On May 29, 2024, at about 3:15 p.m., several pounds of hydrogen sulfide and carbon monoxide gas were released at a Sugar Cooperative. As a result of the release, one employee was fatally injured, and another employee was seriously injured due to inhalation of the gases.
The facility’s investigation found that, at the time of the incident, two employees were performing maintenance on a pump. The workers closed an isolation valve and removed approximately half of the bolts on the connection before water began leaking from the flange onto the floor. The workers and their supervisor determined that the isolation valve was not properly seated. The two workers left the pump house to get a tool to help close the valve. While the workers were away, hydrogen sulfide and carbon monoxide began to be released into the pump house (approximately 400 square feet and 8 feet tall).
When the workers reentered the pump house, they experienced symptoms consistent with toxic gas exposure. One of the workers lost consciousness (“Worker 1”) when trying to escape up a ladder. The other worker (“Worker 2”) escaped the pump house. Worker 2 explained the situation to another supervisor, and emergency responders were contacted.
A third supervisor and two other employees attempted to rescue Worker 1 but realized the area was dangerous and attempted to escape. During the escape, one of the attempted rescuers (“Rescuer 1”) fell, appeared to be unconscious, and could not self-rescue.
An air-monitoring device lowered into the pump house triggered alarms for hydrogen sulfide and carbon monoxide, indicating concentrations exceeding 20 and 35 parts per million, respectively. Because of the high concentrations of the gases, facility employees halted their rescue attempts and waited for emergency responders to arrive.
Emergency responders equipped with self-contained breathing apparatuses rescued the two employees from the lower pump house and transported them to a local hospital for medical treatment. Rescuer 1 died at the hospital later that day. Worker 1 survived and was released from the hospital after a few days. Following the incident, the facility classified the lower pump house as a confined space and installed continuous air-monitoring equipment.
Probable Cause
Based on the facility’s investigation, the CSB determined that the probable cause of the incident was the pump’s leaking isolation valve that allowed hydrogen sulfide and carbon monoxide gas to enter the pump house when the flange was opened. Failure to identify or control the release of these toxic gases in this part of the process contributed to the incident. Contributing to the severity of the incident was that the lower pump house was not classified as a confined space, which allowed employees to enter without safeguards such as respiratory protection, air monitoring, attendants, or a rescue plan.
Source: https://www.csb.gov/assets/1/6/incident_reports_volume_2_2025-03-12.pdf