Physical and thermal strain of firefighters according to ...

1 downloads 0 Views 159KB Size Report
Oct 25, 2011 - ... used to suppress wildfires. J.A. Rodríguez-Marroyo a. , J.G. Villa a ... and Sports, Institute of Biomedicine (IBIOMED), University of Leo´n, ...
This article was downloaded by: [Juan Garcia-Lopez] On: 31 October 2011, At: 15:29 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Ergonomics Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/terg20

Physical and thermal strain of firefighters according to the firefighting tactics used to suppress wildfires a

a

b

b

b

J.A. Rodríguez-Marroyo , J.G. Villa , J. López-Satue , R. Pernía , B. Carballo , J. a

García-López & C. Foster

c

a

Department of Physical Education and Sports, Institute of Biomedicine (IBIOMED), University of León, León, Spain b

Empresa de Transformación Agraria, S.A. (TRAGSA), Madrid, Spain

c

Department of Exercise and Sport Science, University of Wisconsin-La Crosse, La Crosse, WI, USA Available online: 25 Oct 2011

To cite this article: J.A. Rodríguez-Marroyo, J.G. Villa, J. López-Satue, R. Pernía, B. Carballo, J. García-López & C. Foster (2011): Physical and thermal strain of firefighters according to the firefighting tactics used to suppress wildfires, Ergonomics, 54:11, 1101-1108 To link to this article: http://dx.doi.org/10.1080/00140139.2011.611895

PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

Ergonomics Vol. 54, No. 11, November 2011, 1101–1108

Physical and thermal strain of firefighters according to the firefighting tactics used to suppress wildfires J.A. Rodrı´ guez-Marroyoa*, J.G. Villaa, J. Lo´pez-Satueb, R. Pernı´ ab, B. Carballob, J. Garcı´ a-Lo´peza and C. Fosterc a

Department of Physical Education and Sports, Institute of Biomedicine (IBIOMED), University of Leo´n, Leo´n, Spain; bEmpresa de Transformacio´n Agraria, S.A. (TRAGSA), Madrid, Spain; cDepartment of Exercise and Sport Science, University of Wisconsin-La Crosse, La Crosse, WI, USA

Downloaded by [Juan Garcia-Lopez] at 15:29 31 October 2011

(Received 7 January 2011; final version received 3 August 2011) The aim of this study was to analyse the physiological strain of firefighters, using heart rate (HR) and core temperature, during real wildfire suppression according to the type of attack performed (direct, indirect or mixed). Three intensity zones were established according to the HR corresponding to the ventilatory threshold (VT) and respiratory compensation threshold (RCT): zone 1, 5VT; zone 2 (Z2), between VT and RCT; zone 3 (Z3), 4RCT. The exercise workload (training impulse (TRIMP)), the physiological strain index (PSI) and the cumulative heat strain index (CHSI) were calculated using the time spent in each zone, and the HR and core temperature, respectively. Significantly higher mean HR, time spent in Z2 and Z3 and TRIMP h71 were found in direct and mixed versus indirect attacks. The highest PSI and CHSI were observed in the direct attack. In conclusion, exercise strain and combined thermal strain, but not core temperature during wildfire suppression, are related to the type of attack performed. Statement of relevance: Our findings demonstrated that wildfire firefighting is associated with high physiological demands, which vary significantly depending on the tactics chosen for performing the task. These results should be kept in mind when planning programmes to improve wildland firefighters’ physical fitness, which will allow improvement in their performance. Keywords: wildland firefighter; wildfire; heart rate; core temperature; exercise workload

1. Introduction Understanding the energy demands and intensity of work in physically demanding professions is essential for planning programmes to improve the physical condition and improve the workers’ performance, safety and health. A wide range of physically demanding professions have been studied, including soldiers (Kyro¨la¨inen et al. 2008), lifeguards (Prieto et al. 2010), structural firefighters (Smith et al. 2001, Eglin et al. 2004, Richmond et al. 2008) and wildland firefighters (Heil 2002, Ruby et al. 2002, Cuddy et al. 2008). The high physical demands of these professions come not only from the nature of the activities that need to be performed but also from the environmental conditions in which they are performed. Thus, structural and wildland firefighters have to perform physically demanding tasks and deal with a high thermal strain due to high temperatures when working near the fire (Smith et al. 2001) while facing reduced heat dissipation secondary to the use of protective gear (Frank et al. 2001, Petruzzello et al. 2009). Several studies have analysed the thermal and cardiovascular strain of structural firefighters in rescue simulations (Eglin et al.

*Corresponding author. Email: [email protected] ISSN 0014-0139 print/ISSN 1366-5847 online Ó 2011 Taylor & Francis http://dx.doi.org/10.1080/00140139.2011.611895 http://www.tandfonline.com

2004, Richmond et al. 2008). However, relatively fewer studies have analysed these parameters in wildland firefighters (Brotherhood et al. 1997a, Budd et al. 1997c, Budd 2001, Cuddy et al. 2008). Wildfire firefighting is on extremely demanding occupation that mainly takes place during the summer season when forest conditions are dry. It has been estimated using either doubly labelled water (Ruby et al. 2002) or accelerometry (Heil 2002) that the average daily energy consumption by wildland firefighters during fires is 20 MJ d71 (4800 kcal d71). However, energy demands may be affected by the use of different tools (e.g. hoes, rakes, axes, chainsaws, backpack pump, swatter and shovels) that are normally used during wildland firefighting activities (e.g. building fire lines, brush removal, setting backfires and mopping up; Budd et al. 1997b). In addition, the accomplishment of these activities in the presence of fire can increase the thermal and cardiovascular strain experienced by the wildland firefighters (Budd et al. 1997c). Mainly, there are two ways of conducting wildland fire suppression: in a direct or indirect manner (Budd

Downloaded by [Juan Garcia-Lopez] at 15:29 31 October 2011

1102

J.A. Rodrı´guez-Marroyo et al.

et al. 1997a). When wildland firefighters perform a direct attack, they try to extinguish the flames directly and are working relatively near the fire. Alternatively, the indirect attack is carried out at a greater distance from the flames (4 100 m) and is focused on trying to isolate the fuel that is burning from the remaining vegetation, mainly by building fire lines. To the best of our knowledge, no study has evaluated the demands of wildfire suppression in relation to the type of attack on the fire (e.g. tactics) performed by the firefighters. The aim of this study was to analyse the physiological demands and thermal strain of wildland firefighters during real wildfire suppression according to the different attacks, i.e. direct, indirect and mixed attacks. We hypothesise that the exercise demands developed by wildland firefighters could be higher when they are working relatively near the fire, as a result of the higher thermal strain and the faster pace of work used to control the flames. 2. Methods 2.1. Participants

2.2. Experimental design The study was carried out over four consecutive seasons, from 2006 to 2009. In each of the seasons (i.e. June–October), the study was divided into two parts to quantify the effort exerted by the subjects during wildfire suppression. In the first part, all firefighters performed an incremental exercise test in the laboratory to assess their exercise capacity and to determine the heart rate (HR) at which their ventilatory threshold (VT) and respiratory compensation threshold (RCT) occurred. The second part of the study consisted of individual monitoring of the HR and core (gastric) temperature (CT) response during each wildfire suppression analysed, in order to characterise the physiological strain of wildfire suppression, based on the HR and temperature data. 2.3.

Sixty wildland firefighters volunteered and took part in this study (mean + SEM, 28 + 1 year, 76.2 + 0.9 kg, 175.5 + 0.5 cm). They were recruited from different helitack crews (which use helicopters to arrive as early as possible to wildfires) located in different work areas within Spain. We selected a crew (6 subjects) for each of the 10 existing helitack bases. Inclusion criteria included active male free of cardiorespiratory, metabolic disorders and chronic illnesses, not having used any medication and having an experience of at least 2 years as wildland firefighter. Written informed consent was obtained from the subjects before starting the study. Participant physiological characteristics are shown in Table 1. The study protocol was developed in accordance with the guidelines of the Helsinki conference for research on human subjects and was Table 1. Physiological values measured during treadmill exercise testing. Mean + SEM Maximal values VO2max (ml kg71 min71) HR (bpm) RCT VO2 RCT (ml kg71 min71) Percentage of VO2max (%) HR (bpm) VT VO2 (ml kg71 min71) Percentage of VO2max (%) HR (bpm)

approved by the University Institutional Review Board.

54.2 + 1.1 190 + 1 43.3 + 0.6 76.7 + 1.2 168 + 2 26.6 + 0.7 51.2 + 1.1 137 + 2

Note: VO2max, maximal oxygen consumption; RCT, respiratory compensation threshold; VT, ventilatory threshold.

Laboratory testing

All subjects performed a treadmill exercise test (Bruce 1971; PowerJog M30, Sport Engineering Ltd, Birmingham, UK) to assess their aerobic fitness at the onset of the season (i.e. month of June). The test started with a speed of 1.7 mph and a slope of 10%. The treadmill speed and grade were incremented every 3 min. HR (Polar Team, Polar Electro Oy, Kempele, Finland), electrocardiograph (Schiller AG, Baar, Switzerland) and breath-by-breath gas exchange (Medical Graphics System CPX-Plus, Medical Graphics Corporation, St. Paul, MN, USA) were continuously analysed throughout the exercise test. The highest VO2 obtained during the last 30 s of exercise test was accepted as VO2max. The VT was determined from V-slope method (Beaver et al. 1986) in combination with the break point of the ventilatory equivalent for O2 against VO2 (Oshima et al. 1997). The RCT was identified by the break points of the ventilatory equivalent for CO2 and the end tidal CO2 concentration against VO2 (Oshima et al. 1997). 2.4. Wildfire suppression One hundred and fifty-two wildfires with a range of durations were analysed. Wildfires were classified into three categories according to the type of attack performed: direct (n ¼ 53), indirect (n ¼ 36) or mixed attack (n ¼ 63). We considered direct and indirect attacks when the wildland firefighters worked near (55 m) the flames or worked far (4100 m) from the flames, respectively. When the wildland firefighters performed both direct and indirect attacks in the same wildfire,

1103

Downloaded by [Juan Garcia-Lopez] at 15:29 31 October 2011

Ergonomics this was defined as mixed attack. During wildfire suppression, all wildland firefighters wear the same regulation protective gear mass (6 kg) which includes a fireproof overall (65% viscose, 30% nomex and 5% kevlar), helmet, goggles, gloves, face neck shroud, midcalf leather boots, 100% cotton short sleeve undershirt and underpants. Additionally, all of them carried different tools (3–20 kg) to perform their job. The participating firefighters wore a temperature data logger (Termoregister TR-51A, T and Do., Nagano, Japan) to measure the air temperature every 10 s and a HR monitor (Polar Team, Polar Electro Oy, Kempele, Finland) which recorded their HR every 5 s during the analysed wildfires. Three intensity zones were then identified according to the HR values corresponding to the VT and RCT (Rodrı´ guezMarroyo et al. 2011): zone 1 (Z1), below VT (low intensity exercise); zone 2 (Z2), between VT and RCT (moderate intensity exercise) and zone 3 (Z3), above the RCT (high intensity exercise). These zones were used to determine the exercise load (TRIMP) by multiplying the time spent in Z1, Z2 and Z3 by the constants 1, 2 and 3, respectively, the TRIMP score being obtained by summating the scores of the three phases (Foster et al. 2001). CT was measured and recorded continuously using a JonahTM intestinal temperature capsule (VitalSenses, Mini Mitter Co., Inc, Bend, OR, USA). We only recorded the core body temperature when the wildland firefighter had ingested the capsule at least 3 h before the beginning of wildfire suppression activities, to avoid the influence of liquid and food intake on the measured temperature (Byrne and Lim 2007). The physiological strain index (PSI) and cumulative heat strain index (CHSI) were calculated according to Tikuisis et al. (2002), using a modified version of the equation of Moran et al. (1998), and Frank et al. (2001), respectively: PSI ðunitsÞ ¼ ½5  ðCT  CT0 Þ  ð39:5  CT0 Þ1  þ ½5  ðHR  60Þ  ðHRmax  60Þ1  where CT and HR are the mean core (gastric) body temperature (8C) and mean HR (bpm) recorded during the wildfire suppression activity, respectively. CT0 is the baseline core (gastric) body temperature, and HRmax is the subject’s maximal HR measured in the laboratory during incremental exercise. CHSI ðunitsÞ ¼

X t 0

 hb  HR0  t  103

Z t   CT  dt  CT0  t 0

where Shb is the accumulation of heart beats over the period t (min) during which the index is calculated, HR0 is the initial lowest HR (bpm), CT is the core (gastric) body temperature (8C) and CT0 is the baseline CT. 2.5.

Statistical analysis

The results are expressed as mean + SEM. The Kolmogorov–Smirnov test was applied to ensure a Gaussian distribution of the results. The analysed parameters were studied with one-way analysis of variance with repeated measures. When a significant F value was found, Bonferroni’s test was applied to establish significant differences between means. The relationship between variables was determined by using the Pearson correlation coefficient (r). The level of significance was set at 0.05 for all statistics. SPSS þ V.17.0 statistical software (Chicago, Illinois, USA) was used. 3. Results 3.1. Heart rate Both maximal and mean HR were higher (p 5 0.05) in direct (173 + 1 and 128 + 2 bpm, respectively) and mixed (175 + 1 and 126 + 2 bpm, respectively) attacks than in indirect attacks (165 + 3 and 111 + 3 bpm, respectively). When mean HR was given as a percentage of maximal HR, significant differences (p 5 0.05) between direct (67.2 + 1.1%) and mixed (66.3 + 0.9%) attacks versus indirect attacks (58.1 + 1.6%) were observed. 3.2. Intensity zones The percentages of time spent in Z1, Z2 and Z3 in direct (66.1 + 2.5%, 27.0 + 1.5% and 6.9 + 1.0%, respectively) and mixed (64.0 + 2.1%, 28.8 + 1.6% and 7.1 + 0.8%, respectively) attack were significantly different (p 5 0.05) from those observed in indirect attack (84.4 + 2.6%, 12.9 + 2.1% and 2.7 + 0.65%, respectively). Both percentages of time spent in Z2 and Z3 were higher (p 5 0.05) in direct and mixed attacks, whereas the highest (p 5 0.05) percentage in Z1 was found in indirect attack. The same behaviour was observed when we analysed the time spent in the three intensity zones between the different attacks (Table 2). 3.3.

Workload

The lowest TRIMP score was observed in the indirect attack, although no significant differences were found between types of attacks (218.9 + 11.4, 193.4 + 17.9 and 217.6 + 10.5 units in direct, indirect and mixed

1104

J.A. Rodrı´guez-Marroyo et al.

attack, respectively). However, when we calculated the TRIMP h71, we found significant differences (p 5 0.05) between direct and mixed attack versus indirect attack (Table 2).

Downloaded by [Juan Garcia-Lopez] at 15:29 31 October 2011

3.4.

Gastric temperature

CT was not influenced by the type of attack, although the highest maximal air temperature was observed in the direct attack (Table 3). The PSI, an index of combined cardiovascular and thermal stress, was higher (p 5 0.05) in the direct attack (Figure 1). Furthermore, the CHSI, a potentially more sensitive index of combined cardiovascular and thermal stress, was significantly different (p 5 0.05) during direct attacks (3133 + 362 units) from that found in indirect (2119 + 269 units) and mixed attacks (2377 + 333 units). We found significant relationships between the CHSI and the TRIMP (r ¼ 0.87, p 5 0.001), maximal (r ¼ 0.61, p 5 0.05) and mean (r ¼ 0.60, p 5 0.05) CT. In the same way, the PSI was correlated to the maximal (r ¼ 0.71, p 5 0.001) and mean (r ¼ 0.92, p 5 0.001) CT. 4.

Discussion

The main finding of this study was a determination of how the type of attack adopted during real wildfire suppression influenced physiological demands and thermal strain in wildland firefighters. This work investigated three different ways of approaching wildfire suppression (Budd et al. 1997a). We classified as

a direct attack when the wildland firefighters worked close to the flames (55 m). This sort of attack is normally used when the fire is just beginning and the height of the flames is not very great (52–3 m). By contrast, when the flames reach a great height, wildland firefighters work at a distance from them (4100 m) building fire lines so as to try to halt the advance of the fire (i.e. indirect attack). A combination of the two previous methods of working during the same fire was termed a mixed attack. The highest maximal and mean HRs (p 5 0.05), were recorded during direct (173 + 1 and 128 + 2 bpm, respectively) and mixed (175 + 1 and 126 + 2 bpm, respectively) attacks, in comparison with those found in indirect attacks (165 + 3 and 111 + 3 bpm, respectively). Likewise, the greatest time and percentage of total time spent in Z2 and Z3 were observed in wildfires in which either a direct or mixed attack was used (Table 2). It might be thought that the greater closeness of the wildland firefighters to the flames in a direct attack could involve them facing higher air temperatures, thus encouraging an increase in cardiovascular drift (Gonza´lez-Alonso et al. 1999). However, although, at some specific moments, the wildland firefighters did undergo higher maximal air temperatures in this sort of fire, mean air temperatures were similar in all the wildfires analysed (Table 3). Thus, other factors, such as emotional stress, the pace of work or the type of tool in use, give a better explanation of the behaviour of intensity of effort observed in this study. The greater closeness to the flames in a direct attack means that work carried out is

Table 2. Wildfires’ total duration, time spent in the three intensity zones analysed and exercise load expressed as TRIMP h71 according to the type of attack (mean + SEM).

Total duration (min) Z1 (min) Z2 (min) Z3 (min) TRIMP h71

Direct attack

Indirect attack

Mixed attack

160.2 108.5 40.7 9.6 84.6

174.8 147.7 18.9 3.1 68.2

158.1 105.3 41.3 9.9 85.4

+ + + + +

8.0 7.7* 3.0* 1.1* 1.9*

+ + + + +

12.9 14.9{ 2.1{ 0.7{ 1.8{

+ + + + +

8.1 7.5 2.6 1.1 1.8

Note: Z1, exercise intensity below the VT; Z2, exercise intensity between the VT and the RCT; Z3, exercise intensity above RCT. *Significant difference with indirect attack (p 5 0.05). {Significant difference with mixed attack (p 5 0.05).

Table 3.

Air and core temperatures (8C) analysed according to the type of attack [mean + SEM (range)]. Direct attack

Maximal air temperature Mean air temperature Maximal core temperature Mean core temperature

37.8 + 2.7* 28.4 + 1.1 39.2 + 0.3 38.3 + 0.1

(26.0–53.0) (22.0–41.3) (37.9–39.6) (37.6–39.1)

Note: *Significant difference with indirect attack (p 5 0.05).

Indirect attack 28.8 26.1 38.2 37.9

+ + + +

3.9 2.4 0.2 0.3

(20.2–37.3) (19.8–31.3) (37.2–38.5) (36.9–38.2)

Mixed attack 35.4 27.1 38.8 37.9

+ + + +

1.3 1.8 0.2 0.1

(21.2–51.5) (20.1–40.1) (37.3–39) (37.2–38.1)

Ergonomics

Downloaded by [Juan Garcia-Lopez] at 15:29 31 October 2011

Figure 1. PSI score during the wildfires analysed. Values are mean + SEM. *Significant difference with indirect attack (p 5 0.05).

potentially more dangerous, implying a stronger emotional stress in wildland firefighters. This may contribute to raising the HR through an increase in sympathetic activity (Lucini et al. 2002). Furthermore, the work performed in a direct attack is usually done at a quicker pace, in an attempt to control the fire’s advance rapidly (Budd et al. 1997a). This behaviour led to an increase in the exercise intensity by wildland firefighters. Brotherhood et al. (1997a) reported a rise of HR of around 12% when wildland firefighters moved from a normal to a fast pace of work. These data are similar to the rise in the mean HR observed in this study in direct attacks as contrasted with indirect attacks (15%). Finally, the tools were used when wildfires firefighting may also have contributed to increasing the exercise intensity. The majority of the tools employed by wildland firefighters are normally between 2 and 5 kg in weight (e.g. rakes, axes, swatters, shovels and chainsaws). However, backpack pumps (20 kg) were frequently used by individuals participating in the study when they were involved in direct attacks. This implied an extra load for the subjects to carry of 25% of their own body weight, which added to the intensity of effort in the wildfires on which these pumps were employed (Richmond et al. 2008). The use of mean HR to determine the exercise intensity can undervalue the effort exerted by wildland firefighters during the direct attacks. When this tactic is used the work exerted is more intermittent, because more short recovery breaks exist (Budd et al. 1997b), which might decrease the mean HR. Therefore, the effort analysis according to different intensity zones can be more adequate. We analysed three intensity zones according to the HR values corresponding to the VTs. Using these zones, the higher effort spent (above VT) in Z2 and Z3 was analysed in the direct and mixed

1105

attacks. However, these results present potential limitation, since the conditions in which subject performed the laboratory test were different from wildfires; this fact could affect the HR associated to VT and RCT. During firefighting, factors such as temperature, protective clothing, state anxiety, mental stress and hydration status can influence HR responses (Gonza´lez-Alonso et al. 1999, Smith et al. 2001, Eglin et al. 2004, Barr et al. 2010, Webb et al. 2010). However, the magnitude of the errors was small because previous studies have shown a stability of the HR, in which anaerobic thresholds occurred between 23 and 378C (Tyka et al. 2009). Moreover, the wildland firefighters’ experience could have a positive influence either on state anxiety and mental stress (Webb et al. 2010) or on their ability to maintain adequate levels of hydration. Although greater intensities of effort were observed in direct and mixed attacks in comparison with indirect (Table 2), no significant differences were found in the average workload (TRIMP) from one wildfire to another. The slightly longer duration of wildfires suppression with an indirect attack (Table 2), although it was no significant, might contribute to this finding. In this study, we selected wildfires with a similar duration (3 h), so as to diminish the effects of duration on the exercise intensity carried out by the subjects (Rodrı´ guez-Marroyo et al. 2011). Because of the greater influence of duration than the exercise intensity in calculating TRIMP, some authors have proposed analysis of TRIMP h71 so as to compare the workload in activities of different lengths (Rodrı´ guezMarroyo et al. 2011). Through use of this variable, the results reported in this study showed that, in direct and mixed attacks, wildland firefighters had a higher pace of work (Table 2). As was commented above, this behaviour was conditioned by the speed with which the wildland firefighters had to act in this sort of wildfires, in an attempt to prevent it from spreading. Although physiological demands were different according to the type of attack, the physical fitness did not determine the firefighting tactics used to suppress wildfires. Other factors such as fire behaviour (which changes according to the fuel), environmental conditions (i.e. temperature, wind, humidity) and topographic characteristics (i.e. steep terrain, watercourse) influence in the firefighting tactic chosen (Sharples 2009). These factors condition the height of the flames and the spreading speed of the fire, which conditions the wildland firefighters to work nearer or further of the flames. However, the knowledge of the physiological demands is important to plan specific physical conditioning programmes that improve the subjects’ performance. Previous studies have reported the relationship between the level of physical fitness

Downloaded by [Juan Garcia-Lopez] at 15:29 31 October 2011

1106

J.A. Rodrı´guez-Marroyo et al.

and specific tasks’ performance in wildland firefighters (Brotherhood et al. 1997b, Ruby et al. 2003, Phillips et al. 2011). Brotherhood et al. (1997b) observed a more raking productivity and efficiency in fitter wildland firefighters than the less fit during wildfire suppression. Also, Ruby et al. (2003) showed a positive correlation between the higher wildland firefighters’ aerobic fitness and the performance during an escape to safety zone. Moreover, an adequate physical fitness may prevent the risk of coronary heart disease (Kales et al. 2007), improve the tolerance to heat (Cheung and McLellan 1998) and decrease the amount of casualties (Barr et al. 2010). Therefore, different physical competency tests, which determine whether wildland firefighters are fit for duty, had been used (Ruby et al. 2003, Phillips et al. 2011), and it has been recommended a minimal aerobic fitness of at least 45 ml kg71 min71 to perform in a safe and efficient manner (Ruby et al. 2003). VO2max analysed in this study was higher than recommended standard. Our subjects performed a physical conditioning programme 4 days/week throughout the duration of the study, which improved their VO2max (Roberts et al. 2002). These results were similar to those observed in American elite wildland firefighter crews (i.e. Hotshot and Smoke Jumper crews; Ruby et al. 2003). Contrary to what might have been expected, no significant differences were found in CT recorded (Table 3). The greater work intensity performed by the wildland firefighters and the higher maximal air temperatures in direct attacks did not bring an increase in core temperatures in this sort of wildfire. This fact may possibly be due to the frequent short recovery breaks that wildland firefighters take when working close to the flames (Budd et al. 1997b). This strategy for working would have as its aim avoidance of excessive exposure to heat and regulation of effort performed at high intensities, so as to minimise heat storage. To judge by the results obtained in this study, this strategy was effective in avoiding an excessive rise in CT (Table 3). Moreover, the magnitude of the influence over CT that there might be from other factors, such as environmental conditions, the level of hydration, physical fitness and acclimatisation to heat by subjects (Cheung and McLellan 1998, Gonza´lezAlonso et al. 1999) was not probably significance. This is perhaps because the mean air temperatures observed (27 8C) did not indicate that the wildland firefighters worked regularly in a hot environment. In addition, all the subjects were subjected to a regular physical training programme throughout the seasons over which the study lasted. This contributed to an improvement in their training status, as is reflected by the results shown in Table 1. Furthermore, all of them had prior experience amounting to 4 + 1 years

wildfire firefighting, which may have had a positive influence over their heat acclimatisation. The CT found coincided with those previously reported in wildland firefighters (37–388C; Budd 2001, Cuddy et al. 2008) and is lower than those observed in structural firefighters (398C; Eglin et al. 2004, Richmond et al. 2008). These results would seem logical, since structural firefighters work in hotter environments than wildland firefighters (Smith et al. 2001), and the tasks they perform involve a higher intensity of effort (Eglin et al. 2004, Richmond et al. 2008). Moreover, the different characteristics of the protective gear worn by both firefighters (Barr et al. 2010) and the weight of the breathing apparatus used by structural firefighters (Richmond et al. 2008) may also contribute to these differences. It has been proposed the PSI and CHSI as indices to assess the exercise-heat strain (Moran et al. 1998, Frank et al. 2001). These two indices are calculated by using the subjects’ CT and HR, taken either at a given moment (PSI) or as they vary over time (CHSI). Both these indices proved sensitive to the thermal strain undergone by wildland firefighters in the wildfires studied. The highest PSI and CHSI were obtained in wildfires with a direct attack (Figure 1). PSI is on a scale from 0 to 10 for measuring thermal strain, where the highest score is rated 10 (Moran et al. 1998). Wildland firefighters had scores that represented moderate (5.5 PSI units), moderate–low (4.5 PSI units) and low (3.9 PSI units) PSI in direct, mixed and indirect attacks, respectively. Similar results (4–6 PSI units) were obtained in other studies when the PSI of a range of subjects in various hot environments was analysed (Hadid 2008, Hostler et al. 2009, Petruzzello et al. 2009). The CHSI values found in this study in direct (3135 units) and mixed and indirect (2250 units) attacks were slightly higher and slightly lower, respectively, than those recorded by Byrne et al. (2006) in half-marathon runners (2800 units). In conclusion, wildfire firefighting is an extremely demanding activity that varies as a function of the type of attack adopted. The greatest intensities of work were noted in direct and mixed attacks. The highest thermal strain was noted in direct attacks. PSI and CHSI were valid indices for assessing the thermal strain in wildland firefighters.

Acknowledgements This work has been funded by Empresa de Transformacio´n Agraria, S.A. (TRAGSA), Mutua Fraternidad–Muprespa and Empresa de Gestio´n Medioambiental, S.A. (EGMASA). This study was conducted with the collaboration of the A´rea de Defensa contra Incendios Forestales, Direccio´n General de Medio Natural y Polı´ tica Forestal, Ministerio de Medio Ambiente y Medio Rural y Marino, Spain.

Ergonomics

Downloaded by [Juan Garcia-Lopez] at 15:29 31 October 2011

References Barr, D., Gregson, W., and Reilly, T., 2010. The thermal ergonomics of firefighting reviewed. Applied Ergonomics, 41, 161–172. Beaver, W.L., Wasserman, K., and Whipp, B.J., 1986. A new method for detecting the anaerobic threshold by gas exchange. Journal of Applied Physiology, 60 (6), 2020–2027. Brotherhood, J.R., et al., 1997a. Project Aquarius 3. Effects of work rate on the productivity, energy expenditure, and physiological responses of men building fireline with a rakehoe in dry eucalypt forest. International Journal of Wildland Fire, 7 (2), 87–98. Brotherhood, J.R., et al., 1997b. Project Aquarius 11. Effects of fitness, fatness, body size, and age on the energy expenditure, strain, and productivity of men suppressing wildland fires. International Journal of Wildland Fire, 7 (2), 181–199. Bruce, R.A., 1971. Exercise testing of patients with coronary artery disease. Annals of Clinical Research, 3 (6), 323– 332. Budd, G.M., 2001. How do wildland firefighters cope? Physiological and behavioural temperature regulation in men suppressing Australian summer bushfires with hand tools. Journal of Thermal Biology, 26 (4–5), 381–386. Budd, G.M., et al., 1997a. Project Aquarius 4. Experimental bushfires, suppression procedures, and measurements. International Journal of Wildland Fire, 7 (2), 99–104. Budd, G.M., et al., 1997b. Project Aquarius 5. Activity distribution, energy expenditure, and productivity of men suppressing free-running wildland fires with hand tools. International Journal of Wildland Fire, 7 (2), 105–118. Budd, G.M., et al., 1997c. Project Aquarius 7. Physiological and subjective responses of men suppressing wildland fires. International Journal of Wildland Fire, 7 (2), 133–144. Byrne, C. and Lim, C.L., 2007. The ingestible telemetric body core temperature sensor: a review of validity and exercise applications. British Journal of Sports Medicine, 41 (3), 126–133. Byrne, C., et al., 2006. Continuous thermoregulatory responses to mass-participation distance running in heat. Medicine and Science in Sports and Exercise, 38 (5), 803–810. Cheung, S.S. and McLellan, T.M., 1998. Heat acclimation, aerobic fitness, and hydration effects on tolerance during uncompensable heat stress. Journal of Applied Physiology, 84 (5), 1731–1739. Cuddy, J.S., et al., 2008. Effects of an electrolyte additive on hydration and drinking behaviour during wildfire suppression. Wilderness and Environmental Medicine, 19 (3), 172–180. Eglin, C.M., Coles, S., and Tipton, J., 2004. Physiological responses of fire-fighter instructors during training exercises. Ergonomics, 47 (5), 483–494. Foster, C., et al., 2001. A new approach to monitoring exercise training. Journal Strength and Conditioning Research, 15 (1), 109–115. Frank, A., et al., 2001. The cumulative heat strain index – a novel approach to assess the physiological strain induced by exercise-heat stress. European Journal of Applied Physiology, 84 (6), 527–532.

1107

Gonza´lez-Alonso, J., et al., 1999. Influence of body temperature on the development of fatigue during prolonged exercise in the heat. Journal of Applied Physiology, 86 (3), 1032–1039. Hadid, A., 2008. Effect of a personal ambient ventilation system on physiological strain during heat stress wearing a ballistic vest. European Journal of Applied Physiology, 104 (2), 311–319. Heil, D.P., 2002. Estimating energy expenditure in wildland fire fighters using a physical activity monitor. Applied Ergonomics, 33 (5), 405–413. Hostler, D., et al., 2009. The effect of hyperhydration on physiological and perceived strain during treadmill exercise in personal protective equipment. European Journal of Applied Physiology, 105 (4), 607–613. Kales, S.N., et al., 2007. Emergency duties and deaths from heart disease among firefighters in the United States. The New England Journal of Medicine, 356 (12), 1207–1215. Kyro¨la¨inen, H., et al., 2008. Hormonal responses during a prolonged military field exercise with variable exercise intensity. European Journal of Applied Physiology, 102 (5), 539–546. Lucini, D., et al., 2002. Hemodynamic and autonomic adjustments to real life stress conditions in humans. Hypertension, 39 (1), 184–188. Moran, D.S., Shitzer, A., and Pandolf, K.B., 1998. A physiological strain index to evaluate heat stress. American Journal of Physiology, 275 (Regulatory, Integrative and Comparative Physiology, 44), R129–R134. Oshima, Y., et al., 1997. Relationship between isocapnic buffering and maximal aerobic capacity in athletes. European Journal of Applied Physiology, 76 (5), 409–414. Petruzzello, S.J., et al., 2009. Perceptual and physiological heat strain: examination in firefighters in laboratory- and field based studies. Ergonomics, 52 (6), 747–754. Phillips, M., et al., 2011. Pack hike test finishing time for Australian firefighters: pass rates and correlates of performance. Applied Ergonomics, 42, 411–418. Prieto, J.A., et al., 2010. Physiological response of beach lifeguards in a rescue simulation with surf. Ergonomics, 53 (9), 1140–1150. Richmond, V.L., et al., 2008. Physiological demands of firefighter search and rescue in ambient environmental conditions. Ergonomics, 51 (7), 1023–1031. Roberts, M.A., et al., 2002. Fitness levels of firefighter recruits before and after a supervised exercise training program. Journal Strength and Conditioning Research, 16 (2), 271–277. Rodrı´ guez-Marroyo, J.A., et al., 2011. Exercise intensity and load during different races in youth and junior cyclists. Journal Strength and Conditioning Research, 25 (2), 511– 519. Ruby, B.C., et al., 2002. Total energy expenditure during arduous wildfire suppression. Medicine and Science in Sports and Exercise, 34 (6), 1448–1454. Ruby, B.C., et al., 2003. Wildland firefighter load carriage: effects on transit time and physiological responses during simulated escape to safety zone. International Journal of Wildland Fire, 12, 111–116. Sharples, J.J., 2009. An overview of mountain meteorological effects relevant to fire behaviour and bushfire risk. International Journal of Wildland Fire, 18, 737–754. Smith, D.L., Manning, T.S., and Petruzzello, S.J., 2001. Effect of strenuous live-fire drills on cardiovascular and psychological responses of recruit firefighters. Ergonomics, 44 (3), 244–254.

1108

J.A. Rodrı´guez-Marroyo et al.

Downloaded by [Juan Garcia-Lopez] at 15:29 31 October 2011

Tikuisis, P., McLellan, T.M., and Selkirk, G., 2002. Perceptual versus physiological heat strain during exercise-heat stress. Medicine and Science in Sports and Exercise, 34 (9), 1454–1461. Tyka, A., et al., 2009. The influence of ambient temperature on power at anaerobic threshold determined based on blood lactate concentration and myoelectric signals. International Journal of Occupational Medicine and Environmental Health, 22 (1), 1–6.

Webb, H.E., et al., 2010. Cardiorespiratory responses of firefighters to a computerized fire strategies and tactics drill during physical activity. Applied Ergonomics, 41, 376–381.