Dear Sir, B b I write to you expressing my concern about the welfare of dental professionals once we return to routine work in practices and hospitals. Coronavirus particles are between 0.06 m and 0.14 m[4] but what we must understand is that the way in which particles are trapped, or captured, when flowing through the layers of filter media can happen via several different mechanisms: inertial impaction, interception, diffusion or electrostatic attraction.