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/m3 (x̄=1.04 mg/m3) and
chamber operator exposures from 0.05 – 2.22 mg/m3 (x̄=1.05 mg/m3). 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/m3). Results support previous research suggesting risk of ARI
diagnosis after CS exposure is positively associated with CS concentration.