FFP masks have been a household name since the Corona pandemic. The 'filtering face pieces' are widely used to protect both themselves and others. Prior to the pandemic, FFP masks with exhalation valves were the most commonly used. These masks provide extra comfort during heavy work because, as the name suggests, the valve makes it easier to breathe out. However, the exhaled air is not filtered by the valve. The question for COVID-19 is therefore whether the masks are also suitable for protecting other people, i.e. the aforementioned third party protection.
This question was also asked by the National Institute for Occupational Safety and Health (NIOSH). The American institute conducted a study to determine how many aerosols are released into the ambient air through an exhalation valve. FFP masks with and without exhalation valves were compared with each other and with other types of masks. We have summarised the results and background below.
Background: Respirator leakage
Respirators need to fit well and, above all, be tight to provide protection. This can be seen in the example of the fire service: The Barterlass prohibits the wearer from having a beard, as facial hair can interfere with the leaktightness of the mask. But even without a beard, not every mask fits perfectly. Different head and face shapes, for example, mean that there are small gaps between the mask and the face. This is not usually a problem: Depending on the type of mask, a certain amount of leakage is acceptable, and specialists use a risk assessment to decide when to use which mask.
The decisive factor is that breathing air can always escape through the leakage. It is therefore incorrect to assume that only FFP masks with an exhalation valve allow unfiltered air to escape from the mask. Nevertheless, the question arises whether these masks in particular are less suitable for pandemic control than other models. There is no clear answer yet. This is partly because studies of personal protective equipment are primarily concerned with self-protection, not protection from others. The NIOSH study is a first attempt to fill this research gap.
The NIOSH study: FFP masks put to the test
The study tested 13 FFP models from ten different manufacturers. A total of 1,125 tests were carried out. A special respirator tester was used to determine how many aerosols penetrate the mask when the airflow from the outside varies in strength. An additional test was added to this standard procedure. This also looked at how many aerosols from the inside of each mask reached the outside. The following test results could be observed:
- FFP masks without an exhalation valve retain most aerosols. Most of the aerosols accumulate inside the mask and do not escape into the environment.
- Ordinary fabric community masks allowed most of the test aerosols to pass into the ambient air. This was not only due to materials such as plain cotton, but also to poor sealing.
- FFP masks with exhalation valves were in the middle of the test results. Again, a large proportion of the test aerosol remained inside the mask.
- In an emergency, the exhalation valve can be closed from the inside with surgical tape. Taping from the outside or covering the valve with a surgical mask works less well.
The results are subject to a number of limitations and should be interpreted with caution. For example, the particles in the test aerosol were all in a very small size range. Larger particles such as spit droplets may behave differently. In addition, it has not been investigated how masks react to increasing moisture penetration by breathing air. Strong air currents, such as those caused by coughing or sneezing, were also not studied.
Conclusion: What do the results mean?
The NIOSH study shows that even FFP masks with an exhalation valve can reduce the amount of aerosols released into the environment by the wearer. However, the results are from a controlled laboratory environment and should be interpreted with caution. Caution should still be exercised with these models. They are not suitable for use in, for example, retirement homes or nursing homes. Please always follow local guidelines and regulations.
Further information
NIOSH Studie: Filtering Facepiece Respirators with an Exhalation Valve
Hinweise zur Verwendung von FFP Masken des Robert Koch Instituts
