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Oxy-acetylene safety point for FNG and FOGs too

Discussion in 'The Hokey Ass Message Board' started by 61bone, Jan 22, 2009.

  1. 61bone
    Joined: Feb 12, 2005
    Posts: 890

    61bone
    Member

    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.
     
  2. JRODHOTROD
    Joined: Mar 23, 2006
    Posts: 440

    JRODHOTROD
    Member
    from Manor, TX

    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
     
  3. JohnEvans
    Joined: Apr 13, 2008
    Posts: 4,883

    JohnEvans
    Member
    from Phoenix AZ

    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.
     
  4. 39 Ford
    Joined: Jan 22, 2006
    Posts: 1,558

    39 Ford
    Member

    What are backflow preventers (checkvalves)for then?
     

  5. el Scotto
    Joined: Mar 3, 2004
    Posts: 4,435

    el Scotto
    Member
    from Tracy, CA

    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?
     
  6. How does it back flow when there are two seperate lines & regulators??
     
  7. 38plymouth
    Joined: Apr 11, 2008
    Posts: 420

    38plymouth
    Member

    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.
     
  8. 38plymouth
    Joined: Apr 11, 2008
    Posts: 420

    38plymouth
    Member


    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.
     
  9. Still Runnin
    Joined: Jan 16, 2008
    Posts: 1,287

    Still Runnin
    Member
    from VA & FL

  10. Joe Daddy
    Joined: Nov 21, 2007
    Posts: 232

    Joe Daddy
    Member

    Wow, something to look out for. I guess i take my tanks for granted.
     
  11. hoggyrubber
    Joined: Aug 30, 2008
    Posts: 572

    hoggyrubber
    Member

    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.
     
  12. 61bone
    Joined: Feb 12, 2005
    Posts: 890

    61bone
    Member

     
  13. sxdxmike
    Joined: Aug 25, 2004
    Posts: 406

    sxdxmike
    Member

    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..
     
  14. 61bone
    Joined: Feb 12, 2005
    Posts: 890

    61bone
    Member

    Simply, don't let your Oxygen line pressure exceed the acetylene tank pressure.
    You welding supplier can fix you up with approved arrestors.
     
  15. 38plymouth
    Joined: Apr 11, 2008
    Posts: 420

    38plymouth
    Member

    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....
     
    Last edited: Jan 23, 2009
  16. kustomizingkid
    Joined: Sep 6, 2008
    Posts: 225

    kustomizingkid
    Member

    You can never be too safe....

    Does anyone else here use a Dillon/Henrob style torch?
     
  17. 61bone
    Joined: Feb 12, 2005
    Posts: 890

    61bone
    Member

    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.
     
  18. JRODHOTROD
    Joined: Mar 23, 2006
    Posts: 440

    JRODHOTROD
    Member
    from Manor, TX

    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.
     
  19. sxdxmike
    Joined: Aug 25, 2004
    Posts: 406

    sxdxmike
    Member


    ohhh ok that makes sense..but how do i know what the line pressure is?
     
  20. bruce hylton
    Joined: Dec 12, 2008
    Posts: 194

    bruce hylton
    Member
    from toledo wa

    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.
     
  21. stealthcruiser
    Joined: Dec 24, 2002
    Posts: 3,748

    stealthcruiser
    Member


    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 !
     
  22. el Scotto
    Joined: Mar 3, 2004
    Posts: 4,435

    el Scotto
    Member
    from Tracy, CA

    Gotcha! Never knew that!
     
  23. 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 .
     
  24. terrarodder
    Joined: Sep 9, 2005
    Posts: 1,101

    terrarodder
    Member
    from EASTERN PA

    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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