Chlorine

Unique identifier / Notation

CH0016

Synonyms

None identified.

Chlorine is a reactive pale green gas with many uses including disinfection of water that is approximately three times heavier than air and has a characteristic odour similar to bleach. Most significant exposures to chlorine result from loss of containment of chlorine during storage and transport. Human exposure can result in symptoms ranging from mild irritation to rapid death related to pulmonary oedema. It is considered a significant public health hazard (adapted from IPCS, 1982 and PHE, 2019).

Primary reference(s)

IPCS, 1982. Environmental Health Criteria 21: Chlorine and hydrogen chloride. International Programme on Chemical Safety (IPCS). Accessed 2 December 2019.

PHE, 2019. Chlorine: health effects, incident management and toxicology. Public Health England (PHE). Accessed 2 December 2019.

Additional scientific description

Chlorine (chemical symbol Cl, atomic number 17) reacts violently with bases and is a corrosive, strong oxidant. It also reacts violently with combustible substances and reducing agents and most organic and inorganic compounds, causing a fire and explosion hazard. It may also combine with water or steam to produce toxic and corrosive fumes of hydrochloric acid (PHE, 2019).

Chlorine is used in the disinfection of water and in the production of bleach and chlorinated hydrocarbon solvents, polyvinyl chloride and other industrial processes. Large quantities are also used in the bleaching of pulp and paper.

Bleach contains sodium hypochlorite, which, if (inadvertently) mixed with acidic chemicals can result in the generation and release of chlorine gas. If chlorine is released from a tank into the air, the chlorine will evaporate very quickly, forming a highly toxic greenish-yellow cloud (ATSDR, 2010).

Metrics and numeric limits

Drinking water: 5 mg/L (WHO, 2011).

Emergency response and acute exposure: there are Emergency Response Planning Guidelines (ERPG) (NOAA, 2016) and Acute Exposure Guideline Values for Airborne Chemicals (AEGLs) (US EPA, no date) as a result of health risks associated with releases and spills of chlorine.

Key relevant UN convention / multilateral treaty

World Health Organization (WHO) International Health Regulations (WHO, 2016).

Examples of drivers, outcomes and risk management

Minor exposures to chlorine may result in a burning sensation of the eyes and throat. More substantial exposure may cause coughing or breathing difficulties. Exposure to high concentrations of chlorine gas can damage the lungs and airways, hours after the exposure, potentially without preceding warning symptoms; this may cause a build-up of fluid in the lungs (oedema) which can be fatal. Following severe injuries from inhaling chlorine, there may be a shock, coma and death, or when surviving, a chronic disorder of the lungs. Those exposed during physical exertion appear especially vulnerable (IPCS, 1982; PHE, 2019).

Owing to its hazardous nature, the majority of chlorine is transported by rail (ILO, 2004).

The modern use of chemical weapons began with World War I, when both sides in the conflict used poisonous gas to inflict agonising suffering and cause significant battlefield casualties. Such weapons basically consisted of well-known commercial chemicals put into standard munitions such as grenades and artillery shells. Chlorine was a common chemical used in this way historically and still presents a risk (United Nations Office for Disarmament Affairs, no date).

Spillages and run-off should be prevented from entering watercourses as chlorine is harmful to the natural environment; evacuation should be considered in a written emergency plan for significant spills and leaks of chlorine such as from tanks; and harmonised labelling and transport approaches should be adhered to.