Respiratory demand in Individuals Performing Rigorous Physical Tasks in Chemical Protective Ensembles

Abstract

Abstract : Protection afforded by a respiratory filter depends on chemical or biological agent and flow rate. Filtration mechanisms such as chemical adsorption depend on sufficient residence time for the filter media to extract noxious agents from the airstream. Consequently, filter efficiency is a function of inspiratory air velocities. Filter designs account for this by adjusting bed depth and cross-sectional area to anticipated flow rates. The NATO-standard military filter (C2A1) and many commercial filters are designed and tested at 32 liters/min (1pm). The present study investigated respiratory demand while U.S. Marines (n=32) completed operationally relevant tasks in MOPP IV chemical protective ensembles (including M-40 masks and C2Al filters). Respiratory demand greatly exceeded current test conditions during the most arduous tasks; minute ventilation = 96.4 +/- 18.9 1pm (mean +/- SD) with a maximum of 13l.7 1pm observed in one subject. Mean peak inspiratory flow rate (PIF) reached 238.7 +/- 34.0 1pm with maximum PIF often exceeding 300 1pm (maximum observed value = 356.3 1pm). The observed respiratory demand was consistent with data reported in previous laboratory studies imposing very heavy workloads. This study is among the few to report on respiratory demand while subject. perform occupationally relevant tasking in chemical protective ensembles. The results indicate that military and industrial filters will probably encounter higher flow rates than previously anticipated during heavy exertion.