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Old 28-01-2016, 07:10   #1
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Explosion caused by OFF power tool?

Yesterday's fire that destroyed 3 boats has an interesting bit of unsubstantiated gossip that I wanted to get your thoughts. 3 boats on fire in St Martin


Hypothetical scenario: a person is decanting petrol/gasoline so the fluid is going through air. Next to the person is a power tool, say a cutter or drill, which is off, but plugged in.
Could the fuel vapor enter the tool and close the switch contacts making a spark causing an explosion??

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Old 28-01-2016, 07:18   #2
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Re: Explosion caused by OFF power tool???

As a former electrical engineer I would say very unlikely - I can't imagine that vapourized fuel would have sufficient conductivity.

But if someone with more recent experience would like to express another opinion, go for it.
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Old 28-01-2016, 07:23   #3
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Re: Explosion caused by OFF power tool???

In situations of low humidity static electricity can make a Spark...not likely down there, unless there was convectîve weather nearby.
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Old 28-01-2016, 07:27   #4
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Re: Explosion caused by OFF power tool???

Yeah, I guess I wouldn't say that it is COMPLETELY impossible. The odds would have to be billions to one against, though.

If that is the explanation that someone is offering, my guess would be that they did something really stupid, don't want to admit it, and so they came up with this story instead.
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Old 28-01-2016, 07:28   #5
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Re: Explosion caused by OFF power tool???

I wonder if a sander or drill might develop a static electrical charge that could spark a fire. I have also been led to believe that gasoline flowing into/from a plastic container can develop a static electrical charge on the surface of the container near the throat and, if so, such a charge might "spark" to a plugged in tool even if in the off position. (I had the misfortune of being at a gas station on one occasion when a fellow filling a plastic gas jug sitting in the bed of his pick-up had his truck and himself set alight by static electricity. It was pretty horrible.)
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Old 28-01-2016, 07:28   #6
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Re: Explosion caused by OFF power tool???

Heavier than air gasses settling in a low space. Motor brushes, dicey switch, dodgy contacts at the power point/extension lead all form ingredients for creating sparks. But you won't get a spark unless the tool's drawing a load. A gas needs to be ionised before it conducts, which requires a spark. Catch 22.

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Old 28-01-2016, 07:30   #7
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Re: Explosion caused by OFF power tool???

That may point to other possibilities, i.e. anything that could cause a spark close to the fuel. For example, a faulty on/off switch on a power tool (pure speculation, but a possibility).
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Old 28-01-2016, 07:33   #8
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Re: Explosion caused by OFF power tool???

Flowing fuel by itself can develop static, reason why trucks are bottom loaded, and if they are top loaded, there is a long dip tube to provide a constant ground, but that is usually only in areas of extremely low humidity that it's a problem.
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Old 28-01-2016, 07:37   #9
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Re: Explosion caused by OFF power tool???

Static electricity in a humid environment? Not saying it can't be done, but not very likely. Could have lit up a durry or a dose of mary jane at just the wrong moment!

Though seriously, was it at all possible a drill powered pump was being used for the fuel transfer?

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Old 28-01-2016, 08:03   #10
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Re: Explosion caused by OFF power tool???

Maybe the insurance policy rubbing against the payment book ?
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Old 28-01-2016, 08:27   #11
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Re: Explosion caused by OFF power tool???

Quote:
Originally Posted by MarkJ View Post
Yesterday's fire that destroyed 3 boats has an interesting bit of unsubstantiated gossip that I wanted to get your thoughts. 3 boats on fire in St Martin


Hypothetical scenario: a person is decanting petrol/gasoline so the fluid is going through air. Next to the person is a power tool, say a cutter or drill, which is off, but plugged in.
Could the fuel vapor enter the tool and close the switch contacts making a spark causing an explosion??

.

Sent from a stupid phone that replaces words with weird stuff.
Easily, yes. Petroleum vapour is rather clearly ignited by sparking. Vented power tools produce easily ignition quality sparks between the brushes and the rotor. But only in OPERATION. Exceptionally unlikely if off or unused. But there may easily have been other sources of ignition. The dangers of fuel vapour are often badly underestimated. IF the tool was genuinely "next to" the person, all it would have taken in theory is the merest touch of a toe… The ensuing event may wipe out all memory of the fact, if survival at all.

Petroleum on a still day or night is exceptionally dangerous, and can produce what is described as a Fuel Air Explosion. Many years ago when unware of this and tasked with clearing a cattle grid of weeds, on a perfectly still night, I fell foul of this effect. Knocked flat on my back in astonishment at the hollywood style fireball, I was lucky merely to lose the hair on my face… at circa 15 feet. I never even got close to the grid, where I had poured the fuel around three minutes previously. The air mix was such that as I approached with a torch on a stick a flashover occurred several meters distant. I will not forget that! The stupidity and luck of the young…
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Old 28-01-2016, 08:32   #12
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Re: Explosion caused by OFF power tool???

Quote:
Originally Posted by a64pilot View Post
Flowing fuel by itself can develop static, reason why trucks are bottom loaded, and if they are top loaded, there is a long dip tube to provide a constant ground, but that is usually only in areas of extremely low humidity that it's a problem.
This is interesting and didn't know that. So poured fuel in a low humidity environment could theoretically be self igniting?
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Old 28-01-2016, 08:50   #13
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Re: Explosion caused by OFF power tool???

Yes absolutely I was looking for the film I saw years ago of static bolts being discharged in a big fuel tank being filled. Reason it didn't blow we were told was the mixture was too rich, not enough air in the tank.
US Army burned a fuel depot at Ft Irwin when I was there top loading a fuel truck without the dip tube.


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Old 28-01-2016, 08:52   #14
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Re: Explosion caused by OFF power tool???

I was filling an old military style steel 5 gal. jerry can in the back of my pick-up truck which had a factory installed plastic bed liner and when I went to take the fuel nozzle out, it must have created a spark as the can caught fire. I was able to get the flaming nozzle away from the can at which point it went out and then had the presence of mind to put the lid on the can. Quick thinking for an old man. I was lucky.
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Old 28-01-2016, 08:54   #15
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Explosion caused by OFF power tool???

Quote:
Originally Posted by Muckle Flugga View Post
This is interesting and didn't know that. So poured fuel in a low humidity environment could theoretically be self igniting?

Top loading and static are major issues. In NSW Australia, WorkCover made sweeping audits of all depots top filling after an incident in Parkes 2006 killed a driver performing top loading. Static was the root cause. The aim of the game is to have a slow fill rate for 2 mins then ramp up the fill rate before slowing down again. From memory I think a starting flow would be about 300ltr/min ramping up to 1500ltr/min depending on maximum flow rates.

This helps reduce static. Diesel is a major static issue, worse than petroleum.

Generally for earthing requirements, all readings must be below 10ohms here in Oz. This was often fudged in drier places buy pouring water over the grounding area.

When working or near petroleum / diesel etc, anything that's not intrinsically safe can cause a fire or explosion if the fuel / oxygen mix is between the lower and upper explosion limit - commonly referred to in the industry as the LEL and UEL.

A perfect storm when taking large fuel tanks out of service would be a dry windless day.


Quote:
Originally Posted by kimden5 View Post
I was filling an old military style steel 5 gal. jerry can in the back of my pick-up truck which had a factory installed plastic bed liner and when I went to take the fuel nozzle out, it must have created a spark as the can caught fire. I was able to get the flaming nozzle away from the can at which point it went out and then had the presence of mind to put the lid on the can. Quick thinking for an old man. I was lucky.

And this is why fuel cans should always be placed on the ground when being filled and definitely not be filled in the back of a vehicle.

(Sorry to harp on, my background is in downstream petrochem engineering)
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