THE INDIAN INSTITUTE OF WELDING - MUMBAI
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Health, safety and accident prevention Health risks of welding fume/gases Guidelines are given on the principal health and safety considerations to ensure safe welding practices and prevent accidents. Health risks associated with fume and gases generated during welding are highlighted. What is welding fume/gases? Welding fume is a mixture of airborne fine particles and gases. Particulate fume More than 90% of the particulate fume arises from vaporisation of the consumable electrode, wire or rod as material is transferred across the arc or flame. The range of welding particles size is shown in relation to the more familiar types of dust and fume. The respirable fraction of particles (especially less than 3µm) are potentially the more harmful as they can penetrate to the innermost parts of the lung. The range of welding particles size in relation to the more familiar types of dust and fume Gases Gases encountered in welding may be: Fuel gases which, on combustion, form carbon dioxide and sometimes carbon monoxide Shielding gases such as argon, helium and carbon dioxide, either alone or in mixtures with oxygen or hydrogen Carbon dioxide and monoxide produced by the action of heat on the welding flux or slag Nitric oxide, nitrogen dioxide and ozone produced by the action of heat or ultraviolet radiation on the atmosphere surrounding the welding arc Gases from the degradation of solvent vapours or surface contaminants on the metal. The degree of risk to the welder's health from fume/gases will depend on: composition concentration the length of time the welder is exposed the welder's susceptibility Health hazards from particulate fume The potential hazards from breathing in particulate fume are: Irritation of the respiratory tract Fine particles can cause dryness of the throat, tickling, coughing and if the concentration is particularly high, tightness of the chest and difficulty in breathing. Metal fume fever Breathing in metal oxides such as zinc and copper can lead to an acute flu-like illness called 'metal fume fever'. It most commonly occurs when welding galvanised steel; symptoms usually begin several hours after exposure with a thirst, cough, headache sweat, pain in the limbs and fever. Complete recovery usually occurs within 1 to 2 days of removal from the exposure, without any lasting effects. Longer term effects The continued inhalation of welding fume over long periods of time can lead to the deposition of iron particles in the lung, giving rise to a benign condition called siderosis. There is some evidence that welders have a slightly greater risk of developing lung cancer than the general population. In certain welding situations, there is potential for the fume to contain certain forms of chromium and/or nickel compounds - substances which have been associated with lung cancer in processes other than welding. As yet, no direct link has been clearly established. Nevertheless, as a sensible precaution and to minimise the risk, special attention should be paid to controlling fumes which may contain them. Additional hazards A number of other specific substances known to be hazardous to health can be found in welding fume such as barium and fluorides which do not originate from the metal. If the metal contains a surface coating, there will also be a potential risk from any toxic substances generated by thermal degradation of the coating. Health hazards from gases The potential hazards from breathing in gases during welding are: Irritation of the respiratory tract Ozone can cause delayed irritation of the respiratory tract which may progress to bronchitis and occasionally pneumonia. Nitrogen oxides can cause a dry irritating cough and chest tightness. Symptoms usually occur after a delay of 4 to 8 hours. In severe cases, death can occur from pulmonary oedema (fluid on the lungs) or pneumonia. Asphyxiation There may be a risk of asphyxiation due to replacement of air with gases produced when welding in a workshop or area with inadequate ventilation. Special precautions are needed when welding in confined spaces where there is the risk of the build up of inert shielding gases. Carbon monoxide, formed as a result of incomplete combustion of fuel gases, can also cause asphyxiation by replacing the oxygen in the blood. Establishing safe levels of fume in the workplace The COSHH Regulations set specific occupational exposure limits for certain substances. The limits are detailed in EH 40 which is revised periodically. The majority of limits listed are for single substances. Only a few relate to substances which are complex mixtures; welding fume is one of these. It has an occupational exposure limit but account must also be taken of the exposure limits of the individual constituents. So, in considering what would be safe exposure levels to welding fume, not only should exposure be controlled to within the welding fume limit but also the individual components must be controlled to within their own limits. The assessment of exposure to fume from welding processes is covered in EH 54. Substances may have a maximum exposure limit (MEL) or an occupation exposure standard (OES). A MEL is the maximum concentration of an airborne substance to which people may be exposed under any circumstances. Exposure must be reduced as far as is reasonably practicable and at least below any MEL. An OES is the concentration of an airborne substance, for which (according to current information) there is no evidence that it is likely to cause harm to a person's health , even if they are exposed day after day. Control is thought to be adequate if exposure is reduced to or below the standard. The OESs and the MELs of some of the substances found in welding fume are listed in Table 1; the absence of other substances from this list does not indicate that they are safe. Occupational Exposure Limits   8hr TWA 15 min STEL Substances Assigned a Maximum Exposure Limit     Beryllium 0.002 mg/m3   Cadmium oxide fume (as Cd) 0.025 mg/m3   Chromium VI compounds (as Cr) 0.05 mg/m3   Cobalt 0.1 mg/m3   Nickel (soluble compounds) 0.1 mg/m3   Nickel (insoluble compounds) 0.5 mg/m3   Substances Assigned an Occupational Exposure Standard     Welding fume 5 mg/m3   Fluoride (as F) 2.5 mg/m3   Iron oxide, fume (as Fe) 5 mg/m3 10 mg/m3 Zinc oxide, fume 5 mg/m3 10 mg/m3 Manganese, fume (as Mn) 1 mg/m3 3 mg/m3 Ozone   0.2 ppm Nitrogen dioxide 3 ppm 5 ppm Chromium III compounds (as Cr) 0.5 mg/m3   Barium compounds, soluble (as Ba) 0.5 mg/m3   Carbon monoxide 50 ppm 300 ppm Copper fume 0.2 mg/m3   If the fume contains only substances such as iron or aluminium which are of low toxicity, an 8 hour (TWA) OES of 5mg/m3 applies; this figure is the average concentration of particulate fume that should not be exceeded in an 8 hour day. Publications and relevant standards EH 40 Occupation Exposure Limits, HSE Books. EH 54 Assessment of Exposure to Fume from Welding and Allied Processes, HSE Books, 1990. EH 55 The Control of Exposure to Fume from Welding, Brazing and Similar Processes, HSE Books, 1990. The article was prepared by Bill Lucas (E-mail: wlucas@twi.co.uk ) in collaboration with Roger Sykes, Health & Safety Executive. Further information, such as technical data on fume limits, can be obtained from Graham Carter (E-mail: gjcarter@twi.co.uk ) Copyright © 2000, TWI Ltd TWI information: Information and advice from TWI are provided in good faith and based, where appropriate, on the best engineering knowledge available at the time and incorporated into JoinITTM in accordance with TWI's ISO 9001 accredited quality system. 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