Since the pandemic, an additional fear of catching COVID onboard while travelling came to the question. HEPA (High-Efficiency Particulate Air) filter has been the magic word when it comes to air purification from household air purifiers to not surprisingly, airliners. The European Air Purification classifications define a HEPA filter to be able to remove particles that are larger than 100-200nm in size from 85% up to 99.999995%. This standard, however, varies across the globe but the figures are not too far apart. Luckily, modern aircraft are equipped with HEPA filters in accordance with aviation regulations. Let us take a look into what HEPA means for us as passengers.
HEPA effectiveness against Viruses
According to a document published by IATA,
“HEPA or high-efficiency particulate air filters have similar performance to those used to keep the air clean in hospital operating rooms and industrial clean rooms. These filters are very effective at trapping microscopic particles as small as bacteria and viruses.”
Whilst this statement is reassuring, it does not cover the fact that not 100% of the viruses are filtered out. The diameter of a virus particle varies typically from 80-100nm while in extreme cases the range can be up to 20-500nm. It may be true that the air circulation system is highly effective as it takes approximately 3 mins to filter out completely the amount of air in the cabin on an Airbus aircraft. On an Airbus320, HEPA filtered air is distributed in 3 types of vents: the outer skin outlet above the window, the outlet above the overhead luggage compartment, and the adjustable knob outlet above each seat. This design ensures that heavier particles will not be stirred up and will drop to the bottom along with the airflow and be collected by the gap between the outer skin of the cabin and the floor panel. The air collected is then passed through the HEPA filter before it enters the mixing unit which replaces about 60% of the airflow with conditioned atmospheric air. This makes the filtration system of modern aircraft surprisingly effective in trapping airborne particles containing viruses.
Minimising Risk as a Passenger
Despite the highly efficient circulation system against viruses with HEPA filter, the system will not be operated to a full extend while the aircraft is on the ground when the airflow is relatively low. This means that it will take longer for droplets to reach the ground and hence increase the risk of contact with viruses. Therefore, it might be a good idea to just sit back and relax before the aircraft is in its cruising phase. Many airlines have implemented a strict mask-on policy onboard the aircraft and travellers are requested to comply strictly as the crew has the authority to offload any passenger that does not comply with such regulations.
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