Welding fume is an unavoidable by-product of welding. It consists of particulate fume, the part you can see and 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; MMA, MIG, FCAW and plasma cutting tend to produce most, while TIG, plasma welding, laser welding and Submerged Arc give very little under normal circumstances, although TIG can give high levels of gaseous fume.
What is Particulate Welding fume?
Particulate fume is made up of discrete, very small, solid particles, which range in size from 0.01 to 10 microns, but these particles are generally less than 0.5 microns in diameter. This means that most of the fume falls into the 'respirable' size range, meaning that particulate fume can be breathed in, reach the lungs, and stay there.
Sources of Particulate Fume
Particulate fume is generated as a result of the action of a welding arc on, the welding consumable, secondly the parent metal and thirdly any coatings or contaminants on the surfaces of the component to be cut or welded.
The welding current also has a significant effect on the amount of welding fume produced. As most of the fume comes from the consumable, it is obvious that parent metals in general, do not contribute greatly to particulate fume.
Composition of Particulate Fume
Particulate fume is made up mainly of complex oxides and silicates of metals present in the welding consumable being used. Its composition will be directly related to the composition of the filler metal being used in processes where the filler is a solid metal.
Exposure to Particulate Fume
Exposure to welding fume is affected by many factors, the main contributors include:
- The welding process being used.
- The alloy system(s) being welded.
In most fabrication workshops, it is not always possible to control or change these factors because of other considerations such as the requirements of production.
One of the most important factors influencing the degree of exposure to fume, is the welder's head position relative to the rising plume of fume.
Exposure Limits
National health and safety organisations, such as American Conference of Governmental Industrial Hygienists, ACGIH in America and Health and Safety Executive, HSE in Great Britain, issue, annually, lists of mandatory or recommended limits of exposure to hazardous substances for people at work.
Effects of Excessive Exposure
This section not intended as a medical text, but just as a reference. It is always recommended that professional medical or epidemiological opinion should be sought, if assistance is needed.
Some of the more common hazards encountered are outlined below:
Welding Fume (unspecified)
This can cause irritation and dryness of the eyes, nose, and throat and affect the respiratory tract, causing coughing, wheezing, tightness in the chest, and breathing difficulties.
Zinc and Copper
Freshly formed metal oxides in welding fume can cause severe flu-like symptoms to arise some 8 hours or so after exposure.
Chromium and Nickel
Some substances in welding fume, such as chromium and nickel, are thought to be potential human carcinogens, particularly hexavalent chromium (Cr6+).
Aluminium
Aluminium oxide fume is not thought to be harmful, apart from its irritant nature as a particulate fume.
Iron
All welders have iron oxide in their lungs, and these show up as opaque areas on chest X-rays.
Manganese
In its acute form, if inhaled in sufficient quantity, it can cause Metal Fume Fever.
Cadmium
Inhalation of cadmium oxide fume can result in severe respiratory irritation, pulmonary oedema, fluid in the lungs, and there have been deaths reported.
Cobalt
Cobalt is a constituent of some high temperature alloys, such as 'Stellite'. As cobalt oxide, CoO, if inhaled, can cause irritation of the respiratory tract, coughing and shortage of breath.
Barium
Barium is used as a component of some self-shielded cored wires, it is a registered poison.
Lead
Lead is a cumulative poison.
Fluorides
Inorganic fluorides, from basic fluxes, are acrid and very irritant.
Control of Exposure
Exposure to welding fume should be controlled to as low a level as practicably possible, but in any case kept below the current exposure limit.
Fume extraction equipment falls into one of two types:
- Low volume-high velocity unit, sometimes referred to as the vacuum cleaner type.
- High volume-low velocity type, these move five or ten times as much air as the other type.
If these sorts of control measures are not appropriate or do not give adequate protection to welders and allied trades, then the use of suitable Personal Protective Equipment, PPE is the only option.