Tukes investigated the filtration efficiency and breathing resistance of civil masks – significant variation in mask properties
The EU has set strict requirements for surgical masks and respiratory protective equipment. However, the EU has not had any common requirements for civil masks. Standardisation work for civil masks started at a European level in December 2020, and the work is based on a pre-standard issued last summer. To obtain background information and to form the basis of standardisation work, the Finnish Safety and Chemicals Agency (Tukes) has had civil masks available on the market tested and has investigated their filtration efficiency and breathing resistance. The results showed that there is significant variation in the properties of civil masks available for sale.
Tukes assigned the investigations from VTT in October 2020, applying the pre-standard for community face coverings. A total of 22 civil masks that have a different structure and material and were available for sale online and in shops were selected for the investigation. Of these, 20 were reusable and two were disposable. The materials used in the masks or their densities, or the chemical or any antimicrobial properties of the masks were not investigated during this project.
The purpose of civil masks is to reduce the spread of droplets from the user’s respiratory tracts to the surroundings. In addition to the filtration efficiency of the material, it must be ensured that breathing resistance does not make the use of the mask too heavy.
– “When preparing requirements, it is important to ensure that the mask reduces the spread of droplets to the surroundings as effectively as possible, while it does not make breathing unreasonably more difficult”, says Reija Sironen, senior officer at Tukes.
– “The study results provide data for standardisation work. Tukes is a product safety authority, which monitors the compliance of products with requirements, and does not issue any recommendations for the use of masks. However, the test results show that face masks can reduce the spread of droplets to the surroundings.”
A total of six masks designed for children were tested. According to the results, the breathing resistance and filtration properties of the masks did not differ from masks designed for adults.
Significant variation in the filtration efficiency of civil masks
According to the National Institute for Health and Welfare (THL), coronavirus primarily spreads by droplets when an infected person coughs or sneezes.
The study investigated the filtration efficiency of the materials used in face masks. The filtration efficiency value indicates how well the material used filters particles from breathing air. The filtration efficiency was measured within the particle size range of 0.1–5 micrometres (one thousandth of a millimetre). According to the pre-standard’s recommendations, the filtration efficiency value was reported in the test results using the particle size of 3 micrometres. The size of coronaviruses is usually 0.05–0.2 micrometres.
According to the results, the filtration efficiency of reusable masks was low, often under 30%, for particles of less than 0.2 micrometres. Therefore, the results confirm that civil masks do not protect their users from a virus infection. Instead, respiratory protective equipment is intended to protect their users.
The measurement results related to filtration efficiency also confirm that civil masks may reduce the amount of the largest droplets and sprays spreading from users to the surroundings. The filtration efficiency values of civil masks available on the market showed great variation with the particle size of 3 micrometres: 11, i.e. half of the investigated civil masks produced values of over 70%, while the values of very thin materials were under 10%.
Disposable fibre masks were at the top of the test, considering the combination of filtration efficiency and breathing resistance. For reusable masks, it was not possible to define any specific property or material that would show that a certain structural solution is much better than other solutions.
Large differences in breathing resistance values
The breathing resistance value indicates how much a material blocks the flow of breathed air. The higher the value is, the worse air flows through the material. The breathing resistance values of the materials of the studied civil masks showed great variation from one product to the next.
The breathing resistance value is only measured for the mask material, not the whole mask, and it does not, therefore, take into account the leaks from the side of a worn mask, for example, by the side of the nose or from the side of the mask. Even if the breathing resistance value of a mask material is high, the mask may not feel suffocating if air flows through the sides of the mask and the face. In this case, however, the mask is not tight.
The breathing resistance and filtration properties of a mask are affected by the density and thickness of the material used and the number of layers. In addition, it is important, considering the comfort of use, that the mask fits snugly on the face. Consumers should compare different masks to find the model that fits well on their face and that does not make breathing too heavy.
Standardisation work for civil masks has begun
In the summer of 2020, the European Committee for Standardization (CEN) prepared a pre-standard for the properties and testing of civil masks. The preparation of the pre-standard involved the countries that already had recommendations in place for civil masks. The pre-standard for civil masks is not obligatory like a law, and the threshold values defined in it are not mandatory. The pre-standard also presents several different methods for testing products. On the basis of the published pre-standard, a process has been started to process uniform technical specifications into a technical report; however, it is not a legal amendment.
Standards and technical reports are recommendations by nature. The authorities can use standards and technical reports for assistance when assessing whether a product meets a safety level set out in the legislation. Tukes participates in the activities of the working group, which is preparing the report. The test results of civil masks help to define requirements and test methods applied to them.
– “The tests were not primarily conducted from the point of view of market surveillance. Instead, their purpose was to obtain more detailed information about the properties of masks for the standardisation of civil masks”, Reija Sironen says.
Three different types of masks worn in front of the mouth and nose are available for consumers on the market: civil masks, surgical masks, and respiratory protective equipment. Masks have different purposes of use and are covered by different legislation. Tukes is responsible for the market surveillance of civil masks and respiratory protective equipment (RPE) intended for consumers. Tukes does not issue guidelines or monitor the use of masks or RPE. Recommendations for the use of civil masks are issued by the Ministry of Social Affairs and Health and THL.
Further information: Reija Sironen, senior officer, tel. +358 29 5052 016, [email protected]
Appendix: VTT customer report relating to the conducted study
Appendix: Received test results in graphs (in Finnish)
Further information about different RPEs and face masks