One of the criteria for a proper face mask is that it does not hinder the wearer’s capability to breathe. A mask that is very hard to breathe through will be uncomfortable for the wearer and may elicit undesirable behaviour such as taking off the mask.
To this end it is important to measure the breathing resistance a wearer may experience whilst wearing the mask, to ensure that breathing of the wearer is not hindered by the mask.
In the breathing resistance test, the pressure drop over a face mask is assessed during breathing in and out. This is performed according to the NEN-EN 149 7.16 norm.
In this test, a radial fan (Sanyo Denki 9BMB24P2H01) forces air through a face mask that is fitted to a 3d-printed dummy head enveloped in a silicone rubber layer to resemble the face skin. The fan is capable of providing a maximum static pressure of 490 Pa, which is more than sufficient to generate the maximum allowable pressure drop though a face mask. The volumetric flowrate is limited to a maximum of 200l/min to prevent the pressure sensors from overloading. Differential pressure sensors (Sensirion SDP816) measure the static pressure drop over the mask and the volumetric flowrate through the setup. The 3d-printed dummy head can be fitted at the air inlet or outlet so that both breathing in- and out conditions can be tested. It is also possible to clamp a piece of sample material such that a membrane of 40mm diameter is created. In this way, the pressure drop of a material can be assessed to check its suitability for face mask production.