General Major Incident # 1: Emergency Shutdown Systems for Chlorine Transfer
Sep 01, 2020
Main Reference:
www.CSB.gov
Accident Description:
Emergency Shutdown Systems for Chlorine Transfer
Event Date:
August 24, 2002
Location:
Festus, Missouri
General Summary:
Chlorine known to be highly toxic and corrosive leaked after an unsuitable hose used to connect a chlorine rail tanker and an equipment ruptured at the facility of DPC Enterprises, Festus Missouri.
The hose braiding was made from stainless steel instead of the recommended alloy, Hastelloy C, an excellent corrosion material. It was later found that this was a result of lacking proper materials verification procedure.
Emergency shut-off valves at the end of each hose were turned on to stop the emerging leak but still failed to operate because prior inspection was not conducted. The valves didn’t close due to corrosion in the piping system causing the leak to disperse for three long hours.
Over 48,000 pounds of chlorine leaked into the surrounding community which prompted a community evacuation.
Root Cause / Contributing Factors:
Root cause of the accident is Pitting Corrosion. This type of corrosion occurs when a passivation layer (protection) of a material is removed forming pits or cavities which gradually degrades the metal. Corrosion in the piping system caused the emergency valves to malfunction. These pipes are commonly made of carbon steel, corrosion resistant but upon the presence of high water concentrations or temperature, the passivation layer is deliquesced allowing corrosion attack.
Wet chlorine the initiator of pitting corrosion was formed due to presence of water which could have been transported through atmospheric pressure from poor capping of hoses and piping systems or moisture from the pad air supply system.
Estimated Financial Loss:
Eight years after the catastrophic incident at DPC, a settlement amounting to $100,000 was issued by a judge to the area first responders after they were exposed to chlorine and continued to suffer from health problems years after.
Human Impact:
Inhalation of chlorine poses very harmful effects ranging from mucous membrane irritation, chest pain, vomiting, even death depending on its concentration. Sixty three local residents were given medical treatment, three were hospitalized, and hundreds were evacuated or sheltered in place.
Environmental Impact:
High levels of chlorine are toxic to plants. Vegetation and tree leaves near the facility were scorched. The natural green pigment of the plants turned into brown, an evident impact of the chlorine’s toxicity.
RBI/ Reliability or Integrity Program:
Mechanical Integrity (MI) Program was conducted for the chlorine repackaging piping system at DPC however there were lacking practices or strategies which made the detection of corrosion highly improbable.
Missing Inspection / Reliability Practice:
Emergency valves failed because operating procedures to guarantee its closure were poorly checked.
Details in the procedures to ensure proper inspection were insufficient.
Supervision of inspection and test workers were insufficient.
Training of operators on the prevention of corrosion-induced system failure was inadequate.
Prevention:
Pitting corrosion could have been prevented if the moisture from the repackaging piping system was controlled or removed.
Regular inspection and checking could have helped identify the deterioration on equipment conditions.
CSB Recommendations:
Build a quality assurance system for chlorine hoses and create written procedures and best practices to guarantee a reliable emergency shutdown system functionality.
Improve quality of hose fabricator and guarantee correct identification of Hastelloy chlorine hoses through proper materials’ verification procedure.
Reference
- CSB Webpage as below:
https://www.csb.gov/emergency-shutdown-systems-for-chlorine-transfer/
- USCSB Youtube Channel as below:
https://youtu.be/R2Ez7lkjg1Y
