How severe the hazard is depends on the process, the welding or cutting parameters, and the materials, consumables, fluxes and gases used.
All arc processes present an electrical hazard and hazards associated with handling hot metal.
All but submerged arc welding also present infrared (IR) and UV radiation hazards.
Arc welding and cutting processes generate fume. The type and amount of fume depends largely upon the process but also on the materials and consumables.
MMA, cored wire, MIG welding, air-arc gouging and plasma cutting produce the largest quantity of fume, whereas TIG and submerged arc welding produce a smaller quantity.
Gas shielded processes (MIG, TIG, cored wires, plasma) use compressed gases and gas mixtures which present potential physical hazards and risks of asphyxiation.
These gases may also be supplied as cryogenic liquids which themselves pose added hazards.
Some processes are noisy, most notably air-arc gouging and plasma cutting. These can be well in excess of the recommended exposure levels.
For some applications thoriated electrodes are used for TIG welding. These give a small radioactive radiation risk.
General hazard information
All of these hazards may be exacerbated when working in confined spaces, in hot, wet, cramped areas, or if working at height.
Workers should be aware of the potential hazards of each process and the means to avoid or control the risks.
Safety training and the adoption of safe working practices will help to minimise risk.