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Thread: Oxyacetylene Welding Safety Deadly Lesson

  1. #1

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    Oxyacetylene Welding Safety Deadly Lesson

    In the fall of 2005, an unfortunate accident took the life of a local farmer. Following the accident, speculation of the cause of the explosion that took his life and destroyed the building in which he was working, was on the mind of many of us that work in our own shops to maintain our equipment.
    The leading story on the accident involved the use of an Oxyacetylene gas torch system.
    Over the years I have used my Oxyacetylene gas torch to do anything from loosen a stubborn bolt to brazing cracked sheet metal on a piece of farm machinery or automobile.
    Following this unfortunate accident I questioned my safety practices while using this explosive gas.
    After an extensive search for written material on the subject, I have discovered some new information that I hadnít heard or read before. I decided, in the name of safety, that my fellow gas torch users should be given the advantage of my research.
    A thorough understanding of the acetylene gas torch system is the first subject that needs to be covered to make sense of the important safety steps we should all consider.
    An acetylene gas torch basic setup consists of a pressurized cylinder of acetylene, the fuel gas; a pressurized cylinder of oxygen; pressure regulators for both tanks; gas hoses; the torch gas mixing head,; and the torch head attachment. (cutting head, brazing head, or rosebud).
    The proper use of the common Oxygen / Acetylene gas welding system will go a long way to insure that we will not have a dangerous accident.
    Acetylene and Oxygen cylinders must be secured in an upright position prior to and during use.
    Do not weld with the cylinders on their side.
    Acetylene is packaged in a cylinder filled with Diatemaceous Earth. The acetylene is dissolved in acetone and the solution is then pumped into the cylinder. If the cylinder is placed on its side and then set upright again, it takes some time for the system to re-equilibrate and for the acetone to drain out of the dip tube in the valve. If welding is done during this period, the weld will be high in carbon due to the acetone.

    Because regulators are delicate, they must be handled carefully. Never use pliers or pipe wrench to attach them. Never pound valves equipped with wheels to open or close them. "Creeping" regulators must be repaired immediately.
    Hoses should be color coded to avoid using the wrong hose. Any hoses with leaks, worn spots or burns must be replaced or repaired before use.
    If you repair a bad hose, use only fittings that are bronze or brass (less than 65 percent copper). Never use copper because it forms copper acetylide, which can explode. Never use oil, grease or a similar substance on torches or regulators, because in the presence of oxygen they may burn, or if ignited, explode.

    Flashbacks and Backfires are potentially deadly hazards of gas welding.

    Flashback is the burning of gases in places other than the mixing chamber. Backfire is when the flame goes out with a loud pop or snap.
    When Flashback occurs, the flame disappears from the end of the tip and gas burns within the torch or beyond into the hoses and regulators. Flashback can also occur when the gases are allowed to mix somewhere other than in the mixing chamber.
    Consider the following scenarios that would allow such mixing:
    1. The oxygen cylinder empties in use, acetylene, now at a higher pressure, flows into the oxygen hose and regulator. The operator closes the torch valves, changes the oxygen cylinder. Once the cylinder is changed and the bottle valve is opened, the mixture of oxygen and acetylene in the line and regulator is compressed to whatever pressure the oxygen regulator is set which is usually higher than 15 PSI. Acetylene is unstable above 15 psi unless suspended in acetone!
    2. The operator quits work, closes cylinder valves, opens both valves on the torch to bleed the lines. Acetylene, being at the lower pressure, bleeds out first. The oxygen can now reverse up the Acetylene line and into the regulator.
    3. The operator lights the torch with both gases flowing. More oxygen is flowing because of the pressure differential causing backflow of oxygen up the acetylene hose to the regulator.
    Although these scenarios are all caused by operator error, without proper protective equipment to prevent this backflow, the operator is placed in a very dangerous situation.
    To prevent this inadvertent dangerous situation, install Reverse Flow-Check Valves and Flashback Arrestors on the oxygen and acetylene lines to prevent the dangers of flashbacks and backfires.
    Some sources recommend installing the arrestors at the torch end of the hose only but others suggest that the safest procedure is to install them at both the torch and the regulator ends of the hoses. The reasoning for both ends of the hose involves the possibility of burning a hole in a hose with a hot berry and having no way to stop the fire from getting into the tank.
    Many if not all makers of torches today have the backflow/flashback arrestors built in to the torch heads but still do not put the arrestors on the regulators. Most of us are working with older equipment that should be retrofit with the arrestors. They are readily available from area welding supply companies.
    Whenever you are working with explosive materials, learn how to handle them safely and THINK SAFETY.
     

  2. #2
    Mike Switzer's Avatar
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    Quote Originally Posted by BCAIRPORT View Post
    To prevent this inadvertent dangerous situation, install Reverse Flow-Check Valves and Flashback Arrestors on the oxygen and acetylene lines to prevent the dangers of flashbacks and backfires.
    This was the same recommendation given by the instructor at the Sportair workshop I attended a couple years ago. When I talked to my local supplier, he told me that all new torches he sells have the checkvalves (as does mine that he sold me back in the early 90s)

    Evidently there is some controversy about the effectiveness of the flashback arrestors. He recommended against them, I don't remember exactly why, but I know he said of all the shops he supplies, the one that uses them was continually having to buy replacements. (Which was a good revenue stream for him, but that is another matter)

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    Christopher Ingram's Avatar
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    The check valves should be placed on the regulator instead of the torch, most accidents occur from the hose(s) being punctured from pieces being cut falling on top of the hose or hot molten slag falling on top of the hose, a check valve on the working end of the hose will do nothing to prevent the flame from flowing towards the bottles, but a check valve at the regulator will prevent the fire from getting past that point.

    Chris

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    Quote Originally Posted by Christopher Ingram View Post
    The check valves should be placed on the regulator instead of the torch, most accidents occur from the hose(s) being punctured from pieces being cut falling on top of the hose or hot molten slag falling on top of the hose, a check valve on the working end of the hose will do nothing to prevent the flame from flowing towards the bottles, but a check valve at the regulator will prevent the fire from getting past that point.

    Chris
    Every set up I've seen built by Victor has the check valves installed at the torch.

    I've never seen check valves at the regulator.

  5. #5

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    Quote Originally Posted by Tom Downey View Post
    Every set up I've seen built by Victor has the check valves installed at the torch.

    I've never seen check valves at the regulator.
    Mine are at the regulator and that's where I think they should be for the reason alluded to by an earlier poster.
    Bill

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    Budd Davisson, had an article in Sport Avaition a month or so back that I had sent him a reply to a concern about one line in the article. It was stated that you open th acetylne valve fully open! I sent off a reply ASAP stating my concern over this practice. Acetylne valves are by design only suppose to be cracked about a 1/4 turn open. This gives the operator or standby safety person (we all use one don't we?) the ablitiy to close off the gas before the freeze plug can be melted on the top of the tank from fire or flames. Budd relpied to my concerns very quickly over the article. But, I have to date not seen a correction printed to this yet.

    It has been my experience that most all persons using welding equipment of any kind, have not been taught the proper safety procedures for the equipment in use. I have work as a Millwright, Engineer, and Industrial maintenance Instructor for over 40 plus years and don't understand why these things happen. When there is information that can be freely obtained to learn from. But, it keeps the lawyers working.

  7. #7
    Mike Switzer's Avatar
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    Quote Originally Posted by EAAbipJ3 View Post
    Acetylne valves are by design only suppose to be cracked about a 1/4 turn open. This gives the operator or standby safety person (we all use one don't we?) the ablitiy to close off the gas before the freeze plug can be melted on the top of the tank from fire or flames.
    This came up a while back, I read an article somewhere that recommended (I'm going off memory here) opening both tank valves all the way, the torch valves all the way, & using the regulators to control the flame. I didn't like that idea & I thought I posted something questioning it either here or on the AOPA board, but I cant find it now. In high school shop class, and in my industrial maintenance safety seminars (I have also worked several jobs as an industrial maintenance engineer and supervised lots of millwright work, as well as moonlighting with them on the side), we were always told to just crack the acetylene tank valve. (And when you are doing iron work a hundred feet in the air you always have someone on the ground by the tanks to get them shut off. Accidents can happen & hoses do get cut)

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