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The Nature of Risk Assessment and
Its Application to Deployed U.S. Forces
by Joseph V. Rodricks~
ABSTRACT
An analyticalframework applicable to the assessment of the wide range of risks to health and safety
potentially encountered by U.S. forces deployed to unfamiliar environments is presented as a guide to
exnert.s involved in the evaluation of diverse information on specific hazards. Adherence to the guid-
ance should ensure that risk assessment results are clearly and consistently presented, and that they are
suitable for practical, risk management decision-making. The analytical framework presented is that
first described by the National Research Council in 1983 and long in use for assessing risks of hazard-
ous conditions, substances, and agents (referred to collectively as "stressors"~. This paper attempts to
describe how the analytical framework can be applied in diverse situations, and to many types of
stressors (pathogens, toxic chemicals, physical hazards, etc.~. The framework for risk assessment, as
originally conceived by the NRC, is a guide to the organization and evaluation of information and its
attendant uncertainties, and does not require specific methodologic approaches; the methodologies
used should be those appropriate to the relevant scientific disciplines (e.g., toxicology, microbiology,
etc.~. The framework offered in the paper includes a means for reduction of complex information to
usable formats. It recognizes that the purpose of the risk assessment process is not to set standards that
can be usedfor "yes-no " decision-making. Rather, in the current context its purpose is to allow DOD
decision-makers sufficient information to examine a range of risks that might arise in rapidly changing
deployment conditions, and to balance competing risks so that overall risks to deployed forces can be
· · · 1
mlulmlcea.
INTRODUCTION
The National Research Council (NRC) is undertaking a project with the objective of providing
advice to the Department of Defense (DOD) regarding strategies to protect the health of military
The Life Sciences Consultancy, 750 17th Street, NW, Suite 1000, Washington, D.C., 20006.
35
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STRATEGIES TO PROTECT THE HEALTH OF DEPLOYED U.S. FORCES: WORKSHOP PROCEEDINGS
personnel when they are deployed to unfamiliar environments. Such deployments might result in the
exposure of U.S. forces to chemical and biological agents of war, and to other substances released by
enemy forces with the intention of causing harm. Moreover, U.S. forces might also become exposed to
a variety of infectious agents, environmental contaminants, and conditions of stress not necessarily
arising from battle but nonetheless associated with the environments to which they are deployed.
Protection of deployed forces requires an understanding of the risks of disease and injury they face
and the development and implementation of strategies to mitigate those risks. The necessary under-
standing of health risks arises out of the process of risk assessment. Development and implementation
of strategies to mitigate risks falls within the domain of risk management. This paper offers a descrip-
tion of the conceptual and scientific basis for risk assessment, the types of knowledge and data necessary
for its conduct, the accommodation of scientific uncertainties within its conduct, and the various ways in
which risk-assessment results can be used in risk-management decision-making. In addition, the paper
describes the specific problems encountered in the application or risk-assessment methodologies to the
evaluation of risks faced by deployed forces. The overall purpose of the paper is thus to provide a broad,
analytical framework for the assessment of the wide range of health risks potentially encountered by
forces deployed to unfamiliar environments. The framework is expected to serve as a guide to experts
involved in the organization and evaluation of diverse information on specific threats. The purpose of
having such a guide is to ensure that risk-assessment results are clearly and consistently presented, and
that their means of presentation are suitable for practical, risk-management decision-making. It is noted
here, and discussed more fully below, that the analytical framework for risk assessment to be presented
is not intended to replace the scientific evaluations and judgments of experts in the specific technical
areas coming under discussion. Rather, it is only to serve as a guide for the systematic organization and
evaluation of technical information and uncertainties, so that clarity, consistency, and practicality are
achieved in the manner in which risk-assessment results are presented.
The paper is concerned with risk management only to the extent that it offers a discussion of how
risk-assessment results might be used to achieve various degrees of health protection. Issues such as the
options available for achieving risk-management objectives are outside the scope of this paper. Guid-
ance documents for risk management have been developed by several branches of the DOD (Naval
Safety Center 1996; Department of the Air Force 1998; Department of the Army 1998~. The concepts
and terms adopted in those various documents are broadly consistent with those used in this document.
The basic analytical framework presented in this paper is one long in use for assessing health risks
of hazardous conditions, substances, and agents (NRC 1983, 1994~. It will be seen, however, that under
this framework, risk-assessment results might be expressed in different ways. Because risk assessment
is a tool for practical decision-making, the specific means for describing results should be those most
helpful to the ultimate users of the information, the risk managers. This paper proposes an approach that
would seem to be suitable for decision-making in the context of troop deployments, but it would be
recognized that alternative approaches, under the same analytical framework, exist. It is expected that
some modifications in the approach offered here are expected as the NRC project develops, and as
alternative risk-management options come under review.
GENERAL NATURE OF RISK ASSESSMENT
Basic Definitions and Concepts
Risk is the probability that adverse effects will occur under specified conditions. In the context of
risks to human health, adverse effects manifest themselves as specific diseases or as injuries to the
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THE NATURE OF RISK ASSESSMENT AND ITS APPLICATION TO DEPLOYED U.S. FORCES
37
structure or function of the human organism. The nature and magnitude of the risks associated with
substances in the environment vary both with the nature of the substance and with the conditions of
exposure to it. The conditions of exposure that determine risk usually include the magnitude, duration,
and frequency of exposure to the substance, and often also includes the route of entry into the body. In
the present context, and for ease of exposition, the term "stressor" will be used to describe any and all
chemical, biological, and physical entities in the environment that might, singly or in combination, pose
risks to deployed forces.
Risk assessment is the process through which an understanding of risks is acquired (NRC 1994~.
The term might be used in two somewhat different contexts. First, it might be used to describe an actual
scientific investigation of a group of individuals exposed to a specific stressor for the purposes of
determining whether the individuals are at excess risk and, if so, the magnitude and nature of their risk.
Second, it might be used to describe the attempt to predict risks in individuals that are not the subject of
study, but who might become exposed to stressors that, under other conditions, are known to pose risks.
Predictive risk assessment, which is the subject of the present paper, necessarily involves the use of risk
information collected under one set of conditions (including information collected in experimental
settings), together with a number of science-based inferences, to describe risks that might exist under
other conditions (e.g., under conditions expected to be experienced by deployed forces). Predictive risk
assessment is necessary if the goal is to protect human health. It is the only means available to describe
the conditions of exposure that should be avoided if human health is not to be put at significant risk, or
to understand the nature and magnitude of the risks created when exposures become excessive. Human
health protection can be achieved only if knowledge of these conditions is acquired in advance of
exposure (Rodricks 1994~.
Risk management is the term used to describe all activities involved in the development and
implementation of risk-mitication strategies.
~ ~ It involves decisions regarding risk acceptability and
trade-offs in specific circumstances, risk avoidance goals, and the technical means for achieving them.
Risk management relies upon the results of risk assessments, but involves consideration of other factors,
including new risks that might arise when decisions are made to avoid certain risks (risk trade-offs).
Risk management is a very large subject, and a complete discussion of it requires detailed understanding
of the circumstances under which specific populations (in this case, deployed U.S. forces) might face
risks. As such, it is largely outside the scope of this document.
These definitions and concepts were first proposed in 1983 by a committee of the National Research
Council, which issued a report entitled Risk Assessment in the Federal Government: Managing the
Process (NRC 1983~; another committee of the NRC, in a report issued in 1994, Science and Judgment
in Risk Assessment, reaffirmed these concepts. The definitions and concepts are now widely recognized
in the risk-assessment community, and, as will be shown, are applicable to the problem at hand.
Framework for Systematic Organization and
Evaluation of Knowledge and Data
Risk assessment, in its predictive mode, does not create new data and knowledge. Rather, it is the
attempt to organize existing information and knowledge in useful and clear ways, so that inferences
regarding risk can be made. It draws upon knowledge and data developed within the basic scientific and
technical disciplines epidemiology, toxicology, pathology, microbiology, medicine, and biostatistics,
and also all of the disciplines involved in evaluating human exposures to environmental agents and
seeks to organize that information in systematic ways, consistent with the standards of those disciplines.
Scientific evaluation of that organized information is left to experts in the relevant disciplines, although
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STRATEGIES TO PROTECT THE HEALTH OF DEPLOYED U.S. FORCES: WORKSHOP PROCEEDINGS
risk assessment requires that the bases for conclusions reached regarding the available data be explicitly
justified and described. Risk assessment also requires that all significant scientific uncertainties in the
available information be described and accounted for.
Risk assessment does not require any specific methodological approach to data evaluation, but it
does require explicit justification of data choices, methodologies, and of the treatment of scientific
uncertainties (NRC 1994~. Most of the remaining sections of this paper are devoted to a discussion of
how these goals can be achieved, drawing upon precedents established in other areas in which risk
assessment has been used in decision-making, but with due consideration of the special needs of the
present context.
General Content of Risk Assessment
As described by the NRC (1983, 1994), all risk assessments, irrespective of the stressors and
situations to which they are to be applied, contain the same types of information and analysis. The NRC
also proposed that, for the sake of clarity, the information should be organized in a specific way. Thus,
all risk assessments involve, as a first step, a careful description of the specific stressors of concern, and
the specific groups of individuals that might become exposed to those stressors. Once the stressors and
population groups that are the subject of the risk assessment are specified, information is collected
regarding the following questions (see Figure 1~:
The Stressor
Steps ~ and 2
Hazard Identification
- What adverse effects
- Has causation been estahli$hed7
Dose-Response Evaluation
- How clo severity and incidence of adverse
effects change with exposure conditions?
Population(s) Exposed
to the Stressor
Step 3
Exposure Assessment
- What exposure conditions are experienced
by the populations
1
. ......... ... .
Step 4
Risk Characterization
What are the expected adverse effects (responses)
i n the exposed popu lati 0 rlts)7
What uncertainties?
FIGURE 1 Risk assessment involves systematic organization and evaluation of data.
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THE NATURE OF RISK ASSESSMENT AND ITS APPLICATION TO DEPLOYED U.S. FORCES
39
Step 1: Hazard Identification. What types of adverse effects have been shown to be associated with
exposure to the stressor? For each effect, how well has a causal association been established? If hazards
have been identified in experimental (animal) models, are the findings likely to be relevant to humans?
Step 2: Dose-Response Evaluation. For each type of adverse effect (hazard) associated with
exposure to the stressor, how do the severity and incidence of those effects (responses) change as the
conditions of exposure (dose)2 to the agent change?
Information regarding these first two steps is specific to the stressor, and is typically to be found in the
scientific and medical literature. The results of the hazard identification and dose-response evaluations
are then integrated with the results of:
Step 3: Human Exposure Assessment. Under what conditions are the individuals of concern
exposed or potentially exposed to the stressor? "Conditions" includes consideration of those factors
(dose size, duration, frequency, route of entry) that, based on Step 2, are known to relate to response.
The result of the integration of results from Step 3 with those from Steps 1 and 2 is a description of the
risks of adverse effects in the exposed population the nature, severity, and incidence (probability) of
adverse effects expected in the population under its actual or expected conditions of exposure. The NRC
chose to label this fourth step in the assessment process as a risk characterization, because this term best
reflects the fact that accurate and precise quantitative estimates of risk, though desired, are rarely achiev-
able because of limitations in knowledge and data (NRC 1983~. The NRC envisioned that risks would be
described Quantitatively. when possible. but always accompanied by Qualitative descriptions of factors not
~ — , ~ , ~ ~ ~ ~
readily quantifiable. Indeed, in some cases only qualitative characterizations of risk will be possible.
Although all assessments contain these four steps, they need not proceed in the order shown in
Figure 1. This matter will be further discussed in connection with the discussion of the uses of risk-
assessment results.
Need to Deal with Scientific Uncertainties
Although the logic in the organization of information for risk-assessment purposes is apparent, the
difficulties encountered in attempts to complete a risk assessment are often formidable. Indeed, many of
the questions that need to be considered to complete an assessment cannot be completely answered with
available knowledge and information. Typical questions include the following:
1. How do hazard and dose-response data collected in one population group apply to population
groups having a different range of susceptibilities to the agent?
2. How do hazard and dose-response data collected in experimental systems apply (if at all) to
human populations?
3. How do hazard and dose-response data collected over a given period of exposure, or a given route
of exposure, apply to populations exposed over different time periods or exposure routes?
4. Is it possible to predict response (risks) at doses that are lower than the minimum dose at which
risks can be measured? (All risk measurement systems have limited detection power, and cannot detect
many small-to-moderate-sized risks.)
2The NRC, and now common usage, refers to this step as a dose-response evaluation, but it is clear that the term "dose"
is intended to be applied broadly, to include all measure of exposure relevant to the response. A more descriptive term might
be "exposure-risk evaluation."
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STRATEGIES TO PROTECT THE HEALTH OF DEPLOYED U.S. FORCES: WORKSHOP PROCEEDINGS
5. What measures of dose (what conditions of exposure) provide the most accurate prediction of
response (risk)?
6. How can population exposures be described based on data limited to discrete segments of the
population, or limited to specific points in time?
It is often the case that well-documented answers to questions such as these are not available. Because
it is not possible to complete risk assessments without providing answers to such questions, it must be
recognized that risk-assessment results are necessarily uncertain, and specific assessments are uncertain
in rough proportion to the number of unanswered questions that arise in the course of their conduct
(Bogen 1990; Finkel 1990~.
The NRC (1983) has emphasized that any attempt to provide answers to questions for which there
is limited empirical support must be recognized as at least partially based on what was called a "science
policy" choice. The NRC committee promoted the use of science policy choices, as long as the specific
choices to be used were explicitly described, and used consistently in all risk assessments; such choices
thus become "default options," to be used when knowledge or information is highly limited.
Regulatory agencies such as the U.S. Environmental Protection Agency (EPA) have prepared
guidelines for risk assessment that describe the defaults to be used. Some critical regulatory defaults are
presented in Text Box 1 (Barnes and Dourson 1988; EPA 1996~. Many of the defaults presented in Text
Box 1 are used by agencies such as EPA and the Food and Drug Administration (FDA), when their
concern is the general population. For occupational groups, additional considerations enter the picture
and often lead to somewhat difference choices (discussed later).
The insertion of specific factors to account for uncertainties such as the factors of 10 used to deal
with variability in responses to toxicity (Defaults 4 and 5, Text Box 1) has become common practice
in risk assessments. These uncertainty factors, and the criteria for their selection, are critical compo-
nents of any risk assessment (Barnes and Dourson 1988), and they will require considerable discussion
within the context of risks to deployed forces. The examples given in Text Box 1 are not all relevant to
the risk questions posed in this paper, and are presented only to make clear the need to consider such
factors. A final point on the issue of uncertainty in risk assessments is that the regulatory defaults listed
in Text Box 1 are offered in the absence of data relevant to specific stressors. Thus, in all specific cases,
actual data, when sufficient, override defaults (also discussed later).
TYPICAL USES OF RISK-ASSESSMENT RESULTS
General Nature of Decision-Making Based Upon Risk-Assessment Results
Heretofore most decision-making based on risk-assessment results has taken place in the context of
the regulation of chemical and radiation risks. Both the general population and occupational popula-
tions have been the subjects of such regulations. In most cases risk-management decisions have resulted
in some type of numerical standard, usually limiting the allowed concentration of an agent in a specific
environmental medium. With respect to the use of risk-assessment results in such regulatory standard-
setting, the process is generally the following (NRC 1983~:
1. Risks under current exposure conditions are estimated.
2. A risk-reduction goal is established.
3. The exposure level that corresponds to the risk goal is estimated.
4. The level estimated in Step 3 is the maximum level of exposure allowed in the population to be
protected.
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THE NATURE OF RISK ASSESSMENT AND ITS APPLICATION TO DEPLOYED U.S. FORCES
41
5. Standards, expressed as concentrations in air or water or food or soil, or in all of these media, are
calculated so that the maximum allowable exposure level is not exceeded in populations exposed via
these media. (Discussions of how these goals are to be achieved, and how compliance with them is
measured, are outside the scope of this paper.)
It can be seen that the first two steps the conduct of the risk assessment and the risk-reduction
goals are the critical components of this process. In the context of regulations, it is possible to make
certain generalizations about these two steps. First, risk assessments for the general population have
often involved different uses of available data and different default assumptions than have risk assess-
ments directed at occupational groups (NRC 1994~. It has been assumed that, because they generally
involve healthy adults and do not include the most vulnerable segments of the general population,
occupational populations are likely to display less variability in response to hazardous agents than do
members of the general population. Second, with respect to risk-reduction goals, regulators have sought
to ensure that none of the adverse effects of the agent will occur in the populations to be protected and
accordingly, have sought to reduce risks to levels thought to be negligible or insignificant (Rodricks
1992~. Finally, in many cases, the selection of risk-reduction goals is influenced by considerations other
than public health protection technical feasibility, costs that are dictated by the requirements of
applicable laws.
The model for using risk-assessment results described above is not the only possible one, and is
probably not the most useful one for decision-makers who are asked to protect the health of deployed
forces.
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STRATEGIES TO PROTECT THE HEALTH OF DEPLOYED U.S. FORCES: WORKSHOP PROCEEDINGS
.... _ ... _ .
| Mode' I (NRC 1983) | Model 11 (AIternative)
. _ ... ..
Filed
Assess risks of current exposures Anticipate exposure to identified stressor.
1 1
[determine whether risk is excessive. Conduct hazard and dose-response
If yes, identify ri$k-reduction goals. evaluatior,
1 1
Estimate maximum allowable exposure Record hazard, dose-response evaluation
levels, based on identified risk redu~ion in readily usable format.
goal.
1 Second,
Establish standards (limiting concentrations) Estimate expected doses of stressor in
so that maximum allowable exposure levels Population.
are not exceeded ~
Compare dose estimate to hazard, dose-
Response intormat~on recorded above.
1
Determine risk expected in population.
If relevant compare risks of different actions.
Determine action to be taken to minimize
| overall risk.
arose is short hand for all conditions of exposure expected to determine risk.
FIGURE 2 Two models of risk-based decision-making.
Alternative Decision-Making Models Based on Risk-Assessment Results
The model for decision-making described above is applicable when populations are already exposed
to a source of risk, and a determination is made that current risks are excessive and need to be reduced
to insignificant levels, that is, levels that are likely to protect against any of the adverse effects of a
stressor. An alternative model is designed to deal with anticipated, not current, exposures. In such
circumstances (which arise in some regulatory contexts in which premarketing approvals for certain
products are required), the hazard identification and dose-response evaluation steps of a risk assessment
are completed for the agent of concern. These steps of the assessment yield a description of the nature
of the adverse effects associated with exposure to the agent and the relationships between the severity
and incidence of those effects (response) and the dose (conditions of exposure).
This information can be presented to risk-management decision-makers. These decision-makers are
then presented information on the conditions of exposure experienced by the populations of concern:
their exposure conditions might be estimated based on anticipated modes of contact with the agent, or
based on actual data pertaining to such contact. Faced with information on conditions of exposure
(either anticipated or actual), risk-management decision-makers can refer to the hazard and dose-
response assessments and determine the nature and extent of risk to be incurred by the population they
are charged with protecting. At this stage, decision-makers might then evaluate various options for risk
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THE NATURE OF RISK ASSESSMENT AND ITS APPLICATION TO DEPLOYED U.S. FORCES
43
mitigation, and (in the ideal case) choose that which provides the greatest degree of health protection,
given the circumstances in which the decision needs to be made.
The two models for risk-based decision-making are outlined in Figure 2. As discussed in the next
section, it is the second model (Model II, Figure 2) that would appear to be the most applicable to the
problem of risks to deployed forces.
RISKS TO DEPLOYED U.S. FORCES: OVERVIEW OF
PROPOSED ASSESSMENT AND MANAGEMENT FRAMEWORKS
Forces deployed to unfamiliar environments might face a range of battle-related risks, including
those related to chemical and biological warfare agents, and additional risks of infectious disease,
exposure to chemical contaminants in air, water, food, and soil, and a variety of physical threats,
including those associated with accidents and explosions, and with certain forms of ionizing radiation,
and with excessive heat, cold, and noise. Even certain medical treatments designed to protect forces
from certain risks might, themselves, pose other kinds of health threats (Medical NBC Battlebook, U.S.
Army Center for Health Promotion and Preventive Medicine). Forces might be exposed to some of
these sources of risk only infrequently but in other cases might be exposed continuously through the
period of deployment. Several sources of risk might be experienced simultaneously. Actions taken to
avoid certain sources of risk might result in exposure of forces to other sources. The situation is
complex, and can be managed effectively only if suitable risk-based decision models are in place and
their characteristics understood by decision-makers.
The risk-assessment framework described in the foregoing is, it will be suggested, suitable for
organizing and evaluating all of these many types of health threats to deployed forces. It will also be
suggested that Model II of risk-based decision-making, described in Figure 2, will be most useful for the
protection of deployed forces.
Following is a broad overview of how the risk-assessment framework and decision-making model
might be applied to each of the types of threats that might be encountered by deployed U.S. forces. Later
sections will detail each of the steps outlined here. In outline form, the proposed framework is as follows:
1. Identification of all stressors of possible concern, and elaboration of their sources and pathways
to deployed forces.
2. Development of hazard and dose-response information for each stressor, and presentation of
information in a usable format.
3. Development of methods for estimating doses3 of stressors anticipated for or incurred by de-
ployed forces.
4. Estimation of risks to deployed forces and application of decision-making criteria developed with
the goal of maximizing health protection, consistent with the circumstances under which risks are
encountered.
The guidance offered here pertains to the requirements of risk assessment, and does not deal with
specific methodologies that properly fall within the fundamental scientific disciplines upon which
risk analyses depend. The emphasis in risk assessment is on clarity and completeness of presentation,
explicit consideration and accommodation of scientific uncertainties, and usable presentation of risk
3As in the earlier text, the term dose is used for ease of exposition. In the context of discussions of specific stressors, its
characteristics are influenced by whatever measures of exposure are relevant to the risk being assessed.
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STRATEGIES TO PROTECT THE HEALTH OF DEPLOYED U.S. FORCES: WORKSHOP PROCEEDINGS
results. The guidance is thus offered to ensure consistency, explicitness, and usability; the quality of
the underlying scientific information and knowledge, and the appropriate methods for evaluating it
are judgments reserved for experts in their particular, relevant disciplines. Those experts, it is hoped,
will not see risk assessment as a rigid methodology requiring specific methods of scientific evalua-
tion, but rather as a systematic framework for organizing information and for forcing a high degree of
explicitness in the treatment of that information and the uncertainties in it, and for producing usable
results.
STRESSORS OF CONCERN AND THEIR SOURCES AND
PATHWAYS TO DEPLOYED FORCES
Definition of Stressors
For ease of exposition, stressor has been adopted to apply to all entities and environmental condi-
tions that might threaten deployed forces. No single term is clearly appropriate to describe all such
entities and conditions, but this term is arbitrarily selected for convenience. A list of the types of agents
of concern as potential threats to deployed forces is presented in Table 1. The types of hazards usually
associated with each stressor are also listed; further descriptions of the process of hazard identification?
the first step of the proposed risk-assessment framework, is offered in the following section. Implemen-
tation of the risk-assessment strategy proposed here requires a listing of all specific stressors of concern,
and not simply the broad categories listed in Table 1.
Sources of Stressors and Pathways of Human Exposure
Under the risk-assessment framework presented here, complete evaluations of how and to what
extent deployed forces might become exposed to these types of stressors are conducted within the
exposure assessment step, described more fully later. It is important, however, that some characteriza-
tions of the sources of these stressors, the possible pathways by which deployed forces might become
exposed, and the nature of their expected exposure accompany their initial listing. It is also advisable to
list stressors in approximate order of the frequency with which deployed forces are expected to encoun-
ter them, and in order of their degrees of danger. This initial listing is a useful guide to the hazard and
dose-response evaluations. It can be used to set priorities for the conduct of hazard and dose-response
evaluations, so that efforts at information gathering and analysis are first directed at what will likely be
the highest risk stressors and exposures.
In addition, these initial characterizations of exposure will assist in identifying the types of hazard
and dose-response information most relevant to the expected conditions of exposure. Thus, for ex-
ample, little effort need be devoted to inhalation toxicity data for chemicals that are likely to reach
deployed forces only through drinking water, and little effort need be expended researching for chronic
hazard information for stressors that forces are likely to encounter only rarely and for very limited
periods of time.
DOD has already assembled much information regarding stressors, their sources, and the ways in
which forces might encounter them (The Medical NBC Battlebook, The U.S. Army Center for Health
Promotion and Preventative Medicine). This information is no doubt the appropriate starting point for
the proposed risk assessment. As steps are taken to complete the hazard identification and the dose-
response evaluation, it becomes necessary to ensure that risk-assessment criteria for organizing and
drawing inferences from data are met.
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THE NATURE OF RISK ASSESSMENT AND ITS APPLICATION TO DEPLOYED U.S. FORCES
TABLE 1 Types of Stressors That May Pose Health and Safety Risks to
Deployed U.S. Forces
stressorsa
Hazards to be Considered
Chemicals
Pathogens
Toxinsb
Medicines
Physical structures
Moving vehicles
Environmental conditions
Toxicity, flammability, explosivity, radiation
Infections, infectious diseases
Toxicity
Side effects
Traumatic injuries from accidents
Traumatic injuries from accidents
Physical, psychological stresses
aThe term "stressors" is the author's, used for convenience (see text).
bToxins are chemicals produced by microorganisms, plants, and animals and are typi-
cally large (and often not very stable) molecules such as peptides and proteins; it might be
necessary to treat them separately from other chemicals, because of the pathways by which
they might reach deployed forces.
Source: The Medical NBC Battlebook, The U.S. Army Center for Health Promotion
and Preventive Medicine.
HAZARD IDENTIFICATION
Definition
45
Under the risk-assessment framework proposed here, the hazard identification step involves a
description and critical scientific review of the available data concerning the types of adverse health
effects (diseases or injuries) that have been associated with exposures to the stressor under consider-
ation. All stressors in the environment can, under some conditions, cause harm to health (i.e., pose
hazards) and most can cause different types and degrees of hazard as exposures change. Whether one or
more of the hazardous properties of a stressor will be expressed in groups of deployed forces can be
ascertained only after the remaining steps of a risk assessment are completed. The purpose of this first
step is to describe and catalog for each stressor of interest the types of hazards that have been associated
with it, under any conditions; such a thorough catalog ensures that no hazard potentially relevant to risk
assessment will be overlooked.
The Problem of Causation
The ease with which a causal relationship between a stressor and a particular health hazard can be
established depends upon many factors, including the nature of the stressor (whether it is a well-
characterized single substance or a complex mixture), the nature of the hazard (whether it is one that
appears immediately after an exposure, or only after a long delay), and the extent and nature of scientific
investigation it has received (whether information derives from case reports, from epidemiological
studies, or from experimental studies). A few stressors have received significant and intensive study,
most have received limited study, and some have not been studied at all. All of these factors are to be
considered in judgments regarding the evidence for causation.
Many scientific disciplines are involved in the study of the wide variety of stressors of potential
concern to deployed forces: epidemiology, clinical medicine and toxicology, experimental toxicology,
microbiology, physiology, psychology, and pharmacology, among others. Within these various disci-
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STRATEGIES TO PROTECT THE HEALTH OF DEPLOYED U.S. FORCES: WORKSHOP PROCEEDINGS
to deployed forces. For purposes of the present discussion, the phrase conditions of exposure is more
apt. This phrase encompasses one or more of the following:
· the magnitude of exposure to the stressor;
· the frequency and duration of such exposure; and
· the routes of such exposure (i.e., inhalation, ingestion, dermal, other).
In some cases the physical or chemical forms of the stressor might vary (e.g., amphorous versus
crystalline silica), and these variations might affect its hazardous properties; when these forms are
important they are also components of the conditions of exposure. As in the use of the term stressor, the
term dose will be used in the following as a convenient shorthand for conditions of exposure.
Response is the term used to describe the hazards produced at various doses. The response
a description of the risk. Response (risk) generally includes:
a description of the nature of the disease or injury;
· a description of its severity;
· a discussion of whether the disease or injury is reversible, and, if so, the tvoical rate of reversibility:
· a description of the incidence of disease or injury; and
· a discussion of whether the hazard is immediate or delayed.
is thus
, ~ ,,
The dose-response evaluation thus entails the development of a description of the relationship between
dose of stressor and response, over a range of doses.
Measures of Dose
The doses of the wide variety of stressors of concern to deployed forces are measured in many
different ways. Under the criteria for sound risk assessments, it is recommended that whatever mea-
sures of dose are used, they should be those measures that are known to relate to response. It is
important that the dose-response evaluation include a discussion of the reasons for the selection of
specific measures of dose.
The ultimate evaluation of risk will require that the doses likely to be incurred by deployed forces be
measured and expressed in ways that are directly relevant to the measures of dose that are determinants
of response (risk). The means for ensuring that proper measures of dose are used will be discussed in the
next section. In some cases it will be possible to express dose measures quantitatively, but in other cases
it might not be possible to do so. It is expected, for example, that environmental conditions leading to
excessive physiological or psychological stress will be described in largely qualitative ways; such
descriptions are encompassed within the broad definition of dose within the risk-assessment framework
proposed here.
The risk-assessment framework described here allows for evaluations of the risks of physical
trauma and injury from accidents, explosions, fires, floods, and for evaluations of physical and psycho-
logical stress. The use of the term dose is no doubt awkward for these types of risk, and might not be
well received by experts in these subjects. It is not a significant defect in the risk-assessment framework
proposed here that its terms of reference are not readily adaptable to these types of risk. Experts in the
relevant disciplines, using suitable descriptive terms, will nevertheless be asked to arrive at some usable
description of the conditions (dose) under which deployed forces are likely to be at risk from these
various stressors.
It is generally useful, and in fact convenient, to present dose-response evaluations separately for
different exposure durations. It is proposed here to use three categories of exposure duration: acute,
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THE NATURE OF RISK ASSESSMENT AND ITS APPLICATION TO DEPLOYED U.S. FORCES
-
49
intermediate, and chronic. The term acute is used here in its conventional sense of a one-time exposure,
although it is recognized that, for different agents, the one-time exposure might extend from a few
minutes to many hours. In the field of chemical toxicology, acute is often subdivided into periods of 15
minutes, 1 hour, 8 hours, and 24 hours, because the magnitudes of exposure that produce adverse
effects, and the severities of those effects, can, for some agents, vary considerably with these relatively
small changes in exposure duration. Acute exposures might occur more than one time in the life of an
individual; exposures are to be considered acute only if they are sufficiently separated in time to ensure
that any effects produced are not additive or cumulative (NRC 1986~.
The terms intermediate and chronic are more ambiguous in meaning, and there appears to be no
single definition involved in the evaluation of the wide range of stressors of interest here. The three
categories of acute, intermediate, and chronic exposure durations will be used here with the recognition
that precise and consistent definitions can be identified only after all participants in the risk assessment
are able to discuss these usages and their appropriate definitions.
_
Response Measures and Their Relationship to Dose
Responses to various doses of hazardous stressors come in many forms. These responses will have
been tabulated, discussed, and critically reviewed in the hazard identification step. Out of the informa-
tion set forth there, dose-response profiles can be developed for acute, intermediate, and chronic expo-
sure conditions.
There are many ways in which responses can be expressed. For present purposes, it is proposed that
four categories of response be developed and their relationships to dose described as mortality; severe,
irreversible (or slowly reversible) injuries or diseases; minor, readily reversible injuries; and no adverse
effects (Table 2~.
Other categories can be envisioned and, within each of the above categories, information concern-
ing the incidence of these effects within a population might also be included. It is suggested, however,
that these four categories, together with the further categorizations of doses as of acute, intermediate,
and chronic duration, will provide sufficient and readily usable information for risk-management pur-
poses. The information proposed here, together with the information to be provided about doses to be
incurred by deployed forces in different circumstances, will allow risk managers to determine whether
deployed forces are at risk (will incurred doses exceed the maximum no-effect dosed. Methods to be
considered in the development of these types of dose-response profiles for stressors of concern to
deployed forces will now be considered. It is recognized that adjustments might need to be made in the
proposed approach for different categories of stressors, but it is suggested that the general goals of the
evaluation, and the framework into which it fits, should not need to be significantly altered.
The Presentation of Dose-Response Information
It is proposed that, for each stressor of concern, a tabular presentation of dose-response information
be developed; the suggested format is shown in Table 2. The tabular presentation should be accompa-
nied by a narrative description of its basis, synthesized from the hazard identification narrative, and with
an additional description of the reliability and representativeness of the data available relating to dose-
response. Extensive discussion will follow later, on the development of the dose information.
The notes to Table 2 define the Ds consistently with the descriptions given previously. With Table
2, risk managers can, for example, see that for the particular stressor reviewed, acute exposures from
zero up to D1A are likely to be without adverse effects; doses in the range from D1A to D2A are likely
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so
STRATEGIES TO PROTECT THE HEALTH OF DEPLOYED U.S. FORCES: WORKSHOP PROCEEDINGS
TABLE 2 Suggested Format for Presentation of Dose-Response Information for Each "Stressor" of
Concern to Deployed Forces
Responses Doses (for different exposure durations)
(Adverse Effects,
Immediate & Delayed) Acute (A) Intermediate (I) Chronic (C)
Mortality D3A D3I D3C
Serious, Irreversible D2A D2I D2C
Minor, Reversible D1A D1I D1C
No Effect Likely D=0 D=0 D=0
Notes
1. Ds are the doses at which adverse effects, either immediate or delayed, are expected to occur. Generally, D3>D2>D1 and
DA>DI>DC.
2. D3 = min. dose for mortality; D2 = min. dose for serious, irreversible effect; and D1 = min. dose for the most minor
effect.
3. Some Ds can be expressed only qualitatively, as a set of conditions (e.g., conditions leading to physical or psychological
stress). The Ds are expressed in the terms or units that are relevant to the responses.
4. Ds are derived by considering the nature of the data upon which they are based, the nature of the population whose risk is
being assessed, and sources of variability and uncertainty in the data and the population under assessment.
5. Table to be accompanied by narrative description of its scientific basis.
6. In the typical regulatory use of this framework, health protection standards fall somewhere between D=0 and D1.
to cause only minor, reversible effects (e.g., irritation of the eyes, airways, or skin); and doses above
D2A might be highly hazardous; and doses above D3A are likely to be lethal. Again, the measurement
of dose will vary according to the stressor.
For some stressors, to which deployed forces might be exposed by more than one route, it might be
necessary to develop a separate dose-response profile for each route. The risk assessor will need to
determine whether specific responses are restricted to a specific route (in which case doses incurred by
that route are to be considered independent of doses incurred by other routes ~ or whether doses from all
relevant routes are to be combined. If the latter is the case, some means will have to be found to limit
the allowable Ds by each route, so that combined exposures by several routes do not exceed the total
allowable D. Finally, it should be emphasized that for some stressors, the Ds can be expressed only
qualitatively, or semi-quantitatively, as a set of environmental conditions. Some means will have to be
found to define such Ds in usable ways a simple, narrative statement for example that can be
included as footnotes to the table.
Considerations in the Development of Dose-Response Information for Table 2
Thresholds
For many if not most of the stressors of concern, there will be some dose (broadly defined to include
all relevant conditions of exposure) that must be exceeded before even minimal adverse effects are
produced. The so-called threshold dose will vary among stressors, with different effects of the same
stressor, and will also vary among individuals in a population. The doses labeled D1 in Table 2 are
intended to represent minimum-effect doses, and thus will lie just above the threshold dose. Just as
threshold doses will vary among members of a population, according to their individual sensitivities, so
will the Dls and all the other Ds in the dose-response table. One challenge for risk assessment is the
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THE NATURE OF RISK ASSESSMENT AND ITS APPLICATION TO DEPLOYED U.S. FORCES
5
problem of estimating Ds for populations having the characteristics of deployed forces, when the data
from which they are to be estimated derive from different human populations or from experimental
animals (Dourson et al. 1996~.
The Possibility That Some Stressors Do Not Display Thresholds
It might be the case that some stressors, particularly biological and chemical agents designed as
weapons of war, have threshold doses and minimum effective doses that are so small that it is practically
impossible to avoid seriously harmful exposures. For such stressors, it might be that all doses are to be
considered harmful, and the critical assessment of risks comes only in the exposure assessment step,
where the probability of exposure becomes the determinant of risk.
Some chemical carcinogens and forms of radiation are thought to pose risks at all nonzero exposures
(NRC 1994, EPA 1996~. In the regulatory context, described earlier, it was seen that carcinogenic
chemicals and radiation are assumed to pose risks at all exposures greater than zero, and that their risks
increase in proportion to dose. The adoption of linear, no-threshold models to describe low-dose risks
for carcinogenic substances is based in part on biological evidence and in part on science policy
assumptions and public health dictates that involve the precautionary principle (NRC 1994~.
It should be emphasized that with respect to such carcinogenic agents, it has not been consid-
ered necessary to reduce exposures to zero (to ban products) to protect public health. Rather, the
approach has been to reduce exposures to those corresponding to low levels of risk (as estimated
using linear, no-threshold models). The Occupational Safety and Health Administration (OSHA)
and the Nuclear Regulatory Commission have, in a relatively large number of decisions, not forced
lifetime risks for occupational carcinogens to levels below about 1 in 10,000 (Rodricks 1992,
1994~. Standards for carcinogens established by these agencies are, it should be noted, often
accompanied by warnings to workers and other protections to ensure that excessive exposures do
not occur, or occur only rarely.
It is likely that some of the stressors to be encountered by deployed forces will be carcinogenic. In
many, if not most cases, these exposures will be limited in duration and will often occur only intermit-
tently. The occupational groups of concern to the OSHA and the Nuclear Regulatory Commission are
usually exposed every working day, and for a working lifetime. It is possible that exposures to carcino-
gens of the type expected for deployed forces will pose little or no risk because of their limited duration.
Some such stressors (e.g., those that are direct-acting, genotoxic substances) might pose risks of cancer
even after a few exposures (EPA 1996~.
Other mechanistic considerations enter the picture. It is now widely recognized that not all carcino-
gens operate by the same mechanisms, and that, irrespective of the exposure duration, some of these
carcinogens are likely to operate by threshold mechanisms, and so their dose-response evaluation might
proceed as it does for other threshold stressors (see paper by Rozman in these ~roceedincs1.
Judgments regarding the appropriate approach of low-dose risk assessment tor such stressors, In the
context of the exposures to be experienced by deployed forces, will have to be left to experts in
toxicology and carcinogenicity, and case-by-case decisions will have to be made. If threshold and
minimum effect doses (Ds) can be identified and justified, then their estimation will proceed as with
other threshold stressors. If there are some stressors that are thought to present risks at all nonzero
exposures, then a decision will have to be made regarding the level of risk that is to be considered
minimal. Precedents from the OSHA and the Nuclear Regulatory Commission might be useful to guide
such decisions (Rodricks 1992~.
~ ~ ,
.
. . .
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52
RESPONSE
Modal Fit'
Serious
I rrevemible
Effect
MIROrr
Reversible
Effects
kilo Effect
Likely
Oldep
D1 obs D3dep
it'
,~ A
B
UF?
~ OF1
-
~ /R
~ .
STRATEGIES TO PROTECT THE HEALTH OF DEPLOYED U.S. FORCES: WORKSHOP PROCEEDINGS
D2dep O2ob$
03obs
FIGURE 3 Hypothetical dose-response relationships for exposure to a hazardous stressor. Curve A is a compos-
ite relationship derived from the available date relating to Dobs to response. In most actual cases, information for
different portions of Curve A will derive from different studies or sources. Curve B is the relationship intended to
apply to deployed forces. UFs are uncertainty factors applied to deal with uncertainties in the observed data. UFs
vary as a function of the nature, quality, and representativeness of the observed data. The Ds are expressed in
whatever units or terms are relevant to the response for the particular agent under review. Dldep, D2dep, and
D3dep are transferred to table format in Table 2.
Estimating Critical Risk Doses (Ds) for Deployed Forces
Figure 3 displays two hypothetical dose-response curves for a stressor of concern. The response
axis is divided into the four categories of adverse effects already discussed. Along the dose axis are a
range of increasing doses expressed in units or terms appropriate to the stressor. Curve A represents the
dose-response relationship for the agent and, as discussed earlier, one curve will be developed for acute
exposures, another for intermediate exposures, and a third for chronic exposures. It can be seen that the
available evidence suggests that no effects are expected until the dose labeled Dl obs is reached, and that
effects become increasingly serious as the dose is increased to D20bs and D30bs.
This observed dose-response relationship might not, indeed is likely not, to come from any single
study. It is more likely to represent a composite of data from several studies, some involving human
subjects and some involving experimental animal subjects. For some stressors, data might not be
available to describe such a relationship in full; in fact, incomplete data are likely in many cases. For the
present, it will be assumed that the evidence will allow estimation of a relationship approximating Curve
A in Figure 3.
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THE NATURE OF RISK ASSESSMENT AND ITS APPLICATION TO DEPLOYED U.S. FORCES
53
It must now be considered that the data supporting Curve A will in most cases be derived from
studies in population groups that might or might not represent the range of sensitivities expected in the
population of deployed forces. Moreover, in many cases, the observed data will have been derived from
animal studies. As in all areas of risk assessment, it must be decided how well the observed dose-
response data represent the population in this case deployed forces that is the subject of the risk
assessment.
It is the general practice in risk assessment to evaluate potential differences in response between the
subjects studied and those that are the subjects of the risk assessment (NRC 1994; Dourson et al. 1996~.
As a starting point, deployed forces represent a segment of the human population that is generally the
healthiest and, therefore, the least vulnerable to the adverse effects of environmental stressors. In this
respect, they are like many other occupational cohorts children, the aged, the infirm, and individuals
with debilitating health conditions are generally excluded. The importance of these observations lies in
the fact that not only are deployed forces likely to be less sensitive or vulnerable to the adverse effects
of stressors in the environment, but the range of variability in response is also likely to be much smaller
than it is for the general population.
Deployment is, it should be emphasized, an unusual situation that most individuals never have to
face. It is possible that normally healthy individuals, who should be the most resistant to the effects
of environmental stressors, might, under conditions of deployment, become more vulnerable than
would ordinarily be expected. This subject requires more review and analysis by participants in the
risk-assessment process.
It should probably not be assumed, without further investigation, that
deployed forces are no more vulnerable to environmental stressors than are ordinary occupational
cohorts.
Within the context of risk assessment, it is necessary that experts make some judgment regarding
how well the population studied represents the population of deployed forces. Once this judgment is
made, uncertainty factors (UFs) are introduced to estimate critical doses applicable to deployed forces.
These are noted in Figure 3 as Dldep, D2dep, and D3dep, and Curve B represents an approximation of
the dose-response relationship for deployed forces. No particular UP is to be inferred from Figure 3,
although UFs of differing magnitude, including UFs of magnitude 1, are possible, depending upon the
nature of the database used to develop the composite Curve A.
Text Box 1 presented some UFs commonly used by regulatory agencies for assessing variability in
thresholds for toxic chemicals among humans and differences in response between experimental ani-
mals and humans. It should be emphasized that the specific UFs listed in Text Box 1 are intended to
apply to the general population, in which more individuals of greater sensitivity will be present than in
the population of deployed forces, and in which a wider range of sensitivities is expected. No similar
standardized UFs have been established for occupational groups; rather, case-by-case judgments have
been made. It is expected that such case-by-case judgments will also have to be made in the context of
risks to deployed forces, taking into account the ways in which such populations might differ from their
ordinary occupational cohorts.
It should also be pointed out that there are often uncertainties other than those related to variabilities
in response between experimental animals and humans and variabilities among members of the human
population. UFs have been used to compensate for other types of data limitations (e.g., for the absence
of data relating to chronic exposures, or for the absence of data on the minimum effective dose ED11~.
Within the field of toxicological risk assessment, it is accepted practice to introduce UFs, in the manner
described above, as long as some justification is given for their use. It is not clear that such precedents
exist in other areas of risk assessment, so that further discussion of this important issue will be needed
before appropriate methodologies can be described.
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54
STRATEGIES TO PROTECT THE HEALTH OF DEPLOYED U.S. FORCES: WORKSHOP PROCEEDINGS
Creating Dose-Response Tables and Narratives
The derivations of estimated critical doses for each stressor and for each of the three different
exposure durations, as depicted in Figure 3, lead to the estimates necessary to create Table 2. It is
proposed that Table 2 be accompanied by a narrative statement of its basis. With this table and
statement, the hazard identification and dose-response steps of the risk assessment will be complete.
Relationships to Existing Standards
OSHA, EPA, the American Conference of Governmental Industrial Hygienists, and other organiza-
tions have published chemical and biological exposure guidelines for many chemical and some biological
stressors. Several compilations of recommended exposure limits for short-term exposures are also avail-
able for some chemicals (USACHPPM 1999; see references therein). These various recommended expo-
sure limits were developed in a variety of contexts, and for a number of reasons might not be directly
applicable to the risk-assessment goals presented here. Some elaboration of this point is necessary.
First, it should be recognized that most existing occupational exposure guidelines are intended to be
applied as lines of demarcation between safe (risk free) and unsafe (risky) exposures. They were derived
to provide risk managers with a simple yes-no decision model. (Although the developers of these various
limits recognize that occasional excursions above them are not necessarily harmful, they are nevertheless
applied as if such excursions should be avoided.) This yes-no approach is suitable for situations in which
risk mangers are in a position, through careful planning, to control exposures (in a regulatory context), and
to ensure that when (in the case of accidents) exposures cannot be controlled, individuals can be removed
from affected areas. The yes-no model is most useful in circumstances such as these.
The circumstances in which deployed forces might become exposed are often not controllable in the
same way, and in many cases some degree of harm will not be avoidable. The type of information on
risk proposed here, as expressed in Table 2, provides decision-makers far more information on the
likelihood, magnitude, and seriousness of the risks that might arise under different conditions.
Most existing occupational and general population standards are also intended to represent expo-
sures that are not likely to pose any discernible risk. They thus fall somewhere in the no-effects-likely
zones of Table 2 and Figure 3. Their relationships to the minimum-effective dose (D1) is ascertainable
by reference to the data upon which those standards are based, but cannot otherwise be known. In the
context of exposures incurred by deployed forces, it is not sufficient for decision-makers simply to be
aware of the no-likely-risk exposure, but rather it is necessary that such decision-makers have knowl-
edge of the exposure at which adverse effects are first expected (D1), and the levels at which serious
effects are likely to occur (D2 and Day. (It is recognized that recent efforts by EPA and the NRC are
directed at developing the type of dose-response information for acute exposures that is proposed here,
. . . . . . . . . . .. .
,
although with the ~ntenhon that they be applied to the general population.)
Other differences between available occupational standards and those to be developed for deployed
forces need to be considered. For example, occupational standards are generally applicable to workers
exposed 8 hours a day and 5 days a week, for a working lifetime. Deployed forces might be exposed to
some stressors for 24 hours a day, and on every day, but are not likely to be exposed for a working
lifetime. Some stressors for which there are inhalation occupational standards might be present as
contaminants of the food or water of deployed forces. For these several reasons and more as well, great
care must be taken in using available occupational standards, and certainly in using standards developed
by EPA or FDA to protect the general population, without considering their relevance to the nature of
the population of deployed forces and their applicability to the risk-assessment requirements depicted in
~ .' ~ ~
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THE NATURE OF RISK ASSESSMENT AND ITS APPLICATION TO DEPLOYED U.S. FORCES
55
Table 2. No doubt some of the information used to develop available occupational standards can be
used for assessing risks to deployed forces, but wholesale adoption of such standards without critical
reVleW Will lead to a wholly clltterent and tar less useful risk-assessment model. l he earlier point, that
deployed forces might not be similar in sensitivity to ordinary occupational cohorts, needs also to be
considered.
The U.S. Army Center for Health Promotion and Preventive Medicine (ACHPPM) has developed in
an undated draft form, a set of Short-Term Chemical Exposure Guidelines for Deployed Military
Personnel. These guidelines were developed for air and water contaminants, and are intended to cover
a range of exposure durations, from 1 hour to 14 days (air), and from 5 days to 2 weeks (water).
Considerable effort and thought has gone into the development of the guidelines, and ACHPPM has
drawn from the work of the NRC and other expert regulatory and scientific authorities. The guidelines
are, however, conceptually similar to regulatory standards, and do not present the more thorough dose-
response and long-term exposure information envisioned herein. It is, however, a possibly usable model
for yes-no decision-making.
ASSESSMENT OF EXPOSURES OF DEPLOYED FORCES
Using the Results of the Hazard and Dose-Response Evaluations (Table 2)
Referring to Figure 2, and the model proposed herein for decision-making (Model II), it can be seen
that it is now necessary to discuss the problem of assessing the exposures to stressors expected or
incurred by deployed forces. Health risks to be expected or incurred can be identified only if such an
exposure assessment can be completed. In effect, the purpose of the exposure assessment step is to
estimate the doses (Ds) of the stressor to be expected or incurred by forces under the circumstances of
deployment. Such estimates will allow risk managers to understand the extent and severity of the
expected health risk by reference to the proposed dose-response (Table 2~. A discussion of some of the
issues that need to be resolved to develop adequate exposure information for use in risk assessment, as
well as a discussion of the various options for risk-management decision-making, follows.
Measurement or Estimation of Doses
For some stressors of concern, analytical methods are or will be available to measure directly the
doses to which deployed forces might be exposed. In other cases, methods are or will be available to
measure concentrations of stressors in the various environmental media to which deployed forces might
be exposed; these measurements of concentrations might or might not be direct measurements of the
relevant doses, and means will have to be developed to convert concentration information to dose
information. The subject of the availability of reliable analytical methods for measuring stressor doses
or concentrations is not discussed in this paper. It is assumed that such methods are or will become
available. Without such methods, it will not be possible to understand the nature or magnitude of the
risks expected or incurred by deployed forces.
This paper is concerned, instead, with the methods for evaluating exposure information for purposes
of use in risk assessment. Two approaches to acquiring relevant dose estimates are available:
1. Estimation of doses expected to be incurred under various deployment scenarios, in advance of
deployment; and
2. Measurement of doses during deployment (real time measurement).
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56
STRATEGIES TO PROTECT THE HEALTH OF DEPLOYED U.S. FORCES: WORKSHOP PROCEEDINGS
Both of these approaches have value. The first can be used for planning purposes, and can guide risk
management on the stressors expected to be of greatest concern during specific deployments. The
second can provide direct measurement data during deployment; by quick reference to the dose-re-
sponse information, immediate knowledge of potential health risks can be acquired.
As previously discussed, there are some stressors that are so extremely hazardous that there
might be no practical means to ensure health protection of exposure were it to occur. For such
stressors, the exposure assessment would take the form of an estimation of the probability of
exposure expected under various deployment scenarios; the availability of such estimates would
allow appropriate safeguard planning in advance of deployment. The use of this approach for
some stressors falls within the framework for risk assessment proposed in this paper; it simply
recognizes the fact that exposures to certain extremely dangerous stressors must be prevented if
health is to be protected, and uses projected estimates of the probability of exposure as a guide to
risk management.
The Need for Commensurate Measurement of Dose
For each stressor it is necessary that the measurement of dose expected or incurred by deployed
forces be the same as that in which its risk information is presented in Table 2. Thus, the experts
involved in the estimation or measurement of doses need to have knowledge of the requirements for risk
assessment. In many cases there will be little difficulty meeting these requirements. Risk doses for
chemical contaminants of air, for example, will ordinarily be expressed in units of air concentration
times duration (c x t); analytical methods for such contaminants can readily provide the same data for
deployed forces. Similarly, the dose information for risks of contaminants of drinking water can be
expressed as drinking-water concentrations, based on the incorporation of knowledge of the daily water
consumption rates of deployed forces.
Food contamination presents a somewhat more difficult problem, because it might be difficult to
predict the specific dietary component that will become contaminated with a given stressor. Rates of
consumption of different components of the diet vary greatly, so that contamination of a greatly con-
sumed component at a given concentration of a stressor will result in a larger dose than does contamina-
tion (at the same concentration) of a little-consumed item. The most conservative approach for food is
one that assumes that each component of the diet constitutes the total daily diet, but such an approach
might lead to large overestimates of risk in many situations. Further discussion of the question of the
appropriate expressions of dose for food contamination will be necessary before the problem can be
resolved.
The greatest exposure assessment difficulty arises when a given stressor might contaminate all
environmental media. In those instances in which the dose-response evaluation demonstrates that
risks by one route of exposure are different from and independent of risks resulting from other
routes, then the problem is somewhat simplified, in that air exposures can be evaluated separately
from exposures through food and water (and possibly soil), as can dermal exposures. Even in this
simplified case, it will still be necessary to express risk doses as concentrations in food and water
(and perhaps soil) to ensure that the total oral dose from all sources can be estimated. Thus, data or
assumptions regarding relative rates of consumption of food and water will have to be incorporated
into the evaluation. Clearly, if risks are additive across all exposure routes, the problem is even
more difficult. The problem can be at this time only pointed out, but it cannot be resolved without
discussions among the risk-assessment experts during the evaluation of specific stressors (Lioy
1997).
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THE NATURE OF RISK ASSESSMENT AND ITS APPLICATION TO DEPLOYED U.S. FORCES
Risk Characterization and Decision-Making
57
Completion of the exposure assessment step for deployed forces provides the information necessary
to assess risks. At this stage, estimated Ds incurred by deployed forces are evaluated by reference to
Table 2 that is applicable to the stressor of concern. In the ideal, risk managers would have an
understanding of each of the risks faced by deployed forces in a given deployment situation and would
also have an understanding of the new risks that might arise should various actions be taken to alter the
circumstances of deployment. The availability of all this risk information would presumably allow the
best possible decisions, given the deployment circumstances and the alternatives available, to minimize
overall risks to health. The risk-assessment framework proposed here, although identical to that ordi-
narily used in regulations, is not intended to yield results that are used only to establish standards.
Rather, they are intended to give DOD decision-makers sufficient information to examine a range of
risks that might arise in rapidly changing deployment conditions, and to balance competing risks. It
recognizes that a simplistic yes-no decision-making model is inadequate to deal with the circumstances
under which forces are deployed, and that in many cases some risks will have to be incurred. The
framework offered here provides decision-makers sufficient understanding of the range of exposures
over which risks of differing severity might occur (Table 2), and thus maximizes the likelihood that the
most serious hazards can be avoided.
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STRATEGIES TO PROTECT THE HEALTH OF DEPLOYED U.S. FORCES: WORKSHOP PROCEEDINGS
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Representative terms from entire chapter:
hazard identification
