Face masks release water vapour but where does it go? An early observational study
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Abstract
Objectives
The aim of this observational study was to demonstrate the behaviour and trajectory of exhaled material from an individual wearing an FFP3 mask. Valves allow material release, but we theorised that valve design may direct material downwards towards patient and surrounding environment.
Limiting transmission of diseases with aerosolised spread is a current and serious concern within healthcare worldwide. Filtering face piece masks (FFP) are an essential piece of protective equipment when treating patients with ongoing infection. However, valved masks in other settings such as elective theatre and by the general public may have unforeseen negative effects.
Design
A heating coil-based vaporiser was used to produce visible water vapour. A healthy test subject was filmed wearing a variety of different masks and exhaling the water vapour.
Results
Flexible pleated and solid-shell FFP masks direct exhaled material downwards in plumes exceeding 25 cm. Duckbill-shaped masks appear to direct exhaled vapour laterally, with a smaller plume. The effect is influenced by mask design and type of valve. Fluid repellent surgical masks reduce material directed downwards, and when used in conjunction with an FFP3 mask, appear to reduce the size and density of the exhaled vapour plume. The use of a visor was ineffective in reducing plume expulsion.
Interpretation
A properly fit-tested FFP3-rated protective mask may only moderately limit expulsion of aerosolised particles from asymptomatic healthcare workers to patients, particularly in cases where procedures are being performed in close proximity to patients or in cases where mucosal surfaces are exposed. Further research in this area is needed.
Article activity feed
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SciScore for 10.1101/2020.08.09.20154435: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement not detected. Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable A healthy clean-shaven male test subject in his 20s (non-smoker, no known respiratory illnesses, no current medications, average peak expiratory flow of 720 l/min) was used to demonstrate the effects of each mask. Table 2: Resources
No key resources detected.
Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:We are aware of the …
SciScore for 10.1101/2020.08.09.20154435: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement not detected. Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable A healthy clean-shaven male test subject in his 20s (non-smoker, no known respiratory illnesses, no current medications, average peak expiratory flow of 720 l/min) was used to demonstrate the effects of each mask. Table 2: Resources
No key resources detected.
Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:We are aware of the limitations of these results due to the absence of precision measurements, singular tests without repetition and variability in tidal volumes and force of exhalation. To an extent, these will have been minimised by using the same test subject and through attempting to standardise the evaluation protocol. It is difficult to draw definitive conclusions beyond comparing the vapour plume between the tests. In doing so, the images starkly demonstrate that in normal conditions, even in the absence of forced exhalation, the flutter valve permits exhaled material to enter the surrounding environment. Previous studies have demonstrated that fluid-repellent surgical masks are effective at directing exhaled material laterally and away from the patient15,26. Based on our results some FFP3 masks may instead be redirecting the exhaled material towards the patient. This may represent an increased risk of infection in cases where mucosal surfaces are exposed, e.g. during surgery or intubation. Further studies are mandatory to confirm and expand on our findings.
Results from TrialIdentifier: No clinical trial numbers were referenced.
Results from Barzooka: We did not find any issues relating to the usage of bar graphs.
Results from JetFighter: We did not find any issues relating to colormaps.
Results from rtransparent:- Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
- Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
- No protocol registration statement was detected.
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