Why did the crude oil train crash and explode in Canada?

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arydberg said:
Could someone please explain how crude oil could explode as shown in the recent crash in Canada.

An explosion is just very rapid combustion - if something burns slowly it's a fire, if it burns almost instantaneously it's an explosion.

Smash open a tanker car of crude oil moving at 60-plus km/hr and you can spread enough crude oil around in small enough droplets that it will burn very quickly. That's the explosion. Of course only some of the crude oil in that crash exploded - the rest burned for hours before the fire could be put out.
 
So are you saying the crude oil can burn fast enough to kill 50 people?
 
Absolutely. Crude oil does not explode. Cal Tech spent 3 years trying to get kerosene ( jet fuel) to explode.

What do you think?
 
They got a traveling wave front that traveled at 3 miles per hour. In my opinion to call that an explosion is a real stretch. Also kerosene ( as safe as it is) is much much lighter and more flammable than crude oil. Do you think crude oil explodes? This is what I am trying to understand.
 
Well in accidents like these you have to take into account thousands of little things that happen all at once or in short time period , it's not like dropping a pen , it's far more complicated , many train cars , many gallons of fuel wheels and different parts of the train systems like bearings in motion creating heat etc.then the crash itself etc etc.

Now who says it has to explode?It burnt and some of it got fire in a rapid expanding way which is close to explosion.
Oh by the way under normal atmospheric conditions gasoline doesn't explode either it just rapidly catches fire but put gasoline in a containment like a gas tank or some other tightly sealed container get some vapor to be condensed in that container (enough to ignite) and then put a spark plug in it. You will get yourself a pretty decent bomb.
The same applies for diesel and other oil products only in the latter case you need to add pressure.
 
arydberg said:
They got a traveling wave front that traveled at 3 miles per hour. In my opinion to call that an explosion is a real stretch.

That's about right for the laminar flame speed.

Actually gasoline (iso-octane) is very similar. So by your argument, gasoline doesn't explode either.
 
Technically, that's a deflagration, not a detonation. However, if you were in one, and asked what happened, it's not unlikely that the word you would chose to describe it would be "explosion".
 
arydberg said:
So are you saying the crude oil can burn fast enough to kill 50 people?

Sure, if you get enough of it to burn fast enough. Burning one barrel of crude oil will release somewhere north of 109 joules, about the same amount of energy as a ton of black powder. Take a few hundred barrels of crude oil (a small fraction of what was on that train), disperse it as a spray so that it can burn in a few seconds or less, and the results will be comparable to an explosion at a fireworks factory.
 
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Crude Oil is not jet fuel. Unrefined crude oil can contain many of the volatile, lighter density petroleum components which are separated out during the refining process (things like natural gasoline, for instance). If these lighter compounds are ignited, then the rest of the crude oil will burn quite well.

There was once a man named Red Adair who made quite a living traveling the world putting out fires which started in drilling fields, where, coincidentally, a lot of crude oil was present. I would also direct your attention to the first Gulf War when retreating Iraqi forces set fire to as many Kuwaiti oil wells as they had access to.
 
Well just like we divide the electromagnetic radiation spectrum in visible , x rays, infrared , gamma etc according to the wavelength and corresponding strength of the radiation we also divide rapid burning , rapid expansion and explosion etc.
The thing why we don't call gasoline or oil catching fire an explosion is because the expansion is not fast enough to be an explosion I guess.
The same reason why we don't call a public bus a dragster because it just can't accelerate fast enough.
 
After a derailment, tank cars and free oil settle in the low areas such as at the bottom of embankments or in ditches. Once one tank car has ruptured and the volatile component ignited, by say fallen power lines, the remainder of the progressively heavier oil components will “boil” and so start a fierce fire. That fire will heat adjacent sealed tank cars which will generate huge internal pressures. When the tank ruptures due to the high internal pressure there will be a flash vaporisation due to the instant pressure drop. That instant vaporisation will produce a column of hot hydrocarbon gas, the outside of which will burn when it contacts atmospheric oxygen.

It is a common mistake to confuse an explosion with a flame. The flame can be delayed because the vapour released is surrounded by air exhausted of oxygen. Ignition of the column may take place when the vapour plume reaches a few hundred metres.

The rupture and instant vaporisation is a (flame free) explosion with a destructive supersonic shock front. Not a comfortable place to be.