Peter J. Hewitt

The effects of welding parameters on ultra-violet light emissions, ozone and CrVI formation in MIG welding

This paper describes the relationships between ultra-violet emission, ozone generation and CrVI production in MIG welding which were measured as a function of shield gas flow rate, welding voltage, electrode stick-out and shield gas composition using an automatic welding rig that permitted MIG welding under reproducible conditions. The experimental results are interpreted in terms of the physico-chemical processes occurring in the micro- and macro-environments of the arc as part of research into process modification to reduce occupational exposure to ozone and CrVI production rates in MIG welding. We believe the techniques described here, and in particular the use of what we have termed u.v.-ozone measurements, will prove useful in further study of ozone generation and CrVI formation and may be applied in the investigation of engineering control of occupational exposure in MIG and other welding process such as Manual Metal Arc (MMA) and Tungsten Inert Gas (TIG).

Occupational Health in Metal Arc Welding

The physical and often acute effects associated with metal arc welding, such as death by electrocution or physical injuries in the workplace are well recog nised. Increasingly today, attention is focused upon chronic effects, in particu lar cancer risks in welders. This review aims to address these concerns; put the risks into perspective and direct the reader to the means of assessment and control. Attention is drawn to the activities of Commission VIII International Institute of Welding which, through its various working groups, is charged with reviewing world-wide publications on health and safety in welding and with the issue of authoritative statements. The mechanism of gas and fume generation from welding processes is described. Fume particle size and mor phology in relation to inhalation and effects within the body are addressed. Epidemiology studies on cancer and other risks are reviewed. Strategies for the assessment and control of risks from metal arc welding are considered, taking due note of international movements on legislation and standardisation.

The Evolution of Hexavalent Chromium in Metallic Aerosols

Evidence is presented that fumes generated from stainless steels by high temperature processes, can continue to evolve chemically for several minutes. In some cases their hexavalent chromium content appears to rise to a maximum some time after formation of the aerosol and then partly decay again. This finding has important implications for the monitoring of metallic aerosols produced, for example, during the manufacture, cutting, grinding and welding of chromium alloy steels.

Pneumoconiotic effects of welding-fume particles from mild and stainless steel deposited in the lung of the rat.

Rats were exposed to single periods of inhalation of fumes generated by arc welding. Two processes were compared: either manual metal arc (MMA) using flux-coated mild steel (MS) electrodes or metal inert-gas (MIG) welding with stainless steel (SS). Widespread but small deposits of fume particles were cleared effectively from alveoli and airways. Peribronchial and subpleural aggregates of particle-laden macrophages remained. More massive and persistent lung-burdens were established by intratracheal administration of suspensions of fume-particles (10 mg and 50 mg, single doses).Initial pneumonitis was attributed to irritant gases or soluble toxic components of particles. MIG-SS particle deposits were more persistent and lesions more severe, inhibition of phagocytosis or clearance and damage to epithelial cells being associated with possible toxic effects in macrophages. Both types of particle caused alveolar epithelial thickening, with proliferation of granular pneumocytes and exudation of lamellar material. Foam cells appeared in alveoli.Long-term effects (80–300 days) involved formation of nodular aggregates of particle-laden macrophages. Giant cells were formed. Nodules containing MIG-SS material were irregular and surrounded by collapsed and thickened epithelium. Soluble chromium or nickel constituents are cited as probable active agents producing effects resembling those of cytotoxic non-fibrogenic dusts, e.g., soluble silicas. MMA-MS particles produced low-grade fibrotic (collagenised) changes.

An investigation of the experimental induction of hypersensitivity in the guinea pig by material containing chromium, nickel and cobalt from arc welding fumes.

Sensitization of guinea pigs by chromium, cobalt and nickel was compared by four methods. The most effective was the maximization test of Magnusson and Kligman. Sensitizing properties of particles from fumes of either manual metal arc (MMA) or metal inert gas welding were demonstrated. Potent sensitization was attributed to chromium.