How clean is the air on planes?
Because the virus is still relatively new, there’s little data on how it can spread between air passengers. But a 2018 study from Atlanta’s Emory University tried to model the transmission of other respiratory illnesses between crew and passengers moving around an aircraft – and suggested they are unlikely to be transmitted via air to anyone further than one metre from an infectious person. ‘Thus,’ it concluded, ‘transmission is limited to one row in front of or in back of infectious passengers.’
Thanks to top-of-the-range ventilation systems, it should be noted that the air on planes is inherently very clean. (A panel of UK experts recently compared it to the air in an operating theatre.) Air is taken from outside the aircraft and mixed with recycled air from the cabin, which has been passed through an HEPA (high-efficiency particulate air) filter similar to those used in hospitals. The current virus is about 125 nanometres in diameter – well within the particle size range (10 nanometres and above) that the filters can capture.
The flow of air is also designed to reduce the risk of infection on board: it flows vertically from above passengers’ heads before being released into the atmosphere via exhausts beneath your feet.
Aircraft manufacturers have now started publishing their own research into the transmission of the virus. A recent joint publication by Airbus, Boeing and Embraer, for example, found in a series of simulations that airflow systems on their aircraft were largely effective in controlling the movement of particles and limiting the spread of viruses. Separately, Boeing found that the combination of their cabin design and airflow system helped created the equivalent of two metres’ physical distance (say, in an office, bar or restaurant) between every passenger – even on a full flight.
That’s the good news. But while the ventilation systems may be effective, researchers say they cannot prevent all infections. The flow of air is constantly disrupted by crew moving down the aisles and passengers leaving their seats. And according to Dr Tang, the majority of infection during a plane journey will stem from close-range, face-to-face conversations (which are unaffected by the plane’s internal airflow).
‘The ventilation system tries to stop transmission front to rear,’ he says. ‘But it’s not so effective at preventing transmission laterally. If you’re talking to someone right next to you, that may not be very safe, because their air will reach you before it gets filtered by the circulation system in the plane.
‘The problem is that people sit so close together, and the effects of the ventilation system don’t normally kick in until the exhaled air from each passenger has been circulated somewhat.’ And, of course, there’s no way to be sure that your fellow passengers aren’t infected.