To mark the second anniversary of the February 14 Bahraini uprising, Prof Damian McCormack, Prof David Grayson and Tara O’Grady call for a ban on CS gas.
CS gas, 2-chlorobenzylidene malononitrile, is a chemical weapon that is banned in warfare by the Organisation for the Prohibition of Chemical Weapons (OPCW) under the Chemical Weapons Convention, 1993.
However, its misuse as a crowd-control tear gas in peacetime is causing significant mortality and morbidity.

We have retrieved and analysed samples from tear gas canisters used in Bahrain and have unequivocally demonstrated the presence of the CS agent. At least 54 deaths have been attributed to the inappropriate use of this agent in Bahrain alone over the past two years.
It is time for the OPCW and the international community to address the misuse of this chemical weapon.
History
CS gas was first developed in 1928 by two Americans, Ben Corson and Roger Stoughton, and the toxin was named after their last initials. It is an aerosol of the active agent, 2-chlorobenzylidene malononitrile, and is synthesised by the reaction of 2-chlorobenzaldehyde with malononitrile via the knoevenagel condensation reaction: ClC6H4CHO + H2C(CN)2 → ClC6H4CHC(CN)2 + H2O.
As CS gas is a solid at room temperature, a variety of techniques have been used to make this solid usable as an aerosol:
• Melted and sprayed in the molten form;
• Dissolved in organic solvent;
• CS2 dry powder (CS2 is a siliconised, micro-pulverised form of CS);
• CS from thermal grenades by generation of hot gases.
CS was developed and tested secretly at Porton Down in England in the 1950s. It was used first on British Army servicemen volunteers and continues to be used in low concentrations in military training.
The chemical reacts with moisture on the skin and in the eyes, causing a burning sensation and uncontrollable shutting of the eyes. Effects usually include burning and tearing from the eyes, profuse coughing, exceptional nasal discharge that is full of mucus, burning in the eyelid, nose and throat areas, disorientation, dizziness and restricted breathing. It will also burn the skin where sweaty and/or sunburned. In higher doses, it can also induce severe coughing and vomiting.
Although CS is described as a ‘non-lethal weapon for crowd control’, many studies have raised doubts about this classification. As well as creating severe pulmonary damage, CS can also significantly damage the heart and liver.
On September 28, 2000, Prof Uwe Heinrich released a commissioned study investigating the use of CS by the FBI at the Branch Davidians’ Mount Carmel compound in Waco. He suggested that if no gas masks were used and the occupants were trapped, then, “there is a distinct possibility that this kind of CS exposure can significantly contribute to or even cause lethal effects”.
Miscarriages
Many reports have associated CS exposure with miscarriages. This is consistent with its reported clastogenic effect (abnormal chromosome change) on mammalian cells.
CS is a cyanide compound and when it is metabolised, cyanide can be detected in human tissue. Also, when exposed to fire, cyanide compounds are undoubtedly released.
According to the United States Army Center for Health Promotion and Preventive Medicine, CS emits “very toxic fumes” when heated to decomposition, and at specified concentrations CS gas is an immediate danger to life and health. The Center also states that those exposed to CS gas should seek medical attention immediately.
In Israel, CS gas was reported to have been the cause of death of Jawaher Abu Rahmah on December 31, 2010, although the Israeli Defense Forces have questioned the veracity of the report. In Egypt, CS gas was reported to be the cause of death of several protesters near Tahrir Square during the November 2011 protests.
In September 2000, the Guardian newspaper revealed how a UK company, HPP, used legal loopholes to export CS to a private security company in Rwanda, in breach of United Nations sanctions.
The Guardian also reported that CS was previously used by the Hutu militia in Rwanda to flush Tutsis out of buildings before hacking them to death.
Subsequently, Amnesty called for an export ban when the receiving regime is either not fully trained in the use of CS, or has shown usage “contrary to the manufacturer’s instructions”.
Only five nations have not signed the Chemical Weapons Convention and are therefore unhindered by restrictions on the use of CS gas: Angola, Egypt, North Korea, Somalia, and Syria.
Bahrain is a signatory of the Chemical Weapons Convention and the use of CS gas in Bahrain is subject to specific ‘end-user’ conditions specified by the manufacturer. However, it seems apparent in Bahrain and elsewhere that these conditions are not enforced, nor indeed enforceable.
Misuse in Bahrain
CS gas has been used extensively by Bahrain’s police since the start of the Bahraini uprising. The Bahrain Independent Commission of Inquiry concluded that Bahrain’s police used a disproportionate amount of CS gas when dispersing protests, and that in a number of situations, police fired CS gas into private homes in an “unnecessary and indiscriminate” manner.
In one particular incident witnessed by Commission investigators, police fired “at least four tear gas canisters (each containing six projectiles)… from a short range into the kitchen and living room of a home”.

According to opposition activists and families of the deceased, at least 54 persons have died as a result of CS gas since March 25, 2011. Some allegedly died from the impact of the CS gas canister, which is shot at high speed from a modified shotgun. Most are said to have died from the effects of inhaling the gas.
CS gas is regularly used at night to smother villages and is frequently shot directly into houses. Children, the elderly and the disabled who have difficulty escaping from the very high concentrations of the toxin are at greatest risk of death. Pregnant women are suffering miscarriages following exposure to high concentrations of the gas.
Materials and methods
In order to confirm that the authorities in Bahrain were using CS gas and not a simple tear gas (a pepper spray such as OC spray (‘Oleoresin Capsicum’) or Mace ‘Phenacyl chloride’ CN spray), samples from several canisters were taken from Bahrain to Trinity College Dublin and analysed.
Five samples, containing 1 to 1.5 grams of green or beige powder, were chosen for analysis. About 500mg of each sample was extracted using cold methanol (20ml) during one hour.
The extract was filtered and evaporated at reduced pressure (bath temperature 40oC) to yield a significant amount of off-white solid that crystallised from solution as the volume was reduced. All of the extracts obtained from the five samples were examined using GC-coupled high-resolution electron-impact mass spectrometry.
Analysis confirmed the presence of a molecular ion with the accurate mass 188.0135, in line with that calculated for C10H5N2Cl. A second, different spectroscopic technique was then applied to confirm a structural diagnosis for this molecule.
The extracts were examined by high-field NMR spectroscopy in CDCl3 solvent and the spectra obtained were compared with published spectra for the CS compound 2-chloro benzylidenemalononitrile.
600MHz 1H NMR spectrum, identical to those published for authentic CS, were obtained. These analyses clearly show that the tear gas canisters used extensively in Bahrain contain the chemical 2-chlorobenzylidene malononitrile, or CS.
Many thousands of used tear gas canisters have been retrieved in Bahrain, and some have external identification markings confirming their source.
More recently, external markings have been illegally removed to deny that possibility. Canisters from manufacturers in the UK, US, Germany and Korea have been identified.
We conclude that the CS agent is being used as a lethal chemical weapon against the civilian population in Bahrain. As such, it is indiscriminate and constitutes a form of collective punishment of the population. We agree with and reiterate the previous call by Amnesty International to ban the export of CS gas to countries and regimes where it is being used as an offensive weapon and as a means of collective punishment.
Prof Damian McCormack, FRCS Orth, Consultant Paediatric Orthopaedic Surgeon, Head of the Advisory Council, Bahrain Rehabilitation and Anti-Violence Organisation (BRAVO).
Prof David H Grayson, MA PhD CChem FRSC, School of Chemistry, TCD.
Tara O’Grady, General Secretary, BRAVO.

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