CSB Investigators Cite Lack of Effective Management Systems in Hydrogen Sulfide Incident at Cincinnati Waste Disposal Plant

September 17, 2003

(Washington, DC, September 17, 2003) A release of potentially deadly hydrogen sulfide (H2S) at the Environmental Enterprises Inc. (EEI) waste treatment facility in Cincinnati, Ohio, resulted from treating chemical wastes in an inappropriate vessel, according to investigators from U.S. Chemical Safety and Hazard Investigation Board (CSB) speaking today a Board public meeting.

CSB lead investigator Angela Blair stated, "Management systems are the key to preventing this kind of incident," noting that a combination of problems contributed to the event. The incident, which occurred December 11, 2002, caused a maintenance worker to collapse after he walked near the waste vessel and inhaled toxic hydrogen sulfide, which carries a signature rotten egg odor. Inhaling the gas can cause accumulation of fluid in the lungs and respiratory arrest. The victim, who was initially unable to breathe, was treated at a local hospital and released.

"Environmental Enterprises had not adequately trained its employees on the hazards of hydrogen sulfide," according to CSB investigator Johnnie Banks. "Therefore the employees did not recognize the rotten egg odor as a sign of imminent danger."

EEI treats water-based hazardous waste containing various contaminants, including heavy metals, for disposal. CSB investigators said the hydrogen sulfide release occurred after an operator added solid sodium sulfide to a batch of waste in an effort to remove mercury. Later the same operator added an acidic chemical (polyaluminum chloride) to adjust the pH of the waste.

Unknown to the operator, excess sodium sulfide reacted with the acidic chemical to form hydrogen sulfide gas, which was released from the open-top clarifier vessel where the treatment was attempted. Later the maintenance worker entered the treatment area, which was then unattended, to retrieve a tool when he was overcome by the gas. The clarifier was not designed to handle the possibility of toxic gas formation and had no equipment to collect and treat such gases.

"This is the second serious incident we have investigated recently where the reaction of a sulfide salt with acid produced a dangerous gas release," according to CSB Chairman Carolyn W. Merritt. In November 2002 the Board completed its investigation of an incident at an Alabama paper mill where two workers were killed and eight others injured when a similar reaction in a process sewer caused a release of hydrogen sulfide gas. "Clearly there is a strong need for greater awareness of the hazards of reactive sulfides, Merritt said.

The CSB investigators found the EEI incident could have been avoided if workers had been trained on hydrogen sulfide hazards, had been given appropriate written procedures for performing treatment operations, or had been informed about the requirements of an earlier city order to abate hydrogen sulfide hazards at the plant. A hydrogen sulfide warning device, installed under provisions of the city order, was not working at the time of the December 11 incident.

The CSB is an independent federal agency charged with investigating industrial chemical accidents. CSB investigations look into all aspects of such events, including physical causes such as equipment failure as well as inadequacies in safety management systems. Typically, the investigations involve extensive witness interviews, examination of physical evidence, and chemical and forensic testing.

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 the CSB is available from www.csb.gov.

For more information, contact:

Daniel Horowitz, 202-261-7613 or 202-441-6074 (cell)

Sandy Gilmour Communications, 202-261-7614 or 202-251-5496 (cell)

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