inclusion criteria: * full-time employees (defined as direct patient care for more than 24 hours weekly) and work primarily at the study site or co-participants (more than 75% of working hours). * professionals working in emergency departments, icus, and other hospital settings exposed to sars-cov-2. * negative clinical and laboratory results for sars-cov-2 infection (negative rt-pcr). * have previous experience using n95 pff2 respirators.

inclusion criteria: * full-time employees (defined as direct patient care for more than 24 hours weekly) and work primarily at the study site or co-participants (more than 75% of working hours). * professionals working in emergency departments, icus, and other hospital settings exposed to sars-cov-2. * negative clinical and laboratory results for sars-cov-2 infection (negative rt-pcr). * have previous experience using n95 pff2 respirators.

inclusion criteria: - full-time employees (defined as direct patient care for more than 24 hours weekly) and work primarily at the study site or co-participants (more than 75% of working hours). - professionals working in emergency departments, icus, and other hospital settings exposed to sars-cov-2. - negative clinical and laboratory results for sars-cov-2 infection (negative rt-pcr). - have previous experience using n95 pff2 respirators.

inclusion criteria: - full-time employees (defined as direct patient care for more than 24 hours weekly) and work primarily at the study site or co-participants (more than 75% of working hours). - professionals working in emergency departments, icus, and other hospital settings exposed to sars-cov-2. - negative clinical and laboratory results for sars-cov-2 infection (negative rt-pcr). - have previous experience using n95 pff2 respirators.

inclusion criteria: - full-time employees (defined as direct patient care for more than 24 hours weekly) and work primarily at the study site or co-participants (more than 75% of working hours). - professionals working in emergency departments, icus and other hospital settings exposed to sars-cov-2. - negative clinical and laboratory results for sars-cov-2 infection. - have previous experience using n95 pff2 respirators.

inclusion criteria: - full-time employees (defined as direct patient care for more than 24 hours weekly) and work primarily at the study site or co-participants (more than 75% of working hours). - professionals working in emergency departments, icus and other hospital settings exposed to sars-cov-2. - negative clinical and laboratory results for sars-cov-2 infection. - have previous experience using n95 pff2 respirators.