Annual holiday time is approaching for many of us. Which means crystallising our views on mask-wearing for when we travel. In particular, are you going to wear a mask, as a Covid-19 preventive measure, on the flight to your holiday in the sun?
Of course, the choice may not be yours to make. Aer Lingus and Ryanair continue to require mask wearing while on board their aircraft. As do Emirates, Etihad and Air Canada. But following a recent court ruling most of the main US airlines have dropped mandatory mask wearing. Along with British Airways, they leave the decision on whether to wear a mask to each passenger.
Where there is a choice, an important consideration is the issue of ventilation and air quality.
Recirculate
All commercial jet aircraft built after the late 1980s recirculate about 50 per cent of the air in the cabin, mixed with outside air, which is free of micro-organisms at cruising altitude. The recirculated air passes through a series of filters 20–30 times per hour. In most newer-model airplanes, the recycled air passes through high-efficiency particulate air (Hepa) filters, which capture 99.9 per cent of bacteria, fungi, and larger viruses or virus clumps. The Sars-CoV-2 particle diameter ranges from 0.06 to 0.14 µm; however, the droplets and aerosols the virus travels in are larger than 5–10 µm in size and would be captured by the Hepa filters. Furthermore, air generally circulates in defined areas within the aircraft, thus limiting the radius of distribution of pathogens spread by small-particle aerosols. As a result, the cabin air environment is not conducive to the spread of most infectious diseases.
So how safe is the air on a plane?
Filters
The risk of being exposed to an airborne bug on a plane is lower than in many other enclosed spaces because of the filters and more frequent air exchange. The aircraft cabin airflow is laminar, with vertical movement downward from top to bottom. Longitudinal airflow (from forward to back) is minimal, further reducing the risk of respiratory microbes spreading on a plane.
In a major piece of research, published in October 2020, the US Military Transportation Command released the results of its commercial aircraft cabin aerosol dispersion test, the largest such experiment to date. Performed on Boeing 767-300 and Boeing 777-300 wide body aircraft using a 100 per cent seating capacity model, there was a minimum reduction of 99.7 per cent of 1 µm virus aerosol spread from the index source to passengers in the next seat. The model showed no aerosol transmission occurred during 12- hour flights. However, potential droplet or contact transmission was not measured.
The authors say the study indicates that the airplane environment significantly reduces the exposure to aerosol generated by passengers, especially when compared to other indoor environments. However, they warn that the “current established scientific understanding of Sars-CoV-2 transmission dynamics is not sufficient to calculate definitive Sars-CoV-2 transmission risk from these measurements of aerosol transport”.
Passenger movement
A number of other unknowns make it difficult to recommend a no-mask policy when flying. How does passenger movement on a plane contribute to increased transmission risk? And are you flying from an area with high levels of Covid-19 infection?
Many infectious disease experts say they will continue to wear masks while flying. In particular, they recommend using a non-valved N95 mask. Although masks are not 100 per cent effective, wearing them does decrease viral spread.
Wearing a N95 mask is something I plan to do when flying this summer. And being aware that travel is a continuum is important. You may be at greater risk of infection at check-in, in security lines or when passengers are packed together in the boarding tunnel.
The science remains uncertain; it’s probably best to adopt a layered approach to infection risk on your valuable time away.
mhouston@irishtimes.com