Hi all, I have spent hours looking at this, so hopefully someone can help? Does anyone have the technical spec for what constitutes a P3 filter please e.g. the pore size/grams/m3 or whatever measurement is commonly recognised. We are trying to get bespoke filters made for cab ventilation systems and when we say we want them to a P3 standard people look blankly at me, so I need to quantify what P3 means. I hope that, makes sense? Many thanks rob.

Respiratory protective devices — Filtering half masks to protect against particles — Requirements, testing, marking BS EN 149:2001+A1:2009