Respiratory Demand During Rigorous Physical Work in a Chemical Protective Ensemble

Abstract

Protection afforded by a respirator filter depends on many factors, among them 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 depends on inspiratory air velocities, among other factors. Filter designs account for this by adjusting bed depth and cross-sectional area to anticipated flow rates. Many military and commercial filters are designed and tested at 32–40 L/min. The present study investigated respiratory demand while U.S. Marines (n = 32) completed operationally relevant tasks in chemical protective ensembles, including M-40 masks and C2A1 filters. Respiratory demand greatly exceeded current test conditions during the most arduous tasks: minute ventilation = 96.4 ± 18.9 L/min (mean ± SD) with a maximum of 131.7 L/min observed in one subject. Mean peak inspiratory flow rate (PIF) reached 238.7 ± 34.0 L/min with maximum PIF often exceeding 300 L/min (maximum observed value = 356.3 L/min). The observed respiratory demand was consistent with data reported in previous laboratory studies of very heavy workloads. This study is among the few to report on respiratory demand while subjects perform operationally 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.

Keywords:

• breathing frequency
• chemical biological warfare
• chemical filter
• minute ventilation
• peak inspiratory flow rate
• respirator

ACKNOWLEDGMENTS

We would like to thank CBIRF and Marine Corps Systems Command for their support in this endeavor. The highest praise goes to the individuals who volunteered to undergo the physically demanding testing. Without their fortitude this study would have been impossible. The support staff at the CBIRF training center, including both civilian and military personnel, was also outstanding. Three individuals merit special thanks: Sam Pitts made this study happen and was responsible for developing the concept and acquiring support for the study; Karen Coyne and MSTC A.J. St. Germaine, while attending the trials as observers, provided unsolicited help at critical moments and made significant contributions to data integrity. In addition, David Caretti and Richard Newton made significant contributions to the scientific content of this work. We also would like to thank the NAVAIR team for exemplary work: J.J. Armstrong, HMCS Stephen Coleman, Earl Kauffman, HM1 Denise Mercado, HMC Dan Shaller, and LT Deborah White.

Opinions and positions stated in this article are solely those of the authors and do not necessarily reflect the official position of the Department of Defense or the Department of the Navy and Marine Corps.

Notes

^A Modification: 45.4 kg of weight carried during event 1, 22.7 kg carried during events 2–8.

^B Modification: Hoist hose in addition to raising ladder.

^C Modification: 4.9 m added distance, one additional 90° turn.

^A SD = standard deviation.

^A SD = standard deviation.