To ensure the tunnel will never experience a total power failure, electricity is supplied by two separate companies, China Light and Power and the Hong Kong Electric Company via substations located in the West Kowloon and Sai Ying Pun ventilation buildings.

Each system is connected to dual transformers in the substations so that each transformer supplies half the load under 'normal' conditions. In the event of a power failure, automatic change-over facilities are fitted to transfer the load between each transformer. This ensures the tunnel remains operative if there is a shut-down of either company's equipment.

Precautions have been taken to maintain power supply by installing emergency generators which could run essential equipment such as the fire service system, emergency lights and pumps. If a total power failure occurred, an alternative supply can be provided by batteries and generators which will maintain the operation of essential equipment during the period of mains failure.

The engineering department is also responsible for maintaining the ventilation system. A total of 36 fans linked to the central control and monitoring system have been fitted into the ventilation buildings at the end of each tunnel.

'The tunnel ventilation system is automatically operated to control and limit the concentration of emissions to a regulatory standard,' Mr Lee said.

Fans in the ventilation buildings are capable of replacing the air in one tube of the tunnel within five minutes and providing a smoke-free path of no less than two metres high above the road surface for evacuation of passengers and an access for fire-fighting personnel.

Fire protection for the tunnel incorporates hydrants and hose reels with detection and alarm systems located throughout the tunnel. The fire mains within the tunnel have been extended to serve the hydrants on the ground level roads at Sai Ying Pun, the toll plaza on the West Kowloon side and the administration building area.

Ten environmental sensors have been strategically mounted within the immersed, and cut and cover, sections of the tunnel to monitor visibility, carbon monoxide, nitrogen monoxide and air speed. Signals from the environmental sensors help regulate the fans.

Fresh air intakes and exhaust discharge shafts have been fitted with cladding and sound-reduction equipment to limit noise from fans around the ventilation buildings.

More than 100 phones directly linked to the control room have been installed within the tunnels.