Outer Limits 4x4 Board

How is it where at servo's & mines you need electrical equipment to be specially intrinsically safe or flameproof, to prevent vapour explosions, but you can safely make millions of cars, sticking a 12V fuel sender and/or injection pump straight into a tank of petrol, submerged or not?
Not enough oxygen?

The fuel pump sits in a well, or reservoir, inside the fuel tank. The well cannot run out of petrol since it is either lower than the fuel pickup tube or there is a check valve in the reservoir that prevents it from running dry. And, since the pump and motor are constantly covered in fuel, there is no chance that the proper air-fuel mixture can develop to support ignition, much less an explosion, even though there is plenty of oxygen in the tank above the fuel. The submersed, in-tank fuel pump system is proven technology that is absolutely safe. (Just think of the product liability lawsuits the carmakers would be facing if this design were unsafe!) So, chill out; just remember to wear your seat belt.

Pretty much, the vapor is too concentrated to ignite within the tank, and most of the time the pump is submerged anyway where a spark can't even be a problem. Sparks in the proper vapor mix are a problem, not under the surface of the liquid.

Gday
Been playing with pumps lately,did you know that the fuel runs through a 2 stage pump, then up through the motor, between body and armature, before exiting through the top port...so as said earlier, any sparking is under fuel unless you run out of fuel....now i know why they urge you to keep fuel in the tank...to cool pump and reduce explosion risk.
Andrew

Essentially, they're different environments.

Fuel vapour needs to be mixed with the correct amount of air before it becomes highly flammable - I'd guess that inside the fuel tank the vapour concentration is way higher than the critical point. If a fire did start I'm guessing it would very quickly consume the available oxygen, and it wouldn't be able to sustain itself. (You can smother a fire burning in a bucket of petrol.)

At service stations they're worried about the fuel vapour escaping the tank and mixing with the correct amount of air. Much easier to get a flammable mixture, and oxygen to sustain combustion is freely available.

Coal mines (in particular) are very nasty environments - coal dust makes for a nice explosive mixture, and coal seams can also contain pockets of natural gas (or my memory is completely screwed...)

If I've made sense it's time for another drink.

Scott

If you want to do an interesting trick, try getting a bucket of petrol and throwing a lit ciggy into the bucket, if you throw it hard enough it will go into the petrol and not light it. Ive seen it done. But you have to remember to throw hard because if it floats on the top it will catch fire!

Samuel wrote:If you want to do an interesting trick, try getting a bucket of petrol and throwing a lit ciggy into the bucket, if you throw it hard enough it will go into the petrol and not light it. Ive seen it done. But you have to remember to throw hard because if it floats on the top it will catch fire!

Cause fuel doesn't burn as a liquid the vapour does

-Mick- wrote:

Samuel wrote:If you want to do an interesting trick, try getting a bucket of petrol and throwing a lit ciggy into the bucket, if you throw it hard enough it will go into the petrol and not light it. Ive seen it done. But you have to remember to throw hard because if it floats on the top it will catch fire!

Cause fuel doesn't burn as a liquid the vapour does

Good (but dumb) way to scare 1st years at work, get tub of diesel and chuck ciggie but in there. Watch then do the runner away screaming.
Layto....

No responsibility taken for people doing this

Why would throwing a cigy in petrol scare anyone, you could chuck a match in there an all it would do is catch fire, petrol is not explosive, it flamable, petrol vapors are explosive

As the other guys have said, it is safe as there simply is not enough oxygen avaliable to make the vapour flamable, the mixture is way to rich ..

I love the scenes in the moveis where they have the exploding petrol stations etc .

(As a kid I never used to hear the end of it because my dad worked for the govt in the dept of hazardous materials .. he would advise the emergancy services etc what to do in the event of a tanker petrol or gas being involved in an accident .. he knew lots about how stuff burns, but we used to get the best fireworks .. )