CSB: Address Chlorine Railcar Unloading Practices

The U.S. Chemical Safety and Hazard Investigation Board released a safety bulletin warning that some chlorine railcar transfer systems lack effective detection and emergency shutdown devices, thus leaving the public vulnerable to potential large-scale toxic releases. CSB recommended that DOT expand its regulatory coverage to require facilities that unload chlorine railcars to install remotely operated emergency isolation devices to quickly shut down the flow of chlorine in the event of a hose rupture or other failure in the unloading equipment. The safety bulletin cites two previous incidents of accidental chlorine releases that occurred as a result of ruptured transfer hoses.

Chlorine railcars are equipped with an internal excess flow valve (EFV) that is designed to stop the flow of chlorine if an external valve breaks off while the railcar is in transit. Because these EFVs are not designed to stop leaks during railcar unloading, however, the failure of a transfer hose may not activate the valve, and chlorine will continue to escape. Companies should install emergency shutdown systems that can quickly stop the flow of chlorine if a hose ruptures during the unloading operation, the bulletin said.

In August 2002 a hose ruptured at a plant near Festus, Mo. The emergency shutdown valves did not close as designed due to poor maintenance, and the EFV did not close. The only way to stop the release of chlorine from the railcar was to send emergency responders through a four-foot deep yellowish-green fog of chlorine vapor to manually close shutdown valves located on top of the railcar. Incidents such as this one demonstrate why EFVs should not be relied upon to stop hazardous material releases during unloading operations.

However, in a survey of drinking water and wastewater treatment facilities conducted by the CSB, investigators found that approximately 30 percent of the bulk chlorine users contacted continue to rely solely on the EFV to stop chlorine flow in the event of a transfer hose rupture.

The DOT Hazardous Materials Regulations regulate transportation of hazardous materials by rail, aircraft, vessel, and motor vehicle tank truck. They currently require emergency shutdown equipment for motor vehicle tank truck chlorine transfer systems but not for railcar chlorine transfer systems.

CSB Member John Bresland said, "Chlorine is a very useful but a highly toxic substance that needs appropriate safeguards to prevent releases and protect the public. Our safety bulletin reveals the importance of expanding current regulatory coverage to chlorine railcar unloading operations."

The safety bulletin compares two chlorine releases from railcars that were investigated by CSB. The first incident, discussed briefly above, involved a 48,000-pound release of chlorine that resulted in the evacuation and sheltering of hundreds of residents. In addition, 63 residents sought medical attention, and three were admitted to the hospital. The second incident occurred in August 2005 at a Baton Rouge chemical plant when chlorine began to escape from a railcar because of a transfer hose failure. There, the emergency shutdown system functioned properly and the release lasted less than one minute. There was no impact to the surrounding community.

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    July/August 2019

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