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-   -   Do auto mechanics ever blow themselves up? (http://boards.straightdope.com/sdmb/showthread.php?t=808684)

pkbites 10-27-2016 06:32 AM

Do auto mechanics ever blow themselves up?
 
Got a new exhaust put on my Land Rover yesterday. I'm watching the guys work under mine and other cars, using blow torches and welding equipment, back by where the fuel tanks are.

All I could think of was "just one small leak of fumes and Ka-Fucking-B:eek::eek:m!

I've never been sent to such a call. Does anything like that ever happen?

Amateur Barbarian 10-27-2016 06:48 AM

A BMW dealership I was near burned to the ground when a mechanic doing some fuel tank work screwed up. My hazy understanding is that he removed the tank with ten gallons or so still in it, then dropped it, creating a local fuel-air bomb which was set off when he stepped on a trouble light. I don't believe anyone was seriously hurt but the garage and showroom were totaled.

Ludovic 10-27-2016 07:18 AM

...it's just ice cream.

jz78817 10-27-2016 07:24 AM

Quote:

Originally Posted by pkbites (Post 19731779)
Got a new exhaust put on my Land Rover yesterday. I'm watching the guys work under mine and other cars, using blow torches and welding equipment, back by where the fuel tanks are.

All I could think of was "just one small leak of fumes and Ka-Fucking-B:eek::eek:m!

I've never been sent to such a call. Does anything like that ever happen?

there's not going to be any "kaboom." For gasoline to cause anything close to a "bang" it needs to be fairly well mixed with air in the proper ratio. and if it's uncontained you'll only get a "whoof."

what can happen when working on an open fuel system is leaked fuel can ignite and cause a large enough fire you can't put it out with a hand-held extinguisher. if it gets to that point, you can only hope the fire department arrives quickly enough to save the building.

Kobal2 10-27-2016 07:32 AM

Quote:

Originally Posted by jz78817 (Post 19731833)
there's not going to be any "kaboom." For gasoline to cause anything close to a "bang" it needs to be fairly well mixed with air in the proper ratio. and if it's uncontained you'll only get a "whoof."

Well that won't do. There was supposed to be an earth-shattering kaboom.

Machine Elf 10-27-2016 07:34 AM

Quote:

Originally Posted by pkbites (Post 19731779)
Got a new exhaust put on my Land Rover yesterday. I'm watching the guys work under mine and other cars, using blow torches and welding equipment, back by where the fuel tanks are.

All I could think of was "just one small leak of fumes and Ka-Fucking-B:eek::eek:m!

I've never been sent to such a call. Does anything like that ever happen?

Inside the fuel tank, the air/vapor mixture is typically too rich (too much fuel vapor to actually ignite, sort of like leaving the choke on after your lawn mower has already warmed up). When fires happen while refueling a car (generally due to discharge of static electricity), the standard instruction is to just back away; the only thing that's burning is the combustible mixture of air and fuel vapor right at the filler neck (where vapor has been exiting the tank as you fill it with liquid), and the flame won't propagate down the filler neck into the tank. Under these circumstance, things don't generally go badly unless the panicked driver pulls the filler out and sprays liquid fuel all around the general vicinity. The upshot of all this is that performing hotworks on a car's underbody isn't likely to light off anything inside the fuel tank.

Moreover, oxyacetylene torches work pretty fast on the thin metal of an exhaust pipe; any given cut is over pretty fast, so there's not a whole lot of stray warm exhaust gas to dump heat into adjacent components. It would take a dopy, inattentive mechanic to inadvertently point the torch at the surface of the tank for a prolonged period (not saying this has never happened) - and even then I wouldn't expect much of a bang (see previous paragraph).

The only time I would expect a hazard is if a significant quantity of gasoline gets spilled on open ground, where it could conceivably form a combustible mixture and reach an ignition source. Disconnecting a hose from the tank could allow the hose (not the tank) to empty itself on the floor, but this wouldn't be much - only as much fuel as is held inside the hose between the tank and the engine, an ounce or two. If the car is six feet up on a lift, I'm not even sure the flames from such a fire would reach the underbody of the car.

Me_Billy 10-27-2016 11:34 AM

Real life is NOT like TV!

Liquid gas does not go kaboom... It is vaporized gasoline.

Tom Tildrum 10-27-2016 11:52 AM

Of course, if two mechanics decide to break up an otherwise boring workday, and you hear a festive cry go up -- "ACETYLENE FIGHT!" -- I'd suggest leaving the building.

Nars Glinley 10-27-2016 01:28 PM

Depending on your definition of explosion, mechanics have been killed due to tires being over-inflated without the use of safety cages. Here's a non-lethal but terrifying example.

Chimera 10-27-2016 03:21 PM

Google 'garage mechanic explosion'. I did, and this local event was one of the top items.

http://minnesota.cbslocal.com/2016/0...neapolis-fire/

jz78817 10-27-2016 05:18 PM

Quote:

Originally Posted by Nars Glinley (Post 19732849)
Depending on your definition of explosion, mechanics have been killed due to tires being over-inflated without the use of safety cages. Here's a non-lethal but terrifying example.

Yeah, the old style split rim truck wheels were well known as "widowmakers."

Quote:

Originally Posted by Chimera (Post 19733187)
Google 'garage mechanic explosion'. I did, and this local event was one of the top items.

http://minnesota.cbslocal.com/2016/0...neapolis-fire/



That's one thing which didn't occur to me... a gasoline leak inside the garage could lead to a build up of vapors, similar to a natural gas leak.

Marvin the Martian 10-27-2016 06:27 PM

I remember a story some years back about a guy who decided a good way to clean the floor of a garage was to mop the floor with gasoline then use an electric floor buffer to scrub out the oil stains. Kaboom. Fortunately after hours so he was the only one in the building. If true, would have made a good Darwin award but this was before Darwin awards were a thing...

Richox 10-28-2016 03:16 AM

Quote:

Originally Posted by jz78817 (Post 19733483)
Yeah, the old style split rim truck wheels were well known as "widowmakers."


That's one thing which didn't occur to me... a gasoline leak inside the garage could lead to a build up of vapors, similar to a natural gas leak.

A gasoline leak, assuming you had a decent ambient temperature happening, could be much worse than a nat gas leak as the vapours the gasoline source produced are heavier than air, which would allow them to collect at the floor where your easiest ignition sources are. Typically a floor in a closed room is also not well ventilated, whereas a ceiling is commonly.

You'd need a decent exposed surface area of gasoline to get enough vapor generation to have a kaboom moment though, unless a crazy set of circumstances all align.

Marvin the Martian - didn't see your post but yeh, that'd about do it!

HoneyBadgerDC 10-28-2016 04:46 AM

I used to work on propane forklifts. We would have occasional explosions big enough to singe the eyebrows. The fumes would fill up the engine compartment and a spark would set it off.

Isilder 10-28-2016 05:13 AM

Here's a propane fueled garage that loves the outdoors... It blew the mechanics workshop it was in away.. (It seems that the fact its propane fueled means that was probably the cause .. not the acetylene or other gas used for cutting, welding, heating... or any other fuel or accelerant in the place...)

http://flinflononline.com/local-news/256063

People who carry acetylene around with them ... sometimes have their vehicles explode ... with little left of it ... people have died from this.

Quartz 10-28-2016 05:23 AM

Quote:

Originally Posted by pkbites (Post 19731779)
All I could think of was "just one small leak of fumes...

Yes, it does happen. I remember one case where a man was working underneath an ambulance. There was a gas (not petrol, some other gas) leak and an ensuing explosion. Fortunately everything exploded away from him.

Francis Vaughan 10-28-2016 07:48 AM

Working on an actual fuel tank is potentially dangerous. Then again a friend of mine worked at a service station when he was a kid, and remembers how one mechanic was very careful when a fuel tank needed repair. He removed the tank, drained it, rinsed it twice with water, and then took to it with a welder. It exploded violently. :eek: Didn't kill him, but it wasn't good. Other old hands claimed the safest thing to do was to leave the tank half full of fuel. :dubious:

Another friend of mine sold her darling little car, and the new owner took it to be checked over, and have some work done on it. They put it up on a hoist, and somehow managed to set the driver's seat alight with a welder. Totalled the car where it sat. My friend was terribly upset.

Quartz 10-28-2016 08:22 AM

Quote:

Originally Posted by Francis Vaughan (Post 19734621)
Then again a friend of mine worked at a service station when he was a kid, and remembers how one mechanic was very careful when a fuel tank needed repair. He removed the tank, drained it, rinsed it twice with water, and then took to it with a welder. It exploded violently. :eek: Didn't kill him, but it wasn't good.

Well yes, petrol is insoluble in plain water. You need to use a detergent.

Amateur Barbarian 10-28-2016 10:43 AM

Quote:

Originally Posted by Francis Vaughan (Post 19734621)
Other old hands claimed the safest thing to do was to leave the tank half full of fuel. :dubious:

I worked with a guy who claimed his (North Carolina rural white guy) father would routinely weld gas and diesel tanks as long as they were full. The kids always found reason to be somewhere else. LIke South Carolina.

Nars Glinley 10-28-2016 10:59 AM

I have 2 friends that routinely weld on live gas pipelines like this. They've both said that you just keep welding until the flames go out.

No thanks.

cwniles 10-31-2016 07:30 AM

Quote:

Originally Posted by Nars Glinley (Post 19732849)
Depending on your definition of explosion, mechanics have been killed due to tires being over-inflated without the use of safety cages. Here's a non-lethal but terrifying example.

I was working on an old Coats 4050A tire machine trying to bust some tires off of some rims and the "demounter" (basically a large, heavy metal prybar sort of thing) suddenly leapt free which, and I am not 100% clear on the physics here, seemed to suddenly transfer all of the force directly to my arm which then bent in a very unnatural manner. The customer, who had been idling nearby observing, immediately remarked "man, you just broke your arm!".

Not an explosion per se but there was a Kaboom!, injuries resulting.

Amateur Barbarian 10-31-2016 07:34 AM

Quote:

Originally Posted by Nars Glinley (Post 19735107)
I have 2 friends that routinely weld on live gas pipelines like this. They've both said that you just keep welding until the flames go out.

No thanks.

Better than working on million volt powerlines barehanded, from an insulated lift. Yikes.

Emtar KronJonDerSohn 10-31-2016 09:11 AM

Quote:

Originally Posted by Ludovic (Post 19731824)
...it's just ice cream.

;)

MacLir 10-31-2016 11:58 AM

Quote:

Originally Posted by Amateur Barbarian (Post 19735065)
I worked with a guy who claimed his (North Carolina rural white guy) father would routinely weld gas and diesel tanks as long as they were full. The kids always found reason to be somewhere else. LIke South Carolina.

The headspace of a gasoline tank is too rich to explode, and that of a diesel tank is too lean. That's why you NEVER MIX FUEL TYPES!

I torch soldered an emergency repair on a gasoline car tank - empty, but not flushed, and didn't even see a puff from it.

(and yes, I am originally from rural North Carolina. :D )

Nars Glinley 10-31-2016 03:24 PM

Quote:

Originally Posted by Amateur Barbarian (Post 19741061)
Better than working on million volt powerlines barehanded, from an insulated lift. Yikes.

Actually, I work for an electric company and I think we pay our lineman an extra dollar an hour for bare hand work. Again, no thanks.

Sicks Ate 10-31-2016 03:45 PM

Quote:

Originally Posted by Emtar KronJonDerSohn (Post 19741235)
;)

I'm with ya.

jbarro 10-31-2016 09:35 PM

This happened near me a couple of years ago and the mechanic died. http://www.cbc.ca/news/canada/nova-s...n-11-1.3258646

HoneyBadgerDC 10-31-2016 10:13 PM

Lifetime mechanic here, the closest I have ever been to getting killed at work was a few months before I retired. I don't remember if it was nitrogen or CO2. They have a pressure relief valve that blows off when they build too much pressure. Very common in hot weather. All the trucks I had worked on in the past had the blow off valve up high. I was under the truck adjust the breaks and it blew off violently, just as I was rolling out from the truck, I would say it missed me by two feet but the gas cloud still almost took me out, I was on the verge of passing out when I got out of it. My face would have turned to an instant ice cycle had I moved one second later.

Tom Tildrum 10-31-2016 10:19 PM

Quote:

Originally Posted by Nars Glinley (Post 19742359)
Actually, I work for an electric company and I think we pay our lineman an extra dollar an hour for bare hand work.

I once worked for a movie company that did something similar. Anyway, I like to think that electricity is like snake venom, and perhaps you'll build up a tolerance after a while.

Princhester 10-31-2016 11:22 PM

Quote:

Originally Posted by Francis Vaughan (Post 19734621)
Working on an actual fuel tank is potentially dangerous. Then again a friend of mine worked at a service station when he was a kid, and remembers how one mechanic was very careful when a fuel tank needed repair. He removed the tank, drained it, rinsed it twice with water, and then took to it with a welder. It exploded violently. :eek: Didn't kill him, but it wasn't good. Other old hands claimed the safest thing to do was to leave the tank half full of fuel. :dubious:

His mistake was to drain it and rinse it; this would have left just enough fuel in the tank to provide enough vapour to form a nice explosive mixture.

My grandfather ran a mechanical engineering workshop in a rural area and he refused to do hotwork on fuel tanks which cost him business. Most workshops would fill tank with water, to overflowing, before welding on them. This is very safe unless - as has happened more than once - there is a little bit of fuel vapour trapped in a folded seam of the tank. It is of course the seams which tend to require re-welding.


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