INCIDENT DUE TO LONE WORKING WITHOUT ENGINEERING SAFEGUARDS

During the morning of February 24, 2023, an unknown amount of hydrocarbons and hydrogen sulfide were accidentally released, fatally injuring an employee inside an enclosed building at an oil and gas facility in Dakota. The hydrocarbons and hydrogen sulfide displaced the oxygen in the building, and the employee asphyxiated in the oxygen-deficient atmosphere.

The employee was considered a “lone worker” who operated multiple oil and gas facilities in the local area. Some of the oil and gas equipment was housed inside enclosed, insulated buildings, allowing operators to work in a climate-controlled environment. At the time of the event, it was negative 26 °F outside, and the interior of the building where the incident occurred (approximately 8 feet tall and 90 square feet) was about 65 °F.
A pump inside the building was not operating as designed, causing an adjacent vessel to begin overfilling. To prevent the vessel overfill from causing the facility to shut down, the employee began manually draining the vessel and another nearby vessel, both of which were housed inside the building. To drain the vessel, the employee connected a temporary hose to it and drained its liquid, mostly water and hydrocarbons, into a bucket inside the building. The employee then left the building temporarily to conduct operations at other locations in the facility. During this time, the drained hydrocarbons vaporized inside the enclosed building and displaced oxygen. About twenty minutes later, the employee returned to the insulated building and may have accidentally knocked over the bucket of drained liquid. Additional hydrocarbons and hydrogen sulfide likely vaporized, further displacing the oxygen inside the building. The employee breathed in the oxygen-depleted atmosphere and asphyxiated.
The building where the draining occurred did not have detectors installed to monitor for hazardous gases, and it was not ventilated. The employee had a personal gas detection monitor, but it was turned off and in his truck. No company procedure was in place that provided instructions for safely draining liquids from vessels inside buildings.
After the incident, the company evaluated adding additional engineering controls (for example, hazardous gas detection and alarms, forced ventilation) to its enclosed buildings, developed a written procedure requiring that process fluids be drained outside of buildings, and enhanced training and supervisor verification requirements regarding the use of personal gas monitors.
Probable Cause
Based on the company's investigation, the OSHA inspection, and the local Sheriff’s Office investigation, the CSB determined that the probable cause of the incident was the displacement of oxygen inside an enclosed building after an operator drained process liquid into a bucket and the hydrocarbon and hydrogen sulfide components vaporized. Contributing to the incident was the absence of company procedures detailing instructions for safely draining liquids from vessels located inside buildings. Contributing to the severity of the incident was the lack of engineered safeguards (such as installed detectors, alarms, and ventilation) to control or alert of a hazardous atmosphere and an unsuccessful system for ensuring employees wear personal gas monitors.

Source:CSB.gov