During machining metalworking fluid aerosol (MWF) is formed containing both particulate and semivolatile compounds harmful to health. Concentrations of single contaminants, such as oil mist, are usually well below the occupational exposure limits. Still, machinists have respiratory symptoms although the machining centres are usually equipped with air cleaners to purify the recycled air. Therefore, FIOH suggest the use of total alkanolamine concentration as an indicator for metalworking fluid aerosol exposure.
Studies performed in four metal machining companies shows that semivolatile compounds penetrates the conventional air filtering units used in machining centres. The aim of the study was to find out how the different air handling methods influenced the indoor air quality in machining shops.
Studied methods were: 1) the recirculation of the local exhaust ventilation air back to the workspace after particulate filtration, 2) leading the air from the local exhaust ventilation directly to outdoors, and 3) enhance the filtration by adding the filtration of volatile compounds to the existing air filtering systems.
The measured alkanolamine concentrations after HEPA filtering equipment were significantly higher (1.2 – 3.7 times) compared to the measured concentration in the general workplace air. Returning air from the local exhaust ventilations system back to the workspace air increased the contaminant levels and thus, increases the workers’ exposure. If the air from the filtering device was led outdoors, the concentrations of both alkanolamines and volatile organic compounds in workplace air decreased by 60-70%. However, this solution increases energy costs and hinders often needed modifications and enhancements of the processes on the factory site.
The results showed that the new type of multi-stage particulate filtration combined with treatment of volatile contaminants might be the best choice for the cleaning of the exhaust air of the machining centres.