PREVENTING FLASHBACK
Always Follow:
CSA Standard W117.2-94, Safety in Welding, Cutting, and Allied Processes.
All equipment must be CSA Standards C22.2 No.60 or be acceptable to the regulatory authority.
Oxy-acetylene torches have been used for many years for cutting, welding, brazing, and heating of metals. The equipment used today is safe, but improper use may cause fires and violent explosions.
One cause of fires and explosions is high acetylene pressure.
When more than 15 pounds of pressure is used, acetylene becomes unstable and explosively decomposes.
This is the major reason for using other fuel gases such as MAPP, propylene, propane, and natural gas, which may be safely used at higher operating pressures.
If your oxygen cylinder is low or empty, reverse flow of gas may occur.
The fuel gas being at a higher pressure can travel up the oxygen line mixing with gas in the hose, regulator and cylinder.
If you light your torch without purging the lines, a burn back may occur with explosions in the hose, regulator, or cylinder. Of course, the same thing can happen with high oxygen pressure and low fuel gas pressure if a backfire occurs.
Backfires are usually caused by holding the cutting torch too close to your work – causing gas starvation of the cutting flame which results in the flame being sucked into the torch head.
Usually you will hear a popping sound that turns to a whistle when this happens. Unless you shut off the oxygen valve, the flame burning in the torch head may ignite gases in the hoses resulting in a flashback.
A flashback is an explosion that progresses through the torch, hoses, regulators, and into the cylinders. The consequence can range from a burst hose to a violent explosion of the regulator and cylinders.
There are several things you can do to help prevent flashbacks, fires and explosions:
1. If using acetylene, keep the pressure below 15 pounds. 2. Purge your hoses before lighting the torch. 3. Never light your torch with a mixture of fuel and oxygen. After purging the lines, light the torch with only the fuel gas valve open. 4. Be sure check valves are installed on both torch inlets and are operating properly. Check valves can stop the reverse flow of gases, but will not prevent flashbacks. 5. To prevent flashb