On Friday, July 25, 2014 10:45:43 PM UTC-5, dpel...@my-deja.com wrote:   
   > Robert Heller  wrote:   
   > >    
   >    
   > > My understanding about the recent "crude oil" derailments / fires is not a    
   >    
   > > matter of "flammable liquids", but due to the fact that the crude oil in    
   >    
   > > question contains flammable *gases* (eg propane and butane) desolved in   
   the    
   >    
   > > crude oil.  Different grades of crude oil have differing amounts of    
   >    
   > > 'petrolelum gas' (propane and butane) and the current batches being   
   shipped    
   >    
   > > have partitularly high amounts of these gases.    
   >    
   >    
   >    
   > When you dissolve a gas in a liquid, you get a liquid. "Gas" and "liquid"   
   >    
   > describe physical states, not chemical composition.   
   >    
   >    
   >    
   > When you put a liquid in a tank, some of the liquid will evaporate. Exactly   
   >    
   > how much depends on the temperature, volume of the empty space, etc., as   
   >    
   > well as chemical composition. So yes, if Bakken crude contains a higher   
   >    
   > proportion of lighter hydrocarbons than other crude oils, it would form   
   >    
   > more volatile vapors. But, when you put gasoline, ethanol, or jet fuel in a   
   >    
   > tank, you still get volatile vapors through exactly the same evaporation   
   >    
   > mechanism. Google TWA Flight 800 for an example of volatile jet fuel vapors   
   >    
   > forming in a tank.   
   >    
   As you and others have pointed out, it is the combination of combustible   
   vapors and oxygen that is particularly dangerous. At one time, it was quite   
   common for ocean going crude oil tankers to explode at sea due to the volatile   
   fractions of the crude oil    
   combining with the air in the cargo tanks to form an explosive mixture. This   
   problem has largely gone away since tankers have been required to fill the   
   "ullage" space (the space above the liquid in the cargo tanks) with filtered   
   exhaust gas(i.e. nitrogen    
   and carbon dioxide) from the engines so as to exclude oxygen. Similarly, new   
   design airliners are to be required to fill the ullage space in fuselage tanks   
   with inert gas. Is it practical to apply this to rail tank cars?   
        
   Peter Wezeman   
   anti-social Darwinist   
      
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