Facts for Propane Safety
by Andy Juell
© Anvil Magazine
published in ANVIL Magazine, February, 1999
The vast majority of farriers today use a propane forge in either their trucks or shops. The advantages over coal, particularly in mobile units is obvious: cleaner, faster, more efficient. Gas forge technology has advanced over the years by incorporating better refractory materials, atmospheric burners and lower overall fuel consumption. We seem to love the forges, but do we really understand the propane gas running them?
Following are some important things to remember:
Propane is a liquid in the cylinder, but burns as a vapor (or gas) by the process of evaporation. That is why propane gas must be tapped from the top of the cylinder. Evaporation also causes the remaining liquid in the tank to cool (sometimes actually freezing) and the subsequent vapor pressure to drop. Farriers who take part in competitions, where the forges are running for long periods of time, are familiar with this process. However, overheating liquid propane, for whatever purpose, can produce catastrophic results by increasing the vapor pressure above the liquid propane in the cylinder. In effect, it is quite possible to blow the top of the tank off, regardless of the regulated pressure. And, to be sure, any person near the tank is going to be in the line of fire.
What is propane? Basically it is combination of H20 (water), methane, ethane, propylene, isobutane, N-butan and familian sulphur, the latter giving the gas its unique smell. Propane is also produced in four grades, depending upon the application or specific purity required. Forges generally burn “barbecue” grade, the most common on the market, and completely suitable for general forge applications. Liquid propane is not only flammable, but it is also a very effective solvent. Yet the vapor, or gas is not. This may not seem important, but regulators are designed to handle only gases. Solvents have the capacity to damage the internal components of regulators, a good reason why tanks should be kept upright and relatively immobile. Shaking up a low or freezing tank is a bad idea. If the tank is freezing, the best approach is to place the tank in cold water only - never attempt to heat the cylinder.
A regulator contains a diaphragm, a poppet valve, a petcock valve and several fittings, any of which are capable of leaking. These are mechanical parts and subject to failure, sometimes quite suddenly. It is important to understand that regulators are pressure-control components, not shut-off valves. All systems should have a separate shut-off valve upstream of the regulator, in this case, at the tank. Whenever the forge is not in use, the cylinder should be shut off at the source. Never rely on the regulator to guarantee that the flow of gas has stopped. Petcock valves are basically bursting disks designed to vent excess pressure, particularly when the tank is being filled. However, they can burst on their own, the most common cause resulting from laying a full tank on its side, which increases the pressure on the valve. Excess vibration can also be a contributing factor if the tank is full. Heat is rarely a factor, since propane is about 300 degrees colder than gases such as acetylene.
Propane cylinders can leak and it is best to assume it does leak. Murphy’s Law should and must be applied to anything with explosive characteristics. It is important to remember that propane is denser than air, which means that when it leaks it goes down (or settles, in the proper terminology), rather than rising. This means that it can run along the ground to a source of ignition, then flashback. It can also drain into a sewer, or, for that matter, the lowest point of your vehicle, wherever that might be - which means it might be beyond your refractory senses. Propane is purposely “odorized” (the sulphur ingredient), like most industrial gases, to make it identifiable in close proximity or in a closed area. Settling makes it difficult to detect the gas unless your nose happens to be located near your big toe.
So here are the rules: Never allow a propane cylinder to tip in usage, as the liquid may enter the regulator, rendering it unsafe - not to mention causing a surge in propane flow. If, during the cold months, the cylinder cools to the point that pressure flow is decreased, place the tank in cold water. Never artificially heat the tank. Never allow the heat from the forge to heat the propane cylinder. The regulator and hose are vulnerable components and should be treated with care and inspected regularly. Keep the forge on a non-combustible surface, away from both the cylinder and any other combustible materials. Have a dry chemical fire extinguisher (ABC class) handy, just in case. Absolutely, positively, shut off the tank at its source when not in use. Do not assume that the regulator will eliminate the flow of gas. Industry experts recommend a hose length of about twenty-five feet, red (to indicate it is flammable gas) and suitable for the specific application. Tanks should always be stored outside the vehicle (not in a confined area) and discarded after five years. Most tanks are dated for this purpose.
Last, install the regulator by hand, without tools, until the nut (left-handed thread) is fully seated. Immediately tighten the brass nut with a wrench. Do not wait - forgetfulness is what gets people killed. If you even think that anything has gone wrong, turn off the propane at the cylinder valve - not the regulator. Treat a propane tank like a bomb, respect the volatility of liquified gas, and most importantly, never assume that you are immune to the risk. You’re not. Propane forges are a great benefit to the industry, but they do have risks. Don’t take anything for granted.
Okay, so you thought propane was scary. Try oxyacetylene. Oxygen makes up about 21% of the atmosphere. It combines with carbon and hydrogen to produce energy. Normally this takes place slowly. Raise the temperature and oxidation converts to burning. Fortunately, the atmosphere is 78% nitrogen (which forces cooling) or the rules on smoking would need some drastic alteration. That is why pure oxygen should always be kept well clear of greases and oils, as oxidation can take place rapidly with petroleum products. The only lubricants that should ever be used on regulators or O-rings are those products specially designed for such use. The working area should also be cleared of all petroleum-based materials.
Acetylene is what chemists refer to as “a triple bond” molecule. When the acetylene reaches “kindling temperature,” the bonds break and tremendous energy is released. The triple bond is why acetylene burns hotter than any other hydrocarbon gas when combined with oxygen. Acetylene is produced by combining calcium carbide with water. This is the same process that was used in miners’ lamps a century ago. Two things to remember about acetylene: It should never be used at a flow above 15 psi, as this causes the gas in the tank to become unstable, and secondly, acetylene has a broad “flammability range” when combined with any type of air, much broader than any other fuel/gas/air mixture. The range of ignition is 2.5-80% acetylene to air. A fuel leak involving acetylene is extremely hazardous.
Acetylene tanks should always be stored upright. While not particularly dangerous, placing a tank in a horizontal position can cause liquid acetone to get into the cylinder valve, causing the torch to operate erratically. Place it upright for at least 30 minutes before operating the torch. It is also very important not to withdraw acetylene from the tank at a rate of more than 1/7th of the normal full capacity of the cylinder. Again, this will cause acetone to be drawn into the cylinder valve.
Fuel lines should be equipped with check valves, or flash-back arresters - sometimes referred to as reverse flow valves. These insure that no fuel (or potential flame) can find its way back to the regulator. Tanks should be securely chained down and capped when not in use or when moved. A full oxygen tank is pressurized at about 2200 psi, and if the regulator should get knocked off by the tank falling or being struck by something, the result is an industrial-size bottle rocket capable of traveling through the side of a building, not to mention any human who happens to be in its path. It is also highly recommended that both regulators should be completely backed off prior to turning on the cylinder valves. This not only prevents damage to the regulators, but helps insure that a weak regulator will not be blown off the top of the tank. Like propane, regulators are comprised of mechanical parts, subject to failure and not designed to guarantee that gas will not flow.
Finally, this article is only designed to cover the very basics of working with industrial gases. Particularly in the case of oxyacetylene, seek professional advice. Most companies have excellent publications that cover a wide array of applications. Maintain good safety habits - the life you save might be your own. Special thanks to Bruce Freeman, Larry Tankersley and Dave Mudge (via the Internet) who assisted in the production of this article. Thanks also to Praxair, Inc. of Oakland, California. A great deal of the information on oxyacetylene was excerpted from “The Oxyacetylene Handbook,” published by ESAB Welding and Cutting Products, P.O.Box 100545, Florence, SC 29501-0545.