Physiological strain, RPE, and perceived thermal stress during auto extrication simulations by experienced urban firefighters




Soer, Benjamin Trace

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This study examined the physiological response of 22 participants (three groups of six, one group of four) during four auto extrication simulations (AES) wearing full personal protective equipment. Heart rate (HR) and core temperature (C T) were monitored continuously from baseline thoughout the AES until 45-min recovery. Blood pressure (BP), ear canal temperature (EC T), subjective measures of exertion and thermal stress were taken at baseline, post AES and clean-up, and at 45-min recovery. The average extrication completion time was 33 minutes. Average AES HR was 118 beats•min -1, a 50% increase over HR during hall duties (79 beats•min -1). HR during AES was classified as ‘heavy work.’ C T increased significantly from baseline 37.19 °C to 37.83 °C post AES. At 45 -min recovery, C T was significantly elevated from baseline (37.37 °C; p<0.05). C T and EC T did not correlate well (r=0.004), and EC T significantly underestimated C T at al time points. C T and HR were strongly correlated at al measurements (r=0.89). Mean rating of perceived exertion (RPE) post AES and post clean up was 14.0 (between ‘somewhat hard ‘ and ‘hard’) on Borg 20 point scale. RPE showed strong relationships with physiological variables of peak HR expressed as % of age predicted max (r=0.70), and physiological strain index (PSI) (r=0.76). Rating of perceived thermal stress (RPTS) increased significantly from baseline (1.23 `comfortable') to post AES (4.4, `hot'). RPTS had significant moderate strength relationships with PSI (r=0.56) and C T (r=0.52). Differences did exist in al measurements between roles within the AES team with worker firefighters (n=14) demonstrating the highest HR, BP, rise in CT, and RPE. Medics (n=5) had the lowest recorded HR, BP, & RPE. The results suggest that vehicle extrication is a physically demanding task for firefighters and 45 minutes recovery is sufficient for HR, BP, psychophysical measures, but not C T to return to baseline. The findings have implications for those firefighters who may be presented with repeated AE and/or fires and other activities across a shift. It is recommended that ear canal temperature measurements not be used as a field measure of CT as it had no relationship with C T and significantly underestimated actual C T. Future studies are needed to determine oxygen consumption and energy expenditure required to complete auto extrications.



Fire fighters, Vehicle extrication, Accident victims