Revised on
01/26/17 02:04pm
SafetyNet #
2

Oxyacetylene Safety Update

Contact information

Oxygen and acetylene are a common fuel gas mixture for oxyacetylene welding activities.  Oxygen, alone, is not flammable but it is an accelerant, making things it comes in contact with burn hotter and faster.  Acetylene is an extremely flammable gas.  Acetylene cylinders are equipped with a porous material and filled with acetone.  The acetylene gas dissolves in the acetone, allowing the acetylene to be handled safely.  Acetylene cylinders must NEVER be stored on the side.  This can cause the acetylene to come out of solution, causing a dangerous increase in cylinder pressure.  Acetone (a flammable solvent) could also be drawn into the torch and cause an explosion.

Flashback Arrestors
EH&S recommends that all oxyacetylene rigs be equipped with flashback arrestor devices for the best protection against accidental flashback and explosion. Check valves do not provide the same level of protection as flashback arrestors. While properly maintained check valves prevent reverse flow of gases, they may not stop a "flame front" traveling back to the regulator.

Flame arrestors provide triple protection:

  • a filter that stops the flame from traveling back to the regulator;
  • a check valve that stops reverse flow of gases;
  • a cut-off valve that stops the flow of gases.

Flashback arrestors are a one-time cost for a set of two (one for oxygen and one for acetylene) and are permanently mounted on the oxyacetylene rig between the regulators and hoses. They can be regularly tested "in line" without disconnection.

Acetylene Regulator Maximum Pressure

Acetylene line pressure that exceeds 15 psig is extremely DANGEROUS.  At greater than 15 psig, acetylene gas can become unstable and violently decompose.  The pressure must never exceed 15 psig when working with university equipment.
Gas Cylinder Storage

Please refer to Safety Net #60, Compressed Gas Safety, for information on proper storage and handling of backup or empty gas cylinders.  Always store acetylene gas cylinders upright and properly secured.

Fire Department Notification and Permits

Supervisors are responsible for notifying the Fire Department before the start of welding/cutting operations pursuant to UC Davis PPM 390-40 and UC Davis PPM 290-86. A Hazardous Conditions (Hot Work) Permit must be submitted at least 72 hours before the start of work. Notification must be done before the start of each job, unless the work is in a permitted location where welding is routinely done. The fire department requires a fire watch be maintained for at least 30 minutes after the completion of cutting and welding activities.  Contractors must also obtain a UC Davis Fire Department Hazardous Conditions (Hot Work) permit.

If you are unsure whether your procedure requires a permit, consult the Fire Prevention Specialist at (530) 752-3839.

Basic Oxyacetylene Handling Information:

  • Never allow oxygen to contact oil, grease, or other combustible materials
  • Use the proper regulator for each specific gas.
  • Only qualified technicians should repair a regulator.
  • Keep regulators free of oil, grease, and other combustible materials.
  • Check valves stop reverse gas flow, they do not act as a fire stop.
  • Never starve a tip, this can cause a flashback.
  • Always store and use cylinders in an upright position.
  • Never stand in front or behind a regulator when opening the cylinder valve.  Stand to the side.
  • Do not open acetylene cylinder valve more than 1 1/2 turns.
  • Always make sure area is safe and free of combustible materials.