From: bill.sloman@ieee.org   
      
   On 22/12/2025 8:24 pm, Liz Tuddenham wrote:   
   > Bill Sloman  wrote:   
   >   
   >> On 22/12/2025 6:37 am, john larkin wrote:   
   >>> On Sun, 21 Dec 2025 16:58:41 +0000, liz@poppyrecords.invalid.invalid   
   >>> (Liz Tuddenham) wrote:   
   >>>   
   >>>> john larkin  wrote:   
   >>>>   
   >>>>> On Sun, 21 Dec 2025 15:40:21 +0000, Jeff Layman    
   >>>>> wrote:   
   >>>>>   
   >>>>>> On 21/12/2025 05:08, Bill Sloman wrote:   
   >>>>>>   
   >>>>>>> This is roughly equivalent to insisting that petrol-engined car won't   
   >>>>>>> catch fire if you shoot a bullet into the petrol tank.   
   >>>>>>   
   >>>>>> It won't catch fire. You can search for this yourself:   
   >>>>>>   
   >>>>>> bullet gasoline tank fire   
   >>>>>>   
   >>>>>> It's a myth, mainly as a result of many Hollywood movies showing cars   
   >>>>>> exploding from a single bullet to the tank. Even multiple bullets fired   
   >>>>>> into a tank won't cause the fuel to ignite. You need an incendiary   
   >>>>>> bullet, and even then you might require more than one.   
   >>>>>   
   >>>>> We (the good guys) got a great advantage in WWII, with planes that had   
   >>>>> self-sealing gas tanks.   
   >>>>   
   >>>> I think you will find the Germans had them before WWII broke out but we   
   >>>> didn't develop them until later.  Apparently the UK research was bogged   
   >>>> down by mission drift or 'specification-runaway'.   
   >>>   
   >>> Old cars had gas gauges that used a float and a wirewould pot, inside   
   >>> the tank. It didn't blow up because the mix in the tank wasn't   
   >>> flammable.   
   >>   
   >> Wrong. The mix of air and gasoline vapour inside the gas tank can be   
   >> flammable.   
   >   
   > ...but generally isn't.  (It has a very narrow flammability range.)   
   >   
   >   
   >> The wires inside a wirewound pot never got hot enough to   
   >> ignite the mix. I   
   >   
   > You appear to have misunderstood where the risk comes from.  Wirewound   
   > pots can make bad contact and generate small arcs which have quite   
   > enough energy to ignite petrol vapour within the range of flammability.   
      
   Look up "intrinsically safe" electronics. It takes about a microsecond   
   (and an appreciable amount of energy) to get a electric discharge   
   through gas through the "glow to arc" transition. Unless you tied a   
   substantial  capacitor directly to the wiper there wouldn't be enough   
   energy available to get a big enough bubble of the vapour/air mixture   
   hot enough to start a fire.   
      
   There is also the point that it takes a hundred volts or so (the Paschen   
   curve minimum) to start any kind of discharge through gas at any spacing.   
      
   https://en.wikipedia.org/wiki/Paschen%27s_law   
      
   > The high concentration of the vapour is what stops it igniting.   
      
   Not always true.   
      
   > In-tank fuel pumps with commutators are safe for the same reason.   
      
   And other reasons which you don't seem to be aware of.   
      
   > Ford came up with an idea that did away with the carburettor: their   
   > system drew concentrated vapour directly from the fuel tank and diluted   
   > it with air to give the correct concentration for the engine.  They   
   > never put it into production and I imagine the need for a completely   
   > reliable and foolproof flashback arrestor was one of the major   
   > objections to it.   
      
   Getting the evaporation rate in the fuel tank high enough to sustain   
   prolonged acceleration might also have been a problem. A resistive   
   heater to boil off extra vapour when you needed it would have been a   
   solution, but not an attractive one.   
      
   --   
   Bill Sloman, Sydney   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)