Aircraft not a high risk environment for SARS

Air travel is not a high-risk activity, neither is an aircraft itself a high-risk environment for the transmission of severe acute respiratory syndrome (SARS), the Director-General of Civil Aviation, Mr Albert Lam, said today (May 10).

"The entire passenger fleet of the two Hong Kong-based airlines are equipped with High Efficiency Particulate Arrester filters to remove viruses," he told a press briefing during which he outlined the operation of the in-flight air circulation and filtration systems.

Mr Lam said the filters, which were made of micro glass fibres, were 99.97% efficient in removing dust and airborne contaminants with a particle size of 0.3 micron and above, and this included viruses. Most coronavirus droplets are larger than five microns.

Depending on the type of aircraft, there are between two and eight filters installed in every plane. It is the same type of filter used in hospital operating theatres.

Mr Lam said the World Health Organisation agreed the filter systems in commercial aircraft had proven to be effective against infectious diseases.

"In flight, fresh air is introduced into the cabin continuously, and this fresh air is mixed with cabin air, which is passed through filters. The entire cabin air volume is exchanged every two to three minutes," he said.

"During a flight the average relative humidity in the cabin is 15% to 20% as a low humidity environment has been shown to inhibit fungal and bacterial growth.

"Moreover, air supplied to aircraft toilets and galleys is not re-circulated but is expelled from the aircraft, and air in the cabin is drawn down and extracted at floor level."

Mr Lam said there was no longitudinal flow of air through the cabin of an aircraft.

"The air supplied to one seat row leaves at approximately the same seat row, thus minimising airflow in the fore and aft directions. In other words, the air of one person passes another at floor level only," he said.

Since mid-April, temperature checks for all arriving, departing and transit passengers at the Hong Kong International Airport have been implemented.

In line with the WHO guidelines, Hong Kong carriers will not accept passengers with symptoms and signs compatible with SARS. Local air operators also carry out scheduled cabin cleaning with cleansing agents accepted for use on aircraft.

The International Civil Aviation Organisation (ICAO) published guidelines in early May for its member states to help stop the international spread of SARS by air.

It urges contracting states to implement pre-boarding medical screening of passengers at check-in; provide all incoming passengers with a detailed information leaflet on SARS; implement medical screening of passengers arriving directly from or via affected areas; advise pilots to radio ahead if someone on board exhibits SARS symptoms; instruct crew on dealing with suspected SARS-patients in flight; and disinfect aircraft on which a suspected SARS patient has travelled.

Hong Kong has already taken the necessary measures urged by ICAO to prevent the spread of SARS by air transport," Mr Lam said.

End/Saturday, May 10, 2003