The common processes are:
- Gas – brazing, oxyacetylene
- Electric – manual metal arc (MMA), metal inert gas (MIG), tungsten inert gas (TIG), submerged arc welding (SAW)
Airborne contaminants include:
- Dusts/Fumes – metal fumes, flux dusts, flux fumes. Some are extremely toxic (cadmium, beryllium)
- Products of combustion – nitrogen oxides (lungs), carbon monoxide (systemic), carbon dioxide (asphyxiant)
- Others – inert gases (from shielding gas), the toxic ozone and the highly toxic phosgene.
If welding is being done at a workstation in an assembly line then air monitoring and appropriate analysis will give a good indication of exposure to fume/dust. Use a Tyndal Lamp to show dust plumes.
Welding may also be done in the open (a construction site) or in a large workshop (fabrication of a boat or steel components for civil engineering etc). In these settings risk assessment is harder.
1. Substitution of welding rods: some welding rods emit much less fume than others. Seek advice from the supplier.
2. Current control: follow preferred work practices. Keep the current to the minimum to minimize emissions.
3. Flame optimisation: following safe work practices reduces emission of contaminants such as carbon monoxide.
4. Local exhaust ventilation: possibilities include: fixed extraction hoods – for assembly line work portable ‘vacuum cleaner’ type extraction flexible, ducted extraction systems.
5. General air ventilation: Build-up of welding fumes can be unpleasant but can be avoided by having open doors and adequate ceiling extraction. There must be enough air changes per hour and no ‘dead spots’. General air ventilation is no substitute for local exhaust ventilation.
6. Work practice: – like keeping the head away from the rising plume of dust/fume generated by the welding process. Positioning the work piece and/or placement of the body are both obvious possibilities.
7. Personal protective equipment: UV visor – face shields (may be air-supplied for extended periods of work), gloves, overalls and aprons. Specialised help in selection and fitting is advised.
Confined spaces increase hazard levels – through over-exposure, asphyxiation and oxygen deficiency.
Phosgene can be produced when chlorinated solvents are involved in welding process (e.g: if steel is not properly cleaned after degreasing).
Ultraviolet light; electrical hazards; hot metal particles; flammable gases; compressed gases; noise; heat stress; and manual handling.
Welding Fume Control Table
Add the three weightings you obtain from the Tables 1-3 to find out what control actions are needed from Table 4.
1 Process Weighting Factor
|Submerged arc welding (remote); laser cutting and welding; micro plasma; Gas cutting (remote operations).||0|
|Submerged arc welding (manual); submerged arc welding (multi arcs).||2|
|Brazing (manual operation); TIG (manual operations); gas welding and cutting (manual); silver soldering (manual); resistance spot welding (manual); plasma cutting (under water table); plasma arc welding; MIG (remote operation); resistance seam welding (remote operation); electroslag welding.||4|
|MIG (hand held); MMAW; Resistance seam welding (manual operation); thermit welding; electrogas welding.||7|
|Arc cutting; plasma arc gouging; air arc gouging; flux cored arc welding (manual and remote operation).||9|
|Plasma arc cutting||15|
2 Fume Constituent Weighting
|A: Iron, aluminium, tin, titanium – < 5% of B or C. < 0.05% D||0|
|B: Copper, magnesium, manganese, molybdenum, silver, tungsten, zinc. Flux fumes such as fluorides, rosin, phosphoric acid, zinc chloride and boric acid||10|
|C: Barium, chromium, cobalt, lead, nickel, ozone, vanadium, phosgene, organic fume.||20|
|D: Beryllium, Cadmium||55|
3 Work Location Weighting
Add the three scores and compare …
4 Control Requirements
|< 9 or 9||Natural Ventilation|
|> 9 to 21||Mechanical ventilation|
|> 21 to 54||Local exhaust ventilation|
|> 54||Local exhaust ventilation and respiratory protection|