7 Emission Rates: general factorsMany factors affect the rate at whichparticulate fume and pollutant gasesare generated. The most important isgenerally the choice of welding process,but the welding current, voltage andshielding gas are also important. Thisguide looks at the effect of shieldinggases in greater detail in the sectionsthat follow.The main job of welding engineersand supervisors is generally to providea given level of weld quality at thelowest cost, so the welding processand conditions are often effectivelyfixed. However, it is useful to be awareof the health effects of differentwelding processes, and to considerchoosing the process or the weldingconditions to minimise the risks wherepossible. Indeed, in some cases it maybe appropriate to think about usinga metal joining technique other thanwelding, or to avoid the need for joinsaltogether.In practice, most flexibility lies in thechoice of shielding gas for MIG/MAG,TIG and FCAW work.The welding processSome processes inherently producemore fume than others (Figure 4). Thelargest amounts of particulate fumeoccur in open-arc welding processeswhere metal is transferred across thearc: MMA, MIG/MAG and FCAW.Although it is an open-arc process, TIGwelding does not produce significantquantities of particulate fume becausemetal is not transferred across thearc. Submerged-arc welding generateshardly any particulate fume.4040Fume emission rate mg/s353025201510101010MIMA Mild steel4mm rodFCAW Stainless steel250A550.1TIG Stainless steel 220AMAG Mild steel dipMAG Mild steel sprayMIG Aluminium sprayFigure 4: Typical fume emission rates for different processes, materials and conditions17
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