What is sarin?

Sarin is among the most toxic and fast-acting chemical weapons. Developed by German scientists seeking new pesticides in the 1930s, the colorless and odorless chemical is manufactured from dual-use precursor chemicals—that is, commercially available chemicals that serve legitimate industrial uses. Like VX, a more toxic nerve agent, sarin (also known as GB) disrupts the nervous system. Overstimulation of glands and muscles causes the respiratory system to shut down and can induce convulsions, paralysis, and even death if an antidote is not immediately administered.

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While one drop can be fatal, sarin is nonpersistent—it disperses and vaporizes quickly—meaning that large quantities may be required to inflict mass casualties. Sarin is considered a weapon of mass destruction (WMD) under international law, but its lethality is contingent on a variety of factors, including its method of dispersion (principally through munitions such as bombs or warheads) and environmental and atmospheric conditions.

Is sarin banned under international law?

Sarin, like all chemical weapons, is banned under international law. The Organisation for the Prohibition of Chemical Weapons (OPCW), the implementing body of the Chemical Weapons Convention, classifies sarin under Schedule 1, a class reserved for lethal chemicals with few (if any) legitimate, civilian applications.

A long-standing stigma has discouraged the use of chemical weapons. The scholar Richard Price says that the "chemical weapons taboo," in his phrase, is unique—and, perhaps, uniquely effective—because the self-imposed proscription, dating to the late nineteenth century, predates the technology's development. The indiscriminate nature of chemical weapons violates distinction, a bedrock principle of just war theory and the law of armed conflict that enjoins belligerents to distinguish between combatants and civilians. This potential for "catastrophic lethality against civilian populations" has contributed to the resilience of the norm in the century since World War I.

In the Hague Declaration of 1899, thirty-two states "agree[d] to abstain from the use of projectiles the sole object of which is the diffusion of asphyxiating or deleterious gases." The proscription was further institutionalized by the Geneva Protocol of 1925, which prohibits the use "of asphyxiating, poisonous or other gases, and of all analogous liquids, materials or devices" in war. One hundred thirty-seven countries, including Syria, in 1968, have acceded to the protocol, which some legal experts consider to be the basis of customary law applicable to internal armed conflict.

These laws made no mention of the "development, production, and stockpiling of chemical weapons as a deterrent," which signatories vigorously pursued [PDF], the late Jonathan Tucker, a noted arms control expert, observed in 2011.

Negotiations on chemical-weapons law in the 1970s and 1980s gained momentum after Iraq's widespread use of chemical weapons and with improved U.S.-Soviet relations. Talks culminated in the Chemical Weapons Convention (CWC), which entered into force in 1997. The treaty extended the ban, prohibiting the development, production, stockpiling, transfer, and use of chemical weapons, called for the elimination of existing stocks, and established an intrusive verification regime.

In a last-minute bid to avert U.S. airstrikes, Syria acceded to the CWC on September 14, 2013 after years of resisting the treaty. Syria had not previously affirmed it had chemical stocks—indeed, in an interview that aired five days prior, President Bashar al-Assad refused to confirm or deny their existence. Though the CWC will not enter into force for Syria until October 14, 2013, the country is bound by the Geneva Protocol, which it ratified in 1968, from using chemical agents in warfare.

With Syria's accession, all but seven countries are party to the convention; Israel and Myanmar have signed but not ratified the convention, while Angola, Egypt, North Korea, and South Sudan have neither signed nor ratified it.

Under the Rome Statute, from which the International Criminal Court draws its authority, "employing asphyxiating, poisonous or other gases, and all analogous liquids, materials or devices" is considered a war crime. Nationals of countries not party to the Rome Statute can still be prosecuted at The Hague if the UN Security Council makes a referral.

Which countries possess sarin?

Most countries that held chemical weapons destroyed their stocks or are in the process of doing so under the CWC. Progress is detailed in the OPCW's annual report [PDF].

The United States conducted research and development on sarin after World War II; though it has destroyed 96 percent of its declared stockpile, according to the OPCW, the Pentagon has said it may not achieve 100 percent until 2023, despite an April 2012 deadline under the CWC.

Russia also developed sarin stocks during the Cold War. It too missed the 2012 deadline, and while the Kremlin has said it would complete its work by 2015, 53 percent remains, all in weaponized form, according to the OPCW.

In addition to these sarin stocks, the United States and one other state party to the CWC have declared 1,175 metric tons of binary sarin components—chemicals that may be innocuous on their own but form the toxic gas upon contact. (Per its request, the latter state has not been disclosed by the OPCW.)

Ali Akbar Hashemi Rafsanjani, who would later become Iran's president, famously remarked at the end of the Iran-Iraq War, "Chemical and biological weapons are the poor man's atomic bomb." Analysts say that historically, stockpilers of chemical weapons sought a deterrent similar to nuclear weapons that did not require the technical capacity or attract the international scrutiny of nuclear weapons production. In 2004, Syrian president Assad asserted his country's right to a chemical weapons program, saying he would abandon it only if Israel disarmed its nuclear arsenal.

The U.S. intelligence community [PDF] says that Iran maintains an active chemical weapons arsenal, and North Korea's stocks, estimated to be between 2,500 and 5,000 tons, contain sarin—a finding corroborated by a UN Security Council committee and South Korean intelligence estimates [PDF].

Syria has amassed what is considered to be one of the world's largest stockpiles of chemical weapons with assistance from Iran, Russia, and China. Western European and American companies have abetted the process, the New York Times reports, as Assad imported precursor chemicals through a network of front companies. Despite extensive stocks and an advanced program, Syria remains dependent on foreign suppliers [PDF], U.S. intelligence suggests.

Chemical weapons sites are reportedly distributed throughout the country. The Free Syrian Army has trained personnel to secure the depots should the Assad regime lose control, and U.S. military planners have estimated that 75,000 troops could be required for the same task. Director of National Intelligence James Clapper has cast doubt on the United States' ability to secure Syrian stocks.

Syria's disarmement under the CWC was catalyzed by a September 2013 U.S.-Russian agreement that called for the destruction of Syria's chemical weapons program under UN auspices "on an expedited basis." Under the framework, which must now be approved by the UN Security Council, punitive action including military measures could be taken up under Chapter VII of the UN Charter to hedge against noncompliance.

Arms control experts cautioned that the timetable laid out for Syrian disarmament was ambitious by historical standards, and the challenges that inspectors would typically face in monitoring, securing, and dismantling chemical arsenals would be compounded if working in a warzone. No ceasefire to facilitate the process is expected.

Have countries used sarin?

Iraq is the only state to have definitively used chemical weapons since World War II. Saddam Hussein twice deployed sarin: in the Iran-Iraq War (1980–88) and against its own Kurdish minority in the north. Iraq first used chemical weapons against Iranian infantry in 1983 and escalated to sarin in the last eighteen months of the war, causing tens of thousands of casualties. Hussein also used sarin against Iraq's minority Kurdish population, assaulting the northern town of Halabja in 1988. Some 3,200 to 5,000 Kurds were killed, with thousands more injured, as Iraqi planes dropped mustard gas and nerve agents as part of a broader campaign against the Kurds.

World powers did not take legal or military action after Hussein's use of chemical weapons. But the UN Security Council moved to disarm Iraq, and U.S. strikes against the country in 1998 sought to degrade Hussein's WMD arsenal. Iraqi use may also have catalyzed progress on the CWC.

In Syria, Assad is accused of attacking opposition forces and civilians with chemical weapons on multiple occasions, culminating in an August 21, 2013, attack on Ghouta, in the Damascus suburbs, which U.S. and French intelligence say killed well over one thousand people. UN chemical-weapons inspectors concluded: "the environmental, chemical, and medical samples we have collected provide clear and convincing evidence that surface-to-surface rockets containing the nerve agent sarin were used."

A determination of culpability fell beyond the inspectors' mandate. While Syrian and Russian officials have suggested that rebel forces bore responsibility for the attacks, the American and British ambassadors to the UN said circumstantial evidence included in the report, including details about munitions, implicated the Assad regime. Opposition forces are not known to have such missiles.

Have nonstate actors used sarin?

Chemical weapons can be an "insidious equalizer," to use Price's phrase, which can give marginal groups the ability to cause mass casualties and widespread terror. Yet there is only one documented case of a nonstate actor using sarin, in part because of the technical sophistication required to manufacture and disseminate the poison.

Aum Shinrikyo, a messianic Japanese cult, attacked the Tokyo subway with sarin during a morning rush hour in 1995. Aum members brought sarin onto five subway cars in packages made to look like lunch boxes and bottled drinks, killing twelve and wounding thousands more. Aum, which mass-produced chemical weapons, was also implicated in the Matsumoto incident a year prior, in which the group targeted judges for assassination. A breeze shifted the plume, killing seven and injuring two hundred.

Reflecting on the subway massacre, CFR Director of Studies James M. Lindsay says, "[Advances in] technology make it possible for groups and individuals to carry out the kinds of attacks that once only governments could undertake." With purer chemicals and more effective dissemination techniques, death tolls could have been far higher [PDF]; the ratio of those killed to those injured on the Tokyo subways could have been inverted, says Raymond Zilinskas, director of the Chemical and Biological Weapons Nonproliferation Program at the Monterey Institute's Center for Nonproliferation Studies.

Two U.S. soldiers were exposed to small amounts of sarin in Iraq in May 2004 when an artillery shell containing the nerve agent, rigged as an IED, exploded. The incident was isolated, leading experts to believe that, rather than evidence of an active WMD program prior to Saddam Hussein's ouster, the shell was a "dud" left over from Iraq's pre–Gulf War arsenal.

Since the outbreak of the civil war in Syria, the prospect of chemical weapons stocks falling into the hands of al-Qaeda–affiliated rebels, or being transferred by the Assad regime to Hezbollah, has been chief among Western concerns. Zilinskas questions whether these groups have the engineering capacity to weaponize chemical weapons, however. "I could imagine them capturing conventional rockets, but then to adapt them for chemical-weapons use would be quite a difficult feat," he says.

Further Reading

The Economist and the New York Times provide concise histories of chemical weapons use since World War I and concomitant efforts to constrain their use.

Daniel Kevles offers a history of chemical weapons, focusing on the evolution of the United States' role in stockpiling weapons, forming strategy, and shaping international law, in the New York Review of Books.

Richard Price argues that the chemical weapons taboo is "one of the great success stories" in placing restraints on the conduct of war, and the Syria case—in which both rebels and the regime have denied using chemical weapons—has reinforced rather than undermined the norm, in the Boston Globe.

CFR's Laurie Garrett argues that "the CWC needs more teeth" and calls for more stringent international agreements covering the monitoring, surveillance, and interdiction of precursor chemicals, in an op-ed for Politico.

This Congressional Research Service report [PDF] provides background on Syria's chemical weapons program, the challenges of securing its arsenals, and alleged attacks.