Intended for healthcare professionals


Is CS gas dangerous?

BMJ 2000; 320 doi: (Published 19 February 2000) Cite this as: BMJ 2000;320:458

Current evidence suggests not but unanswered questions remain

  1. F T Fraunfelde, professor of ophthalmology
  1. Department of Ophthalmology, Oregon Health Sciences University, Portland, OR 97201-4197, USA

    CS gas (2-chlorobenzylidene malononitrile) is one of the most commonly used tear gases in the world. Law enforcement agencies have found this agent invaluable when faced with combative suspects, for riot control, and for alleviating hostage and siege situations. They use it to help control individuals or groups without the need for lethal force. The chemical was used for crowd control as early as the 1950s, but not until the mid-1960s did it come into common use in several countries. In Britain there has been persistent concern about the use of CS gas in the media, numerous complaints to the Police Complaints Authority, and an editorial two years ago in the Lancet that called for a moratorium on the use of CS tear gas.1 This editorial was unusual in calling for a moratorium on an agent used widely for decades with little data on permanent damage. Nevertheless, it did correctly identify the need for some further studies, as did a report recently commissioned by the British government.2

    At standard daily temperatures and pressures CS forms a white crystal with a low vapour pressure and poor solubility in water. CS aerosols thus act as a “powdered barb” with microscopic particles which are potent sensory irritants becoming attached primarily to moist mucous membranes and moist skin. The eye is the most sensitive organ in riot control because CS causes epiphora, blepharospasm, a burning sensation, and visual problems. Coughing, increased mucous secretion, severe headaches, dizziness, dyspnoea, tightness of the chest, difficulty breathing, skin reactions, and excessive salivation are common. The onset of symptoms occurs within 20to60 seconds, and if the exposed individual is placed in fresh air these findings generally cease in 10 to 30 minutes.In the main the medical literature supports the safety of CS gas.35

    Significant reactions have been reported,68 which may be a result of the way the gas is used. In the heat of a crisis both sides may overreact by excessive use of this agent (the police using too much, rioters throwing canisters back), or the combatants may not leave the area and thus remain exposed and away from the gas's natural antidote—fresh air. In over 30 years of active use of 1% CS gas no lawsuits for damages have been awarded in the litigious environment of the United States. In Britain, however, the spray used by police contains 5% CS in methyl isobutyl ketone (MIBK).

    There are no scientific data on the relative safety of 1% versus 5% CS. This is hard data to obtain, since most damage is from aerosol fired at close range, and over half the injuries are “self inflicted” in the sense that the victims voluntarily expose themselves to the gas and remain exposed. Many suspect that the most significant side effects occur in those individuals most active in continuing civil disobedience.

    The British Department of Health, with the support of the Home Office, asked three of its advisory committees (on Toxicity, Mutagenicity, and Carcinogenicity of Chemicals in Food; Consumer Products; and the Environment) to study the use of CS spray as a chemical incapacitant because of public health concerns. The report, released last year, stated that many data were available on the toxicity of CS and, to a lesser extent, on methyl isobutyl ketone, but only limited data on the formulated product.2 Based on the data, they concluded that 5% CS in methyl isobutyl ketone did not, in general, raise major health concerns. The committee cautioned, however, that no comprehensive investigations of the effect of CS sprays with follow up in humans are available and they need to be done. They targeted susceptible groups to study in particular: those with asthma or chronic obstructive disease, hypertension, and cardiovascular disease and possibly those taking neuroleptic drugs. The committees also pointed out the need for recommendations for aftercare guidelines for anyone exposed to CS.

    This is especially true for ocular exposure. The current recommendations in Britain for treating ocular exposure are to “blow dry air directly onto the eye.”9 The recommendation of the manufacturers of CS in the United States is copious ocular irrigation to dislodge, dilute, and wash away the irritant. The US Army recommends flushing with water or saline and says that impact particles may need to be removed, although no impact CS particles have caused significant ocular damage.10

    This long-awaited report for the British government will not satisfy many because this issue has marked social and political overlay, and there is incomplete scientific data available to make comprehensive recommendations. Nevertheless, at this point, the committees' recommendations appear reasonable. Based on our current knowledge, if CS tear gas is used by properly trained law enforcement officers and exposed combatants leave the area rapidly, few, if any, significant or long-term human disabling effects should occur.


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