A. Background

In 1996, the Central Intelligence Agency (CIA) published a report examining the release of chemical warfare agents from Muhammadiyat in which the CIA concluded the potential hazard area from possible chemical releases did not reach US forces.^[2] In a subsequent analysis of this report, the CIA and other reviewers pointed out improvements we could make with weather and dispersion modeling, and details about the chemical warfare agent released—amount of agent involved, agent purity, date and time of release, etc. On November 2, 1996, the Department of Defense (DoD) requested the Institute for Defense Analyses (IDA) to convene an independent panel of experts in meteorology, physics, chemistry, and related disciplines^[3] to review the computer modeling related to the Khamisiyah investigation. The IDA panel recommended using some non-DoD models and a combination of models to compensate for deficiencies in the initial modeling.^[4]

Because these suggestions would improve DoD’s modeling methodology, the Special Assistant to the Deputy Secretary of Defense for Gulf War Illnesses promised the Congress to examine the possible release at Muhammadiyat using meteorological and multiple dispersion models (as recommended by the IDA panel).^[5] We formed an investigation and analysis team to evaluate the possible exposure of Gulf War veterans as an indirect result of Coalition air attacks against Iraq’s chemical and biological weapons facilities. The team’s initial effort focused on the air war’s overall planning process and execution including the air attacks on Iraq’s facilities at Ukhaydir, Al Muthanna, and Muhammadiyat. After the war, United Nations Special Commission on Iraq (UNSCOM) inspectors discovered chemical weapons that had leaked at the latter two sites. We have published an Information Paper on modeling and simulation in planning the air war,^[6] and Case Narratives on both Ukhaydir^[7] and Al Muthanna.^[8] This narrative examines the possibility that air attacks on Iraq’s Muhammadiyat ammunition storage site exposed Gulf War veterans to chemical warfare agents, and if so, assesses the possibility of exposure.

To support our re-modeling, the DoD and CIA jointly re-analyzed in detail the characteristics of the chemical warfare agent released at Muhammadiyat, including the amount of agent involved, agent purity, date and time of release, etc., collectively called the source characterization. The re-analysis included studying UNSCOM photography and inspection reports, interviews, and information not available at the time of the 1996 CIA report. The re-analysis estimated a slightly smaller nerve agent release, but a mustard agent release nearly twice as large as the 1996 CIA report estimated.

This narrative uses the DoD-CIA’s most recent assessment of the source characterization for the agent released at Muhammadiyat and follows IDA guidance by using additional meteorological and dispersion models to estimate the extent of potential hazard areas. Consequently, we used several well-accepted models that treat inputs slightly differently and produce similar but not identical hazard areas. Combining the resulting hazard areas gives a greater insight about the extent of a possible hazard, and, therefore, of the extent of possible veterans’ exposures. This analysis should better estimate the release of chemical warfare agent at Muhammadiyat and US forces’ possible exposure. Tab F contains more detail on our modeling methodology for Muhammadiyat.

1. Pre-Campaign Considerations

Coalition forces recognized Iraq’s nuclear, biological, and chemical (NBC) program as a serious threat during Desert Storm. Therefore, Coalition planners intended to destroy weapons research installations, production facilities, and delivery vehicles. Because of Iraq’s elaborate efforts to hide its NBC programs, Coalition forces were uncertain about exactly where Iraq located these facilities and delivery vehicles.^[9]

Initially, the Coalition identified eight NBC targets for attack during the Desert Storm air campaign, "Instant Thunder." By January 15, 1991, the NBC list grew to 23 targets. Although the NBC target list originally included Iraq’s Scud missile locations, by December 18, 1990, planners moved the Scuds into a separate target category.^[10] During the war, planners generated many lists of suspected chemical warfare sites—the result of different groups analyzing available information. It is unlikely anyone was absolutely certain chemical weapons were at these sites. However, Coalition planners included suspected storage locations on the targeting lists.^[11]

Coalition aircraft began attacking Iraq’s chemical warfare targets on the first day of the air offensive^[12] and these attacks continued throughout the 43-day air campaign, for 990 total attacks against suspected NBC-related research, production, and storage facilities.^[13] It is unclear whether planners had identified Muhammadiyat as a chemical weapons storage site before the war, but message traffic suggests that once Desert Storm began they believed Muhammadiyat contained chemical weapons and possibly Scud warhead canisters.^[14] Regardless of whether planners targeted Muhammadiyat because it was a suspected chemical weapon storage site or because it was an ammunition and Scud depot, Coalition forces bombed it repeatedly throughout the Gulf War.

2. Description of the Muhammadiyat Site

After the Gulf War, Iraq declared its Muthanna State Establishment (MSE)—which it also called the State Enterprise for Pesticide Production—as its sole chemical weapon research, development, production, and filling organization. The MSE consisted of the production complex at Al Muthanna, the three production sites in Al Fallujah, and the munitions stores at Muhammadiyat.^[15] Iraq also stored some chemical weapons and bulk agents at Al Muthanna.

The Muhammadiyat ammunition depot (latitude, 33°15’ north, longitude, 42°41’ east) is approximately 95 miles west of Baghdad (Figure 2) and covers about 12 square miles. In separate fenced areas, the depot contained earth-covered bunkers in the southern section and metal-frame warehouses in the northern section (Figure 3).^[16] Iraq stored weapons produced at Al Muthanna at the Muhammadiyat depot. Before Desert Storm, empty weapons repeatedly moved from Muhammadiyat to Al Muthanna for filling, back to Muhammadiyat for storage, and eventually out of Muhammadiyat to army and air force sites. Due to this movement and the damage Coalition bombing caused, Iraq and UNSCOM found it difficult to accurately re-create the Muhammadiyat’s weapons inventory at the start of the Gulf War—thereby complicating our efforts to determine how much agent Coalition bombing released.^[17]

Figure 2. Muhammadiyat was part of Iraq's Al Muthanna State Establishment.

Figure 3. Muhammadiyat site layout

Pre-Gulf War intelligence, dating to the Iran-Iraq War, indicated Iraq typically stored chemical weapons in concrete storage bunkers with approximately 500 square meters of floor space, which could store about 200 500-kilogram bombs.^[18] However, at Muhammadiyat, Iraq stored both chemical and conventional weapons in metal-framed warehouses (Figure 4). Additionally, Iraq dispersed the chemical weapons at Muhammadiyat throughout the chemical weapons’ storage area in open areas between the warehouses.^[19]

An UNSCOM inspection team (UNSCOM 20^[20] ) visited Muhammadiyat on October 30 and 31, 1991, and found evidence of chemical weapons stocks and chemical warfare agent contamination in the separately fenced northeastern section that consisted of 40 warehouses (Figure 5). The UNSCOM team also found munitions between several of the warehouses.^[21]

Figure 4. Typical storage warehouse in Muhammadiyat's chemical weapons storage area

Figure 5. Muhammadiyat chemical weapon storage area showing location of warehouses, chemical warfare bombs, and hazard sites

B. Air Campaign Against Muhammadiyat

A variety of Coalition aircraft—F-15s, F-16s, F-111s, A-6s, FA-18s, B-52s, and British Tornadoes began attacking Muhammadiyat on the air campaign’s third day (January 19, 1991), and periodically through February 24, 1991. According to mission reports, Coalition forces successfully bombed Muhammadiyat using at least 42 precision-guided munitions and more than 1200 unguided, conventional munitions, saturating sections of the storage area.^[22] Tab E summarizes the Coalition air strikes on Muhammadiyat that possibly damaged the chemical weapons stored there, and we briefly describe how we identified these strikes.

Figure 6. US Air Force F-111s like this one attacked several targets at Muhammadiyat.

C. Bomb Damage Assessment

The Defense Threat Reduction Agency’s^[23] Weapons Effects and Performance Data Archival^[24] database contains only a few strike videos of the Muhammadiyat raids, compared, for instance, to the large number of existing videos of attacks on Al Muthanna. The only videos available for Muhammadiyat were from a small number of successful F-111 attacks.^[25] F-111 aircrews routinely used video recorders^[26] to preserve the history of their attacks against Iraq’s targets, whereas Navy attack crews used their videos for post-mission critique and then routinely re-used their videotapes, recording over their previous strike videos,^[27] thereby destroying the video record of what targets they struck and when.

UNSCOM found leaking munitions and ground contamination at several Muhammadiyat locations. Since a wide variety of aircraft struck this target, we correlated particular strikes with the contaminated areas to determine chemical warfare agent release dates. Then we modeled weather patterns for dates when any chemical warfare agent contamination could have occurred. The scarcity of strike videos complicated this task.

During their inspection at Muhammadiyat in October 1991, UNSCOM 20 inspectors took still photographs and videos showing the damage and destruction to chemical munitions at the site; these visual records were essential in determining the number and type of munitions destroyed. However, these UNSCOM pictures taken months after the bombing attacks did not help us determine precise dates for the chemical warfare agent release.

D. Chemical Weapons Found at Muhammadiyat After the War

The devastation at Muhammadiyat was considerable, with almost all structures in the chemical weapons storage area damaged or destroyed. Figure 7 shows some of the damage Coalition bombing inflicted. Destroyed munitions covered much of the storage area, and mustard agent contaminated several areas.

Figure 7. Some of the damage to Muhammadiyat caused by Coalition bombing; arrows show damage or destroyed warehouses.
(Warehouse not marked by arrow was damaged several years prior to the war.)

In various declarations after the war, Iraq claimed it stored sarin-cyclosarin-filled DB-2 aerial bombs, mustard-filled 250-gauge and 500-gauge bombs, and mustard-filled 155mm artillery shells at the site (Table 1). At Muhammadiyat, UNSCOM 20 inspectors found mustard-filled 250-gauge and 500-gauge bombs, and sarin-cyclosarin-filled DB-2 bombs, almost all of them outside buildings. UNSCOM 20 recommended destroying burned and leaking bombs of chemical warfare agent at the site, and moving intact chemical weapons to Al Muthanna for destruction—objectives UNSCOM 38 accomplished in 1993. After UNSCOM 38 completed this work, inspectors did not return to Muhammadiyat until February 7, 1998, when they returned to try to verify Iraq’s new assertions that the Coalition bombing had destroyed 550 mustard-filled 155mm artillery rounds. Supposedly, Iraq stored these rounds between buildings in the facility. On examining the locations, inspectors found the remains of about 15 to 20 155mm artillery rounds. Iraq later retracted its declaration that Coalition bombing destroyed 550 155mm mustard-filled rounds at Muhammadiyat.^[28] We do not believe Iraq stored any sarin-filled 122mm rockets or mustard-filled 130mm artillery shells at Muhammadiyat despite Iraq’s claims in the first Full, Final, and Complete Disclosure because no UNSCOM team uncovered any evidence of storage of these munitions there.

E. Iraq’s Chemical Weapon Declarations

United Nations’ Resolution 687 required Iraq to declare the locations, amount, and types of all chemical weapons and agents, as well as all related research, development, support, and manufacturing facilities.^[29] Fully analyzing Iraq’s compliance, or lack thereof, with United Nations’ Resolution 687 is outside this investigation’s scope. Nevertheless, Iraq’s incomplete and occasionally contradictory disclosures provide an analytical basis, and in some cases, the only data from which to work. Table 1 summarizes Iraq’s declarations and disclosures of chemical weapons and UNSCOM’s discoveries at Muhammadiyat. Dashes in the table indicate that the document or inspection did not address the particular chemical munitions in question.

Table 1. Summary of information UNSCOM collected about chemical weapons
deployed and/or destroyed at Muhammadiyat^[30]

(a) FFCD - Full, Final, and Complete Disclosure
(b) Iraq’s declaration to UNSCOM 38: "Number of munitions at Muhammadiyat credited as destroyed due to direct results of Coalition bombings during the Gulf Conflict or damage to munitions and storage facilities rendering them too dangerous to dispose of"
(c) Declared as stored but not declared as destroyed
(d) This number 116 is possibly Iraq’s attempt to balance its chemical weapons inventory accounts, and is not an accurate number of the quantity of mustard-filled 500-gauge bombs destroyed

In its first declaration after the war (1991/1992), Iraq disclosed it used the Muhammadiyat facility as a chemical weapons storage site, with 200 DB-2 bombs and 200 mustard-filled 250-gauge bombs destroyed or damaged by bombing. Table 1 shows Iraq’s subsequent declarations on the type and number of munitions destroyed at Muhammadiyat varied drastically from these initial numbers. The imprecision of Iraq’s declarations complicated joint DoD-CIA efforts to determine exactly what chemical munitions Coalition bombing destroyed.

F. Current Estimate of Weapons Damaged or Destroyed at Muhammadiyat

In addition to Iraq’s contradictory declarations, the extensive damage resulting from the bombing at Muhammadiyat made it difficult to determine exactly what weapons Coalition forces destroyed. Table 2 summarizes our conclusions about the number and types of weapons destroyed at Muhammadiyat. DoD and CIA jointly developed the data from Iraq’s declarations, documents UNSCOM collected, UNSCOM inspection reports and photography, and discussions with UNSCOM inspectors.

Table 2. Assessment of maximum number of munitions releasing agent at Muhammadiyat

1. DB-2 Bombs

Based on Iraq’s declarations and UNSCOM inspections, we believe that at most 12 DB-2 aerial bombs filled with sarin and cyclosarin nerve agents were at Muhammadiyat. UNSCOM inspectors found nine of them. In analyzing UNSCOM photography, we determined seven of the nine bombs leaked. It is tempting to dismiss the three unaccounted-for bombs from our calculations, but we assumed they too released agent. Consequently, we assumed 10 bombs released agent—the seven leaking bombs UNSCOM inspectors found and the three missing bombs.^[35] By assuming that the three unaccounted for bombs released agent, we have increased the amount of agent released into the atmosphere, resulting in a larger hazard area.

We also recognize it is possible Coalition bombing destroyed no DB-2s and the DB-2s found at Muhammadiyat were part of a deception program. UNSCOM 20 inspectors were suspicious of Iraq’s damage claims. The inspectors believed some of the damage declared by Iraq actually occurred after the war and Iraq possibly had moved weapons from other unidentified sites to Muhammadiyat. Based on intelligence information, Iraq moved the DB-2s after the bombing campaign and before UNSCOM 20’s inspection to several locations where UNSCOM inspectors found them. It is possible Iraq scattered several bombs around the site in an effort to support its 1991 declaration of 200 filled DB-2 bombs and deceive the inspectors. In subsequent declarations to UNSCOM, Iraq modified its count to 12 DB-2 bombs, when it either realized it could no longer support its declaration of 200 bombs or found indications of error in its declaration. Since according to UNSCOM at least three filled DB-2 bombs were at Muhammadiyat in May 1990, we believe a nerve agent release is possible. In any case, Iraq’s claims about the number of DB-2s at Muhammadiyat are suspect.^[36] Accepting Iraq’s claims of the number of DB-2s at Muhammadiyat, will result in a larger release and hence a larger hazard area.

2. Mustard-filled 250-gauge Bombs

UNSCOM recovered 200 mustard-filled 250-gauge bombs at Muhammadiyat—119 intact and 81 that leaked.^[37] Based on the 81 bombs that leaked, we assess this release was definite.

3. Mustard-filled 500-gauge Bombs

Analysts used two different approaches (counting bombs in UNSCOM photography and analyzing Iraq’s declarations) to determine the number of mustard-filled 500-gauge bombs damaged or destroyed at Muhammadiyat. These two approaches yielded, respectively, 265 and 266 bombs damaged or destroyed. To ensure the largest prediction of agent release, we assessed bombing damaged or destroyed 266 mustard-filled 500-gauge bombs at Muhammadiyat. CIA’s analysis of UNSCOM photography indicated 27 burst open, while the remaining 239 leaked.^[38] Based on UNSCOM photography and information, we believe this release was definite.

4. Mustard-filled 155mm Artillery Rounds

In 1997, Iraq claimed Coalition bombing destroyed 550 mustard-filled 155mm artillery rounds at Muhammadiyat. UNSCOM 221 (February 1998) attempted to verify this claim. The inspection team could find the remnants of only 15 to 20 155mm artillery rounds, challenging Iraq’s claim of 550. After this inspection, Iraq dropped its claim Muhammadiyat bombing destroyed 550 rounds. While the information about the mustard-filled 155mm artillery rounds is conflicting and confusing, we assessed that at most 20 mustard-filled 155mm artillery rounds released mustard agent^[39] and included this possible release in our mustard agent dispersion modeling.

5. Other Munitions

We do not think Iraq stored any sarin-filled 122mm rockets or mustard-filled 130mm artillery shells at Muhammadiyat. Iraq claimed the sarin-filled 122mm rockets only once in its 1992 Full, Final, and Complete Disclosure, eliminating the claim from subsequent declarations. Additionally, no UNSCOM team uncovered any evidence of such chemical-warfare-agent-filled munitions at Muhammadiyat.

G. Bombing Dates

To correlate weather data with the time of release, determining the date and time of bombing attacks that damaged or destroyed the chemical weapons was essential.

Coalition forces bombed Muhammadiyat on several occasions during Desert Storm, but we have been unable to determine which of these attacks damaged or destroyed the chemical weapons. The significantly different condition of the DB-2 bombs (some almost untouched in crates and some outside their crates showing obvious damage), the four widely separated locations where UNSCOM found them; and the many Coalition bombing dates (Tab E) make different nerve agent release dates likely. If bombing released nerve agent on multiple days, the amount released on any one day would be only a fraction of the total released. However, since we cannot determine the date(s) Coalition bombing actually damaged or destroyed the bombs, we modeled scenarios that would simulate the greatest potential hazard to US forces: Coalition bombing damaged or destroyed all the DB-2 bombs at the same time on the same day. Any date the Coalition attacked the warehouse area during the bombing campaign was a possible agent release date; any time attack aircraft flew over the target was a possible time of release.^[40] Consequently, we assumed the time of release of all the nerve agent could have been any of 17 bombings on 15 days. We had similar difficulties with the mustard-filled bombs. However, bomb damage assessments and intelligence information allowed us to limit the days of possible release to three—February 10, 12, or 16, 1991.^[41] For both nerve-agent-filled and mustard-filled munitions, we modeled each attack as if it were the attack that released all the agent and analyzed each attack’s potential for endangering US forces. Assuming all the agent was released on a single day, rather than in smaller releases over several different dates, will result in a larger potential hazard area.

H. Agent Purity

Iraq had difficulty producing good-quality chemical warfare agents. Technical failures introduced impurities causing storage and handling problems, particularly with sarin and cyclosarin. Impurities significantly reduce both storage shelf life and toxic battlefield effects.^[42]

Table 3 summarizes our conclusions about the purity of agent found at Muhammadiyat. The source characterization reference specifically details how we derived these numbers. In brief, we used UNSCOM information on agent purity of DB-2 bombs stored at Muhammadiyat in May 1990, combined with our understanding of how Iraq's nerve agent degrades in storage,^[43] to derive the purity of the sarin and cyclosarin in February 1991. The 90% purity of the mustard agent in the 250- and 500-gauge bombs as well as the 96% purity for mustard agent in the mustard-filled 155mm artillery came from UNSCOM estimates.

Table 3. Agent purity for chemical warfare agents found at Muhammadiyat

I. Percent Agent Released from Damaged or Destroyed Munitions

The damaged or destroyed munitions at Muhammadiyat probably did not release all their agent into the atmosphere—the soil and weapon crates likely absorbed and retained some of the agent. Table 4 summarizes the estimated percentage of agent released into the atmosphere for each of the chemical munitions found at Muhammadiyat.

Table 4. Percentage of chemical warfare agents released at Muhammadiyat that goes into the atmosphere

The source characterization references specifically detail how we derived the numbers in Table 4. Briefly, we estimated the percentage of nerve agent released from the DB-2 bombs using test data from the US Army Dugway Proving Ground.^[52] These test data showed the amount of leaked nerve agent that is retained by wooden shipping crates and the soil, as well as the amount of nerve agent that eventually evaporates back into the atmosphere from the crates and soil. We believe burning conventional rockets flying out of warehouses damaged or destroyed by air strikes and landing on stacked mustard-filled bombs set them on fire. The percentage of mustard agent released depends on estimates of how much agent the fire consumed and whether the agent leaked from the munitions (the 250-gauge and most of the 500-gauge bombs) or the munitions burst (a small percentage of the 500-gauge bombs and all the 155mm artillery rounds). The CIA’s analysis indicates fire consumed most of the mustard agent from leaking 250- and 500-gauge bombs while more agent from burst munitions escaped the fire into the atmosphere. As a worst case, we assumed all nerve agent release was instantaneous while the mustard release occurred over one hour.

J. Total Agent Release

We can calculate the total release of agent at Muhammadiyat by using this formula:

Number of Munitions

times

Fill per Munition

times

Purity(a)

times

% Agent Released(a)

=

Total Release

(a) Mathematically, we express these numbers as decimals rather than percentages (e.g., 50% is expressed as 0.50).

Table 5 contains the results of the calculation for each of the chemical weapons damaged or destroyed at Muhammadiyat. We estimate 180 kilograms (kg) of nerve agent and 2,969 kg of mustard agent released into the atmosphere.

Table 5. Total release of mustard and nerve agents

(a) For modeling, we rounded this number to 2,970 kg.

K. Source Characterization

Tables 6 and 7 summarize the information contained in the preceding sections and contain the source characterization of the nerve agent (sarin-cyclosarin mixture) release and the mustard agent release at Muhammadiyat. Investigators used the data from these tables to model the possible chemical warfare agent release.

Table 6. Nerve agent release source characterization^[53]

Table 7. Mustard release source characterization^[54]

L. Modeling the Muhammadiyat Agent Release

To this point, the narrative has:

• Defined the chemical warfare agents present at Muhammadiyat when the air campaign attacks occurred; and
• Identified the dates of the attacks that possibly released chemical warfare agent and the quantities of chemical warfare agent possibly released into the environment by these air attacks.

Subsections L, M, and N explain how we determined whether the air campaign against Muhammadiyat might have exposed US forces. This analysis relies heavily on modeling and simulation to reconstruct the release and project the resulting chemical hazard area from Coalition bombing attacks. The state of hostilities at the time of the attacks, the site’s remoteness, and the intermittent poor weather limited bomb damage assessment and prevented sampling. Furthermore, UNSCOM did not conduct on-site inspections to assess the damage to chemical weapons at Muhammadiyat until October 30 and 31, 1991—eight months after the bombing ended—nor did Iraq, to the best of our knowledge, collect or record data that would assist in our analysis of the release. Consequently, we carried out extensive, detailed research to compile reliable information to support the modeling and simulation.

1. Research

The research for the Muhammadiyat investigation focused initially on identifying and collecting data to run the models, most importantly the dispersion models, which project the chemical warfare agents’ downwind travel. The dispersion models require several inputs quantifying weather conditions and characterizing the source of the chemical warfare agent release. Weather data are key influences on the dispersion models’ outputs.

a. Defining weather conditions. Since weather conditions change rapidly in short time periods, analysts first identified the times when the suspected release occurred. Documenting the weather conditions for these times required detailed research into databases and sources maintained by the US Air Force, US Navy, Department of Defense (DoD), and intelligence community.

With the dates and times of the releases determined, it was then necessary to simulate the weather over Muhammadiyat and surrounding areas for several days after the air strike. There were essentially no weather observations available over Iraq. This required research into national and international weather archives to retrieve observed regional weather data outside Iraq to support global meteorological models. The output from these models provided the input to the high-resolution weather models to simulate the weather in the vicinity of Muhammadiyat.

b. Characterizing the release of chemical warfare agents. As discussed previously, this effort, constituting most of the research in this investigation, estimated the amount and type of agent released into the environment. Researchers studied data supplied by UNSCOM and the intelligence community. The paper, "Analysis of the Source Terms for Muhammadiyat,"^[55] describes in detail how we used this information to arrive at a source characterization for this narrative.

2. Modeling

The meteorological conditions at the time and place of release and during the period following the release of agents into the environment greatly influence the chemical warfare agents’ dispersion. The Muhammadiyat hazard projection is a retrospective analysis. Since there are no existing weather data for Iraq during the Gulf War, we use meteorological modeling to simulate local weather conditions.

We used DoD dispersion models to model the release of chemical warfare agents. These dispersion models (sometimes-called transportation models) produce hazard projections predicting the area where the agent spread.

As shown in Figure 8, dispersion modeling requires weather modeling data projections combined with the source characterization data to produce a hazard projection. The US Army Center for Health Promotion and Preventive Medicine matched this hazard projection with unit location data to create a graphic showing possible areas of US forces’ exposure. Tab F describes the modeling process in more detail.

Figure 8. Modeling for Muhammadiyat

M. Exposure Levels

The two chemical warfare agents released at Muhammadiyat were nerve agent—a sarin-cyclosarin mixture—and mustard agent. Sarin and cyclosarin attack the central nervous system; lethal doses kill in less than 15 minutes.^[56] Mustard agent is a blister agent (or vesicant) readily absorbed by the body. Mustard vapors attack moist tissue and vulnerable areas, including eyes, mucous membranes, and the respiratory tract.^[57] See the glossary in Tab A for additional details on blister (HD) agents and nerve agents.

In either liquid or vapor form, both nerve and blister agents can endanger humans. Our analysis models these agents’ vapor release because a vapor release will extend over the largest geographical area and have the highest probability of reaching areas US forces occupied.

One measure of the effectiveness of a chemical warfare agent is its median lethal dosage (LCt₅₀)—the dosage that kills 50 percent of exposed, unprotected personnel.^[58] A second measure of effectiveness is first noticeable effects (FNE). Persons exposed to the FNE dosage for nerve agent reasonably could be expected to demonstrate noticeable effects from the exposure, specifically effects to the eyes e.g., miosis—constriction (pinpointing) of the pupil.^[59]

Military leaders naturally are very concerned about lethal and first-noticeable-effects dosages, but this investigation also considered the effects associated with exposure to nerve and mustard agent at concentrations well below those needed to cause observable effects. The measure of effectiveness we chose for this study is the general population limit (GPL), the maximum permissible airborne exposure level for long-term general population exposure. Below the GPL exposure level, one would expect no observable adverse effects after a lifetime exposure.^[60] Since the Muhammadiyat mustard and nerve agent releases resulted in one-time exposures for only a few hours, to determine potential hazard areas, our modeling used a GPL for short-term exposure based on the recommendation of the US Army Center for Health Promotion and Preventive Medicine.^[61] Tab G contains specific details about how investigators derived and chose these dosages.

N. Modeling Results

Tabs H and I show the respective modeling results for the nerve and mustard agent release, with a graphic showing the potential hazard area for each of the 17 strikes that might have released the nerve agent and each of the four strikes that might have released the mustard agent. These graphics show no nerve or mustard agent hazard area reached US forces in Saudi Arabia. The closest the potential nerve agent hazard area approached to US forces in Saudi Arabia occurred February 6, 1991, when the outer edge of the potential hazard area extended to within 35 miles of a single company-size unit in western Saudi Arabia (Figure 9). The closest the nerve agent hazard area came to the main concentration of US forces in Saudi Arabia occurred January 27, 1991, when the potential hazard area came within 80 miles of the forces near Rafha (Figure 10).

Similarly, the closest the mustard agent hazard area came to US forces in Saudi Arabia occurred February 12, 1991, with the outer edge of the hazard area coming within 125 miles of a single company-size unit in western Saudi Arabia. The closest the mustard agent came to the main concentration of US forces occurred the same day, when the potential hazard area came within 150 miles of the forces near Rafha (Figure 11).

Figure 9. Closest approach of the nerve agent hazard area to US forces in Saudi Arabia

To estimate the largest potential hazard areas, we modeled the GPL for short-term exposure. Exposure below this level would not result in long-term health effects. Even using this extremely conservative measure, no nerve or mustard agent hazard area reached US forces in Saudi Arabia. According to the US Special Operations Command, small groups of its soldiers operated in Iraq during the air campaign.^[62] If these soldiers were in Iraq on the day of a release, a few of them possibly were in the vicinity of a potential nerve agent hazard area.^[63]

Figure 10. Closest approach of nerve agent hazard area to main concentration of US forces in Saudi Arabia

Figure 11. Closest approach of mustard hazard area to any US forces in Saudi Arabia

Our analysis indicates the nerve agent hazard area reached its maximum extent in approximately 10 to 12 hours and then dissipated. Consequently, no long-term hazard area from the nerve agent release endangered US forces. Likewise, we found the mustard agent hazard area reached its maximum extent in approximately 24 hours and then dissipated. So again, no long-term hazard area from the mustard agent release endangered US forces.