Thursday, January 6, 2011

CS gas


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 Summary points:
•        Tear gas and pepper spray used for crowd control are not without risks, particularly for people with pre-existing respiratory conditions.
•        Pulmonary, cutaneous, and ocular problems can result from exposure to these agents
•        Treatment for the effects of exposure to tear gas requires chemical decontamination, including protective measures for healthcare staff.
•        Some people are at risk of delayed complications that can be severe enough to warrant admission to hospital and even ventilation support.
Tear gases (along with pepper sprays, toxic emetics, and some sedative substances) are among the so called (riot control agents). A tear gas is actually (not a gas) at all, but a toxic chemical irritant in the form of powder or drops mixed to variable concentrations (1%-5%) in a solvent, and delivered with a dispersion vehicle (a pyrotechnically delivered aerosol or spray solution).
Of the known disabling chemical irritants (of which there are more than a dozen), the five that are traditionally used in the European Union are chlorobenzylidene-malononitrile (also known as CS, after the chemists Corson and Stoughton who first synthesised it),…..
A toxic effect of the solvent methyl-isobutyl-ketone or of certain metabolites has also been documented in animal experimental studies, in particular for chlorobenzylidene-malononitrile (formation of cyanide and thiosulfate derivatives) and chloroacetophenone (formation of hydrogen chloride).
CS is metabolized to o-chlorobenzyl malononitrile (CSH2), o-chlorobenzaldehyde, o-chlorohippuric acid, and thiocyanate. Presence of these metabolites in the body is a strong indicator of CS exposure.
The irritant effects of crowd control agents probably result from the action of chlorine or cyanide groups in addition to alkalising compounds. These agents interact with muco-cutaneous sensory nerve receptors such as TRPA1 cation channels.
Assessments of the effects of riot control agents must take into account the weather (wind, rain, and ambient temperature) in addition to the characteristics of the site of deployment (open or closed space) as the effects of tear gas are enhanced by heat and by high ambient humidity.
The agents differ from one another by their duration of action, their toxicity and their physical and chemical characteristics based on in vitro and animal studies.
Effects of CS gas: (Heinrich, 2000)
CS is a peripheral sensory irritant and the exposure-related symptoms include eye irritation, excessive lacrimation, blepharospasm, burning sensation in the nose and throat, excessive salivation, constricting sensation in the chest, feeling of suffocation, sneezing and coughing, and stinging or burning sensation on the exposed skin. In higher concentrations, CS can also irritate the stomach, leading to vomiting and diarrhea.
Besides the direct toxic effect of high concentrations of CS on the lung, the formation of hydrogen cyanide (HCN) from malononitrile, a metabolite of CS, and its toxic effect, especially on the most sensitive brain cells, possibly leading to respiratory arrest, cannot be ignored when possible lethal effects of CS exposure are discussed. In animal experiments, a synergistic lethality induced by the combination of carbon monoxide and cyanide was reported. This effect could not be explained by altered carbon monoxide or cyanide blood concentrations (Norris et al. 1986).

Cells of the brain, especially the brain stem, are very sensitive to the effects of HCN and a dysfunction in this area of the brain may lead to respiratory arrest. A blood cyanide level of greater than 0.2 μg/ml blood is considered toxic. Lethal cases have usually had levels above 1 μg/ml blood (Casarett and Doull's Toxicology, 1980).
The dose of an inhaled aerosol that is responsible for a certain effect is not the inhaled aerosol concentration in μg/l or mg/m3 but the amount of aerosol that remains in the respiratory tract after inhalation (Heinrich, 2000). CS-related toxicity in the respiratory tract needs some time to actually cause death (Heinrich, 2000).
The following major symptoms in the respiratory tract were reported during controlled human exposure to CS (over 30 minutes), gradually attaining a concentration of 6.6 mg/m3: slight burning, coughing, sneezing, eye irritation, burning became painful with constricting sensation in the chest, gasping when aerosol was inhaled, holding breath and slow and shallow breathing, and paroxysms of coughing that forced the individuals to leave the exposure chamber (Punte et al. 1963).
Is CS gas dangerous? ( Peter J Gray, BMJ 25 February 2000)
Current evidence suggests not but unanswered questions remain.
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. 

This study suggests that the CS preparation used by the UK police may cause more adverse effects than other PIS preparations. A detailed study is now required into the potential adverse effects of the CS used by police. The effectiveness and adverse effects of less concentrated or differently formulated CS gas may also need to be reviewed (Euripidou et al., 2004).
Factors influencing the effect of exposure to tear gas:
* Pre-existing conditions and characteristics of the affected person:
•        Asthma.
•        Chronic obstructive pulmonary disease.
•        Cardiovascular disease.
•        Severe hypertension.
•        Young children.
•        Patients over 60 years.
•        Ocular diseases.
•        Contact lenses.
* Environmental factors:
•        Confined space.
•        Poor ventilation.
* Amount and potency of exposure:
•        High concentration.
•        Prolonged exposure.
•        Repeated exposure.
•        Potent toxicity of the product (chloroacetophenone is more toxic than chlorobenzylidene-malononitrile).
Tips for non-specialists:
•        Medical teams should wear protection for their own safety and to prevent secondary contamination.
•        Contaminated clothes must be removed; eyes and affected skin surfaces should be cleaned with water.
•        For persistent ocular symptoms, ophthalmological assessment is recommended.
•        For severe pulmonary symptoms, oxygen therapy, β2-mimetics and ipratropium aerosols may be required.
•        For pulmonary symptoms, a 24-48 hour stay in hospital or a discharge home with detailed information about potential complications is recommended.
Sources:
Pierre-Nicolas Carron and, Bertrand Yersin. Clinical Review: Management of the effects of exposure to tear gas. BMJ 2009; 338:b2283.
***
F T Fraunfelde. Is CS gas dangerous? Editorial: BMJ 2000; 320 : 458 .
 ***
Peter J Gray. Response to previous article: CS gas is not CS spray - formulation is important . BMJ 25 February 2000.
***
John C. Danforth. By Prof. Dr. Uwe Heinrich. Hannover, Germany, September, 2000. Possible  lethal effects of CS tear gas on Branch Davidians during the FBI raid on the Mount Carmel compound near Waco, Texas. April 19, 1993. Prepared for The Office of Special Counsel.
***
E Euripidou, R MacLehose, A Fletcher. An investigation into the short term and medium term health impacts of personal incapacitant sprays. A follow up of patients reported to the National Poisons Information Service (London). Emerg Med J 2004;21:548–552.

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