Inter-relationship between ultraviolet, ozone and hexavalent chromium in metal inert gas (MIG) welding process.
Welding is a common metal fabrication process within industry. Epidemiology
suggests that welders as an occupational group demonstrate slight, but significant,
increased risks of respiratory ill-health. This might be expected as welding processes
often present high levels of occupational exposure to oxidising gasses and weld fumes
which are often inadequately controlled through local exhaust ventilation or personal
respiratory protection because of high costs and the burden of worker participation.
Fundamental control strategies of occupational hygiene encourage development and
use of engineering controls as the best means to optimally control occupational
exposure. However, engineering controls have not yet been successfully developed to
control occupational exposure to welding fume and gases. This thesis investigates the
interrelationships between ultra-violet radiation (UV). ozone (0:;). and hexavalent
chromium (CrVI) in metal inert gas (MIG) welding in order to investigate possible
methods to control occupational exposure to welding fume and gases by engineering
Past studies of occupational ill-health in welders are reviewed as is the currently
understanding of the physico-chemical principles by which the various components of
welding fume evolves. Experiments were designed to investigate the mechanisms of
formation of UV, 0 3 and CrVI formation from which a number of possible control
strategies were developed further. Among these results emerge two process
modifications with exciting potential to reduce two toxic components. 0, and CrVI ,
in stainless steel welding fume and gas. The addition of trace amounts of Zinc to
chromium containing steel wires virtually eliminates all 0, and significantly reduces
hexavalent chromium within the weld plume. As Zn is a volatile metal, it does not
contaminate weld quality but increases the zinc oxide le\els in the fume slightly. A
second method developed in this thesis involves the addition of a dual shield gas
shroud containing reducing gases such as C2H .. to remove 0, and consequently.
reduce Cr(VI) levels. Preliminary results suggest that these methods can be used
separately. or in combination, to provide a practical means of controlling occupational
exposure to two of the more toxic components of welding fume and gases.
This thesis describes in details the experiments and results culminating in successful
preliminary development of engineering controls for 0 3 and CrVI through process
modification of the stainless steel MIG welding process. Further work for further
development of these methods is outlined and funding to extend this area of applied
research is being actively pursued with the support of major UK industry.