CSB Releases Safety Bulletin Warning of Dangers of Sodium Hydrosulfide (NaHS) in the Workplace; Outlines Safe Practices to Prevent Harm

July 15, 2004

Washington, DC, July 15, 2004 - The U.S. Chemical Safety and Hazard Investigation Board (CSB) today released a Safety Bulletin that warns of the dangers of sodium hydrosulfide and recommends safe practices to prevent accidents when handling the chemical.

CSB investigators uncovered 45 accidents associated with sodium hydrosulfide that have caused 32 deaths and 176 injuries since 1971. They noted, however, that accident data are incomplete and there may have been additional deaths and injuries attributable to the chemical. The Safety Bulletin is an outgrowth of the Board's investigation of a January 2002 accident involving sodium hydrosulfide that caused two deaths and eight injuries at an Alabama paper mill.

Sodium hydrosulfide, known by its chemical symbol NaHS (often pronounced "nash") is used in the leather tanning, pulp and paper, chemical, dye, and mineral extraction industries. NaHS is used as a pure solid (flake) or more commonly as a solution in water.

The Safety Bulletin points out that when NaHS is inadvertently combined with acid materials, deadly hydrogen sulfide gas is produced. Such inadvertent mixing can occur in a chemical process sewer, for example. Hydrogen sulfide gas has the characteristic smell of rotten eggs. The bulletin notes that hydrogen sulfide is insidious, because even moderate exposures impair a human's ability to smell the gas by deadening the nerves in the nose. Health effects from inhalation range from shortness of breath and severe lung damage at lower concentrations (50-150 parts per million in air) to rapid unconsciousness and death at higher levels (800-1,000 parts per million).

The Bulletin describes several common themes in NaHS incidents: spills, leaks, or inadvertent mixing that bring NaHS solutions into contact with acid; engineering controls that are inadequate, including lack of detection devices or ventilation systems; and inappropriate emergency response, where workers and responders may rush to help a fallen worker before sampling the air or donning protective gear.

The CSB Bulletin noted that companies handling NaHS must provide workers with material safety data sheets to apprise them of the chemical's potential danger. However, the CSB found that the hazard information in MSDSs varies significantly among NaHS manufacturers. The CSB recommended that companies that use NaHS review safety information from several sources, including the CSB Safety Bulletin, to gain a full understanding of the hazards.

The Bulletin urges companies to reduce NaHS hazards through engineering and design improvements and lists specific ways that companies can improve NaSH safety, such as air monitoring, safe storage, and proper use of protective gear. The Safety Bulletin was to be considered for final approval by the full Board at a public meeting in Washington today.

CSB is an independent federal agency charged with investigating industrial chemical accidents. The agency's board members are appointed by the president and confirmed by the Senate. CSB investigations look into all aspects of chemical accidents, including physical causes such as equipment failure as well as inadequacies in safety management systems.

The Board does not issue citations or fines but does make safety recommendations to plants, industry organizations, labor groups, and regulatory agencies such as OSHA and EPA. Further information about CSB is available from www.csb.gov. For more information, contact Sandy Gilmour (Public Affairs Contractor), 202-261-7614 or 202-251-5496 (cell), or Daniel Horowitz, CSB 202-261-7613.

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