Evaluation of an Intervention to Reduce Tear Gas Exposures and Associated Acute Respiratory Illnesses in a US Army Basic Combat Training Cohort

Joseph J. Hout*, 1, Duvel W. White1, Michael Stevens1, Alex Stubner1, Anthony Arino1, Joseph Knapik2
1 Uniformed Services University of the Health Sciences, 4301 Jones Bridge Rd, Bethesda, MD 20814, USA
2 United States Army Institute of Public Health, 5158 Blackhawk Rd, Aberdeen Proving Ground, MD 21005, USA

© 2014Hout et al..

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: ( This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Department of Preventive Medicine and Biometrics Uniformed Services University of the Health Sciences 4301 Jones Bridge Road, Bethesda, MD 20814, USA; Tel: 410-733-5134/301-319-6953; Fax: 301-295-0933; E-mail:


Exposing unmasked US Army recruits to elevated levels of o-chlorobenzylidene malononitrile (CS tear gas) during Mask Confidence Training (MCT) increases the risk of Acute Respiratory Illness (ARI) diagnosis in the period following CS exposure when compared to the period before exposure. All Army Activities Message (ALARACT) 051/2013 was implemented in March 2013 to reduce CS exposure concentrations during MCT and associated ARI rates. This observational, prospective cohort studied CS exposures and associated ARI health outcomes after implementation of ALARACT 051/2013 in 5 298 recruits attending US Army Basic Combat Training (BCT). These data indicate a 10-fold reduction (p<0.001) in CS exposure concentrations; recruit exposures ranged from 0.26 – 2.78 mg/m (x̄=1.04 mg/m) and chamber operator exposures from 0.05 – 2.22 mg/m (x̄=1.05 mg/m). The overall risk of ARI diagnosis following CS exposure also decreased when compared to period before exposure (RR=1.79, 95%CI=1.29, 2.47) resulting in 26.85% (95%CI=-0.17, 0.54) intervention effectiveness. Post-chamber ARI rates were dependent upon CS exposure concentration (p=0.02), and pre/post-chamber ARI rate ratios were significantly elevated at all concentration categories higher than the Threshold Limit Value Ceiling (TLV-C) (0.39 mg/m). Results support previous research suggesting risk of ARI diagnosis after CS exposure is positively associated with CS concentration.

Keywords: CS, tear gas, riot control, o-chlorobenzylidene malononitrile, mask confidence.