High CO2 levels of buses increase risks on road

Double-decker buses have higher carbon dioxide levels than other public transport and this could cause drivers and passengers to feel dizzy and sleepy - increasing road risks.

The concentration of CO2 can reach up to three times higher than the government's recommended level, research by Hong Kong Chu Hai College has found.

On a bus from Tuen Mun to Lam Tin in March, researchers discovered that after half an hour the level of CO2 surpassed 1,000 parts per million - the boundary between satisfying and worrying ventilation. The level continued rising during another hour to nearly 3,000 ppm.

The upper deck recorded a peak CO2 level of 2,950 ppm, while the lower recorded 2,840 ppm.

Researchers measured the CO2 level on MTR cabins, with the maximum reaching 1,860 ppm on the route from Admiralty to Tsuen Wan, followed by 1,426 ppm from Tuen Mun to Hung Hom.

The CO2 level in double-deckers was about 60 percent higher than that on the MTR.

"The difference could be because the MTR opens its doors every several minutes when it arrives at a station, while long-haul buses remain closed for a longer period," said Louis Lam Chi-hung, head of the Department of Civil Engineering.

"The same reason may also explain the difference between bus decks - doors open on the bottom deck so the CO2 level there is lower."