- The round one is an inlet – It brings in outside air to the mechanical systems, so nothing will be discharged from it.
- The middle one is an outlet – It is the over track exhaust, but also has battery/uninterruptable power supply (UPS) room exhaust in the event they are called on. During normal operations, the over track exhaust extracts heat locally from the air conditioner condensers which are onboard the train and braking devices of the stationary trains. In the unlikely event of a fire, this would be used to extract smoke from the trackway, platform and concourse.
- The tall one is a tunnel ventilation system (TVS) inlet exhaust –The TVS shaft can either exhaust or supply depending on the requirements of the tunnel (two shafts – one supply and one exhaust). The TVS is an environmental control e.g provide fresh air within tunnel and discharges oncoming air from approaching trains. In the unlikely event of a fire, the TVS is designed to prevent smoke spreading and to maintain acceptable conditions in the non-incident tunnel.
The Botanica 