Gaseous Fume

Gaseous fume is process dependent, and doesn't originate from the welding consumable or parent plate. Processes most likely to give gaseous fume are those with an open arc, such as MIG, TIG and Plasma Cutting.

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 Gaseous Fume?

Gaseous fume consists of either one or more specific pollutant gases, mixed in the air around the welding area. As it is present at gaseous form it can easily enter the lungs. Whether the fume is likely to cause damage, depends largely on precisely what the gas, or gases are and on the concentration breathed in and the length of time of exposure to the specific pollutant(s).

Sources of Gaseous Fume

Gaseous fume may be formed by the action of a welding arc, or the radiation from it, on either the air surrounding the arc, some component within a flux or from coatings or contaminants on the component surfaces. Gaseous fumes are not emitted by the parent metal or the welding consumable.

Exposure to Gaseous Fume

Exposure to welding fume is affected by many factors, the main contributors include:

- The welding or cutting 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. However, understanding the choices available and their effects can make it easier to make an informed judgement.

Exposure Limits

National health and safety organisations, such as ACGIH in America and HSE in Great Britain, issue, annually, lists of mandatory or recommended limits of exposure to hazardous substances for people at work. These limits represent maximum concentrations of welding fume and its component parts in air in breathing zones of workers.

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.

The effects of exposure to fume may become apparent very quickly during welding, shortly afterwards, or at a much later date, and only for some hazards can indications be given.

Some of the more common hazards encountered are outlined below: 

Ozone

Ozone is a very active and highly toxic gas, probably the most poisonous gas encountered in welding industry and must be treated with extreme caution.

Oxides of Nitrogen

These oxides, notably NO + NO2, react with moisture, possibly in the nose and throat, to form nitric and nitrous acids, and are extremely irritant and corrosive.

Carbon Monoxide

This has a high affinity for haemoglobin in the blood, and low concentrations can cause headache, shortage of breath.

Dichloro-acetyl-chloride (DCAC), Phosgene

If a welding arc is struck when vapours, from degreasing agents are in the immediate vicinity, an irritant gas, DCAC, will be produced.

Hydrogen Chloride

These acid vapours are extremely irritant to the upper respiratory tract.

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. If an occupational hygiene assessment shows unacceptable concentrations, then additional controls will need to be put in place. Most health and safety bodies require that there should be engineering controls as a first option.