AN engineer who used mountaineering techniques to clean the windows and walls of a luxury Mid-Levels apartment block was critically injured after plunging eight floors yesterday. Geoff Robertson, 30, fell onto the fifth-floor podium of the Albany while working outside the 13th floor with three colleagues. He was taken to Queen Mary Hospital where he underwent a brain scan and an emergency operation. He sustained serious head and leg injuries. Mr Robertson, a Briton employed by CAN Civil and Structural Engineering Services, was in a critical condition last night. The accident occurred just before 1.20 pm when Mr Robertson and three other colleagues abseiled down the building using two ropes. One of the ropes broke outside a 13th-floor apartment, sending Mr Robertson plunging to the fifth-floor podium. The 38-storey apartment block is the home of some of Hong Kong's rich and famous as well as senior civil servants. Among the occupants are Senior Executive Councillor Lady Dunn and her husband, Michael Thomas, who occupy one of the two 6,000-square-foot penthouses. The building, overlooking the Botanical Gardens, is owned by Swire Properties. It was designed in a ''Y'' shape to give all the apartments a panoramic view of Victoria Harbour.