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