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The overall aim of this thesis was to investigate the interactions between firefighters’ sleep, ambient temperature, hydration status, and cognitive performance during simulated single and multi-day wildfire suppressions. These exact aims are addressed through four studies: 1. To assess the effect of ambient heat during day-(33-35°C) and night-time (23-25°C) exposures on firefighters’ sleep quantity and quality during a simulated multi-day wildfire suppression compared to thermoneutral temperatures (18-20°C; Study 1 -Chapter 4). 2. To quantify the effect of sleep restriction in either ambient heat with day- (33-35°C) and night-time (23-25°C) exposures or thermoneutral conditions (18-20°C) on firefighters’ sleep architecture during a simulated multi-day wildfire suppression compared to a control condition with normal sleep in temperate conditions (18-20°C; Study 2 –Chapter 5). 3. To examine the association between firefighters’ hydration status and cognitive performance during a simulated prolonged wildfire suppression shift in the heat (33-35°C) compared to thermoneutral temperatures (18-20°C; Study 3 –Chapter 6). 4. To examine the effect on cognitive performance of sleep restriction in either ambient heat with day-(33-35°C) and night-time (18-20°C) temperature changes or temperate conditions (18-20°C) during a simulated multi-day wildfire suppression compared to a control condition with full sleep opportunities in thermoneutral temperatures (18-20°C; Study 4 –Chapter 7).

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. Refereed/Peer-reviewed

Wildland firefighting exposes personnel to combinations of occupational and environmental stressors that include physical activity, heat and sleep restriction. However, the effects of these stressors on sleep have rarely been studied in the laboratory, and direct comparisons to field scenarios remain problematic. The aim of this study was to examine firefighters’ sleep during a three-day, four-night simulated wildfire suppression that included sleep restriction and physical activity circuits representative of firefighting wildfire suppression tasks in varied temperatures. Sixty-one volunteer firefighters (37.5 ± 14.5 years of age, mean ± SD) were assigned to one of three conditions: control (n = 25; 8 h sleep opportunities and 18–20 °C), awake (n = 25; 4 h sleep opportunities and 18–20 °C) or awake/hot (n = 11; 4 h sleep opportunities and 33–35 °C during the day and 23–25 °C during the night). Results demonstrated that amounts of N1, N2 and R sleep, TST, SOL and WASO declined, whilst sleep efficiency increased significantly in the awake and awake/hot conditions compared to the control condition. Results also demonstrated that SWS sleep remained relatively stable in the awake and awake/hot conditions compared to control values. Most importantly, no significant differences were found for any of the sleep measures between the awake and awake/hot conditions. Thus, working in hot daytime temperatures in combination with sleep restriction during the night did not affect patterns of sleep compared to working in temperate conditions in combination with sleep restriction during the night. However, the effects on sleep of high (>25 °C) night-time temperatures with sleep restriction in addition to physical activity remains to be studied. Refereed/Peer-reviewed