Hydrogen Chloride

What is hydrogen chloride?

Hydrogen chloride (HCl) is a slightly yellow gas that has a pungent, irritating odor. Hydrogen chloride gas easily dissolves in water. The resulting solution is hydrochloric acid.

The dominant global sources of hydrogen chloride are attributed to natural events like atmospheric reactions with ocean sea salts and volcanic eruptions. Smaller amounts come from forest fires, weathering rocks and dust. Oceans are the largest global source of chloride emissions (including HCl) to the atmosphere, releasing 77 million to 660 million tons each year.

By contrast, global human-induced releases of hydrogen chloride and chlorides are less than 4 million tons each year, 22% of which is contributed by U.S. industry. The primary manmade sources of gaseous hydrogen chloride in the U.S. include combustion of fuels, incineration of refuse, smelting of metal scrap, and manufacture of aluminum, plywood, and particle board.

How is hydrogen chloride used?

As hydrochloric acid, it is used to fabricate iron and steel, clean and electroplate metals, etch circuit boards and make solvents, bleaches, chloride salts, fertilizers, dyes, textiles, and rubber. It is also used in analytical chemistry.

Our stomachs produce hydrochloric acid to digest food.

Do electric utilities release hydrogen chloride into the environment?

Yes. U.S. power plants are estimated to produce about 150,000 tons of hydrogen chloride, accounting for about 80 percent of all hydrogen chloride from human activities released into the air each year. Trace amounts of chloride are present in coal and oil. When electric utilities burn coal or oil in their power plants, chloride is released in small amounts. Some of that chloride then combines with hydrogen in the air to form hydrogen chloride. The hydrogen chloride can combine with moisture in the air to form a hydrochloric acid aerosol, which becomes more dilute as it continues to move through the atmosphere. The amount of hydrochloric acid aerosol that stays in the air or falls to the ground depends on local wind and rain and moisture conditions in the air.

How could hydrogen chloride affect me?

Hydrogen chloride is not classified as a human carcinogen.

Breathing the vapor can irritate the lungs and cause bronchitis. Higher exposures can cause a build up of fluid in the lungs.

Continued contact with dilute solutions may cause a skin rash or irritation. Also, contact can cause eye damage or erosion of the teeth.

However, there is no evidence that common exposures to dilute hydrochloric acid in airborne droplets or particles (such as that attributed to power plants) can harm human health. The concentrations discussed in this paper are too low to cause these types of health effects.

What does EPA say?

It is unlikely that dilute hydrogen chloride from power plants poses a significant risk to human health.

In its 1998 Report to Congress on hazardous air pollutants from electric utilities, EPA assessed non-cancer risks for hydrogen chloride. EPA estimated maximum short- and long-term human health exposures to hydrogen chloride at power plants and determined that utility HCl emissions do not pose a significant health risk.

The Occupational Safety and Health Administration and the National Institute for Occupational Safety and Health have set concentration limits for occupational exposure to hydrogen chloride. The concentration of hydrogen chloride emissions from coal and oil fired power plants is well below this standard.

Where can I get more information?

• Electric Utility Trace Substances Synthesis Report, Volumes 1-4, Electric Power Research Institute, Palo Alto, California, 1994.
  
  
• Electric Power Research Institute
  3412 Hillview Ave.
  P.O. Box 10412
  Palo Alto, California 94303
  phone (650)855-2000
  
  
• Integrated Risk Information System, U.S. Environmental Protection Agency.
  
  
• Study of Hazardous Air Pollutant Emissions from Electric Utility Steam Generating Units - Final Report to Congress, Volume 1 and 2, U.S. Environmental Protection Agency, Office of Air Quality and Planning Standards, 1998.
  
  
• Toxicological Profile for Hydrogen Chloride, U.S. Department of Health and Human Services, Public Health Service, Agency for Toxic Substance and Disease Registry, 1997.