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If inhaled, welding fumes can be harmful to health, thus exposure must be controlled. A commonly used method of control is local exhaust ventilation (LEV) in the form of moveable capturing hoods but, to achieve efficient capture, this type of ventilation must be positioned close to the fume source and moved as welding progresses, although in practice re-location may not always occur. Alternatively, control may be exercised using a low volume high velocity system (LVHV), fitted either to an existing welding torch or manufactured as an integral part of a torch. This type of system is commonly referred to as ‘on-gun’ extraction. Its primary benefit is that the extraction is always positioned close to the fume source and that it extracts less air than traditional moveable capture hoods. However, welders complain that the high velocity of the extracted air can remove the shielding gas and, hence, compromise weld metal integrity.
Following tests to evaluate the effect of extract nozzle position, the capture efficiency of an integrated on-gun system was measured during bead on plate and horizontal/vertical fillet welding both in the flat and in position. Weld metal integrity was assessed by examining the welds produced during testing for porosity. Other factors such as ergonomics and operability were not assessed.
The work showed that the integral on-gun fume extraction system evaluated provided efficient fume capture, without compromising weld metal integrity, and that the system was easy to optimise. However, some ambiguities remained regarding the capture efficiencies achievable during fillet welding in the flat and further work is required before the use of on-gun extraction can be recommended for this particular welding configuration.