If a cylinder is leaking, mark it and put it outdoors, away from all sources of ignition. Post warning signs on it and keep it well away from other cylinders. Call the cylinder supplier or gas distributor.

High-pressure gas cylinders commonly are fitted with a back-seating valve. In use, the valve hand wheel must be turned so that the valve is fully open. Close the valve completely when the cylinder is not being used, even when the cylinder gauge registers empty. An empty cylinder contains residual gas. Furthermore, leaving the valve open exposes the cylinder to contamination.

• Always use the proper regulator for the gas in the cylinder. Gas regulators reduce the pressure inside the cylinder to a safe level for use. They are designed for use with specific gases, within prescribed pressure ranges. Different gases have different densities. The spring inside the regulator is designed to provide correct flow rate for a particular kind of gas. In addition, using the wrong regulator may cause some gases (acetylene, oxygen) to react with the materials inside the regulator. For example, materials used in some regulators are not designed for oxygen and will ignite if used for oxygen. Plaques or decals on the regulator indicate which gas the regulator is designed for. Cylinder valve outlets and inlet connections on regulators also are designed to minimize the chances of using the wrong regulator.
• Always check the regulator before attaching it to a cylinder. If the connections do not fit together readily, the wrong regulator is being used. Damaged threads on the connecting nut or valve outlet can also make a regulator difficult to attach and likely to leak.

Most gas-welding and flame-cutting accidents are caused by incorrect equipment set up and disassembly. Certain procedures should be followed in a specific sequence:

• Always "crack" the cylinder valve (open it slightly and close it immediately) before attaching a gas regulator to any cylinder-except a hydrogen or fuel gas cylinder. Cracking removes any dirt that may be lodged in the valve outlet, and prevents dirt from entering the regulator. Do not stand in front of the valve outlet while cracking it, and do not point the outlet at anyone.
• Wipe the outlet with a clean, dry, lint-free cloth once the cylinder valve has been cracked. The threads and mating surfaces of the regulator and hose connections should also be cleaned before the regulator is attached.
• Always use a cylinder wrench or other tightly fitting wrench to tighten the regulator nut and hose connections. Using an oversized wrench, pliers or pipe wrench may damage the fittings and make it impossible to tighten them properly. A connection problem caused by dirty or damaged threads will result in leaks when the cylinder is used.
• Do not crack hydrogen and fuel gas cylinder valves. Merely wipe out the outlet connections with a clean, dry, lint-free cloth. Hydrogen is highly flammable and will ignite if it is released into the air too fast. Hydrogen burns with a colorless, nearly invisible flame. Burning hydrogen coming out of a cylinder might not be seen, but it will be felt.
• Attach the regulator securely before opening the valve wide.

Stand to the side of the regulator when opening the cylinder valve. Cylinder regulators have a relief device to prevent excessive pressure from developing. High-pressure cylinder gauges have solid-front, safety-back construction. When subjected to excessively high pressure, the light-metal safety back will blow off to relieve the pressure. Even if the gauge glass breaks, the burst of venting gas can be startling. On rare occasions, old or improperly maintained oxygen regulators will ignite. But even a new oxygen regulator can burst into flame if the cylinder valve is suddenly turned on full. The quick burst of high-pressure gas from the cylinder into the regulator recompresses the oxygen inside the regulator and heats it to several thousand degrees Fahrenheit. Oxygen cylinders with regulators attached should always be opened slowly.