Joyce Ng – Updated on Mar 09, 2009 – SCMP
A green group has called for the return of buses without air conditioning to improve ventilation after finding the air inside some air-conditioned buses had carbon dioxide concentrations four to eight times higher than that in average outdoor air.
The higher concentrations inside buses could encourage the spread of illnesses such as influenza among passengers, Green Sense president Roy Tam Hoi-pong said.
His group in December conducted half-hour measurements on eight KMB buses and one New World First bus, which were all air-conditioned. The tests found carbon dioxide concentrations ranging from 824 to 3,144 parts per million (ppm), the average being 1,643ppm. The highest was recorded on a KMB route 15 bus running from Lam Tin to Hung Hom.
None of the readings exceeded the Environmental Protection Department’s air quality guideline for air-conditioned buses, which regards an hourly average below 2,500ppm to be good and anything below 3,500ppm not harmful to health.
However, Mr Tam and Medical Association vice-president Alvin Chan Yee-shing said the guideline was too loose. Outdoor air normally had a concentration of 400ppm to 500ppm, Mr Tam said. “The higher the concentration, the poorer the ventilation inside the bus. It makes passengers feel tired and dizzy.”
Air-conditioned buses also wasted 5 to 10 per cent of their fuel driving the air-conditioning system, he said.
Dr Chan said the result was “alarming”, especially in the flu season; viruses would linger in stagnant air and spread among passengers.
A survey of 517 passengers by the group found 65 per cent supported use of non-air-con buses in winter.
KMB principal engineer Kane Shum Suet-hung said more than half the company’s fleet had electronic air cleaners to filter out contaminants. He said the opening and closing of doors brought in, on average, 8,000 cubic metres of fresh air per hour.