Contaminant Clouds Part 4 – Welding Fume
Welding fume is very complex. It is a mixture of airborne particles, vapours and gases which are generated from the thermal manipulation of metal materials. Fine fume particulates form metal oxides from the vaporisation of molten metal, with the composition depending on which alloys or rods we are using. Welding may also produce hazardous levels of by-product vapours and gases depending on the situation e.g. shielding gases, flux-containing consumables, coatings, ventilation provisions. We may be dealing with a range of exposure scenarios each of which may produce specific hazards. For example, manganese is highly hazardous and may be present in the consumables used for MIG welding. The WEL for manganese was in fact recently lowered as exposure can cause neurological effects similar to Parkinson’s disease. Welding stainless steel can produce hexavalent chromium which is a lung carcinogen. Stainless steel fume may also contain chromium and nickel oxides which are asthmagens. Welding onto galvanized metals and mild steel can cause fume exposure leading to metal fume fever. Iron is of course also present in steel. Exposure to iron in the welding fume may cause siderosis which is the deposition of iron oxides in lung tissue.
We have only covered the welding fume so far, as this is the main health hazard associated with many welding operations. But there may also be by-product gases and vapours. For example, welding onto a surface which had been degreased with a chlorinated-hydrocarbon can produce phosgene which is a toxic gas. Inert shielding gases used can be asphyxiants in cases of confined space or very poor ventilation. Ozone is produced by the interaction of oxygen in the air with the UV produced from the arc. It is highly irritating to the respiratory system and eyes. Other gases like carbon monoxide and oxides of nitrogen can also be produced. These are asphyxiants and blood poisonous. Furthermore, physical hazards may arise from welding – noise, vibration, UV radiation, EMF exposure and thermal stress.
Although welding fume composition is variable, it is classed as carcinogenic. In February 2019, the HSE published a bulletin entitled Change in Enforcement Expectations for Mild Steel Welding Fume. This followed IARC volume 118 which stated that ‘’There is sufficient evidence in humans for the carcinogenicity of welding fumes. Welding fumes cause cancer of the lung. Positive associations have been observed with cancer of the kidney’’ and ‘’There is sufficient evidence in humans for the carcinogenicity of ultraviolet radiation from welding. Ultraviolet radiation from welding causes ocular melanoma’’. Due to the highly hazardous nature of welding fume, the exposure must be controlled to a high level. Starting with the hierarchy of control.
Let’s begin by asking ourselves a few questions. Do we have to weld? Can we us adhesives, brackets or fasteners to join metals together instead? Can we choose a welding method that produces the least fume (TIG produces less fume than MMA)? Can we limit the duration of welding? Can we choose alloys and consumables with the least hazardous content? If elimination or reduction of the fume produced is not reasonably practicable to achieve, then we move down the hierarchy to engineering controls and RPE. When selecting local exhaust ventilation (LEV), it is important to understand that the design and installation of suitable LEV systems is a job for professionals. We highly recommend contacting organizations such as the Institute of LEV Engineers (ILEVE) for guidance on how to select a competent LEV designer.
ILEVE also provide guidance for welding fume control, see their technical note WF01 which goes through several LEV buying options. The British Occupational Hygiene Society (BOHS) has a campaign ‘’Breathe Freely’’ with a website full of guidance for welder, including LEV and RPE guidance. The Breathe Freely welding fume control selector tool is particularly helpful (https://www.breathefreely.org.uk/WST/). The tool allows you to select the type of weld, materials in use, duration of welding, and the size of your workpiece. This then provides an example of a suitable control measure for that particular scenario. The control selection should however always be made in-line with the process-specific risk assessment. The COSHH essentials WL series is also an excellent source of information. Document WL3 offering guidance on good control practices. There is plenty of information available to help employers understand the risks and how to choose the right controls. EEUK Group’s occupational hygiene consultants can help the employer assess the level of exposure and give guidance on how to select suitable controls.