Evaluation of CS (o-Chlorobenzylidene Malononitrile) Concentrations During U.S. Army Mask Confidence Training

All soldiers in the U.S. Army are required to complete mask confidence training with o-chlorobenzylidene malononitrile (CS). To instill confidence in the protective capability of the military protective mask, CS is thermally dispersed in a room where soldiers wearing military protective masks are required to conduct various physical exercises, break the seal of their mask, speak, and remove their mask. Soldiers immediately feel the irritating effects of CS when the seal of the mask is broken, which reinforces the mask's ability to shield the soldier from airborne chemical hazards. In the study described in this article, the authors examined the CS concentration inside a mask confidence chamber operated in accordance with U.S. Army training guidelines. The daily average CS concentrations ranged from 2.33-3.29 mg/m^sup 3^ and exceeded the threshold limit value ceiling, the recommended exposure limit ceiling, and the concentration deemed immediately dangerous to life and health. The minimum and maximum CS concentration used during mask confidence training should be evaluated.

Publication: Journal of Environmental Health
Author: Hout, Joseph J
Date published: October 1, 2011


Environmental health professionals in the U.S. military are often faced with unique and challenging issues in the field of environmental health. These issues can arise from a variety of scenarios including evaluating food and water sources in countries torn apart by war, assessing the health impacts of air quality in locations where environmental standards are not as stringent as those in the U.S., and conducting assessments of exposures to levels of biological, chemical, and physical Stressors presumed to be safe. We evaluated one such exposure: the intentional exposure to o-chlorobenzylidene malononitrile (CS) riot control agent during army mask confidence training.

The U.S. military has used CS as their standard riot control agent for operations and training since 1959 (Blain, 2003; O Iajos & Salem, 2001). Army personnel are first exposed to CS during initial entry training where CS is dispersed into a room by placing CS capsules on top of an inverted coffee can that is heated by an open flame (Salem et al, 2008; U.S. Army, 2007). Soldiers wearing military protective masks enter the CS-filled room and conduct a series of activities intended to give them confidence in the protective mask's ability to shield them from the effects of CS. Incapacitating effects (intense irritation of the eyes, mouth, throat, and lungs) are immediately felt when a mask is defective or has an improper fit and when soldiers are required to break the seal of their mask and attempt to speak as part of the training (U.S. Army, 1982, 2008). Army personnel repeat this training annually and immediately before military deployments (U.S. Army, 2009). Our research described in this article quantified the CS concentrations soldiers are exposed to when conducting this training.


To measure the CS concentrations during mask confidence training, a 58 m3 mask confidence chamber located at Gunpowder Military Reservation, Glen Arm, Maryland, was swept, cleaned with high pressure water, and allowed to dry for 48 hours. A CS dispersal device was constructed and positioned in accordance with U.S. Army guidelines (Salem et al, 2008). CS capsules were placed on top of the dispersal device and the heat from a Sterno« canister caused CS dispersion into the chamber.

The National Institute for Occupational Safety and Health (NIOSH) physical and chemical analytical method (P&CAM) 304 was used to sample for both the aerosol and vapor phase of CS. The sampling train began with a preassembled 37-mm polytetrafluoroethylene (PTFE) filter supported by a backup pad encased within a three-piece filter holder. The cassette was then connected to a ??-cm section of Tygon tubing followed by a Tenax TA sorbent tube (8 mm OD x 100 mm length, 100/50 mg sorbent). The Tenax TA tube was then connected to a 5-liters-per-minute (lpm) personal sampling pump using 1.0 m of Tygon tubing. All pumps were calibrated to 1.5 lpm using a Mini Buck Calibrator. The sampling trains were placed on 30.5 cm-tall bricks at a 1-m distance from the aerosol generator, consistent with previous CS research (Hout, Hook, Lapuma, & White, 2010).

Two blank samples were taken at the beginning of each day to account for the background CS concentration. Blank sampling began by igniting the heat source, waiting two minutes, then operating the sampling pumps for a period of 60 minutes to capture the 90 L required by NIOSH P&CAM 304 (National Institute for Occupational Safety and Health [NIOSH], 1979). The sampling trains were then capped, sealed in individual 1-L plastic bags, and placed into an ice-filled cooler for transport to the laboratory for analysis. The chamber doors were then opened, and the dispersal device was allowed to cool for 30 minutes.

To sample for CS, the heat source was again ignited and allowed to heat for two minutes before placing two CS capsules on the dispersal platform. U.S. Army guidelines require one CS capsule for every 30 m3 of volume to establish an initial concentration of CS (U.S. Army, 1994). Eleven sampling pumps were then started in a sequential order (the same order was maintained when turning pumps off). Under normal operating conditions, soldiers enter the chamber as a group of 10 and exit individually upon completion of the 10-minute confidence exercise. To simulate this procedure, the entry door was held open for 10 seconds to simulate the arrival of 10 soldiers. After a period of 10 minutes, the exit door was opened and closed 10 times (at ??-second intervals) to simulate 10 soldiers exiting the chamber at slightly different times. Upon completion of this sequence, one additional CS capsule was placed on the aerosol generator as required by army procedures (one new CS capsule is added for every 10 soldiers that pass through the chamber) (U.S. Army, 1994). After a sampling period of 60 minutes, the pumps were sequentially turned off and sampling trains were sealed and stored as previously described. A total of 33 samples and six blanks were taken over three separate days (Table 1).

Sample analysis was conducted by an industrial hygiene laboratory accredited by the American Industrial Hygiene Association (AIHA) using a gas Chromatograph coupled to an electron capture detector (GC/ECD). The GC/ECD consisted of an HP 689ON series gas Chromatograph (GC) fitted with an Agilent 19095S-100 (5 m ? 0.53 mm ID x 2.65 Ám film thickness) column. The injector port was maintained at 25O0C and was operated in split-less mode. Helium was used as the carrier gas at a flow rate of 8.5 mL/min. The GC oven was programmed to hold at 10O0C for one minute, followed by a temperature ramp of 250C per minute to 16O0C, and then held for 5.6 minutes. The ECD was operated at 20O0C with a combined carrier and make-up gas flow of 60 mL/min. and a data rate of 20 Hz. A seven-point calibration curve was developed using a CS standard ranging from 0.05 pg/mL-1.5 pg/mL, which captured all concentrations in this study.


Mean daily CS concentrations ranged from 2.33 to 3.29 mg/m3 (Table 1) and were not significantly different when compared in analysis of variance (ANOVA). CS background concentrations (less than .002 mg/ m3) had little effect on these concentrations. Although CS concentrations appear to be related to sampling conditions, no statistically significant correlations were found between mean CS concentration and wind speed (p = .189), relative humidity (p = .811), or temperature (p = .364).


To put these concentrations into perspective, Figure 1 illustrates the individual CS sample concentrations along with toxicological significant values. The odor threshold is 0.004 mg/m3, the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value ceiling (TLV-C) is 0.39 mg/m3, the NIOSH recommended exposure limit ceiling (REL-C) is 0.40 mg/ m3, and the concentration NIOSH deems immediately dangerous to life and health (IDLH) is 2.0 mg/m3 (American Conference of Governmental Industrial Hygienists [ACGIH], 2008; NIOSH, 2007). All 33 individual measures taken during this study exceeded the odor threshold, TLV-C, and REL-C; 30 exceeded the IDLH. The mean CS concentrations and their corresponding 95% confidence intervals were all above the odor threshold, TLV-C, REL-C, and the IDLH on all three days of sampling.

The TLV-C and REL-C for CS were developed to protect against "eye and respiratory irritation" and "damage to the respiratory epithelium" and should not be exceeded, even for instantaneous exposures (ACGIH, 1991; NIOSH, 1992). Both exposure limits also bear a skin notation, designating the skin, mucous membranes, and eyes as additional exposure routes (ACGIH, 2008; NIOSH, 2007). IDLH is defined as a condition "that poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment (Bolinger, 2004; NIOSH, 2007)." NIOSH incorporates a 30-minute safety factor into all IDLH values; however, personnel are advised to evacuate immediately if a respirator fails or if equipped with the wrong respirator for IDLH conditions. The NIOSH respirator selection logic requires a pressure-demand self-contained breathing apparatus (SCBA) with a full-face piece or a pressure-demand supplied air respirator with a full-face piece in combination with an auxiliary pressuredemand SCBA for safe entry into an IDLH environment (Bolinger, 2004). The military protective mask does not fit this definition. Furthermore, personnel are required to break the seal, speak, and remove their mask during mask confidence training, ensuring exposure (U.S. Army, 2008).


These findings suggest the need to evaluate the CS concentrations used during military mask confidence training. CS can be detected by both the human nose and eyes at the odor threshold (Blain, 2003). Therefore, a concentration range bounded by the odor threshold and the TLV-C should demonstrate the mask's ability to shield the user from airborne chemical hazards while eliminating the potential for exposure to concentrations deemed excessive by ACGIH and NIOSH. Once an acceptable concentration range is determined, CS dispersal should be conducted under various weather conditions to assure that concentration remains within the newly established maximum and minimum values. Although no correlation was found between CS concentration and weather conditions in our study, it is reasonable to expect a correlation given a larger sample size.


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Author affiliation:

Joseph J. Hout, MSPH, REHS

Timothy Kluchinsky, DrPH, MSPH, MBS, RS/REHS

Peter T. LaPuma, PhD, PE, CIH

Duvel W. White, PhD, REHS

Author affiliation:

Corresponding Author: Major Joseph J. Hout, Assistant Professor, Department of Preventive Medicine and Biometrics, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814. E-mail; jhout@usuhs.mil.

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