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CS / Smoke Information Guide

R.S. Eden

The following information has been obtained from US Military manuals in regards to Smoke and Riot Agents. This information can be invaluable to anyone training for K9 deployment in chemical munitions. Due to recent unusual events at one of our training programs, we believe there are concerns regarding the use of HC in an enclosed environment and may soon recommend some guidelines to assist agencies in determining how to train and deploy in HC environments once our studies are complete.

Zinc Chloride Smokes. (HC)

Several methods of producing smoke by dispersing fine particles of zinc chloride have been developed. The mixture in common use is zinc chloride smoke mixture (HC), which contains hexachloroethane, grained aluminium and zinc oxide. Upon burning, the mixture produces zinc chloride, zinc oxychlorides and HCl vapour which rapidly absorb moisture from the air to form a greyish white smoke. HC mixtures can be dispersed by several methods, including grenades, candles, smoke pots, cartridges, and air bombs.


Some countries require the use of a respirator to protect the respiratory tract whenever zinc chloride smokes are used.

Clinical-Pathological Effects.

a. Toxicity. The toxicity of zinc chloride is mainly due to the formation of the strongly acidic HCl, but is also to a lesser extent due to thermal lesions. These are caused by the exothermic reaction of zinc chloride with water. The acidic HCl vapour causes lesions of the mucous membranes of the upper airways. The damage and clinical symptoms following zinc chloride exposure therefore appear immediately after the start of the exposure. However, damage to the lower airways also occurs and may result in delayed effects. These have been attributed to the presence of fine zinc chloride particles and phosgene.

Acute Effects. In high concentrations or with prolonged exposure HC smoke is highly irritating and may be very dangerous when inhaled. Symptoms following inhalation of high concentration of zinc chloride smoke include dyspnoea, retrosternal pain, hoarseness, stridor, lachrymation, cough, expectoration and occasionally haemoptysis. Cyanosis and bronchopneumonia may develop. Due to the irritant and astringent nature of the compound, delayed pulmonary oedema may occur even in the presence of distinct and short-lasting initial symptoms. It is caustic to mucous membranes and can also cause subacute interstitial fibrosis.

c. Chronic Effects. Recent studies of the HC canister and of HC smoke reaction by-product gases indicate the presence of suspected carcinogens. Metal analysis of HC canisters showed, besides zinc, small amounts of cadmium and trace amounts of lead, arsenic and mercury. The by-product gases include chlorinated compounds, phosgene, HCl, carbon monoxide and chlorine. Although zinc chloride, the main constituent, is not felt to be a carcinogenic hazard, certain of the other by-products are known carcinogens in laboratory animals or in humans.


The casualty should don his or her respirator or be removed from the source of exposure. Oxygen should be administered in cases of hypoxia. Bronchospasm should be treated appropriately as should secondary bacterial infection. Early steroid therapy has been considered efficacious by some and, when used, steroids should be given in high doses similar to those used in the treatment of phosgene exposure and exposure to other lung damaging agents. Adequate analgesia is recommended.


The prognosis is related entirely to the extent of the pulmonary damage. All exposed individuals should be kept under observation for 8 hours. Most individuals recover in a few days. At moderate exposures, some symptoms may persist for 1 to 2 weeks. In severe exposures, survivors may have reduced pulmonary function for some months after exposure. The severely exposed patient may progressively develop marked dyspnoea, cyanosis and die.



Riot control agents are irritants characterised by a very low toxicity (chronic or acute) and a short duration of action. Little or no latent period occurs after exposure. Orthochlorobenzylidene malononitrile (CS) is the most commonly used irritant for riot control purposes. Chloracetophenone (CN) is also used in some countries for this purpose in spite of its higher toxicity. A newer agent is dibenzoxazepine (CR) with which there is little experience. Arsenical smokes (sternutators) have in the past been used on the battlefield. Apart from their lachrymatory action they also provoke other effects, e.g., bronchoconstriction and emesis and are some times referred to as vomiting agents. For historical reasons some older, more toxic compounds are briefly mentioned.


CS (Orthochlorobenzylidene Malononitrile).

CS is used as a riot control agent in many countries. It is also commonly used as a training agent for simulation of chemical warfare conditions and for testing of respirators. The limit of perception by taste ranges from 0.25-0.5 mg.m-3. The minimal irritant concentration ranges from 0.1-1.0 mg.m-3, the ICt 50 from 5-10 mg.m-3, and the LCt 50 for persons very much larger, estimated as 60,000 mg.min.m-3. This provides a high margin of safety in its use.


CS is the code name for orthochlorobenzylidene malononitrile. On account of its stronger irritant effects and its lower toxicity it has superseded CN. It is a white crystalline solid substance. Solubility is very poor in water, moderate in alcohol and good in acetone, chloroform, methylene dichloride, ethylacetate and benzene. CS is unstable in aqueous solution. If enough CS can be dissolved in water (e.g., by adding propylene glycol or other organic co-solvent) spraying fluids with an irritant action of short duration result. Although the smoke is non-persistent, CS may stick to rough surfaces (e.g., clothes) from which it is released only slowly. At least 1 hour of aeration is necessary to cleanse such materials from CS after exposure. CS is usually dispersed as an aerosol generated pyrotechnically, or by spraying a solution of CS in a suitable solvent.


The CS cloud is white at the point of release and for several seconds after release. Exposure is associated with a pepper-like odour, the presence of intense eye effects, dyspnoea, coughing and rhinorrhoea.


Full individual protective equipment will provide complete protection. Protection against field concentrations of irritant agents is provided by the respirator and ordinary field clothing secured at the neck, wrists and ankles. Individuals who handle CS should wear rubber gloves, hood, rubber boots, rubber apron and respirator and secure their field clothing at the neck, wrists and ankles.


a. Exposed persons should if possible move to fresh air, separate from fellow sufferers, face into the wind with eyes open and breathe deeply.

Following exposure, clothing and individual equipment should be inspected for residue. If a residue is found, individuals should change and wash their clothing to protect themselves and other unmasked persons.

Mechanism of Action.

a. Lachrymators act on the nerve endings, the cornea, mucous membranes and the skin. The reaction is very rapid.

The toxicity of CS is very low, the estimated lethal concentration over 1 hour for people being 1000 mg.m-3, whereas a concentration of 1 mg.m-3 is intolerable to most people.


Pathological examination of rabbits exposed to CS revealed an increase in number of goblet cells in the respiratory tract. Pulmonary oedema occurred after inhalation at very high concentrations, in excess of 20000 mg.min.m-3. Experiments in dogs showed that the animals dying as a result of exposure to very high concentrations died from obstruction of the upper respiratory tract; inhalation of CS through an intratracheal cannula, on the other hand, caused pulmonary oedema.

Signs and Symptoms.

During exposure an individual is incapable of effective concerted action.

CS Exposure Symptoms.

Exposure to CS causes the following symptoms:

a. Eyes. Symptoms include a violent burning sensation, conjunctivitis (lasting up to 30 minutes), erythema of the eyelids (lasting about an hour) blepharospasm, violent lachrymation (over 10-15 minutes) and photophobia.

Respiratory Tract. The first symptom is a burning sensation in the throat, developing into pain and extending to the trachea and bronchi. At a later stage a sensation of suffocation may occur, often accompanied by fear. In addition a burning sensation in the nose, rhinorrhoea, erythema of the nasal mucous membranes and sometimes mild epistaxis occurs. The sense of taste is often distorted for some hours after exposure. Nausea, diarrhoea and headache have been observed. Sneezing occurs after mild exposure and may be persistent. Many exposed people have reported fatigue for some hours afterwards. Coughing, choking, retching and (rarely) vomiting occur after exposure.

c. Skin. A burning sensation occurs especially in moist areas, but soon disappears. This burning sensation may recur some hours later, often while washing the area. Prolonged exposure to large amounts (e.g., when handling CS in bulk) can cause erythema and vesicle formation. Prolonged exposure, continuous or intermittent, to high concentrations, combined with high temperatures and humidity in the field may result in a cumulative effect. Sensitivity to CS may be provoked. It has been shown that the particle size affects the clinical result. Small particles (1-5 *m) affect the eyes and respiratory tract more rapidly than larger ones (20-30 *m), but recovery after exposure to small particles is more rapid. Very large particles (50 *m) affect the eyes more than the respiratory tract, while recovery is slower.

First Aid.

a. In practically all cases it is sufficient to take the patient into fresh air where the symptoms will soon disappear. Clothing should be changed. If symptoms persist the eyes, mouth and skin may be washed with water (and with soap in the case of the skin). Oil based lotions should not be used. Skin decontaminants containing bleach should not be used, but should be reserved for more dangerous contamination (e.g., vesicants or nerve agents); bleach reacts with CS to form a combination which is more irritant to the skin than CS alone. Chest discomfort can usually be relieved by reassurance.

CS hydrolyses more rapidly in alkaline solutions and an acceptable skin decontamination solution is 6.7% sodium bicarbonate, 3.3% sodium carbonate and 0.1% benzalkonium chloride.


a. Eyes. Ordinarily the eye effects are self limiting and require no treatment. If large particles or droplets of agent have entered the eye, treatment as for corrosive materials may be required. Prompt irrigation with copious amounts of water is the best treatment for solid CS in the eye. After complete decontamination corticosteroid eye preparations may be used. Patients who have been heavily exposed must be observed for possible development of corneal opacity and iritis.

Skin. Early erythema and stinging sensation (up to 1 hour), especially in warm moist skin areas, are usually transient and require no treatment. Inflammation and blistering similar to sunburn may occur after heavy or prolonged exposure, especially in fair skin. Acute contact dermatitis should be managed initially in the same way as any other acute dermatitis. Corticosteroid cream or calamine lotion may be applied to treat existing dermatitis or to limit delayed erythema. Oozing may be treated with wet dressings of 1 in 40 aluminium acetate solution for 30 minutes three times daily. A topical steroid should follow the wet dressing immediately. Secondary infection is treated with appropriate antibiotics. Significant pruritus can be treated with calamine lotion or corticosteroid preparations. If blisters develop these should be treated as any other second degree burn.

c. Respiratory Tract. In the rare event of pulmonary effects from massive exposure, evacuation is required. Management is the same as that for lung damaging agents (Chapter 4).

Course and Prognosis.

Most personnel affected by riot control agents require no medical attention and casualties are rare.

CN (Chloracetophenone).

CN is a riot control agent and as a training agent is now superseded by CS, the latter being much less toxic. However, it is still in use by police in some countries.


CN is a clear yellowish brown solid, with a melting point of 54°C. It is poorly soluble in water, but dissolves in organic solvents. The white smoke smells like apple blossom. The minimal irritant concentration is 0.3 mg.m-3. It has been estimated from experimental data that the LCt50 for people is 7000 to 14000 mg.min.m-3, but inhalation of 350 mg.m-3 for 5 minutes may be dangerous. The ICt50 is 20 to 40 mg.min.m-3. CN is more toxic than CS.

Mode of Action and Toxic Effects.

The mode of action is similar to that of CS; CN causes stimulation of sensory nerve endings.

Signs and Symptoms.

Exposure to CN primarily affects the eyes, producing a burning sensation, lachrymation, inflammation and oedema of the eyelids, blepharospasm, photophobia and, at high concentrations, temporary blindness. The severest of these symptoms is reached in a few minutes and then gradually decreases. After about 1 or 2 hours all symptoms disappear. High concentrations can cause irritation of the upper respiratory tract, inflammation of the skin with vesicle formation, visual impairment and pulmonary oedema. Drops or splashes in the eye may cause corrosive burns, corneal opacity and even permanent visual impairment. Drops or splashes on the skin may cause papulovesicular dermatitis and superficial skin burns. Ingestion of food or water contaminated with CN causes nausea, vomiting and diarrhoea.

First Aid.

After limited operational exposure ill effects will be adequately neutralised by letting fresh air blow into the open eyes. If necessary the eyes may be washed with water from the water bottle (canteen). The eyes should never be rubbed as mechanical injury may complicate the chemical effect. Patients suffering from temporary blindness should be reassured; permanent blindness from exposure to vapour has never been observed even at very high concentrations.

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