Respiratory protective devices with filters - Effect of the environmental conditions of storage and use on the performance of the filters

Filters used in respiratory protective devices come in two categories: electret filters, used mainly in manufacturing disposable masks (made of electrically charged polymer fibres); and glass fibre filters, to be found in pleated form in cartridges (non-charged microfibres).
This study concerns identifying the environmental conditions of storage and use of these filters that can influence their performance. It constitutes a preliminary step in establishing a protocol for accelerated ageing of such filters.
The experimental approach consisted in measuring penetration (ratio of particle concentration exiting from the filter to particle concentration entering it) when new, and after exposure to an external parameter and the electric fields in the vicinities of the filters, in particular for electret filters. This study made it possible to verify that variations in relative humidity and temperature over the ranges recommended by manufacturers, did not generate any reduction in the efficiency of the filters. The same applies for storing masks equipped with filters in the vicinity of machinery generating high electromagnetic fields and during accidental electrostatic discharges into the air in the vicinities of the filters.
Of all of the parameters studied, only forced neutralization generated a significant reduction in the filtering efficiency of the electrets filters. The charges carried by such filters and that impart their very high level of performance to them are unstable. Thought is currently being given to these electrostatic effects in the course of work in updating the standardized protocols for testing such filters.