Classification of metabolic and respiratory demands in fire fighting activity with extreme workloads

Fire fighting work comprises work tasks requiring an energy yield at maximal or close to maximal levels of the individual. Due to the very nature of fire fighting more complex physiological variables are difficult to measure. We measured metabolic and respiratory responses in 15 male, professional fire fighters during simulated work tasks on a test ground. Work time was on the average 22 min with individual components of work tasks lasting 2-4 min. The mean oxygen consumption for the whole exercise (22 min) was 2.75+/-0.29 l/min. The most demanding work task demanded an oxygen uptake of 3.55+/-0.27 l/min. Corresponding values for respiratory minute volumes were 82+/-14 and 102+/-14l/min, respectively. Heart rates averaged 168+/-12 for the whole test and 179+/-13 beats/min for the heaviest work task. Two new classes for classification of intensive and exhausting, short term physical work are proposed for inclusion in ISO8996 and values for relevant parameters are proposed.     

Fire fighting and its influence on the body

Working conditions for fire fighters can be described according to the environment temperature and the incident radiant heat flux. Measurements for this study in buildings for fire fighting training have shown that fire fighters are typically exposed to radiant heat fluxes of between 5 and 10 kWm(-2) during this kind of exercise. The heat load can nevertheless be much higher. In one case, 42 kWm(-2) was measured. The temperatures reached between 100 and 190 degrees C at 1 m above ground, going up to 278 degrees C in one case. Human trials have been performed with 17 fire fighters. After exercises (about 15 min) in a heated room, the mean core temperature of the fire fighters rose by 0.6 degrees C with a surrounding temperature of 31 degrees C and 1.0 degrees C with 38 degrees C. The sweat production varied from 0.7 to 2.1 lh(-1); 16% to 45% of sweat remained in the clothing layers. During the exercises in the training buildings, a mean of 48 degrees C has been measured between fire fighters' clothing and workwear. These conditions lead to an increase of the relative humidity in all the jackets up to 100%. When the fire fighters came out of the fire, the humidity remained at this level in the PVC coated jackets while it was in some cases strongly reduced in breathable jackets.     

Fire fighting and its influence on the body

Working conditions for fire fighters can be described according to the environment temperature and the incident radiant heat flux. Measurements for this study in buildings for fire fighting training have shown that fire fighters are typically exposed to radiant heat fluxes of between 5 and 10 kWm ^-2 during this kind of exercise. The heat load can nevertheless be much higher. In one case, 42 kWm ^-2 was measured. The temperatures reached between 100 and 190°C at 1 m above ground, going up to 278°C in one case. Human trials have been performed with 17 fire fighters. After exercises (about 15 min) in a heated room, the mean core temperature of the fire fighters rose by 0.6°C with a surrounding temperature of 31°C and 1.0°C with 38°C. The sweat production varied from 0.7 to 2.1 lh ^-1; 16% to 45% of sweat remained in the clothing layers. During the exercises in the training buildings, a mean of 48°C has been measured between fire fighters' clothing and workwear. These conditions lead to an increase of the relative humidity in all the jackets up to 100%. When the fire fighters came out of the fire, the humidity remained at this level in the PVC coated jackets while it was in some cases strongly reduced in breathable jackets.     

Relationship between fire fighting suppression tasks and physical fitness.

This investigation evaluated the relationship between physical fitness and performance of fire suppression tasks. The following mean +/- SD values were associated with 91 fire fighters: age 31.69 +/- 7.39 years, height 177.29 +/- 6.38 cm, weight 83.97 +/- 10.86 kg, % fat 13.78 +/- 4.31, fat free weight (FFW) 71.52 +/- 7.66 kg, pull-ups 9.03 +/- 4.79, push-ups 41.02 +/- 14.08, 1.5 mile run 737.60 +/- 108.11 s, sit and reach 32.00 +/- 8.5 cm, sit-ups 39.88 +/- 7.75, and total grip strength 116.75 +/- 17.67 kg. The physical performance assessment (PPA) consisted of the following: stair climb, hoist, forcible entry, hose advance, and victim rescue. Significant correlations (p < 0.01) were found between the PPA and the following: total grip strength (r = -0.54), FFW (r = -0.47), height (r = -0.40), pull-ups (r = -0.38), push-ups (r = -0.38), 1.5 mile run (r = 0.38), sit-ups (r = -0.32), weight (r = -0.30) and % fat (r = 0.30). Multiple regression analysis indicated that the best multiple predictor of PPA was the 1.5 mile run, FFW, and pull-ups, r = 0.73, p < 0.001. This investigation shows the importance of physical fitness as related to performance of fire suppression job tasks.     

Heart rate strain in cable hauler choker setters in New Zealand logging operations.

This study examined the physical strain experienced by cable hauler choker setters, and the applicability of heart rate indices for measuring physical strain in commercial forest harvesting operations in New Zealand. The heart rate of four choker setters were recorded continuously throughout the working day and applied to heart rate indices. Based on the relative heart rate at work (%HRR), ratio of working heart rate to resting heart rate and 50% level indices, the mean working heart rate (HRw) of 106 bt. min(-1) +/- 6.9 (mean +/- SD) placed choker setting in the moderate workload category. The specific tasks of line shifts (120.3 +/- 4.8 bt. min(-1)), hooking up drags (118.8 +/- 6.6 bt. min(-1)) and uphill travel (126.1 +/- 12.9 bt. min(-1)), imposed the most severe workloads on the choker setters. This research also demonstrated that heart rate indices could be used as an effective means of determining the physiological strain of subjects working in New Zealand's commercial forest harvesting operations.     

The energy demands of portable gas analysis system carriage during walking and running

The aim of this study was to evaluate the carriage of a portable gas analyser during prolonged treadmill exercise at a variety of speeds. Ten male participants completed six trials at different speeds (4, 8 and 12 km h^? 1) for 40 min whilst wearing the analyser (P) or where the analyser was externally supported (L). Throughout each trial, respiratory gases, heart rate (HR), perceptions of effort and energy expenditure (EE) were measured. Significantly higher EE occurred during P12 (p = 0.01) than during L12 (855.3 ± 104.3; CI = 780.7–930.0 and 801.5 ± 82.2 kcal; CI = 742.7–860.3 kcal, respectively), but not at the other speeds; despite this, perceptions of effort and HR responses were unaffected. This additional EE is likely caused by alterations to posture which increase oxygen demand. The use of such systems is unlikely to affect low-intensity tasks, but researchers should use caution when interpreting data, particularly when exercise duration exceeds 30 min and laboratory-based analysers should be used where possible.     

Physiological responses of fire-fighter instructors during training exercises

Thirteen male instructors were monitored during a total of 44 live fire training exercises (ambient temperature 74+/-42 degrees C). Exposure time during the 'Hot Fire' (HF), 'Fire Behaviour' and 'Fire Attack' exercises was 33.0+/-7.9 min (n=30); 26.3+/-5.5 min (n=6); and 7.3+/-2.6 min (n=8) respectively. At the end of the exercises, mean core temperature (t(core)) was 38.5+/-0.9 degrees C (n=32), however eight instructors had a t(core) above 39 degrees C. The mean maximum temperature under the fire hood was 41.2+/-4.6 degrees C (n=40). Mean maximum heart rate (HR) was 138+/-26 bpm (n=34) however, in five exercises, HR exceeded 90% of the instructors' HR reserve. Mean fluid deficit was 0.62+/-0.6 l (n=30) at the end of the HF exercises, the maximum being 2.54 l. Four instructors doubted their ability to perform a rescue at the end of the exercise. The energy cost of performing simulated rescues of a 50 kg dummy in the cool was investigated in a pilot study. Mean HR during the rescues was 79+/-7% of the instructors' HR reserve and it was estimated that this could increase t(core) by 0.4 to 0.6 degrees C. The physiological responses to the fire-fighting exercises varied considerably and reflected the differences in work performed and external heat load. The results obtained from some individuals give cause for concern, and signs of heat strain were seen in at least two individuals.     

Physiological responses to working with fire fighting equipment in the heat in relation to subjective fatigue

Heart rate (HR), rectal temperature (Tre), blood pressure, temperature and relative humidity changes inside clothing were measured on 18 professional firemen (mean age 29.4 +/- 7.4 yr, VO2 max 41.4 + 8.8 ml kg-1 min-1) wearing fire fighter's uniforms (SU) or aluminized, fire resistant, impermeable clothing with self contained breathing apparatus (FE). The subjects exercised on a cycle ergometer with a work load of 1.5 W kg-1, at 39 +/- 1 degree C and at 70 +/- 5% relative humidity. They stopped exercising at a point of subjective fatigue and overheating which--according to their judgement--would cause them to stop working during real fire fighting. The working time until fatigue for subjects wearing FE was considerably lower than the corresponding value for SU. The HR and Tre values rose progressively throughout the exercise with no tendency to reach a plateau. In some cases the HR reached near maximal level. The Tre continued to rise even during 10 min of recovery and in many subjects exceeded 39 degrees C. These data showed that despite spontaneous termination of exercise, the limit of tolerance was reached by most of the subjects.     

Estimation of energy expenditure in a work environment: comparison of accelerometry and oxygen consumption/heart rate regression

The aim of this study was to compare estimation of energy expenditure (EE) in working environments, either from accelerometry or from an individual oxygen consumption/heart rate (VO(2)/HR) regression curve. The study participants were 46 volunteer workers aged 27+/-6 years old. A significant correlation between EE predicted by the VO(2)/HR curve and the accelerometer was observed (r=0.78, p <0.01). However, more disparities were observed between the two methods when the mean job intensity was not within 16% and 23% higher than resting HR. The accelerometer overestimated by a mean of 34.4% the prediction by VO(2)/HR regression if the intensity of the task was lower than a total of 1000 kcal/shift and underestimated the prediction by a mean of -24.9% if EE estimation of the work shift was higher than a total of 1500 kcal/shift. Despite a high correlation between both methods in the whole group, EE evaluated by accelerometry does not correspond to EE predicted by the VO(2)/HR regression curves when evaluated individually.     

Intermittent microclimate cooling during exercise-heat stress in US army chemical protective clothing

The effectiveness of intermittent, microclimate cooling for men who worked in US Army chemical protective clothing (modified mission-oriented protective posture level 3; MOPP 3) was examined. The hypothesis was that intermittent cooling on a 2 min on-off schedule using a liquid cooling garment (LCG) covering 72% of the body surface area would reduce heat strain comparably to constant cooling. Four male subjects completed three experiments at 30 degrees C, 30% relative humidity wearing the LCG under the MOPP 3 during 80 min of treadmill walking at 224 +/- 5 W . m(-2). Water temperature to the LCG was held constant at 21 degrees C. The experiments were; 1) constant cooling (CC); 2) intermittent cooling at 2-min intervals (IC); 3) no cooling (NC). Core temperature increased (1.6 +/- 0.2 degrees C) in NC, which was greater than IC (0.5 +/- 0.2 degrees C) and CC (0.5 +/- 0.3 degrees C) ( p < 0.05). Mean skin temperature was higher during NC (36.1 +/- 0.4 degrees C) than IC (33.7 +/- 0.6 degrees C) and CC (32.6 +/- 0.6 degrees C) and mean skin temperature was higher during IC than CC ( p < 0.05). Mean heart rate during NC (139 +/- 9 b . min(-1)) was greater than IC (110 +/- 10 b . min(-1)) and CC (107 +/- 9 b . min(-1)) ( p < 0.05). Cooling by conduction (K) during NC (94 +/- 4 W . m(-2)) was lower than IC (142 +/- 7 W . m(-2)) and CC (146 +/- 4 W . m(-2)) ( p < 0.05). These findings suggest that IC provided a favourable skin to LCG gradient for heat dissipation by conduction and reduced heat strain comparable to CC during exercise-heat stress in chemical protective clothing.     

A review of: “Human Motor Actions: Bernstein Reassessed.” Edited by H. T. A. WHITING. (Oxford: North-Holland, 1984.) [Pp. xxxv + 633.] ISBN 0-444-86813-5.

The physical work performance of eight fit fire fighters wearing fire brigade uniforms and wearing breathing apparatus was assessed. They were tested in a climatic chamber set at temperatures of 15 and 45°C respectively. The test was performed with and without fire fighting equipment. The subjects walked on a treadmill at a speed of 3.5km/h, which produce a workload equivalent of 20% of the subjects' maximal oxygen uptake without equipment, and 30% with equipment. The test lasted for 60 min. Heart rate, oxygen uptake, skin and deep body temperatures were measured during the test. The subjects estimated perceived physical exertion and perceived temperature. Wearing fire fighting equipment increased the oxygen uptake by 0.4 1min^-1. Heart rate at the end of the experiments reached near-maximum levels when the temperature was 45°C with equipment, and deep body temperature increased to an average of 38.7°C. The subjects' ratings of perceived exertion were highly correlated to heart rate. The loading induced by heat and protective equipment reduced the ability to perform strenuous work. The combination of thick clothing and heavy breathing apparatus was found to have a significant limiting effect on the endurance of fire fighters.     

Heat stress while wearing long pants or shorts under firefighting protective clothing

It was the purpose of this study to examine whether replacing long pants (P) with shorts (S) would reduce the heat stress of wearing firefighting protective clothing during exercise in a warm environment. Twenty-four Toronto Firefighters were allocated to one of four groups that performed heavy (H, 4.8 km x h(-1), 5% grade), moderate (M, 4.5 km x h(-1), 2.5% grade), light (L, 4.5 km x h(-1)) or very light (VL, 2.5 km x h(-1)) exercise while wearing their full protective ensemble and self-contained breathing apparatus. Participants performed a familiarization trial followed by two experimental trials at 35 degrees C and 50% relative humidity wearing either P or S under their protective overpants. Replacing P with S had no impact on the rectal temperature (Tre) or heart rate response during heavy or moderate exercise where exposure times were less than 1 h (40.8 +/- 5.8 and 53.5 +/- 9.2 min for H and M, respectively while wearing P, and 43.5 +/- 5.3 and 54.2 +/- 8.4 min, respectively while wearing S). In contrast, as exposure times were extended during lighter exercise Tre was reduced by as much as 0.4 degrees C after 80 min of exercise while wearing S. Exposure times were significantly increased from 65.8 +/- 9.6 and 83.5 +/- 11.6 min during L and VL, respectively while wearing P to 73.3 +/- 8.4 and 97.0 +/- 12.5 min, respectively while wearing S. It was concluded that replacing P with S under the firefighting protective clothing reduced the heat stress associated with wearing the protective ensemble and extended exposure times approximately 10 - 15% during light exercise. However, during heavier exercise where exposure times were less than 1 h replacing P with S was of little benefit.     

Calibration and validation of the relative differenced Normalized Burn Ratio (RdNBR) to three measures of fire severity in the Sierra Nevada and Klamath Mountains, California, USA

Multispectral satellite data have become a common tool used in the mapping of wildland fire effects. Fire severity, defined as the degree to which a site has been altered, is often the variable mapped. The Normalized Burn Ratio (NBR) used in an absolute difference change detection protocol (dNBR), has become the remote sensing method of choice for US Federal land management agencies to map fire severity due to wildland fire. However, absolute differenced vegetation indices are correlated to the pre-fire chlorophyll content of the vegetation occurring within the fire perimeter. Normalizing dNBR to produce a relativized dNBR (RdNBR) removes the biasing effect of the pre-fire condition. Employing RdNBR hypothetically allows creating categorical classifications using the same thresholds for fires occurring in similar vegetation types without acquiring additional calibration field data on each fire. In this paper we tested this hypothesis by developing thresholds on random training datasets, and then comparing accuracies for (1) fires that occurred within the same geographic region as the training dataset and in similar vegetation, and (2) fires from a different geographic region that is climatically and floristically similar to the training dataset region but supports more complex vegetation structure. We additionally compared map accuracies for three measures of fire severity: the composite burn index (CBI), percent change in tree canopy cover, and percent change in tree basal area. User's and producer's accuracies were highest for the most severe categories, ranging from 70.7% to 89.1%. Accuracies of the moderate fire severity category for measures describing effects only to trees (percent change in canopy cover and basal area) indicated that the classifications were generally not much better than random. Accuracies of the moderate category for the CBI classifications were somewhat better, averaging in the 50%-60% range. These results underscore the difficulty in isolating fire effects to individual vegetation strata when fire effects are mixed. We conclude that the models presented here and in Miller and Thode ([Miller, J.D. & Thode, A.E., (2007). Quantifying burn severity in a heterogeneous landscape with a relative version of the delta Normalized Burn Ratio (dNBR). Remote Sensing of Environment, 109, 66-80.]) can produce fire severity classifications (using either CBI, or percent change in canopy cover or basal area) that are of similar accuracy in fires not used in the original calibration process, at least in conifer dominated vegetation types in Mediterranean-climate California.     

Impact of fluid replacement on heat storage while wearing protective clothing

This study used partitional calorimetry to determine the influence of fluid replacement on heat storage during uncompensable heat stress. Eight males performed either light (L; level treadmill walking at 0.97 m x s(-1) (3.5 km x h(-1)) or heavy (H; 1.33 m x s(-1) (4.8 km x h(-1)) at a 4% grade) exercise at 40 degrees C and 30% relative humidity while wearing nuclear, biological and chemical (NBC) protective clothing. Subjects received either no fluid (NF), or 200 or 250 ml of fluid (F) as warm water at approximately 35 degrees C immediately before and every 15 min during the L and H trials respectively. Similar reductions in heart rate were observed at both metabolic rates with F but rectal temperature responses were not different between F and NF. Tolerance time was extended during L/F (106.5 +/- 22.1 min) compared with L/NF (93.1 +/- 20.8 min) but fluid replacement had no influence during H (59.8 +/- 9.5 min and 58.3 +/- 11.1 min for F and NF respectively). Fluid replacement also had no effect on the rate of heat storage during L (108.2 +/- 20.6 W x m(-2) and 111.0 +/- 22.6 W x m(-2) for F and NF respectively) and H (172.5 +/- 11.5 W x m(-2) and 182.1 +/- 15.8 W x m(-2) for F and NF respectively). However, heat storage expressed per unit of mass was significantly increased during L/F (18.5 +/- 4.0 kJ x kg(-1) ) compared with the other trials (16.3 +/- 4.8 kJ x kg(-1), 16.6 +/- 3.0 kJ x kg(-1) and 16.7 +/- 4.0 kJ x kg(-1) for L/NF, H/F and H/NF respectively). It was concluded that fluid replacement does not alter the rate of heat storage during uncompensable heat stress but does increase the heat storage capacity during light exercise when tolerance times are > 60 min.     

Mapping wildfire occurrence at regional scale

When assessing fire danger, interpolation of the dependent variable—historic fire occurrence—is required in order to statistically compare and analyze it with human factors, environmental parameters and census statistics. To confirm the compatibility between the distinct data types, occasionally, for this kind of spatial analysis, historical observations of the primary wildland fire (given as x and y coordinates) must be transformed either to continuous surfaces or to area data. The simple overlay approach converts single point observations to area data. However, this procedure assumes lack of spatial uncertainties that would otherwise result in serious errors caused by the positional inaccuracies of the original point observations.Here, we used kernel density interpolation to convert the original data on wildland fire ignition into an expression of areal units, defined by a raster grid and, subsequently, by the administrative borders of the municipalities in two study areas in Spain. By overlaying a normal bivariate probability density function (kernel) over each point observation, each ignition point was considered an uncertain point location rather than an exact one.     

Mapping wildfire occurrence at regional scale

When assessing fire danger, interpolation of the dependent variable—historic fire occurrence—is required in order to statistically compare and analyze it with human factors, environmental parameters and census statistics. To confirm the compatibility between the distinct data types, occasionally, for this kind of spatial analysis, historical observations of the primary wildland fire (given as x and y coordinates) must be transformed either to continuous surfaces or to area data. The simple overlay approach converts single point observations to area data. However, this procedure assumes lack of spatial uncertainties that would otherwise result in serious errors caused by the positional inaccuracies of the original point observations.Here, we used kernel density interpolation to convert the original data on wildland fire ignition into an expression of areal units, defined by a raster grid and, subsequently, by the administrative borders of the municipalities in two study areas in Spain. By overlaying a normal bivariate probability density function (kernel) over each point observation, each ignition point was considered an uncertain point location rather than an exact one.     

Evaluation of novel thermally enhanced spectral indices for mapping fire perimeters and comparisons with fire atlas data

We evaluated the potential of two novel thermally enhanced Landsat Thematic Mapper (TM)‐derived spectral indices for discriminating burned areas and for producing fire perimeter data (as a potential surrogate to digital fire atlas data) within two wildland fires (1985 and 1993) in ponderosa pine (Pinus ponderosa) forests of the Gila Wilderness, New Mexico, USA. Image‐derived perimeters (manually produced and classified from an index image) were compared to fire perimeters recorded within a digitized fire atlas. For each fire, the highest spectral separability was achieved using the newly proposed Normalized Burn Ratio‐Thermal (NBRT₁) index (M = 1.18, 1.76, for the two fires respectively). Correspondence between fire atlas and manually digitized fire perimeters was high. Landsat imagery may be a useful supplement to existing historical fire perimeters mapping methods, but the timing of the post‐fire image will strongly influence the separability of burned and unburned areas.     

Effects of the self-contained breathing apparatus and fire protective clothing on maximal oxygen uptake

To examine the effects of firefighting personal protective ensemble (PPE) and self-contained breathing apparatus (SCBA) on exercise performance, 12 males completed two randomly ordered, graded exercise treadmill tests (GXTPPE and GXTPT). Maximal oxygen consumption (VO2max) during GXTPPE was 17.3% lower than the GXTPT in regular exercise clothing (43.0 +/- 5.7 vs. 52.4 +/- 8.5 ml/kg per min, respectively). The lower VO2max during the PPE condition was significantly related (r = 0.81, p < 0.05) to attenuated peak ventilation (142.8 +/- 18.0 vs. 167.1 +/- 15.6 l/min), which was attributed to a significant reduction in tidal volume (2.6 +/- 10.4 vs. 3.2 +/- 0.4 l). Breathing frequency at peak exercise was unchanged (55 +/- 7 vs. 53 +/- 7 breaths/min). The results of this investigation demonstrate that PPE and the SCBA have a negative impact on VO2max. These factors must be considered when evaluating aerobic demands of fire suppression work and the fitness levels of firefighters.     

Exercise thermoregulation and hyperprolactinaemia

The anterior pituitary hormone prolactin (PRL), measured in the peripheral blood circulation, reflects alterations in central brain 5-hydroxytryptamine (serotonin) and dopaminergic activity and is used as a marker of 'central fatigue' during active heat exposure. Significant correlations have consistently been found between PRL and core temperature (T(CORE)) during prolonged exercise. There has been no investigation into the relationship between PRL and other key thermoregulatory variables during exercise, such as weighted mean skin (T(SK)) and mean body temperature (T(B)), heat storage (HS), thermal gradient (T(GRAD)), heart rate (HR) and skin blood flow (cutaneous vascular conductance, CVC). Therefore, the aim of this study was to ascertain if a significant relationship exists between PRL and these thermoregulatory variables during prolonged exercise. Nine active male subjects conducted three trials of approximately 60% VO(2peak) at 70-80 rpm for 45 min on a semi-recumbent cycle ergometer at three different ambient temperatures [6 degrees C (Cold), 18 degrees C (Neutral) and 30 degrees C (Hot)] to elicit varying levels of thermoregulatory stress during exercise. Significant differences existed in T(SK), T(B), HS, T(GRAD) and CVC across the environmental conditions (p < 0.001). Core temperature (T(CORE)), HR and PRL were significantly elevated only in Hot (p < 0.05). Moderate correlations were found for T(CORE), T(SK), T(B), HS, T(GRAD), HR and CVC with post-exercise PRL (rho = 0.358-0.749). The end-of-exercise <38.0 degrees C T(CORE) responses were not (rho = -0.129, p > 0.05) but the >38.0 degrees C T(CORE) responses were (rho = 0.845, p < 0.001) significantly related to their corresponding PRL responses. The significant relationships between PRL release and T(SK), T(B), HS, T(GRAD), HR and CVC have extended previous research on T(CORE) and PRL release and indicate an association between these thermoregulatory variables, as well as T(CORE), and serotonergic/dopaminergic activity during prolonged exercise.