Standard N95 face mask dust filters were found not to perform well enough against particles < 100 nm effective diameter.
Evidence from:
A Balazy et al. Ann. Occup. Hyg. (2006)Vol. 50(3) p. 259–269
“Manikin-Based Performance Evaluation of N95 Filtering-Facepiece Respirators Challenged with Nanoparticles”
N95 filters were tested for their ability to exclude nano particles (sodium chloride). Standard procedures require that penetration in excess of 5% be regarded as failure.
Particle diameters ranged from10 to 300 nm diameters with a mode at 30 nm. At flow rates of 85 l/min there was significant penetration of nanoparticles. Penetration was reduced for the so-called high fit masks. There were no failures at 30 l/min. Penetration peaked at 40 to 50 nm.
30 l /min represents light work load, 85l/min represents heavy work load. Filters must pass the 85l/min condition.
Comment
The N95 filters tested here were, by current standards, not adequate.
The question that is not answered is whether or not current standards are the right standards for nano particle exposure. In particular, for which size of nanoparticle is protection needed?