I was reading somewhere here about the use of a 55 gallon drum for a forge. And the worries expressed about cutting barrels that have contained flammable stuff.

Yes, given the choice, I will cut a food barrel, instead of a fuel barrel.  But sometimes we don't have a choice. After years of repairing gas tanks of all kinds, I've learned that it can be safely done with no worries.  There are 3 things that are required for combustion, take away any one of those, and combustion cannot/will not happen.  those 3 things are; #1 fuel, #2 oxygen, #3 ignition source.

The easiest to remove is ignition source, by not cutting that barrel.   2nd easiest is to remove the oxygen,  I purge the tank, or barrel, with exhaust from a running engine. Then I cut, weld, or whatever.   There are some fuels with their own oxidizing agent, Nitromethane, and alcohol, come to mind. But, you can still make the mixture of fuel to oxygen too rich to burn by the exhaust purge process. 

  Now if it's a solid fuel, such as that used in rocket motors, all bets are off. That stuff is designed to burn in a vacuum. But chances of getting a drum that's had any in it are very slim.

It's what works for me, and has since 1985.

Look for a barrel that contained a known substance that does not cause problems.

I cut drums swith a fine tooth hacksaw and patience...

 

Here's how you do not cut a barrel for a 55 forge.

  I found a burn barrel that wasn't being used and after asking if I could have it the gentleman asked if I wanted him to cut off the ragged party. I said, "Sure that would be mighty nice of you." 

He started to cut it with an angle grinder with no PPE whatsoever. He had the barrel on its side with one foot on the barrel the other on the ground cutting away with the angle grinder. Not a nice cut either but a start and stop jagged mess. I didn't want to carry it the block or so home. Luckily I have gloves with me most of the time. It was nerve wracking watching him do everything you've been told not to do your whole life. He wouldn't stop either. He thought I was trying to be polite and save him the trouble but I was trying to save my nerves, possibly his body parts, and the barrel he nearly ruined. It wasn't so much a barrel as a tall hoop and his terrible cut nearly didn't leave enough for a forge after it was evened out. 

Pnut

 

When I was a very young kid I can remember my dad cutting them with a cold chisel and drilling holes, for hinges and legs, with a hand held hand crank drill to make a bbq pit. There’s not many people around now with that much patience. 

I drilled 1/2" holes in 1/2: steel plate with a cole drill when I built the extension to my smithy.  I think a lot of folks don't realize that you can do it that way anymore.   Back about 25 years ago I once won a speed race in installing lag bolts with a brace and a bit that fit in the brace and would drive bolt heads vs a fellow using one of the battery powered drivers of the time.  My "batteries" lasted longer and I could torque them down all the way at the end. 

Of course they make stronger drivers nowadays.  I had a number of hand crank/line shaft drill presses as part of the big deal---I'm going to sell them and use the $$ to put electricity in my shop! (I still prefer corded to cordless tools).

Same here on the corded tools. For some reason a battery operated tool will not hold a charge for me ten minutes and it's dead (at least a half dozen in a scrap box with twice the batteries). My wife claims I have negative polarity.

Rechargable batteries have a memory. If not fully discharged before recharging can cause problems. They won't fully recharge.  Google will explain it better. It's more prevalent in nicad and nimh than lithium batteries but they also have the problem to a lesser extent.

Pnut