The time to discover oxygen in the fuel gas line, or fuel gas in the oxygen line, is before lighting the torch. Once regulators, hoses, and welding or cutting equipment have been attached and tested (test for leaks with soapy water), all lines should be purged before work is started. Purging also rids the lines of water vapor - a must if inert shielding gases for welding, blanketing, purging, or heat treating are being carried. The inert gases used to shield weld metal are very dry. If the water vapor is not removed, problems (from weld porosity to hydrogen embrittlement) will develop.

Purging a gas line involves opening the appropriate valve on the torch or depressing the trigger on the welding gun to allow new gas to enter the line and push out all the old gas. When a flammable gas is involved, the out-flowing gas should be kept away from any ignition source.

Work should be performed in a well-ventilated area. Each torch valve should be held open until the line contains only pure gas. The two lines should be purged one at a time, and the torch valve on the other line should be closed. This action eliminates any explosive oxygen-fuel gas mixtures in a line and purges the torch.

Always use hoses, manifolds, and regulators with the gases for which they were designed. Following this rule prevents contamination of equipment and, ultimately, of welds or other work. In addition, some gases may react with each other inside the hose or regulator. (This condition will be discussed in detail in the second part of this series.)

Never hang tools, gloves, clothes, or spark lighters on top of the cylinder. They may interfere with the operation of the valve and prevent the gas from being shut off quickly in an emergency. In addition, clothes hung on a oxygen cylinder can become saturated with oxygen if there is a leak at the valve or connecting threads. Oxygen-saturated clothes will burn intensely if they come in contact with an ignitions source, even a small spark.

• Specific procedures also should be followed when removing a regulator from a gas cylinder
• Close the cylinder valve first.
• Bleed off the gas remaining in the regulator.
• Unscrew the regulator.

If a regulator were removed from an open-valved cylinder, the gas pressure would probably blow the regulator all the way across the work area.