<VV> Will it stink? (...And Other Stuff.)

[RoboMan91324 at aol.com]

Joel,
 
Obviously, I can't comment on the specific experience of your  insurance 
guy but car explosions do occur.  I am more than willing to admit  that they 
are rare and occur only under unusual circumstances.  I believe  that the 
situation Ignatio described might be just such a set of  circumstances.
 
I agree that the inside of a gas tank is not that best  environment for an 
explosion because of the fuel/oxygen ratio, as you  said.  An empty tank is 
more susceptible to an explosion than a full  one.  Of course, your 
definition of a "precisely mixed" ratio is  arbitrary.  You can have an explosive 
mixture over a fairly broad range of  air/fuel ratios.  Yes, that is an 
arbitrary statement too.
 
The scenario I posed was where the car might be on fire in a  relatively 
enclosed space or "stall" as was described by Ignacio.  When a  small space in 
this case is enclosed by a firewall, as required by building  code, the 
fire is hotter and/or lasts over a longer period of time depending on  
availability of oxygen and fuel.  The hotter and/or longer burn means that  the fuel 
in the tank boils off and might even rupture the tank.  Because of  a lack 
of Oxygen, the liquid gas only burns moderately.  The vapor fills  the 
immediate area burning somewhat but waiting for an influx of oxygen to  create an 
explosive situation.  The venting in the garage allows some  oxygen but 
that probably never makes it to the "stall" because that is likely  protected 
from the major convection caused by the fire.  The most dangerous  faze in 
this scenario is when the garage door or maybe even  the door into the kitchen 
is opened depending on where it is in relation to the  car fire.  The 
influx of oxygen into the hot gasoline vapor will almost  certainly cause an 
explosion.  Firefighters are trained to open doors with  great caution in a 
burning building because they know that an oxygen starved  fire in an enclosed 
space is an explosion waiting to happen.  To add  emphasis, those explosions 
are fueled mostly by wood, carpets, etc.  A  gasoline vapor fueled explosion 
is likely to be more violent once oxygen reaches  it.  I assume you must 
have seen video of burning buildings explode outward  suddenly.  Those occur 
under the exact circumstances I describe.  A  door was opened or breaking 
windows suddenly allowed air in.  These are the  circumstances which might 
occur in Ingnacio's "stall."

The TV show you referenced is Mythbusters.  It is a very  entertaining show 
and I never miss it.  They were trying to prove or  disprove the 
commonality of car explosions on TV and in movies caused by  gunshots.  By the way, 
they always use explosives in case the expected  explosion does not occur.  It 
is more entertaining.  Their results  were as expected; the fire caused by 
the tracer rounds they used was due to  burning liquid gasoline escaping 
onto the ground.  The burning phosphorus  (or other substance) in the tracers 
ignited it.  This situation in  outside air would not be expected to create 
an explosion.  If the car were  surrounded by gas vapor and not liquid, there 
would probably be a fairly  significant explosion.  If the vapor was 
enclosed (as in a stall)  before it was ignited in the presence of Oxygen, the 
explosion would be more  intense.
 
If you have an open container of gas sitting outside, you can  probably 
throw a lit match into it and merely cause the gas to burn.  More  than likely, 
the match would be extinguished.  If you take the same open  container of 
gas and put it in an enclosed space for a few hours and tried the  same 
trick, you would probably have an explosion.  As they say on  Mythbusters, "Do 
not try this at home."  This is why it is so important to  have good 
ventilation in your garage.
 
With all this said, car explosions are very rare but you can  create an 
environment where it can occur.
 
Doc
 
1960 Corvette, 1961 Rampside, 1962 Rampside, 1964 Spyder  coupe, 1965 
Greenbrier, 1966 Canadian Corsa turbo coupe, 1967 Nova SS, 1968  Camaro ragtop  
(None have exploded yet.)

~~~~~~~~~~~~~~~~~~~~~~~~
 
In a message dated 4/8/2013 3:42:52 P.M. Pacific Daylight Time,  
virtualvairs-request at corvair.org writes:

Message:  2
Date: Mon, 08 Apr 2013 21:46:08 +0000
From: Joel McGregor  <joel at joelsplace.com>
Subject: Re: <VV> Will it stink?   (...And Other Stuff.)
To: "virtualvairs at corvair.org"  <virtualvairs at corvair.org>
Message-ID:
<27D1EC0369826D478297DD86D9DE5E2C260D0A2B at 2012SBS.joelsplace.local>
Content-Type:  text/plain; charset=us-ascii

How many cars have you seen explode?   I've seen a lot of burned cars and 
never once seen one explode.  One of  my customers does fire investigations 
for insurance companies and has  investigated numerous car fires that ended 
up burning houses - also not one  explosion.  Gasoline has to be fairly 
precisely mixed with oxygen to  explode and that doesn't happen inside a fuel 
tank.  Years ago I saw a  show where they set out to try to make a car fuel 
tank explode.  They  shot it with everything they could think of and at best 
could only make it  catch on fire.  They ended up having to use explosives to 
make it  happen.

Joel McGregor