Abbott and Schulmann (1976), Hoschke (1981), and Foster and Roberts (1994) have classified the environmental conditions that firefighters are exposed to into categories ranging from routine to emergency and critical. Routine conditions apply to the majority of operational conditions encountered by firefighters. Foster and Roberts (1994) proposed a time limit of 25 min when operating in temperatures of 100  C and thermal radiation limits of 1 kW m2. Hazardous conditions reflect environmental conditions outside a burning building, in which firefighters would be expected to work for only a short time period due to extreme temperatures and radiant heat flux. The proposed limits for operating in hazardous conditions would be w1 min at 160  C and thermal radiation of 4 kW m2. Extreme and critical conditions refer to those encountered during a flashover; extreme conditions were found to be greater than those reported for hazardous but do not exceed 235  C and 10 kW m2. Foster and Roberts (1994) reported that these conditions can be tolerated for a duration of w1 min, however, they reported an unacceptable level of damage to equipment and protective clothing that occurred which would put fire-fighting personnel at risk, and therefore these conditions would be too dangerous to operate under. Critical conditions are considered potentially life threatening, and firefighters would not be expected to persevere with operating in such an environment. Problems exist when monitoring and controlling environmental conditions during live fire simulations. Many researchers have reported temperature data collected by means of temperaturesensitive thermocouples which are held in fixed positions at a variety of locations within fire-fighting training facilities (Rossi, 2003). In some cases where temperature readings have been reported, no means of how and where environmental temperature was monitored was provided (Smith et al., 2001; Smith and Petruzzello, 1998). Without accurate details of actual exposure time to a given temperature, it is difficult to establish whether the physiological strain induced by the activities were the result of the physical demands of the activities or the heat stress imposed by the environment, or a combination of the two. Eglin et al. (2004) have shown that environmental temperature readings using thermocouples attached at fixed positions within the training facility do not reflect temperature at the surface of the protective clothing worn by fire-fighting personnel. Environmental temperature was monitored on each floor where each instructor observed recruits during fire-fighter training. Measurement was achieved using

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thermocouples attached to a metal pole positioned at heights of 0.3, 0.6, 0.9, 1.2, 1.5, and 1.8 m above ground level. Additionally, thermocouples were attached to the outside of the instructor’s tunics at heights level with the shoulder, waist, and hip. Higher temperatures were reported from the thermocouples attached to the metal pole (74  42  C) compared to the instructor’s tunics (shoulder 55  14  C, 48  17  C, and hip 42  12  C). Although these results were taken from fire-fighting instructors whose brief it is to shelter in cool places, they demonstrate that fixed thermocouples do not provide accurate data on the actual temperatures experienced by fire-fighting personnel. 5. Physiological responses to firefighting No published data exist on thermoregulatory responses during real-life operations, as it is impractical and could be dangerous to kit out a firefighter with physiological monitoring equipment during hazardous events. Nevertheless, it has been possible to monitor heart rate continuously throughout the entire shift of a firefighter (Barnard and Duncan, 1975; Kuorinka and Korhonen, 1981; Sothmann et al., 1992; Bos et al., 2004). Lack of control in the monitoring and regulation of environmental conditions during real fire-fighting operations make it difficult to collect data suitable for research purposes. Consequently, research into physiological responses during fire-fighting activities is reliant on data collected during simulations of live fires performed in facilities that are used to train newly recruited firefighters. 5.1. Live fires A few research groups have monitored heart rate responses during actual emergencies (Barnard and Duncan, 1975; Kuorinka and Korhonen, 1981; Sothmann et al., 1992; Bos et al., 2004) but provide no data on environmental conditions. Both Barnard and Duncan (1975) and Kuorinka and Korhonen (1981) reported sharp increases in heart rates (approximately 60 beats min 1) after responding to an alarm; heart rates dropped slightly but still remained elevated compared to the pre-alarm value whilst travelling on the truck to a fire. These initial increases in heart rate cannot be attributed to high environmental temperatures or increased metabolic demands induced by the addition of protective clothing, but more likely to be the combination of a sudden increase in physical activity and the high level of psychological stress. These findings emphasise the need for caution when using heart rate as a measurement during real-life fire-fighting activities as the relative contributions of the cardiovascular, nervous, and thermoregulatory system are difficult to determine. 5.2. Fire-fighting simulations The levels of thermal and cardiovascular stress of firefighting vary depending on the intensity, duration, and nature of the physical tasks and environmental stressors that firefighters are exposed to. Romet and Frim (1987) documented the physiological responses of various activities of a fire-fighting crew during a training simulation. The most demanding activity, which was a 24-min victim search and rescue, resulted in average heart rates of 153 beats$min 1 (85% of age predicted maximum), a rise in rectal temperature from 37.7 to 39  C. and mean skin temperature from 34.5 to 37.4  C. The least-demanding activity, which was that of the crew captain, resulted in average heart rates of 112 beats$min 1 (65% of age predicted maximum), and rises in rectal temperature and mean skin temperature of 0.3 and 1.5  C, respectively. The authors concluded that rotating duties with those crew members performing less strenuous activities could reduce heat stress during

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firefighting. No subjective measurements of rating of perceived exertion, subjective thermal strain, or ambient temperature data were reported in this study. Subsequent studies have included subjective measurements, which are important in helping to separate the thermal and cardiovascular effects of firefighting. A study by Smith et al. (1996) consisted of a 16-min training drill split into 8 min of advancing a hose followed by 8 min of wood chopping in a building containing live fires in which ambient temperatures and relative humidity ranged from 76.7 to 93.3  C and 60–92%, respectively. At the end of the hose task perceived exertion and perceptions of thermal sensations were ‘somewhat hard’ (RPE of 13) and warm (thermal sensation of 5), respectively, complemented with tympanic temperature and heart rate responses of w38.8  C and 170 beats$min 1 (89% of age predicted maximum). Blood lactate rose to 4.2 mmol l 1 at the end of the first 8-min bout. Ratings of perceived exertion and perceptions of thermal sensations at the end of the second tasks were 16 (very hard) and 6 (hot), respectively; these subjective measurements were coupled with heart rates of 186 beats$min 1 (97% of age predicted maximum) and a tympanic temperature increase from 37 to 40  C. Using a training drill of similar duration and intensity as the above study, Smith et al. (2001) reported rectal temperature and heart rate increases from 36.7 to 38.1  C and 70 to 186 beats$min 1, respectively. Rectal temperature continued to rise and peaked approximately 10 min into the recovery period to 38.7  C. The author stated that RPE and thermal sensations increased significantly throughout the training drill but did not provide any data. The discrepancies in core temperature between Smith et al. (1996, 2001) are most likely to be due to the different measurement sites used; it appears that tympanic temperature could be affected by environmental temperature as the drills in both studies were of similar nature and duration and produced similar heart rate responses, but the reported tympanic temperature measurements were almost 2  C higher than the rectal temperature reported by Smith et al. (2001). These studies highlight the limitations of using tympanic temperature during fire-fighting activities. Performing fire-fighting activities under different thermal conditions allows for the effects of environment and activity to be determined separately. Under temperate conditions, Smith et al. (1997), Rayson et al. (2005), and Carter et al. (2007) reported increases in tympanic and intestinal temperature of 0.01, 0.017, and 0.05  C min 1, respectively. However, under hot conditions (89.6  C) Smith and co-workers reported an increase in rate of rise in tympanic temperature (0.11  C min 1) compared to Carter et al. (2007) and Rayson et al. (2005) who reported an increases in the rate of rise of 0.03 and 0.054  C min 1, respectively. This finding suggests that environmental conditions may have impacted on tympanic temperature readings. In all of these studies, compared to the temperate conditions, the firefighters were under greater physiological strain during hot conditions as indicated by the significantly higher heart rates and skin temperature, greater thermal sensation, and perceived exertion. When operating in a temperate environment the level of heat strain is determined by the intensity and duration of exercise performed. For example, in the absence of high ambient temperatures, Rayson et al. (2005) investigated the physiological responses of ascending a tall building (climbing 28 flights of stairs) both with without carrying extended duration breathing apparatus (EDBA) and a hose (w25 kg of external load). When carrying EDBA and hose it took w30 s to ascend each flight yielding a heart rate response of 81% of heart rate reserve during which core temperature and skin temperature rose by w0.02 and 0.07  C per flight, respectively. Without carrying EBDA or hose, the firefighters were able to climb more quickly, taking w15 s to climb each flight. Heart

rate responses of 69% of heart rate reserve were reported and core temperature increased by w0.01  C per flight. Carter et al. (2007) documented the physiological responses from a simulated deep underground tunnel penetration in which firefighters walked at a pace of w4.2 km$h 1 for 89 min at an ambient temperature of w17  C and relative humidity of 44%. During this study in which the firefighters wore gas-tight suits and EDBA, core (intestinal) temperature increased from 37.51 to 38.31  C, a rate of rise of 0.009  C$min 1 and skin temperature increased from 32.65 to 34.12  C. The firefighters on an average worked at 56% of heart rate reserve and estimated sweat rate was 0.72 l$h 1. The above studies show that the physiological strain associated with firefighting results from a number of factors. Even in the absence of high ambient temperatures the endogenous heat production is sufficient at imposing heat strain when the physical activity is of a strenuous nature. Transportation of vital equipment against gravity which is often required exacerbates the physiological strain further. Active cooling would be beneficial following search and rescue activities and between repeated bouts of fire-fighting activities in a hot environment where recovery periods of short duration are permitted. 6. Physiological consequences of wearing fire-fighters protective clothing Firefighters encounter a range of physical and chemical hazards, therefore, wearing protective clothing is essential as it affords protection from such harmful exposures. Protective clothing worn during firefighting shields the firefighter from the extreme environmental temperatures which vary as a function of how long the fire has been burning and the materials involved. Firefighters’ protective clothing consists of an outer shell, moisture barrier, and a thermal liner; with each layer having a specific purpose. The total ensemble is made up of boots, heavy-duty gloves, bunker pants, coat, flash hood, and also worn during fire fighting is SCBA. A typical fire-fighting ensemble (including SCBA) weighs w26 kg. The protective clothing of firefighters has an insulation value of w0.47 m2 K W 1 (clo rating of 2.44) (Holmer et al., 2006). The overall function is to provide the firefighter with adequate protection from heat, flames, and other hazardous environments. However, this protection is often achieved at the expense on body heat balance. The limited vapour permeability across the protective clothing’s layers and the added metabolic heat production resulting from the increased weight impact on the thermoregulatory system by reducing the ability to dissipate generated heat. The end result is continued heat storage in the body (Cheung et al., 2000). 6.1. Effects of firefighter protective on oxygen consumption Firefighter protective clothing increases the metabolic cost (measured using oxygen consumption) of work in two ways, by resisting movement and increasing the total mass of the individual (Huck, 1988). The restriction of movement caused by the added bulk alters the mechanics of gait and the efficiency of movement of the body’s joints, resulting in a ‘hobbling’ or ‘binding’ effect (Coca et al., 2007). A pronounced ‘forward lean’ imposed by the shift in the centre of gravity also impacts on locomotion. The metabolic costs of ‘fire-fighting protective clothing’ have been well documented in well-controlled laboratory conditions with comparisons usually made with uniform or physical education kit. Studies indicate that during treadmill walking performed at low (Skoldstrom, 1987), moderate (Graveling et al., 1999), or high intensity (Baker et al., 2000; Dreger et al., 2006) fire-fighting protective clothing significantly increased metabolic rate.

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Skoldstrom (1987) reported significant increases in oxygen consumption from 0.8 to 1.2 l$min 1 when wearing fire-fighter protective clothing and SCBA (total weight w30 kg), equivalent to 20% and 30% of maximal oxygen uptake while walking on a treadmill at a low intensity (3.5 km$h 1) for 60 min in temperate conditions (15  C). Heart rate was also 25 beats$min 1 higher, and perceived exertion was greater when wearing protective clothing compared to a reference condition. The difference between clothing conditions in oxygen uptake was the same regardless of the ambient temperature even though operating in 45  C resulted in greater heart rate response, increased sweat rate, and subjective responses compared to performing the same work at 15  C. Graveling et al. (1999) reported a 15–20% increase in oxygen uptake during high-intensity treadmill walking (5 km$h 1, 7.5% gradient.) when firefighters wore protective clothing without SCBA. A further increased oxygen uptake by a similar margin was observed when operating with the use of SCBA. However, increases imposed by SCBA appear to be dependent on the weight of the apparatus. Hooper et al. (2001) compared lightweight (15 kg) with conventional (27 kg) SCBA on oxygen consumption. The lightweight apparatus was of significant benefit, requiring 0.26 l$min 1 less than the conventional set. Heart rate was also significantly lowered with the lightweight apparatus, a finding which demonstrates a reduced cardiovascular strain when operating with lightweight SCBA. This favourable cardiovascular response could prolong work tolerance in firefighters during operational activities. 6.2. Thermoregulatory responses of wearing fire-fighter protective clothing Heat stress associated with fire-fighter protective clothing has been documented under different environmental conditions and at various exercise intensities of activity. Under temperate conditions, White and Hodous (1987) reported that treadmill walking (5 km$h 1 and 8% gradient) while wearing fire-fighter protective clothing and SCBA significantly reduced the time to a predetermined level of physiological strain. Fire-fighter protective clothing also impacted on skin temperature, heart rate, and on the rate of rise in core temperature compared to wearing light work clothing (1.85 vs 0.23  C$h 1). Skoldstrom (1987) reported a greater rate of increase in core body temperature when performing treadmill walking at a lower intensity (3.5 km$h 1) but in the presence of heat (45  C and RH 15%) rectal temperature while wearing protective clothing increased at a rate of 2.24  C compared to 0.23  C in a standard uniform. These studies demonstrate the relative contribution of both intrinsic and extrinsic factors on physiological strain. Fogarty et al. (2004) examined the cardiovascular and thermal impact of a ‘fire-fighter protective ensemble’ under conditions of uncompensable heat stress. The use of an exercise protocol consisting of semi-recumbent cycle ergometry permitted the use of impedance cardiography and venous occlusion plethysmography for the measurement of stroke volume and skin blood flow, respectively. Significantly greater core and skin temperature and heart rate responses were found when wearing protective clothing compared to the ‘unclothed’ condition confirming the finding of previous studies. Significant increases in sweat rate in the ‘firefighter protective ensemble’ (1.2 vs 1.9 l h 1) were accompanied by a higher stroke volume, cardiac output, and skin blood flow values compared to the ‘unclothed’ condition. The thermoregulatory responses of three kinds of firefighters’ ‘turnout gear’ with different clo ratings ranging from 2.77 to 3.03 were investigated by Holmer et al. (2006); firefighters engaged in treadmill walking at 5 km$h 1 for 30 min in a climatic chamber with an ambient temperature and relative humidity of 55  C and 30%, respectively. No differences in

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heart rate, skin temperature, or core temperature were found between either turnout suits. These authors concluded that small differences in terms of design, thickness, and insulation value had no effect on the resultant thermoregulatory strain. 7. Cognitive function During fire-fighting search and rescue activities, maintaining adequate performance of mental function in situations of extreme heat and emotional stress is a matter of significant importance as the health and safety of the firefighter, the crew, and the public may be compromised. Under potentially life-threatening conditions, firefighters must make important decisions, remain vigilant, and also remember various geographical points located within a structure on fire in order to be able to navigate their way out of a building either when ambient oxygen levels become low or a casualty is located. In addition to heightened emotional responses, the intensity of the work performed during firefighting and the environmental conditions experienced result in increased core temperature and levels of dehydration which are associated with deteriorations in cognitive performance, specifically those pertinent to central executive tasks (Cian et al., 2000, 2001). It is postulated that during times of increased stress, individuals reallocate attention resources to appraise and cope with stress, which reduces the capacity to process task-relevant information. Profuse sweating resulting in body mass reductions of around 2% bodyweight have been observed in firefighters during simulated firefighting search and rescue activities (Rayson et al., 2005). Such changes in body mass imposed by heat stress have been shown to impact on mental concentration and working memory (Sharma et al., 1986). Data on the cognitive performance of firefighters are limited; with the few studies that have attempted to measure changes in cognitive performance of firefighters following simulated firefighting activities have done so using mental performance tests such as simple reaction time which are not of primary importance during firefighting. The matter of major importance during firefighting is that the correct decision is made and that a few milliseconds are unlikely to incur any detrimental consequences. It has also been reported that such tasks may not be challenging enough to detect differences between different environmental conditions (Smith and Petruzzello, 1998). In a study involving UK firefighters, Rayson et al. (2005) reported no change in rapid visual information processing, spatial memory span, and choice reaction time following a fire-fighting simulation. However, these tests were administered 30 min post-event, the authors acknowledging that any lack of effect could have been lost during the transition period. In the absence of environmental heat, Kivimaki and Lusa (1994) investigated the effects of stress choice reaction, as measured from changes in heart rate from resting heart rate on cognitive function during a solitary ‘smoke-diving’ exercise. It was reported that as the physical stress during firefighting increased, task-focused thinking (measured using the ‘think out aloud method’ for which firefighters were required to speak their thoughts) decreased. No thermoregulatory measurements were taken in this study, making it difficult to ascertain the impact of heat stress that occurs when performing strenuous smoke-diving activities on cognitive function processes. Questions remain unanswered with respect to the impact of heat stress and dehydration on mental performance in firefighters. First, it is not known whether any decline in mental performance during firefighting is dictated solely by the physiological strain; the psychological aspects (anxiety) and experience of firefighters may also be contributory factors. It may be that mental performance declines when cerebral blood flow is reduced as a result of heat stress (Nybo and Nielsen, 2001; Wilson et al., 2003) which impacts

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on tasks associated with the central executive (working memory) (Collette and Van der Linden, 2002). While maintenance of proper hydration levels and active body cooling can help to reduce the physiological strain, their effects on mental performance in firefighters are unknown. Future work on cognitive function in firefighters may be performed in climatic chambers in hot conditions using computer-based cognitive function tests that have ecological validity whilst firefighters perform physical tasks at the typical duration and intensities that reflect the energy expended during firefighting. 8. Recovery strategies In sporting events, cooling of the body often occurs prior to the event but in firefighting this is not really possible or practical due to the unexpected demands of the role. As a consequence, cooling may only be permitted during or following the activity, the latter being important when repeated bouts of fire-fighting activities are undertaken. The purpose of a cooling strategy following heat exposure during firefighting is to restore the body to physiological equilibrium in as quick a time as possible, both for the health and safety of the individual and in preparation for any subsequent operation that may occur. In order to meet the demands of firefighting activity there may be a need for practical cooling strategies that are quick and easy to use, and also possess sufficient capacity to reduce thermal stress in a relatively short period of time. Cooling strategies in firefighters, whilst wearing personal protective equipment (PPE) and self-contained breathing apparatus (SCBA), have been investigated in both laboratory and field settings using several modalities. These methods vary in their effectiveness and practicality and have included passive recovery (Barr et al., 2008, 2009; Carter et al., 1999, 2007; Selkirk et al., 2004), the use of extractor fans (Carter et al., 1999), misting fans (Selkirk et al., 2004), and hand and forearm immersion in water (House, 1994, 1996, 1997; McTiffin, 1994; Selkirk et al., 2004). The benefits of combining cooling strategies have also been investigated (Barr, 2008, 2009). Vests containing ice, cold air, and phase change material have been worn during fire-fighting activities (House 1996; Smolander et al., 2004; Carter et al., 2006), and shorts under PPE have been also examined (McLellan and Selkirk, 2004). 8.1. Passive recovery Passive cooling is an inexpensive and practical method, which consists of firefighters removing breathing apparatus and tunic, having access to drinking water and sitting in shaded area where possible. During cooling research in firefighters, passive recovery has been generally employed as a control condition in both laboratory (Carter et al., 1999; Selkirk et al., 2004; Barr et al., 2008) and field settings (Carter et al., 2007; Barr et al., 2009). The data from studies which have used rest periods in high temperatures indicate that passive cooling is an ineffective method of reducing physiological strain as reflected by a continued rise in core temperature. However, during which the recovery took place in a more temperate environment (w15  C), Carter et al. (2007) reported a drop in core temperature with the use of passive cooling. This finding suggests that passive cooling may only be beneficial in conditions where outdoor temperature is cool, possibly during the winter months of the year and should not be employed in hotter climates or during the summer months. 8.2. Hand and forearm immersion The distal regions (mainly the hands and feet) of the circulatory system are rich in arteriovenous anastomoses (AVAs) which control

blood flow by shunting blood directly to the venous system from arterioles, bypassing capillaries. During heat stress it is purported that AVAs become maximally dilated allowing for greater blood flow to increase heat dissipation (Krogstad et al., 1995). Immersion of the hands in water therefore serves as an effective cooling strategy due to the reduction in the temperature of the cutaneous blood supply imposed by the cold water, which would in turn cool the blood returning to the core, thereby reducing the body temperature (Tipton et al., 1993). Studies using hand and forearm immersion as a cooling strategy are summarised in Table 2. The general consensus is that hand and forearm immersion is an effective method of reducing heat strain in firefighters, with most of the heat loss occurring within 10 min of immersion. The benefits of hand and forearm immersion are also evident during a subsequent bout of work in the heat (Giesbrecht et al., 2007; House, 1996). Hand and forearm immersion may be of benefit in warmer climates or during the summer months when ambient temperatures are higher than at other times of the year (Carter et al., 2007). An important question to address is the optimal water temperature that should be used during hand and forearm immersion? It seems that as a function of increasing water temperature, immersion of a greater surface area of the arm is required for a similar cooling rate to be maintained (Giesbrecht et al., 2007). The fastest cooling rates occur in water of around 10  C (Giesbrecht et al., 2007; House et al., 1997). Tap water which has a temperature of w15  C would be a simple solution due to its accessibility. Water with a temperature of up to 20  C can also be effective if both the hands and forearms are immersed fully (Giesbrecht et al., 2007). In order for hand and forearm immersion to be successful in reducing core temperature, the maintenance of peripheral blood flow is a requirement. Studies indicate that when an individual is in a hyperthermic state, vasodilation of arteriovenous anastomoses is not compromised at water temperatures ranging between 10 and 20  C (House, 1994, 1996; McTiffin and Pethybridge, 1994; House et al., 1997; House and Groom, 1998; Selkirk et al., 2004). 8.3. Cooling vests Cooling vests have been traditionally worn prior to exercise in an attempt to reduce the level of cardiovascular and thermoregulatory strain and increase exercise capacity. Cooling vests operate by conducting heat from the body and can contain either phase change material or ice packs. Chou et al. (2008) compared ice vests with cooling vests containing phase change material (PCM) using cycle ergometry. Firefighters donned vests 10 min prior to exercise. The PCM vests attenuated the rise in rectal temperature and skin temperature compared to ice vests and control. The authors claimed that the phase-change vests were a better alternative to ice vests, although caution must be displayed when interpreting these finding as non-weight-bearing activity was used and as the PCM vest (1.7 kg) was heavier than the ice vests (1.2 kg). During activities such as stair and ladder climbing, cooling vests may be of limited benefit due to the increase in metabolic rate imposed by the extra weight which could outweigh any potential benefits. Wearing an ice vest has been shown to promote marked decrements in thermal strain during laboratory-based treadmill walking activities in the heat during work bouts of low (Bennett et al., 1995), moderate, and high intensity (Smolander et al., 2004). Bennett et al. (1995) reported that wearing an ice vest for 40 min prior to exercise led to a 0.7  C reduction in rectal temperature following 30 min of moderate intensity exercise in the heat. Despite ice vests clearly providing physiological benefits to firefighters working in the heat, this method lacks practicality during firefighting activity in real-life situations since the timing of incidents

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Table 2 Summary of studies reporting the effectiveness of hand and forearm immersion at reducing core body temperature. Study (year)

Subjects

Exercise mode (temperature, RH)

Cooling (room temperature, RH)

Water temperature (oC)

Main outcomes

Selkirk et al. (2004)

Toronto firefighters

Treadmill walking (35  C, 50%) for 55 min

20 minutes of hand and forearm immersion in room with ambient temperature (35  C, RH 50%)

17.4  0.2

House and Groom (1998)

RN firefighters

Stepping exercises (40  C) until rectal reached 38.5

40 min of hand immersion in room with ambient temperature (40  C)

11.9  0.8

McTiffin and Pethybridge (1994)

RN fire-fighting personnel

60 min of hand, foot, and hand and foot immersion (40  C, 50%)

10

House (1994)

RN fire-fighting personnel

Carter et al. (2006)

UK firefighters

Exercise until aural temperature reached 38.5  C (40  C, 50%) Repeated bouts of stepping exercise until aural temperature reached 38.5  C (30  C) Fire-fighting simulation

Y Rectal temperature of 1.06  C hr 1 Y Skin temperature and heart rate [ Work tolerance time Y In aural temperature of 08  C after 10 min Y Rectal temperature of 0.3  C within 20 min No Y in control Y Aural temperature of 0.9  C within 20 min

Giesbrecht et al. (2007)

Canadian firefighters

Repeated bouts of stepping exercise until aural temperature reached 38.5  C (30  C)

is unknown, and only relatively short periods of preparation may be permitted prior to initial entry into the heat. 8.4. Air movement systems The use of an extractor fan is based on the idea that all fire appliances carry a fan; therefore, it would be economical and simple to administer in a hot environment, providing a source of convective heat loss. The use of extractor fans as a cooling strategy was investigated in a laboratory setting by Carter et al. (1999) who reported that an extractor fan alleviated the physiological stress by significantly reducing heart rate and attenuating the rise in rectal temperature during a subsequent 10-min work period. Selkirk et al. (2004) examined the use of a misting fan which delivered a fanpropelled fine mist water vapour at subjects who were seated at a distance of 1.5 m in front of the fans. The misting fan had a significant effect on cardiovascular and thermal strain, attenuating the rise in both heart rate and rectal temperature, which allowed work time to be increased by 25% compared to control condition. A possible disadvantage of this method is that the firefighter could be put at risk of overheating due to the increased moisture content in the protective clothing gained from the misting system.

20

Significant attenuation in aural temperature compared to control

Hand immersion (w15  C)

17

Hand immersion, and hand and forearm immersion (21  C)

Hand immersion in 10, 20, and 30  C. Hand and forearm immersion in 10, 20, and 30  C

Non-significant Y in core temperature, compared to control condition Significant Y in aural temperature with hand immersion in 10  C water, and hand and forearm in 10, 20, and 30  C water No Y with hand immersion in 20 and 30  C

accelerating the physiological recovery by reducing core temperature by 0.5 and 0.7  C laboratory study and live fire study, respectively. Other parameters such as heart rate, skin temperature, and the firefighters’ perception of thermal sensation were significantly lower following the use of this cooling strategy. The core temperature responses in the cooling condition in these two studies are greater than reported in other studies which have used hand and forearm immersion alone following a single bout of activity in the heat. Both House (1998) and Selkirk et al. (2004) reported a 0.3  C reduction in rectal temperature following 20 min of hand and forearm immersion. The findings in both the studies from Barr and co-workers suggest that cooling via application of an ice vest in conjunction with hand and forearm immersion is more effective in mediating decrements in physiological strain during repeated bouts of strenuous fire-fighting activity than hand and forearm immersion alone. However, differences in heat strain with other studies due to methodological differences make it difficult to draw direct comparisons as to the relative contribution of each cooling method. Future research in this area should serve to try and derive the simplest but most effective strategy for cooling firefighters. 8.6. Clothing configurations

8.5. Combination cooling Research into cooling strategies for firefighters which have included cooling vests, the use of fans and hand and forearm immersion has generally been carried out under laboratory conditions following bouts of moderate intensity work in the heat. Barr et al. (2008, 2009) examined the effects of wearing a cooling vest in conjunction with hand and forearm immersion administered during a 15-min recovery period between two bouts of strenuous work in the heat and also in a separate study during simulated search and rescue activities in a building containing live fires. This cooling strategy was successful in

Modern day firefighters’ protective clothing provides greater thermal protection than the traditional fire-fighter clothing. Fire authorities in the USA responded to this change by replacing long pant and long-sleeve T-shirts with short pants and short-sleeve Tshirts. McLellan and Selkirk (2004) investigated the wearing of shorts underneath PPE as an alternative to long pants in an attempt to reduce heat stress. During work tasks of a very light and light intensity, wearing shorts significantly attenuated the rise in rectal temperature, but this difference was not apparent during moderate and heavy work. Indeed, altering clothing configurations can be an effective way of alleviating heat stress. Perhaps of greater concern

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for replacement of long pants with shorts is whether the protection of the firefighters’ clothing ensemble is in any way compromised such that personnel would be at increased risk of heat injury or burns. Prezant et al. (2001) found no significant difference in upper and lower extremity burns when wearing short pants and short sleeve T-shirt or long pants and long sleeve T-shirt.

8.7. Hydration status and fluid replacement Working in protective clothing in extreme heat results in profuse sweating and consequently dehydration. Dehydration is known to impair both cognitive and cardiovascular function (Gonzalez-Alonso et al., 1997) and reduces tolerance time when working in uncompensable conditions compared to euhydrated individuals (McLellan et al., 1999). Brown et al. (2007) investigated the effects of hydration status which was determined from urine specific gravity (USG) in 190 firefighters prior to participation of a series of simulated fire-fighting activities performed under live fire conditions. During these simulations, the firefighters deemed to be in dehydrated state (USG > 1.020) demonstrated significantly greater cardiovascular strain (heart rate 151  3.4 vs 135  9.3 beats min 1) than firefighters deemed to be in a euhydrated state (USG < 1.020). These findings highlight the importance of being in a euhydrated state prior to commencement of work. Investigations into rehydrating firefighters with water during rest periods between work bouts in the heat (Selkirk et al., 2006) and following live fire simulations (Smith et al., 2001) have yielded positive findings in both the cases. A variety of rehydration strategies during rest periods were investigated by Selkirk et al. (2006). In this study three levels of rehydration were examined, with 78%, 63%, and 37% of fluid loss, respectively, being replaced with water. Each level of rehydration improved tolerance time and attenuated the rise in core temperature in a graded manner. Smith et al. (2001) reported that drinking w1.5 l of water during a 10-min rest period and a 90min recovery period restored plasma volume to pre-work values. However, it must be stated that dinking 1.5 l of water in such a short time period is a fairly aggressive hydration strategy.

9. Conclusion In order to meet the demands of firefighting, a firefighter must possess high levels of muscular, anaerobic, and aerobic fitness and have a favourable body composition. However, some research indicates that firefighters fall short of the mark and therefore struggle at times to meet the demands of the occupation. The combination of strenuous work, wearing protective clothing, and thermal environments encountered by firefighters impose severe physiological strain. The level of this physiological strain is in the range reported to impact on cognitive function processes. Reporting to work in a euhydrated state is of considerable benefits for firefighters when performing fire-fighting activities. During the warm months of the year active cooling may be required to accelerate the physiological recovery. Hand and forearm immersion in water appears to be the most effective method, however, research is needed under conditions representative to firefighting in order to determine the most effective and efficient method.

Acknowledgements The authors are grateful for the grant for this work provided by Merseyside Fire and Rescue Service, who have no commercial interest in the outcomes in any of the material reviewed.

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Glossary of fire-fighting terms Advancing a hose: navigating through a building with uncharged hose lines while searching for a reported fire. Boundary cooling: a technique employed during shipboard firefighting in which the external walls of a ships compartment are cooled so that a fire may be controlled and confined to the compartment of origin. Ceiling overhaul: careful examination of building that occurs during the latter stages of an operation when firefighters look for hidden fire inside attics, ceilings, and walls, searching for remaining sources of heat that may re-ignite. Charging a hose: to make water pressure available on a hose in final preparation for its use. This is done on the scene after the hose is advanced.

Forcible entry: gaining entry to an area using force to disable or bypass security devices, typically using force tools, sometimes using tools specialized for entry (e.g. Halligan, K-tool). Halligan tool: forcible entry tool with a pointed pick and a wedge at right angles on one end of a shaft and a fork or cat’s paw at the opposite end. Used in combination with maul or flat-headed axe for forcing padlocks, doors, and windows. High-rise pack: hose bundle prepared for carrying to a standpipe in a high-rise building, usually consisting of 50 or more feet of hose and a combination nozzle. Hose hoist: from the top of the tower, using a hand-over-hand motion, pulling a rope to hoist a donut roll of a hose. Ladder raise: lifting the end of a ladder and using hand-over-hand technique on each rung, walking up the ladder until it is fixed against a wall. Search and rescue: entering a fire building or collapse zone for an orderly search and removal of live victims. Smoke diving: entering into smoke-filled enclosures to perform search and rescue activities and hose advancing.