Special filters suck out virus in cabin, assure airlines

Safety measure

How safe is air travel in Covid times since the cabin is a confined space? As this anxiety lowers flight occupancy rates, international airlines are now beckoning travelers with a safety fix: High Efficiency Particulate Air (HEPA) filters that are claimed to suck out 99% of airborne contaminants in the cabin.

Leading the information campaign is Emirates with this statement: “Cabin air is extracted into the air conditioning unit through HEPA filters that remove 99.9% of microscopic particles such as bacteria viruses, and fungi from the air-as effective as the filters used in hospital operation theatres.”

Much before the Covid-19 outbreak, the International Air Transport Association (IATA) had come out with a briefing on HEPA in 2018: “The risk on airplanes is probably lower than in many confined spaces as modern airplanes have cabin air filtration systems equipped with HEPA filters. These have similar performance to those used to keep the air clean in hospital operating rooms and industrial clean rooms.”

Despite the resumption of domestic flights on May 25, occupancy rates in most Indian airlines have remained low. Uncertainty and anxiety over the virus presence in enclosed spaces and the complex safety precautions were contributing factors.

So, how does the HEPA filters work? Once the cabin air is sucked into the AC unit through HEPA filters, the contaminants are removed. “The cleaned and filtered cabin air is then mixed with fresh air drawn in from out. This mixed air is circulated back into the cabin at the right pressure and temperature for passenger comfort,” explained an Emirates statement.

The air circulates downwards from the ceiling to the floor to minimise the movement of particles along the cabin. “The air is completely changed every two to three minutes even more frequently than in a hospital.”

Based on inputs from Airbus and Boeing, IATA had explained earlier that the cabin air system is designed to operate most efficiently by delivering approximately 50% outside air and 50% filtered, recirculated air. “This normally provides between 15 to 20 cubic feet of total air supply per minute per person in economy class.”

The majority of modern, large, and commercial aircraft that use the recirculation-type cabin air system have HEPA filters. According to Emirates, the Boeing 777 has eight filters, while the Airbus 380 has 18 or 19 filters based on configuration.