Hydrogen cyanide (C.A.S. 74-90-8) is a colorless or pale blue liquid or gas. As a compressed gas, it is used for exterminating rodents and insects in ships, and for killing insects on trees. With hydrocyanic acid gas, it has been used to reduce bird populations in grain storages. It is used in the manufacturing of metal polishes, acrylates, cyanide salts, dyes, rodenticides, pesticides, synthetic fibers, plastics, and electroplating solutions. It is used in metallurgical and photographic processes, and to produce cyanuric acid. It is an intermediate for methyl methacrylate, sodium cyanide, aminopolycarboxylic and acid chelating agents, and a raw material for nitriloacids. Hydrogen cyanide and its derivatives (acrylonitrile, cyanamide, cyanogen chloride, cyanides, and nitroprusside) are used to fumigate ships and warehouses, and in ore-extracting processes. Hydrogen cyanide is used as a starting material for nylon 66.

Chemical properties:

Hydrogen cyanide has a bitter, almond-like odor and bitter, burning taste. Its boiling point is 25.6 degrees C, and melting point is -13.4 degrees C. It has a corrosive effect under two conditions: water solutions of hydrogen cyanide cause stress-cracking of carbon steels under stress even at room temperature and in dilute solution, and water solutions of hydrogen cyanide containing sulfuric acid as a stabilizer severely corrode steel above 40 degrees C. Liquid hydrogen cyanide will attack some forms of plastics, rubber and coatings. Hydrogen cyanide is miscible with water and alcohol, and slightly soluble in ether. It is incompatible or reactive with amines, oxidizers, acids, sodium hydroxide, calcium hydroxide, sodium carbonate, caustics, and ammonia. It is intensely poisonous even when mixed with air, and is highly toxic to all species in water. Synonyms are hydrocyanic acid, prussic acid, aero liquid HCN, carbon hydride nitride, formic anammonide, and formonitrile.

Economics:

U.S. manufacturers of hydrogen cyanide are American Cyanamid Co., Avondale, LA; BP America, Inc., Green Lake, TX; Ciba-Geigy Corporation, St. Gabriel, LA; DeGussa Corporation, Theodore, AL; Dow Chemical, Freeport, TX; E.I. DuPont de Nemours, Beaumont, TX, Orange, TX, and Victoria, TX; Monsanto Co., Chocolate Bayou, TX; Rohm and Haas Company, Deer Park, TX; and Sterling Chemicals, Inc., Texas City, TX.

Identification:

• Chemical Name: Hydrogen Cyanide
• Regulatory Name: Hydrocyanic Acid
• Formula: CHN
• CAS: 74-90-8
• UN Number: 1613

Health effects:

Hydrogen cyanide is acutely poisonous; both the vapor and liquid are extremely poisonous if absorbed through lungs, skin, or eyes. Massive doses may cause sudden loss of consciousness, asphyxiation, and death from respiratory arrest. Unconsciousness can also be followed by violent convulsions, paralysis, protruding eyeballs with dilated and unreactive pupils, and foaming mouth. Exposure can cause blindness and damage optic nerves and retina. Other symptoms of hydrogen cyanide exposure in lesser concentrations include salivation, nausea, vomiting, hyperpnea, dyspnea, an irregular and weak pulse, anxiety, confusion, tachypnea, vertigo, giddiness, stiffness of the jaw, neurasthenia, breathlessness, bradycardia, arterial hypotonia, polycythemia, hepatic impairment, and thyroidal hypofunction. Chronic exposure to hydrogen cyanide gas can cause eye irritation, conjunctivitis, or superficial keratitis. Laetrile and amygdalin-containing fruit pits, in cherries, peaches, apricots, apples, and pears, have been implicated as causes of acute cyanide poisoning. People with chronic diseases of the kidneys, respiratory tract, skin, or thyroid are at greater risk of developing toxic cyanide effects.

Exposure Values:

• IDLH: 50 ppm(NIOSH 1997)
• TLV TWA: 4.7 ppm (NIOSH 1997)
• ERPG-2: 10 ppm (AIHA, 1999)
• ERPG-3: 25 ppm (AIHA, 1999)
• NIOSH REL: ST 4.7 ppm
• OSHA PEL: TWA 10 ppm

Economics:

U.S. manufacturers of Hydrogen Cyanide are BP Amoco Corp., Chicago, IL; Cyanco Co., Winnemucca, NV; Cytec Industries Inc., Paterson, NJ; Degussa-Huls Corp., Ridgefield Park, NJ; Dow Chemical USA, Midland, MI; Du Pont, Wilmington, DE; FMC Corp., Chicago, IL; Novartis Crop Protection Inc., Greensboro, NC; Rhone-Poulence Ag Co., Research Triangle Park, NC; Rohm and Haas Texas Inc., Philadelphia, PA; Solutia Inc., St. Louis, MO; and Sterling Chemicals Inc., Houston, TX.

Regulation:

OSHA lists Hydrogen Cyanide as a highly hazardous chemical under the Process Safety Management Standard at a threshold quantity of 1000 pounds.

Under the Emergency Planning and Community Right-to-Know Act, releases of more than one pound of hydrogen cyanide into the air, water, and land must be reported annually and entered into the Toxics Release Inventory (TRI).

Under Section 302 of the Emergency Planning and Community Right to Know Act of 1986, Hydrogen Cyanide is listed as an Extremely Hazardous Substance and has a threshold planning quantity of 100 pounds.(EPA)

Facilities having a threshold quantity of 2500 pounds of Hydrogen Cyanide are subject to the Risk Management Program Rule (RMP), Section 112r of the 1990 Clean Air Act. The RMP toxic endpoint for Hydrogen Cyanide is 0.011 mg/L.

National Overview of 1998 Toxics Release Inventory

See EPA's Toxic Release Inventory.

Notations:

The NIOSH recommended exposure limits (RELs) are time-weighted average (TWA) concentrations for up to a 10-hour workday during a 40-hour workweek. A short-term exposure limit (STEL) is designated by "ST" preceding the value; unless noted otherwise, the STEL is a 15-minute TWA exposure that should not be exceeded at any time during a workday. A ceiling REL is designated by "C" preceding the value. Any substance that NIOSH considers to be a potential occupational carcinogen is designated by the notation "Ca."

The OSHA permissible exposure limits (PEL) are found in Tables Z-1, Z-2, and Z-3 of the OSHA General Industry Air Contaminants Standard (29 CFR 1910.1000). Unless noted otherwise, PEL are TWA concentrations that must not be exceeded during any 8-hour workshift of a 40-hour workweek. A STEL is designated by "ST" preceding the value and is measured over a 15-minute period unless noted otherwise. OSHA ceiling concentrations (designated by "C" preceding the value) must not be exceeded during any part of the workday; if instantaneous monitoring is not feasible, the ceiling must be assessed as a 15-minute TWA exposure. In addition, there are a number of substances from Table Z-2 (e.g., beryllium, ethylene dibromide, etc.) that have PEL ceiling values that must not be exceeded except for specified excursions. For example, a "5-minute maximum peak in any 2 hours" means that a 5-minute exposure above the ceiling value, but never above the maximum peak, is allowed in any 2 hours during an 8-hour workday.

Information Sources:

• CAMEO®, U.S. Environmental Protection Agency, National Oceanic and Atmospheric Administration, www.epa.gov/ceppo.
• Chemical Manufacturers Association, 1300 Wilson Blvd., Arlington, VA 22209: (703) 741-5000 or Chemical Referral Library, (800) 262-8200.
• National Institute of Environmental Health Sciences, Clearinghouse on Environmental Health Effects, 100 Capitola Drive, #108, Durham, NC 27713; (800) 643-4794; fax (919) 361-9408.
• TOXNET, National Library of Medicine, National Institutes of Health; www.toxnet.nlm.nih.gov
• U.S. Environmental Protection Agency, 401 M St., SW, Washington, DC 20460; Right to Know Hotline (800) 535-0202.
• U.S. Department of Labor, Occupational Health and Safety Administration, Washington, DC, www.osha.gov
• OSHA PEL: Z-1 Table: www.osha-slc.gov/OshStd_data/1910_1000_TABLE_Z-1.html
• OSHA PEL: Z-2 Table: www.osha-slc.gov/OshStd_data/1910_1000_TABLE_Z-2.html