CSB Describes Fatal Chemical Release at Maine Pulp Mill

The U.S. Chemical Safety and Hazard Investigation Board (CSB) has released an update on its investigation of a hydrogen sulfide gas release that caused two deaths at the Woodland Pulp Mill in Baileyville, Maine, on Jan. 27. According to CSB’s news release, the mill chemically processes wood chips for papermaking in the “Bleach Plant,” an area within a building known as the “Kraft Mill.” Management had decided on the day before the incident to shut down most of the mill, after an increase in natural gas prices resulted in significantly higher operating expenses. Draining of equipment in the Bleach Plant led to liquid waste accumulating in the mill’s acid sewer pipe, triggering an automatic release of sulfuric acid into the pipe to control pH. The sulfuric acid reacted with the sulfuric compounds in the liquid waste to produce toxic hydrogen sulfide gas. Any hydrogen sulfide produced in the sewer pipe during normal operations would have been removed by a scrubber, but the scrubber fan had been turned off due to the shutdown. Consequently, hydrogen sulfide began to leak into the Kraft Mill.

A 20-year-old chemical engineering co-op student and a 26-year-old chemical engineer were working together on the second floor of the Kraft Mill at the time of the release. They were found collapsed on the floor more than six hours later, after emergency response efforts by other mill employees caused the hydrogen sulfide to dissipate. The co-op student died the day after the incident. The engineer remained on life support until he passed away on Feb. 16. Ten other employees were exposed to hydrogen sulfide in the Kraft Mill, with some reporting symptoms such as burning eyes, burning throat, and headache.

Although CSB’s investigation is still ongoing, the agency has found the Kraft Mill building lacked ventilation, as well as a system for keeping track of employees’ whereabouts during the shutdown. No stationary hydrogen sulfide detectors were located in the Bleach Plant, and the employer did not issue or require workers to wear personal hydrogen sulfide monitors. 

CSB stated in a news release that it will continue to evaluate the mill’s hydrogen sulfide detection, alarms, and response; personnel access to the Kraft Mill; and site safety practices. The agency’s findings and recommendations will be eventually published in a final report. More information is available in CSB’s investigation update document (PDF).