In the course of the Covid 19 pandemic, protective masks are on everyone's lips - and now also in front of everyone. The various initiatives for the production of improvised masks and not least the introduction of a compulsory wearing of masks led to a broad discussion about the most diverse materials as protection against infections. Due to the scarcity of reliable protective masks for hospital and nursing staff, the question of the recommended wearing time is also being intensively discussed.
Change mask in case of moisture penetration - but how quickly does that happen?
For effective protection, not only the filtration properties of the material used are important. It is known that the protective effect (filter efficiency) decreases with increasing moisture in the material. Moisture and body heat also favour increasing germination on the side of the wearer. At the latest when the mask is completely soaked through, the mask must be changed, because then there is a risk of an infection bridge between the wearer and the environment. This applies to the efficient masks for self-protection, but even more so to the simpler variants for external protection. This is because droplets can be flung into the environment from the outer surface of the soaked mask when coughing or sneezing.
Simulations for efficient use of masks
If there is a recommended wearing time for a mask (e.g. by the manufacturer), it is usually a guide value. How quickly and to what extent the mask is soaked through depends mainly on the physical effort involved in wearing it. The period of time cannot be deduced in a simple way from the physical strain on the wearer, which usually varies over time. A visual inspection of the mask is usually not possible without outside help and is not reliable enough to determine if the mask is wetted.
With the help of adapted models and simulations, researchers at the Fraunhofer ITWM are working on a better prediction of the duration of wear, which takes into account the intensity progression of the physical load and thus supports a safe and optimal use of the existing masks. The results should lead to a timely change of masks and at the same time counteract the waste of masks by changing them too early. This enables clinics and care facilities, for example, to plan their requirements better, taking into account not only the necessary protection classes but also the individual job profiles of the employees.
Results also relevant for product development after the corona crisis
»These developments are relevant for product development beyond the current pandemic,« says Dr. Ralf Kirsch of the Fraunhofer ITWM, »because, for example, in the case of multilayer filter materials, we can predict optimal combinations for the respective application (protection class, self or third-party protection) and various activity profiles. This greatly reduces the time-consuming examination of prototypes«. Kirsch heads the Filtration and Separation team and has been working for many years on the mathematical modelling and simulation of various filters.