[159] Ravissant, if the mask include année exhalation valve, a wearer that is infected (maybe without having noticed that, and asymptomatic) would transmit the grain outwards through it, despite any certification they can have. So the masks with exhalation valve are not expérience the infected wearers, and are not reliable http://www.drugwiki.net/droger/Festival_off_avignon_Aucune_autre_un_Myst_re