Short answer is "depends".
Long answer is: the risk is due to the fumes being heavier than air, which typically applies to most "fuel" fumes. If the shape of the "Vessel" is such
that the fumes cannot naturally flow out then you have a potential problem.
Your greatest risk is not when the engine is running UNLESS you have a fuel leak or a badly designed device - it is when you energise the electrical system prior to or during starting.
The greatest risk is when the device has been sitting and the fumes build up, be it due to a fuel leak or a venting issue. Thus, there is an explosive mixture waiting for something to set it off. The something is usually a spark from a battery being hooked up, a starter solenoid energising, a relay closing that is not properly sealed etc. Up to this point, no fan is turning so there is no air/fume scavenging happening.
I also need to caution about batteries, even in a well ventilated location, a battery that is off gassing hydrogen is a dangerous thing.
TAKE NOTE - Far more people are blown up every year by battery explosions than ever happens with vessel fume explosions.
Batteries will off gas hydrogen when a change of state happens ie, being charged or being discharged. The off gassing can generate hydrogen quick enough that even with the bonnet/hood/cover open on say a car, natural air movement will not scavenge the gas quickly enough. Much worse with a battery down inside say an AFV hull.
Hence why my Ferret batteries are located in one of the panniers and not
in the original location (the other being that constantly having to lift them out
through the turret above my head was no fun).
If you have to jump start a vehicle, hook up the positive clamps first, hook up the negative lead to the bad battery and then make the last connection to the body of the "donor" vehicle NOT to the negative post of its battery. Typically you will then get a spark, that spark needs to happen as far away from either battery as possible, but most importantly as far away AS POSSIBLE from the bad battery - typically the bad battery will be off gassing due to failed starting attempts. Wear glasses ALWAYS when dealing with batteries - if a battery blows up, sulphuric acid goes everywhere, most injuries associated with battery explosions are permanent blindness.
Remember the Hindenburg - that was a Hydrogen event, what few people realise is that it was a hydrogen fire, rather than a hydrogen explosion. Were it an actual explosion nobody would have been around to tell the tale.
A couple of years ago, a tradesman and his apprentice had a lucky escape in Oz when the tradie triggered the remote door lock on his work van as they were walking towards it one morning. The resultant explosion disassembled the van
(Toyota Hi-Ace size) and doubtless scared most of the neighbourhood out of their sleep. They were blown to the ground, but were ok. Unbelievably lucky. Both of them had forgotten to turn off the
Oxy/Acetylene bottles the day before, the handset had leaked and filled the van with fumes. We have all seen door remote solenoids, they are small, normally sealed by a rubber boot and not the sort of thing you would expect to make a spark. Either that or a relays somewhere inside the vehicle made the spark.
Oh, just found the link to the tradie van explosion: more devastating than I remembered.
<http://www.abc.net.au/news/2009-10-22/exploding-van-blows-up-melbourne-street/1112474>
Regards
Doug
Quote:
Originally Posted by Phil Waterman
Hi All
After reading this thread and the most recent post concerning carrying a modern fire extinguishers, I have a question do carriers and similar armored vehicles have the same problem with gas fumes collecting in their hulls as boats do?
Over the years I have seen several boat fires/explosions blamed or explained as fumes collecting in the hull not being vented prior to starting. Is this a problem with carriers, or do the cooling fans do a good enough job of purging the air?
Cheers Phil
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