Tear Gases: An Overview of Riot Control Agents
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Tear Gases: An overview of some riot control agents
Source: A FOA Briefing Book on Chemical Weapons
Tear gases is the common name for substances which, in low
concentrations, cause pain in the eyes, flow of tears and difficulty
in keeping the eyes open. Tear gases are used mainly in military
exercises and in riot control, etc., but have also been used as a
method of warfare. Irritating gases have been used in war since
ancient times but it was not until after the Second World War that a
more systematic search for effective substances was started.
Among a long series of substances, three have become of greater
importance than the others. They are effective and imply low risks
when used. These substances are chloroacetophenone (codename
CN), orto-chlorobenzylidene-malononitrile (codename CS) and
dibenz (b,f)-1,4-oxazepine (codename CR). CN was formerly the
most widely used tear gas. Today, CS has largely replaced CN and
is probably the most widely used tear gas internationally.
At room temperature, these tear gases are white solid substances.
They are stable when heated and have low vapour pressure.
Consequently, they are generally dispersed as aerosols. All of them
have low solubility in water but can be dissolved in several organic
solvents. Hydrolysis of CN is very slow in water solution, also
when alkali is added. CS is rapidly hydrolyzed in water solution
(half-life at pH 7 is about 15 min. at room temperature) and
extremely rapid when alkali is added (half-life at pH 9 is about 1
min.). CR is hydrolyzed only to a negligible extent in water
solution.
CN and CR are, thus, difficult to decompose under practical
conditions, whereas CS can easily be inactivated by means of a
water solution. Skin is suitably decontaminated by thorough
washing with soap and water. CS is then decomposed whereas CN
and CR are only removed.
Decontamination of material after contamination with CS can be
done with a 5-10 % soda solution or 2 % alkaline solution. If this
type of decontamination cannot be accomplished (e.g.,
contaminated rooms and furniture), then the only other means is by
intensive air exchange - preferably with hot air.
In contrast to human beings, animals generally have low sensitivity
to tear gases. Dogs and horses can therefore be used by police for
riot control even when tear gas is used.
Symptoms
All tear gases have in common that they cause almost instant pain
in the eyes, flow of tears and cramp of the eyelids. The strongly
irritating effect leads to a more or less pronounced incapacitation of
exposed persons. Apart from the effects on the eyes, most tear
gases cause irritation in the nose and mouth, throat and airways and
sometimes also in the skin, particularly in moist and warm parts. In
situations of massive exposure, tear gas which is swallowed may
also cause vomiting.
Disagreeable sensations caused by exposure to tear gas are so
strong that victims cannot behave rationally, which explains why
tear gases cause incapacitation. The irritating effect remains as long
as there is sufficient concentration of tear gas present but
disappears fairly quickly (15-30 min.) after exposure has ceased.
The irritating properties of tear gases depend on nerves in mucous
membrane and skin being affected. Sensitivity to tear gases varies
considerably between different individuals. Factors influencing
individual reactions may be emotional state, motivation, physical
activity, ambient temperature and humidity.
The expressions "threshold concentration" (TC) and "incapacitating
or intolerable concentration" (IC) are frequently used to express the
efficiency of a tear gas. TC50 thus implies the concentration
required to obtain no more than a perceptible effect on 50 per cent
of the people exposed to the gas for one minute. ICt50 is the
concentration felt to be intolerable by 50 per cent of the people
exposed to the gas for one minute. TC50 and ICt50 values for the
most important tear gases are listed in the table.
Acute toxicity of tear gases is very low, i.e., the margin between the
concentration giving intolerable effect and that which may cause
injury is large. It is not until very high concentrations are reached
that injury may be serious or lethal. In practice, this requires
exposure in closed spaces. Toxicological investigations have been
unable to demonstrate effects of tear gases on genetic material or on
foetal development in experimental animals or humans. Neither has
any increased risk of cancer been observed.
The dominating use of tear gases in Sweden is within the defence
forces. High concentrations of CS (a couple of hundred mg/m3) in
the test chamber are used when the correct fitting of protective
masks is tested. The exposure which may occur if the mask leaks is,
however, extremely brief and withouttoxicological importance.
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Chemical formulas for the three most common tear gases
Code-name
CN<br>
CS<br>
CR
Chemical name
Chloroacetophenone
Orto-chlorobenzylidene-malononitrile
Dibenz(b,f)-1,4-oxazepin
Chemical formula to be inserted
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Threshold concentrations (TC50) and incapacitating concentrations (IC50) for tear gases (mg/m3)
.CN<br>
CS<br>
CR<br>
TC50 (eyes)0.30.0040.004TC50<br>
(airways)0.40.0230.002IC5020 - 503.60.7
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