PROCEDURE FOR USE OF OXY-ACETYLENE EQUIPMENT (Revision 2 – 20th January 2011) Toolbox Talk

HAZARDS ASSOCIATED WITH THE USE OF OXY-ACETYLENE EQUIPMENT Oxygen The air we breathe contains about 21% oxygen, even a small increase of oxygen in the air to 24% can cause a dangerous situation. In oxygen enriched atmospheres some materials may spontaneously ignite. A fire will burn hotter and more fiercely than in normal air and will be difficult to extinguish. Acetylene An extremely flammable gas that can become unstable under certain conditions.

The main hazards associated with the use of oxy-acetylene equipment include: Leaking equipment that can lead to fires or explosions. Backfires occur when the torch flame burns back into the blowpipe, sometimes it can continue burning back to the point where oxygen and the fuel gas are mixed causing a potentially serious situation. Flashbacks are caused by a reverse flow of oxygen into the fuel gas hose (or fuel gas into the oxygen hose) – this then produces an explosive mixture in the hose. The flame can then burn back through the blowpipe, into the hose and may even reach the pressure regulator and the cylinder. This can result in damage or destruction of equipment, and could even cause the cylinder to explode. This could end in serious injury (or worse) and severe damage to property. Decomposition of acetylene back to its constituent elements inside cylinders which can lead to an explosion. Poor handling (i.e. dropping them or leaving them on their sides) or storage of cylinders usually causes this situation.

The main hazards associated with the use of oxy-acetylene equipment include: Pure oxygen at high pressure in cylinders coming in contact with greases and oils which can then spontaneously combust. Over-pressurisation of acetylene leading to an explosion. Inhalation of harmful welding fume Setting fire to adjacent flammable materials Risks of burns Risk of injury to eyes Bodily injury when manually handling cylinders

HOT WORKS PERMIT TO WORK With the exception of welding carried out in the workshop welding bays at Bedford Road and Rowett, a Hot Works permit MUST be issued for all works involving oxy-acetylene equipment. PPE TO BE WORN AT ALL TIMES WHILST WELDING OPERATIONS ARE CARRIED OUT Welders goggles (both the person using the equipment and any other personnel assisting) Welders gauntlets Welders cap Boilersuit – flameproof, flame retardant material Remove loose items of jewellery and tie back long hair.

EQUIPMENT REQUIRED AFFF fire extinguisher Portable fan and ducting Cylinder valve keys (one for each cylinder) Spark igniter

STORAGE OF CYLINDERS Cylinders must be stored in a secure, well-ventilated area away from any heat sources and combustible materials. Spare oxygen and acetylene cylinders must be kept in a designated store at least 3m apart OR be separated by a fire separating wall. Cylinders must be kept upright at all times, to prevent them falling over they should be chained or clamped individually.

TRANSPORTATION OF CYLINDERS Purpose built trolleys must be used for transporting cylinders. Vehicles used for transporting cylinders must be open backed and have the facility for keeping the cylinders in an upright position. Flammable compressed gas warning triangles must be displayed on the vehicle.

TRANSPORTATION OF CYLINDERS (continued) Do not do not leave the cylinders unattended if unable to secure from access/use. When using passenger lifts to transport cylinders, persons MUST NOT accompany the cylinders in the lift. When working with larger cylinders, persons should never turn their back on a freestanding cylinder.

MAINTENANCE AND TESTING OF EQUIPMENT The following is to be carried out by trained University staff: Pressure regulators - Test annually. Replace every 5 years from date of manufacture (including spare regulators as seals deteriorate even if equipment has not been used). Flashback arrestors – Test annually. Replace every 5 years. Hoses (including non-return valves) – Test annually. Note: Replacement components for oxygen service must be compatible for use with oxygen. Lubricants and tape should not be used on oxygen service equipment unless specifically designed for oxygen use.

PRE-USE CHECKS Equipment Ensure cylinders are clean. Cylinders must be free from any oils or greases (particularly important for oxygen cylinders). Cylinders must be labelled with their contents, do not use cylinders which are not labelled. Pressure regulators must be set at correct working pressures (acetylene maximum 0.62 bar, 9 psi).

Once pressure regulators are set at correct working pressure examine the following for wear, damage or leaking, ensure that all connections are tight: Cylinder valve group Non-return valves at blowpipe inlets Flash back arresters Hoses Blowpipe and nozzle

A proprietary leak detecting spray should be used to confirm any suspected leaks on any of the above, DO NOT use soapy water. Nozzle sizes on blowpipes should be appropriate for the job to be carried out. Inspect these regularly and ensure that they are not blocked by dirt or spatter. Replace damaged nozzles.

Welding area and the material to be worked on Remove any combustible material within a radius of 10m to the work area. Ensure that the item to be worked on does not contain any flammable liquids or residues – people have been killed whilst working on containers which had residues of flammable liquids or contained gases (see the following article on a fatal accident which occurred locally) Ensure that you have a hot works PTW if not carrying out the work in the welding bay. 

USE OF EQUIPMENT Lighting up procedure Ensure all valves are closed including outlets of adjustable pressure regulators. Check that blowpipe valves are closed. Slowly open the cylinder valve while the blowpipe valve is closed, if necessary adjust the pressure regulator to the correct working pressure.

Lighting up procedure (continued) Prior to lighting the blowpipe purge each hose separately and consecutively (oxygen first, then acetylene). Note:This procedure must be done in a well ventilated area away from any potential sources of ignition. Purging is important. It removes flammable gas mixtures from the hoses and equipment which could result in explosions and fires when the blowpipe is first lit. -Open the oxygen blowpipe valve until the hose contains only pure oxygen, then close the valve. If necessary, reset the pressure regulator to ensure correct working oxygen pressure. -Open the fuel blowpipe valve until the hose contains only acetylene. If necessary, reset the pressure regulator to ensure correct working fuel gas pressure. Light fuel gas immediately using a spark igniter, then open the oxygen blowpipe valve. Adjust it and the fuel valve to obtain the correct flame.

General operation Pressure regulators must always be set at the correct working pressure (acetylene must never exceed 0.62 bar, 9 psi). Never hang lit blowpipes or leave them unattended even for a short period of time. The flame must be extinguished when stopping work temporarily. Hoses should be of equal length, no longer than necessary, but at least 3m total length (i.e. ignition source at least 3m from cylinders).

Hoses should always be fully extended when in use, do not coil hoses. The practice of kinking hoses to stop the supply of fuel is not permitted. Mechanical extract should be located as close to work area as possible to remove any fumes. Do not hold the nozzle too close to the workpiece. The nozzle can overheat and cause a flashback. Inspect nozzles regularly. Make sure they are not blocked by dirt or spatter.  

Shutting down procedure Close the fuel gas valve at the blowpipe. Immediately close the oxygen valve at the blowpipe. Close the cylinder valves for both oxygen and acetylene (not necessary if equipment is to be used again in the immediate future). Close the outlets of adjustable pressure regulators. Open both blowpipe valves to vent any pressure in the equipment then close again. Ensure that the pressure adjusting screw of the pressure regulator is fully unwound. At the end of the operation remove the cylinder from the work area, either return to the approved storage area on site or for contractors remove from the site completely.

What to do if a flashback or dangerous situation occurs Immediately close the cylinder valves, both acetylene and oxygen, if it is safe to do so. The flame should go out when the fuel gas (acetylene) is shut off. If the flame cannot be put out at once, evacuate the area and call the emergency fire services and the gas supplier*. Check any acetylene cylinder which has been involved in a flashback or which may have been affected by fire or flames. If it becomes warm or starts to vibrate, evacuate the building immediately and call the emergency fire services. Also call the gas supplier*. Do not attempt to move an unstable cylinder. Direct water spray at the cylinder body, only if it is safe to do so. Before using again, check flashback arresters and other components which may have been damaged by the flashback. Replace if necessary. If in doubt, consult the gas supplier*. *The emergency number for BOC gases is