Welding and flamecutting
Welding and flame cutting equipment is used in various MVR activities, including removing or repairing components and releasing seized parts. Hazards arise from:
- misuse of welding gear and using the wrong equipment for the job;
- direct contact with flame or hot parts;
- fires caused by the ignition of flammable material on or near vehicles such as trim,carpets and upholstery and petrol in tanks, fuel lines and nearby containers – often started by sparks or drips of molten metal;
- gas bottles/cylinders (in use or storage), for example acetylene is extremely unstable (potential explosion) in the event of a fire;
- fire or explosion caused by hot work on or near containers/pipework that contain or previously contained flammable material; and
- harmful fumes and gases generated during hot work, including those from surface treatments, such as paint underseal and galvanized coatings.
Consideration should be given to all these hazards, particularly when working inside or underneath vehicles (confined areas with restricted personal space). For 'hot work' on wheels see information at our 'Hot work on wheels' page.
Arc welding and arc brazing
Severe and sometimes fatal electric shocks happen at electric welding apparatus, whether single or three-phase. At all installations:
- provide fuse (overload) protection and a suitably rated residual current device (RCD) for protection against electric shock. It is best practice to mechanically interlock the switch fuse or isolator with the socket outlet, so the plug cannot be inserted or withdrawn with the switch in the ‘on’ position;
- earth the workpiece to protect the operator if there is an interwinding fault between the primary and secondary windings of the transformer. A robust flexible cable, terminating in a clamp connected to the workpiece and with its other end attached to the metalwork or earth terminal of the power source, is an efficient means of earthing;
- during MIG (metal inert gas) or similar welding, prevent contact between the electrode wire and any earthed metalwork to avoid heavy welding current flowing through the earth continuity conductor and destroying it. Use a safe design such as an insulated spool in an insulated chamber in the power source with the wire being fed, through insulated rollers and a tube inside the welding cable, to the torch;
- for MMA (manual metal arc, known as stick welding) and equipment being used in a similar configuration, use an insulated box or hook to rest the electrode holder (as this tends not to have a trigger or equivalent and remains 'live' until switched off at the machine) - Do not use the face shield, clothing or rags
- maintain the welding torch/electrode holder welding current return cables, clamps and safety earths in good condition.
Prevent exposure to direct and reflected ultraviolet (UV) light and infrared rays by wearing protective clothing, and using welding screens. If possible, use dark coloured wall coating to reduce reflections. To protect against splatter when welding, wear appropriate clothing that covers arms and legs, and use suitable gloves. Wear goggles when chipping slag or wire-brushing welds during preparation or finishing off work.
Specific eye protection including filters for welding operatives (to prevent arc eye) should conform to relevant British and European standards. There are standards covering impact resistance, auto-darkening welding filters and fixed filters. Reputable welding equipment suppliers will be able to assist in the correct choice.
Controlling fumes and gases
Exposure to welding fume is usually infrequent in the MVR environment. However, local exhaust ventilation (LEV) should be used wherever possible and always in confined locations or when welding stainless steel. LEV should also be used when surface treatments, such as paint, paint underseal and galvanized coatings may be affected by heat from welding or flamecutting. LEV such as mobile extraction units with flexible trunking and exhaust hoods can remove fumes and gases from most locations (the hood needs to be located as close as possible to the source of the fume). This LEV should be examined and tested by a competent person every 14 months.
For small scale work and where there is no LEV available, then make sure there is a free flow of air (ie good general ventilation - mechanical and/or natural ventilation) to disperse fumes.
Preventing fires and explosions
Never apply heat to containers, tanks or drums that may contain flammable residues. This can result in fatal explosions. All containers must be thoroughly cleaned of all contaminants and purged of all flammable gases before any heat can be applied to them. Alternatively, cold methods of work should be used which avoid the use of heat altogether. Remove adjacent flammable trim and upholstery before carrying out hot work, especially where molten metal or sparks may fall onto them. Check that fuel lines and tanks will not be affected; empty and remove any which are near or shield them. Check that body cavities next to welding or flamecutting are not filled with plastic foam, which may be easily ignited. Remove this where necessary and use a heat shield to protect adjacent areas.
Resistance (‘spot’) welding
Spot welding tends to be a more controlled process and produces much less fume and splatter and negligible UV. Eye protection is only required to safeguard against splatter and good general ventilation is usually sufficient. All portable welding guns should have suitable counterbalanced devices for supporting the guns, including cables, unless the design of the equipment makes counterbalancing unnecessary.
Safeguards for flammable gas cylinders
Gas cylinders are a convenient way to transport and store gases under pressure but they have a number of hazards, including:
- cylinder explosion or rapid release of compressed gas;
- impact from flying debris or parts after a rupture;
- contact with the released gas or fluid (at high pressure and very low temperatures);
- fire resulting from the escape of flammable gases or fluids (such as LPG);
- impact from falling cylinders; and
- manual handling injuries.
To reduce the risk of an accident:
- use propane in preference to acetylene where possible;
- store full and empty cylinders in a safe, well-ventilated place, preferably outside buildings and away from bulk oil storage tanks or anything similar;
- never keep or use cylinders below ground level, or next to drains, basements and other low-lying places – heavy gases will not disperse easily;
- Do not leave charged hoses for extended periods where ventilation is poor;
- store gas cylinders upright;
- chain cylinders to racks or suitable trolleys to prevent them falling;
- change cylinders away from sources of ignition in a well-ventilated place;
- use the correct hoses, clamps, couplers and regulators for the particular gas and appliance being used;
- don’t leave hoses where they may be damaged, for example across traffic routes;
- ensure the equipment is checked by a competent person before use (including flexible hoses and gauges and replace as necessary). Where equipment is deemed unserviceable, make sure it is withdrawn and clearly identified as not for use;
- never apply grease, oil or other lubricants to oxygen fittings;
- at the end of each day’s work – turn off cylinder valves, purge the hoses of gas, and then turn off the valves at the blowpipe;
- only allow trained, competent people to use the plant.
- Minimise the risk of flame ‘flashback’ into hoses or cylinders by fitting flashback arresters near the regulator, on both the fuel and oxygen supply. For long lengths of hose, you should fit arresters on both the blowpipe and the regulator;
- check any acetylene cylinder which has been involved in a flashback or 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;
- when a gas leak is suspected use a leak-testing fluid to test for leaks – never a flame;
- where flammable gas cylinders are transported for roadside or on-site repair, they should be transported in a well-ventilated (preferably open-topped) vehicle, secured in an upright position, and with both the cylinder and blowpipe valves turned off.
- A garage was prosecuted by a local authority in 2012 following an investigation after an employee attempted to hot cut a drum containing car engine oil which then suddenly exploded. Fortunately, in this case the employee survived - often this is not the case. The company owning the garage were prosecuted and fined a total of £40K and paid costs of nearly £17K at magistrates court. The CCTV footage from the garage showed how this occurred - follow this link 'Hot cutting an oil drum containing residual vapour' - the important message here is don't carry out hot cutting without considering the risks involved and the precautions needed.