A correctly fitted P2/N95 respirator will block 99% of total viral influenza particles, but effectiveness drops to 66% if poorly fitted (e.g. not matched to the size and shape of the face). A poorly fitted P2/N95 mask performs little better than a poor fitting surgical mask.
Fit checking is the appropriate minimum standard at the point of use for healthcare workers using P2/N95 respirators. Fit checking is required when using a P2/N95 respirator to treat low risk and medium risk patients. Fit checking is performed by the practitioner every time they put on a P2/N95 respirator to ensure it is fitted correctly, and air is not leaking around the perimeter of the mask. A good seal must be achieved over the bridge of the nose and mouth, with no gaps between the respirator and face. Facial hair (beards and stubble) prevent an air-tight seal being obtained. No clinical activity should be commenced until a satisfactory fit has been achieved with the respirator.
The following Queensland Health PowerPoint presentation describes a fit-check procedure for a P2/N95 respirator:
https://www.health.qld.gov.au/clinical-practice/guidelines-procedures/diseases-infection/infection-prevention/transmission-precautions/p2n95-mask
Fit-testing is carried out to select the ideal respirator for each individual. A risk-management approach should be applied to ensure that staff working in areas with a significant risk of exposure are professionally fit -tested and are trained in how to correctly use the respirator including performing a fit-check at the time of use. Fit testing is conducted by an appropriately trained technician, using a qualitative or quantitative method to evaluate the fit of a specific make, model and size of respirator on an individual. The test verifies that the mask has achieved an adequate seal and that this seal is being maintained in reasonable challenge conditions such as when deep breathing, talking, when the head moves or when exertion occurs. No high-risk patient in the context of COVID-19 should be treated without a properly fit-tested respirator.