These FFP3 NR (D) face masks are intended to protect against solid and liquid particles, according to the UNE-EN 149:2001+A1:2009 standard. They are suited to protect against extremely toxic harmful materials in concentrations up to 50x0EL or 20xAPF. OEL: Occupational Exposure Limit. APF: Assigned Protection Factor. (D): dolomite clogging test for a more comfortable breathing.