"Adam H. Kerman"  wrote:   
   > dpeltier@my-deja.com wrote:   
   >> "Adam H. Kerman"  wrote:   
   >>> dpeltier@my-deja.com wrote:   
   >> The cars are not pressurized, but they are sealed. So yes, you quickly   
   >> reach a point where the number of high-energy liquid molecules that escape   
   >> the surface tension of the liquid (i.e. evaporate) is equal to the number   
   >> of low-energy gas molecules get captured by the surface tension of the   
   >> liquid (i.e. condense). Then you reach an equilibrium where some of the   
   >> material is in gas form and some in liquid. And if the cars are loaded to   
   >> near their volume capacity, it will mostly still be liquid.   
   >   
   > They're not sealed against the evaporation of gases, nor from the atmosphere.   
      
   They are pressure tested at up to 100 psi, so yes, they are sealed from the   
   atmosphere (except for a pressure relief valve).   
      
   In fact, I believe that a beefed up pressure relief valve is part of the   
   proposed new federal standards, the idea being that, if an uncompromised   
   tank car finds itself in the middle of a fire, it is better to vent the   
   gases out into the fire than I build up enough pressure to crack open the   
   tank. It is believed that the mushroom cloud explosions that make national   
   news wen caught on video result from this kind of "boiling liquid expanding   
   vapor explosion" (BLEVE for short).   
      
   >> The behavior of Bakken crude is not at all outside of the usual spectrum   
   >> of behaviors one sees with flammable liquids. Until Lac Megantic people   
   >> lots of people had assumed (either by failing to do the proper tests,   
   >> or by ignoring the results) that it would behave more like the other   
   >> kinds of crude commonly transported log distances. Turns out, it actually   
   >> behaves more like ethanol.   
   >   
   > . . . because of the dissolved propane, right?   
      
   I don't think there's a definitive answer yet. Propane and other "natural   
   gas liquids" are one suspect. Others have suggested hydrogen sulfide or   
   some as-yet-identified fracking chemicals. I haven't been following every   
   news release closely enough to know if any have been ruled out yet.   
      
   Dan   
      
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