The most conceivable incident involving a rail car leading to release of cargo is a derailment. The most vulnerable section of the car is its side where there are no guard plates installed. Guard plates and structures are installed at the two ends and at the top of the car, which limit the impact of a possible accident. Thus, most accidents leading to cargo release will result from a side impact.

In scenario #1 it is assumed that as the result of a derailment, flying objects, such as pieces of rail or other debris, hit the side of the tank and creates a rectangular opening with an approximate size of 12 inches by 6 inches. The car leaves the rails, slides down the embankment and comes to rest such that the leak occurs at 50% of the tank height defined by its diameter.

The second most vulnerable part of a rail car is its flanges. In order to limit the consequences of a possible flange failure, the US DOT requires that cars transporting EHS materials be equipped with safety valves in the shell side of the flanges.

In scenario #2 it is assumed that as the result of a derailment, the rail car leaves the tracks and slides or rolls down from the embankment. In doing so, one of the flanges shears off and creates an opening at 50% of the tank height defined by its diameter. The safety valve behind the flange engages but does not provide a hermetic seal. The cargo leaks at a rate equivalent to that provided by a 0.5-inch diameter hole.