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Chemical Weapons: Frequently Asked Questions

Last Reviewed: 
January 2022

Contact: Daryl Kimball, Executive Director, 202-463-8270 ext. 107; Kelsey Davenport, Director for Nonproliferation Policy, 202-463-8270 ext. 102.

Last Reviewed: January 2022

The use and possession of chemical weapons is prohibited under international law. However, several nations continue to maintain active chemical weapons programs, despite a prevailing norm against the use of chemical weapons and international efforts to destroy existing stockpiles.

The following are basic answers to frequently asked questions regarding the different types of chemical weapons and delivery systems, the history of chemical weapons use, international legal regimes that seek to curb the use and stockpiling of chemical weapons, and current efforts to verifiably destroy chemical weapons arsenals.

I. What are chemical weapons?
II. How are chemical weapons delivered?
III.  When have chemical weapons been used?
IV. Are chemical weapons prohibited?
V. What are riot control agents? What is the status of riot control agents under the CWC?
VI. Who has chemical weapons?
VII. How are chemical weapons destroyed?

I. What are chemical weapons?

A chemical weapon is any toxic chemical that can cause death, injury, incapacitation, and sensory irritation, deployed via a delivery system, such as an artillery shell, rocket, or ballistic missile. Chemical weapons are considered weapons of mass destruction and their use in armed conflict is a violation of international law.

Primary forms of chemical weapons include nerve agents, blister agents, choking agents, and blood agents. These agents are categorized based on how they affect the human body.

Nerve agents. Generally considered the most deadly of the different categories of chemical weapons, nerve agents – in liquid or gas form - can be inhaled or absorbed through the skin. Nerve agents inhibit the body’s respiratory and cardiovascular capability by causing severe damage to the central nervous system, and can result in death. The most common nerve agents include Sarin, Soman, and VX.

Blister agents. Blister agents can come in forms of gas, aerosol, or liquid and cause severe burns and blistering of the skin. They can also cause complications to the respiratory system if inhaled and digestive tract if ingested. Common forms of blister agents include Sulfur Mustard, Nitrogen Mustard, Lewisite and Phosgene Oximine.

Choking agents. Choking agents are chemical toxins that directly attack the body’s respiratory system when inhaled and cause respiratory failure. Common forms of choking agents include phosgene, chlorine, and chloropicrin.

Blood agents. Blood agents interfere with the body’s ability to use and transfer oxygen through the bloodstream. Blood agents are generally inhaled and then absorbed into the bloodstream. Common forms of blood agents include Hydrogen Chloride and Cyanogen Chloride.

Certain common industrial chemicals, such as chlorine, are not prohited under the 1997 Chemicals Weapons Convention, but if used as a weapon, such use is prohibited by the treaty.

Riot control agents, such as tear gas, are considered chemical weapons if used as a method of warfare. States can legitimately possess riot control agents and use them for domestic law enforcement purposes, but states that are members of the Chemical Weapons Convention must declare what type of riot agents they possess.

II. How are chemical weapons delivered?

A chemical weapon attack occurs in two phases: delivery and dissemination. The delivery phase refers to the launching of the rocket, bomb, or artillery shell. The dissemination phase involves the dispersal of the chemical agent from the weapon.

Chemical weapons can be delivered via a variety of mechanisms including but not limited to; ballistic missiles, air-dropped gravity bombs, rockets, artillery shells, aerosol canisters, land mines, and mortars.

Artillery shells are conventional shells that have been converted to disperse chemical weapons. The most traditional delivery vehicle of chemical agents, dispersion occurs through an explosive charge that expels the chemical agent laterally.

Air delivered systems can be deployed via gravity bombs, spray tanks, or rockets. Ground detonated and airburst gravity bombs are generally delivered through fixed-wing aircraft, while helicopters have been traditionally deployed with spray tanks and rockets.

Ballistic missiles carrying chemical weapons – via a fill tank or submunitions - utilize an airburst to disperse chemical agents over a broad area. The use of submunitions increases the area in which chemical agents can be dispersed. Compared to other delivery systems, ballistic missiles expand the range of targets that combatants can target with chemical weapons. However, the use of explosives to disperse the chemical agent reduces the potency of the weapon in combat situations.

Cruise missiles. Unlike ballistic missiles, which utilize explosives to discharge the agent, cruise missiles can disperse chemical agents in a gradual and controlled fashion.

Unmanned Aerial Vehicles or UAVs are another platform that combatants may utilize to disperse chemical agents. Like cruise missiles, UAVs are ideal platforms for slower dissemination due to controllable speeds, and dispersal over a wide area. UAVs can fly below radar detection and change directions, allowing them to be retargeted during flight.

Dissemination is the most critical phase of a chemical weapon and generally determines its effectiveness. Generally, dissemination has been done via explosives that expel the agent laterally. Other forms of dissemination include aerodynamic dissemination, a non-explosive delivery mechanism that deploys the chemical agent through dispersion lines.

III.  When have chemical weapons been used?

The use of harmful chemicals in warfare, personal attacks, and assassinations dates back centuries, but the rise of industrial production of chemicals in the late 19th century opened the door to the more massive use of chemical agents in combat. The first major use of chemicals on the battlefield was in World War I when Germany released chlorine gas from pressurized cylinders in April 1915 at Ypres, Belgium. Ironically, this attack did not technically violate the 1899 Hague Peace Conference Declaration, the first international attempt to limit chemical agents in warfare, which banned only “the use of projectiles the sole object of which is the diffusion of asphyxiating or deleterious gases.” Historians estimate that, with the introduction of mustard gases in 1917, chemical weapons and agents injured someone million soldiers and killed 100,000 during the 1914-1918 war.

The 1925 Geneva Protocol sought to ban the use of biological and chemical weapons, but many of its signers joined with major reservations. China, France, the Soviet Union, and the United Kingdom all joined in the 1920s, but Japan did not join until 1970 and the United States until 1975. Between the two world wars, there were a number of reports of the use of chemical weapons in regional conflicts: Morocco in 1923-1926, Tripolitania (Libya) in 1930, Sinkiang (China) in 1934, Abyssinia (Ethiopia) in 1935-1940, and Manchuria (China) in 1937-1942. World War II saw no major use of chemical weapons on the battlefield, with the exception of the Sino-Japanese conflict, and both President Franklin Roosevelt and German leader Adolf Hitler had stated publicly that they were personally against the first use of chemical weapons. Germany, however, did use deadly chemicals in the gas chambers of the Holocaust.

Most of the major powers in World War II developed, produced, and stockpiled large amounts of chemical weapons during the war. Since the end of the war in 1945, there have been only sporadic reports of limited use of chemical weapons, including in the Yemen war of 1963-1967 when Egypt bombed Yemeni villages, killing some 1,500 people. The United States heavily used herbicides such as Agent Orange and tear gas in the Vietnam War in the 1960s; although such chemicals are not covered under the Chemical Weapons Convention (CWC), some observers saw this as chemical warfare. Iraq used chemical weapons in the 1980-1988 Iran-Iraq war and against the Kurds in Halabja in 1988. These two cases provoked widespread public opposition to the horrors and indiscriminate nature of deadly chemical agents and certainly helped advance CWC negotiations, which had begun in the early 1980s, to their conclusion in 1992.

For more on the history of chemical weapons, use see “Abolishing Chemical Weapons: Progress, Challenges, and Opportunities” in November 2010 Arms Control Today.

The use of the nerve agent sarin by the Japanese terrorist group Aum Shinrikyo in June 1994 in Matsumoto, Japan, and again on March 20, 1995, in the Tokyo subway system, killing 19 people and injuring some 5,000, suddenly brought to light the potential threat of non-state actors intent on using weapons of mass destruction. The first official on-site inspection by the United States of a Russian chemical weapons stockpile in the Kurgan Oblast along the border of Kazakhstan in July 1994 illustrated that Russian chemical weapons arsenals left much to be desired regarding security against theft, diversion, and terrorism.

Iraqi insurgents in recent years have combined tanks of chlorine gas with improvised explosive devices, but with little success. There were reports of the possible limited use of chemical agents by Taliban insurgents in Afghanistan and by Turkish troops against Kurdish rebels in eastern Turkey, but these allegations remain unproven. In public statements, Osama bin Laden and al Qaeda threatened to use nuclear, chemical, biological, and radiological weapons.

In Syria, intelligence reports by the United States, the United Kingdom, and France assess that the Assad regime has used chemical weapons against opposition forces on numerous occasions since 2012, including an August 2013 attack in Ghouta, outside of Damascus, that killed more than 1,400 people. The UN-OPCW Joint Investigative Mechanism (JIM) has found the Syrian government responsible for numerous chemical weapons attacks, including in April 2014, March 2015, March 2016 and April 2017 and the Islamic State responsible for chemical weapons attacks in August 2015 and September 2016. The OPCW Investigation and Identification Team (IIT) also attributed a series of March 2017 chemical attacks to the Syrian Air Force. Reports of chemical weapons use in Syria continue to surface. For a complete timeline of Syrian chemical weapons use see Timeline of Syrian Chemical Weapons Activity, 2012-2020.

Kurdish and Iraqi military forces claim the Islamic State used chlorine gas in attacks in December 2014 and March 2015 in Iraq, but these accounts have not been verified by the OPCW.

In February 2017, North Korean agents used VX, a nerve agent, to assassinate Kim Jong-nam, the half-brother of North Korean leader Kim Jong-un in the airport in Kuala Lumpur, Malaysia.

In March 2018, the UK accused Russia of using a Novichok agent to assassinate a former Russian spy, Sergei Skripal, and his daughter, Yulia, in the UK.

IV. Are chemical weapons prohibited?

Yes. The horrendous and widespread use of chemical weapons in World War I prompted international efforts to curb the use and production of chemical agents.

The two major protocols that target chemical weapons are the 1925 Geneva Protocol and the Chemical Weapons Convention (CWC). The former provides the initial international legal framework for controls on the use of chemical weapons, while the latter establishes comprehensive international standards that ban the development, production, acquisition, stockpiling, use, transfer, or retention of chemical weapons for all CWC state parties.

1925 Geneva Protocol: Signed in 1925, the Geneva Protocol was drafted and signed at the Conference for the Supervision of the International Trade in Arms and Ammunition, and prohibits the use of chemical and biological weapons in the field of conflict. While it prohibits the use of chemical weapons, the Geneva Protocol does not regulate the production, research or stockpiling of these weapons. It allows nations to reserve the right to retaliate with chemical weapons should it be subject to an adversarial chemical attack. It also does not regulate the use of chemical weapons for internal conflicts. However, over time, through customary international law, it is widely considered applicable to these conflicts as well. Interest in verifiable elimination of existing stockpiles of chemical weapons fueled the push for the more robust CWC in 1993.

Chemical Weapons Convention: The Chemical Weapons Convention is a multilateral treaty that bans the development, production, acquisition, stockpiling, transfer, and use of chemical weapons and requires all possessor states to destroy their stockpiles safely. Opened for signature in Paris on January 13, 1993, the CWC entered into force in April 29, 1997, and has 193 members, including Palestine. Currently one nation– Israel– has signed but not ratified the treaty, while three nations (Egypt, North Korea, and South Sudan) have neither signed nor acceded to the CWC.

The CWC requires universal adherence to its protocols and establishes verification regimes that assure the destruction of member nations' chemical weapon stockpiles. The CWC requires member nations to declare all chemical weapons and chemical weapons sites, including research, development, and testing sites, to be subject to on-site inspection. According to Article VI of the treaty, destruction of a state party’s declared chemical weapons arsenal should begin no later than two years after the state joins the treaty and should finish no more than ten years after it has joined, although the treaty does allow a deadline extension of up to five years from that date. Verification is implemented through the Organization for the Prohibition of Chemical Weapons (OPCW), located in The Hague, Netherlands, and involves routine on-site inspections and reporting. The CWC also promotes multilateral cooperation on peaceful uses of chemistry and undertakes over 400 on-site inspections of the chemical industry annually.

For more information on the CWC, see Chemical Weapons Convention at a Glance.

V. What are riot control agents? What is the status of riot control agents under the CWC?

Riot control agents (RCAs) are chemical agents used both to control and disperse crowds and as personal protection. RCAs temporarily impede human function by irritating the eyes, mouth, throat, lungs, and skin. Prolonged exposure or exposure to a high concentration of an RCA can cause blindness, respiratory failure, or death.

The OPCW defines a chemical weapon as “a chemical used to cause intentional death or harm through its toxic properties.” In this respect, while the CWC does not overtly ban the production, stockpile, or use of RCAs, an RCA used as a method of warfare is prohibited by the CWC under this definition. States Parties agree under Article 1, Paragraph 5 of the Convention, “not to use riot control agents as a method of warfare.”

The Treaty permits use of RCAs by States for “domestic law enforcement purposes,” but requires States Parties to declare what RCAs they possess. Examples of common RCAs include Tear Gas (CS gas), Pepper Spray (OC), and Mace (CN).

In some states, groups are advocating for tightened restrictions on RCA use by domestic law enforcement, citing the prohibition of their use in warfare under the CWC, their indiscriminate nature, and the possible long-term health effects that exposure to them can cause.

VI. Who has chemical weapons?

Eight countries declared chemical weapons stockpiles when they joined the CWC: Albania, India, Iraq, Libya, Syria, the United States, Russia and an anonymous state widely believed to be South Korea. Of those eight countries, Albania, South Korea, India, Iraq, Syria, Libya and Russia have completed destruction of their declared arsenals. Syria, however, has not declared its entire stockpile. The United States plans to complete the destruction of its chemical weapons by September 2023.

When Russia, the United States, and Libya declared that they would be unable to meet their final destruction deadlines in 2012, CWC state parties agreed to extend the deadlines with increased national reporting and transparency.

Russia declared the largest stockpile with approximately 40,000 metric tons at seven arsenals in six regions of Russia. Russia's arsenal originally consisted of VX, sarin, soman, mustard, lewisite, mustard-lewisite mixtures, and phosgene.

Russia officially completed the destruction of its chemical weapons arsenal in 2017. Russia’s destruction program benefited from technical assistance and funding through the Cooperative Threat Reduction Program.

However, Russia still retains some chemical weapons capacity. In March 2018, Russia used the advanced chemical agent Novichok to assassinate a former Russian spy, Sergei Skripal, and his daughter Yulia, in the UK. In a 2021 State Department report on compliance with the CWC, the United States accused Russia of non-compliance with the CWC for its alleged use of Novichok. The report also noted that “The United States cannot certify that Russia has met its obligations" under the Convention and asserted that Russia had not made a complete declaration of its stockpile.

The United States declared 28,577 metric tons at nine stockpiles in eight states and on Johnston Atoll west of Hawaii. Albania and Libya declared the smallest stockpiles, with 16 and 23 metric tons respectively. India and South Korea declared stockpiles in the 500-1,000 metric ton range but maintained a high degree of secrecy around the size, location, composition, and destruction of their weapons.

Syria admitted that it had chemical weapons in July 2012. It joined the CWC on September 12, 2013, declaring its chemical weapons stockpile and determining a plan for its elimination soon after. The OPCW announced that the entirety of Syria’s declared stockpile of 1,308 metric tons of sulfur mustard agent and precursor chemicals had been destroyed by January 2016. The destruction processes were carried out on board the US Merchant Marine ship, Cape Ray, and in four countries – Finland, Germany, the United Kingdom, and the United States. However, reports continue to surface of chemical weapon use in Syria, raising questions about the accuracy of its initial declaration. In July 2020, the OPCW Executive Council adopted a resolution addressing the ongoing possession and use of chemical weapons by Syria. That resolution called on the Syrian government to declare the remainder of its chemical stockpile and to resolve any inconsistencies regarding its initial stockpile declaration within 100 days, or by mid-October, 2020. Thusfar, Syria has not done so.

North Korea, a non-signatory to the CWC, is widely reported to possess a large arsenal of chemical weapons, likely over 5,000 metric tons, including mustard, phosgene, and nerve agents. The use of VX nerve agent in the 2017 assassination in Kuala Lumpur strongly indicates that VX is part of North Korea’s chemical arsenal.

For more information, see Chemical and Biological Weapons Status at a Glance.

VII. How are chemical weapons destroyed?

The United States: The United States began construction of its first prototype incinerator on Johnston Atoll in the 1980s. In 1990, it began burning 1,842 metric tons of chemical weapons, which had been secretly shipped from forward deployment in Germany and Okinawa many years earlier. When the CWC entered into force in 1997, the United States was already operating its first two incinerators on Johnston Atoll and in Tooele, Utah, which was the largest U.S. chemical weapons stockpile with 12,353 metric tons. The U.S. Army burned 1,436 metric tons, about 5 percent of the total chemical stockpile, at the two sites before the April 1997 entry into force.

The U.S. Army initially planned to construct three centralized incinerators to destroy the U.S. chemical weapons stockpile, and early schedules optimistically showed the United States completing operations in 1994. Congress subsequently banned transportation of chemical munitions on safety and security grounds, necessitating the current plan for a destruction facility at each of the nine U.S. sites at which chemical weapons are stored.

When the U.S. Senate finally approved the CWC, on April 25, 1997, after a long and contentious debate, the articles of ratification specified, among many other conditions, that the president place the highest priority on protection of public health and the environment and that the Army undertake the development and demonstration of nonincineration technologies for chemical weapons destruction.

Today the United States has constructed and operated five large incinerators: on Johnston Atoll and in Tooele, Utah, as previously noted; in Umatilla, Oregon; in Anniston, Alabama; and in Pine Bluff, Arkansas. The Johnston Atoll incinerator finished operations in 2000; the other four completed operations in 2012. In addition, neutralization facilities were built in Newport, Indiana, and Edgewood, Maryland; they chemically treated and destroyed bulk VX nerve agent and mustard agent. The remaining two chemical weapons stockpiles in Pueblo, Colorado, and Blue Grass, Kentucky, will each be destroyed by chemical neutralization, followed by second-stage treatments of bioremediation and super-critical water oxidation (SCWO). The Pueblo facility began operations in 2016, and Blue Grass began shortly after, in June 2019.

In the OPCW’s annual report for 2018 it declared that the United States had destroyed approximately 90.6 percent - about 25,154 metric tons - of the chemical weapons stockpile it had declared as the CWC entered into force. The United States has destroyed all of Category 2 and Category 3 weapons. As of July 2020, the United States has 1,445.5 metric tons of mustard and nerve agents remaining in its stockpile. The United States is projected to complete destruction by September 2023.

Russia: Russian officials made it clear in 1997, when they ratified the CWC, that they would need technical and financial support from other CWC members to meet its treaty deadlines. During the 1994 U.S. visit to Russia, Russian military officials and the chairman of the Duma defense committee rejected a U.S. offer made by the assistant to the secretary of defense for nuclear, chemical, and biological defense programs to construct an incinerator at the Shchuch’ye chemical weapons stockpile. Russian officials wanted to determine their own technologies for demilitarization and were very wary of incineration as too complex, too expensive, too dangerous, and too politically contentious.

The first Russian chemical weapons demilitarization facility, built and funded as a prototype facility by Germany for neutralizing lewisite, an older, arsenic-based chemical agent, opened in 2002 at Gorny in the Saratov Oblast. Since then, Russia has been able to open five more destruction facilities, the last at Kizner in the Udmurt Republic.

Most of these facilities have been supported financially by the Global Partnership Against the Spread of Weapons and Materials of Mass Destruction, founded by the Group of Eight at its summit meeting in Kananaskis, Canada, in 2002. As of 2010, the United States through the Cooperative Threat Reduction (CTR or Nunn-Lugar) program committed more than $1 billion since the mid-1990s to the planning and construction of the neutralization facility at Shchuch’ye, while Germany has committed $475 million (340 million euros) to construction at Gorny, Kambarka, and Pochep. Canada and the United Kingdom have contributed some $82 million and $39 million, respectively, while at least another 10 additional countries have contributed some $25 million.

On September 27, 2017, the OPCW announced that Russia had completed the destruction of its chemical weapons arsenal.

Libya: Libya joined the CWC in 2004 and, in its submittal at the time, declared 23 metric tons of mustard agent in bulk containers. In addition, it declared one inactivated chemical weapons production facility, two chemical weapons storage sites, 1,300 metric tons of precursor chemicals, and 3,563 unfilled aerial bombs. It first planned on eliminating its chemical agent stockpile by the 2007 deadline.

However, after aborted attempts at U.S. and Italian partnerships in its demilitarization program, it asked for several OPCW deadline extensions. Destruction of the stockpile was halted in February 2011 due to the armed uprising that resulted in the overthrow of the Gaddafi regime. At that time, 11.5 metric tons of chemical weapons remained in Libya’s declared stockpiles.

Libya subsequently declared an additional chemical weapons stockpile and completed the destruction of its Category 1 chemical weapons in January 2014. With assistance from the OPCW and other member states including Canada and Denmark, Libya removed all of the remaining precursor chemicals from its territory for destruction in August 2016. The Syria case, which set the precedent for destroying chemical weapons outside of the country of origin, paved the way for shipping the remaining chemicals out of Libya for destruction in Germany. Libya completed the destruction of all its chemical weapons in January 2018.

For more information on the destruction of Libya’s chemical weapons see Chronology of Libya’s Disarmament and Relations with the United States.

Iraq: Iraq joined the CWC in early 2009 and declared two large, sealed "Al Muthana" bunkers in the Fallujah region with chemical weapons and related equipment and debris from the 1991 Persian Gulf War. Because at least one of these bunkers had been hit by aerial bombs in the war, there is no final inventory of weapons and agents, nor a thorough evaluation of the possible risks of open agents or unexploded ordnance in the bunkers. The OPCW declared Iraq's destruction complete in March 2018.

Albania: Albania was the first possessor state to destroy its stockpile. Although it joined the CWC in 1994, it did not acknowledge its possession of 16 metric tons of mustard agent (as well as small quantities of lewisite and other chemicals) until 2003. The OPCW declared Albania’s destruction complete in July 2007.

South Korea: South Korea refused to acknowledge its stockpile in any public presentations, including the annual speeches by its ambassador to the OPCW, and has claimed full confidentiality (“highly protected information”) under the Confidentiality Annex of the CWC; all OPCW delegations and staff therefore refer to it as “A State Party” in reference to declared possessor states. South Korea completed the destruction of its chemical weapons in 2008.

India: India declared a stockpile of 1,044 tons of sulfur mustard in 1997 after ratifying the CWC in 1996. India completed the destruction of its entire chemical weapons stockpile in 2009.

-Research Assistance by Julia Masterson