Welding fume is an unavoidable by-product of welding. It consists of particulate fume, the part you can see and the gaseous fume, which you cannot see but can sometimes smell. All welding processes generate welding fume, the type and amount varying from process to process.
Particulate fume is made up of discrete solid particles, normally complex oxides and silicates of metals, which are generally under 0,5 microns in diameter. This falls into the "respirable" size range meaning that the particles can be breathed in and reach the lungs.
By far the most important source of particulate fume, when welding on clean plate, is the welding consumable, the carbon or alloy steel filler wire, and to a lesser extent, the parent plate.
Gaseous Fumes
Composition
As good welding practice demands that the steel is clean and as no fluxes are used the only significant source of gaseous fume is from the ultraviolet light (UV) produced by the welding process.
Concentration
In laboratory tests with both Argoshield gases and CO2 ozone
production is relatively low at low currents rising as the
welding current increases.
As expected the amount of ozone produced decreases as the
distance from the arc increases.
Particulate Fume
Composition
Particulate fume from carbon steel MIG welding will contain, as oxides iron, manganese, and copper, with only insignificant traces of other elements, like chromium and nickel.
Typical percentages of the above elements in fume, are as follows:
Low alloy steel MIG wires also contain small amounts of some of the following:
Work by BOC has studied the influence of different shielding gas compositions on fume composition and concentration. It was found that, in occupational hygiene terms, there was very little difference in fume composition generated with any of the Argoshield type gases or pure CO2.
Concentration
The term "Fume concentration", is generally taken to mean the concentration of fume present in the breathing zone of the welder or other operative.
The welding current has a significant affect on the FFR. Tests have shown that as the current increases the amount of fume produced rises slowly at first and then at about 180 amps when a 1.2mm diameter wire is used there is a significant increase in fume production.
Control Measures
Fume from carbon and low alloy steel MIG welding will comprise particulate fume and may contain ozone depending on shielding gas and current levels.
The particulate fume may be controlled by use of local fume extraction.
Practical Considerations
Choosing Welding Conditions
Choosing and setting the correct welding conditions can have a significant effect on the volume and type of fume produced.
Choosing the Right Shielding Gas
The choice of shielding gas can significantly affect how much fume is produced.