Firefighters' thermal environment was continuously measured while they attempted to suppress well-developed experimental bushfires of intensities commonly faced by hand-tool crews, and also while they built fireline in the same way without fire, during three summers in Australian eucalypt forests. They worked far enough from the flames to avoid painful intensities of radiant heat (>2 kW m-2) on bare skin and usually experienced 1.6 kW m-2 - little more than the intensity of sunlight Fire had negligible effects on average air temperature, humidity, or wired speed. Exertion accounted for 71% of the total heat load, fire and weather for the remainder. Evaporation was effectively the sole means of heat dissipation, and predicted sweat loss exceeded one litre per hour. Indices of heat stress usually exceeded occupational limits proposed for heat-acclimatized men, although little additional strain resulted. We conclude that firefighters should be fit and acclimatized, wear light and loose clothing that imposes minimal resistance to evaporation, and drink at least 1 litre of water per hour.

Four crews of firefighters built fireline for 7 min periods (with intervening rests), without fire, at self-chosen 'slow', 'normal', and 'fast' rates in Australian eucalypt forests. Individuals differed twofold for energy expenditure (EE, measured as oxygen uptake by the Douglas bag technique) and relative work load (RWL, i.e % of maximum oxygen uptake), and threefold for productivity and efficiency (productivity per unit EE). They maintained their differences in all stages of the test and also while suppressing free-running wildland fires, showing that the work rate adopted was a stable characteristic of the individuals' work behaviour. The technique of raking fireline did not constrain EE but instead allowed firefighters to call upon their maximum work capacity for urgent tasks with no reduction in efficiency. EE, RWL, and heart rate increased linearly with productivity whereas perceived exertion and pulmonary ventilation increased curvilinearly, rising steeply at 'fast' work rates. We suggest that perceived exertion and the ventilatory threshold (the upper limit of comfortable breathing) provide the cues by which firefighters pace themselves at sustainable work rates that balance their fireline productivity against its physiological cost. The findings were highly consistent over four crews, three summers, and two regions and are thus generally applicable to bushfire suppression in southern Australia.

Timed-activity studies were made of four crews while they attempted to suppress well-developed experimental bushfires of intensities commonly faced by handtool crews, and also while they built fireline in the same way without fire, during three summers in Australian eucalypt forests. Fireline construction with rakehoes (including step up) occupied, on average, 63% of the crew's time. Firefighters raked for 38 seconds followed by 10 seconds of step up, thus obtaining frequent brief rests for the arm muscles involved in raking. Energy expenditure (EE) of all fire-suppression activities averaged 516 W, equivalent to a relative work load (RWL) of 45% of the men's maximum work capacity. Pulmonary ventilation averaged 55 (range 38-83) 1 min-1 during raking and 40 (range 23-73) 1 min-1 during all activities. Each firefighter built 1.90 m2 of fireline per minute of raking, and 1.21 m2 min-1 over the whole period of the attack. Each hour the six men engaged in fireline construction built and held 436 m2, i.e. 512 metres of fireline 0.85 metres wide. Individuals consistently differed twofold in their self-chosen levels of raking EE and RWL and threefold in productivity and efficiency (productivity per unit EE), whereas average raking EE did not differ between crews, nor between attacks with and without fire. We conclude that wildland firefighters pace themselves at their own preferred and sustainable work rates.

The purpose of this study was to investigate the thermoregulatory mechanisms underlying artificial acclimatization to cold and to compare them with those of naturally acclimatized men. Six white men were cooled, nude, in air at 10 degrees C for 2 h before and after they had been acclimatized by ten daily cold (15 degrees C) baths of 30-60 min followed by rapid rewarming in hot (38-42 degrees C) water, and again 4 months later after acclimatization had decayed. Six control subjects also underwent the same tests, providing an opportunity to discriminate between changes caused by the immersions and those caused by extraneous influences. Acclimatization significantly reduced heat production and heat loss (P < 0.05) but did not change heat debt. The reduced heat production was accompanied by reductions in shivering (P < 0.10) and in cold-induced muscle tenseness; no evidence of nonshivering thermogenesis or active brown fat was found. These findings are attributed to increased tissue insulation, mediated by an enhanced vascular response to cold that did not involve the cutaneous circulation and was probably located in skeletal muscle. Thermal sensation and discomfort did not change, although perceived strain tended to increase (P = 0.08). Acclimatization was accompanied by, but was unrelated to, slower cooling of the finger and toe. The main conclusions, and many specific findings, agree with those of two previous studies made by the same techniques in naturally acclimatized men wintering in Antarctica. Other significant findings included changes--in particular reduced thermoneutral rectal temperature and a delayed onset of shivering--that are commonly regarded as evidence of acclimatization but were in fact unrelated to it as they also occurred in the control group. They are attributed to extraneous influences, in particular the relaxation of heightened arousal ('first-time effects') found in the baseline tests.

Firefighters' fluid balance was measured while they attempted to suppress well-developed experimental bushfires of intensities commonly faced by hand-tool crews, and also while they built fireline in the same way without fire, during three summers in Australian eucalypt forests. They consistently sweated at rates of 1-2 kg h-1 while building fireline and at half these rates for the whole work day. Drinking and dehydration were proportional to sweat loss: on average firefighters replaced 43% of their sweat loss during fireline construction and 63% for the whole work day. During fireline construction they dehydrated at an average rate of 654 g (0.9% body mass) per hour and a maximum rate of 2 kg per hour (2.6% body mass). The scientific observers sweated less than half as much as the firefighters but also drank less and became almost as dehydrated. These findings emphasise the need for work practices that guarantee an adequate water intake before, during, and after firefighting. Regression equations are presented for predicting sweat rate (hence water requirements) from activity, fire, body mass, and air temperature.