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Monitoring at Chemical Agent Disposal Facilities 2 Chemical Agent Monitoring Challenges CHEMICAL DEMILITARIZATION AND STORAGE MONITORING REQUIREMENTS Monitoring for airborne chemical agents in storage and demilitarization operations is accomplished through three types of activities: Historical monitoring is employed to ensure and document that there are no ongoing emissions of chemical agents from either storage areas or demilitarization processing activities to which unprotected workers or the public might be exposed. Historical monitoring is typically employed in areas where chemical agents would not be expected, and thus, a positive finding would initiate an investigation to determine the nature and source of contamination. Near-real-time (NRT) monitoring (i.e., having a response time of approximately 3 to 15 minutes) is employed in areas where the presence of agent is likely or possible, and is conducted to ensure that any exposures to which stockpile and/or demilitarization process workers might be subjected during their employment at the facility do not exceed recommended guidelines for worker protection. NRT monitoring is also employed to detect process upset conditions. Confirmation monitoring is employed to validate or invalidate a positive result from another monitoring system (historical or NRT). It may involve multiple sampling and analytical methods. Both NRT and historical monitoring systems are employed to ensure that regulatory (permit) requirements for demilitarization operating facilities are met. The underlying technology for all current monitoring systems in use at demilitarization facilities is essentially the same, in that these systems rely on gas chromatographic techniques. The monitoring strategies employed by the Army have, in general, served to provide assurance that chemical demilitarization has proceeded in a manner that is protective of human health and the environment. Even so, false-positive results—especially with NRT monitoring—have been problematic at times because they have triggered unnecessary disruptions in the destruction process and delays in program execution. False-positive monitoring results remain a challenge for improving the overall monitoring program. For additional information on this topic, see the NRC report Evaluation of Chemical Events at Army Chemical Agent Disposal Facilities (NRC, 2002). CHEMICAL AGENT PROPERTIES The chemical weapons stockpile includes both nerve and blister agents. Nerve agents include VX, tabun (GA), and sarin (GB). All of the nerve agents are organophosphonate compounds. Blister agents include various formulations of sulfur mustard (H, HD, and HT) and arsenicals such as lewisite. Figure 2-1 shows the chemical structures of the major components of the chemical weapons stockpile, and Table 2-1 gives some of their physical properties. Physical properties that are particularly relevant to monitoring strategies are the vapor pressures and volatility values, because they indicate the relative ability of chemicals to become airborne. VX and the three types of mustard agent are essentially nonvolatile, in that they are thousands of times less volatile than water is. For either VX or the three types of mustard agent to be detected outside chemical demilitarization facilities or storage areas at potentially harmful concentrations would require a catastrophic event such as an explosion (in Chapter 6, see the section entitled “Potential Major Release Scenarios” for discussion). Agent GB, which is more volatile (somewhat similar to water) than the other agents, could conceivably be transported off-site in the event of a significant spill in a storage area that went undetected for an extended period of time.
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Monitoring at Chemical Agent Disposal Facilities TABLE 2-1 Physical Properties of Chemical Warfare Agents Agent Characteristic Nerve Agents Blister (Mustard) Agentsa GB (Sarin) VX HD HT Chemical formula (CH3)2CHO(CH3) FPO C11H26NO2PS (CICH2CH2)2S 60% HD, 40% ((ClCH2CH2)2SCH2 CH2)2O and homologues CAS Registry No. 107-44-8 50782-69-9 505-60-2 N/A Molecular weight 140.10 267.38 159.08 (mixture—188.96 based on 60/40 weight percent) Boiling point, oC 150 (extrapolated) 292 (extrapolated) 218 No constant boiling point Freezing point, oC −56 <−51 14.5 0 to 1.3 Vapor pressure, mm Hg @ 25 oC 2.48 0.0009 0.106 0.077 × 10−2 (calculated based on Raoult’s law equation and 60 weight percent HD and 40 weight percent HT) Volatility, mg/m3 3,370 at 0 oC 187,000 at 25 oC 12.6 at 25 oC 75 at 0 oC (solid) 906 at 20 oC (liquid) 783 at 25 oC Surface tension, dynes/cm 26.5 at 20 oC 32.0 at 20 oC 43.2 at 20 oC 42.4 at 25 oCb 42.0 at 25 oC Kinematic viscosity, cS 1.28 at 25 oC 12.26 at 20 oC 3.52 at 20 oC 6.50 at 20 oC Liquid density, g/cm3 at 20 oC 1.0887 1.0083 1.27 1.26 Latent heat of vaporization, cal/g 82.9 71.8 94.3 N/A Solubility, g/L H2O at 25 oC Completely miscible 50 at 21.5 oC 0.92 Similar to HD Heat of combustion (cal/g) 5,600 8,300 4,500 N/A aThe blister agents are labeled HD and HT. The active ingredient in all of these agents is bis(2-chloroethyl) sulfide, (ClCH2CH2)2S. HD, called distilled mustard, is nominally pure bis(2-chloroethyl) sulfide. H, often called Levenstein mustard, is approximately 70% bis(2-chloroethyl) sulfide and 30% impurities, which tend to be polysulfides such as (ClCH2CH2)2Sn. HT is a mixture of ca. 60% (ClCH2CH2)2S and 40% ((CICH2CH2)2SCH2CH2)2O. bThe surface tension of HD at both 20°C and 25°C is shown to allow the reader to compare the surface tensions of HD and HT under the same physical conditions, while also allowing a general comparison of the surface tensions of nerve agents and blister agents across constant physical conditions. SOURCE: Based on data provided to the NRC Committee to Assess Designs for the Pueblo and Blue Grass Chemical Agent Destruction Pilot Plants and on data from Abercrombie, 2003. FIGURE 2-1 Chemical structures of the major components of the U.S. chemical weapons stockpile. SOURCE: Adapted from original source. NRC, 2001a. CHEMICAL AGENT AIRBORNE EXPOSURE LIMITS AND DEMILITARIZATION ACTION LEVELS General Definitions Airborne exposure limits (AELs) for the nerve agents and sulfur mustard were established by the Centers for Disease Control and Prevention (CDC) in 1988 (Federal Register, 1988). The Army adopted the 1988 AELs as exposure standards to protect workers in demilitarization facilities and the surrounding general populations. The AELs accepted by the Army were a worker population limit (WPL)1 and a general population limit (GPL) for sarin (GB), tabun (GA),2 VX, and sulfur mustard (distilled) (HD). Their initial values are presented in Table 2-2, along with newer values proposed in 2003/2004. The 1988 AELs were used as the basis for the Army’s monitoring program from the commencement of 1 In 1988, the CDC identified the AELs as “Control Limits” for the general population and workers. The Army termed the worker control limit as a “TWA” (time-weighted average) but has used the value as a ceiling value limit. WPL is used here for the 1988 TWA for ease of comparison with new WPLs. 2 As noted in Figure 1-1 in this report, there is a relatively small amount of GA in the stockpile.
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Monitoring at Chemical Agent Disposal Facilities TABLE 2-2 CDC’s 1988 and 2003/2004 Recommended Airborne Exposure Limits (AELs) and U.S. EPA/NRC 2003 Acute Exposure Guideline Levels (AEGLs) for GA, GB, VX, and HD Airborne Exposure Limits GA/GB VX HD Type of Limit Year of Recommendation (mg/m3 (1 mg/m3 = 160 ppb)) (mg/m3 (1 mg/m3 = 84 ppb)) (mg/m3 (1 mg/m3 = 141 ppb)) Short-term exposure limit (STEL) 1988 2003/2004 N/A 1 × 10−4 N/A 1 × 10−5 N/A 3 × 10−3 Worker population limit (WPL) 1988 2003/2004 1 × 10−4 3 × 10−5 1 × 10−5 1 × 10−6 3 × 10−3 4 × 10−4 General population limit (GPL) 1988 2003/2004 3 × 10−6 1 × 10−6 3 × 10−6 6 × 10−7 1 × 10−4 2 × 10−5 Immediately dangerous to life and health (IDLH) 1988 2003/2004 N/A 1 × 10−1 N/A 3 × 10−3 N/A 7 × 10−1 Acute Exposure Guideline Levelsa 1-hr AEGL-1a 2.8 × 10−3 1.7 × 10−4 6.7 × 10−2 1-hr AEGL-2a 3.5 × 10−2 2.9 × 10−3 1.0 × 10−1 8-hr AEGL-1a 1 × 10−3 7.1 × 10−5 8.0 × 10−3 8-hr AEGL-2a 1.3 × 10−2 1 × 10−3 1.3 × 10−2 aAcute exposure guideline levels (AEGLs) are a hazard communication measure developed by the National Advisory Committee to Establish Acute Exposure Guideline Levels for Hazardous Substances. The committee developed detailed guidelines for devising uniform, meaningful emergency response standards for the general public. The guidelines define three tiers of AEGLs as follows: AEGL-1: The airborne concentration of a substance above which it is predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain asymptomatic nonsensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure. AEGL-2: The airborne concentration of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape. AEGL-3: The airborne concentration of a substance above which it is predicted that the general population, including susceptible individuals, could experience life-threatening health effects or death. NOTE: GA, tabun nerve agent; GB, sarin nerve agent; VX, nerve agent; HD, sulfur mustard (distilled). SOURCE: Federal Register, 1988, 2003, 2004; NRC, 2003. agent destruction operations until 2005, when the 2003/2004 values were implemented. Following are two terms that warrant definition when discussing monitoring systems for NRT monitors: Alarm level. A predetermined value for an NRT method that, when equaled or exceeded, will result in an audible and/or visual alarm at the location of the NRT monitor. The alarm level must be set so that the statistical response rate at the alarm level is greater than or equal to 95 percent (U.S. Army, 2004a). Action level. A predetermined value, usually for an NRT method, that, when equaled or exceeded, indicates the need to conduct a series of required actions in response to the apparent detection of agent. An action level is typically less than the alarm level for an NRT monitor. Actions taken when the action level is exceeded (but the alarm level is not exceeded) may include checking to ensure that the NRT monitor is functioning properly, locating and correcting a leak before the concentration of agent at the location being sampled exceeds the alarm level, and so on.3 Specific Limit Definitions In 2003 and 2004, the CDC published new recommendations for WPLs and GPLs for the nerve agents (Federal Register, 2003) and for sulfur mustard (Federal Register, 2004). The CDC also recommended values for two additional AELs—a short-term exposure limit (STEL) and an immediately dangerous to life and health (IDLH) concentration. The CDC determined that the GA and GB STEL exposures should be for no longer than 15 minutes (the same STEL exposure recommended for VX and HD), not to occur more than four times per day, and that at least 60 minutes 3 Personal communication between Robert Durgin, chief, Monitoring Team, CMA; Jeff Kiley, Monitoring Office, Risk Management Directorate, CMA; and Gary Sides, committee member, on November 30, 2004.
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Monitoring at Chemical Agent Disposal Facilities should elapse between successive exposures. The STEL for VX was recommended to occur no more than one time per day. Exposure at the IDLH concentration can be for no longer than 30 minutes, the time in which an unprotected worker could escape without experiencing impaired or irreversible health effects. Both old and new AELs are listed in Table 2-2. The new WPLs were reduced approximately threefold for the nerve agents and sulfur mustard, while the STELs were established at the old WPL levels. Thus, the 1988 WPLs and the 2003/2004 STELs are numerically identical for the respective agents. Although the CDC lowered the AELs in 2003/2004 by using updated and minimally modified risk assessment assumptions including consideration of uncertainties, it stated that the prior AELs have protected humans from the effects of these agents (Federal Register, 2003) (see Box 2-1). For more detail on the derivation of the new AELs and their comparisons to the 1988 AELs, see the NRC report Impact of Revised Airborne Exposure Limits on Non-Stockpile Chemical Materiel Program Activities (NRC, 2005). The WPL is typically referred to as an 8-hour-per-day, 5-day-per-week exposure and is used as a time-weighted average (TWA) during the 8-hour exposure period. The Army, however, has been using the CDC WPL as a ceiling level rather than as a typical TWA, and it has consistently identified this AEL as a “TWA.” Moreover, in the stockpile facilities, the Army has historically set the alarm level at 0.2 of the WPL. For example, the 1988 WPL for GB is 1 × 10−4 mg/m3, while the alarm was set to sound at 0.2 of this value (2 × 10−5 mg/m3). The reason for using 0.2 of the WPL is to ensure protection within the 99 percent con BOX 2-1 Why Were the 1988 CDC AELs Changed? The CDC reevaluated the 1988 AELs by using conventional reference concentration risk assessment methodology described by the U.S. EPA (Federal Register, 2003). It is recognized by the CDC that this method is conservative and the AELs are not numerically precise values to differentiate between nonharmful and dangerous conditions, nor are they precise thresholds of potential human toxicity. The CDC further states (Federal Register, 2003, p. 58350): The recommended changes to the AELs do not reflect change in, nor a refined understanding of, demonstrated human toxicity of these substances but rather the changes resulted from updated and minimally modified risk assessment assumptions. Overt adverse health affects have not been noted in association with previously recommended exposure limits. fidence limit, taking into account the variation in the responses of analytical monitoring equipment to airborne agent concentrations. The Army has accepted the new CDC AELs for the nerve agents and sulfur mustard, and it will use the STEL to set the alarm and action levels (U.S. Army, 2004a). Although the Army is recommending that the alarms in the stockpile facilities be set at the actual STEL, the environmental regulatory agencies in the states hosting demilitarization facilities have traditionally required that the alarms be set at a level less than the actual AEL. For instance, for GB, the states have required that the alarms be set at or near 0.2 of the AEL that comprises the current alarm level for GB. Thus, implementing the new AELs at 0.2 of the STEL has resulted in no changes in the monitoring alarm and action levels in the chemical demilitarization facilities. The Army plans to use the new WPL as an 8-hour-per-day, 5-day-per-week TWA. The Army’s intent is to analyze monitoring data at the new WPL rather than at 0.2 of the WPL (U.S. Army, 2004b). There are factors to consider in determining alarm and/or action levels. The current practice of setting the action levels at 0.2 of the WPL (Army TWA) has proven to be protective of worker populations (Federal Register, 2003). Thus, continuing with the same scenario (0.2 of STELs) seems to be practical. However, should a facility experience a large number of false alarms, the Army can encourage the states to seriously consider relaxing the 0.2 action level requirement. In fact, the Army has a permit from the state of Utah to use 0.5 of the STEL for VX at the Tooele demilitarization facility. The CDC developed the new AELs without recommending further reductions in the monitoring levels that the Army uses to protect the workers. The new GPLs present additional problems because they are near the detection limit of the current historical monitoring system. The GPLs are based on continuous exposures for long periods of time that are unlikely to occur in the stockpile demilitarization operations. Army personnel have indicated that the public seems to be most interested in the Army being able to quickly identify a release that would be of concern to the surrounding general population. In order to satisfy that concern, the Army could consider area monitoring within the site and at the perimeter at much higher concentrations than at the GPL—that is, at a level of health concern that may require additional protective measures. For example, this alarm level within the site could be at or above the 1-hour AEGL-1 level (see Table 2-2), which would reduce false alarms and be indicative of a potential (above AEGL-1 level) health hazard for areas adjacent to the site. More detailed information concerning AEGLs can be found in the NRC reports, Standing Operating Procedures for Developing Acute Exposure Guidelines Levels for Hazardous Chemicals (NRC, 2001b), and Acute Exposure Guideline Levels for Selected Airborne Chemicals: Volume 3 (NRC, 2003).
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Monitoring at Chemical Agent Disposal Facilities Finding 2-1. The Army’s use of CDC’s newly promulgated short-term exposure limits (STELs) as a basis for monitoring at demilitarization facilities is appropriate to ensure that workers are protected. Recommendation 2-1. The committee recommends that the Army continue to use short-term exposure limits (STELs) as the basis for near-real-time monitoring. REFERENCES Abercrombie, P.L. 2003. Final Physical Property Data Review of Selected Chemical Agents and Related Compounds. Updated Field Manual 3-9, ECBC-TR-294, September. Aberdeen Proving Ground, Md.: Chemical Materials Agency. Federal Register. 1988. Final recommendations for protecting the health and safety against potential adverse effects of long-term exposure to low doses of agents GA, GB, VX, mustard agent (H, HD, T), and lewisite (L). Federal Register 53(50): 8504−8507. Federal Register. 2003. Final recommendations for protecting human health from potential adverse effects of exposure to agents GA (tabun), GB (sarin), and VX. Federal Register 68(196): 58348−58351. Federal Register. 2004. Interim recommendations for airborne exposure limits for chemical warfare agents H and HD (sulfur mustard). Federal Register 69(85): 24164−24168. NRC (National Research Council). 2001a. Occupational Health and Workplace Monitoring at Chemical Agent Disposal Facilities. Washington, D.C.: National Academy Press. NRC. 2001b. Standing Operating Procedures for Developing Acute Exposure Guideline Levels for Hazardous Chemicals. Washington, D.C.: National Academy Press. NRC. 2002. Evaluation of Chemical Events at Army Chemical Agent Disposal Facilities. Washington, D.C.: The National Academies Press. NRC. 2003. Acute Exposure Guideline Levels for Selected Airborne Chemicals: Volume 3. Washington, D.C.: The National Academies Press. NRC. 2005. Impact of Revised Airborne Exposure Limits on Non-Stockpile Chemical Materiel Program Activities. Washington, D.C.: The National Academies Press. U.S. Army. 2004a. Implementation Guidance Policy for Revised Airborne Exposure Limits for GB, GA, GD, GF, VX, H, HD, and HT. June 18. Washington, D.C.: Department of the Army, Office of the Assistant Secretary of the Army (Installations and Environment). U.S. Army. 2004b. Programmatic Laboratory and Monitoring Quality Assurance Plan. Final, June. Aberdeen Proving Ground, Md.: Chemical Materials Agency.
Representative terms from entire chapter: