To minimize worker exposure to nanoparticles, a team of researchers has developed a methodology to assess the effectiveness of respiratory protective devices (RPDs) by reproducing, in a laboratory, conditions of exposure to particles of various sizes. Using an experimental test bed fitted with an air purification device, the scientists analyzed the performance of N95 filters, the type most commonly used; in addition, they studied the effect of air flow and particle size on the penetration of particles through the RPD, and the effect of duration of use and relative humidity on the efficiency of the filtration. The filters were tested at high airflow rates, specifically, constant flow rates of 85, 135, 270 and 360 litres of air per minute.

The laboratory tests revealed that increasing the air-flow rate reduced the efficiency of the N95 filters to a level below the critical threshold of 95%. The researchers also observed that at a constant air-flow rate, filter efficiency decreased when relative humidity increased, especially when smaller-size particles were present. On the other hand, N95 filter performance was higher when exposure time increased, something that could be explained by the formation of aggregates of particles on the surface of the filter. "Though more research is needed, given these results it seems that more precise guidelines should be developed for the selection and use of RPDs if we are to ensure a high level of respiratory protection for those exposed to nanoparticles in factories and laboratories", said researcher Ali Bahloul, the researcher in charge of this experimental work at the IRSST. Note that these results are consistent with one of the recommendations of the Best Practices Guide to Synthetic Nanoparticle Risk Management, namely, that use of the N95 filter may be acceptable in cases where the risk has been quantified and is relatively low, but that its performance decreases in situations requiring a lot of effort on the part of the worker. Research in progress at the IRSST will allow us to verify the validity of these results by simulating the breathing of workers exposed to tasks of varying intensity.

Note that inhalation is the most common route of exposure to nanoparticles, and that the filtration method for controlling this exposure is simple and widespread. Funded by the Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST) and NanoQuebec, the study is helping to build the knowledge that will protect workers. When inhaled nanoparticles are compared to similar but larger particles, it will be seen that a greater proportion of the nanoparticles penetrate the lungs; also, translocalization may occur to other parts of the body, such as the bloodstream and other organs.

To view this study free of charge, click on the following link: http://www.irsst.qc.ca/media/documents/PubIRSST/R-754.pdf.

-30-

Source
Jacques Millette
Public Affairs Manager
IRSST