A range of face masks could all potentially help reduce Covid-19 transmission, a study shows.
The distance and direction travelled by air expelled when a person breathes or coughs when wearing different face coverings was measured by a team led by engineers at the University of Edinburgh, using a technique called Background Oriented Schlieren imaging.
Measurements were taken from people wearing different face coverings while standing or lying down, and from a manikin connected to a cough-simulating machine.
Researchers found that all face coverings without an outlet valve reduce the forward distance travelled by a deep breath out by at least 90 per cent.
Surgical masks and the tested hand-made masks were found to limit the forward flow of a breath out, but also generate far-reaching leakage jets to the side, behind, above and below. Heavy breathing and coughing, in particular, were shown to generate intense backward jets.
Only masks that form a tight seal with the face were found to prevent the escape of virus-laden fluid particles, the team says.
Researchers found that full-face shields worn without masks enabled the release of a strong downward jet.