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  1. #16
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    A quick Google offers a few explanations for oxy off first. The most convincing I've seen argues that if there's a leak in the acetylene valve, having the oxy blow out the flame means you'd never realise it was leaking. However, if you turn off the oxy first, after closing the acetylene valve, a leak will be evident by the lingering flame.

  2. #17
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    A vote for Acetylene off first for me. If nothing else, it avoids the horrible black soot floating in the air from a pure Acetylene flame.

  3. #18
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    Those who are keen on turning the oxy off first need to experience using a full bore 32 heating torch.
    These animals take a lot of oxy and a lot of acetylene and the close down is always acetylene first.

    Do it the other way and you are unlikely to forget the banging popping and some times squealing emitted. That is the sound that has been been heard before they blow up.
    It is to do with the explosive range of acetylene.

    Not convinced then.? Go then and look up the lower and upper explosive limits range of acetylene.
    LEL is 2.5% and UEL is 100%!

    Do you still want to turn of the oxygen first because U tube said?

    Translated, the explosive potential is simply neutralized by shutting off the acetylene first.

    Remember not every oxy acetylene set up in the land may have anti backfire protection fitted.

    Grahame

  4. #19
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    That is a good explanation Graham, going by all the replies I don't think I will be changing what I was taught.

    When I was much younger, you that time when you are invincible always considered flashback arrestors as over kill until I viewed a safety video of what can happen without them

  5. #20
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    Quote Originally Posted by Grahame Collins View Post
    Do you still want to turn of the oxygen first because U tube said?
    Not YouTube, Grahame, manufacturers' instructions.

    As per Bob's link, BOC advise acetylene off first:
    https://www.boc.com.au/wcsstore/AU_B...nd-Cutting.pdf

    As do Harris (Lincoln):
    https://www.harrisproductsgroup.com/...off-first.aspx

    While it's not what I was taught with regard to oxy/acetylene, I was taught that in general, always to defer to the advice provided by the manufacturer.

  6. #21
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    Quote Originally Posted by China
    When I was much younger, you that time when you are invincible always considered flashback arrestors as over kill until I viewed a safety video of what can happen without them
    Might be worth mentioning, if we're relying on flashback arrestors, they have a finite life.

    I've seen ones that looked like they were from the bronze age in some dirty old workshops. At the other extreme, one site we worked at wouldn't allow them to be over 12 months old, but that was a large multinational.

  7. #22
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    Quote Originally Posted by Hunch View Post
    Might be worth mentioning, if we're relying on flashback arrestors, they have a finite life.

    I've seen ones that looked like they were from the bronze age in some dirty old workshops. At the other extreme, one site we worked at wouldn't allow them to be over 12 months old, but that was a large multinational.
    12 month test or replace is the Australian standard. AS4839.
    As with most things, the larger the company, the more they seem to be proactive for safety going above and beyond the standard alone.

    WITT who makes the arrestors suggest replacement after a flashback event. They have a spring loaded cutoff valve inside, as well as a sintered filter and a fusible plug- some of the engineering controls inside that little flashback arrestor are rooted once they do their job.

    I recall hearing that a long hose length and associated pressure drop contributes to flashback- to the extent that some workplaces specify the max hose length on their cutting equipment. Pressure drip is also a factor when there is a restriction in the line (like a FBA)... so go figure huh- only effective up to a point of diminishing return.

  8. #23
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    I truly wonder how the human race survives.
    We are scared of change in general, but once an item or technology becomes accepted, not a single care is given. In my 30 or so years playing with industrial gasses, I've seen acetylene superheating tips designed for a manifold system used on a single cylinder, dodgy hoses, acetylene regs cranked up as high as they will go, oxy and acetylene regs with seriously dodgy gauges used without a thought, cigarette lighters used to light the gas axe and gas cylinders with valves turned all the way on.
    Apprentices are not taught properly anymore ad the public can buy from Bunnings with no proper advice.
    This leads me to conclude that we are either very lucky, or oxy fuel gas processes are a lot more forgiving than we deserve.
    Rant over, but I wish that just for once people would paint by the numbers and actually read the instruction book.
    I can't answer the BOC versus Harris discrepancy. I support the BOC view across the board (I bet you never thought that you'd see me agree with BOC ) and I can see the Harris argument regrding leak detection when smaller tips are used. But I positively HATE THAT BLACK SOOT, so it's Acetylene off first for me still.

  9. #24
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    Is the black soot really avoidable? Still have to put up with it at the beginning in any event.

    Quite amazed, must be 40 years ago, lit off the torch at one place, had smoke detectors going nuts and fire doors slamming shut within a few seconds of the acetylene starting, black stuff was swirling around a foot or two off the floor with the detectors mounted on a 10' ceiling quite a distance away.....must be a lot more stuff than you can see suspended....probably doing wonders for your lungs too!

    Regarding dangerous processes, I guess refueling a car would be right up there. There was a time, not so long ago, when it was considered not a job for the general public, yet in the old days you'd come across the servo proprietor with the fag end hanging from his mouth pumping away merrily - lot of dumb luck in the human race. I'd wonder if hydrogen ever takes off (how many decades has that been promised to be the next thing?), if that will be self serve, yikes!!

  10. #25
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    Quote Originally Posted by Karl Robbers View Post
    I truly wonder how the human race survives.
    We are scared of change in general, but once an item or technology becomes accepted, not a single care is given. In my 30 or so years playing with industrial gasses, I've seen acetylene superheating tips designed for a manifold system used on a single cylinder, dodgy hoses, acetylene regs cranked up as high as they will go, oxy and acetylene regs with seriously dodgy gauges used without a thought, cigarette lighters used to light the gas axe and gas cylinders with valves turned all the way on.
    Apprentices are not taught properly anymore ad the public can buy from Bunnings with no proper advice.
    This leads me to conclude that we are either very lucky, or oxy fuel gas processes are a lot more forgiving than we deserve.
    Rant over, but I wish that just for once people would paint by the numbers and actually read the instruction book.
    You mention some valid workshop sins there.
    There is even a preferred way to keep the cylinders on the trolley-Acetylene on the left. The thought is that vertical regs have the outlet pointing down at 7o'clock to the reg body. Any leaks on the acetylene reg at the hose joiner or reg body won't be directed into the side of the oxygen cylinder or it's associated hose, reducing risk of rupture and a more volatile explosive gas mixture. Some cylinder trolleys for the G size cylinders actually have the larger diameter cutout on the left as a result. The home gamers wouldn't think of that in a month of sundays.


    Quote Originally Posted by Karl Robbers View Post
    I can't answer the BOC versus Harris discrepancy. I support the BOC view across the board (I bet you never thought that you'd see me agree with BOC ) and I can see the Harris argument regrding leak detection when smaller tips are used. But I positively HATE THAT BLACK SOOT, so it's Acetylene off first for me still.
    I alluded to that I went looking for a gas company's view on the 'correct way'. My understanding is that Harris just make equipment. BOC makes gas. I couldn't find any safe use, technical reference to any of the other gas companies out there... so I'm pleasantly surprised that they have this reference published, and at least try to educate and have some ownership of their user's safety. At least with my dealings with some of the other companies out there, you'd be pushing it uphill to get any technical sense out of them further than the colour of the cylinder. A certain 'super' industrial gas company rep told me their gas would weld '99% faster' once...



    Quote Originally Posted by Hunch View Post
    I'd wonder if hydrogen ever takes off (how many decades has that been promised to be the next thing?), if that will be self serve, yikes!!
    CSIRO are working on ammonia technology which converts NH4 (ammonia) to nitrogen and Hydrogen. So more than likely, instead of hydrogen, which is a highly flammable and uncompressible gas being used in fuel tanks, it will be stored as ammonia- a relatively harmless low pressure liquid that gets converted in the car to the fuel with a harmless nitrogen byproduct from conversion, and water vapour as a combustion byproduct. Neat, huh?

  11. #26
    BobL is online now Member: Blue and white apron brigade
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    Quote Originally Posted by Commander_Keen View Post
    CSIRO are working on ammonia technology which converts NH4 (ammonia) to nitrogen and Hydrogen. So more than likely, instead of hydrogen, which is a highly flammable and uncompressible gas being used in fuel tanks, it will be stored as ammonia- a relatively harmless low pressure liquid that gets converted in the car to the fuel with a harmless nitrogen byproduct from conversion, and water vapour as a combustion byproduct. Neat, huh?
    Interesting topic.

    Ammonia is also flammable and explosive and will burn in air, and as a (very minor) vehicle fuel has been around for some time (19th century) eg was used to power busses in Belgium in WWII .

    CSIRO's breakthrough is to make a membrane that decomposes the NH3 into very pure H2 and N2 and uses the H2 as the fuel and exhausts the N2 into the atmosphere. However, the H2 is not burnt like fuel in an internal combustion engine as this would make NOx. Instead it is used in a fuel cell that combines it with O2 at low temperature to convert it direct to water vapour and electricity to run an electric motor. The stumbling block is that in terms of overall efficiency, fuel cell powered vehicles still have a some ways to go.

    Ammonia is NH3 (NH4(OH) is NH3 dissolved in water) has a boiling point of -33 so it still has to be kept under some pressure (8 bar) to stop it boiling away although the cost of compression and storage is much smaller than hydrogen. Apart from being highly corrosive to lungs and skin, humans have a natural defence mechanism that prevents NH3 from building up and becoming toxic inside us but not so many other organisms - dilute forms are after all used as an anti bacterial. Above 25% concentrations in water i is considered as a environmental hazard. When used in a fuel celled vehicle, given its greater volume etc it's probably only about as risky as the sulphuric acid in a conventional car battery. It also does not necessarily mean that ammonia fuel stations will stink. Most people don't realise there are already millions of tons of ammonia moved annually by road, rail and ships around the world.

    NH3 is not free and requires energy and H2 gas (made from water) to be made. The proposal is to use spare renewable energy to make it. Then one has to take into account the overall efficiency ie the NH3 production, transport and distribution and fuel cell efficiency. Currently it is still more efficient to directly store renewable energy produced electricity in batteries for vehicle use. NH3 is likely to be more useful in higher energy demand vehicles like trucks etc.

    For anyone interested in reading a detailed technical but easily readable document on the topic of NH3 power maybe have a look at this
    https://www.sciencedirect.com/scienc...60128517302320

  12. #27
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    [QUOTE=Hunch;1948097]Is the black soot really avoidable? Still have to put up with it at the beginning in any event. /QUOTE]

    To avoid this, contained in the Linde Air Products book 'The Oxy-Acetylene Handbook published in 1955 is the following advice:

    "In general, the procedure followed in lighting a blowpipe is first to open the blowpipe oxygen valve a small amount and the blowpipe acetylene valve either fully or somewhat more than the oxygen valve, depending on the type of blowpipe. The mixture of oxygen and acetylene issuing from the tip is then lighted by means of a friction lighter or stationary pilot flame."
    The book also states "17. When welding or cutting is to be stopped close the blowpipeacetylene valve, then the blowpipe oxygen valve."

    I have followed these procedures since learning oxy-acetylene welding at Technical College (now TAFE) in 1957. No soot and no dramas.

    Chas.

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