Synonyms: 925; Chlor; Chlore; Chlorium; Cloro; Klor.
Cyrillic synonym: Хлор.

💊 Chemical information

Chemical formula: Cl2 = 70.906.
CAS — 7782-50-5.


Chlorine is a greenish-yellow gas with a suffocating odour; commonly available as a pressurised liquid.

💊 Adverse Effects and Treatment

Chlorine gas is irritant and corrosive producing inflammation, burns, and necrosis. Inhalation may result in coughing, choking, headache, dyspnoea, dizziness, expectoration of frothy white sputum (which may be blood stained), a burning chest pain, and nausea. Bronchospasm, laryngeal oedema, acute pulmonary oedema with cyanosis, and hypoxia may occur. There may be vomiting and development of acidosis. Death may result from hypoxia. Some of the toxicity of chlorine may be due to its dissolution in tissue water to produce hydrochloric acid and hypochlorite. After exposure to chlorine, conjunctivitis may require a topical anaesthetic and frequent irrigations of water or saline. Respiratory distress should be treated with inhalations of humidified oxygen and bronchodilators; mechanical ventilation may be required. Corticosteroids have been given in an attempt to minimise pulmonary damage but their benefit is unproven. Acidosis may require the intravenous use of sodium bicarbonate or other suitable alkalising agent.
Thirteen children who were accidentally exposed to chlorine products and gas at a community swimming pool complained of eye and throat irritation, chest pain and tightness, shortness of breath, wheezing, and anxiety and 5 children with hypoxia required hospital admission. These children received humidified oxygen, salbutamol, and, in 4 patients, methylprednisolone, and all were discharged 1 to 2 days later.2 Another report on 76 children with chlorine poisoning revealed that the longest period of hospitalisation was 12 hours after treatment with oxygen and corticosteroids.3 A 14-year-old boy with a history of asthma exposed to chlorine gas developed acute respiratory distress syndrome and required intubation, ventilatory support, salbutamol, and corticosteroids. He was extubated after 19 days and recovered well.4 There have been reports of deliberate inhalation of chlorine,5,6 in one instance for pleasure,5 leading to severe adverse effects. Some individuals may be unduly insensitive to chlorine-induced irritation and workers should be warned that concentrations of chlorine which can be tolerated for short periods without undue discomfort can still cause serious injury which may not be immediately apparent.6 Guidelines7,8 have been issued for the management of chlorine exposure.
1. Barret L, Faure J. Chlorine poisoning. Lancet 1984; i: 561–2
2. Sexton JD, Pronchik DJ. Chlorine inhalation: the big picture. Clin Toxicol 1998; 36: 87–93
3. Fleta J, et al. Intoxication of 76 children by chlorine gas. Hum Toxic ol 1986; 5: 99–100
4. Traub SJ, et al. Case report and literature review of chlorine gas toxicity. Vet Hum Toxicol 2002; 44: 235–9
5. Rafferty P. Voluntary chlorine inhalation: a new form of selfabuse? BMJ 1980; 281: 1178–9
6. Dewhurst F. Voluntary chlorine inhalation. BMJ 1981; 282: 565–6
7. Department of Health. Chlorine: guidelines for action in the event of a deliberate release (issued February 2004). Available at: 1194947362398 (accessed 27/08/08
8. Agency for Toxic Substances and Disease Registry. Medical management guidelines (MMGs) for chlorine (Cl ). Available at: (accessed 15/03/06)

Effects on the eyes.

Eye examinations of 50 subjects immediately before and after swimming in a chlorinated pool (chlorine range 1.0 to 1.5 ppm) showed that 68% had symptoms of corneal oedema and 94% had corneal epithelial erosions. No subject had a measurable decrease in visual acuity.1
1. Haag JR, Gieser RG. Effects of swimming pool water on the cornea. JAMA 1983; 249: 2507–8.

💊 Precautions

The antimicrobial activity of chlorine disinfectants is reduced by the presence of organic material and by increasing pH. Hypochlorite solutions may delay wound healing.

💊 Uses and Administration

Chlorine is a disinfectant with a rapid potent brief bactericidal action. It is capable of killing most bacteria, and some fungi, yeasts, algae, viruses, and protozoa. It is slowly active against spores. It is used for the treatment of water, but for most other purposes it is used in the form of hypochlorites, organic and inorganic chloramines, chlorinated hydantoins, chlorinated isocyanurates, and similar oxidising compounds capable of releasing chlorine. In the presence of water these compounds produce hypochlorous acid (HOCl) and hypochlorite ion (OCl − ) and it is generally considered that the lethal action on micro-organisms is due to chlorination of cell protein or enzyme systems by nonionised hypochlorous acid, although the hypochlorite ion may also contribute. The activity of most of the compounds decreases with increase of pH, the activity of solutions of pH 4 to 7 being greater than those of higher pH values. However, stability is usually greater at an alkaline pH. The potency of chlorine disinfectants is expressed in terms of available chlorine. This is based on the concept of chlorine gas (Cl 2 ) as the reference substance. Two atoms of chlorine (2 × Cl) yield in water only one molecule of hypochlorous acid (on which activity is based), while hypochlorites and chloramines yield one molecule of hypochlorous acid for each atom of chlorine as shown in the following equations: Cl 2 +H 2 O ↔ HOCl + H + +Cl − NaOCl + H 2 O ↔ HOCl + NaOH Thus the assayed chlorine in such compounds has to be multiplied by 2 to produce ‘available chlorine’. The term ‘active chlorine’ has been used confusingly for either ‘available chlorine’ (Cl 2 ) or ‘combined chlorine’ (Cl). Because they have relatively low residual toxicity, chlorine compounds are useful for the disinfection of relatively clean impervious surfaces, such as babies’ feeding bottles, baths, and food and dairy equipment. A concentration of 100 to 300 ppm of ‘available chlorine’ is used; a detergent may be added to ensure wetting of the surface. Solutions containing 1000 ppm ‘available chlorine’ are recommended for minor surface contamination and as part of general good hygiene practice. Solutions containing 10 000 ppm ‘available chlorine’ are used to disinfect surfaces contaminated with spilled blood or body fluids; this strength is effective against viruses including human immunodeficiency virus (HIV) and hepatitis B virus. A concentration providing 20 000 ppm ‘available chlorine’ is used for material from patients with CreutzfeldtJakob disease. On a large scale, chlorine gas is used to disinfect public water supplies. On a smaller scale, the use of chlorine compounds is more convenient and sodium hypochlorite, tosylchloramide sodium, chlorinated lime, chlorine dioxide, or halazone are used. After satisfying the chlorine demand (the amount of chlorine needed to react with organic matter and other substances), a free-residual content of 0.2 to 0.4 ppm ‘available chlorine’ should be maintained, though more is required for alkaline waters with a pH of 9 or more. For the disinfection of potentially contaminated water a concentration of 1 ppm is recommended. Excessive residual chlorine may be removed by adding a little citric acid or sodium thiosulfate. For use in small swimming pools, sodium or calcium hypochlorite may be added daily to maintain a freeresidual ‘available chlorine’ concentration of 1 to 3 ppm. Tosylchloramide sodium, chlorinated lime, and the isocyanurates may also be used. To minimise irritation of the eyes, maintain disinfectant activity, prevent precipitation of salts, and prevent metal corrosion, a pH of 7.2 to 7.8 should be maintained. Solutions of chlorine-releasing compounds are also used in wound desloughing and disinfection.
Published December 10, 2018.