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4 A New Set of Exposure Guidelines: Chemical Casualty Estimating Guidelines INTRODUCTION As discussed in Chapter 2, predictive guidelines are needed to properly assess the chemical risks to missions. To that end, the subcommittee rec- ommends that the Army develop and use chemical casualty estimating guidelines (CCEGs). CCEGs are media and duration-specific estimated chemical concentrations that would be expected to cause health impairments that degrade the performance of enough individuals to reduce unit strength (i.e., to pose a medical threat). They would be used to evaluate course-of- action options expected to involve chemical exposures. To be practical, CCEGs must accurately predict casualties and be in a form that can be applied in the field. This chapter addresses the development of CCEGs for individual chemicals, the application of CCEGs, and the estimation of cu- mulative risk. The development and application of MEGs is considered in Chapter 5. The criteria in Box 4-1 indicate the differences between CCEGs and the U.S. Army Center for Health Promotion and Preventive Medicine (USA- CHPPM) military exposure guidelines (MEGs) and provide goals for CCEG development. The dichotomy presented has some apparent overlaps that will become more clear in practice. For example, a short-term exposure could reduce pulmonary function and could preclude healthy but suscepti- 76
CHEMICAL CASUALTY ESTIMATING GUIDELINES 77 BOX 4-1 Criteria for CCEGs and MEGs CCEGs â¢ Include chemicals likely to be encountered in sufficient quantities to degrade mission effectiveness. â¢ Include health effects that are manifested within minutes, hours, or several days that could immediately affect the functioning of troops (e.g., loss of cognitive ability, loss of visual acuity, significantly reduced cardiopulmonary functioning, muscular weakness) performing a mission. Does not include long-term health effects (e.g., cancer). â¢ Consider exposure time frames of hours, days, and weeks, rather than months or years. â¢ Relate to the military population, which includes generally healthy adult men and women with typical variations in genetic susceptibilities. â¢ Provide exposure-response and population-response information, insofar as possible. Include concentrations likely to cause effects in humans, along with a descrip- tion of the severity and incidence expected. This information would enable chemical threats to be weighed in comparison to other mission threats (e.g., Table 3-1 in TG-230 would be more useful). â¢ Provide guidance primarily for the air exposure pathway, because troops have no choice but to breathe the air (except when gas masks are used). Theoretically, the water pathway might influence CCEGs, but the availability of alternative sources of water makes it relatively less important. Water exposure scenarios of special concern should be identified and addressed. Soil also deserves some consideration, but is unlikely to be a significant source of exposure. MEGs â¢ Include a large number of chemicals likely to be present in deployments. â¢ Include concerns over longer-term health of individuals recognize that expo- sures at these levels would have no to minimal impact on immediate missions. â¢ Include virtually all exposure durations from 1 hour to 1 year. â¢ Relate to the military population. â¢ Indicate protective levels (i.e., levels assumed to represent no adverse effects or very low risk) for the exposure durations of interest. â¢ Provide guidance for management actions when MEGs are exceeded. ble soldiers from engaging in heavy exercise. At a higher concentration, the average soldier might be affected, further reducing unit strength. Long-term exposure at lower concentrations of the same chemical might not cause near-term effects on pulmonary function, but could cause alterations in lung structure much later. Some chemicals might produce a continuum of ef- fects; others might elicit different acute and chronic effects. For example, the likelihood that short-term exposures to relatively low concentrations of chemicals would cause cancer many years later is remote. But, consider chemicals that adversely affect fertility. Knowledge that those chemicals
78 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS are present at levels of concern would not affect the performance of troops during missions lasting only a few days, but would be useful in fulfilling the Armyâs responsibility to protect the long-term health of the force. The goal is for command to have broad, reliable information for a full range of decision making. It is complicated by the variables included, but it begins with making maximum use of the data available to evaluate expo- sures that might affect imminent decisions or missions and exposures that are of longer-term concern. DERIVATION OF CHEMICAL CASUALTY ESTIMATING GUIDELINES The existing health-protective exposure guidelines set by other organi- zations usually do not satisfy the criteria for CCEGs outlined in Box 4-1. The closest in form are the U.S. Environmental Protection Agency (EPA) acute exposure guidelines levels (AEGLs) that are set for different exposure durations and increasing severity of health effects. However, AEGLs deri- vation includes consideration of susceptible subpopulations not present in the military population. Also, AEGLs typically are derived on the basis of a critical or most sensitive effect. In some cases, that particular effect might not influence mission-related performance. For example, the 1-hour MEG for nitrogen dioxide was developed to prevent âmild irritationâ at the âse- vere effect levelâ; the 1-hour MEG for sulfur dioxide is based on alteration in pulmonary function in exercising asthmatic individuals; the 8-hour MEG for aldrin appears to be based on prolonged exposure leading to effects on the liver and central nervous system; and the 8-hour MEG for diesel fuel smoke is based on weight losses and focal pneumonitis in rats after multiple exposures. In addition, none of the 1- and 8-hour MEGs was adjusted with the military inhalation adjustment factor (see Chapter 3). Thus, the existing 1- and 8-hour MEGs are not directly useful to the quantitative assessments necessary for course-of-action risk comparisons. The subcommittee recom- mends that USACHPPM develop CCEGs by evaluating and using the pri- mary scientific literature on individual chemicals as source material and deriving guidelines that meet the criteria in Box 4-1. In this section, the subcommittee outlines approaches and concepts that should be considered in developing CCEGs. The discussion is intended as general guidance and not as detailed instructions on how to proceed, be- cause alternative approaches are also possible.
CHEMICAL CASUALTY ESTIMATING GUIDELINES 79 Approaches for All Classes of Chemicals The three major steps to developing CCEGs will be â¢ identifying the chemicals of interest, â¢ establishing standard procedures for developing CCEGs, and â¢ developing CCEGs for individual chemicals. The subcommittee envisions that CCEGs will be necessary for a small subset of the chemicals for which MEGs have already been developed. Those would include chemicals that are likely to be encountered in suffi- cient concentrations to cause medical threats. They are likely to be air contaminants almost exclusively, because exposures to air contaminants are the most difficult to avoid or mitigate. However, the potential for water risks might need to be considered because of the variability in the quality of water sources available during missions. The subcommittee was told of an ongoing effort by an international task force (ITF-40) to prioritize acute chemical hazards and suggests that it might be a starting point for identify- ing chemicals of interest. Standard procedures should be developed to derive CCEGs for individ- ual chemicals. That will help ensure that the CCEGs specifically address the needs of the U.S. Department of Defense (DOD), are developed on a consistent basis, and are distinguishable from other standards used within the military (e.g., MEGs and standards from the Occupational Health and Safety Administration). Similar procedures have been developed by other organizations for similar purposes, including the standing operating proce- dures for developing EPAâs acute exposure guideline levels (AEGLs) (NRC 2001) and the National Aeronautics and Space Administration guidelines for developing spacecraft maximum allowable concentrations (NRC 1992). Some of the considerations that should figure in the methodology for deriv- ing CCEGs are discussed below. Making appropriate comparisons of estimated impacts on troop viability and vulnerability requires two types of information: (1) the severity of the immediate medical consequences during the course of the mission, and (2) the likely number of troops affected in the exposure scenario envisioned for the specific mission. In addition, the commander should have information on potential long-term health effects, which might be captured best from MEGs. Although that information is not relevant to mission performance, it is essential to overall force health protection. Knowledge of potential
80 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS long-term hazards might enable commanders to avoid those hazards without significant disruption to the mission. The Army should carefully identify the relevant end points for casualty estimation, because those end points likely will be different from those used to establish health-protective exposures guidelines. For health-based stan- dards, the adverse effect occurring at the lowest dose level in experimental studies is selected as the critical effect, under the assumption that an expo- sure level based on that effect will provide protection from other effects that occur at higher doses. The goal of CCEGs is to provide risk estimates of impacts on troop strength, including consideration of individuals affected to different extents by the exposure. Because there is a spectrum of effects that could have an impact, depending on the specific mission, it would be useful to consider categorizing health effects by graded severity levels, such as mild pathological responses (e.g., sensory discomfort, irritation, mild nonsensory effects), moderate pathological responses (e.g., temporarily debilitating systemic dysfunctions), and severe pathological responses (e.g., reversible or irreversible damages to organ functions that are incapacitating, life-threatening, or lethal). That scheme resembles the graded AEGLs in several respects. The data on individual chemicals should be subjected to some form of weight-of-evidence analysis in which the quality of the data is examined critically and the degrees of consistency and concordance are evaluated closely. The process should include some rules for deciding the relative value of, and reliance on, human data versus animal data. In addition, many of the studies relevant to CCEGs will not have been designed for such a purpose. Thus, confidence in the incidence level per unit of dose and dose range can range from high to low depending on how well the range has been bracketed by field observations or experimental studies. The chal- lenge for the military will be in not only defining the uncertainty for each data set but also in assuring consistency in the application and interpretation process. CCEG values must be unbiased estimates of risk. They should be pre- dictive estimates of casualties and they should not incorporate margins of safety or adjustments for missing information except under unusual circum- stances. The available data should be used to derive the CCEGs and to inform the selection of uncertainty factors (UFs). For example, when the CCEGs are based on animal studies, interspecies extrapolation, typically assumed to consist of pharmacokinetic and pharmacodynamic components, is required. In some cases, data will be available to estimate pharmaco- kinetic differences or to at least allow for allometric adjustments. However, in most cases, the database will be insufficient to quantitatively assess
CHEMICAL CASUALTY ESTIMATING GUIDELINES 81 pharmacodynamic differences, and it might be necessary to use a UF. The need to consider pharmacokinetic, pharmacodynamic, and other factors in selecting an interspecies UF has been described by the NRC (2001). The data supporting some of the CCEGs could have significant defi- ciencies. For example, mortality data might be drawn from accidental exposures in a small number of people, raising concerns about the dataâs reliability to military populations and missions. If assessment and evalua- tion suggests that the data analyses could be biased by database deficien- cies, an adjustment factor of 3 might be warranted. As predictive values, the CCEGs should not include protection for civilian population sensitivities (e.g., pre-existing disease), which is typi- cally achieved by applying an intraspecies UF. When chemicals of interest have known susceptible subpopulations, it might be necessary to formulate more reliable estimates of the mean responses of the entire deployed popu- lation at risk if those susceptible groups were not represented appropriately in the key studies. The CCEGs should consider factors that might increase doses in deployed personnel (e.g., higher ventilation rates, greater water consumption), as discussed in Chapter 3. CCEGs should be designed to inform decision making within a rela- tively short time frame. The subcommittee assumes that most missions requiring course-of-action evaluation would be short (i.e., less than a few days). Although a mission might be executed over several days, specific events requiring CCEG evaluation would be more brief (i.e., less than 24 hours). If different time frames were of interest, the duration adjustment would be based on Cn Ã t, and n would be determined by the information available and the slope of the dose-response curve. In Appendix C, the subcommittee presents an illustration of one of the possible approaches to creating CCEGs, namely probit analysis. The ap- pendix shows that knowing the percentage of troops responding (at three severity categoriesâmild, moderate, and severe) to a variety of exposure scenarios would be useful to commanders when comparing the possible risks to mission success. However, the subcommitteeâs illustration also shows how limitations in the underlying database could preclude the use of probit analyses for some chemicals of interest. Furthermore, the Army must consider how to factor in the issue that at levels at which casualties are seen, there will be a fraction of the exposed population that is affected to a lesser degree and that those lesser effects could also degrade mission capability. The methodology for developing the CCEGs as well as the draft CCEG values should be externally peer-reviewed before their application. Because the CCEGs will be based on advanced quantitative analysis of available data and theory, they will incorporate a lot of scientific judgment. In addi-
82 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS tion, they will be predicting casualties, not suggesting safe levels buffered for error. Hence, peer-review will be especially useful to assess the robust- ness of the CCEGs. The subcommittee recognizes the difficulty of this effort and the time needed to address it. One approach to minimizing the workload might be to form working relationships with organizations currently developing acute health guidelines. The subcommittee was told that TG-230 is being used in the field. Until CCEGs are developed, it is important that USACHPPM amend TG- 230 to warn users of the guide that MEGs should be applied with some caution. Because they are protective in nature, it is exceptionally difficult (if not impossible in some instances) to use them for direct comparisons with other operational threats. Chemical Warfare Agents CCEGs for chemical warfare agents (CWAs) might be needed in some circumstances, because exposures to those chemicals are expected to be acute; the effects can be severe; the potential for their use has several paral- lels with other operational threats; and troops will likely have personal protective equipment to greatly reduce the chances of exposure. This sec- tion reviews how USACHPPM developed MEGs for CWAs, illustrates some of the special considerations for those agents, and discusses the diffi- culties of using existing exposure guidelines for those chemicals as the basis for CCEGs, particularly with regard to the use of UFs. In RD-230, AEGL values for CWAs are used directly as air MEGs for the 1-hour and 8-hour exposure durations. The 24-hour air MEGs for the agents were derived by straight-line extrapolation of the 8-hour AEGLs (C Ã t = k). According to RD-230, analysis of CWA exposure scenarios indi- cates that a continuous exposure of deployed personnel to nerve agents or vesicants for a time period greater than 24 hours is very unlikely. There- fore, there are no MEGs for the agents for time periods greater than 1 day. USACHPPM did not use other toxicity estimates, such as the Armyâs acute human toxicity estimates (NRC 1997), for developing air MEGs. Those values were derived for wartime operations and casualty estimation on a gross scale. RD-230 asserts that although AEGLs are designed for the general popu- lation, the AEGLs for CWAs are not overly conservative for military per- sonnel on the basis of following arguments:
CHEMICAL CASUALTY ESTIMATING GUIDELINES 83 â¢ For nerve agents, the identified susceptible subpopulations are those with abnormally low cholinesterase activity, which is a genetic sensitivity and is not screened out in the military. â¢ For sulfur mustard, the key health concern is effects on the eye. The variation in susceptibility to those effects in the military population is similar to that in the general civilian population. â¢ In general, variations in susceptibility among military personnel and variations within the general population are believed to be similar. AEGLs are developed for the general population and usually consider individuals that might be more sensitive because of their age (e.g., infants, children, and the elderly) or health status (e.g., the ill or infirm) in their calculations. In the case of CWAs, one or more UFs were incorporated. Appendix D is a summary of the critical studies and UFs used in the devel- opment of the AEGL-1, AEGL-2, and AEGL-3 values for GB (adapted from NRC 2003). The AEGLs for GA, GD, GF, and VX were developed using GB data and a relative potency approach. A default UF of 10 was used for intraspecies variability (protection of susceptible populations) in the development of the AEGLs for all G agents and VX. The differences among individuals in (1) blood cholinesterase and carboxylesterase activity; (2) gender (female subjects being more sensitive); (3) polymorphic paraoxonase gene (PON1); (4) levels of paraoxonase (which are particularly low in newborns); and (5) age-related sensitivity were discussed as sources of intraspecies variability in the NRC (2003) report. Given the criterion that CCEGs relate to the military population, a UF of 10 for intraspecies variability might overstate the expected adverse outcome, particularly when the exposure estimates are based on female rat data used to derive the AEGL-1 and AEGL-3 for GB (see Appendix D). Thus, the application of that UF should be re-examined in CCEG develop- ment. The subcommittee agrees with USACHPPM that the NRCâs recent assessment of CWAs for the development of AEGLs (NRC 2003) provides the most comprehensive evaluation of the existing data and should be relied on in the development of CCEGs. However, the subcommittee believes that the direct use of AEGLs as CCEGs would be inappropriate, because that approach does not satisfy the criterion that CCEGs provide exposure-re- sponse and population-response data, including the concentrations likely to cause effects in humans, along with descriptions of the magnitude and incidence of the expected effects. However, the supporting studies and end points for AEGL-1 and AEGL-2 should provide that information (see Ap- pendix C for example using GB).
84 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS Other issues to consider when setting exposure guidelines for CWAs include the following: â¢ The C Ã t = k temporal extrapolation from 8 hours to 24 hours by USACHPMM should be re-examined in light of the Cn Ã t = k relationship described in the AEGLs documents. â¢ The NRC (2003) AEGL report indicates that accounting for breathing rates is not necessary for local effects (e.g., miosis) but is neces- sary for systemic effects. However, it did not include a factor for breathing rates in the development of AEGLs because of numerous uncertainties associated with the issue. The ERDEC-TR-489 provides occupational exposure limits for G agents that incorporate adjustments from experimental breathing rates to occupational conditions. The air MEGs for toxic indus- trial chemicals were developed on the basis of the estimated breathing rates (29.2 m3/day) in soldiers. Differences between experimental breathing rates (under various conditions and different species) and actual battlefield breathing rates should be considered in the development of CCEGs for CWAs. â¢ An intraspecies UF of 3 was incorporated into the AEGLs for sulfur mustard to protect potentially sensitive individuals (Appendix D). How- ever, the NRC (2003) report notes that there was little variability in ocular responses among subjects (Anderson 1942). For purposes of CCEGs, that UF introduces an unnecessary level of conservatism. A modifying factor (MF) of 3 was used in the AEGL-2 to account for the potential onset of long-term ocular and respiratory effects. That also is unnecessary for the CCEGs. The AEGLs for sulfur mustard, like the AEGLs for G agents, should not be used directly to develop CCEGs. The source data (critical study or studies) should be used to develop CCEGs in accordance with the criteria described in Box 4-1. APPLICATION AND INTERPRETATION OF CCEGs The CCEGs, which ultimately are intended to be used in the field, need to be readily interpretable by those who will apply them. A substantial amount of highly technical material must be evaluated comprehensively and synthesized into a summary matrix that can be used by preventive-medicine personnel in the field. The effort will require expressing probabilistic CCEGs, as illustrated in Appendix C, in the framework of the operational risk-management (ORM) risk levels to enable simultaneous evaluation and comparison of all the main classes of operational risks. The subcommittee
CHEMICAL CASUALTY ESTIMATING GUIDELINES 85 recommends that a table be created for each CCEG chemical defining the concentrations that correspond with the boundaries between green and amber, amber and red, and red and black unit-strength levels (i.e., between low and moderate, moderate and high, and high and extremely-high risk levels) as defined in TG-230. Table 4-1 provides an example of how CCEGs derived in Appendix C for seven chemicals could be used to estimate impacts on troop strength in place of the three-step categorical MEG-based procedure now described in TG-230. The chemical concentrations estimated to severely affect 15%, 30%, 40%, and 50% of the unit are listed with the corresponding ORM risk level and unit status, assuming that the entire unit is exposed. Any mea- sured or modeled field concentration of any given chemical can be com- pared with the values in the table to estimate the potential impact on the mission in the color-coded ORM terms used by the decision maker. To make this comparison, a measured or modeled concentration (C) for a given chemical would be compared with each listed concentration (Ctest), starting with the right-most column and proceeding left until the first in- stance in which C $ Ctest; the color of that current table column then defines the unit status. Table 4-1 can always be used to determine ORM risk levels by comparing measured or modeled concentrations with table entries when 100% of the unit is assumed to be exposed (as explained in footnote a). However, in cases where only a percentage of the unit (i.e., a subunit) is exposed and C is greater than the concentration that corresponds to a âgreenâ unit status, an additional calculation might be required to derive the percentage of the entire unit affected. That calculation determines the cor- responding ORM risk level. The percentage P* of a unit affected seriously or severely (i.e., in a mission-incapacitating way) by chemical exposure is defined as P* = P Ã F, where F is the estimated fraction of the unit exposed to the chemical and P is the predicted percentage of that fraction that will be severely affected by the exposure. It is P*, not P, that must be used to determine the color-coded ORM risk level, because those levels are defined in terms of troop strength percentage ranges (i.e., 100% - P*). The following procedure can always be used to calculate P* when <100% of the unit has been exposed, using only information in a CCEG table such as Table 4-1. In the context of a mission-threatening (i.e., severe) toxic response from acute respiratory exposure to a specified chemical, the lognormal dose- response model that was used to generate Table 4-1 predicts that the percent P of exposed individuals to incur a specified toxic response is lognormally distributed as a function of ambient concentration C (i.e., as the quasi- threshold lognormal exposure-response function).
86 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS TABLE 4-1 Sample CCEGs for Seven Chemicals for âSevereâ Responsea Approximate Concentration in Breathing Zone (ppm-hour) Chemical C15 C30 C40 C50 Aniline 1,400 1,600 1,800 1,850 1,1-Dimethylhydrazine 250 540 800 1,400 Hydrogen sulfide 640 680 700 710 Hydrogen cyanide 95 115 130 140 Propylene glycol dinitrate 40 70 90 120 Acrolein 34 40 45 48 Sarin 10 30 52 90 Evaluation Degree of Medical Threat % of unit severely affected, P* 15% 30% 40% 50% a Unit troop strength 85% 70% 60% 50% a ORM risk level Low Moderate High Extremely High Unit statusa Green Amber Red Black a Assumes 100% of the unit is exposed. Abbreviations: C15, concentration estimated to effect 15% of the unit; C30, concentration estimated to effect 30% of the unit; C40, concentration estimated to effect 40% of the unit; C50, concentration estimated to effect 50% of the unit. Unit Status Black: Unit requires reconstitution. Unit below 50% strength. Red: Combat ineffective. Unit at 50-69% strength. Amber: Mission capable, with minor deficiencies. Unit at 70-84% strength. Green: Mission capable. Unit at 85% strength or better. P = Î¦ [Ï â1 log(C / C50 )] Ã 100% (4-1) where F is the cumulative normal (Gaussian) probability distribution func- tion, log denotes logarithm (using any specified base, such as 10 or e), C50 is the model (âlocationâ) parameter that represents the concentration that elicits a 50% response, and s is the model (âshapeâ) parameter the inverse of which specifies the steepness of the dose-response curve. This lognormal model has only two estimated parameters, C50 and s. The parameter s may be defined in terms of the concentrations C15 and C50 (defined in Table 4-1
CHEMICAL CASUALTY ESTIMATING GUIDELINES 87 above) as s = 0.9648 log(C50/C15). Therefore, Equation 4-1 can be rewritten as the following function of the measured (or modeled) concentration C and the concentrations C15 and C50 obtained from Table 4-1: ï£® log(C / C50 ) ï£¹ (4-2) P = Î¦ ï£¯1036 . ï£º Ã 100% ï£° log(C50 / C15 ) ï£» After first calculating P using Equation 4-2, the percentage P* = P Ã F can be calculated as described above to estimate the unit status. AGGREGATE EXPOSURE AND CUMULATIVE RISK As discussed earlier, air is the most likely exposure pathway of concern for CCEGs. Although aggregate exposures theoretically could occur and could affect mission performance, such a scenario is unlikely. Therefore, establishing formal procedures for CCEGs for aggregate exposures is not a high priority. However, risks are likely to accumulate, making procedures to assess medical risks from mixtures of chemicals desirable. As it did for individual chemicals, the subcommittee recommends a well-grounded and applicable approach for mixtures. Analytic frameworks that have occurrence probabilities modeled explic- itly as functions of corresponding chemical exposure have been developed specifically for application to quantitative health-risk assessments involving multiple toxic chemicals and/or multiple toxicity end points (NRC 1994; Bogen 2001). This framework can be generalized to illustrate a quantitative approach that could be used to estimate the percent P* of a unit expected to be affected by mission-hindering (typically serious) symptoms resulting from acute respiratory exposure(s) to multiple chemicals that might affect similar toxic end points and/or different toxic end points. Using that ap- proach, P* is calculated by applying a basic rule for aggregating independ- ent likelihoods (known as de Morganâs rule [Parzen 1960; Ang and Tang 1975]) to an appropriate modification of Equation 4-2, above. The quantita- tive approach recommended by the subcommittee for exposures to multiple chemicals is described in Appendix E. RECOMMENDATIONS The development of CCEGs for informing course-of-action decisions
88 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS in the field is of highest importance. To assist in obtaining and managing resources for that effort, DOD should analyze the staff and funding neces- sary to accomplish the subcommitteeâs recommendations and should estab- lish priorities and a time estimate for the work. This section summarizes the major recommendations made in this chapter for the development of CCEGs. The text itself should be consulted for more thorough discussion of these issues and for several other recommendations that are more special- ized, are more chemical-specific, or are of secondary importance. â¢ CCEGs should be developed and used in TG-230 to support mission risk assessment. This will involve identifying the set of chemicals for which CCEGs should be created, developing a method for creating them, and performing the necessary analyses for each chemical. The fol- lowing are important elements to consider in addressing this recommenda- tion: âCCEGs should be established for those chemicals having some finite probability of being encountered in sufficient quantity to degrade unit effectiveness. âCCEGs should be derived primarily for air contaminants, be- cause inhalation is the exposure route most likely to result in incapaci- tation. The potential for water risks should also be considered, depend- ing on the quality of the water supplies during particular missions. Some consideration might also be given to the need for assessing risk from less conventional routes of exposure, such as water emersion, that might occur with small unit and special operations. âCCEGs should provide predictive, probabilistic exposure-re- sponse information that will enable chemical threats to be weighed in comparison with other mission threats. CCEGs ideally would be deter- mined by modeling chemical-specific data to predict effects on unit strength at various exposure levels (e.g., probit analysis). âThe methodology for deriving CCEGs and the derivation of the CCEGs themselves should be peer-reviewed. âAssistance from other organizations working on health-related guidelines should be pursued. Many existing exposure guidelines (es- pecially EPAâs AEGLs) have key information available in their docu- mentation. Future working relationships between DOD and other agen- cies that routinely develop acute exposure guidelines might make the development of CCEGs more resource-effective.
CHEMICAL CASUALTY ESTIMATING GUIDELINES 89 âIf the Army chooses to use MEGs in the interim, TG-230 should be revised to clearly articulate the deficiencies of MEGs and their limi- tations for assessing mission-related performance risks. â¢ CCEGs should be provided to users in an ORM format differ- ent from that currently proposed in TG-230. Personnel in the field will need to be able to make comparisons rapidly between estimated exposure concentrations for specified durations and the CCEGs to identify estimated unit status (i.e., green, amber, red, black) and to weigh chemical threats against other operational risks. â¢ Consider cumulative risks in the ORM context. The number of chemicals for which CCEGs are needed appears limited, making it feasible to identify those compounds that are likely to be present in mixtures and combinations of concern. Additivity assumptions could be applied using a probabilistic method consistent with the probabilistic nature of the CCEGs. REFERENCES Anderson, J.S. 1942. The effect of mustard gas vapour on eyes under Indian hot weather conditions. CDRE Report No. 241. Chemical Defense Research Establishment (India). Ang, A.H-S., and W.H. Tang. 1975. Probability Concepts in Engineering Planning and Design, Volume I: Basic Principles. New York, NY: John Wiley & Sons. pp. 34-35. Bogen, KT. 2001. Methods for Addressing Uncertainty and Variability to Characterize Potential Health Risk from Trichloroethylene Contaminated Ground Water at Beale Air Force Base in California: Integration of Uncertainty and Variability in Pharmaco- kinetics and Dose-Response. UCRL-ID-135978 Rev. 1 (www.osti.gov/servlets/ purl/793701-BslGOu/native/). Lawrence Livermore National Laboratory, Livermore, CA. EPA (U.S. Environmental Protection Agency). 2002. A review of the reference dose and reference concentration processes. EPA/630/P-02/002F. EPA (U.S. Environmental Protection Agency). 1994. Methods for derivation of inhalation reference concentrations and application of inhalation dosimetry. EPA/600/8-90/066F. Available from NTIS Springfield, VA. NRC (National Research Council). 2003. Acute Exposure Guideline Levels for Selected Airborne Chemicals. Volume 2. Washington, DC: The National Academies Press. NRC (National Research Council). 2001. Standard Operating Procedures for Developing Acute Exposure Guideline Levels for Hazardous Chemicals. Washington, DC: Na- tional Academy Press. NRC (National Research Council). 1997. Review of Acute Human-Toxicity Estimates for Selected Chemical-Warfare Agents. Washington, DC: National Academy Press. NRC (National Research Council). 1994. Science and Judgment in Risk Assessment. Washington, DC: National Academy Press.
90 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS NRC (National Research Council). 1992. Guidelines for Developing Spacecraft Maximum Allowable Concentrations for Space Station Contaminants. Washington, DC: National Academy Press. Parzen, E. 1960. Modern Probability Theory and Its Applications. New York, NY: John Wiley & Sons. pp. 11-16.