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Huge fire/explosion in quebec

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PottedMeat said:
http://www.bbc.co.uk/news/world-us-canada-23221939



anyone know why they keep it under pressure?
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I believe that is a mistake. Oil tank cars typically aren't pressurized I believe. They are pressurized for unloading as they use a siphon pipe out of the top rather than out the bottom, and they may put a "blanket" gas at low pressure (under 100psi, usually nitrogen I think) to keep oxygen out but I don't think they're pressurized for transport. I think the pressure relief valves are typically set really low anyways, like 75psi. They're only ~1/2" thick plate anyhow, that's not gonna stand up to too much pressure

So, nothing explosive, although if its sitting in the middle of a huge damn fire, the relief valve may not be able to vent fast enough, leading to a pressurized-style explosion
 
yh125d said:
I believe that is a mistake. Oil tank cars typically aren't pressurized I believe. They are pressurized for unloading as they use a siphon pipe out of the top rather than out the bottom, and they may put a "blanket" gas at low pressure (under 100psi, usually nitrogen I think) to keep oxygen out but I don't think they're pressurized for transport. I think the pressure relief valves are typically set really low anyways, like 75psi. They're only ~1/2" thick plate anyhow, that's not gonna stand up to too much pressure

So, nothing explosive, although if its sitting in the middle of a huge damn fire, the relief valve may not be able to vent fast enough, leading to a pressurized-style explosion
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Doesn't it have high flow pressure relief valve/s?

Perhaps it couldn't vent quick enough due to very high heat that built pressure quicker than the valve can vent, or the valve/s was malfunctioned/tampered with.
 
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iGas said:
Doesn't it have high flow pressure relief valve/s?

Perhaps it couldn't vent quick enough due to very high heat that built pressure quicker than the valve can vent, or the valve/s was malfunctioned/tampered with.
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I'm not familiar with the codes as they apply to relief valve sizing on railcars, but on typical pressure vessels I'm more familiar with they are usually "fire-sized", meaning they should have sufficient volume to keep pressure lower than I think 110% of the pressure vessels MAWP (max allowable working pressure).

But those calculations work off of some sort of assumed conditions, if the vessel were exposed to more extreme conditions than it was sized for it could go over 110% and eventually rupture, or if exposed for an extended period it could be something like propane tank style BLEVE explosions, which can occur despite a properly sized and functional relief valve under extended fire exposure

http://www.youtube.com/watch?v=UM0jtD_OWLU
 
horrible accident, they better revise the braking systems/parking spots of those trains so that they can resist a locomotive turning off (maybe just avoid parking them on slopes so that passive braking is enough or something), and the firemen who intervened on those trains were probably not trained on how those trains stay still when parked.
 
I thought air brakes stick on if you lose air pressure? All the air brakes I ever heard of would be stuck on if you lost air pressure. The trucks I drove in the military worked that way. No air pressure = stuck on brakes.

I see from a little research that the train brakes are also supposed to be fail safe, although they seem to work a little differently.
 
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