Way back when I took welding in high school they taught not to open the acetylene valve all the way. Open it one turn or less in case it needs to be shut off quickly.
A Google search for "Oxy-Acetylene safety" turned up a bunch of references. I chose
http://www.metalwebnews.com/howto/weld/weld.html It says 1 to 1½ turns.
It also lists recommended pressures, lens shades and other helpful info.
Their list of safety rules:
"Never use Acetylene gas at a pressure over 15 psig.
Never use damaged equipment.
Never use oil or grease on or around Oxygen equipment.
Never use Oxygen or fuel gas to blow dirt or dust off clothing or equipment.
Never light a torch with matches or a lighter. Always use a striker.
When opening a Oxygen or fuel cylinder valve, always crack it open first.
Always make sure regulators have their adjusting screws released by turning them counter clockwise till free before opening cylinder valves. Stand to the side of a regulator, not in front of it when opening cylinder valves.
Always wear the proper welding goggles, gloves and clothing when operating Oxy-Acetylene equipment. Pants should not have cuffs.
Always have a fire extinguisher handy when operating Oxy-Acetylene equipment.
Always replace cylinder caps when finished using cylinders.
Do not rely on the color of the cylinder to identify its contents as some suppliers may use different color codes.
Always use the proper regulator for the gas in the cylinder.
Always use cylinders in the upright position only.
Never store cylinders in temperatures over 130deg. F.
Always keep the valve wrench on the Acetylene cylinder valve when in use. Only open valve a maximum of 1 1/2 turns.
Do not carry lighters, matches or other flamable objects in pockets when welding or cutting.
Always be aware of others around you when using a torch.
Becareful not to let welding hoses come into contact with torch flame or sparks from cutting."
