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Article Title

EFFECTS OF ENVIRONMENTAL CONDITIONS ON SELF-SELECTED WORK AND PHYSIOLOGICAL STRAIN DURING WILDLAND FIREFIGHTING

Abstract

J.A. Sol1,2, M.R. West1, J.W. Domitrovich1, B.C. Ruby, FACSM2

1USDA Forest Service – National Technology and Development Program, Missoula, MT, 2University of Montana, Missoula, MT

The combination of thermal extremes and metabolic demands associated with wildland firefighter (WLFF) job tasks may elicit acute impairment in work capacity. As heat injuries persist in WLFF and other tactical occupations, field evaluations can gather insight into characteristics of job tasks that may contribute to thermoregulatory challenges. PURPOSE: To evaluate the activity and physical demands of wildland firefighting as they relate to the associated environmental conditions. METHODS: Direct observation and real- time wireless physiological monitoring allowed for weather and physiological metrics, including heart rate (HR), percentage of HR max (%HRmax), core temperature (Tc) and physiological strain index (PSI), of male (n=301) and female (n=33) WLFFs to be monitored during wildfire management activities. Activity levels (ACT; counts·min⁻ ¹) were recorded using an ActiCal activity monitor (Mini Mitter) located in the left pectoral pocket. Heat Index estimations (HI) were calculated using temperature (TEMP) and relative humidity (HUM) inputs recorded using an OMEGA Temperature Data Logger. One-way ANOVAs were used to compare means of HI quartiles data using HR, ACT, and PSI as dependent variables. RESULTS: TEMP and HUM values were computed to heat index (n = 3891 hours) and divided into quartiles (Q1: 13.3-25.1°C; Q2: 25.2-26.4°C; Q3: 26.5-28.9°C; Q4: 29.0-49.1°C). Average ACT displayed a negative, linear correlation with HI (Q1: 535 ± 731 counts·min⁻ ¹; Q2: 423 ± 615 counts·min⁻ ¹; Q3: 384 ± 571 counts·min⁻ ¹; Q4: 309 ± 416 counts·min⁻ ¹; p < 0.05). However, this reduction in activity level resulted in only a moderating effect on HR and PSI as average HR (Q1: 113 ± 27 bpm; Q2: 116 ± 26 bpm; Q3: 116 ± 26 bpm; Q4: 111 ± 25 bpm) and PSI values (Q1: 3.5 ± 1.6; Q2: 3.7 ± 1.6; Q3: 3.7 ± 1.5; Q4: 3.5 ± 1.5) were lowest in Q1 and Q4. Average Tc values increased only slightly with increasing HI (Q1: 37.49 ± 0.46°C; Q2: 37.59 ± 0.48°C; Q3: 37.60 ± 0.43°C; Q4: 37.59 ± 0.41°C). CONCLUSION: Although physical activity occurred for approximately half of a typical 12 to 16-hour work shift, physical exertion was the primary indicator of challenges to thermoregulation in this population. Reductions in activity levels with increasing heat index values suggest adequate regulation of body temperature in the majority of WLFF field operations.

Supported by the US Forest Service.

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