Results • Case status was dependent on exposure above 3.00 mg/m3 when compared to exposure below 3.00 mg/m3. • Mean CS exposure differed between Cases and Non-cases (p= 0.03). • Cases occurred with exposure > 3.00 mg/m3 (1.5x IDLH). • Median time in chamber and time out of mask did not differ significantly between cases and non-cases. • Cases were associated with greater than moderate allergy symptoms (p= 0.03) and a reduction in capacity for vigorous physical activity after MCT (p= 0.01). • The odds of developing symptoms meeting case criteria, OR 5.6 (95% CI 1.3 – 37), increased as CS exposure increased. • Predictor: CS Exposure Concentration • Outcome: Case Status Introduction • The RCA commonly known as CS or tear gas is known for its debilitating ocular, respiratory, and dermal irritant effects (3; 4). • U.S. Army soldiers are exposed to CS during a common military training task known as MCT, where CS is thermally disbursed as a training aid to build confidence in a soldier’s military protective mask. Discussion An association between above-threshold CS exposure and respiratory outcomes was present in the study population. • An increase of 1.00 mg/m3 in individual CS exposure was associated with 5.6 times greater odds (95%CI 1.3-36.9) of developing symptoms of acute respiratory illness one-week after MCT. • The risk of developing new-onset symptoms sufficient to meet case criteria one-week after MCT: ̶ Increased as exposure concentration increased ̶ Was dependent on exposure above the threshold concentration of 1.5 times the IDLH (3.00 mg/m3) ̶ Was associated with three excess cases per 25 participants compared with those exposed to CS concentrations below 3.00 mg/m3 • A history of respiratory allergies may modify the effect between CS exposure above 3.00 mg/m3 and acute respiratory illness, but a larger sample is necessary to confirm the effect. • Risk factors assessed in the study did not meet confounding criteria however, a larger sample is necessary to veri, This prospective cohort study examined the association between riot control agent (RCA) exposure and self-reported acute respiratory illness (ARI) symptoms following mask confidence training (MCT) in a U.S. Army officer population attending Basic Officer Leaders Course (BOLC) from June 12 – July 2015. U.S. Army officers are exposed to the RCA o-chlorobenzylidene malononitrile (CS) as part of MCT where they don air purifying respirators, enter an enclosed structure containing aerosolized CS, perform a variety of tasks, and remove their respirators prior to exiting the chamber. This unprotected exposure to CS causes immediate ocular, respiratory, and dermal irritation, which demonstrates the effectiveness of the respirator, but may be a contributor to the new-onset ARI. Developing new-onset symptoms of ARI during the week following MCT was dependent on CS exposure above 1.5 times the Immediately Dangerous to Life and Health (IDLH) concentration (3.00 mg/cu.m). Those with respiratory allergies developed ARI symptoms with exposure to lower CS concentrations than those without respiratory allergies. While this study lacked the statistical power to create a multivariate model or to analyze stratum specific effects, the results are consistent with previous research suggesting that ARI is positively associated with CS exposure concentration.