THE INDIAN INSTITUTE OF WELDING - MUMBAI
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Health, safety and accident prevention Arc welding This article gives guidelines on health and safety considerations when arc welding to ensure safe practice and prevent accidents. The hazards associated with this process are highlighted. The wrong and right ways to carry out arc welding processes are shown schematically in the figure at the end of this page. Regarding safe welding practices, the principal hazards are associated with electric shock and arc radiation. Electric shock As the principal danger is an electric shock from the live parts of the welding circuit (the electrode and the workpiece), the following practices are recommended. Checking the equipment Installation of welding equipment should be carried out by suitably qualified staff who must check that the equipment is suitable for the operation and connected in accordance with the manufacturer's recommendations. The welder is responsible for checking the equipment (cable, electrode holder and coupling devices) daily for damage and reporting defects. All external connections should be clean and tight and checked each time a reconnection is made. The welding return clamp should be connected directly to the workpiece, as close as possible to the point of welding or to the work bench on which the workpiece is placed. Changing electrodes In MMA welding, the electrode holder should be isolated when changing the electrode. Where a workpiece is earthed, if the electrode is changed without isolating the electrode holder, the welder is relying on the insulation properties of the glove to avert shock from the OCV which can be 80V between the electrode and earth. If the glove is wet, the electrode a bad insulator or the welder in contact with a conductive surface, one or more of these layers of insulation may be ineffective. Working in the open air When welding outside, the equipment should have the appropriate level of waterproofing; see manufacturer's Rating Plate (Fig. 2, Job Knowledge for Welders, No 28 ) which should display one of the following ingress protection (IP) codes for enclosures: IP 23 protection against limited spraying IP 24 protection against spraying from all directions If there is a risk of heavy rain, a cover for the welder, equipment and workpiece should be in place. Multiple welder operations When two or more welders with separate power sources are working on the same workpiece, or electrically-connected workpieces, it is essential that they are segregated. This will reduce the possibility of electric shock from simultaneous contact with any part of the two different systems. Safe practice and accident avoidance Welders should not wear jewellery (especially rings) or metallic watch straps Appropriate clothing should be worn. Gloves, boots and overalls will provide some protection from electric shock The welder should check daily, and after each reconnection, that all external connections are clean and tight When changing the MMA electrode, the electrode holder should be isolated When welding stops for a short time, the MMA electrode holder should not be put on the face shield or flammable material as it may still be 'live' at 80V or hot enough to cause damage When two or more welders (with separate power sources) are operating on the same workpiece, they should work out of reach of each other Environments with increased hazard of electric shock These are as follows: locations where the welder has restricted freedom of movement, working in a cramped position (kneeling or sitting) or in contact with conductive parts areas which are fully or partially restricted by conductive elements with which the welder is likely to make accidental contact welding in wet, damp or humid conditions which reduces the skin resistance of the body and insulating properties of accessories Where electrically conductive parts have been insulated close to the welder, there is no increased shock hazard. The equipment should conform to BS 638 Part 10. In MMA welding DC is safer than AC welding. However, if AC is used the OCV or no-load voltage should be limited, where possible, by a voltage reduction device. This limits the OCV to less than 48V until the electrode touches the workpiece. Suitable power sources may be marked with S on the manufacturer's Rating Plate (see Fig. 2, Job Knowledge for Welders No 28 ) and it is also often displayed on the front of the power source. Safe practice and accident avoidance Wear protective clothing including insulating safety boots Stand or kneel on a mat of insulating material which should be kept dry Only use an all-insulated electrode holder Place the welding power source outside the working environment Ensure qualified support staff are in close proximity outside the working space to give first aid and switch off the electrical supply When welding outside, check the power source protection rating is adequate for the environment and do not weld in the rain without a suitable cover High frequency In TIG welding, high frequency (HF) is used to start the arc and to stabilise the AC arc. HF consists of sparks of several thousand volts but because they last for only a few microseconds and are at a very low current, will not give an electric shock. However, HF can startle the welder who could injure himself. If HF is concentrated on the skin, for example through a hole in the glove, it can cause small, deep burns. HF generates electromagnetic (EM) emission, both airborne or transmitted along power cables. Care must be taken to avoid interference in equipment control systems and instruments in the vicinity of welding. Guidance on installation and use of arc welding equipment to minimise the risk of EM interference is given in BS EN 50199:1995. In practice, the welder is advised to keep welding cables as short as possible, close together and near to the ground. Workpiece earthing may be effective but should only be done if it does not increase the risk to users or damage other electrical equipment through stray currents (see Job Knowledge for Welders, No 28). Arc radiation The welder must be protected from light radiation emitted from the arc by a hand or head shield and protective clothing. The shield is fitted with filter glass, dark enough to absorb infrared and ultraviolet rays. Filter glasses conform to EN 169:1992 and are graded according to a shade number. This specifies the amount of light allowed to pass through - the lower the number, the lighter the filter. The shade number is selected according to welding process and current level. For a given current level, the same shade number can be used for MMA and MIG welding on heavy metals such as steel. However, a higher shade number is needed for MIG welding light metals such as aluminium, and for MAG welding. Screens must be used to protect other workers in the vicinity. Publications and relevant standards HS(G) 107 Maintenance of portable and transportable electrical equipment HS(G) 118 Electrical Safety in Arc Welding, HSE Books, 1995 The Arc Welder at Work Welding Manufacturer's Association BS EN 60 974-1990 Arc welding power sources, equipment and accessories, Part 10, Specification for safety requirements of arc welding equipment: welding power sources BS EN 169:1992 Personal eye protection equipment used in welding and similar operations BS EN 60 529:1992 Specification for degree of protection provided by enclosures (IP codes) BS EN 60 974-11:1995 Arc-welding equipment: electrode holders BS EN 470-1:1995 Protective clothing for use in welding and allied processes-general requirements BS EN 50199:1996 Electromagnetic compatibility (EMC)-Product standard for arc welding equipment The contrast between good and bad practice in arc welding Bad practice Hazards Good practice No face protection No arm protection Exposed cloth Exposed solvent Bystander exposed to arc Fire exit obstructed Fire bucket unsuitable for electrical fires - should contain sand Fume extraction not effective No work earth (if required) Cable damaged arc eye, burn burn fire fire/explosion, toxic vapour arc eye fire, burns electric shock fume electric shock stray arc, burns, electric shock This information was prepared in collaboration with Roger Sykes, Health & Safety Executive and Geoff Melton, Chairman, BSI WEE-6 Committee. 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