Why Train Derailment Causes Fire?

[jjoll]

What causes train car that is full of crude oil to catch fire (after derailment)? Does the collision create enough heat for the crude oil to catch fire? I have watched Mythbuster and I can remember once in their show they were trying to shoot at gas tanks to make them explode but they couldn't since the bullets were not creating enough energy or the gas to ignite.

[pgrmdave]

It looks like there was a recent study about this - like just a few days ago! The energy released in a train crash *is* likely to generate enough heat to ignite the crude, basically. "the energy generated from an accident has the potential to greatly exceed the flammability impact of...crude oil property-based criteria."

 

You can read more here:

Basic overview

Some more in depth about how it relates to transporting oil

Actual study

[pgrmdave]

Some basic back-of-the-envelope math seems to confirm this, too. A full oil tank would weigh in the neighborhood of 119,000kg, and would travel at around 60mph. That gives a single tank car about 24,000,000 Joules of energy. A bullet, on the other hand, weighs about 8 grams, and travels at about 1175mph. Because it weighs so much less though, it's only got 640 Joules of energy.

 

It takes 2.13 Joules to heat 1 gram of oil by 1 degree C. The autoignition point of oil is 400C, so assuming the oil is at room temp (20C) then there's enough energy in a moving train (assuming 100% conversion of kinetic energy to heat, which obviously wouldn't happen) to ignite 29.65kg of oil. While that's significantly less than the amount of oil in the tank, it only takes a little bit to ignite.

 

 

(all numbers taken from a combination of wikipedia, google, and wolfram alpha. I cannot confirm that any of them are accurate.)

Edited March 27, 2015 by pgrmdave

[Buffy]

There are a couple of things that affect the computations:

• The US dragging its feet on requiring even a slight safety improvement on the standard DOT-111 tank cars, let alone upgrading to the DOT-112/114 that Canada already requires for all petroleum transportation.
• With the huge increase in production in North Dakota, lack of state regulation has allowed producers to skip the step of adding stabilizers to the petroleum being shipped that even regulation-averse Texas requires before shipping via rail car. These stabilizers significantly reduce the ability to induce ignition of the oil.

 

All this of course is subject to statistical probabilities, so any discussion of "can you ignite it or not" is really "what's the likelihood" and unfortunately with these two facts in combination with the fact that the number of cars transporting petroleum has gone up an entire order of magnitude in the last few years, that likelihood is going through the roof, which is why we hear about a tank car explosion at least once a week now.

 

 

I do not understand why everything in this script must inevitably explode, :phones:

Buffy

[jjoll]

It looks like there was a recent study about this - like just a few days ago! The energy released in a train crash *is* likely to generate enough heat to ignite the crude, basically. "the energy generated from an accident has the potential to greatly exceed the flammability impact of...crude oil property-based criteria."

 

You can read more here:

Basic overview

Some more in depth about how it relates to transporting oil

Actual study

great references, thanks