GAO

United States General Accounting Office

Report to Congressional Requesters

September 1999 COMBATING 

TERRORISM

Need for 

Comprehensive Threat 

and Risk Assessments 

of Chemical and 

Biological Attacks

GAO/NSIAD-99-163

Page 1 GAO/NSIAD-99-163 Combating Terrorism

United States General Accounting Office

Washington, D.C. 20548

National Security and

International Affairs Division

B-282772 Letter

September 14, 1999

The Honorable Arlen Specter

Chairman

The Honorable John D. Rockefeller IV

Ranking Minority Member

Committee on Veterans’ Affairs

United States Senate

The Honorable Ike Skelton

Ranking Minority Member

Committee on Armed Services

House of Representatives

The Honorable Christopher Shays

Chairman

Subcommittee on National Security, Veterans’ Affairs, and 

 International Relations

Committee on Government Reform

House of Representatives

As you know, many conflicting statements have been made in public 

testimony before Congress and in the press concerning the ease or 

difficulty with which terrorists could effectively disseminate a chemical or 

biological agent on U.S. soil and cause mass casualties. Nevertheless, 

numerous federal agencies are spending billions of dollars to prepare for 

the possibility of a terrorist attack with chemical or biological weapons. 

The President’s fiscal year 2000 budget proposes $10 billion1

 for 

counterterrorism programs—an increase of more than $3 billion over the 

requested funding of $6.7 billion for fiscal year 1999. Some agencies have 

experienced rapid increases in funding for programs and activities to 

combat terrorism in recent years. For example, the Department of Health 

and Human Services (DHHS) increased its spending from $7 million in 

fiscal year 1996 to about $160 million in fiscal year 1999 and has requested 

$230 million for fiscal year 2000 for its bioterrorism initiative. As part of the 

same initiative, the Centers for Disease Control and Prevention (CDC), an 

1

Of the $10 billion, $8.6 billion is for combating terrorism, including defending against weapons of mass 

destruction, and $1.4 billion is for critical infrastructure protection.

Letr
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operating division within DHHS, will continue to develop the national 

pharmaceutical stockpile to prepare for terrorist incidents involving 

chemical or biological agents. 

In view of the conflicting information and the substantial investments being 

made to counter an uncertain threat, you asked us to review the scientific 

and practical aspects of a terrorist carrying out large-scale chemical or 

biological attacks on U.S. soil. Specifically, we examined the technical ease 

or difficulty for terrorists to acquire, process, improvise, and disseminate 

certain chemical and biological agents that might cause at least 1,000 

casualties (physical injuries or deaths)—the number DHHS uses for 

planning purposes—without the assistance of a state-sponsored program. 

You also asked us to determine the extent to which the U.S. government 

has assessed the threats and risks posed by chemical and biological 

terrorism in the United States to serve as a basis for planned investments. 

As agreed with your offices, for the purposes of our work, we defined 

terrorists as non-state actors not provided with a state-developed weapon. 

The terrorists could be of foreign or domestic origin and would be 

operating illegally and outside a state-run laboratory infrastructure or 

weapon program. As also agreed, we will later report on the mechanisms in 

place to track medical inventories and the adequacy of medical inventory 

tracking systems.

Results in Brief Chemical and biological experts and intelligence agency officials believe 

that the ease or difficulty for terrorists to cause mass casualties with an 

improvised chemical or biological weapon2

 or device depends on the 

chemical or biological agent selected. Experts from the scientific, 

intelligence, and law enforcement communities told us that terrorists do 

not need sophisticated knowledge or dissemination methods to use toxic 

industrial chemicals such as chlorine. In contrast, terrorists would need a 

relatively high degree of sophistication to successfully cause mass 

casualties with some other chemical and most biological agents. 

Specialized knowledge would be needed to acquire the right biological 

agent or precursor chemicals,3

 process the chemical or biological agent, 

2

A few biological agents (e.g., plague and smallpox) are communicable and can be spread beyond those 

directly affected by the weapon or dissemination device. Every biological agent, even one that is highly 

communicable, must be disseminated by some means that infects enough individuals to initiate a 

disease epidemic.

3

Precursor chemicals are materials from which chemical agents are synthesized.

Letr
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improvise a weapon or device, and effectively disseminate the agent to 

cause mass casualties. Throughout the different stages of the process, 

terrorists would run the risk of hurting themselves and of being detected 

and would have to overcome technical and operational challenges. Some 

virulent biological agents and precursor chemicals are difficult to obtain, 

and others are difficult to process or produce, especially in the quantities 

needed to cause mass casualties. In addition, effective dissemination of 

chemical and biological agents can be disrupted by environmental and 

meteorological factors. Terrorists with less sophistication could make a 

chemical or biological weapon and disseminate agents, but these would be 

less likely to cause mass casualties. Preventive measures and medical 

treatments are available for some, but not all chemical and biological 

agents that might be used by terrorists.

The intelligence community has recently produced National Intelligence 

Estimates (NIE) and other high-level analyses of the foreign-origin terrorist 

threat that include judgments about the more likely chemical and biological 

agents that would be used. Unlike the foreign-origin terrorist threat, the 

Federal Bureau of Investigation’s (FBI) analysts’ judgments concerning the 

more likely chemical and biological agents to be used by domestic-origin 

terrorists have not been captured in a formal, authoritative, written 

assessment. A formal assessment of the domestic-origin threats, combined 

with existing assessments of the foreign-origin threat, would provide an 

authoritative, written, comprehensive, intelligence community view on 

specific chemical and biological terrorist threats. Moreover, a national-level 

risk assessment of potential chemical and biological terrorist incidents also 

has not been performed. A risk assessment is a decision-making support 

tool that is used to establish requirements and prioritize program 

investments. Soundly performed risk assessments could help ensure that 

specific programs and related expenditures are justified and targeted 

according to the threat and risk of validated terrorist attack scenarios 

generated and assessed by a multidisciplinary team of experts. To perform 

a sound risk assessment, a multidisciplinary team of experts would use 

valid, current, documented threat information, including NIEs, to develop 

valid threat scenarios, rank the likelihood of a successful attack, and assure 

that program countermeasures are not based solely on worst-case 

scenarios. 

We have previously reported that federal programs to combat terrorism, 

such as DHHS’ national pharmaceutical and vaccine stockpile, are being 

initiated without the benefit of a sound threat and risk assessment process 

that helps prioritize and focus investments on appropriate 
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countermeasures and programs.4 In the case of the DHHS national 

stockpile initiative, without valid threat and risk assessments, we question 

whether stockpiling for the items and quantities discussed in the 

Department’s plan is the best approach for investing in medical 

preparedness.

We are recommending that the Attorney General direct the FBI Director to 

produce an authoritative threat assessment of the more likely chemical and 

biological agents that would be used by domestic-origin terrorists working 

outside a state-run laboratory infrastructure. In addition, we are 

recommending that the Attorney General direct the FBI Director to 

sponsor a national-level risk assessment using NIEs and other inputs to 

help guide and prioritize appropriate countermeasures and programs 

designed to combat chemical and biological terrorism.

Background The 1995 attack by Aum Shinrikyo, an apocalyptic religious sect, in the 

Tokyo subway using the chemical nerve agent sarin elevated concerns 

about chemical and biological terrorism. Twelve people were killed and 

many more were injured as a result of that incident. Some experts have 

noted that despite substantial financial assets, well-equipped laboratories, 

and educated scientists working in the laboratories, Aum Shinrikyo did not 

cause more deaths because of the poor quality of the chemical agent and 

the dissemination technique used. Although not as widely publicized, a 

limited number of incidents involving biological agents have also occurred 

in the United States. For example, in 1984, the Rajneeshee religious cult in 

Oregon contaminated salad bars in local restaurants with salmonella 

bacteria to prevent people from voting in a local election. Although no one 

died, 751 people were diagnosed with the food-borne illness. 

These events and concerns about other threats prompted Congress to 

establish a commission to assess the federal government’s organization 

concerning weapons of mass destruction proliferation and to make

4

Combating Terrorism: Observations on Federal Spending to Combat Terrorism

(GAO/T-NSIAD/GGD-99-107, Mar. 11, 1999); Combating Terrorism: Threat and Risk Assessments Can 

Help Prioritize and Target Program Investments (GAO/NSIAD-98-74, Apr. 9, 1998); and Combating 

Terrorism: Observations on Biological Terrorism and Public Health Initiatives (GAO/T-NSIAD-99-112, 

Mar. 16, 1999).
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recommendations for improvements.5 In July 1999, the commission 

concluded that the United States is not effectively organized to combat the 

threat of nuclear, chemical, and biological weapons proliferation. The 

commission believes that an effective capability to respond to the use of 

these weapons by state or subnational groups, whether at home or abroad, 

is critical not only in the event of an attack, but also as a deterrent. This 

panel recommended that the President name a national director for 

combating proliferation who could coordinate the response of government 

agencies.

While intelligence agencies continuously assess and report on various 

threats, an NIE analyzes issues of major importance and long-term interest 

to the United States and is the intelligence community’s most authoritative 

projection of future developments in a particular subject area.6

 An NIE is 

intended to help decisionmakers think through critical issues by presenting 

the relevant key facts, judgments about the likely course of events in 

foreign countries, and the implications for the United States. Examples of 

critical issues are threats from foreign terrorism and foreign missiles. NIEs 

are generally focused on foreign-origin threats. The National Intelligence 

Council (NIC), an organization composed of 12 National Intelligence 

Officers--including one from the FBI--who report directly to the Director of 

Central Intelligence, produces NIEs. To prepare an NIE, the NIC brings 

together analysts from all the intelligence agencies that have expertise on 

the issue under review.7

 In the final analysis, an NIE is the Director of 

Central Intelligence’s assessment, with which the heads of the U.S. 

intelligence agencies concur, except as noted in the NIE’s text. Other 

high-level intelligence community products include Intelligence 

Community Assessments.

Intelligence and law enforcement threat information is a key input into a 

risk assessment process. Risk assessments are widely recognized as valid 

5

The Intelligence Authorization Act for Fiscal Year 1997 (P.L. 104-293) created the commission. The 

Omnibus Consolidated and Emergency Supplemental Appropriations Act for Fiscal Year 1999 

(P.L. 105-277) extended the commission’s reporting deadline to July 18, 1999. John Deutch, former 

Director of Central Intelligence, was the commission’s chairman. Senator Arlen Specter served as vice 

chairman.

6

Foreign Missile Threats: Analytic Soundness of Certain National Intelligence Estimates

(GAO/NSIAD-96-225, Aug. 30, 1996).

7

The following organizations may participate in preparing an NIE: NIC, Central Intelligence Agency, 

Defense Intelligence Agency, National Security Agency, State Department’s Bureau of Intelligence and 

Research, FBI, intelligence organizations of the Departments of the Treasury and Energy, and military 

services.
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decision support tools to establish and prioritize program investments and 

are grounded in risk management, an approach to dealing with security 

issues. Risk management is the deliberate process of understanding risk—

the likelihood that a threat will harm an asset or individuals with some 

severity of consequences—and deciding on and implementing actions to 

reduce it. A threat analysis--the first step in determining risk--identifies and 

evaluates each threat on the basis of various factors such as its capability 

and intent to attack an asset and the likelihood and the severity of the 

consequences of a successful attack. Valid, current, and documented threat 

information, including NIEs, in a risk assessment process is crucial to 

ensuring that countermeasures or programs are not based solely on 

worst-case scenarios and are therefore out of balance with the threat. Risk 

management principles acknowledge that (1) while risk generally cannot 

be eliminated, it can be reduced by enhancing protection from validated 

and credible threats and (2) although many threats are possible, some are 

more likely to be carried out than others. Risk assessments form a 

deliberate, analytical approach that results in a prioritized list of risks (i.e., 

threat-asset-vulnerability combinations) that can be used to select 

countermeasures to create a certain level of protection or preparedness. 

Because threats are dynamic and countermeasures may become outdated, 

it is generally sound practice to periodically reassess threat and risk. To 

perform a realistic risk assessment of terrorist threats, a multidisciplinary 

team of experts would require several inputs, including written foreign and 

domestic threat analyses from the intelligence community and law 

enforcement.

Chemical and biological agents pose different sets of problems for 

emergency planning and preparedness. For example, most chemicals 

quickly affect individuals directly exposed to the agent within a given 

geographical area. In contrast, the release of a biological agent may not be 

known for several days, and both perpetrators and victims may be miles 

away from the point of release when an incident is identified. Also, some 

biological agents produce symptoms that can be easily confused with 

influenza or other less virulent illnesses. If communicable, the biological 

agent can spread throughout the population. 

Many federally funded programs and initiatives have been established to 

better prepare for dealing with a possible large-scale chemical or biological 

terrorist incident, but no federal agency has defined what constitutes mass 

casualties. The Federal Emergency Management Agency, the Department 

of Defense (DOD), the Department of Justice, and DHHS (including CDC) 

do not have a working definition of what constitutes mass casualties. The 
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metropolitan medical response systems that DHHS is establishing across 

the nation use 1,000 casualties as a basis for planning local medical systems 

and for equipping and supplying the response teams.8

 DHHS acknowledges 

that this number is arbitrary but believes it is reasonable for planning 

purposes. Other federal agency representatives stated that whatever 

number overwhelms the local medical system could be considered mass 

casualties.

Terrorists operating outside a state-run laboratory infrastructure would 

have to improvise a weapon or device and effectively disseminate an agent 

through a delivery system. There are different stages in the process of 

improvising a chemical or biological weapon to cause mass casualties. 

Figure 1 shows the stages required for such an undertaking.

8

Combating Terrorism: Opportunities to Improve Domestic Preparedness Program Focus and 

Efficiency (GAO/NSIAD-99-3, Nov. 12, 1998) and Combating Terrorism: Observations on the 

Nunn-Lugar-Domenici Domestic Preparedness Program (GAO-T-NSIAD-99-16, Oct. 2, 1998).
B-282772

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Figure 1: Stages for Terrorists Working Outside a State-run Laboratory to Conduct 

Chemical and Biological Terrorism

Source: GAO, on the basis of analysis and discussion with chemical and biological warfare experts.

Scope and 

Methodology

To perform our review, we obtained lists of potential chemical and 

biological agents that might be used by terrorists from intelligence 

agencies, military medical health experts, the FBI, and documents provided 

by government officials. We discussed in detail the characteristics of these 

agents with numerous experts in the disciplines of science, medicine, law 

enforcement, intelligence, and chemical and biological warfare. We spoke 

with and obtained documentation from officials at the U.S. Army Medical 

Research Institute of Infectious Diseases in Frederick, Maryland; the CDC 

in Atlanta, Georgia; the DHHS Office of Emergency Preparedness in 

Rockville, Maryland; the Department of Veterans’ Affairs in Washington, 

D.C.; the Soldier and Biological Chemical Command and its Technical 

Escort Unit in Edgewood, Maryland; and the Defense Threat Reduction 

Agency in Dulles, Virginia. We discussed the production, weaponization, 

and dissemination of chemical and biological agents with experts formerly 

with U.S. and foreign biological warfare programs and with several medical 

and scientific experts in academia. We analyzed manuals, handbooks, and 

Acquire precursor chemicals or

virulent biological seed cultures

Acquire precursor chemicals or

virulent biological seed cultures

Process the chemical or biological agents into a

form which can be effectively disseminated

(unnecessary for some chemical agents)

Process the chemical or biological agents into a

form which can be effectively disseminated

(unnecessary for some chemical agents)

Disseminate chemical or biological

agents to effectively to cause mass

casualties

Disseminate chemical or biological

agents to effectively to cause mass

casualties

Improvise an agent delivery device Improvise an agent delivery device

Synthesize chemical agents

from precursors or grow

biological agents in culture

(unnecessary for toxic industrial chemicals)

Synthesize chemical agents

from precursors or grow

biological agents in culture

(unnecessary for toxic industrial chemicals)
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texts on infectious diseases and biological and chemical casualties. We 

gathered and reviewed materials, studies, and reports on chemical and 

biological terrorism and attended conferences on the topic.

To develop the report’s appendixes on selected chemical and biological 

agents, we analyzed and summarized information obtained from different 

sources. Specifically, for chemical agents, we reviewed Army Field Manual 

3-9, Potential Military Chemical/Biological Agents and Compounds, as well 

as other information that we supplemented with discussions with the 

Defense Threat Reduction Agency and CDC. The primary source of our 

appendix on selected biological agents was the Medical Management of 

Biological Casualties Handbook (July 1998) by the U.S. Army Medical 

Research Institute of Infectious Diseases. Also, we discussed the 

characteristics of each biological agent with infectious disease experts, 

including those from the U.S. Army Medical Research Institute of 

Infectious Diseases and CDC. Renowned academicians from Stanford 

University, Johns Hopkins University, the Rockefeller University, the 

Monterey Institute of International Studies, and RAND Corporation 

provided information from the disciplines of physics, meteorology, 

virology, biology, microbiology, and terrorism—all of which are technical 

and operational aspects of chemical and biological terrorism. Biological 

warfare experts formerly with offensive programs of the United States, the 

United Kingdom, and the former Soviet Union gave us detailed information 

on the acquisition, growth, production, and dissemination of biological 

agents. We also discussed biological and chemical agents and obtained 

documentation from chemical and biological defense experts and the 

Defense Threat Reduction Agency. We reviewed classified documents and 

reports from the intelligence community and unclassified handbooks, 

manuals, textbooks, reports, and other open-source materials. Chemical 

and biological experts reviewed portions of the draft report and provided 

comments. In addition, technical experts from the Office of the Assistant 

Secretary of Defense for Special Operations and Low-Intensity Conflict 

reviewed the draft appendixes and offered comments as appropriate.

As agreed with your offices, we limited our review to terrorist chemical or 

biological attacks that could be carried out by individuals or groups 

without access to state-run laboratories or weapon programs and that 

would not receive chemical or biological agents or weapons from such 

countries. We assumed that potential terrorists would have to acquire a 

biological agent or precursor chemicals, produce the agent, weaponize the 

agent, and deliver it. We limited our evaluation to agents that could cause 

mass casualties using the DHHS planning guidance of 1,000 casualties. We 
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focused on methods that cause mass casualties among humans by means of 

improvised weapons or devices and not through contamination of water, 

food supply, agriculture, or livestock. 

Officials from individual intelligence agencies briefed us and provided 

access to analyses on specific chemical and biological agents and on the 

threat of chemical and biological terrorism in general. In addition, we 

reviewed pertinent NIEs and Intelligence Community Assessments. We 

also reviewed other intelligence analyses related to terrorism. FBI officials 

provided their assessment of the domestic-origin terrorist threat and 

information on past cases of terrorism, including data on terrorist incidents 

in the United States from 1987 through 1998. 

We interviewed and obtained documentation from DHHS and CDC officials 

about the proposed national stockpile of pharmaceuticals and vaccines, 

including the methodology used in developing an operating plan to 

establish a stockpile and continuing efforts to further develop the 

stockpile. Information on the threat and risk assessment process was 

developed in our previous work on combating terrorism.

Ease or Difficulty 

Depends on Chemical 

or Biological Agent 

Selected

Chemical and biological experts and the intelligence agencies believe that 

the ease or difficulty with which terrorists could cause mass casualties 

with an improvised chemical or biological weapon9

 or device depends on 

the chemical or biological agent selected. Experts from the scientific, 

intelligence, and law enforcement community told us that terrorists do not 

need sophisticated knowledge or dissemination methods to use toxic 

industrial chemicals. In contrast, these experts believe that terrorists face 

serious technical and operational challenges at different stages of the 

process (described in fig. 1) to cause mass casualties when working with 

other chemical or any biological agents in the scope of our review.

According to these experts, to cause mass casualties with many chemical 

and all biological agents in our review, terrorists would have to handle the 

risk of hurting themselves and of being detected, overcome acquisition and 

production difficulties, and effectively disseminate a chemical or biological 

9

A few biological agents (e.g., plague and smallpox) are communicable and can be spread beyond those 

directly affected by the weapon or dissemination device. Every biological agent, even those that are 

highly communicable, must be disseminated by some means that infects enough individuals to initiate a 

disease epidemic. 
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agent. In addition, these experts believe that capability, access, and 

specialized knowledge that are not readily available are needed when 

weaponizing or disseminating certain chemical agents and nearly all 

biological agents. Further, obtaining access to the proper strains of 

biological agents is a difficult hurdle to overcome. Chemical experts 

believe that many variables may deter terrorists from using chemical 

agents (other than toxic industrial chemicals). For example, precursor 

chemicals necessary for the production of some chemical agents are 

controlled by the 1993 Chemical Weapons Convention that has been in 

force since April 1997. According to chemical experts, illegal acquisition of 

precursor chemicals would raise suspicions and attention due to the 

provisions of the convention. Moreover, the Special Assistant to the 

Director of Central Intelligence for Nonproliferation recently testified that 

“the preparation and effective use of BW [biological weapons] by both 

potentially hostile states and by non-state actors, including terrorists, is 

harder than some popular literature seems to suggest.”10 

Individuals with expertise in the disciplines of chemistry, biology, virology, 

microbiology, physics, meteorology, and former chemical and biological 

warfare programs described the more salient technical and operational 

challenges of working with chemical and biological agents. We discuss 

these challenges in more detail in the following chemical and biological 

sections. Specifically, 

• the right precursor chemicals and biological agents or strains are very 

difficult to obtain, and some chemical and many biological agents are 

difficult to produce, especially in sufficient quantities to produce mass 

casualties;

• except if using toxic industrial chemicals, terrorists would need a 

relatively high degree of sophistication to successfully and effectively 

process agents, improvise a device or weapon, and disseminate the 

agents to cause mass casualties;

• a crude weapon can be made with less sophistication, but it would be 

less likely to cause mass casualties;

• environmental (e.g., pollution) and meteorological conditions (e.g., sun, 

rain, mist, and wind) might disrupt the effective dissemination of 

chemical and biological agents; and 

10Unclassified statement on the worldwide biological warfare threat to the House Permanent Select 

Committee on Intelligence, March 3, 1999.
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• location of the weapon or device (interior or exterior) can play a critical 

role in its effectiveness.

Ease and Difficulty of Using 

Chemical Agents

Experts from the scientific, intelligence, and law enforcement communities 

we spoke with agreed that toxic industrial chemicals can cause mass 

casualties and require little if any expertise or sophisticated methods. 

Generally, toxic industrial chemicals can be bought on the commercial 

market or stolen, thus avoiding the need to manufacture them. Chlorine, 

phosgene, and hydrogen cyanide are examples of toxic industrial 

chemicals. DOD classified further details concerning the use of toxic 

industrial chemicals. 

Experts believe that unlike toxic industrial chemicals, for various reasons, 

most G and V chemical nerve agents are technically challenging for 

terrorists to acquire, manufacture, and produce. Examples of the G-series 

nerve agents are tabun (GA), sarin (GB), and soman (GD). VX is an 

example of a V-series nerve agent. According to chemical experts, 

developing nerve agents requires synthesis of multiple precursor 

chemicals. On the basis of our review of a technical report,11 we concluded 

that some steps in the production process are difficult and hazardous. 

Although tabun production is relatively easy, containment of a highly toxic 

gas (hydrogen cyanide) is a technical challenge. Production of sarin, 

soman, and VX requires the use of high temperatures and generates 

corrosive and dangerous by-products. Moreover, careful temperature 

control, cooling of the vessel, heating to complete chemical reactions, and 

distillation could be technically infeasible for terrorists without a 

sophisticated laboratory infrastructure. Blister chemical agents such as 

sulfur mustard, nitrogen mustard, and lewisite can be manufactured with 

ease or with only moderate difficulty. However, experts told us that buying 

large quantities of the precursor chemicals for these agents is difficult due 

to the Chemical Weapons Convention. Appendix I describes some chemical 

agents’ key characteristics that we developed on the basis of technical data 

and reviews with experts. DOD classified additional details for appendix I. 

Chemical experts believe that chemical agents need to be in vapor or 

aerosol form (a cloud of suspended microscopic droplets) 12 to cause 

11Technologies Underlying Weapons of Mass Destruction, U.S. Congress, Office of Technology 

Assessment (Dec. 1993). 

12Fog and smoke are examples of visible aerosols.
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optimal inhalation exposure to cause an effect. Vapors and aerosols remain 

suspended in the air and are readily inhaled deep into the lungs. Another 

method is to spray large droplets or liquid for skin penetration. A chemical 

agent could be disseminated by explosive or mechanical delivery. Further, 

chemical agents can be disseminated in vapor, aerosol, or bulk droplet 

form from delivery devices. According to the experts, terrorists could 

disseminate chemical agents using simple containers such as glass bottles 

with commercial sprayers attached to them or fire extinguishers. However, 

the chemical agent would need to withstand the heat developed if 

disseminated by explosives. 

Moreover, according to chemical experts, the successful use of chemical 

agents to cause mass casualties requires high toxicity, volatility (tendency 

of a chemical to vaporize or give off fumes), and stability during storage 

and dissemination. Rapid exposure to a highly concentrated agent in an 

ideal environment would increase the number of casualties. These experts 

agree that disseminating a chemical agent in a closed environment would 

be the best way to produce mass casualties. Weather affects exterior 

dissemination, particularly sunlight, moisture, and wind. Some chemical 

agents can be easily evaporated by sunlight or diluted by water. The 

experts stated that it is also difficult to target an agent with any precision or 

certainty to kill a specific percentage of individuals outdoors. For example, 

wind could transport a chemical agent away from the designated target 

area. 

General Difficulties of Using 

Biological Agents 

According to experts in the many fields associated with the technical 

aspects of dealing with biological agents, including those formerly with 

state-sponsored offensive biological weapon programs, terrorists working 

outside a state-run laboratory infrastructure would have to overcome 

extraordinary technical and operational challenges to effectively and 

successfully weaponize and deliver a biological agent to cause mass 

casualties. Terrorists would require specialized knowledge from a wide 

range of scientific disciplines to successfully conduct biological terrorism 

and cause mass casualties. For example, biological agents have varying 

characteristics. Information and technical data from these experts, 

intelligence, and authoritative documented sources indicate that some 

biological agents such as smallpox are difficult to obtain.13 In the case of

13Known smallpox culture stocks exist only in the United States at CDC and in Russia.
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other biological agents such as anthrax14 and tularemia (both of which are 

bacteria), it is difficult to obtain a virulent strain (one that causes disease 

and injury to humans). Other agents such as plague are difficult to produce. 

Biological toxins such as ricin require large quantities to cause mass 

casualties, thereby increasing the risk of arousing suspicion or detection 

prior to dissemination. Furthermore, some agents such as Q fever 

incapacitate rather than cause death. Finally, many agents are relatively 

easy to grow, but are difficult to process into a form for a weapon. 

Appendix II describes some biological agents’ key characteristics we 

developed from technical documents and reviews with experts. DOD 

classified additional details for appendix II.

According to experts from former biological warfare programs, to survive 

and be effective, a virulent biological agent must be grown, handled, and 

stored properly. This stage requires time and effort for research and 

development. After cultivation, the agent is wet. Terrorists would need the 

means to sterilize the growth medium and dispose of hazardous biological 

wastes. Processing the biological agent into a weaponized form requires 

even more specialized knowledge. According to a wide range of experts in 

science, health, intelligence, and biological warfare and the technical 

report we reviewed, the most effective way to disseminate a biological 

agent is by aerosol. This method allows the simultaneous respiratory 

infection of a large number of people. Microscopic particles that are 

dispersed must remain airborne for long periods and may be transported by 

the wind over long distances. The particles are small enough to reach the 

tiny air sacs of the lungs (alveoli) and bypass the body’s natural filtering 

and defense mechanisms. According to experts, if larger particles are 

dispersed, they may fall to the ground, causing no injury, or become 

trapped in the upper respiratory tract, possibly causing infections but not 

necessarily death. From an engineering standpoint, it is easier to produce 

and disseminate the larger particles than the microscopic particles. Other 

critical technical hurdles include obtaining the proper size equipment to 

generate proper size aerosols, calculating the correct output rate (speed at 

which the equipment operates), and having the correct liquid composition. 

According to key experts with experience in biological warfare, biological 

agents can be processed into liquid or dry forms for dissemination. Both 

14Anthrax is the disease caused by the biological agent Bacillus anthracis. Throughout the report we use 

the related disease term when referring to biological agents. We found that the disease term is used 

synonymously with the biological agent in discussions with the many experts we interviewed and 

documentation we reviewed.
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forms pose difficult technical challenges for terrorists to effectively cause 

mass casualties. These experts told us that liquid agents are easy to 

produce. However, it is difficult to effectively disseminate aerosolized 

liquid agents with the right particle size without reducing the strength of 

the mixture. Further, the liquid agent requires larger quantities and 

dissemination vehicles that can increase the possibility of raising suspicion 

and detection. In addition, experts told us that in contrast, dry biological 

agents are more difficult to produce than liquid agents, but dry agents are 

easier to disseminate. Dry biological agents could be easily destroyed when 

processed, rendering the agent ineffective for causing mass casualties. A 

leading expert told us that the whole process entails risks. For example, 

powders easily adhere to rubber gloves and pose a handling problem. 

Effectively disseminating both forms of agent can pose technical 

challenges in that the proper equipment and energy sources are needed. A 

less sophisticated product and dissemination method can produce some 

illness and/or deaths. DOD classified further details on technical challenges 

of effectively processing and disseminating biological agents.

According to the experts we spoke with, exterior dissemination of 

biological agents can be disrupted by environmental (e.g., pollution) and 

meteorological (e.g., sun, rain, mist, and wind) conditions. Once released, 

an aerosol cloud gradually decays and dies as a result of exposure to 

oxygen, pollutants, and ultraviolet rays. If wind is too erratic or strong, the 

agent might be dissipated too rapidly or fail to reach the desired area. 

Interior dissemination of a biological agent through a heating and air 

conditioning ventilation system could cause casualties. But this method 

also has risks. Security countermeasures could intercept the perpetrators 

or apprehend them after the attack. Successful interior dissemination also 

requires knowledge of aerodynamics. For example, the air exchange rate in 

a building could affect the dissemination of a biological agent. Regardless 

of whether a liquid or dry agent is used in interior or exterior environments, 

experts believe that testing should be done to determine if the agent is 

virulent and disseminates properly. The numerous steps in the process of 

developing a biological weapon increase the chances of a terrorist being 

detected by authorities.

Availability of Pre- and 

Post-exposure Medical 

Treatments Varies

Medical preventive measures and treatments are available for some but not 

all chemical and biological agents. Early treatment following exposure to 

chemical agents is critical. The availability of effective medical defenses 

from or treatments for a chemical or biological agent could be a risk factor 

and influence terrorists’ choice of weapon. The lack of an effective vaccine 
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or antibiotic/antiviral treatment for biological agents—or of an antidote for 

chemical agents—would pose a potential public health challenge but also 

pose a significant risk for terrorists as well. In the absence of medical 

defenses, a chemical or biological agent—if effectively acquired, 

processed, and disseminated—could become a more desirable choice 

because it might result in greater casualties. However, processing, testing, 

and disseminating the agent could equally endanger terrorists because they, 

too, would have no effective protection against the agent.

Medical and biological warfare experts agree that anthrax when inhaled is 

an agent of concern due in large part to the difficulty of diagnosis and 

treatment once symptoms appear and its very high lethality.15 We recently 

testified on DOD’s anthrax vaccination program,16 pointing out that

• the anthrax vaccine is effective for preventing anthrax infections 

through the skin such as those sometimes contracted by unprotected 

workers who handle wool and hides and

• the vaccine appears to be effective against inhalation anthrax in some 

animal species for some, but not all, strains.

However, due to the absence of known correlates of immunity,17 the results 

of the animal studies cannot be extrapolated with certainty to humans. 

DOD is in the process of vaccinating military personnel against anthrax. 

The efficacy of the vaccine for inhalation anthrax in humans has not been 

proven.18

According to CDC, supplies of the plague vaccine do not exist in the United 

States; however, small supplies of killed plague vaccine may exist in 

Australia and the United Kingdom. CDC does not consider a vaccine useful 

to control an outbreak nor protect a population against a terrorist incident. 

Further, there are no vaccines for other potential biological agents such as 

ebola and other hemorrhagic fevers, brucellosis, glanders, or 

15Post-exposure treatment for inhalation anthrax consists of using the vaccine and the antibiotic 

ciproflaxin, but treatment must begin immediately after exposure and before the influenza-like 

symptoms appear. Because the symptoms mimic common influenza, proper diagnosis may come too 

late for effective treatment. 

16Medical Readiness: Safety and Efficacy of the Anthrax Vaccine (GAO/T-NSIAD-99-148, Apr. 29, 1999).

17Correlates of immunity refer to biological markers that represent immunity against disease.

18DOD believes it is prudent to vaccinate U.S. military forces against anthrax exposure, even though 

efficacy for inhalation anthrax has been based on animal testing. 
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staphylococcal enterotoxin B. Similarly, there are no specific antidotes for 

a number of chemical agents such as the toxic industrial chemicals 

chlorine and phosgene. Treatment for exposure to these chemical agents 

consists largely of decontamination, first aid, and respiratory support. An 

antidote kit comprised of amyl or sodium nitrite exists for hydrogen 

cyanide. Appendixes I and II contain information on medical treatments for 

chemical and biological agents, respectively.

Prevention and treatments are available for a number of other agents. For 

example, there is an effective vaccine for known strains of smallpox, 19 and 

there are new investigative vaccines for several other possible biological 

agents, including botulinum, Q fever, Venezuelan equine encephalitis, and 

tularemia. Antidotes such as atropine, pralidoxime chloride, and diazepam 

can be used to counteract the effects of a number of chemical nerve agents. 

The treatment for some chemical and biological agents includes respiratory 

support with a ventilator. The types and quantities of vaccines, 

pharmaceuticals, and other items that should be available in the event of a 

chemical or biological attack can be determined through a 

methodologically sound threat and risk assessment.

U.S. Intelligence 

Assessments of the 

Foreign and Domestic 

Terrorist Threat in the 

United States

To determine the extent to which the foreign- and domestic-origin chemical 

and biological terrorist threat in the United States has been assessed, we 

obtained information from U.S. intelligence agencies. The U.S. intelligence 

community has issued classified NIEs and Intelligence Community 

Assessments that discuss the foreign-origin chemical and biological 

terrorist threat in some detail. However, the FBI’s assessment of the 

chemical and biological agents that would more likely be used by 

domestic-origin terrorists working outside a state-run laboratory 

infrastructure has not been formally reflected in a written threat 

assessment. Producing assessments of both foreign- and domestic-origin 

threats could provide an authoritative, written, comprehensive intelligence 

community view on specific chemical and biological terrorist threats.

The possibility that terrorists may use chemical or biological materials may 

increase over the next decade, according to intelligence agencies. 

According to the Central Intelligence Agency (CIA), interest among 

19Vaccination after exposure to weaponized smallpox or a case of smallpox is effective in preventing 

disease if given within 7 days after exposure. However, it is unclear whether post-exposure treatment 

with smallpox vaccine would be effective due to the difficulty in diagnosing the disease within 7 days. 
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non-state actors, including terrorists, in biological and chemical materials 

is real and growing and the number of potential perpetrators is increasing. 

The CIA also noted that many such groups have international networks and 

do not need to be tied to state sponsors for financial and technical support. 

Nonetheless, the CIA continues to believe that terrorists are less likely to 

use chemical and biological weapons than conventional explosives. We 

previously reported that according to intelligence agencies, terrorists are 

less likely to use chemical and biological weapons than conventional 

explosives, at least partly because chemical and biological agents are 

difficult to weaponize and the results are unpredictable. 

Intelligence Analyses of the 

More Likely Chemical and 

Biological Terrorist Threat 

Agents

The intelligence community has analyzed and made judgments about the 

more likely foreign-origin chemical and biological terrorist threat agents. 

This information has been produced in a new NIE and Intelligence 

Community Assessments. The CIA classified the specific agents identified 

in intelligence assessments that would more likely be used by 

foreign-origin terrorists. The CIA also classified the intelligence judgments 

about the chances that state actors with successful chemical and/or 

biological warfare programs would share their weapons and materials with 

terrorists or terrorist groups. Unlike the foreign-origin threat, the FBI’s 

analysts’ judgments concerning the more likely chemical and biological 

agents that may be used by domestic-origin terrorists have not been 

captured in a formal assessment. However, FBI officials shared their 

analyses of the more likely biological and chemical threat agents on the 

basis of substances used or threatened in actual cases.

In analyzing domestic-origin threats, FBI officials grouped chemical and 

biological agents and did not specify individual agents as threats. Although 

the FBI has not addressed the specific types of chemical or biological 

weapons that may be used by domestic terrorists in the next 2 to 5 years, 

FBI officials believe that domestic terrorists would be more likely to use or 

threaten to use biological agents than chemical agents. The FBI’s 

observation is based on an increase in reported investigations involving the 

use of biological materials. In 1997, of the 74 criminal investigations related 

to weapons of mass destruction, 30 percent (22) were related to the use of 

biological materials. In 1998, there were 181 criminal investigations related 

to weapons of mass destruction, and 62 percent (112) were related to the 

use of biological materials. Most of these investigations involved threats or 

hoaxes. The FBI estimated that in 1997 and 1998, approximately 60 percent 

of biological investigations were related to anthrax hoaxes.
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The FBI ranks groups of chemical and biological agents on its threat 

spectrum according to the likelihood that they would be used.

• Biological toxins: any toxic substance of natural origin produced by an 

animal or plant. An example of a toxin is ricin, a poisonous protein 

extracted from the castor bean.

• Toxic industrial chemicals: chemicals developed or manufactured for 

use in industrial operations such as manufacturing solvents, pesticides, 

and dyes. These chemicals are not primarily manufactured for the 

purpose of producing human casualties. Chlorine, phosgene, and 

hydrogen cyanide are industrial chemicals that have also been used as 

chemical warfare agents.

• Biological pathogens: any organism (usually living) such as a bacteria or 

virus capable of causing serious disease or death. Anthrax is an example 

of a bacterial pathogen. 

• Chemical agents: a chemical substance that is intended for use in 

military operations to kill, seriously injure, or incapacitate people. The 

FBI excludes from consideration riot control agents and smoke and 

flame materials. Two examples of chemical agents are sarin (nerve 

agent) and mustard gas (blister agent).

Risk Assessments Can 

Help Guide Investment 

Decisions for 

Chemical/Biological 

Preparedness Efforts 

Risk assessments are widely recognized as valid decision-making support 

tools to establish and prioritize program requirements. We have previously 

reported on the need for threat and risk assessments performed by a 

multidisciplinary team of experts to properly focus programs and 

investments for combating terrorism and to establish program 

requirements.20 Risk assessments incorporate but go beyond intelligence 

threat analyses by using a multidisciplinary team of experts to 

• generate valid attack scenarios, 

• assess and rank the risks (likelihood and severity of consequences) of 

the attack scenarios, and 

• decide on actions or programs focused on reducing or otherwise dealing 

with the risks as assessed. 

Risk assessments should include sound inputs and information, such as the 

best available intelligence and law enforcement information and analyses, 

20Combating Terrorism: Threat and Risk Assessments Can Help Prioritize and Target Program 

Investments (GAO/NSIAD-98-74, Apr. 9, 1998).
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including NIEs and Intelligence Community Assessments. Soundly 

established requirements could help ensure that specific programs and 

initiatives and related expenditures are justified and targeted, given the 

threat and risk of validated terrorist attack scenarios. We have testified and 

reported on several occasions21 that individual government programs to 

combat terrorism have not been based on soundly determined 

requirements derived from a formal threat and risk assessment process.22 A 

national-level assessment has not been performed that addresses the 

overall threat and risk of terrorism, including terrorist attacks using 

specific chemical or biological materials. Performing a sound threat and 

risk assessment at this level could provide a strategic guide to help shape, 

focus, and prioritize federal efforts to combat terrorism.

Many Counterterrorism 

Efforts Are Not Based on 

Risk Assessments 

Individual agencies request funding for numerous programs and initiatives 

without the benefit of a threat and risk assessment. For example, under the 

Nunn-Lugar-Domenici Domestic Preparedness Program, first responders in 

120 cities are being trained and equipped to enhance their capabilities to 

respond to terrorist chemical attacks, and DHHS is funding medical 

response teams in 27 cities as well as deployable national teams. The 

Department of Justice has sponsored training programs, has funded several 

centers and training venues related to combating terrorism, and is 

implementing an equipment grant program. The Army National Guard is 

establishing 10 of possibly 54 assessment and detection teams.

We recently testified about another example in which a threat and risk 

assessment process would be beneficial.23 Beginning in fiscal year 1999, 

DHHS is establishing a national pharmaceutical and vaccine stockpile to 

prepare medical responses for possible use of chemical or biological 

weapons by terrorists. We found that several of the items DHHS plans to 

21Combating Terrorism: Observations on Federal Spending to Combat Terrorism

(GAO/T-NSIAD/GGD-99-107, Mar. 11, 1999); Combating Terrorism: Observations on Crosscutting Issues

(GAO/T-NSIAD-98-164, Apr. 23, 1998); and Combating Terrorism: Spending on Governmentwide 

Programs Requires Better Management and Coordination (GAO/NSIAD-98-39, Dec. 1, 1997).

22However, several federal government organizations apply some formal threat and risk assessment 

process in their programs. For example, as required by the Federal Aviation Reauthorization Act of 1996 

(P.L. 104-264), the Federal Aviation Administration and the FBI perform joint threat and vulnerability 

assessments on each airport determined to be high risk. The FBI provides threat data (i.e., intelligence 

and law enforcement information) that the Federal Aviation Administration is using to develop threat 

assessments specific to the airport or the metropolitan area in which the high-risk airport is located.

23Combating Terrorism: Observations on Biological Terrorism and Public Health Initiatives

(GAO/T-NSIAD-99-112, Mar. 16, 1999).
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procure (1) do not match intelligence agencies’ judgments, as explained to 

us, of the more likely chemical and biological agents terrorists might use 

and (2) seem to be based on worst-possible consequence scenarios 

generated by an ad hoc interagency group of health and medical 

representatives. The DHHS decision-making process was not formal, based 

on a particular methodology, or documented and did not incorporate the 

many disciplines of knowledge and expertise or divergent thinking that is 

warranted to establish sound requirements for such an emerging, complex, 

and challenging threat. For example, experts in processing and 

weaponizing chemical and biological agents, intelligence, terrorism, law 

enforcement, and other related areas not necessarily associated with 

program and funding stakeholders would comprise a multidisciplinary 

team qualified to (1) generate valid threat scenarios, (2) assess and 

prioritize scenario risks in terms of likelihood and severity of 

consequences, and (3) determine appropriate countermeasures or other 

programmatic responses.24 As we previously reported, without valid threat 

and risk assessments, we question whether stockpiling for the items and 

quantities discussed in the Department’s plan is the best approach for 

investing in medical preparedness.

Conclusions The ease or difficulty for terrorists to cause mass casualties with an 

improvised chemical or biological weapon or device depends on the agent 

selected. Experts agree that toxic industrial chemicals can cause mass 

casualties and require little if any expertise or sophisticated methods. Most 

chemical nerve agents, however, are technically challenging for terrorists 

to acquire, manufacture, and produce. Also, terrorists working outside a 

state-run laboratory infrastructure would have to overcome extraordinary 

challenges to effectively and successfully weaponize and deliver a 

biological agent and cause mass casualties. The intelligence community 

has issued NIEs and other assessments that discuss foreign-origin chemical 

and biological terrorist threats, including judgments about the more likely 

chemical and biological agents that would be used. However, the FBI has 

not produced a formal written assessment of its judgments concerning the 

most likely domestic-origin chemical and biological terrorist threats. Such 

an assessment would complement existing assessments of the 

foreign-origin threat and provide a comprehensive view of the threats. 

Taken together, these assessments of the foreign- and domestic-origin 

24CDC officials told us that since CDC is responsible for establishing the stockpile, it intends to review 

the planned items and quantities based on a multidisciplinary assessment.
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threats would be important inputs for a risk assessment that could help 

form the basis for and prioritize programs to combat chemical and 

biological terrorism. 

Moreover, a sound national-level risk assessment that could provide a 

strategic guide to help shape, focus, and prioritize federal efforts to combat 

terrorism has not been performed. Such an assessment--which 

incorporates but goes beyond intelligence threat assessments--would be 

conducted by a multidisciplinary team of experts on intelligence, terrorism, 

chemical and biological agents, weapons, law enforcement, and health and 

could include other experts not necessarily associated with program and 

funding stakeholders. This team could use sound inputs, including NIEs, to 

(1) generate valid threat scenarios, (2) assess and prioritize scenario risks 

in terms of likelihood and severity of consequences, and (3) determine 

appropriate countermeasures or other programmatic responses. Without a 

valid threat and risk assessment, it is questionable whether federal 

agencies will be able to establish soundly defined program requirements 

and prioritize and focus the nation’s investments to combat terrorism.

Recommendations We recommend that the Attorney General direct the FBI Director to 

prepare a formal, authoritative intelligence threat assessment that 

specifically assesses the chemical and biological agents that would more 

likely be used by domestic-origin terrorists—non-state actors working 

outside a state-run laboratory infrastructure. 

We further recommend that the Attorney General direct the FBI Director to 

sponsor a national-level risk assessment that uses national intelligence 

estimates and inputs from the intelligence community and others to help 

form the basis for and prioritize programs developed to combat terrorism. 

Because threats are dynamic, the Director should determine when the 

completed national-level risk assessment should be updated.

Agency Comments and 

Our Evaluation 

DOD, CIA, the Department of Justice, and DHHS provided official 

comments on a draft of this report. Comments from DOD, CIA, and DHHS 

were classified and could not be printed in this report. Comments from the 

Department of Justice appear in appendix III. All of the agencies provided 

technical comments that we incorporated as appropriate.
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DOD and CIA commented that recently produced intelligence community 

products partially responded to the first recommendation in our draft 

report. Also, Justice commented that the FBI is the appropriate entity to 

implement the recommendation. As originally written, our 

recommendation suggested that the Director of Central Intelligence 

request an NIE assessing the more likely chemical and biological terrorist 

threats and incorporate an FBI assessment of domestic-origin terrorist 

threats. On the basis of our subsequent review of these intelligence 

community documents, we believe that these assessments partially satisfy 

our recommendation. However, the intelligence community assessments 

do not incorporate a written, authoritative FBI analysis of the more likely 

chemical and biological threats from domestic-origin terrorists. As a result 

of our review of recent intelligence assessments and Justice’s comments, 

we adjusted the recommendation to call for the Attorney General to direct 

the FBI Director to prepare a formal written assessment of domestic-origin 

threats.

DOD, the CIA, and Justice agreed with the second recommendation in our 

draft report calling for a national-level risk assessment. However, the CIA 

suggested that we change the wording so that the Director of Central 

Intelligence not be the sponsor of such a risk assessment. Justice stated 

that the FBI, as the lead agency in domestic terrorist incidents, is the 

appropriate federal agency for coordinating a threat and risk assessment. 

Justice also commented that it already had a statutory mandate to develop 

assessments similar to those we recommend in this report. We are aware 

that legislation requires the Attorney General, in consultation with the FBI 

and others, to develop and test methodologies for assessing the threat and 

risk of terrorist employment of weapons of mass destruction against cities 

and other local areas.25 However, these assessments do not substitute for 

the broader national-level risk assessment that we are recommending in 

this report. The former assessments are intended to be city-specific 

whereas the latter would provide an overarching guide for program 

investments at the national level. At the time of our review, the FBI was 

considering methodologies for risk assessments at the city level, and had 

not yet actually performed such an assessment.

We agree that the FBI could sponsor a national-level threat and risk 

assessment. Further, the national-level threat and risk assessment process 

and results should provide a valuable guide for the city-specific threat and 

25Section 1404(a) of the National Defense Authorization Act for Fiscal Year 1999 (P.L. 105-261).
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risk assessments to be facilitated by the FBI. Based on Justice’s comments, 

we have modified our recommendation to suggest that the Attorney 

General direct the FBI Director to sponsor a national-level threat and risk 

assessment. Justice otherwise generally concurred with the draft report. 

DHHS generally agreed with our recommendations but commented that the 

assessment that we recommended should include all possible sources of 

the chemical and/or biological threats such as state-sponsored terrorists. 

The scope of our work was to examine aspects of the terrorist threat 

operating outside a state-run program. Nevertheless, we agree that a risk 

assessment should consider a wide range of possible chemical and 

biological threats. A multidisciplinary team of experts should then assess 

these possible threats in terms of their likelihood of occurrence and 

severity of consequences, since funding countermeasures for all possible 

scenarios is not likely to be affordable. Assessing the risk of these threats 

through generating validated scenarios would allow agencies to focus their 

program countermeasures and investments on the more likely scenarios 

with the more severe consequences.

DHHS also commented that we underestimated the threat of a bioterrorist 

event and relied on data that relates to war-zone activities and conditions 

and not specifically to urban and metropolitan civilian populations. As our 

report states, our objective was to assess the technical ease or difficulty of 

executing a successful, large-scale bioterrorist incident. To satisfy this 

objective, we obtained information from biological warfare experts who 

have in-depth experience and knowledge of processing and effectively 

disseminating biological agents to cause large numbers of human 

casualties (whether military or civilian). Also, we obtained information 

from a wide range of experts, including those in the fields of infectious 

diseases, virology, and civilian disaster management, and reviewed 

pertinent intelligence assessments. We believe that the collective expertise 

of those consulted for our report provided a sound basis for our 

conclusions about threats to civilian populations. We did not discuss 

biological warfare between combatants on a battlefield with these experts.

We conducted our work from September 1998 through April 1999 in 

accordance with generally accepted government auditing standards. 

As agreed with your offices, unless you publicly announce the contents of 

this report earlier, we plan no further distribution of this report until 

30 days after the distribution date. At that time we will send copies to 
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Page 25 GAO/NSIAD-99-163 Combating Terrorism

appropriate congressional committees, the federal agencies discussed in 

this report, and the Honorable Jacob Lew, Director, Office of Management 

and Budget. We will also make copies available to other interested parties 

upon request.

If you have any questions about this report, please contact me or Carol R. 

Schuster at (202) 512-5140. Key contributors to this report are Davi M. 

D’Agostino, Deborah A. Colantonio, Richard A. McGeary, and Richard H. 

Yeh.

Norman J. Rabkin

Director, National Security 

 Preparedness Issues 
Page 26 GAO/NSIAD-99-163 Combating Terrorism

Contents

Letter 1

Appendix I

Characteristics of 

Selected Chemical 

Agents

28

Appendix II

Characteristics of 

Selected Biological 

Agents

30

Appendix III

Comments From the 

Department of Justice

33

Related GAO Products 36

Figure Figure 1: Stages for Terrorists Working Outside a State-run Laboratory to 

Conduct Chemical and Biological Terrorism 8

Abbreviations

CIA Central Intelligence Agency

CDC Centers for Disease Control and Prevention

CWC Chemical Weapons Convention

DHHS Department of Health and Human Services

DOD Department of Defense

FBI Federal Bureau of Investigation

IND investigational new drug

NIC National Intelligence Council

NIE National Intelligence Estimate
Page 27 GAO/NSIAD-99-163 Combating Terrorism
Page 28 GAO/NSIAD-99-163 Combating Terrorism

Appendix I

Characteristics of Selected Chemical Agents ApendxIi

Agent Ease of manufacture 

and precursor 

availability

Agent 

persistence

Lethality First aid treatment GAO observationsa

Choking agents

Chlorine (CL) Industrial product. No 

precursors required.

Not persistent Low Move to fresh air. For skin contact, 

flush with water. No antidote. 

Provide supportive therapy for 

respiratory and cardiovascular 

functions.

Likely agent due to 

availability as a 

commercial product.

Phosgene 

(CG)

Industrial product. No 

precursors required.

Not persistent Low Move to fresh air. For skin contact, 

flush with water.

Likely agent due to its 

availability as a 

commercial product.

Nerve agents

Tabun (GA) Not readily available 

manufacturing 

instructions, but 

precursors available. 

Relatively easy to 

manufacture. 

Intermediate High Move to fresh air. For skin contact, 

flush with water. Provide atropine or 

pralidoxime chloride or diazepam 

injections.

Likely agent due to 

availability of 

precursor chemicals 

and relative ease of 

manufacture.

Sarin (GB) Moderately difficult to 

manufacture. 

Precursor chemical 

covered by Chemical 

Weapons Convention 

(CWC).

Not persistent High Move to fresh air. For skin contact, 

flush with water. Provide atropine or 

pralidoxime chloride or diazepam 

injections.

Likely agent due to 

demonstrated use by 

Aum Shinrikyo, 

although restrictions 

on precursors could 

create difficulties for 

production.

Soman (GD) Difficult to 

manufacture. Precursor 

chemical covered by 

CWC.

Intermediate High Move to fresh air. For skin contact, 

flush with water. Provide atropine or 

pralidoxime chloride or diazepam 

injections.

Not likely agent due to 

difficulty of 

manufacture and 

control of precursor 

chemical.

GF Moderately difficult to 

manufacture. 

Precursor chemical 

covered by CWC.

Intermediate High Move to fresh air. For skin contact, 

flush with water. Provide atropine or 

pralidoxime chloride or diazepam 

injections.

Not likely agent due to 

difficulty of 

manufacture and 

control of precursor 

chemical.

VX Difficult to 

manufacture. Precursor 

chemicals covered by 

CWC.

High Very high Move to fresh air. For skin contact, 

flush with water. Provide atropine or 

pralidoxime chloride or diazepam 

injections. 

Not likely agent due to 

difficulty of 

manufacture and 

control of precursor 

chemical.

Blood agents

Hydrogen 

cyanide (AC) 

Industrial product. 

Precursor chemicals 

covered by CWC. 

Very low Low to moderate Move to fresh air. Provide 

supportive therapy. Provide amyl 

nitrite or sodium nitrite or sodium 

thiosulfate. 

Likely agent due to its 

availability as a 

commercial product. 

Precursor availability 

may be a problem.

(continued)
Appendix I

Characteristics of Selected Chemical Agents

Page 29 GAO/NSIAD-99-163 Combating Terrorism

a

Our observations are based on a research synthesis of discussions with experts in chemical warfare, 

science, intelligence, law enforcement, and medicine and of an analysis of manuals, handbooks, 

textbooks, studies, and reports on chemical agents.

Note: The following assumptions are used:

1. Dosage and concentration are maximized for an interior environment.

2. The venue occurs at a high-profile event where a large population has gathered.

3. The terrorists have the technical competence (first-year graduate student in chemistry) and 

motivation to obtain and implement the dispersion of agents.

4. The interior environment has an accessible heating, ventilation, and air conditioning distribution 

system.

Cyanogen 

chloride (CK)

Not easily produced. 

Available as 

commercial product. 

Low Low to moderate Move to fresh air. Provide 

supportive therapy. Provide sodium 

nitrite or sodium thiosulfate. 

Likely agent, although 

precursor availability 

may be a problem.

Blister agents

Sulfur 

mustard (HD) 

Easy to synthesize. 

Large quantity buys of 

precursor chemicals 

without detection 

difficult. Precursors 

are covered by CWC.

Intermediate 

to high

Can produce 

incapacitation 

because of 

blistering. Can 

also produce 

death if inhaled 

or a toxic dose 

absorbed. 

Flush skin with water and 

decontaminate clothing. Provide 

oxygen/intubation, bronchodilators.

Not likely agent due to 

difficulty in obtaining 

precursor materials 

and moderate 

production 

requirements.

Nitrogen 

mustard 

(HN-2)

Easy to synthesize. 

Large quantity buys of 

precursor chemicals 

without detection 

difficult. Precursor 

chemicals covered by 

CWC.

Intermediate Can produce 

incapacitation 

because of 

blistering. Can 

also produce 

death if inhaled 

or a toxic dose 

absorbed.

Flush skin with water and 

Decontaminate clothing. Provide 

oxygen/intubation, bronchodilators. 

Provide culumine ophthalmic and 

topical antibiotics and dressings.

Not likely agent due to 

difficulty in obtaining 

precursor materials 

and moderate 

production 

requirements.

Nitrogen 

mustard 

(HN-3)

Easy to synthesize. 

Large quantity buys of 

precursor chemicals 

without detection 

difficult but available. 

High Can produce 

incapacitation 

because of 

blistering. Can 

also produce 

death if inhaled 

or a toxic dose 

absorbed.

Flush skin with water and 

Decontaminate clothing. Provide 

oxygen/intubation, bronchodilators.

Not likely agent due to 

difficulty in obtaining 

precursor materials 

and moderate 

production 

requirements.

Lewisite (L, 

HL)

Moderately difficult to 

manufacture and 

moderately difficult to 

acquire precursor 

chemicals. 

Intermediate 

to high

Can produce 

incapacitation 

because of 

blistering. Can 

also produce 

death if inhaled 

or a toxic dose 

absorbed.

Flush skin with water and 

Decontaminate clothing. Provide 

British anti-lewisite for systemic 

effects.

Not likely agent due to 

difficulty in obtaining 

precursor materials 

and production 

requirements.

Agent Ease of manufacture 

and precursor 

availability

Agent 

persistence

Lethality First aid treatment GAO observationsa
Page 30 GAO/NSIAD-99-163 Combating Terrorism

Appendix II

Characteristics of Selected Biological Agentsl ApendxIi

Agent Ease to acquire 

and process

Agent stability Lethality Laboratory 

safety levela Vaccine Treatment GAO observationsb

Bacterial agents

Inhalation 

anthrax

Difficult to obtain 

virulent seed 

stock and to 

successfully 

process and 

disseminate.

Spores are very 

stable. Resistant to 

sun, heat, and some 

disinfectants.

Very high. Level 3. Yes, primate 

tested. Some 

sources view 

efficacy for 

inhalation 

anthrax as 

questionable.

Virtually always 

fatal once 

symptomatic. 

Treatable very 

early with 

antibiotics and 

supportive 

therapy.

Possible terrorist 

biological agent, but 

requires 

sophistication to 

effectively 

manufacture and 

disseminate to create 

mass casualties. 

Use could indicate 

state sponsorship. 

Symptoms mimic flu 

and might not be 

quickly identified. 

Very high fatality rate 

once symptomatic. 

Not transmissible 

from person to 

person. 

Plague Very difficult to 

acquire seed 

stock and to 

successfully 

process and 

disseminate.

Can be long-lasting, 

but heat, 

disinfectants, and 

sun render 

harmless. 

Very high. Level 3. No. Very early 

treatment with 

antibiotics can 

be effective, 

supportive 

therapy.

Possible agent, but 

not likely. Fairly 

difficult to acquire 

suitable strain and 

difficult to weaponize. 

Glanders Difficult to 

acquire seed 

stock. 

Moderately 

difficult to 

process.

Very stable. Moderate 

to high.

Level 3. No. Antibiotics, but 

no large 

therapeutic 

human trials.

Potential agent, but 

not easy for a 

non-state actor to 

acquire, produce, 

and successfully 

disseminate. 

Tularemia Difficult to 

acquire 

correct 

strain. 

Moderately 

difficult to 

process.

Generally unstable 

in environment. 

Resists cold but is 

killed by mild heat 

and disinfectants.

Moderate 

untreated, 

low 

treated.

Level 3. Investigational 

new drug 

(IND).

Antibiotics very 

effective in early 

treatment.

Possible agent but 

difficult to stabilize. 

Low lethality when 

treated.

Brucellosis Difficult to 

acquire seed 

stock. 

Moderately 

difficult to 

produce.

Very stable. Long 

persistence in wet 

soil or food.

Very low. Level 3. No. Antibiotics 

moderately 

effective if given 

early when 

infected.

May not be a highly 

likely agent because 

of difficulty in 

obtaining virulent 

strain, long 

incubation period, 

and low lethality.

(continued)
Appendix II

Characteristics of Selected Biological Agents

Page 31 GAO/NSIAD-99-163 Combating Terrorism

Q Fever 

(rickettsial 

organism)

Difficult to 

acquire seed 

stock. 

Moderately 

difficult to 

process and 

weaponize.

Stable. Months on 

wood and in sand.

Very low if 

treated.

Level 3. IND. Tested in 

guinea pigs. 

Produces 

adverse 

reactions.

Self-limited 

illness without 

treatment. 

Antibiotics 

shorten illness.

Not a likely agent. 

Low lethality.

Viral agents

Hemorrhagic 

fevers (e.g., 

Ebola)

Very difficult 

to obtain and 

process. 

Unsafe to 

handle. 

Relatively unstable. Depending 

on strain, 

can be 

very high.

Level 4. No. Antiviral drug 

and aggressive 

supportive care. 

Effectiveness of 

any treatment is 

questionable.

Unlikely agent due to 

difficulty in acquiring 

pathogen, safety 

considerations, and 

relative instability.

Smallpox Difficult to 

obtain seed 

stock. Only 

confirmed 

sources in 

United 

States and 

Russia. 

Difficult to 

process.

Very stable. Moderate 

to high.

Level 4. Yes. One potential 

antiviral, but 

generally no 

effective 

chemotherapy.

Very high 

consequence agent, 

but likelihood of 

usage questionable 

due to limited access 

to the pathogen 

beyond state actors. 

Venezuelan 

Equine 

Encephalitis

Difficult to 

obtain seed 

stock. Easy 

to process 

and 

weaponize. 

Relatively unstable. 

Destroyed by heat 

and disinfectants.

Low. Level 3. IND. Supportive 

therapy, 

anticonvulsants. 

Antimicrobial 

therapy 

ineffective.

Possible agent if 

seed stock can be 

acquired, but 

unstable with low 

lethality.

Toxins

Ricin Readily 

available. 

Moderately 

easy to 

process but 

requires ton 

quantities for 

mass 

casualties.

Stable. Very high. Not available. No, but 

candidate 

vaccines 

under 

development.

None (unless 

ingested).

Not a mass casualty 

agent.

Botulinum 

(Types A-G)

Widely 

available but 

high toxin 

producers 

not readily 

available or 

easy to 

process or 

weaponize.

Stable. Weeks in 

non-moving water 

and food. 

Deteriorates in 

bright sun.

High 

without 

respiratory 

support.

Level 3. IND. Tested in 

primates. 

Toxoid vaccine 

against some 

types (A-E). 

Antitoxin (IND) 

and respiratory 

support.

Difficult to weaponize 

and not considered a 

mass casualty agent.

Agent Ease to acquire 

and process

Agent stability Lethality Laboratory 

safety levela Vaccine Treatment GAO observationsb
Appendix II

Characteristics of Selected Biological Agents

Page 32 GAO/NSIAD-99-163 Combating Terrorism

a

Biosafety level 3 applies to agents that may cause serious or potentially lethal disease as a result of 

exposure by inhalation. Among the many precautions is a ducted exhaust air ventilation system that 

creates directional airflow that draws air from clean areas into the laboratory toward contaminated 

areas. The exhaust air is not recirculated to any other area of the building and is discharged to the 

outside with filtration and other optional treatment. Passage into the laboratory is through two sets of 

self-closing doors and a changing room. Showers may be included in the passageway. Biosafety level 

4 is required for work with dangerous and exotic agents that pose a high risk of aerosol-transmitted 

laboratory infections and life-threatening disease. A dedicated non-recirculating air ventilation system 

is provided. The supply and exhaust components are balanced to ensure directional airflow from the 

area of least hazard to the areas of greatest potential hazard. The differential pressure/directional 

airflow between adjacent areas is monitored and alarmed. The airflow in the supply and exhaust 

components is monitored, and the components are interlocked to ensure inward, or zero, airflow. A 

specially designed suit area requires a one-piece positive pressure suit that is ventilated by a 

life-support system. Entry to the area is through an airlock fitted with airtight doors. A chemical 

shower is provided to decontaminate the surface of the suit before the worker leaves the area. 

b

Our observations are based on a research synthesis of discussions with experts in biological warfare, 

science, intelligence, law enforcement, and medicine and of an analysis of manuals, handbooks, 

textbooks, studies, and reports on biological agents. 

Staphylococcl

Enterotoxin B

Difficult to 

acquire high 

yielding seed 

stock. 

Moderately 

difficult to 

process.

Very stable in dry 

form.

Low. Not available. No. No effective 

antimicrobial 

treatment. 

Ventilatory 

support for 

inhalation 

exposure, fluid 

management.

Lower likelihood due 

to low lethality, lack of 

transmissibility.

Agent Ease to acquire 

and process

Agent stability Lethality Laboratory 

safety levela Vaccine Treatment GAO observationsb
Page 33 GAO/NSIAD-99-163 Combating Terrorism

Appendix III

Comments From the Department of Justice ApenIdxi
Appendix III

Comments From the Department of Justice

Page 34 GAO/NSIAD-99-163 Combating Terrorism
Page 35 GAO/NSIAD-99-163 Combating Terrorism
Page 36 GAO/NSIAD-99-163 Combating Terrorism

Related GAO Products

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Combating Terrorism: Federal Agencies’ Efforts to Implement National 

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Chemical Weapons Stockpile: Changes Needed in the Management 

Structure of Emergency Preparedness Program (GAO/NSIAD-97-91, 

June 11, 1997).

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