[Jewelry making - Article 00371] - Re: [Orchid] LP Tank and Fire Inspection

[Ed Howard]

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    No fuel gas is "safe" because they are all meant to produce hot
    flames, but the degree and kind of danger each presents is unique.
    There have been several good safety points made so far in this
    conversation but I will add a few I haven't seen yet. 

    Acetylene - 

    First, acetylene is highly combustible compared to other gases. If
    acetylene leaks it will combust in a mixture in air of anywhere from
    2% to 80% and a static electricity spark is sufficient to ignite this
    mixture. 

    By comparison, natural gas, propane and other similar gases have a
    range of combustibility between 5% to 15%, meaning that in the case
    of a leak there is a much lower range in which the leak will combust.
    It also takes a hotter spark to ignite these gases. 

    The point is that a much smaller, by volume, acetylene leak is much
    easier to ignite than other gases. 

    Second, handling the cylinder is much more important with acetylene
    than other gases. 

    Acetylene is naturally unstable, meaning that it will explode
    (violent decomposition is usually the term in the safety manuals) if
    not handled properly. Improper handling can be as simple as dropping
    the cylinder or knocking it over. In the safety literature this is
    referred to as "mechanical shock", i.e. the cylinder is struck or
    jarred. While people may be careful when moving and changing
    cylinders you still might have butterfingers or just be having a bad
    day - dropping an acetylene cylinder can make it a really bad day. 

    Third, how acetylene is withdrawn from the cylinder can create
    danger. 

    Acetylene should never be used at higher than 15 psi pressure
    because to do so will cause the gas to "dissociate" from the acetone
    in which it is dissolved too quickly and this can lead "violent
    decomposition", an explosion. This is why acetylene regulators have a
    red field marked on them, yet I have seen people purposely set their
    regulators in this red zone thinking if some pressure is good, more
    should be better. And these were trained people who should know
    better - the danger is in a novice who is not properly aware of the
    unique danger acetylene cylinders represent. 

    The other thing about using acetylene is that you cannot withdraw
    more than 1/7 of the cylinder's contents per hour or again, "violent
    decomposition" occurs. This becomes an issue when using a small
    cylinder, say a B-tank and the tank is nearing empty. It becomes
    easier to reach the 1/7th limit. The issue is not the volume of gas
    in the cylinder but the rate at which it dissociates from the acetone
    - do this too quickly and you have an explosion. 

    Propane - 

    People are more comfortable with propane because it is more familiar
    - many use it to heat their homes in areas where there is no natural
    gas service. However, the propane tank is kept some distance from the
    house - nobody puts the propane tank in the basement! 

    Everyone is familiar with propane being heavier that air such that
    leaks will sink and pool, and if there is a flame source like a pilot
    light in the hot water heater, it will ignite. 

    The danger that is less often considered is the amount of energy
    stored in a propane cylinder, or an acetylene tank for that matter.
    Because propane is liquefied it is easier to put more energy in a
    smaller container. Compare a B-tank of acetylene, which holds 59,000
    BTUs of energy with a 20 lb propane tank which holds more than
    432,000 BTUs - a lot more explosive power in a container about the
    same size. To visualize what this means, one BTU is about the same
    energy released by burning a single wooden kitchen match so consider
    storing 59,000 or 432,000 kitchen matches in your studio and what
    would happen if they ignited all at once! 

    A larger propane cylinder, say a 100 lb cylinder, holds more than
    2-million BTUs and the power in this cylinder was demonstrated in
    Chicago when such a cylinder exploded in a jeweler's shop on the 6th
    floor of a downtown office building. Nine people were injured, some
    seriously, smoke filled the building and the windows were blown out.
    http://findarticles.com/p/articles/mi_qn4155/is_20020402/ai_n12457092 


    Besides the danger of the cylinder itself, if a fire occurs there is
    greater danger to responding firemen. In commercial and industrial
    buildings fire companies make site visits and pre-plan where gas is
    stored so if they respond to a fire they know what to expect. This
    isn't the case in a home studio with a cylinder in the basement -
    consider your obligation to the local volunteer fire company. 

    When a propane cylinder explodes it does so in a manner referred to
    as a BLEVE - Boiling Liquid Expanding Vapor Explosion. What happens
    is that because propane is in liquid form the heat from a fire causes
    it to evaporate in the tank and increase tank pressure. The pressure
    rises faster than the relief valve can exhaust the gas and pressure
    builds to a point where the cylinder ruptures. The explosion spreads
    liquid propane over a wide area which itself then combusts, making
    the fire worse. If you are old enough to recall Napalm, the effect is
    somewhat similar. 

    Natural Gas - 

    Many people connect their torches directly to the city natural gas
    line and while this solves the problem of having gas cylinders in the
    building there is a unique danger here too. 

    In most places standard city gas service is too low a pressure,
    often 1/4 psi, to allow a flashback arrestor to be used effectively.
    Most flashback arrestors are designed to work with supply pressure of
    at least 3/4 psi - if the pressure is less than that they completely
    block gas flow. Jewelers don't use them because they won't get any
    gas! 

    Without a flashback arrestor there is the potential for flame to
    travel back through the torch, through the black pipe and to the gas
    meter which explodes violently. There is flying shrapnel as the case
    of the gas meter is destroyed and a significant gas leak is created.
    This occurred several times in New York City last year, causing Con
    Edison, the local gas utility, to do some investigation into ways to
    prevent these explosions. 

    My company, G-TEC Natural Gas Systems, worked with Con Ed and
    learned (1) while there are devices marketed as being designed
    specifically to work with low pressure gas, none proved 100%
    effective when tested by an independent laboratory and (2) standard
    flashback arrestors, using 3/4 psi and more, which are available from
    the well-known supply companies are 100% effective at preventing
    flashbacks. The problem is getting sufficient gas pressure so the
    flashback arrestor protects the gas line and does not block gas
    flow. 

    The Plug - 

    Permit me a few words about the G-TEC Natural Gas Torch Booster,
    which solves many of these problems. It is a CSA Certified device
    that can boost low pressure gas pressure high enough for great torch
    performance (most jewelers use 5 psi for brazing/soldering and 20 psi
    for casting) and can be installed in home studios, shopping malls,
    strip shopping centers and other places that may prohibit cylinder
    gases. It provides high-pressure gas as it is used; there is no gas
    storage. Natural gas itself, while dangerous like any gas, also has
    advantages in being stable and lighter than air. By boosting gas
    pressure above 3/4 psi it works with any standard flashback arrestor.
    If you are interested you can find out more at www.safe-t-gas.com . 

Ed Howard
G-TEC Natural Gas Systems
ehoward AT gas-tec.com
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