INTRODUCTION
Chemical mustard agents were first used as chemical warfare agents during World War I. Since then, there have been at least 12 confirmed and suspected uses of mustard agents; chemical mustard agents are believed to be the most frequently used chemical warfare agent [Sidell, et al., 1997] and [Dire, 2003]. Chemical agent attacks, as with other weapons of mass destruction attacks, pose several significant medical challenges. They may occur with little warning, may be hard to detect, and may be difficult to diagnose without medical intervention [North Atlantic Treaty Organization (NATO), 1999]. Therefore, it is extremely important for military forces to have a planning methodology that allows for the estimation of casualties that might result from these events.
To address this issue, the Human Response Injury Profile (HRIP) methodology was developed to improve Chemical, Biological, Radiological, and Nuclear (CBRN) casualty estimation capabilities for planning purposes. For purposes of this methodology, a human response model is defined as “that portion of the casualty estimation methodology which determines the effects of CBRN exposures on individuals. It calculates the type and severity of illness or injury suffered by individuals, as well as their subsequent death or recovery [NATO, 2010b].” HRIP relies on time-based progressions of underlying symptoms and their severity changes over time to determine user-defined casualty estimates from CBRN events. The purpose of this article is to describe one application of that methodology: the HRIP methodology to be used to estimate casualties resulting from exposure to sulfur mustard (HD, CAS 505-60-2, Bis(2-chloroethyl)sulfide).
The HRIP methodology provides the capability to estimate the time-dependence of the numbers of individuals wounded and killed, which aids in the development of medical and logistics requirements, acquisition, and planning. The methodology also characterizes the incidence of injury by severity, which may provide additional information to assist planners. Further, the HRIP methodology allows the user to define the casualty threshold-the severity at which casualties occur; this means that the user can determine the patient loads and how they might change as a function of injury (and symptom) severity. The methodology is designed to provide injury progressions for HD exposures likely encountered in battlefield scenarios [NATO, 1999].
Methodologies exist for estimating casualties as a result of HD exposure. While many of these approaches estimate casualties as a result of agent dose or effect, most do not provide information about when these casualties occur or how their numbers change over time. Additionally, the HRIP HD methodology incorporates injury as a function of time and severity and allows the user to define the casualty threshold.
At present, the HRIP HD methodology consists of the information necessary to estimate human response due only to the HD variant of mustard. Other chemical blister agents (such as Lewisite and the nitrogen mustards) may be incorporated into the model at a later time, as availability of data and necessity permit.
The methodology described is proposed solely for deliberative or crisis action planning purposes and does not account for real-time or dynamic (i.e., evolving exposure) use. Moreover, this methodology is not intended for any post-event uses, such as diagnosis, medical treatment, or epidemiology.
HRIP FUNDAMENTAL CONCEPT
The HRIP HD methodology is built upon three precepts: that the severity of symptoms can be expressed on a single uniform scale, regardless of the cause of the symptoms; that an HD-related injury can be described by a progression of symptoms over time (known as an injury profile); and that the casualty status of an injured individual can be directly related to the severity of symptoms manifest at any specified time. The fundamental concept of the HRIP methodology builds on these to state that an individual is considered a casualty at the time of first onset of injury-specific symptoms at or above a user-specified severity (or casualty) threshold.
METHODOLOGY DEVELOPMENT
The foundation of the HRIP HD methodology is the injury profiles. This section will describe the process by which these profiles were developed.
Beginning in the mid-1990s, the North Atlantic Treaty Organization (NATO) published a series of Allied Medical Publications on CBRN planning and casualty estimation, beginning with a nuclear volume. The nuclear human response and casualty estimation methodology was developed for the Intermediate Dose Program (IDP) and used signs and symptoms maps developed for four radiation dose ranges to calculate performance degradation ([Anno et al., 1989] and [Baum et al., 1984]); performance degradation was defined as the inverse of the increase in time required to complete specific military tasks following exposure [McClellan, 1998]. IDP provided the basis for the Defense Nuclear Agency Improved Casualty Estimation (DICE) methodology, which used a similar signs and symptoms-based performance degradation algorithm to estimate human response and casualties.
In developing the HRIP methodology for HD, the authors returned to the original IDP and DICE methodologies. Building on the underlying concepts of dose-based symptoms dictating the resulting casualties, the military's HD toxicity values, shown in Table 1, were utilized to develop new dosage ranges to represent clinically differentiable injury progressions as a function of dosage.
HD can affect humans through three main routes of exposure: inhalation, ocular, and percutaneous. HD vapor exposure alone will be considered for inhalation and ocular effects, but skin injuries are a consequence of exposure to both vapor and liquid HD. Vapor dosages and liquid doses are fundamentally different in that vapor dosages are expressed as a time-integrated concentration for a particular individual or group of individuals, whereas liquid doses are expressed as a mass of agent per 70 kilogram male (with all agent dose assumed to be received at one time).
To calculate percutaneous dosage to skin resulting from both vapor and liquid exposure, it is necessary to calculate an “equivalent” dosage to the skin from HD exposure. This is accomplished by applying a conversion factor to the liquid percutaneous dose to determine the equivalent percutaneous vapor dosage. The resulting calculated percutaneous vapor dosage is expected to produce the same symptoms as those received from the combined percutaneous vapor dosage and liquid dose. The conversion factor is calculated as the ratio of the vapor percutaneous ECt50 for severe effects to the liquid percutaneous ED50 for severe effects as shown in Equation 1 [McClellan, et al., 1998]:
where:
CFHD is the percutaneous HD liquid to equivalent vapor conversion factor [(mg-min/m3)/(mg/man)],
ECt50,severe (HD/PC/V) is the median vapor percutaneous severe toxicity (the dosage of vapor required to produce severe effects in 50% of exposed individuals) [mg-min/m3], and
ED50,severe (HD/PC/L) is the median liquid percutaneous severe toxicity (the dose of liquid required to produce severe effects in 50% of exposed individuals) [mg/man].
The severe ECt50/ED50 values were selected for use over those given for a lethal endpoint because the use of the lethal percutaneous ECt50/ED50 values may overestimate the severity of disease since the ratio of lethal percutaneous vapor dosage to lethal percutaneous liquid dose is very large. Using the median toxicity values given in Table 1, the resulting calculated conversion factor is 0.833 (mg-min/m3)/(mg/man). Using the conversion factor, the equivalent percutaneous HD vapor dosage is then calculated as shown in Equation 2:
where:
DHD,epc is the equivalent percutaneous HD vapor dosage [mg-min/m3],
DHD,pc is the percutaneous HD vapor dosage [mg-min/m3],
CFHD is the percutaneous HD liquid to equivalent vapor conversion factor of 0.833 [(mg-min/m3)/(mg/man)], and
DHD,l is the percutaneous HD liquid dose [mg/man].
Three sets of dosage ranges were developed: one each for inhalation vapor dosages, percutaneous vapor ocular dosages, and equivalent percutaneous vapor dosages. These dosage ranges, all expressed in mg-min/m3, are shown in Table 2.
Literature reviews were conducted to determine the physiological systems in which symptoms would manifest and cause an individual to seek medical treatment. Two representative physiological systems were chosen to represent the systems in which inhaled HD vapor would be expected to manifest: upper gastrointestinal and respiratory systems. One physiological system each was chosen for ocular vapor and equivalent percutaneous vapor: ocular and skin, respectively.
Symptoms anticipated for each physiological system were developed, and injury severity levels were associated with each set of symptoms assigned. The HRIP methodology is based on the concept of injury severity levels, which are distinguished by the magnitude of symptoms exhibited by affected individuals. Five injury severity levels are used in the HRIP methodology (see Table 3):
Each physiological system has only the number of injury severity levels necessary to achieve the maximum injury severity at which symptoms for that physiological system occur. Symptom severity levels for all four physiological systems are shown in Table 4. The respiratory and skin physiological systems require five symptom severity levels to describe the possible symptom manifestations following chemical HD exposure; as shown below, the ocular physiological system requires four, which the upper gastrointestinal system requires only three.
For each of the dosage ranges and routes of exposure, individual symptom progressions were generated for the relevant physiological systems. A symptom progression tracks the injury severity levels (on a scale from 0 to 4, as described above) over time in the physiological system (e.g., respiratory or ocular) in which the symptoms manifest rather than in the physiological system that causes the symptoms. The severity of symptoms and their times of onset depend on the dosage received and the route of exposure (inhalation, ocular, or percutaneous). For a given dosage range and exposure route, the symptom progressions for all of the representative physiological systems can be compared (or plotted together) to determine the highest injury severity level reached at each time point following exposure; these maximum injury severity level values, selected for each point in time as a function of all applicable physiological systems, represent the injury profile for that dosage range and exposure route. The general injury profile development process is summarized in Figure 1.
Symptom progressions and injury profiles, depicted graphically, were used in the development of the HRIP blister agent methodology and presented to subject matter experts for review and comment. The HRIP development process, the symptom progressions, and the injury profiles can be represented mathematically by the HRIP Methodology Development Functional Form, defined in Table 5.
HRIP MUSTARD AGENT METHODOLOGY IMPLEMENATION
The HRIP HD methodology consists of three sets of injury profiles shown in Figure 2 through 4: one each for inhalation vapor dosages, ocular vapor dosages, and equivalent percutaneous vapor dosages. Any scenario describing an HD attack will include a collection of individuals, each of whom will receive some combination of these three dosages. A set of these three values for each individual is required as input to the methodology as well as the time the HD exposure ends relative to some starting time (t0 typically taken as the time of the agent release). Given these inputs, the HRIP HD methodology can be used to estimate the casualty status of each individual. The methodology produces as output an aggregate casualty status over time for all the individuals contained in the scenario. The HRIP methodology itself consists of two components, as shown in Figure 5: “Human Response Estimation” and “Casualty Estimation and Reporting.” Each component will be described in turn below.
A. Human Response Estimation Component
The first component of the HRIP HD methodology, the human response estimation component, is used to estimate the response of individuals to a combination of inhalation vapor, ocular vapor, and equivalent percutaneous vapor dosages in terms of the type and severity of injury over time (i.e., the injury profile). This entails a three-step process: determination of inhalation vapor, ocular vapor and equivalent percutaneous vapor dosage ranges; assignment of the inhalation vapor, ocular vapor and equivalent percutaneous vapor injury profiles based upon those ranges; and combining those injury profiles into a single composite injury profile.
Step 1: Dosage Range Determination: The first step in the human response estimation process is to determine the inhalation vapor, ocular vapor, and equivalent percutaneous vapor dosage ranges for each individual according to the individual's dosage value for each route of entry. The three sets of dosage ranges are shown in Table 2.
Step 2: Injury Profile Assignments: Based upon an individual's dosage values, the three appropriate dosage range-based injury profiles are chosen.
Step 3: Composite Injury Profile Generation: Finally, the injury profiles associated with inhalation vapor, ocular vapor, and equivalent percutaneous vapor can be overlaid on the same graph. The composite injury profile is generated by selecting the maximum individual severity at each point in time on the overlain graph. For HD, the composite injury profile is used to determine if and when individuals become KIA, WIA and (with one exception) DOW.
Example: To demonstrate the creation of a composite injury profile, consider, as an input to the HRIP methodology, individuals who receive a notional vapor dosage of 400 mg-min/m3 and an equivalent percutaneous dosage of 150 mg-min/m3. An inhalation vapor dosage of 400 mg-min/m3 would place the individuals into the “[250, 1200) mg-min/m3” dosage range. An ocular vapor dosage of 400 mg-min/m3 would place the individuals into the “>100mg-min/m3” dosage range. Finally, an equivalent percutaneous dosage of 150 mg-min/m3 would put the individuals into the “[125, 180) mg-min/m3” dosage range. The corresponding injury profiles are then chosen and overlaid onto a single plot (figure 6). The composite injury profile (figure 7) is generated by selecting the maximum severity level at each point in time in Figure 6.
B.Casualty Estimation and Reporting Component
For the purposes of the HRIP HD methodology, a chemical casualty is defined as any person who is lost to his organization by reason of having been declared dead or wounded as a result of exposure to a chemical agent [NATO, 2002]. The HRIP HD methodology estimates three classes of casualty: individuals killed in action (KIA), individuals wounded in action (WIA), and individuals who died of wounds (DOW). A KIA is defined as “a battle casualty who is killed outright or who dies as a result of wounds or other injuries before reaching a medical treatment facility [NATO, 2010a]” and may also be referred to as a “prompt fatality.” A WIA is “a battle casualty other than ‘killed in action’ who has incurred an injury due to an external agent or cause [NATO, 2010a].” Finally, a DOW is “a battle casualty who dies of wounds or other injuries received in action, after having reached a medical treatment facility [NATO, 2010a]” and may also be referred to as a “delayed fatality.” The methodology only considers acute injuries which manifest within the time period during which operational and medical estimates are made (typically, 45 days or less).
The primary output of the human response estimation component of the HRIP methodology is one or more composite injury profiles and the number of people for whom each composite injury profile applies. This information is used to determine casualty status as categorized by KIA, WIA, and DOW and to compile the resulting casualty estimates in a manner useful to the planner. The general criteria for use in the casualty estimation process are shown in Table 6.
Because the definitions of KIA and DOW rely on reaching a medical treatment facility, the first step in the casualty estimation process is defining the minimum time at which this can occur, measured relative to time, t0 (usually defined as the start of the event that results in exposure). In most cases, the time to reach a medical treatment facility will be assumed to be a fixed time and one that is the same for everyone in the scenario.
Because the estimation of WIA relies on the user-selected casualty threshold, the next step in the casualty estimation process is establishing the injury severity level that would result in an individual becoming a loss to the unit. Again, this value is the same for everyone in the scenario. Note that the casualty threshold chosen can be no higher than Injury Severity Level 3 as Injury Severity Level 4 leads to death.
With these two values established, the casualty estimation process turns to the estimation of KIA, DOW, and WIA.
KIA/DOW Estimation: An individual can only be assessed as KIA during the time it takes to reach a medical treatment facility. An individual who dies after reaching a medical treatment facility is classified as a DOW. Before becoming a DOW, an individual would have previously been designated as a WIA.
An individual is classified as a KIA only if the composite injury profile reaches Injury Severity Level 4 and remains there for fifteen minutes prior to reaching a medical treatment facility. An examination of the injury profiles indicates that the earliest an individual could become a fatality is more than 2 days (48.25 hours) post-exposure, suggesting that—unless a very long time is required to reach a medical treatment facility—no individuals will be classified KIA as a result of HD exposure. For an individual to be classified as a DOW one of two criteria must be true: 1) the composite injury profile reaches Injury Severity Level 4 and remains there for fifteen minutes after reaching a medical treatment facility, or 2) the individual is exposed to percutaneous HD liquid in excess of 1400 mg.
Percutaneous Liquid Threshold and DOW: Exposure to large quantities of percutaneous liquid HD results in physiological damage to the bone marrow and eventual death, in excess of the injury described by the equivalent vapor percutaneous injury profiles. To account for this injury, subject matter experts recommended assuming that individuals receiving a percutaneous HD liquid dose in excess of 1400 mg will die at 2 weeks (336 hours) following exposure. Therefore, unless they have not been declared DOWs (or KIAs) before this time, individuals exposed to 1400 mg or more of percutaneous HD liquid will be declared DOWs at 336 hours.
WIA Estimation: An individual not already classified as a KIA is considered to be a WIA once the individual's injury severity level is at or exceeds the user-defined casualty threshold. WIAs are estimated using the composite injury profiles: an individual becomes a WIA at the point in time at which the severity of the composite injury profile—and therefore of any one of the physiological symptoms—reaches the casualty threshold. In other words, if the injury profile severity at some time t is greater than or equal to the specified casualty threshold, then the individual is a classified as a WIA at time t.
Casualty Estimation Examples: Two examples will be used to illustrate the casualty estimation process. In all cases, the time to reach a medical treatment facility will be set to 30 minutes after exposure to the HD agent has been completed.
Example 1. The first example looks (again) at individuals who receive an inhalation vapor dosage of 400 mg-min/m3, an ocular vapor dosage of 120 mg-min/m3, and an equivalent percutaneous vapor dosage of 150 mg-min/m3. Furthermore, the individuals’ exposure to the HD ends 15 minutes after the agent is released (t0). The composite injury profile for these individuals is shown in Figure 8.
Because of the time progression of the injury profile severity, the individuals would be classified as WIA less than one hour post-exposure (or less than 1.25 hours after agent release) if WIA(1) was chosen as the casualty threshold. The individuals would be classified as WIA at three hours post-exposure (or 3.25 hours after agent release) if WIA(2) (Injury Severity Level 2 or higher) was chosen as the casualty threshold. The individuals would be classified as WIA at 11 hours post-exposure (11.25 hours after agent release) if WIA(3) (Injury Severity Level 3 or higher) was chosen as the casualty threshold. Finally, because Injury Severity Level 4 is reached at 72 hours, the individuals would be classified as DOW 72.25 hours post-exposure (or 72.5 hours after agent release).
Example 2. In a second example, individuals receive an inhalation vapor dosage of 80 mg-min/m3, an ocular vapor dosage of 120 mg-min/m3, an equivalent percutaneous vapor dosage of 1450 mg-min/m3. As part of their whole body exposure, they are exposed to 1500 mg of percutaneous HD liquid. Again, their exposure to HD ends 15 minutes after agent release. The composite injury profile for this case is shown in Figure 9.
Because of the time progression of the injury profile severity, the individuals would be classified as WIA at 2, 3, or 11 hours post-exposure (i.e., 2.25 hours, 3.25 hours, or 11.25 hours after agent release), depending on whether WIA(1), WIA(2), or WIA(3), respectively, were chosen as the casualty criterion. Finally, because the individuals were exposed to more than 1400 mg of percutaneous HD liquid, they would be classified as DOW at 2 weeks after the agent is released.
Casualty Summation: The final step in the casualty estimation process is summarizing and reporting the casualty estimate. The methodology provides four types of output: population at risk (PAR), rates, profile, and flow. PAR is simply the total number of troops included in the scenario characterization. Rates provide the number of new casualties (KIA, WIA, and DOW) per 100 of the PAR each day. The profile demonstrates how the number of new casualties changes over time. Finally, the flow characterizes the movement between casualty categories (e.g., from WIA to DOW). An illustration of a notional casualty estimate is provided in Table 7. This table shows rates for new individuals meeting the casualty criterion of WIA(1) (Injury Severity Level 1 or higher), and further categorizes the rates by the injury severity level of individuals at the time at which they become casualties. Note that Table 7 does not provide information about the progression of injury after the casualty criterion is met, although users could use the provided information to show injury progression, if so desired.
HRIP Implementation Functional Form: The mathematical representation of the HRIP methodology implementation is shown in Table 8.
ASSUMPTIONS AND LIMITATIONS
The HRIP HD methodology includes a number of assumptions and limitations. The assumptions enable the utilization of data and concepts previously established for other methodologies to be incorporated into the current methodology. Ideally, they also make the representations and estimation of casualties easier for planners to use and understand. The limitations scope the applicability of the model and describe its intended uses.
The model assumes that prior to exposure, individuals are healthy. In other words, individuals have no pre-existing symptoms and no pre-existing physiological conditions that would be expected to alter human response or contribute increased risk factors.
The model assumes that all cumulative dosages and doses are the function of 2-minute exposures, independent of the actual duration of exposure. Input dosages and doses from exposure modeling tools would, in actuality, be of varying lengths. To simplify calculations and the derivation of dosage ranges, however, a 2-minute exposure is assumed. Further, it is assumed that human response and the associated injury profile begin at the completion of the exposure.
Following from the previous assumptions, the methodology assumes a toxic load exponent of one or, in simpler terms, assumes that Haber's Law applies. If the concentration exposures were of varying lengths, toxic load studies indicate that some variation in the onset time and severity of human response would occur; variations would depend on the agent and the period of exposure.
It is assumed that the median individual represents the unit's response. Distributions of dosage-related effects are not modeled.
The symptom progressions and injury profiles assume exposure to a 70 kilogram man, breathing 15 liters per minute. As toxicity effects values are usually expressed in gram of agent per kilogram individual and then extrapolated to a 70 kilogram man, changes to this assumption could require recalculation of existing injury profiles.
Additionally, the injury profiles for multiple routes of exposure are assumed to be non-synergistic. Although the interaction of human response resulting from exposure to inhaled HD and percutaneous HD may result in higher injury severity than result from any single route of exposure alone, there is currently insufficient information to determine in detail the extent to which injury severity might be expected to change over time under these conditions.
The physiological systems from which the injury profiles were derived do not necessarily represent all the systems that might be affected by exposure to HD. Rather, they represent those systems for which symptoms would be expected to cause individuals to seek medical attention: i.e., those that were expected to manifest symptoms earliest and at the highest severity. There may be other symptoms, of a lesser medical significance or severity or which manifest later, which are not described as they would not be expected to impact the casualty estimate.
Medical countermeasures and medical treatments are not addressed—all symptom progressions and injury profiles assume no medical intervention. While medical countermeasures may be available, limited data are available to suggest how general human response would change as a function of the use of these medical countermeasures. Further, since medical treatment is highly dependent on several factors, including the severity and combination of symptoms, the time of treatment, and the ratio of individuals to be treated to available medical resources; the model does not attempt to account for this complex impact on human response. The addition of treatment would likely change an individual's prognosis, but would not be expected to change the time when the individual seeks medical treatment in the first place.
The methodology does not address several types of casualties. For example, psychological casualties are not currently included in the model due to lack of information regarding methods of estimating the numbers and types of psychological casualties that might occur. Secondary, higher order, and indirect casualties and secondary infections/diseases also are not modeled. Secondary casualties are scenario dependent; the actions an individual was participating in, as well as the individual's environment, prior to exposure will contribute to the possibility of secondary casualties after exposure. For example, pedestrians hit by a truck driven by an individual suffering from HD symptoms would be considered secondary casualties. Secondary infections/diseases include opportunistic infections. Although these are risks, limited data exist to support including this category of casualty in the model at this time.
Finally, the methodology does not attempt to account for recovery, either with or without medical countermeasures or medical treatment.
CONCLUSIONS
The HRIP methodology provides a process for describing human response over time resulting from an HD attack and utilizing this information to estimate personnel status, including KIA, WIA, and DOW. The HRIP methodology is designed to support medical, operational, and logistical planners in preparations for casualty-causing events.
The HRIP HD methodology serves as a casualty estimation tools for planning purposes. It provides linkages from symptomatology at the level of individual physiological systems to the determination of casualty status. This will make it easier to modify the underlying data as warranted by future research. The methodology also allows the planner the ability to set the criteria for determining when individuals become casualties—by setting the injury severity level at which individuals become WIA. Finally, this methodology estimates casualties over time, allowing medical planners to estimate the flow of incoming patients and fatalities in the days and weeks following a CBRN event.
This methodology has been incorporated into the proposed Allied Medical Publication 8(C), North Atlantic Treaty Organization (NATO) Planning Guide for the Estimation of Chemical, Biological, Radiological, and Nuclear (CBRN) Casualties and has also been briefed to the U.S. military and federal government agencies for consideration. The next steps include considering changes necessary to expand the methodology for civilian casualty estimation and planning.
tables
Table 1. HD median toxicity and probit slope values* [go to text reference]
| Endpoint or Symptom | Median Toxicity (mg-min/m3 or mg) | Probit Slope | |
| Vapor | Ocular Mild | 25 | 3 |
| Ocular Severe | 75 | 3 | |
| Inhalation Lethal | 1,000 | 6 | |
| Percutaneous Mild | 50 | 3 | |
| Percutaneous Severe | 500 | 3 | |
| Percutaneous Lethal | 10,000 | 7 | |
| Liquid | Percutaneous Severe | 600 | 3 |
| Percutaneous Lethal | 1,400 | 7 | |
The median toxicity values represent the vapor dosage or liquid dose at which 50% of the population would be expected to experience applicable symptoms (i.e., ocular miosis, lethality). The probit slope explains the change in probability of the specific effect; the higher the number, the steeper the slope, the smaller range in doses or dosages producing effects in 10% to 90% of the population. The median toxicity and probit slope values were used to calculate the dosage ranges shown below in Table 2.
* Multiservice Publication, FM 3-11.9/MCWP 3-37.1B/NTRP 3-11.32/AFTTP(I) 3-2.55, Potential Military Chemical/Biological Agents and Compounds. January 2005.
Table 2. Dosage ranges (mg-min/m3) for HD [go to text reference]
| Inhalation vapor | < 50 | [50, 70) | [70, 100) | [100, 150) | [150, 250) | [250, 1200) | ≥1200 |
| Percutaneous Vapor (Ocular) | < 4 | [4,26) | [26, 50) | [50, 70) | [70, 100) | ≥100 | |
| Equivalent Percutaneous Vapor | < 12 | [12, 125) | [125, 180) | ≥180 | |||
| Range Reference Number | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
Three sets of dosage ranges, representing three routes of exposure—inhalation, ocular, and percutaneous—are used to describe the dosage-dependent injury progressions following exposure to HD vapor (and percutaneous liquid exposure).
Notation: [50, 70) mg-min/m3 is the notation for the mathematical interval equal to the set of exposure values for which exposure is greater than or equal to 50 mg-min/m3 and less than 70 mg-min/m3. The notation is as defined by The Chicago Manual of Style. http://www.chicagomanualofstyle.org/16/ch12/ch12_sec030.html, accessed 17 November 2010.
Table 3. Injury severity levels—definitions [go to text reference]
| Severity | Degree | Description |
| 0 | No Observable Effect | Although some exposure to an agent or effect may have occurred, no observable injury (as would be indicated by manifested symptoms) has developed. |
| 1 | Mild | Injury manifesting symptoms of such severity that individuals are able to care for themselves or be helped by untrained personnel; condition may not affect ability to conduct the assigned mission. |
| 2 | Moderate | Injury manifesting symptoms of such severity that medical care may be required; general condition permits treatment as outpatient and some continuing care and relief of pain may be required before definitive care is given; condition may be expected to interrupt or preclude ability to conduct the assigned mission |
| 3 | Severe | Injury manifesting symptoms of such severity that there is cause for immediate concern but there is no imminent danger to life; individual is acutely ill and likely requires hospital care. Indicators are questionable–condition may or may not reverse without medical intervention; individual is unable to conduct the assigned mission due to severity of injury |
| 4 | Very Severe | Injury manifesting symptoms of such severity that life is imminently endangered. Indicators are unfavorable–condition may or may not reverse even with medical intervention; prognosis is death without medical intervention; individual is unable to conduct the assigned mission and is unexpected to return to the mission due to severity of injury |
Five injury severity levels, distinguished by the magnitude of symptoms exhibited by affected individuals, provide the basis for the HRIP methodology
Table 4. Sample symptom severity levels associated with HD exposure [go to text reference]
| Severity | Respiratory | Ocular | Skin | Upper Gastrointestinal |
| 0 | No observable effect | No observable effect | No observable effect | No observable effect |
| 1 | Mild shortness of breath; tight chest, coughing, and runny nose (rhinorrhea) | Irritation with eye pain; conjunctival erythema and/or edema | Skin sensitive to touch in crotch, armpits, and on inside of elbow and knee joints | Upset stomach and nausea; watering mouth and frequent swallowing to avoid vomiting |
| 2 | Frank shortness of breath; difficult to breathe, wheezing breath, respiratory congestion, bronchorrhea | Eye pain and/or irritation with conjunctival erythema and/or edema; blepharospasm; difficulty opening the eyes; sensitivity to light | Skin sore in crotch, armpits, elbow and knee joints, and painful when moving, red swollen skin, tiny blisters on hands and neck | Episodes of vomiting, possibly including dry heaves; severe nausea and possibility of continued vomiting |
| 3 | Severe dyspnea | Severe eye inflammation and pain leading to an inability to open the eyes | Skin raw and painful in crotch, armpits, elbow and knee joints, red swollen body skin, large blisters on hands and neck | |
| 4 | Breathing stops completely or struggling to breathe; prostration | Skin sloughage after blisters or swollen skin |
Symptoms from HD exposure resulting in injuries requiring medical attention are anticipated in four physiological systems. Each physiological system is represented by the number of symptom severity levels necessary to describe the maximum injury severity at which symptoms for that system occur.
Table 5. HRIP methodology functional form [go to text reference]
The HRIP development process, the symptom progressions, and the injury profiles can be represented mathematically by the HRIP Methodology Development Functional Form.
Table 6. Casualty estimation process general criteria [go to text reference]
| Severity | Degree | Description |
| 0 | No Observable Effect | Although some exposure to an agent or effect may have occurred, no observable injury (as would be indicated by manifested symptoms) has developed. |
| 1 | Mild | Injury manifesting symptoms of such severity that individuals can care for themselves or be helped by untrained personnel; condition may not impact ability to conduct the assigned mission. |
| 2 | Moderate | Injury manifesting symptoms of such severity that medical care may be required; general condition permits treatment as outpatient and some continuing care and relief of pain may be required before definitive care is given; condition may be expected to interrupt or preclude ability to conduct the assigned mission |
| 3 | Severe | Injury manifesting symptoms of such severity that there is cause for immediate concern but there is no imminent danger to life; individual is acutely ill and likely requires hospital care. Indicators are questionable–condition may or may not reverse without medical intervention; individual is unable to conduct the assigned mission due to severity of injury |
| 4 | Very Severe | Injury manifesting symptoms of such severity that life is imminently endangered. Indicators are unfavorable–condition may or may not reverse even with medical intervention; prognosis is death without medical intervention; individual is unable to conduct the assigned mission and is unexpected to return to the mission due to severity of injury |
The HRIP casualty estimation process determines the status of personnel over time based on the injury profiles output from the human response estimation component and the criteria, including minimum times and casualty severity thresholds, for KIA, WIA, and DOW.
Table 7. Estimated casualty rates for notional chemical HD attack (per 100 per day) [go to text reference]
| Estimated Casualty Rates | Day 1 | Day 2 | Day 3 | Day 4 | Day 5 | Day 6 | Day 7 | Day 15 | Day 30 |
| Prompt Fatalities (KIA) | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Delayed Fatalities (DOW) | 0 | 0 | 0.12 | 0.98 | 2.33 | 3.43 | 3.68 | 11.03 | 0.25 |
| Total Fatalities | 0 | 0 | 0.12 | 0.98 | 2.33 | 3.43 | 3.68 | 11.03 | 0.25 |
| Mild Casualties | 0.37 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Moderate Casualties | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Severe Casualties | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Total Wounded | 0.37 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
This table shows the rates for new casualties, for a casualty threshold of WIA(1), and fatalities over time. With HD, all casualties occur within the first day post-exposure, however, fatalities may be stretched over several days depending on the route of exposure leading to fatality.
Table 8. HRIP methodology implementation functional form [go to text reference]
The HRIP implementation process and the estimation of casualties can be represented mathematically by the HRIP Methodology Implementation Functional Form.
Figure 6: Injury profiles for inhalation vapor dosage of 400 mg-min/m3, ocular vapor dosage of 120 mg-min/m3, and equivalent percutaneous dosage of 150 mg-min/m3 [go to text reference]
Figure 7: Composite injury profile for inhalation vapor dosage of 400 mg-min/m3, ocular vapor dosage of 120 mg-min/m3, and equivalent percutaneous dosage of 150 mg-min/m3 [go to text reference]
Figure 8: Composite injury profile for inhalation vapor dosage of 400 mg-min/m3, ocular vapor dosage of 120 mg-min/m3, and equivalent percutaneous vapor dosage of 150 mg-min/m3 [go to text reference]
Figure 9: Composite injury profile for inhalation vapor dosage of 80 mg-min/m3, ocular vapor dosage of 120 mg-min/m3, and equivalent percutaneous vapor dosage of 1450 mg-min/m3 [go to text reference]
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