Process Puzzler: Put Railcar Loading Back on Track

Readers suggest how to stop serious safety snags.

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We had six railcars in a propylene loading bay. One of the tankers was overfilled and was vented to fixed piping via hose at the loading station; the fill valves on the car and the loading arm were open. The other cars' valves and their loading valves on the fixed piping were closed per standard procedure. Sometime during the night two additional cars were brought down the line to be filled, pushing the first six cars towards the exit and blocking the entrance track point. The locomotive crew — believing the first six railcars were full and disconnected — bumped the cars further down to access other bays. In the process, a hose snapped. The emergency cut-off valve for the bay failed. The only way to prevent a major catastrophe was for an operator to rush in to manually close the valve. He stopped the flow but received serious cold burns. Fortunately, the propylene vapor cloud didn't ignite. How can we ensure that nothing like this ever happens again?

I encountered a similar problem while working in a plant that constantly unloaded propylene rail cars in a remote unloading rack located approximately ½-mile from the control room. On more than one occasion a hose had failed, resulting in a major leak and very dangerous situation. The Department of Transportation stipulated that the unloading station be manned continually; the unloading process took six to eight hours. We implemented the following changes: 1) the hoses were replaced with piped swing arms (which are safer than hoses); 2) remote-operated vapor and liquid block valves were installed on the base of each arm, allowing local control; 3) liquid valves were fail-closed with open/closed indicator switches; 4) valves were cycled each time a set of cars was unloaded; 4) cameras were installed on the rack to monitor the process; and 5) propylene sensors were placed strategically around the loading area to detect leaks.

In your particular case I would also add a sign and derail on the railroad tracks ahead of the loading area. Only the operator should be permitted to remove this derail once loading/unloading is complete. If your plant lacks these procedures then you should implement them.

P. Hunter Vegas, senior project engineer
Avid Solutions, Inc., Winston Salem, N.C.

I'm not sure how far reaching this requirement is, but in Ontario it is required to erect a blue "tank car connected" flag on the track leading to a connected rail car. It is also common practice to install a lockable derailer about 25 feet up the track from the first loading spot.

James Miller, process engineer
Chemtura, Elmira, Ontario

Make sure that the emergency cut-off valve is fail-close and regularly maintained. Install a limit switch for the valve closed position, to check the regular operation of the valve. A spill-detection system is needed — ground temperature probes or filling hose failure detection, e.g., filling hose low pressure. If you cannot guarantee regular maintenance of the valve, install a high-performance valve with an oversized actuator.

Michele Murino, maintenance manager
Air Liquide Italia Produzione, Milan, Italy

Put the operator in charge of setting up the cars to be filled. Have a chock with a safety flag after the last car at the filling station; only the operator is allowed to remove the chock. The train crew drops off railcars but is not to be permitted to push the cars. If a loading spot is empty the chock will be on the car in the next loading spot. This would allow the crew to fill the empty spots — but only the empty spots. Before any cars are pushed if the cars are filled, the operator should disconnect the cars and remove the chocks. Only an operator is permitted to move the chocks.

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