'Air is the same as you breathe in station'

Can an MTR ventilation shaft introduce filthy air into the environment? The Transport and Housing Bureau does not think so, and one green group agrees.

'Ventilation shafts act like windows of a house,' a bureau spokeswoman said. 'It enables air exchanges inside the stations and tunnels with the external environment.

'The flow is generated by train movements inside the tunnel through pushing and suction action.

'As the trains are powered by electricity, combustion of fossil fuels is not required, and hence no harmful or hazardous gases are discharged. 'Furthermore, the rail tracks and tunnels are washed regularly in order to maintain the cleanliness of the railway. The air coming out of ventilation shafts should not be harmful. It should be the same as that inhaled by the passengers inside the station.'

Edwin Lau Che-feng, director of Friends of the Earth and a member of the Advisory Council on the Environment, said a ventilation shaft only served to regulate air pressure inside train tunnels.

'The quality of air that comes out of the shafts will, at least, be the same as what you would breathe inside a train compartment or on the platform,' Mr Lau said.