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Hydrocyanic Acid
Description: Cyanides are a group of compounds based on a common structure formed when elemental nitrogen and carbon are combined. Cyanides are produced by certain bacteria, fungi, and algae, and may be found in food and plants. Cyanide itself is an ion, or combining form that carries a positive or negative charge. It is a powerful and rapid-acting poison. When cyanide combines with metals and organic compounds, it forms simple and complex salts and compounds. Hydrogen cyanide (C.A.S. 74-90-8) is a compound of cyanide and hydrogen. It is classified separately, apart from other cyanide compounds and salts, by the EPA’s Toxic Release Inventory (TRI) because it is a unique compound. [NOTE: The other cyanide compounds and salts will be profiled in a future issue of EW.] Hydrogen cyanide is a colorless gas with a faint, bitter, almond-like odor. It has been used in gas-chamber executions and as a war gas. Hydrogen cyanide is used in producing adiponitrile for nylon, methyl methacrylate, sodium cyanide, cyanuric chloride, chelating agents, and miscellaneous other uses, including in the manufacture of insecticides and rodenticides for fumigating enclosed spaces, ferrocyanides, acrylates, lactic acid, pharmaceuticals, and specialty chemicals. The largest cyanide source in air results from vehicle exhaust. Other sources include releases from certain chemical industries, industrial and municipal waste burning, and the use of cyanide-containing pesticides. The largest cyanide sources in water result from discharges from some metal mining processes, organic chemical industries, iron and steel works, and publicly owned waste water treatment works. Chemical properties: Hydrogen cyanide is miscible in water, alcohol, and ether, and soluble in ethanol. It is incompatible or reactive with amines, oxidizers, acids, sodium hydroxide, calcium hydroxide, sodium carbonate, water, caustics, and ammonia. Hydrogen cyanide is a very dangerous fire hazard when exposed to heat, flame, or oxidizers. It reacts violently with acetaldehyde. It is a severe explosion hazard when exposed to heat or flame, or by chemical reaction with oxidizers. Under certain conditions, particularly contact with alkaline materials, hydrogen cyanides can polymerize or decompose explosively. It is a highly dangerous disaster hazard; the gas forms explosive mixtures with air and will react with water, steam, acid, or acid fumes to produce highly toxic fumes of cyanides. Synonyms for hydrogen cyanide are formonitrile, hydrocyanic acid, prussic acid, aero liquid HCN, and zaclondiscoids. Identification: Health effects: Exposure to large amounts of all forms of cyanide for a short time can harm the brain, lungs, and heart, and cause coma and death. Exposure to large amounts of hydrogen cyanide can result in asphyxia, weakness, headache, confusion, nausea, and vomiting. The health effects of all forms of cyanide are similar when large amounts are eaten, drunk, breathed, or touched. The first symptoms of cyanide poisoning are rapid, deep breathing and shortness of breath, followed by convulsions and loss of consciousness. In cases of acute cyanide poisoning, death is extremely rapid. Skin contact with hydrogen cyanide can produce skin irritation and sores. The primary organs affected by exposure to hydrogen cyanide are the central nervous system, liver, kidneys, and cardiovascular system. Exposure Values: Economics: U.S. manufacturers of Hydrocyanic Acid Solution are American Cyanamid Co, Avondale, LA; BP America, Inc, Green Lake, TX; Ciba-Geigy Corporation, St Gabriel, LA; DeGussa Corporation, Theodore, AL; Dow Chemical USA, Freeport, TX; E I du Pont de Nemours & Co, Inc, Memphis, TN 38127; Petrochemicals Department; Beaumont, TX;Orange, TX; Victoria, TX; Monsanto Co, Chocolate Bayou, TX; Rohm and Haas Company, Philadelphia, PA; and Sterling Chemicals, Inc, Texas City, TX. Regulation: Hydrogen cyanide is regulated by the Occupational Safety and Health Administration (OSHA). EPA’s Office of Drinking Water regulates cyanide, with a proposed maximum contaminant level goal of 200µg/L. Hydrogen cyanide is regulated under the Emergency Planning and Community Right-to-Know Act; Comprehensive Environmental Response, Compensation and Liability Act; National Primary Drinking Water Regulations; and Resource Conservation and Recovery Act. OSHA lists hydrocyanic acid solution as a Highly Hazardous Chemical under the Process Safety Management Standard at a threshold quantity of 1000 pounds. Under Section 302 of the Emergency Planning and Community Right to Know Act of 1986, hydrocyanic acid is listed as an Extremely Hazardous Substance and has a threshold planning quantity of 2,500 lbs. Under Section 313 of the Emergency Planning and Community Right to Know Act of 1986, releases of more than one pound of hdyrocyanic acid into the air, water, and land must be reported annually and entered into the Toxic Release Inventory (TRI). Facilities having a threshold quantity of 2,500 lbs of hydrocyanic acid are subject to the Risk Management Program Rule (RMP), Section 112r of the Clean Air Act. with a toxic endpoint of 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:
Originally published in Environment Writer by the National Safety Council. Reprinted with permission. Environment Writer Metcalf Institute for Marine and Environmental Reporting University of Rhode Island Graduate School of Oceanography Office of Marine Programs Narragansett, RI 02882 Tel: 401-874-6211; Fax: 401-874-6485 Disclaimer * Copyright 2002-2006 * All rights reserved. * University of Rhode Island |