[TowerTalk] OT: Propane Tank near lightning ground

[Bob Gates]

Hi Doc,

Enjoyed your informed response.  Please don't think I'm being critical or nitpicking here, because I assure you I am not.  But I'm retired from Shell Oil Company after a 30 year career, part of which was managing our rail fleet for two years.  During that time, I learned more than I ever wanted to know about "BLEVE"s and it scared the crap out of me.  It actually is an acronym for "Boiling Liquid Expanding Vapor Explosion".  I've seen films of gas cars containing 33,000 gallons of pressurized gas catching fire in a derailment situation, and eventually exploding.  The resulting BLEVE was akin to an atomic bomb going off, mushroom cloud and all.  The resulting carnage and devastation was impossible to imagine.  Most of the films were from news crews taping "a big fire".  One, in Houston, TX back in the late sixties, resulted in the total evaporation of the cameraman up on a fire truck ladder.  Shot up there to get a better view.

So you're quite right to be extremely cautious around any pressurized flammable gas container.  But the direction of the BLEVE is a lot more nebulous than many would like to think.  The key is where is the heat source coming from to create the over pressurization and the tank structural degradation, and the construction of the tank itself.  Most probably, the explosion, if it occurs, will be a total envelopmental pattern around the tank, most probably not off the end caps at all.  If you look at the construction of a cylindrical tank, you have a preformed one-piece bottom and top section, plus a rolled and, possibly,  welded middle tube section.  The weakest link, to me, is the longitudinal section, with the longest length of unreinforced steel. Remember, weld points are stronger than the elements they join.  And not the end caps as your hazmat responder indicated.  Consider also that the explosion would be generated through the expanding gases to all surfaces of the tank structure.

If it were me, I'd certainly press him for more details on his theory.  Especially if you're going to have to be on the scene! Rule number one:  Don't put your communications setup in a place where it can be disintegrated.

As to your last point, not having gas on the property is obviously the safest solution. :)  But, always a but, when installed properly, gas tanks are as safe as your electrical system, and they can coexist quite nicely.  And your question about keying a1500 watt amp at the same time there is a tiny leak from a gas line and a weak arcing point in your feedline or at the grounding panel for your cables prior to entry to the shack system,  AND you can't smell the leak, can only say that one can create a catastrophe-in-the-making on just about any subject, including getting electrocuted while sitting on the toilet while using your electric razor and dropping the razor into the bowl, thus creating a "possible" electrical jump connection to one of your most private parts, then moving to the heart and causing massive cardiac failure.  Possible, but I don't expect to read about it in my lifetime.  "Mathematical possibility" vs. "real world dynamics."
  Even the little propane tank on my grill makes
  me nervous, so I am probably a bit more nervous
  around those "big white bombs" than most!

  That said, I learned when I worked for the Office
  of Emergency Management that the key concern
  from a tank is the direction of the "blevy".

  This was illustrated for me by our lead hazmat
  responder who described driving up to the scene
  of a huge propane tank with a fire under it.  He
  exclaimed that they had set up their command post
  in direct line with one end of the tank -- the
  hottest end -- and would have been obliterated
  had the tank "blevied" and sent that end ... and
  many superheated shards ... flying their way.

  So, if the "ends" are the top and bottom I
  suppose you are in less danger then if they
  are pointed at the house.

  I will not own property with gas of any sort
  running under or near it, but that is my "thing"!

  I wonder if there is a risk of keying the KW
  amp at the same time there is a tiny leak from
  the tank and a weak arcing point in your
  feedline or at the grounding panel for your cables
  prior to entry to the shack?  Mathematically
  unlikely for sure ... ;-)

  -- 
  Thanks! & 73, doc kd4e  http://bibleseven.com