Shedding of Particles from Masks

Particle Shedding Comparisons

During the course of particle counting experiments it was observed that the N95 showed much higher counts on initial tests that diminished with continued use. Analysis of that data suggested that this N95 was shedding fine particles from the filter matrix itself. To test for this, a new unused N95, an N95 used approximately 20 times and an ION Gaiter that had been laundered were fitted over the manikin. Particle counts were measured in a typical office environment with air composed of dust and microbial particles in the range of 0.1 to 1.0 microns. Prior to performing shed particle counting, each device was purged of any air or particles with in the matrix with 10L of air flow. Background readings were performed to count environmental air particles in two size ranges not filtered by each device and are recorded in columns 2 & 3 of the table below. Each device was then subjected to touching or tapping on the outside to simulate energy imparted in fitting and adjusting the device. Columns 4 & 5 in the table below show the particle counts over 1 minute of filtering after applying the shedding energy and after subtracting the background particle shredding from columns 2 & 3.  All devices showed some shedding with the new N95 shedding 10 times more particles than the ION Gaiter.  N95 respirators are constructed from spun, melt blown polymeric fibers that are bonded together with heat and chemical agents. In addition, some N95s may be treated with fire retardant agents and other chemicals to reduce moisture absorption, odor and to minimize microbial growth. Not all N95 respirators have been tested in this study nor do we know the chemicals used. To our knowledge the observation of particles shedding has not been investigated but perhaps this is a potential health concern that should be addressed particularly for workers required to wear these devices frequently.