IRSST - Institut de recherche Robert-Sauvé en santé et en sécurité du travail

Granite Processing ─ Characterization and Control of Silica Dust Released by Polishing


The Eastern Townships (Estrie) and Montréal areas of Québec have many industrial facilities manufacturing granite products that contain crystalline silica (SiO2). The dust released during processing can have a high quartz content and therefore pose a serious health risk for exposed workers. Manual polishing, especially dry, presents the worst exposure scenario. Air movement generated by the rotating grinder pushes the dust in all directions. Larger particles settle due to the effect of gravity; however, fine and ultrafine particles are entrained into the whirlwind created by the emery wheel and tend to remain in the worker’s respiratory zone. Centrifugal force then sends the dust beyond the worker’s immediate area and into the general work environment. The higher the rotational speed of the grinder, the greater the dispersion of fine and ultrafine particles, contaminating areas even farther away. Workers in the immediate area are no longer the only ones exposed. In addition, the rotational movement presents an additional complexity for the source reduction system. Studies have already shown the inefficacy of installing an exhaust duct near the grinding process.

This study contributes to the advancement of knowledge needed to determine the means for source elimination and reduction of the crystalline-silica-containing fine and ultrafine dust released during granite processing. Source elimination and reduction of emissions are the best ways to ensure a healthy, safe work environment; personal protection equipment is the solution of last resort.

To find solutions that really work, we first conducted a laboratory study on characterization and control of the crystalline silica dust released from wet or dry polishing operations. Characterization was needed, since emissions control solutions depend on the grain size and concentration of the pollutants. Control measures involved changing certain work parameters (rotation speed, advancement speed, choice of wet vs dry polishing, quantity of water).

Two granite blocks were chosen for this study: one black and one white. Black granite has a very low crystalline silica content compared to white granite. The dry and wet grinding operations were performed with a machine-tool in a controlled environment. Observing just the grinding operation and without any control measures, the dust emission, dispersion and crystalline silica content were characterized according to the process parameters (speed, abrasive used, disk size, type of granite, dry or wet, quantity of water) and fine or ultrafine dust emissions. Out of a concern to avoid compromising the quality of the final product, the surface finish was also evaluated. The results show that black granite releases more dust than white granite, and the particles are more ultrafine than fine. Granite polishing releases mainly ultrafine particles.

Through laboratory and digital simulations, dust dispersion under disk rotation was then analyzed by observing a grinding operation with no movement of the grinding tool. By using particles released from a salt solution (NaCl), these simulations enabled the researchers to understand the effect of rotation on the dispersion of aerosols around the wheel, according to grain size and rotation speed. Ultrafine particle dispersion analysis shows that these particles are highly concentrated in the entire measured area, regardless of distance from the grinder.

Based on these simulations, three at-source reduction concepts were analyzed to determine their suitability for polishing operations. The concepts were as follows: (1) ventilation, (2) crankcase ventilation, 3) ventilation built into the disk. This analysis made it possible to determine the efficacy of these three concepts according to the ventilation parameters. At the same time, the behaviour of the particles was compared to that of a trace gas. Trace gas is an interesting technique for predicting dust behaviour and ventilation efficiency in a work space. The suction crankcase and the suction slots built into the disk provide an effective means of removing polishing dust.

To conclude, this study has yielded greater understanding of the mechanisms underlying the releasing and dispersal of particles from the wet or dry grinding of granite. The aim is to control the behaviour of fine and ultrafine dust, both through industrial processes and through workspace ventilation.


Additional Information

Category: Research Report
  • Ali Bahloul
  • Rafael Francisco Vanterpool Jorge
  • Abdelhakim Djebara
  • Victor Songmene
  • Mohamed Nejib Saidi
  • Jules Kouam
  • Marcelo Reggio
  • Fernando Villalpando
Research Project: 2010-0058
Online since: June 06, 2019
Format: Text