From: nilknocgeo@earthlink.net   
      
    wrote in message   
   news:1652632102428122304.212863dpeltier-my-deja.com@news.aioe.org...   
   > "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   
      
   What about the thinking that an accident ruptures the tank car itself and   
   thus all this is rather irrelevant?   
      
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