PROJECT-AQUARIUS .3. EFFECTS OF WORK RATE ON THE PRODUCTIVITY, ENERGY-EXPENDITURE, AND PHYSIOLOGICAL-RESPONSES OF MEN BUILDING FIRELINE WITH A RAKEHOE IN DRY EUCALYPT FOREST

Four crews of firefighters built fireline for 7 min periods (with inte rvening rests), without fire, at self-chosen 'slow', 'normal', and 'fa st' 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 up take), 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 capac ity for urgent tasks with no reduction in efficiency. EE, RWL, and hea rt rate increased linearly with productivity whereas perceived exertio n and pulmonary ventilation increased curvilinearly, rising steeply at 'fast' work rates. We suggest that perceived exertion and the ventila tory threshold (the upper limit of comfortable breathing) provide the cues by which firefighters pace themselves at sustainable work rates t hat 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 suppress ion in southern Australia.