Particle size and metal composition of gouging and lancing fumes

Abstract

Background: Gouging (used for preparation of the weld groove) and lancing (severs or removes metal) processes during mining maintenance operations liberate fumes of unknown particle sizes and metal composition. These fumes are formed when vaporised materials condense in cool air. These processes give rise to very fine solid particles of sizes usually smaller than 1 μm in diameter which will generally agglomerate to form bigger clusters of particles. Inhalation of such a “metal fume mixture” may lead to adverse health effects. Gouging and lancing, specifically, liberate fumes of unknown particle sizes and metal composition, as most studies only focus on welding fumes. Aims and objectives: A field study was conducted to determine the particle size fractions as well as metal composition of fumes emitted during gouging and lancing processes. This study provided the necessary information to employers on what their workers are exposed to and therefore, how to prevent or control exposure to these fumes and this may improve occupational health and hygiene of workers utilising these gouging and lancing methods. The study also aimed to include metal fumes and particle fractions not previously included (such as nanoparticles) during respiratory exposure sampling. The determination of the particle size fractions and metal composition of the metal fume mixtures made it possible to determine the possible health effects associated with the inhalation thereof. Methods: Randomised side-by-side area samples were collected of metal cutting fumes liberated during gouging and lancing processes, respectively. These processes form part of maintenance work and was performed in three workshops at an open cast iron ore mine in South Africa. Samplers included the Institute of Occupational Medicine (IOM) sampler (inhalable fraction), a GK2.69 cyclone (thoracic fraction), an aluminium cyclone (respirable fraction), a Nanoparticle Respiratory Deposition (NRD) sampler (nano-size fraction) and an open-face filter cassette (particle size distribution). These samplers were mounted at a minimum height of 1.3 m and a maximum height of 1.7 m which is representative of the height of workers standing up by means of a randomised sampling station. Samples were collected 2 m from the source during gouging processes and at a range of between 5 and 10 m from the source during lancing processes. A total of 46 samples were collected during gouging processes (23 in the maintenance workshop and 23 in the mining contractor’s workshop) and 26 during lancing processes. Results: Particles in all fractions were present in the metal fumes emitted during gouging and lancing processes. Ambient workplace concentrations of the nano-sized fraction indicated a range of 1.01 – 3.40 mg/m3 in the workshops. A total of 26 metals were present in the various particle fraction sizes and included arsenic, chromium, cobalt, lead, manganese, mercury and nickel. Lead was mostly found during lancing whereas manganese and nickel were found in all of the workshops and fractions sampled. Lancing processes (x̄ = 32.3 nm) emit on average smaller particles than gouging processes (x̄ = 171.8 nm). The various fraction sizes did not statistically differ between gouging and lancing. Statistically significant differences were found between gouging and lancing for copper, iron, molybdenum and nickel emission, with copper, iron and nickel emission showing a higher concentration during gouging processes and molybdenum emission showing a higher concentration during lancing processes. In the nano-size fraction, the head nut liberated the highest mean ambient concentration level (2.46 mg/m3) and backhoe shovel 2 the lowest (1.74 mg/m3). Fumes emitted from backhoe shovel 1, the crusher liner and the axle liner contained the smallest particles with averages of 40.3 nm, 28.5 nm and 36.1 nm, respectively. Conclusions: Particle size fractions within the inhalable, thoracic, respirable as well as nano-size fractions were present in the metal fumes. Lancing could be considered more hazardous than gouging as mean particle sizes are smaller than particles emitted during gouging. Nanotoxicology is still an unfamiliar field and nanoparticles may cause detrimental health effects beyond the respiratory system. This indicates the necessity to include the nano-size fraction during future personal exposure assessments and monitoring in addition to inhalable and respirable sampling and may guide the mine to implement various control and safety measures, specifically for nanoparticles, to protect their workers’ health