CHICAGO • The risk of exposure to the coronavirus on flights is very low, a United States Department of Defence study released on Thursday found, a positive sign for the airline industry as it tries to rebound from the pandemic's crushing effect on travel.

When a seated passenger is wearing a mask, an average 0.003 per cent of air particles within the breathing zone around a person's head are infectious, even when every seat is occupied, it found.

The testing assumed only one infected person on the plane and did not simulate the effects of passenger movement around the cabin.

The study, conducted aboard United Airlines Boeing 777 and 767 aircraft, showed that masks helped minimise exposure to infection when someone coughed, even in neighbouring seats.

About 99.99 per cent of particles were filtered out of the cabin within six minutes due to fast air circulation, downward air ventilation and filtration systems on the aircraft.

It estimated that to receive an infectious dose, a passenger would need to fly 54 hours on a plane with an infectious person.

United, which also provided pilots for the test, took pains to present the results in its favour. "These results... mean your chances of Covid exposure on a United aircraft are nearly non-existent, even if your flight is full," said its chief customer officer Toby Enqvist.

The study was led and funded by Transportation Command, which operates Patriot Express flights that use commercial planes like United's for members of the military and their families.

The research over six months involved 300 tests over 38 hours of flight time and 45 hours of ground testing. Particles the same size as the coronavirus were released across the cabin by section, each of which had 42 sensors representing passengers who could potentially come in contact with the particles.

Each test released 180 million particles - the number of particles that would be produced by thousands of coughs.

REUTERS