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Fume is generated by arc welding processes used for welding stainless steels, both the flux-shielded processes (manual metal arc and flux cored arc) and the gas-shielded processes (tungsten inert gas and metal inert/active gas). Plasma arc cutting also produces fume.
Fume can be defined as the airborne particles and gases arising during welding or cutting by vaporisation and reaction. Flux-shielded processes form particles of complex composition. Ozone is created by the action of ultraviolet radiation on the atmosphere in the gas-shielded processes. The tungsten inert gas process produces little particulate fume but the metal inert/active gas processes generate both particles and ozone.
There have been concerns that fume from welding of stainless steels, particularly the particles containing hexavalent chromium formed in flux-shielded processes, is a cause of cancer. Extensive studies over a long period have not supported this view but have nevertheless shown that there is a slight excess of lung cancer among all welders, whether of mild steel or alloy steels. It is therefore sensible to take action to limit contact with welding fume by process selection and/or engineering controls, such as ventilation and extraction. Local fume extraction is more effective than general ventilation. While personal protective equipment such as an air-fed helmet may also safeguard the wearer, it should only be considered for situations such as confined spaces, if only because ancillary workers are otherwise left unprotected.
There is a statutory requirement to control exposure to welding fume, expressed as a general exposure limit for welding fume and OES (occupational exposure standards) and MEL (maximum exposure limits), for individual elements, as specified by the Health and Safety Executive. Sampling to determine exposure is expensive and should only be considered when control measures have been taken and a residual risk has been identified. There are also methods of calculating exposure levels from consumable manufacturers’ data.
A typical safety data sheet relating to stainless steel can be downloaded from here.