Why was the East Palestine tank car blown up?

While much has been written about the aftermath of the East Palestine train wreck burn, there is little regarding why the rail tank containing hazardous chemicals needed to be blown up.

I am a retired engineer having significant experience with pressure vessels and some background with DoT tank regulations.  I offer my thoughts based on limited knowledge and a little thinking.

From what I could learn, the contents of the tank(s) were becoming unstable, and pressure was increasing.  It was feared that the tank would explode and send shrapnel everywhere.  So the decision was made to relieve the pressure with a "controlled burn."  This story raises many questions that must be answered.

The first question is, what was causing the pressure to build?  Physically, there is no difference between a tank sitting on its wheels on a track and a tank lying on its side on the ground.  There is nothing about a tank lying on the ground that would cause pressure to build.  Was there a fire around the rail cars?  I've seen nothing indicating that this was the case, nor is it likely there was a wild land fire in the middle of winter in Ohio.  How did they know pressure was building?  Were they monitoring a pressure gauge on the tank?  If so, they were close enough to put out any fire that might be threatening the tank.  Furthermore, transport tanks are equipped with a pressure relief valve that would not allow pressure to build enough to burst them.  Note: If the contents of a transport tank are so hazardous that they are unsafe to vent via a relief valve, additional requirements are imposed on tank strength and integrity during accidents.

Because rollovers and derailments are expected, hazardous transport tanks are designed to survive them.  They are also designed with rollover protection so that fill connections are protected to remain accessible and functional in the case of these accidents.  This would have allowed responders to connect to and empty the tanks into alternates such as over-the-road tanks and then hauled away.  Why was this approach rejected?

Finally, these tanks are made of ductile material, typically mild carbon steel.  They do not eject shrapnel when they burst.  Rather, they split apart, with all material remaining contiguously attached.  The tank itself might become airborne, but it would not break up into pieces.  Why was the governor of Ohio told the tank would produce shrapnel?  Even if the shrapnel scenario were true, how would that be more hazardous than releasing tons of hazardous acid and toxic fumes?

Admittedly, my knowledge of these topics is limited and I welcome any corrections.  However, I believe these are serious considerations that need to be addressed — if for no other reason but to prevent future incidents like this from recurring.

Image: David Brossard.

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