The adequacy of user seal checking for N95 respirators compared to formal fit testing, a multicentred observational study

As part of a quality and safety initiative fit testing was provided for staff working in the intensive care units (ICU) at Epworth Richmond, Freemasons and Geelong. Respirator Allocation Staff were fit tested on one of the 2 brands of N95 respirators available for use and these were randomly chosen for each participant. The masks available were either the 3M N95 Healthcare Particulate Respirator and Surgical Mask 1860 Regular or Halyard Fluidshield N95 Particulate Filter Respirator and Surgical Mask Regular. Sensitivity Testing Using a 3M Qualitative Fit Test Apparatus, FT-30, a qualitative fit test was performed by a 3M trained tester for each participant. The subject placed their head within a 3M Test Hood wearing a N95 mask. The Sensitivity Test agent, Bitter ('Bitrex', Denatonium Benzoate, 3M FT-31), was sprayed directly into the hood device using the 1st 3M nebuliser device. This is a dilute form of the 3M Bitter ('Bitrex', Denatonium Benzoate) Test Solution. Up to 30 sprays were administered. The subject alerted the tester when they could taste the solution and this was recorded on the form. The subject was required to detect the solution prior to commencement of the test, i.e. pass the sensitivity test. A fail was inability to taste the solution at 30 sprays. The subject was offered the opportunity to return for a re-test on another day during another session. Issues were discussed with subject such as factors affecting taste, for example strong foodstuffs consumed prior to the testing. The hood was removed and the inside was wiped with an alcoholic wipe. A pass allowed the subject to proceed to fit testing. They cleaned their face with a face cloth and rinsed their mouth with water. After 10 minutes the subject returned to conduct the test. User Seal Check (USC) A user seal check (USC) is a internationally recognised means of assessing gross leakage of N95 respirators. 3M and Halyard each provide their own information on the details of the USC for their N95 respirators. Using the randomly chosen N95 respirator the staff member conducted an ‘unassisted user seal check’. A written copy of the manufacturers’ instructions for both types of respirators were placed in front of the subject on a table as reference if required. The tester observed the user seal check and made a note of any errors in their technique. The subject was asked if they felt the user seal was adequate and recorded a pass or fail. If the tester also observed critical errors in the user seal check i.e. poorly fitting mask, the unassisted user check was also recorded as a fail. A fail resulted in the tester performing an ‘assisted user seal check’ on the subject e.g. making adjustments to the strap and/or mask position. If despite the tester attempting to make adjustments and the fit was obviously inadequate the respirator was recorded as a fail. This assessment identifies any gross leakage which is felt as air leakage on the hands around any point of the respirator (as per manufacturer's instructions). An assisted user seal check fail resulted in the subject performing a user seal check on the other available mask. If either the unassisted or assisted user seal check failed on the 2nd mask the subject was offered another session to perform testing on the PAPR (CleanSpace® HALO). Fit testing commenced with a pass of the unassisted user seal check or assisted user seal check. Fit Test The subject continued to wear the respirator and placed their head in the same 3M Test Hood. The 3M Fit Testing Solution Bitter ('Bitrex', Denatonium Benzoate, 3M FT-32) was sprayed in the hood using the 2nd 3M Nebuliser device on regular timed occasions. The participants conducted a series of 7 breathing exercises, lasting 1 min each. The test agent is used to detect leakage via the respirator interface seal of the mask by detection of a bitter taste. If during any of the exercises the bitter solution was detected the mask was deemed to have failed and the test was ceased. For staff failing the initial respirator type the alternative N95 respirator available was then tested (user seal check and fit testing). The overall time allocated for each fit testing session was approximately 20 min. Staff failing fit testing on both N95 respirators were offered a repeat session with a Powered Air Purifying Respirator (PAPR), specifically CleanSpace® HALO. Quantitative Fit Testing For a minority of staff who are unable to perform the test due to failure of the sensitivity test with the Sensitivity Test Agent Bitter ('Bitrex', Denatonium Benzoate, 3M FT-31), a further session was offered using the quantitative fit testing with the TSI PortaCount 8040. Briefly this is a particle counter device that counts the number of particles of a predefined particle size inside and outside the mask. This calculates the ratio of particles known as a fit factor (>100 = pass). In this way the intent is to identify at least one successfully fitted respirator for each staff member.