A significant number of professionals subjected to high-risk situations have been infected by Covid-19, due to the lack of adequate respiratory protection equipment or poor marginal sealing adjustments. Then, the objective of this study is to determine if there are statistically significant differences in the level of respiratory protection of type IIR surgical face masks and filtering face masks, used with and without a peripheral sealing device, against the contagion of Covid-19 or other harmful biological agents. The proposed device is a thermoplastic resin ring composed of a reusable and biodegradable polylactic acid designed to be used in a healthcare environment. The individuals of the study will be submitted to qualitative fit tests, that meet current Ocupational Security and Health Administration (OSHA) standard. The mentioned qualitative fit test uses a sodium saccharin solution to evaluate the respiratory protection equipment in professionals in hospitals, emergency centers, and early childhood education centers.

The purpose of the research is to determine if there are statistically significant differences in the level of respiratory protection in situations of high risk against the contagion of Covid-19 or other harmful biological agents, in subjects who use filtering face pieces (FFP2) with or without a peripheral sealing device (AMS), Type IIR surgical face masks with or without a AMS, and subjects using the FFP2 filtering face mask simultaneously with the Type IIR surgical face mask. For this, a total of 210 individuals were selected from different environments in order to attain diversity, while controlling for representativeness bias. They were selected from the ADEMA University School - UIB, nursing staff from the Infectious Diseases Service at Son Espases University Hospital, 112 Emergency Service of the Autonomous Community of the Balearic Islands and the General Directorate of Planning and Centers of the Ministry of Education and Professional Training (Balearic Islands, Spain).

Participants were assigned to one of the 5 groups and subgroups, after accepting their participation in the study voluntarily and freely by signing the consent form approved by the CEI-IB.

To evaluate the adjustment of the respiratory protective equipment with and without the personalized peripheral sealing device (AMS), a sweet sensitivity test was performed with the 3M FT-10 Qualitative Fit-Test Kit (Saint Paul, Minnesota, USA), which complies with the current standards of the Occupational Security and Health Administration (OSHA) and according to the protocol described in Riutord-Sbert et al. (2021). During the qualitative fit test, a total of seven mobility exercises of 60 seconds each were performed, and the nebulizer was squeezed, every 30 seconds:

Phase 1 - Normal breathing Phase 2 - Slow and deep breathing Phase 3 - Breathing whilst moving the head to both sides Phase 4 - Breathing whilst moving the head up and down Phase 5 - Breathing spelling the alphabet Phase 6 - Breathing whilst moving up and down from the waist Phase 7 - Normal breathing

If the fit test was completed within 7 minutes without the individual having detected the sweet taste, the seal was considered optimal or adequate and the experiment was graded as APPROVED. If the subject detected the sweet test before seven minutes, the adjustment was considered inadequate and was scored as FAILED, noting the time it took to detect the sweet taste as established in the protocol of the 3M FT-10 Fit test (Riutord-Sbert et al. 2021).

Inclusion Criteria:

• people familiar with the use of face masks, absence of allergy or intolerance to sodium saccharin or materials used, absence of relevant systemic diseases, age between 18-65 years, absence of obvious facial hair and signing the informed consent.

Exclusion Criteria:

• people not familiar with the use of face masks, presence of allergy or intolerance to sodium saccharin or materials used, presence of relevant systemic diseases, presence of obvious facial hair and not signing the informed consent.