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.

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 associated 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.

Department of Defense (DOD) framework for assessing risks to deployed forces. Use of that paradigm would “facilitate integration of the results of hazard-specific assessments and tracking of the complex process of simultaneous consideration of multiple threats…and [would aid in] developing risk management strategies, including trade-offs” (NRC 2000). That recommendation follows from a more detailed discussion of related issues in which the following key points are made:

• “Troops 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 deployment risk assessment” (NRC 2000, p. 41)

• “The NRC (1983) paradigm for risk assessment…is readily adaptable to deployed forces protection…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 exposure…. [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 risks” (NRC 2000, p. 43)

• “[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 meaning and robustness of the analysis are expressed. …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 solutions” (NRC 2000, pp. 60-61; italics added).

• “…the establishment of ‘conservative’ 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 objective, it is important to make these trade-off decisions with unbiased esti-

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. …[Analyses should be] conducted and…results presented, so that different uses appropriate for different risk-management settings can be made” (NRC 2000, pp. 66-67; italics added).

• “A 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 consideration of the spectrum of risks faced by deployed troops, along with the possibility that actions taken to avoid or ameliorate some risks might exacerbate others” (NRC 2000, pp. 83-84; italics added).

• “[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 … If the risk analysis is to effectively contribute to such decisions, 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 approached” (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 commanders to make trade-off decisions concerning uncertain risks in the context of potentially competing goals, ranging from combat success to preventive public or occupational health, that might differ in urgency. Such tradeoffs should reflect unbiased assessments of net risk associated with alternative 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 “decisions 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.”

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 individual health risk. Thus, TG-248 facilitates classification of OEH/ED hazards using a standard component of military ORM—the risk-assessment matrix (see Table 2-1). The risk-assessment matrix is a qualitative classification scheme that reflects four categories of “severity” of risk to a military mission and five categories of “probability” 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 success, which refers to mission-specific military goals including, but not limited to, the minimization of health risks to deployed military personnel.

TG-230 (USACHPPM 2001a) adapts the generalized framework of TG-248 and proposes a specific process to evaluate the chemical subset of

OEH/ED hazards. In the first step of this process, chemical hazards are identified through available intelligence data, field sampling, and/or exposure 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 individual. 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 exposure of specified duration. They were designed to address the wide variety of exposure scenarios that could be encountered during deployment, ranging from catastrophic release of a large amount of chemical to regional pollution. MEGs were developed by modifying the existing exposure standards 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 “unit status” 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 discussed 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 assessment, such as the quality of the field sampling data and understanding of the exposure conditions.

Finally, using all the information at hand, the threat category is re-evaluated 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 operational threats when comparing threats that have similar risk estimates.

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 framework in TG-248 also comprises innovative features that are suited for practical use in the field. The framework attempts a quantitative implementation of a matrix approach to assess risk levels that are implied by different categories of hazard severity and hazard probability. It uses familiar categories previously defined in DOD’s overall approach to military risk management, as described in field manuals FM 100-14 and FM 3-100.12. This

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 categorical 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 “negligible” 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 USACHPPM’s attempt to use one set of exposure guidelines (i.e., MEGs) for the dual purposes of “characteriz[ing] the level of health and mission risks associated with identified or anticipated exposures to chemicals in the deployment environment” (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:

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 believes 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 mission’s needs and potential health impacts presented by the deployment mission under consideration.

To assess mission risks, it will be necessary for USACHPPM to develop a set of unbiased, predictive estimates of casualties that might occur if the unit is exposed to a particular concentration of a chemical. The subcommittee has termed such values chemical casualty estimating guidelines (CCEGs) and recommends that they be used instead of MEGs to characterize 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

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 significant 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 specific 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-

cially when establishing a base of operations. However, water contamination generally is the easiest to mitigate by avoidance, treatment, or use of alternative sources. Air contamination is probably the most important consideration 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 following:

• Risk should be defined as an unbiased or “best” 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-

mate would be its expected value, or “population mean,” defined mathematically as the arithmetic average of all possible likelihood-weighted values.²

• TG-230 makes it clear that “unit strength” should refer not only to directly affected personnel but also to individuals affected to a lesser extent

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 corresponding defined-target ranges of “fractional unit incapacitation” (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 support necessarily would reduce unit effectiveness, insofar as required medical support personnel would be performing their intended function.)

• The need for a categorical confidence-level scheme (high vs medium vs low) in TG-248 and TG-230 should be reconsidered. The assignment 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

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.

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-management actions to take, such as documenting exposures in soldiers’ 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.

• TG-230 should be revised to provide separate guidance on assessing chemical hazards for the purposes of mission and health risk assessment.

• For the purposes of mission risk assessment, risks should be evaluated 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 commanders 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.

• 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 toxicological 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 considered.

• The need for assigning confidence levels to mission-risk estimates should be reconsidered.

• For the purposes of health protection, chemical risks should be assessed independently of operational goals. USACHPPM’s 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.

• 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.

• 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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