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2 Review of the Armyâs Technical Guidance This chapter reviews the approach used in Technical Guide 248 (TG- 248) and Technical Guide 230 (TG-230) for assessing and characterizing chemical hazards for deployment decision making. First, important aspects of risk comparison that were identified in previous reports of the National Academies are briefly revisited. Second, the adequacy of the technical guides for providing appropriate characterizations of health and mission risks from exposure to chemicals is evaluated. EARLIER ACADEMIES REPORTS ON DEVELOPING RELIABLE COMPARATIVE RISK ASSESSMENTS FOR DEPLOYMENTS The Institute of Medicine report Protecting Those Who Serve (IOM 2000) and the National Research Council report Strategies to Protect the Health of Deployed U.S. Forces: Analytical Framework for Assessing Risks (NRC 2000) provide a number of recommendations relevant to developing a systematic process to prospectively evaluate non-battle-related risks asso- ciated with deployment activities and settings. For example, NRC (2000) specifically recommends that the conceptual paradigm for quantitative risk assessment described in Risk Assessment for the Federal Government: Managing the Process (NRC 1983) be used as a basis for developing a U.S. 27
28 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS Department of Defense (DOD) framework for assessing risks to deployed forces. Use of that paradigm would âfacilitate integration of the results of hazard-specific assessments and tracking of the complex process of simulta- neous consideration of multiple threats â¦ and [would aid in] developing risk management strategies, including trade-offsâ (NRC 2000). That rec- ommendation follows from a more detailed discussion of related issues in which the following key points are made: â¢ âTroops during deployment could become exposed to a number of threats simultaneously. Exposures that are individually tolerable without appreciable risk might not be so when several are experienced together, and the question of interactions among agents looms particularly large for de- ployment risk assessmentâ (NRC 2000, p. 41) â¢ âThe NRC (1983) paradigm for risk assessment â¦ is readily adapt- able to deployed forces protection â¦ to analyze (1) the likelihood of the presence of a hazard associated with a deployment; (2) the likelihood of releases of agents into the environment; (3) the likelihood that troops will suffer exposure (of various magnitudes), given the releases; and (4) the likelihood that health effects will be caused among them, given the expo- sure. â¦ [E]fforts would be focused on how activities and practices come to present threats, how likely it is that threats will be manifested in practice, and how mitigating one risk might raise other risksâ (NRC 2000, p. 43) â¢ â[R]isk analysis must be content to say what can be said and not only to acknowledge the inevitable remaining uncertainty, but to try to characterize that uncertainty so that appropriate perspectives on the mean- ing and robustness of the analysis are expressed. â¦ Characterization of uncertainty and the limitations of available data are important to all risk analysis, but they might play an especially important role in the analysis of deployment threats, where high-consequence decisions might require taking one risk to avoid others, Risk management approaches exist to help make such decisions, but when the risks to be compared are quite uncertain, or uncertain to different degrees, good characterizations of uncertainty is [sic] necessary in order to arrive at sound solutionsâ (NRC 2000, pp. 60-61; italics added). â¢ ââ¦ the establishment of âconservativeâ estimates of dose-response relations, that is, those designed to err on the side of safety when faced with uncertainty about how to project expected human responses from available data, might not be appropriate for certain military uses. When risks cannot be avoided and decisions are made to accept some risks rather than others, or to bear some risk in furtherance of a more fundamental military objec- tive, it is important to make these trade-off decisions with unbiased esti-
REVIEW OF THE ARMYâS TECHNICAL GUIDANCE 29 mates of the impacts of various courses of action. In other applications, such as the setting of health-protective exposure standards for application in less severe circumstances, conservative estimates might be much more acceptable. â¦ [Analyses should be] conducted and â¦ results presented, so that different uses appropriate for different risk-management settings can be madeâ (NRC 2000, pp. 66-67; italics added). â¢ âA final special aspect of risk analysis for deployment is the large role that risk-risk comparisons must play. Given the high level of tactical risk that might be inherent in the deployment situation, some health and safety risks may be appropriate to avoid or mitigate even greater risks. Determining how to optimize the trade-offs requires simultaneous consider- ation of the spectrum of risks faced by deployed troops, along with the possibility that actions taken to avoid or ameliorate some risks might exac- erbate othersâ (NRC 2000, pp. 83-84; italics added). â¢ â[DOD decisions concerning deployed military personnel involve issues including] the need to call for individual troops to put life, limb, and health at risk in the interests of the military mission and the nation at large; [and] problems of trading off possibilities of health effects in later life with immediate risks of casualties and impacts on military mission of military capabilities â¦ If the risk analysis is to effectively contribute to such deci- sions, it will require an articulation of a doctrine on how risk trade-offs are to be considered. In addition, DOD should attempt to articulate a set of principles on how the balance of long-term risks to the troops and risks to the military mission should be approachedâ (NRC 2000, p. 89; italics added). These key points highlight the importance of using a comprehensive, quantitative risk-assessment paradigm as the basis for a formal framework for the integrated management of risks to deployed personnel, particularly in view of the multiple exposures, chemicals, toxic end points, and/or sources of uncertainty likely to be involved. The italicized portions focus on the critical need for comparative risk analysis that would allow com- manders to make trade-off decisions concerning uncertain risks in the con- text of potentially competing goals, ranging from combat success to preven- tive public or occupational health, that might differ in urgency. Such trade- offs should reflect unbiased assessments of net risk associated with alterna- tive courses of action (NRC 2000). The same recommendation appears in an earlier NRC report, Science and Judgment in Risk Assessment (NRC 1994), which states that âdecisions involving risk-trading or priority setting ... should take into account information on uncertainty in quantities being ranked so as to ensure that such trades do not increase expected risk.â
30 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS THE ARMYâS RISK-ASSESSMENT GUIDANCE FOR DEPLOYMENT Description Technical Guide 248 (TG-248) TG-248 (USACHPPM 2001) outlines the processes and tools that could be used to evaluate and communicate all categories of occupational and environmental health (OEH) and endemic disease (ED) hazards in accordance with the military operational risk-management (ORM) process discussed in Chapter 1. TG-248 focuses on the first two steps of the ORM process, identifying OEH/ED hazards and assessing the threat they pose to the mission in terms of their probability and severity. TG-248 was designed to enable preventive-medicine personnel to express the risks from each OEH/ED hazard in the same metric used for other more traditional military hazards (e.g., enemy forces, mechanical problems) as well as other OEH/ ED hazards so that decision makers can make rational comparisons of the various risks faced during deployment and make decisions about courses of action. The approach used by the U.S. Army Center for Health Promotion and Preventive Medicine (USACHPPM) is necessarily different from those used for traditional occupational or environmental risk assessments because military decision making must consider mission impact in addition to indi- vidual health risk. Thus, TG-248 facilitates classification of OEH/ED haz- ards using a standard component of military ORMâthe risk-assessment matrix (see Table 2-1). The risk-assessment matrix is a qualitative classifi- cation scheme that reflects four categories of âseverityâ of risk to a military mission and five categories of âprobabilityâ with regard to one or more military assets and/or soldiers. These two dimensions are combined to comprise 20 cells that are separated into four qualitative categories of mission-related risk: extremely high, high, moderate, and low. These risk categories pertain specifically to the qualitative likelihood of mission suc- cess, which refers to mission-specific military goals including, but not limited to, the minimization of health risks to deployed military personnel. Technical Guide 230 (TG-230) TG-230 (USACHPPM 2001a) adapts the generalized framework of TG- 248 and proposes a specific process to evaluate the chemical subset of
REVIEW OF THE ARMYâS TECHNICAL GUIDANCE 31 TABLE 2-1 Risk-Assessment Matrix Probability Frequent Likely Occasional Seldom Unlikely Severity A B C D E Catastrophic I E E H H M Critical II E H H M L Marginal III H M M L L Negligible IV M L L L L Definitions Hazard Severity Catastrophic (I): Loss of ability to accomplish the mission or mission failure. Death or perma- nent disability. Loss of major or mission-critical system or equipment. Major property (facility) damage. Severe environmental damage. Mission-critical security failure. Unacceptable collat- eral damage. Critical (II): Significantly degraded mission capability, unit readiness, or personal disability. Extensive damage to equipment or systems. Significant damage to property or the environment. Security failure. Significant collateral damage. Marginal (III): Degraded mission capability or unit readiness. Minor damage to equipment or systems, property, or the environment. Injury or illness of personnel. Negligible (IV): Little or no adverse impact on mission capability. First aid or minor medical treatment. Slight equipment or system damage, but fully functional and serviceable. Little or no property or environmental damage. Risk Levels E â Extremely high risk: Loss of ability to accomplish the mission if threats occur during mis- sion. A frequent or likely probability of catastrophic loss (IA or IB) or frequent probability of critical loss (IIA) exists. H â High risk: Significant degradation of mission capabilities in terms of the required mission standard, inability to accomplish all parts of the mission, or inability to complete the mission to standard if threats occur during the mission. Occasional to seldom probability of catastrophic loss (IC or ID) exists. A likely to occasional probability exists of a critical loss (IIB or IIC) oc- curring. Frequent probability of marginal losses (IIIA) exists. M â Moderate risk: Expected degraded mission capabilities in terms of the required mission standard will have a reduced mission capability if threats occur during mission. An unlikely probability of catastrophic loss (IE) exists. The probability of a critical loss is seldom (IID). Marginal losses occur with a likely or occasional probability (IIIB or IIIC). A frequent probabil- ity of negligible (IVA) losses exists. L â Low risk: Expected losses have little or no impact on accomplishing the mission. The prob- ability of critical loss is unlikely (IIE), while that of marginal loss is seldom (IIID) or unlikely (IIIE). The probability of a negligible loss is likely or less (IVB through IVE). Hazard Probability Frequent (A): Occurs very often, continuously experienced. Likely (B): Occurs several times. Occasional (C): Occurs sporadically. Seldom (D): Remotely possible; could occur at some time. Unlikely (E): Can assume will not occur, but not impossible. 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. Source: TG-230 and U.S. Army Field Manual 3-100.12.
32 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS OEH/ED hazards. In the first step of this process, chemical hazards are identified through available intelligence data, field sampling, and/or expo- sure modeling. Potential chemical hazards are then prioritized on the basis of whether they pose no threat, a health threat, or a medical threat. Health threats are hazards that could result in adverse health effects in an individ- ual. Medical threats are those health threats that have the potential to render a field unit ineffective for combat or for other mission-related activities. Threats of chronic or delayed disease (e.g., cancer, liver disease, or kidney disease) are categorized as threats of concern to the command, which are generally considered health threats, but on occasion could be considered medical threats. Each chemical is categorized by comparing measured or predicted concentrations of that chemical with its most relevant military exposure guideline (MEG). MEGs are estimated chemical concentrations above which certain types of adverse health effects might begin to occur in individuals within the exposed population after a continuous, single expo- sure of specified duration. They were designed to address the wide variety of exposure scenarios that could be encountered during deployment, rang- ing from catastrophic release of a large amount of chemical to regional pollution. MEGs were developed by modifying the existing exposure stan- dards set by other agencies for application to the military context. The process by which MEGs were derived is described in Reference Document 230 (RD-230) (USACHPPM 2001b). That process is evaluated by the subcommittee in Chapter 5. Chemical threats are further categorized by using a hazard severity ranking chart that refers to the four categories of severity defined by the risk-assessment matrix. The severity ranking charts provided in TG-248 and TG-230 also incorporate specific ranges of probabilities of symptoms grouped by severity category (see Tables 2-2 and 2-3). Chemical risks are finally classified using the risk levels defined in the military risk-assessment matrix. The risk levels correspond to âunit statusâ levels that are color coded. Unit status refers to effective unit strength expressed as a percentage (see Table 2-4). In both guidance documents, these probabilistic unit strength levels are related to hazard severity levels and hazards probability categories, but those relationships are made quantitatively explicit in TG- 230 insofar as that document defines the hazard probability categories dis- cussed above in terms of corresponding troop exposure probability ranges (see Table 2-5). A confidence level is then assigned to the risk estimate by using criteria outlined in TG-248 (see Table 2-6). That judgment is made by considering key sources of uncertainty associated with the risk assess- ment, such as the quality of the field sampling data and understanding of the exposure conditions.
TABLE 2-2 TG-230 Chemical Hazard Severity Ranking Chart for Military Deployments Magnitude of Chemical Concentration Associated Health Outcome Attributable to Exposure Hazard Severity Air Water Soil (General)a Onset of Symptoms Rank Hazard Type <1-year MEG <MEG <MEG No cases of illness or AFTER THE NONE NO or <14-day noncancer disease and <1 MISSION HEALTH MEG cancer case in 10,000 THREAT $1-year MEG $MEG that is $MEGc 0-10% of personnel might NEGLIGIBLE HEALTH or $14-day not based on develop illness or chronic THREAT MEG TB MED 577b disease but #1-24 hour min-MEG $1-year MEG 0-10% of personnel might DURING THE or $14-day develop mild illness or MISSION MEG temporary irritation but >1-24 hour min-MEG >1-hour min- $MEG that is âc >10% of personnel might MARGINAL MEDICAL MEG based on TB experience mild illness and THREAT but #1-hour sig- MED 577b irritation; MEG 0-10% of personnel might develop more severe illness that begins to impair functional capabilities (Continued) 33
34 TABLE 2-2 Continued Magnitude of Chemical Concentration Associated Health Outcome Attributable to Exposure Hazard Severity Air Water Soil (General)a Onset of Symptoms Rank Hazard Type b c >1-hour sig- â â 10-25% of personnel might During the mission CRITICAL MEDICAL MEG experience severe illness or THREAT but #1-hour irritation and more noticeable sev-MEG degradation of performance capabilities; Other personnel will, at least, suffer some mild effects >1-hour sev- âb âc >25% of personnel might CATASTROPHIC MEG experience severe, incapacitating effects; Fatalities will begin to occur just above the sev-MEG for air exposur and will increase as concentrations increase a Percentages are very uncertain and will vary by chemical and by other confounding factors. b Concentrations greater than the MEG might result in hazard severity from marginal to catastrophic if certain chemicals are present in large enough quantities and there is sufficient consumption. Additional information in the âNotesâ column of the MEG tables should be evaluated regarding effects of higher levels of exposure. c Soil is unlikely to represent a hazard that would yield a medical threat. Additional information in the âNotesâ column of the MEG tables should be evaluated for data regarding higher levels of exposure. Abbreviations: min-MEG, minimal effects level; sig-MEG, significant effects level; sev-MEG, severe effects level. Source: Modified from USACHPPM 2002a.
TABLE 2-3 TG-248 Hazard Severity Ranking Chart for Military Deployments Nature of Individual Health Effects Associated with Exposures Near the Guideline Symptoms Occurring Percent of Exposed After the Mission Symptoms Occurring During the Mission People to Exhibit Chronic or Permanent Mild Illness or Injury or Illness That Impairs Incapacitation or Symptoms (Attack Rate) Injury or Diseasea Temporary Irritationb Functional Capabilities Death >50% Marginal Critical Catastrophic Catastrophic 31-50% Negligible Marginal Critical Catastrophic 10-30% Negligible Marginal Marginal Critical <10% Negligible Negligible Marginal Critical a For example, cancer. b Reversible, short-term, nuisance. Source: Modified from USACHPPM 2001. 35
36 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS TABLE 2-4 TG-230 Risk Level Definitions Risk Level Defined Consequencea Unit Statusb,c Extremely Expected loss of ability to accomplish the Black (unit requires re- high mission constitution) Unit below 50% strength High Expected significant degradation of mis- Red (combat ineffective) sion capabilities in terms of the required Unit at 50-69% strength mission standard, inability to accomplish all parts of the mission, or inability to complete the mission to standard if haz- ards occur during the mission Moderate Expected degraded mission capabilities in Amber (mission capable, terms of the required mission standard with minor deficiencies) will have a reduced mission capability if Unit at 70-84% strength hazards occur during mission Low Expected losses have little or no impact Green (mission capable) on accomplishing the mission Unit at 85% strength or better a Field Manual 100-14 (U.S. Department of the Army 1998) b Field Manual 3-100.12 (U.S. Department of the Army 1997) c The unit rates provided under âUnit Statusâ are to be determined by the commander. Charts similar to the example hazard probability and severity ranking charts presented in Tables 2- 1, 2-2, and 2-3 should be aligned with the acceptable risk levels provided by the commander. Source: USACHPPM 2000a. Finally, using all the information at hand, the threat category is re-eval- uated in terms of whether the chemical poses no threat, a health threat, a threat of concern to the command, or a medical threat. The purpose of this final step is to provide perspective on which hazards pose greater opera- tional threats when comparing threats that have similar risk estimates. TABLE 2-5 TG-230 Chemical Hazard Probability Ranking Chart for Military Deployments Percent of Personnel That Will Experience Exposures to Concentrations Equal To or Greater Than the MEGa <10% 10-25% 25-50% 50-75% >75 % Unlikely Seldom Occasional Likely Frequent a Determination of the percent of personnel exposed to a chemical or mixture specifically above a guideline level can be based on modeling, gridding, or generalized assumptions. Source: USACHPPM 2002a.
REVIEW OF THE ARMYâS TECHNICAL GUIDANCE 37 TABLE 2-6 TG-230 Example Criteria for Assigning Confidence Levels Confidence Level Criteria High Sampling data quality is good Field activity patterns are well known True exposures are reasonably approximated Knowledge of the symptoms of hazard exposure relative to guideline is well known No important missing information The predicted health outcome is plausible or already demon strated Medium Field data quality is good Field exposures are likely to be overestimates of true exposures due to incomplete data coverage relative to actual expo sure durations Detailed information is lacking regarding true personnel activ ity patterns in the field Symptoms are well known for each individual hazard, but some scientific evidence suggests that the combined effects of all hazards may exacerbate symptoms Predicted health outcome is plausible Low Important data gaps and/or inconsistencies exist Exposure conditions are not well defined Field personnel activity patterns are basically unknown Predicted health outcome is not plausible because it is not consistent with real-world events/experience Source: USACHPPM 2002a. Evaluation1 The risk-management framework presented in TG-230 and TG-248 reflects much of the guidance and recommendations provided by the NRC (2000) and IOM (2000). DOD, and in particular USACHPPM, is to be commended for developing a risk-management framework that implements the recommendations contained in those reports. The generalized frame- work in TG-248 also comprises innovative features that are suited for prac- tical use in the field. The framework attempts a quantitative implementa- tion of a matrix approach to assess risk levels that are implied by different categories of hazard severity and hazard probability. It uses familiar cate- gories previously defined in DODâs overall approach to military risk man- agement, as described in field manuals FM 100-14 and FM 3-100.12. This 1 Minor errata and inconsistencies found in TG-248, TG-230, and RD-230 are discussed in Appendix A.
38 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS framework is particularly well-suited to convenient characterization and evaluation of individual health or medical threats and simple comparisons of those individual threats, provided comparable levels of uncertainty are involved. When applied to assess chemical risks in TG-230 (Table 2-2), the framework enables the use of a simple, tabular approach to characterize exposure scenarios chemical by chemical in terms of a corresponding cate- gorical risk level that in turn refers to a corresponding range of unit strength (expressed as a percentage). The approach also incorporates traditional procedures used to identify noncompliance with occupational safety and health guidelines pertaining to chemical exposures that are expected to produce health effects (i.e., hazards of ânegligibleâ severity). The latter involves the use of MEGs to assess the significance of field exposures to specific chemicals. Overall, the subcommittee found that TG-248 provides a reasonable categorization process for assessing OEH/ED hazards within the context of ORM. The process allows for predicting impacts on missions and making reasonable comparisons between the potential hazards, be they hazards to equipment, troops, or some other facet of deployment. However, the chemical-risk guidance (i.e., the MEGs) in TG-230 is inconsistent with the intent of TG-248 and could lead to mischaracterization of the significance of chemical risks in comparison with other deployment risks. This potential for mischaracterization is the result of USACHPPMâs attempt to use one set of exposure guidelines (i.e., MEGs) for the dual purposes of âcharac- teriz[ing] the level of health and mission risks associated with identified or anticipated exposures to chemicals in the deployment environmentâ (USACHPPM 2001, p.1; italics added). These conflicting purposes could lead to different interpretations and uses of the MEGs. For example, RD- 230 states the following: In some cases, exposures greater than the MEG can induce immedi- ate adverse health effects, in other cases exposures greater than the MEG simply indicate that there is an increased likelihood that a health problem could arise either during or post deployment â¦ In general, environmental concentrations equal to, or slightly greater than the specified MEG are expected to result in the specified type and degree of health effects in none to a small portion of individu- als in the exposed military population. In some cases, MEG repre- sents a purely âprotectiveâ level where health effects should not be observed at all.
REVIEW OF THE ARMYâS TECHNICAL GUIDANCE 39 The subcommittee summarized the differing goals of mission and health risk assessment in Table 2-7. The table shows that the parameters for achieving each of those goals are quite different from each other on all levels. Those differences make it extremely difficult for one set of guidance values (MEGs) to adequately address both sets of goals. The risk-assessment matrix used in TG-230 is a device for categorizing chemical risks in terms of mission impact (e.g., mission capable, combat ineffective) so that chemical hazards can be weighed against and compared with other hazards to missions (e.g., mechanical failures, weather). To make comparative assessments among all potential deployment hazards, it is important to assess all hazards in terms of their potential impact on unit strength. Assessment of those hazards requires an understanding of the chemical exposure levels at which casualties that would render the unit ineffective might begin to occur. MEGs are inappropriate for making this type of assessment because they are health protective values that provide an estimated threshold at which health effects might begin to occur. Those threshold concentrations could be several orders of magnitude below those that would be anticipated to produce enough casualties to compromise a mission. Thus, mission risks characterized using the MEGs would not be comparable to the risk levels assigned to other operational hazards using the risk-assessment matrix. See example in Box 2-1. The subcommittee be- lieves that separate sets of chemical risk assessment guidance are needed for assessing mission and health risks. Those assessments should be presented simultaneously to help decision makers balance the necessary trade-offs between the missionâs needs and potential health impacts presented by the deployment mission under consideration. Mission Risk Assessment To assess mission risks, it will be necessary for USACHPPM to de- velop a set of unbiased, predictive estimates of casualties that might occur if the unit is exposed to a particular concentration of a chemical. The sub- committee has termed such values chemical casualty estimating guidelines (CCEGs) and recommends that they be used instead of MEGs to character- ize mission risks using the ORM categorization scheme. CCEGs would be media and duration-specific chemical concentrations expected to cause health impairments that degrade the performance of enough individuals to reduce unit strength, also known as medical threats. As discussed in more detail in Chapter 4, CCEGs cannot be established from existing exposure
40 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS TABLE 2-7 Characteristics Associated with the Major Goals of TG-248 and TG-230 Health Risk Assessment Mission Risk Assessment Goal To assess impacts on indi- To predict impacts of health vidual soldier health; re- risks on the mission; requires quires the use of protective the use of predictive casualty exposure values estimates Effects Short- and long-term effects Primarily short-term effects Length of exposure Long-term exposure Short-term exposure Situation More like occupa- More like short-term tional/environmental (OSHA, emergency planning EPA) Availability of data More likely to have data avail- More qualitative assessment of able to assess exposure exposure; relies more on subjective judgment Availability of time More time to assess Decisions must be made quickly Exposure Assess proportion likely to Assess proportion likely to assessment receive exposure in excess of receive any mission- MEGs compromising level of exposure Number of Many of concern Limited number of concern chemicals Likelihood that Lower Higher effect(s) will occur Confidence in Higher Lower estimated exposure(s) standards, but should be derived by conducting independent evaluations of each chemical and developing exposure-response and population-response information to make casualty estimations. Although this will be a signifi- cant undertaking, the number of chemicals and the scope of the data needed for evaluation are expected to be far less than those that were required to set the MEGs. USACHPPM should further prioritize the general risks posed by spe- cific media of exposure, including air, soil, and water, and the available risk-management options for various durations of missions. For example, water contamination could be a serious risk for long-term missions, espe-
REVIEW OF THE ARMYâS TECHNICAL GUIDANCE 41 BOX 2-1 Scenario: Securing a River Crossing The mission is to secure a major river crossing. If the enemy succeeds in crossing the river, thousands of lives will be lost. The commander has the choice of two routes to get to the crossing. One is a very rugged road that poses a threat to the mission be- cause of potential vehicle roll-over, mechanical failure, and other hazards related to terrain impacts on vehicles. The other route is paved but goes by a chemical plant that has structural damage and is believed to be leaking chemical X. Chemical X can cause irritation of the mucous membranes and respiratory system, headache, and nausea that could impair the functional capabilities of the troops. In addition, chemical X is associ- ated with potential long-term effects. To decide which route to take, the commander needs to know the potential terrain risks and chemical risks to the unit. For the terrain risks, the commander will be provided with an assessment of whether enough vehicles will be disabled during the rugged terrain crossing such that an insufficient number of troops and equipment will be able to reach and secure the river crossing. For a comparable assessment of chemical risks, a predic- tion is needed of whether the exposure incurred by passing the chemical plant will disable enough troops to the extent that they could not perform their duties. However, using the current set of guidance, it would be impossible to get a chemical assessment comparable to the terrain assessment, because the relevant MEG for chemical X in TG-230 will not be a casualty estimate but a health protective guideline. The short-term MEGs for chemical X will define a level at which respiratory irritation, headache, and nausea would begin to occur, and using them as benchmarks in conjunction with the risk-assessment matrix would result in overestimating the risk that chemical X poses to the mission. In addition to the assessment of risks to the mission, the commander will also need to be informed of the long-term health risks posed by chemical X. cially when establishing a base of operations. However, water contamina- tion generally is the easiest to mitigate by avoidance, treatment, or use of alternative sources. Air contamination is probably the most important con- sideration for short-term missions. Short-duration releases of chemical warfare agents or deliberate releases of toxic industrial chemicals could have immediate acute effects. A general example of risks prioritization on the basis of duration of exposure and mitigation options is provided in Table 2-8. USACHPPM should use a similar scheme to establish a set of criteria for CCEGs. A preliminary characterization of those guidelines is provided in Box 2-2. Important issues to consider in developing CCEGs include the follow- ing: â¢ Risk should be defined as an unbiased or âbestâ estimate. When an integrated quantitative approach is used to estimate risk and its uncertainty, an appropriate corresponding attribute of a risk or casualty number to esti-
42 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS TABLE 2-8 General Prioritizations of Exposure Routes in Relation to Exposure Duration and Possible Mitigation Exposure Dura- tion Routes of Exposurea and Mitigation Short mission Air Soil Water Respirator PE (booties) Avoid Long mission Water Air Soil Treatment Filtered shelter Avoid a In order of decreasing risk, left to right. mate would be its expected value, or âpopulation mean,â defined mathemat- ically as the arithmetic average of all possible likelihood-weighted values.2 â¢ TG-230 makes it clear that âunit strengthâ should refer not only to directly affected personnel but also to individuals affected to a lesser extent 2 âLikelihoodâ weights in this context mean probabilities from a distribution that reflects uncertainty in a true but unknown value that must be estimated. Expected values have two key properties that do not generally apply to other measures of central tendency, such as medians or modes. First, the arithmetic mean of a random sample of observed values of any uncertain variable always provides an unbiased (i.e., not systematically error-prone) estimate of the (unknown) expected value of that variable. Second, the expected value of any func- tion of uncertain but statistically independent input variables can always be estimated conve- niently (at least to a first order of approximation) by calculations that involve only estimates of the expected value of each separate input variable. If a function of independent input variables is âlinearâ (i.e., involves only the sum, difference, product, and/or ratio of those variables), then the expected value of the function always exactly equals the function of the expected values of the input variables. For example, using e(z) to denote âthe expected value of an estimated variable z,â if a total number (n) of casualties is estimated as the product of independent and uncertain variables representing concentration (c), potency (q), and number (x) of potentially exposed personnel, then it will always be true that e(n) = e(c) Ã e(q) Ã e(x), regardless of the shapes of the distributions that characterize uncertainty in c, q, and x, respectively. These two useful properties of expected values can be applied conveniently to compare alternative courses of action (say, COA1 vs COA2) expected to generate two corresponding numbers (N1 vs N2) of casualties. A reasonable and consistent rule often used for this type of decision is to always reject COA2 if e(N2 - N1) > 0. This rule by definition minimizes the expected number of predicted casualties (Raiffa 1970). By virtue of the expected-value properties mentioned above, this rule always can be re-expressed validly in a form that conveniently involves only the expected value of each separate casualty predictionânamely, always reject COA2 if e(N2) > e(N1). Although more elaborate decision rules can be used to account for the shape of the distribution of uncertainty in the difference (N2 - N1) rela- tive to a specified set of risk-aversion preferences, complex rules of this type typically require quantitative uncertainty analysis methods likely to be impractical for most current military operational risk-management contexts.
REVIEW OF THE ARMYâS TECHNICAL GUIDANCE 43 BOX 2-2 CCEG Characteristics 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. and support personnel required to tend to directly affected personnel. The multiplication of hazard severity probabilities (i.e., illness likelihood ranges) by hazard probability ranges clearly is not intended to yield corre- sponding defined-target ranges of âfractional unit incapacitationâ (i.e., the opposite of unit strength, as defined in TG-230). Therefore, USACHPPM must consider developing CCEGs that provide an assessment of overall unit incapacitation with increasing exposure levels. (TG-230 also mentions that severe toxic effects will lead to increased medical support requirements for affected personnel, but it was not clear to the subcommittee how that sup- port necessarily would reduce unit effectiveness, insofar as required medical support personnel would be performing their intended function.) â¢ The need for a categorical confidence-level scheme (high vs me- dium vs low) in TG-248 and TG-230 should be reconsidered. The assign- ment of confidence levels is not a recommendation in the ORM process presented in Field Manual 3-100.12 (DOD 2001), so other operational risks will not be assigned confidence levels. It is unclear how decision makers are to interpret a specified confidence level, particularly a low one, when trying to balance competing operational risks. A low confidence in the risk characterization gives no indication of whether actual risk might be higher
44 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS or lower than the predicted risk. Furthermore, it is unclear how confidence level description for chemical risks would be of value to decision makers if confidence levels are not assigned to other operational risks. Chapter 4 presents more specific guidance for developing CCEGs and discusses how the guidelines should be applied. Health Risk Assessment Another goal of TG-230 is to provide force health protection, with the understanding that mission success has primacy over some health risks that might be considered unacceptable under less hazardous conditions. With some modifications, MEGs can be used to fulfill that goal. To that end, MEGs would be concentrations of chemicals in air, water, and soil that can be used to estimate the potential impact of field exposures on soldier health during deployments. A preliminary characterization of MEGs is presented in Box 2-3. MEGs would be used to determine the appropriate management actions that could be taken to avoid or mitigate risks. Depending on the particulars of the deployment scenario, commanders could decide whether the benefits of the mission outweigh the possible health risks to individual soldiers. In cases where commanders decide to accept the health risks to soldiers, MEGs could be used to determine what kinds of health-manage- ment actions to take, such as documenting exposures in soldiersâ records, conducting additional environmental sampling, or conducting follow-up health monitoring. Chapter 5 provides a more detailed description of how MEGs should be derived and applied. BOX 2-3 MEG Characteristics â¢ Include a large number of chemicals likely to be present in deployments. â¢ Include concerns over longer-term health of individuals, but recognizing that exposures 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.
REVIEW OF THE ARMYâS TECHNICAL GUIDANCE 45 RECOMMENDATIONS â¢ TG-230 should be revised to provide separate guidance on assess- ing chemical hazards for the purposes of mission and health risk assess- ment. â¢ For the purposes of mission risk assessment, risks should be evalu- ated within the context of mission success. The subcommittee recommends the development of chemical casualty estimating guidelines (CCEGs) to provide an appropriate basis for comparison with other mission hazards. CCEGs would be media and duration-specific chemical concentrations expected to cause health impairments that debilitate the performance of enough individuals to significantly reduce unit strength and effectiveness. They would be predictive values that provide unbiased quantitative exposure-response and population-response information that enables com- manders to compare the risks from chemical threats to those from other mission threats (e.g., combat casualties, logistical problems) using the same metric. The goal is to provide reasonably accurate estimates of impacts on unit strength. Chapter 4 provides guidance on how to derive CCEGs. â¢ CCEGs should be developed for a subset of the chemicals for which MEGs have already been derived. Chemicals should be selected on the basis of their potential as immediate medical threats to missions. Warfare agents and high-production-volume industrial chemicals with high toxico- logical potency are the most likely candidates. Inhaled volatile chemicals or toxic particulate matter also are likely to fall into that category, although chemical exposures by ingestion and skin contact should likewise be con- sidered. â¢ The need for assigning confidence levels to mission-risk estimates should be reconsidered. â¢ For the purposes of health protection, chemical risks should be assessed independently of operational goals. USACHPPMâs current set of military exposure guidelines (MEGs) are health-protective values that, with some modification, could fulfill that need. MEGs should be used to define risk-management actions that can be taken to avoid or mitigate potential health risks. Chapter 5 expands on this recommendation. â¢ Mission-risk and health-risk information should be provided to decision makers simultaneously, so that risks can be balanced explicitly and appropriate management actions can be taken. â¢ As guidance on applying TG-248 to other OEH/ED hazards (e.g., radiological and biological hazards) is developed, USACHPPM should consider combining all of the guidance into a single document to facilitate consideration of cumulative risks from all environmental hazards.
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