Guidance

CS gas: incident management

Updated 16 November 2022

Main points

General

CS is a white solid at room temperature with a pepper like odour. It is usually dissolved in an organic solvent such as methyl isobutyl ketone to be used as an aerosol or microparticulate cloud.

It reacts violently with strong oxidants causing fire and explosion hazard.

It also reacts with strong bases acids producing ammonia; the substance decomposes on burning producing toxic fumes including hydrogen chloride hydrogen cyanide nitrogen oxides.

Health

CS gas is a potent sensory irritant; however, symptoms should resolve 15 to 30 minutes after removal from exposure.

Discomfort, pain, lacrimation, blurred vision, periorbital oedema and blepharospasm are common following ocular exposure.

Inhalation may cause sneezing, coughing, sore throat, wheeze, shortness of breath, rhinorrhoea, bronchorrhea and chest tightness.

It may cause a stinging or burning sensation in the mouth with increased salivation, nausea and vomiting.

Stinging or burning sensation, pruritus, scaling, erythema and blistering can occur following skin contact.

Casualty decontamination at the scene

Decontamination should not be necessary following exposure to CS gas, as the agent is expected to disperse within minutes and recovery from symptoms expected to occur spontaneously (15 to 30 minutes). Dry decontamination should be considered if symptoms persist for longer than 30 minutes after the end of exposure.

Environment

Avoid release to the environment.

Inform the Environment Agency where appropriate.

Hazard identification

Standard (UK) dangerous goods emergency action codes

There are currently no specific dangerous goods emergency action codes and no GB CLP harmonised classification for CS Gas (2-chlorobenzylidene malononitrile).

Physicochemical properties

Table 1. Physicochemical properties

CAS number	2698-41-1
Molecular weight	188.61
Formula	C10H5ClN2
Common synonyms	2-chlorobenzylidene malononitrile, o-chlorobenzylidene malononitrile
State at room temperature	White crystalline solid
Volatility	Vapour pressure: 3.4 x 10-5 mm Hg at 20°C
Vapour density	6.5 (air=1)
Flammability	Combustible
Lower explosive limit	-
Upper explosive limit	-
Water solubility	0.1 - 0.5 g per 100 mL at 20°C (slightly soluble)
Reactivity	Reacts violently with strong oxidants causing fire and explosion hazard
Reaction or degradation products	Reacts with strong bases acids producing ammonia. The substance decomposes on burning producing toxic fumes including hydrogen chloride hydrogen cyanide nitrogen oxides
Odour	Pepper like odour

Structure

References

1. Bethesda (MD): National Library of Medicine (US), National Center for Biotechnology Information PubChem Compound Summary for CID 17604, 2-Chlorobenzylidenemalononitrile, 2004 (viewed in April 2022)
2. International Programme on Chemical Safety. International Chemical Safety Card entry for Chromium trioxide ICSC 1065, 2002. World Health Organization (WHO): Geneva

Reported effect levels from authoritative sources

Table 2. Exposure by inhalation

mg/m³	Time	Signs and symptoms
0.5-1	90 minutes	Lachrymation, blepharospasm, burning mouth, nasal irritation, chest tightness and difficulty breathing (1)
<5	-	Conjunctivitis, lachrymation, sensation of eye burning and pain (2)
6.7	10 minutes	Severe pain, profuse tears and redness of the conjunctiva (following exposure to CS powder) (1)

These values give an indication of levels of exposure that can cause adverse effects.

They are not health-protective standards or guideline values.

References

1. Department of Health. Committees on Toxicity, Mutagenicity and carcinogenicity of chemicals in Food, Consumer Products and the Environment. Statement on 2-Chlorobenzylidene Malononitrile (CS) and CS Spray, 1999

2. Maynard, R. L. (2007) Chapter 19: Mustard Gas. T.C. Marrs, R.L. Maynard and D.R. Sidell, Chemical warfare agents: toxicology and treatment. John Wiley and Sons Ltd, Chichester

Table 3. Exposure by eye contact

%	Signs and symptoms
0.1-1	Severe pain, profuse tears and redness of the conjunctiva (following exposure to CS gas in a mixture including solvents)

These values give an indication of levels of exposure that can cause adverse effects. They are not health-protective standards or guideline values.

Reference

Department of Health. Committees on Toxicity, Mutagenicity and carcinogenicity of chemicals in Food, Consumer Products and the Environment. Statement on 2-Chlorobenzylidene Malononitrile (CS) and CS Spray, 1999

Table 4. Exposure by skin

%	Signs and symptoms
0.0005	Marked transient skin and eye irritation (1)
0.001-0.005	Rapid onset of stinging eyes and skin with blapherospasm and excess lacrimation (following a full body drenching with CS in aqueous solution) (2)

These values give an indication of levels of exposure that can cause adverse effects.

They are not health-protective standards or guideline values.

References

1. Department of Health. Committees on Toxicity, Mutagenicity and carcinogenicity of chemicals in Food, Consumer Products and the Environment. Statement on 2-Chlorobenzylidene Malononitrile (CS) and CS Spray, 1999

2. Maynard, R. L. (2007) Chapter 19: Mustard Gas.T.C. Marrs, R.L. Maynard and D.R. Sidell, Chemical warfare agents: toxicology and treatment. John Wiley and Sons Ltd, Chichester

Published emergency response guidelines

Table 5. Acute exposure guideline levels (AEGLs) showing concentrations in mg/m³

	mg/m³
	10 min	30 min	60 min	4 hours	8 hours
AEGL-1 [note 1]	NR	NR	NR	NR	NR
AEGL-2 [note 2]	0.083	0.083	0.083	0.083	0.083
AEGL-3 [note 3]	140	29	11	1.5	1.5

Notes to Table 5

[note 1] Level of the chemical in air at or above which the general population could experience notable discomfort.

[note 2] Level of the chemical in air at or above which there may be irreversible or other serious long-lasting effects or impaired ability to escape.

[note 3] Level of the chemical in air at or above which the general population could experience life-threatening health effects or death.

NR = not recommended.

Reference

US Environmental Protection Agency. ‘Acute Exposure Guideline Levels’ (viewed in April 2022)

Exposure standards, guidelines or regulations

Table 6. Occupational standards

	LTEL (8-hour reference period)		STEL (15-min reference period)
	ppm	mg/m³	ppm	mg/m³
WEL	No data		No data

Abbreviations

WEL: workplace exposure limit

LTEL: long-term exposure limit

STEL: short-term exposure limit

Reference

HSE. ‘EH40/2005 Workplace Exposure Limits’. Fourth Edition (2020)

Table 7. Public health guidelines

Drinking water standard	No guideline value specified
WHO air quality guideline	No guideline value specified

Health effects

Major route of exposure

Inhalation, dermal or ocular exposure.

Symptoms develop rapidly but should resolve 15 to 30 minutes after removal from exposure, as CS breaks down rapidly in the body.

Marked toxicity would only be expected after exposure to a high concentration within a confined space for a prolonged time.

Table 8. Immediate signs or symptoms of acute exposure

Route	Signs and symptoms
Inhalation	Sneezing, coughing, sore throat, wheeze, shortness of breath, rhinorrhoea, bronchorrhoea and chest tightness. Respiration may be irregular with periods of apnoea. Exacerbation of asthma has been reported. Reactive airways dysfunction syndrome (RADS) may follow a high-level exposure to CS where the above initial features are followed by paroxysmal cough and shortness of breath that may persist for up to 2 years. This is more likely following heavy exposure in a confined space.
Ingestion	A stinging or burning sensation in the mouth with increased salivation, nausea and vomiting.
Dermal	Stinging or burning sensation, pruritus, scaling, erythema and blistering occur. Prolonged contact, especially in association with wet skin or clothing, can result in chemical burns that are usually minor. Allergic contact dermatitis, leukoderma, initiation or exacerbation of seborrhoeic dermatitis and aggravation of rosacea can occur. Burns can be sustained from direct contact with hot metal canisters used to disperse these agents.
Ocular	Discomfort, pain, lacrimation, blurred vision, periorbital oedema and blepharospasm are common. Photophobia, conjunctivitis, diffuse conjunctival and scleral injection and eyelid erythema can occur. If CS is sprayed into the eye at close range, there may also be physical injury due to the pressure jet from the canister or particles embedded in the eye. Exposure to explosive devices discharged near the face and eyes can result in more severe ocular injuries.

Reference

TOXBASE. CS (2-chlorobenzylidene malononitrole), January 2019 (viewed in April 2022)

Decontamination at the scene

Chemical-specific advice

The approach used for decontamination at the scene will depend upon the incident, location of the casualties and the chemicals involved. Therefore, a risk assessment should be conducted to decide on the most appropriate method of decontamination.

Decontamination should not be necessary following exposure to CS gas, as the agent is expected to disperse within minutes and spontaneous recovery from symptoms is expected to occur rapidly (15 to 30 minutes). Dry decontamination should be considered if symptoms persist for longer than 30 minutes after exposure ends.

Emergency services and public health professionals can obtain further advice from the UK Health Security Agency (Radiation, Chemicals and Environment Directorate), using the 24 hour chemical hotline number: 0344 892 0555.

Disrobe

The disrobe process is highly effective at reducing exposure to HAZMAT/CBRN material when performed within 15 minutes of exposure.

Therefore, disrobing must be considered the primary action following evacuation from a contaminated area.

Where possible, disrobing at the scene should be conducted by the casualty themselves and should be systematic to avoid transferring any contamination from clothing to the skin.

Consideration should be given to ensuring the welfare and dignity of casualties as far as possible.

Improvised decontamination

Improvised decontamination is an immediate method of decontamination prior to the use of specialised resources. This should be performed on all contaminated casualties, unless medical advice is received to the contrary. Improvised dry decontamination should be considered for an incident involving chemicals unless the agent appears to be corrosive or caustic.

Improvised dry decontamination

Any available dry absorbent material can be used such as kitchen towel, paper tissues (for example blue roll) and clean cloth.

Exposed skin surfaces should be blotted and rubbed, starting with the face, head and neck and moving down and away from the body.

Rubbing and blotting should not be too aggressive, or it could drive contamination further into the skin.

All waste material arising from decontamination should be left in situ, and ideally bagged, for disposal at a later stage.

Additional notes

Following improvised decontamination, remain cautious and observe for signs and symptoms in the decontaminated person and in unprotected staff.

If water is used to decontaminate casualties this may be contaminated, and therefore hazardous, and a potential source of further contamination spread.

All materials (paper tissues and so on) used in this process may also be contaminated and, where possible, should not be used on new casualties.

The risk from hypothermia should be considered when disrobing and any form of wet decontamination is carried out.

People who are contaminated should not eat, drink or smoke before or during the decontamination process and should avoid touching their face.

Consideration should be given to ensuring the welfare and dignity of casualties as far as possible. Immediately after decontamination the opportunity should be provided to dry and dress in clean robes or clothes.

References

1. Home Office. ‘Initial operational response to a CBRN incident’ Version 2.0 (July 2015)
2. NHS England. ‘Emergency Preparedness, Resilience and Response (EPRR): Guidance for the initial management of self-presenters from incidents involving hazardous materials’ (February 2019)

Clinical decontamination and first aid

Clinical decontamination is the process where trained healthcare professionals using purpose designed decontamination equipment treat contaminated persons individually.

Detailed information on clinical management can be found on TOXBASE.

Important notes

Resuscitate the patient according to standard guidelines. Decontamination procedures and the use of Personal Protective Equipment will be specific to given situations and dry decontamination should be considered.

Remove from the site of exposure, particularly if in a confined space; the agent should disperse in fresh air in a few minutes.

If exposure to CS alone is confirmed, hospital treatment is rarely needed because spontaneous recovery usually occurs rapidly (within 15 to 30 minutes of cessation of exposure), unless exposure has been to high concentrations within a confined space for a prolonged time.

Follow procedures below if features persist for longer than 30 minutes after the end of exposure.

Dermal exposure

Move the patient away from other casualties to a clean atmosphere.

Remove all contaminated clothing and seal in plastic bags; disposable rubber gloves should be used when handling contaminated clothes.

Exposed skin should be blotted and wiped with any available dry, absorbent material such as paper tissue, towels, medical dressings and so on. Do not blot or wipe aggressively. Avoid transferring contamination from one part of the body to another.

Manage skin burns conventionally and other measures as indicated by the patient’s clinical condition.

Ocular exposure

Remove contact lenses if present.

Anaesthetise the eye with a topical local anaesthetic (oxybuprocaine, amethocaine or similar) – if local anaesthetic is not immediately available, do not delay irrigation.

Immediately irrigate the affected eye thoroughly with 1000 mL 0.9% saline or equivalent crystalloid (for example via an infusion bag with a giving set) for a minimum of 10 to 15 minutes irrespective of initial conjunctival pH. A Morgan Lens may be used if anaesthetic has been given.

Aim for a neutral conjunctival pH of 7 to 8. The conjunctivae may be tested with indicator paper. Retest 20 minutes after irrigation and use further irrigation if necessary.

Any particles lodged in the conjunctival recesses should be removed.

Repeated instillation of local anaesthetics may reduce discomfort and help more thorough decontamination; however, prolonged use of concentrated local anaesthetics may be damaging to the cornea so should not be prescribed for home use.

Refer to an ophthalmologist if eye symptoms persist.

Other supportive measures as indicated by the patient’s clinical condition.

Inhalation or ingestion

Patients with features of severe poisoning, particularly respiratory complications, should be admitted to hospital and managed appropriately.

Other supportive measures as indicated by the patient’s clinical condition.

References

1. TOXBASE (viewed in April 2022)
2. TOXBASE CS (2-chlorobenzylidene malononitrole) - features and management, 2019