The Kaimai Tunnel used by KiwiRail was closed on Saturdays and Sundays whilst being accessed for maintenance. The tunnel is over 7km long and when there is no wind flow the oxygen levels drop too low for anyone to be in the tunnel safely. We were challenged to design a solution to this problem and together with a team of contractors and Vitruvius, the civil engineers, it was decided that we would manufacture a door, at the Waikato entrance to the tunnel, out of 900gsm structural PVC, with a 2m fan outlet. A large industrial fan could then be attached to pump air into the tunnel. This ensures there is enough air in the tunnel, raising the oxygen levels so that contractors can safely work inside the tunnel. This has been a very successful project and certainly one of our most unusual requests. The door has been very successful and has meant that thousands of wasted hours due to lack of airflow are no longer an issue in this tunnel.