This is something that is rarely brought up even in welding courses. Low side- set line pressure highside- tank pressure FACT: Never run the high side pressure in the acetylene tank below the low side pressure of the oxygen tank. For instance, if your oxygen pressure is set to 25psi, your acetylene tank is effectively empty at 26psi on the high side acetylene gauge. 1 psi more than lowside o2 pressure is the cutoff level. The reason for this is that when o2 low side exceeds Acetylene high side a backflow can be created which lets o2 flow backward in the line into the Acetylene tank. Backflash preventers don't recognise this and will not stop it. Free acetylene gas is unstable above 12psi and is explosive at 15 psi. and the introduction of oxygen into it creates a very hazardous situation. Conjecture: While I have no sources or figures to support my hypothesis, I believe that most tank fires that are blamed on backflash are in reality originated in the tank by the very condition described. The company I have spent most of my life with has never had a Oxyacetylene incident so I have no first hand experience with tank fires. I have only seen the result of one and that one burned about a foot off the tank end of the hose which tells me the fire originated on that end.
so, whats the safest way to put out a tank fire. close the valve real fast and run? Im not trying to poke fun, just curious since I just got a set and have no formal training other than the inter-web. Thanks
Makes some sense ,but in damm near 50 years of O/A welding and squezing the last drop out of the bottles never had a prob. Saying that watch what happens to me the next time the bottles get low. As far as that goes never had back flow valve untill the last few years.
Well, you've effectively spooked me, but I need a little more info. In laymen's terms, always keep the oxy pressure lower than the acetylene?
So what you're saying is during a flashback there is a combination of oxy/acetylene coming from one tank and igniting in the hose. Rather than the fire originating on the torch end its from the tank end? Is this correct. In my youth I was present when a rosebud became too hot and the hose popped about every foot making its way towards the tank end of things. The welder got to the tanks before anything real bad happened. Can't remember which hose was blowing, maybe both. Not sure if arresters were used back then or not. I always heard to shut the acetylene tank off first in case of flashback. I've personally had a few flashbacks into the handles and get they real hot and make that high pitched sizzle. I leave the knobs open and run for the tanks, acetylene first then oxy. Then rebuild the torch, mostly o-rings though. I've always had arresters as well. Your theory could be valid in other instances though. I've still got alot to learn.
Possibly when the tip becomes plugged and is hot enough to ignite. I guess then the oxy or aceyt could flow against each other. I dunno, my instructor told me I was an idiot and I always believed what he told me.
wow, never heard of such a thing. i rarely use my acet set any more unless i am brazing. i mostly use one of my propane torch sets, a lot cheaper.
im happy to read some safety posts about oxy torch use because i enjoy using it more and more. though, im alittle confused by your original post. i dont suppose you could reword it with caveman terms? and where is a good place to get arresters? good brand/type? i dont have any and i feel like i shouldnt cheap out on this..
Simply, don't let your Oxygen line pressure exceed the acetylene tank pressure. You welding supplier can fix you up with approved arrestors.
61Bone, thanks for clarifying that. I had never looked at it that way (oxygen entering the acetylene tank). Makes perfect sense. Excellent thread & thanks for sharing your knowledge. So this could be the most common cause of flashback fires? Also as another mentioned, could you reword this in a possible "do's, don't" manner, etc for us dummies... Another thought just entered my clouded mind. I wonder how many people know about laying the acetylene bottle on its side. If you've moved or transported a bottle and had to lay it down, then upright it and wait a half hour before using it. The propellant has to separate from the acetylene. Not sure how much of a safety issue this is but results in a odd colored flame thats not very hot....
If you've moved or transported a bottle and had to lay it down, then upright it and wait a half hour before using it. The propellant has to separate from the acetylene. Not sure how much of a safety issue this is but results in a odd colored flame thats not very hot....[/quote] Some authorities say it is alright to use a Acetylene tank at a 45Dg angle, but I wouldn't. There is just a small volume at the top of the tank to hold free gas. Having the tank tilted would just increase the possibility of drawing Acetone. This is probably not dangerous, as it just burns off. What it does do is damage the regulators. It is corrosive to some of the materials used in them.
Anyone feel its neccessary to inform the local Fire Dept about the gas contents in my detached garage. Sounds like a good idea, however, I dont want to get stuck with a fine.
I burn for a portion of my living, and have never had anything get past the torch handle. I run 10 lbs on the gas side and 60 lbs oxygen side. Always open and close gas first, then oxygen. All the rest of the safety stuff I do automatically and I use up to 4 large bottles a day of oxygen or go for liquid oxygen and use one of them in about a week. Loose fittings at hose connections will show up when they catch on fire. Pay attention and check your equipment everytime you use it to survive.
I do, but I have not used it yet.........I just got a set of regulators and hoses........Still gotta' get some tanks, and I have never heard of this. Then again, I have never had an oxy-acetylene setup before now..... And the Henrob's claim to fame is a super low acetylene pressure......... I'll be watching this one..........AND my bottle pressure !
All gasses that are volatile have an LEL ( lower explosive limit ) and a UEL ( upper explosive limit) . This basically means that not enough gas and air or too much gas and air and there is no explosion . Acetylene has one of the widest ranges of all . This , of course , means that almost any ratio is trouble . In that respect it is one of the most hazardous of gases .
Some authorities say it is alright to use a Acetylene tank at a 45Dg angle, but I wouldn't. There is just a small volume at the top of the tank to hold free gas. Having the tank tilted would just increase the possibility of drawing Acetone. This is probably not dangerous, as it just burns off. What it does do is damage the regulators. It is corrosive to some of the materials used in them.[/quote] I worked in construction all my life and I was told never lay tanks flat. We were told to always raise the valve end up a little, sometimes we would jist use a 4 x 4 to do this, not a good idea I guess. That articile is what I was told in night school, did alot of welding before I went to school, changed the way I did things after that. Also never carry an acc. bottle in an enclosed trunk. Herd of a woman doing that,popped the latch, the rest was history. Thanks for the safty tips
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