On December 3, 2020, at approximately 2:30 p.m., an accidental release of chlorine gas occurred at a plastics facility and seriously injured one employee. At the time of the incident, four (4) employees were involved in replacing an empty chlorine container with a full 2,000-pound (one-ton) container at the facility’s Ethylene Glycol unit. The unit used chlorine gas as a biocide in its cooling water treatment system.
As an employee disconnected the supposedly empty chlorine container from the process equipment, chlorine gas escaped because, unknown to the workers, the container still held 1,250 pounds of chlorine (62.5 percent of its original inventory). Because the chlorine container was understood to be empty, the employee was not wearing respiratory protection. After three failed attempts to stop the release, an emergency responder was able to close the chlorine container’s vapor valve and stop the release after 50 minutes.
The employee who disconnected the chlorine container was life-flighted to the hospital after showing respiratory difficulties from exposure to chlorine. The facility reported that approximately 10 pounds of chlorine gas were released.
The investigation team recommended installing a scale for each container to prevent future false indications of an empty ton container of chlorine. Knowing the weight of the chlorine container could help plant workers confirm whether a container is empty or alert them if it is not. In addition, the facility strengthened its operating procedures to clarify that respiratory protection is needed when changing a chlorine container.
Probable Cause
Based on the facility’s investigation, the CSB determined that the probable cause of the accidental chlorine release was disconnecting process equipment from the chlorine container while the system was pressurized with chlorine. The lack of instrumentation or other equipment to allow the operators to confirm the amount of chlorine in the container contributed to the incident.
Another factor contributing to the incident was the facility’s use of chlorine in its cooling water treatment program. Had it used a safer alternative, such as bleach, this incident could have been prevented.
Source: https://www.csb.gov/assets/1/6/csb_incident_reports_volume_one_2025-01-14_rev_1.pdf