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Hydrogen chloride

Anhydrous hydrochloric acid, Spirits of salts

SPRI Emission Reporting Threshold
10,000 Kg/yr Pollutant Emissions to Air
This sheet is a generic summary, designed to give the reader a basic level of background information about the substance in question. Great care has been taken to represent as effectively and correctly as possible the broad range of (not necessarily consistent) information which is available from a variety of sources. The reader must accept therefore that this sheet has no legal status and cannot be relied upon in any legal proceedings. SEPA disclaims any responsibility or liability whatsoever for errors and omissions in this sheet.
What is it?
Under normal conditions, Hydrogen chloride is a colourless gas, which has a choking, pungent smell. It is highly corrosive and toxic. Hydrogen chloride readily dissolves in water to give Hydrochloric acid. In moist conditions, Hydrogen chloride gas reacts with water in the air to give clouds of Hydrochloric acid.
What is it used for?
Hydrogen chloride is used in the manufacture of a variety of industrial chemicals, fertilizers and dyes. It is used in the textiles industry, to separate cotton from wool and fluff, and in the electronics industry, to etch semiconductor crystals. Hydrogen chloride is also used to treat synthetic rubber and in metal prcessing treatments.
Where does it come from?
The most significant releases of Hydrogen chloride occur when coal is burned (particularly from coal-fired power stations) and when waste is incinerated. This occurs because coal and waste foods contain common salt (sodium chloride), which reacts with hydrogen to give Hydrogen chloride. Incineration of plastics such as PVC also results in releases of Hydrogen chloride. Relatively small quantities of Hydrogen chloride are released naturally from volcanoes.
How might it affect the environment?
Hydrogen chloride gas is highly corrosive and will damage metal structures and buildings or monuments made of limestone. If high levels of Hydrogen chloride gas dissolve in a water body, aquatic organisms will be harmed and even killed. This is only likely as a result of an accidental spill of much larger amounts of Hydrogen chloride than are typically released to the environment. The very high solubility of Hydrogen chloride gas means that releases to the atmosphere are quickly washed out by rain and moisture in the air. Some soils and lakes may be sensitive to this acid rain if amounts of it falling are above certain amounts defined as "critical loads". This makes Hydrogen chloride pollution a global as well as local environmental problem.
How might exposure to it affect human health?
Hydrogen chloride can enter the body either by inhalation of air containing hydrogen chloride, accidental ingestion of liquid hydrogen chloride or hydrochloric acid, or by dermal contact with liquid hydrogen chloride or hydrochloric acid (dissolved hydrogen chloride). Dermal contact mainly occurs in the occupational setting. Inhalation of air containing low levels of hydrogen chloride over short periods of time can cause throat irritation. Exposure to higher levels may result in effects including rapid breathing, blue colouring of the skin, fluid accumulation in the lungs and in extreme cases severe swelling of the throat, suffocation and death. Inhalation of hydrogen chloride can also lead to reactive airways dysfunction syndrome (asthma caused by inhalation of corrosive substances) in some individuals. Ingestion of hydrogen chloride or hydrochloric acid can cause severe burns to the lips, mouth, throat, oesophagus and stomach. Dermal contact with liquid hydrogen chloride or hydrochloric acid may cause burns to the skin. Contact with the eyes can cause irritation and burns. The International Agency for Research on Cancer has not designated hydrogen chloride in terms of its carcinogenicity. The International Agency for Research on Cancer has designated hydrochloric acid as being not classifiable as to its carcinogenicity to humans. However, exposure to hydrogen chloride at normal background levels is unlikely to have any adverse effect on human health.
What steps are being taken to limit the potential impacts?
Releases of Hydrogen chloride are regulated through the UK Pollution, Prevention and Control (PPC) Regulations. It is also regulated through the European Directive concerned with emissions from waste incinerators (96/61/EC). Internationally, substances contributing to acid rain are controlled through the UN/ECE Convention on Long-Range Transboundary Air Pollution.