Sunday, August 10, 2014

Oxy-Acetylene Torch Safety

One of my e-buddies, Dave Christensen, suggested that I write about oxy-acetylene torches. He recently bought a new torch and confessed that he read the instructions before using it. In the instructions, he noticed that the regulator settings were different from the ones he had used for years. When we teach students to use torches in school, we typically teach them the regulator settings that work for the equipment we have. I am afraid we may not always make sure students understand that torch settings are not universal. The correct regulator setting depends upon the torch manufacturer, the tip size, and the application. Torch manufacturers typically provide these settings in the instructions.

There are a few guideposts that stay the same. For example, you NEVER, NEVER, NEVER set acetylene above 15 psi. In fact, I get nervous above 10. The reason is that acetylene is unstable at pressures above 15 psi and can explode. So how does it not explode in the acetylene cylinder at 250 psig? It is dissolved in acetone liquid which is stabilized in a porous core. That is why you should never transport or use acetylene cylinders on their side – it lets the liquid run out of the cylinder into the valve area. Also, you really don’t need the oxygen above 20 psig. Many tip charts have it about half that for most applications. However, the exact settings you should use are ... in the instructions!

Another common safety issue is leaving your regulators set and just opening and closing the tank valves when you want to use the torch. This is convenient and saves time, but it is dangerous. Regulators can fail because of the sudden bump in pressure. This can cause parts to fly and high pressure gas to stream down the hoses. The last thing you should do when shutting off your torch is to adjust the regulator T handles out counterclockwise until all the spring pressure is released. When the cylinder valves are opened they should be in this position. AFTER opening the cylinder valves you can adjust the regulators to he correct pressures.

When lighting the torch, you should light the acetylene first by itself and then bring in the oxygen. Opening both the acetylene and oxygen simultaneously can cause oxygen to flow into the acetylene hose and regulator if the oxygen pressure is higher than the acetylene pressure. This can create a very dangerous situation – a mixture of fuel and oxygen under pressure in the hose and regulator. The only place we want this type of combustible mixture is in the tip.  When shutting down, reverse the process. Close the oxygen first and then the acetylene.

Torch manufacturers have some very good training material available for free. Here are some links to some good training resources.

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