# Forum Home Renovation Metalwork & Welding  Cutting gas bottles

## PlatypusGardens

Let gas out
Remove valve
Sit upside down for a week
Hold a lighter by the hole to make sure there's no gas left
Purge with soapy water anyway just to be safe
Cut with the water still inside it without electrocuting yourself    
Or just cut the darn thing in half!!!!   :Roll Eyes (Sarcastic):

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## Bros

Done a few still here. One of the things that put doubt into your mind is that odoriser they add to the gas seems to permeate the bottle metal as it stays for a long time.

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## OBBob

Big hacksaw.   :Biggrin:

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## Marc

If you open and put upside down, LPG heavier than air flows out, leave a day in the sun or just blow air in it with a compressor for a few minutes, nothing left after that, no explosion possible. only a bit of flames from the oil residue.
Your test with the lighter reminds me of a dad joke my father use to tell us about the wording on an epitaph. 
"Johnny lit a match to see if there was petrol in the tank.
There was ... "   :Rofl5:

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## ringtail

That guy deserves to have his foot cut off too. I just remove the valve and fill with water then tip upside down for an hour.

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## Smurf

Something to bear in mind if you were to cut an acetylene bottle.  
There's acetone inside which keeps the gas stable and without that it doesn't like being under pressure. I'm not sure exactly what would happen but you'd be wise to make sure the gas is out or at least not under any pressure before draining that acetone out. That's what I've been told anyway.

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## Marc

Wow ... who would cut an acetylene bottle?

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## PlatypusGardens



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## Marc

Ha ha, looks like made up though. 
The idea of using exhaust fumes instead of compressed air is a bad one. A rich idle mix can provide fuel instead of venting the existing LPG

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## intertd6

We got the army in to shoot a heap of acetylene bottles with armour piercing rounds to vent them, that was more successful than the time before that, where boxes of old detonators were blown up & spread over hundreds of m2 without actually destroying them & making them safe.
inter

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## Marc

Much better to make a big fire around them and retrieve with great alacrity  :Smilie:

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## PlatypusGardens

> The idea of using exhaust fumes

  
I've heard stories of people welding fuel tanks like that.....

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## commodorenut

Very common among car guys I know who restore cars and need to modify tanks (especially EFI tanks into earlier cars, where they need to cut them open & remove the swirl pot).
A lot of vintage tanks rust around the seams, and haven't held fuel for decades, so they are normally pretty safe, but more modern stuff it always a risk. 
First step is to drain as much fuel from the tank as possible, from ever angle, and then leave it open for a week to let the remainder evaporate.
You can remove the sender unit (creating a nice vent) and prop the filler neck open with a screwdriver if it's an ULP neck with the flap in it. 
Then a week later it's simply a matter of directing exhaust gas through the filler neck, which will work it's way around inside the tank, and vent out via the sender hole - flushing it out for 1/2 hour or so with the car idling away. 
Some will fill the tank with water & drain it first, just to remove any traces of liquid fuel. 
In modern cars the mixture is so lean there's no chance of any unburnt fuel making it out (and the oxygen sensors that are in just about all cars built in the last 20 years would log an error in the computer if the mixture was even heading slightly rich (say from a failing spark plug or coil, resulting in incomplete combustion)

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## Marc

half a kilo of dry ice will fill the tank with CO2 and so no bang.

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