The effect of prescribed fluid consumption on physiology and work behavior of wildfire fighters

A systematic review of measurement methods used to estimate fluid and beverage intake in free-living, working-age adults

BACKGROUND

Beverage intake in employees is important to quantify due to the potential of dehydration to increase the risk of errors and reduced work performance. This systematic review aimed to (1) characterise existing fluid intake measurement tools used in the workplace setting or among free-living, healthy adults of working age and (2) report the current validation status of available assessment tools for use in a UK setting.

METHODS

Three electronic databases were searched for publications measuring beverage intake using a defined tool or method. Additional studies were identified by hand from trial registers, grey literature and reference lists. Eligibility was determined using predefined inclusion/exclusion criteria. Study quality was assessed using a modified Strengthening the Reporting of Observational Studies in Epidemiology framework. Narrative synthesis was performed.

RESULTS

The review identified 105 studies. The most frequently reported beverage assessment methods were total diet diaries/records (n = 22), fluid specific diaries/records (n = 18), food and fluid frequency questionnaires (n = 17), beverage-specific frequency questionnaires (n = 23) and diet recalls (n = 11). General dietary measurement tools (measuring beverages as part of total diet) were used in 60 studies, and 45 studies used a beverage-specific tool. This review identified 18 distinct dietary assessment tools, of which 6 were fluid/beverage specific. Twelve tools published relative validity for a beverage-related variable and seven tools for total daily fluid intake (from whole diet or from beverages only).

CONCLUSIONS

Several fluid intake assessment tools were identified; however, few have been fully evaluated for total beverage intake, and none in a UK working population.

Health research priorities for wildland firefighters: a modified Delphi study with stakeholder interviews

OBJECTIVES

The increase in global wildland fire activity has accelerated the urgency to understand health risks associated with wildland fire suppression. The aim of this project was to identify occupational health research priorities for wildland firefighters and related personnel.

DESIGN

In order to identify, rank and rate health research priorities, we followed a modified Delphi approach. Data collection involved a two-stage online survey followed by semi-structured interviews.

SETTING

British Columbia, Canada.

PARTICIPANTS

Participants included any current or past wildland firefighter or individuals engaged in related roles. There were 132 respondents to the first survey. Responses to the first survey were analysed to produce 10 research topics which were ranked by 75 participants in the second survey (response rate: 84%).

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary outcome was the identification, ranking and level of agreement of research priorities through a two-round online survey. We contextualised these findings through deductive and inductive qualitative content analysis of semi-structured interviews.

RESULTS

The most important research priorities identified were (% consensus): effects of smoke inhalation on respiratory health (89%), fatigue and sleep (80%), mental health (78%), stress (76%) and long-term risk of disease (67%). Interviews were completed with 14 individuals. Two main themes were developed from an inductive content analysis of interview transcripts: (1) understanding the dynamic risk environment; and (2) organisational fit of mitigation strategies.

CONCLUSIONS

Participants expressed a general concern with the unknown mental and physical health impacts of their jobs, including the long-term risk of morbidity and mortality. Future research must address knowledge gaps in our understanding of the health impacts of wildland fire and work to develop appropriate mitigation strategies while considering the needs of workers and unpredictable workplace environment.

TRIAL REGISTRATION NUMBER

Open Science Framework, https://osf.io/ugz4s/.

Health risks and mitigation strategies from occupational exposure to wildland fire: a scoping review

OBJECTIVES

Due to accelerating wildland fire activity, there is mounting urgency to understand, prevent, and mitigate the occupational health impacts associated with wildland fire suppression. The objectives of this review of academic and grey literature were to: 1. Identify the impact of occupational exposure to wildland fires on physical, mental, and emotional health; and 2. Examine the characteristics and effectiveness of prevention, mitigation, or management strategies studied to reduce negative health outcomes associated with occupational exposure to wildland fire.

METHODS

Following established scoping review methods, academic literature as well as government and industry reports were identified by searching seven academic databases and through a targeted grey literature search. 4679 articles were screened using pre-determined eligibility criteria. Data on study characteristics, health outcomes assessed, prevention or mitigation strategies studied, and main findings were extracted from each included document. The results of this scoping review are presented using descriptive tables and a narrative summary to organize key findings.

RESULTS

The final sample was comprised of 100 articles: 76 research articles and 24 grey literature reports. Grey literature focused on acute injuries and fatalities. Health outcomes reported in academic studies focused on respiratory health (n = 14), mental health (n = 16), and inflammation and oxidative stress (n = 12). The identified studies evaluated short-term outcomes measuring changes across a single shift or wildland fire season. Most research was conducted with wildland firefighters and excluded personnel such as aviation crews, contract crews, and incident management teams. Five articles reported direct study of mitigation strategies, focusing on the potential usage of masks, advanced hygiene protocols to reduce exposure, fluid intake to manage hydration and core temperature, and glutamine supplementation to reduce fatigue.

CONCLUSIONS

While broad in scope, the evidence base linking wildland fire exposure to any one health outcome is limited. The lack of long-term evidence on changes in health status or morbidity is a clear evidence gap and there is a need to prioritize research on the mental and physical health impact of occupational exposure to wildland fire.

Deterioration of Lipid Metabolism Despite Fitness Improvements in Wildland Firefighters

OBJECTIVE

Determine serum lipid and general health/fitness alterations following a 5-month wildfire suppression season.

METHODS

We recruited 100 wildland firefighters (WLFFs) to a 5-month pre- to post-season observational study. Nude body mass, blood pressure (BP), grip strength, and step-test heart rate (HR) were recorded. Blood samples were collected for lipid panel analysis (total cholesterol, HDL-cholesterol, LDL-cholesterol, VLDL-cholesterol, triglycerides, triglyceride:HDL-cholesterol ratio). Two-tailed dependent t-tests determined statistical significance (p < 0.05).

RESULTS

There were pre- to post-season changes in nude body mass (+2 ± 4%, p = 0.001), systolic BP (-2 ± 10%, p = 0.01), step-test HR (-5 ± 10%, p < 0.001), and all serum lipids (total cholesterol: +5 ± 14%, p = 0.02, HDL-cholesterol: -1 ± 17%, p = 0.04, LDL-cholesterol: +8 ± 22%, p = 0.02, VLDL-cholesterol: +31 ± 49%, p < 0.001, triglycerides: +30 ± 49%, p < 0.001, triglyceride:HDL-cholesterol ratio: +37 ± 58%, p < 0.001). Pre- to post-season diastolic BP (p = 0.12) and grip strength (p = 0.60) remained stable.

CONCLUSIONS

WLFFs demonstrate maladaptive serum lipids and body mass alterations despite subtle aerobic fitness improvements.

Workshift Changes in Hydration Status During Wildfire Suppression

OBJECTIVE

Document wildland firefighters (WLFFs) hydration status during a singular workshift (13.7 ± 1.4 hours).

METHODS

WLFF researchers documented real-time WLFF (n = 71) urine metrics and fluid consumption. Body weight and blood samples (n = 25) were also collected. Two-tailed dependent t tests determined statistical significance (P < 0.05).

RESULTS

Body weight significantly decreased (-0.3 ± 1.1%, P > 0.05). Fluid consumption totaled 6.2 ± 2.3 L including food and 5.0 ± 2.1 L without food. Morning versus afternoon urine frequency (2.6 ± 1.3, 3.1 ± 1.9 voids), urine volume (1.2 ± 0.7, 1.3 ± 0.8 L), urine volume per void (440 ± 157, 397 ± 142 mL), and urine specific gravity (1.010 ± 0.007, 1.010 ± 0.007) were not significantly different (P > 0.05). Pre- to post-workshift serum chloride (103.2 ± 1.9, 101.4 ± 1.7 mM) and blood glucose (5.2 ± 0.4, 4.5 ± 0.7 mM) significantly decreased (P < 0.05), while serum sodium (141.5 ± 2.4, 140.8 ± 2.0 mM) and serum potassium (4.3 ± 0.3, 4.2 ± 0.3 mM) remained stable (P > 0.05).

CONCLUSIONS

WLFFs can ingest fluid and food amounts that maintain workshift euhydration and electrolyte status.

Participatory Development Process of Two Human Dimension Intervention Programs to Foster Physical Fitness and Psychological Health and Well-Being in Wildland Firefighting

Intervention programs designed, delivered, and evaluated by and within organizations are a critical component in the promotion of employee health and well-being and in the prevention of occupational injury. Critical for transference of findings across complex occupational settings is a clearly articulated development process, a reliance on and evaluation of underlying theoretical foundations, and the inclusion of relevant outcomes emerging out of participatory action processes. To date, there have been no documented efforts outlining the development, implementation, or evaluation of human dimension intervention programs targeting wildland firefighters. The purpose of this paper is to outline the development of two collaborative and participatory intervention programs, targeting wildland firefighters’ physical and psychological health and well-being. Two human dimension intervention programs were developed in a collaborative, iterative and participatory process following the Context–Content–Process–Outcomes Framework. First, a physical fitness training intervention program was designed to maintain wildland firefighter’s physical fitness levels and attenuate risk of injury. Second, a psychosocial education intervention program was developed to mitigate the impact of psychosocial risk factors, foster work engagement, and decrease job stress. The current study provides evidence for the capacity of researchers and organizations to collaboratively develop practical programs primed for implementation and delivery.

Firefighter's Acute Inflammatory Response to Wildfire Suppression

OBJECTIVES

The purpose of this study was to determine the inflammatory response to a 12-hour wildfire suppression shift, in firefighters attending the "Black Saturday" natural disaster.

METHODS

Thirty-eight male volunteer firefighters provided venous blood samples before and after a 12-hour firefighting shift. Pre- to post-shift changes in pro-inflammatory (Interleukin [IL]-1β, IL-2, IL-6, IL-8, IL-12P70, granulocyte macrophage-colony stimulating factor [GM-CSF], tumor necrosis factor-alpha [TNF-α], interferon-gamma [IFNγ]), and anti-inflammatory (IL-4, IL-5, IL-7, IL-10, IL-13) cytokines were measured with paired sample t tests, or Wilcoxon t tests for non-parametric data.

RESULTS

Interleukin (IL)-6 (P = 0.003) and IL-8 (P = 0.017) were significantly increased following 12-hours of wildfire suppression. There was also a significant decrease in IL-10 (P = 0.021).

CONCLUSIONS

The observed acute inflammatory response may have resulted from multiple stressors including physical exertion, thermal strain, or smoke inhalation experienced during the shift, and may be a necessary response for the body to adapt to stressor exposure.

The accumulation of, and associations between, nurses' activity levels within their shift in the emergency department

The aim of this study was to examine emergency nurses' activity levels and associations between hourly activity levels within-shifts. Fifty emergency nurses (45 females, 5 males) wore ActiGraph accelerometers and completed work diaries for up to 4 weeks. A sub-group (n = 42) also wore activPALs. Multilevel analyses examined temporal associations between hourly periods. In any hourly period, increased time spent in moderate- to vigorous-intensity physical activity (MVPA) was associated with less time spent in MVPA in the following hourly period. In any afternoon hourly period, increased time spent in MVPA was associated with more time spent in light-intensity physical activity in the following hourly period. No other associations were significant. Emergency nurses maintain activity levels within-shifts, except when more time spent in MVPA was associated with less time spent in MVPA in the following hour; a potential recovery strategy. Future research should determine how emergency nurses maintain their activity levels within-shifts. Practitioner Summary: Emergency nursing is physically demanding; however, it is unknown how active they are during hourly periods within-shifts. Emergency nurses' activity levels were maintained within hourly periods of a shift. Except for an increase in MVPA in 1 h was associated with a decrease in MVPA in the following hour. Abbreviations: CPR: cardiopulmonary resusitation; LPA: light-intensity physical activity; MPA: moderate-intenisty physical activity; MVPA: moderate- to vigorous-intensity physical activity; SED: sedentary.

The effects of hydration on cognitive performance during a simulated wildfire suppression shift in temperate and hot conditions

The effects on dehydration and cognitive performance from heat and/or physical activity are well established in the laboratory, although have not yet been studied for personnel working in occupations such as wildland firefighting regularly exposed to these types of conditions. This study aimed to investigate the effects of temperature and dehydration on seventy-three volunteer firefighters (35.7 ± 13.7 years, mean ± standard deviation) during a simulation of wildfire suppression under either control or hot (18-20; or 33-35 °C) temperature conditions. Results showed cognitive performance on the psychomotor vigilance task declined when participants were dehydrated in the heat and Stroop task performance was impaired when dehydrated late in the afternoon. Firefighters may be at risk of deteriorations in simple cognitive functions in the heat whilst dehydrated, although may also experience impairments in complex cognitive functions if dehydrated late in the day, irrespective of the environmental temperature.

The Effects of Simulated Wildland Firefighting Tasks on Core Temperature and Cognitive Function under Very Hot Conditions

Background: The severity of wildland fires is increasing due to continually hotter and drier summers. Firefighters are required to make life altering decisions on the fireground, which requires analytical thinking, problem solving, and situational awareness. This study aimed to determine the effects of very hot (45°C; HOT) conditions on cognitive function following periods of simulated wildfire suppression work when compared to a temperate environment (18°C; CON). Methods: Ten male volunteer firefighters intermittently performed a simulated fireground task for 3 h in both the CON and HOT environments, with cognitive function tests (paired associates learning and spatial span) assessed at baseline (cog 1) and during the final 20-min of each hour (cog 2, 3, and 4). Reaction time was also assessed at cog 1 and cog 4. Pre- and post- body mass were recorded, and core and skin temperature were measured continuously throughout the protocol. Results: There were no differences between the CON and HOT trials for any of the cognitive assessments, regardless of complexity. While core temperature reached 38.7°C in the HOT (compared to only 37.5°C in the CON; p < 0.01), core temperature declined during the cognitive assessments in both conditions (at a rate of -0.15 ± 0.20°C·hr-1 and -0.63 ± 0.12°C·hr-1 in the HOT and CON trial respectively). Firefighters also maintained their pre-exercise body mass in both conditions, indicating euhydration. Conclusions: It is likely that this maintenance of euhydration and the relative drop in core temperature experienced between physical work bouts was responsible for the preservation of firefighters' cognitive function in the present study.

The Impact of Heat Exposure and Sleep Restriction on Firefighters' Work Performance and Physiology during Simulated Wildfire Suppression

This study was designed to examine the effects of ambient heat on firefighters' physical task performance, and physiological and perceptual responses when sleep restricted during simulated wildfire conditions. Thirty firefighters were randomly allocated to the sleep restricted (n = 17, SR; 19 °C, 4-h sleep opportunity) or hot and sleep restricted (n = 13, HOT + SR; 33 °C, 4-h sleep opportunity) condition. Firefighters performed two days of simulated, intermittent, self-paced work circuits comprising six firefighting tasks. Heart rate, and core temperature were measured continuously. After each task, firefighters reported their rating of perceived exertion and thermal sensation. Effort sensation was also reported after each work circuit. Fluids were consumed ad libitum. Urine volume and urine specific gravity were analysed. Sleep was monitored using polysomnography. There were no differences between the SR and HOT + SR groups in firefighters' physiological responses, hydration status, ratings of perceived exertion, motivation, and four of the six firefighting tasks (charged hose advance, rake, hose rolling, static hose hold). Black out hose and lateral repositioning were adversely affected in the HOT + SR group. Working in hot conditions did not appear to consistently impair firefighters work performance, physiology, and perceptual responses. Future research should determine whether such findings remain true when individual tasks are performed over longer durations.

The impact of fire suppression tasks on firefighter hydration: a critical review with consideration of the utility of reported hydration measures

Background

Firefighting is a highly stressful occupation with unique physical challenges, apparel and environments that increase the potential for dehydration. Dehydration leaves the firefighter at risk of harm to their health, safety and performance. The purpose of this review was to critically analyse the current literature investigating the impact of fighting ‘live’ fires on firefighter hydration.

Methods

A systematic search was performed of four electronic databases for relevant published studies investigating the impact of live fire suppression on firefighter hydration. Study eligibility was assessed using strict inclusion and exclusion criteria. The included studies were critically appraised using the Downs and Black protocol and graded according to the Kennelly grading system.

Results

Ten studies met the eligibility criteria for this review. The average score for methodological quality was 55 %, ranging from 50 % (‘fair’ quality) to 61 % (‘good’ quality) with a ‘substantial agreement’ between raters (k = .772). Wildfire suppression was considered in five studies and structural fire suppression in five studies. Results varied across the studies, reflecting variations in outcome measures, hydration protocols and interventions. Three studies reported significant indicators of dehydration resulting from structural fire suppression, while two studies found mixed results, with some measures indicating dehydration and other measures an unchanged hydration status. Three studies found non-significant changes in hydration resulting from wildfire firefighting and two studies found significant improvements in markers of hydration. Ad libitum fluid intake was a common factor across the studies finding no, or less severe, dehydration.

Conclusions

The evidence confirms that structural and wildfire firefighting can cause dehydration. Ad libitum drinking may be sufficient to maintain hydration in many wildfire environments but possibly not during intense, longer duration, hot structural fire operations. Future high quality research better quantifying the effects of these influences on the degree of dehydration is required to inform policies and procedures that ensure firefighter health and safety.

Firefighters' Physical Activity across Multiple Shifts of Planned Burn Work

Little is currently known about the physical activity patterns of workers in physically demanding populations. The aims of this study were to (a) quantify firefighters’ physical activity and sedentary time within (2-h periods) and across planned burn shifts; and (b) examine whether firefighters’ activity levels during one shift or 2-h period was associated with their activity levels in the following shift or 2-h period. Thirty-four salaried firefighters (26 men, 8 women) wore an Actical accelerometer for 28 consecutive days. Time spent sedentary (SED) and in light- (LPA), moderate- (MPA) and vigorous-intensity physical activity (VPA) were derived using validated cut-points. Multilevel analyses (shift, participant) were conducted using generalised linear latent and mixed models. Firefighters spent the majority of a planned burn shift (average length 10.4 h) or 2-h period engaged in LPA (69% and 70%, respectively). No significant associations were observed between SED and physical activity levels between consecutive planned burned shifts or 2-h periods. The physical activity that a firefighter engaged in during one shift (or 2-h period) did not subsequently affect their physical activity levels in the subsequent shift (or 2-h period). Further research is needed to establish how workers in physically demanding populations are able to sustain their activity levels over long periods of time.

Associations between firefighters' physical activity across multiple shifts of wildfire suppression

The aim of this study was to examine the associations between firefighters' physical activity levels across consecutive wildfire suppression shifts and to determine whether sleep duration moderated these associations. Forty volunteer firefighters (31 males, 9 females) wore an activity monitor to concurrently measure physical activity and sleep duration. Sedentary time and time spent in light- (LPA), moderate- (MPA), and vigorous-intensity physical activity (VPA) during each shift were determined using monitor-specific cut points. During any given shift, every additional 60 min spent in LPA was associated with 7.2 min more LPA and 27.6 min MPA the following shift. There were no other significant positive or negative associations. No significant moderating effect of total sleep time was observed. Firefighters are able to maintain and/or increase their physical activity intensity between consecutive shifts. Further research is needed to understand firefighters pacing and energy conservation strategies during emergency wildfire deployments. Practitioner Summary: To examine associations between firefighters' physical activity levels across consecutive shifts during a multi-day emergency wildfire and determine whether sleep duration moderated these associations. Firefighters are able to maintain and/or increase their physical activity intensity between consecutive shifts. No significant moderating effect of total sleep time was observed.

Relationships between inflammatory cytokine and cortisol responses in firefighters exposed to simulated wildfire suppression work and sleep restriction

The interplay between inflammatory and cortisol responses modulates an appropriate response to a stressor. Exposure to severe stressors, however, may alter the actions and relationships of these responses and contribute to negative health outcomes. Physical work and sleep restriction are two stressors faced by wildland firefighters, yet their influence on the relationship between inflammatory and cortisol responses is unknown. The aim of the present study was to quantify the relationship between the cytokine and cortisol responses to sleep restriction while performing simulated physical wildfire suppression work. Firefighters completed 3 days of simulated physical firefighting work separated by either an 8-h (Control condition; n = 18) or 4-h sleep (Sleep restriction condition; n = 17) opportunity on each of the two nights. Salivary cortisol and inflammatory cytokines (IL-6, IL-8, IL-1β, TNF-α, IL-4, and IL-10) were measured throughout each day. An increase in morning IL-6 was related to a rise (6.2%, P = 0.043) in evening cortisol among firefighters in the sleep restriction condition. Higher morning IL-6 levels were related to increased (5.3%, P = 0.048) daily cortisol levels, but this relationship was not different between conditions. Less pronounced relationships were demonstrated between TNF-α, IL-10, IL-4, and cortisol independent of the sleep opportunity, but relationships did not persist after adjusting for demographic factors and other cytokines. These findings quantify the relationship between cytokine and cortisol responses among wildland firefighters exposed to simulated occupational stressors. Potential disturbances to the IL-6 and cortisol relationship among sleep-restricted firefighters’ supports further investigations into the negative health effects related to possible imbalances between these systems.

Simulated Firefighting Task Performance and Physiology Under Very Hot Conditions

PURPOSE

To assess the impact of very hot (45°C) conditions on the performance of, and physiological responses to, a simulated firefighting manual-handling task compared to the same work in a temperate environment (18°C).

METHODS

Ten male volunteer firefighters performed a 3-h protocol in both 18°C (CON) and 45°C (VH). Participants intermittently performed 12 × 1-min bouts of raking, 6 × 8-min bouts of low-intensity stepping, and 6 × 20-min rest periods. The area cleared during the raking task determined work performance. Core temperature, skin temperature, and heart rate were measured continuously. Participants also periodically rated their perceived exertion (RPE) and thermal sensation. Firefighters consumed water ad libitum. Urine specific gravity (USG) and changes in body mass determined hydration status.

RESULTS

Firefighters raked 19% less debris during the VH condition. Core and skin temperature were 0.99 ± 0.20 and 5.45 ± 0.53°C higher, respectively, during the VH trial, and heart rate was 14-36 beats.min(-1) higher in the VH trial. Firefighters consumed 2950 ± 1034 mL of water in the VH condition, compared to 1290 ± 525 in the CON trial. Sweat losses were higher in the VH (1886 ± 474 mL) compared to the CON trial (462 ± 392 mL), though both groups were hydrated upon protocol completion (USG < 1.020). Participants' average RPE was higher in the VH (15.6 ± 0.9) compared to the CON trial (12.6 ± 0.9). Similarly, the firefighers' thermal sensation scores were significantly higher in the VH (6.4 ± 0.5) compared to the CON trial (4.4 ± 0.4).

CONCLUSIONS

Despite the decreased work output and aggressive fluid replacement observed in the VH trial, firefighters' experienced increases in thermal stress, and exertion. Fire agencies should prioritize the health and safety of fire personnel in very hot temperatures, and consider the impact of reduced productivity on fire suppression efforts.

The Impact of Sleep Restriction and Simulated Physical Firefighting Work on Acute Inflammatory Stress Responses

OBJECTIVES

This study investigated the effect restricted sleep has on wildland firefighters' acute cytokine levels during 3 days and 2 nights of simulated physical wildfire suppression work.

METHODS

Firefighters completed multiple days of physical firefighting work separated by either an 8-h (Control condition; n = 18) or 4-h (Sleep restriction condition; n = 17) sleep opportunity each night. Blood samples were collected 4 times a day (i.e., 06:15, 11:30, 18:15, 21:30) from which plasma cytokine levels (IL-6, IL-8, IL-1β, TNF-α, IL-4, IL-10) were measured.

RESULTS

The primary findings for cytokine levels revealed a fixed effect for condition that showed higher IL-8 levels among firefighters who received an 8-h sleep each night. An interaction effect demonstrated differing increases in IL-6 over successive days of work for the SR and CON conditions. Fixed effects for time indicated that IL-6 and IL-4 levels increased, while IL-1β, TNF-α and IL-8 levels decreased. There were no significant effects for IL-10 observed.

CONCLUSION

Findings demonstrate increased IL-8 levels among firefighters who received an 8-h sleep when compared to those who had a restricted 4-h sleep. Firefighters' IL-6 levels increased in both conditions which may indicate that a 4-h sleep restriction duration and/or period (i.e., 2 nights) was not a significant enough stressor to affect this cytokine. Considering the immunomodulatory properties of IL-6 and IL-4 that inhibit pro-inflammatory cytokines, the rise in IL-6 and IL-4, independent of increases in IL-1β and TNF-α, could indicate a non-damaging response to the stress of simulated physical firefighting work. However, given the link between chronically elevated cytokine levels and several diseases, further research is needed to determine if firefighters' IL-8 and IL-6 levels are elevated following repeated firefighting deployments across a fire season and over multiple fire seasons.

Multiple Days of Heat Exposure on Firefighters' Work Performance and Physiology

This study assessed the accumulated effect of ambient heat on the performance of, and physiological and perceptual responses to, intermittent, simulated wildfire fighting tasks over three consecutive days. Firefighters (n = 36) were matched and allocated to either the CON (19°C) or HOT (33°C) condition. They performed three days of intermittent, self-paced simulated firefighting work, interspersed with physiological testing. Task repetitions were counted (and converted to distance or area) to determine work performance. Participants were asked to rate their perceived exertion and thermal sensation after each task. Heart rate, core temperature (Tc), and skin temperature (Tsk) were recorded continuously throughout the simulation. Fluids were consumed ad libitum. Urine volume was measured throughout, and urine specific gravity (USG) analysed, to estimate hydration. All food and fluid consumption was recorded. There was no difference in work output between experimental conditions. However, significant variation in performance responses between individuals was observed. All measures of thermal stress were elevated in the HOT, with core and skin temperature reaching, on average, 0.24 ± 0.08°C and 2.81 ± 0.20°C higher than the CON group. Participants' doubled their fluid intake in the HOT condition, and this was reflected in the USG scores, where the HOT participants reported significantly lower values. Heart rate was comparable between conditions at nearly all time points, however the peak heart rate reached each circuit was 7 ± 3% higher in the CON trial. Likewise, RPE was slightly elevated in the CON trial for the majority of tasks. Participants' work output was comparable between the CON and HOT conditions, however the performance change over time varied significantly between individuals. It is likely that the increased fluid replacement in the heat, in concert with frequent rest breaks and task rotation, assisted with the regulation of physiological responses (e.g., heart rate, core temperature).

Fluid intake, hydration, work physiology of wildfire fighters working in the heat over consecutive days

PURPOSE

(i) To evaluate firefighters' pre- and post-shift hydration status across two shifts of wildfire suppression work in hot weather conditions. (ii) To document firefighters' fluid intake during and between two shifts of wildfire suppression work. (iii) To compare firefighters' heart rate, activity, rating of perceived exertion (RPE), and core temperature across the two consecutive shifts of wildfire suppression work.

METHOD

Across two consecutive days, 12 salaried firefighters' hydration status was measured immediately pre- and post-shift. Hydration status was also measured 2h post-shift. RPE was also measured immediately post-shift on each day. Work activity, heart rate, and core temperature were logged continuously during each shift. Ten firefighters also manually recorded their food and fluid intake before, during, and after both fireground shifts.

RESULTS

Firefighters were not euhydrated at all measurement points on Day one (292±1 mOsm l(-1)) and euhydrated across these same time points on Day two (289±0.5 mOsm l(-1)). Fluid consumption following firefighters' shift on Day one (1792±1134ml) trended (P = 0.08) higher than Day two (1108±1142ml). Daily total fluid intake was not different (P = 0.27), averaging 6443±1941ml across both days. Core temperature and the time spent ≥ 70%HRmax were both elevated on Day one (when firefighters were not euhydrated). Firefighters' work activity profile was not different between both days of work.

CONCLUSION

There was no difference in firefighters' pre- to post-shift hydration within each shift, suggesting ad libitum drinking was at least sufficient to maintain pre-shift hydration status, even in hot conditions. Firefighters' relative hypohydration on Day one (despite a slightly lower ambient temperature) may have been associated with elevations in core temperature, more time in the higher heart rate zones, and 'post-shift' RPE.

Trunk postures and upper-body muscle activations during physically demanding wildfire suppression tasks

This study examined the trunk postures and upper-body muscle activations during four physically demanding wildfire suppression tasks. Bilateral, wireless surface electromyography was recorded from the trapezius and erector spinae muscles of nine experienced, wildfire fighters. Synchronised video captured two retroreflective markers to allow for quantification of two-dimensional sagittal trunk flexion. In all tasks, significantly longer time was spent in the mild and severe trunk flexion (p ≤ 0.002) compared to the time spent in a neutral posture. Mean and peak muscle activation in all tasks exceeded previously established safe limits. These activation levels also significantly increased through the performance of each task (p < 0.001). The results suggest that the wildfire suppression tasks analysed impose significant musculoskeletal demand on firefighters. Fire agencies should consider developing interventions to reduce the exposure of their personnel to these potentially injurious musculoskeletal demands.