Surveyors yesterday called for mandatory checks on old buildings to prevent a repeat of the accident in which a mother of two was killed by a slab of falling concrete. Lingerie hawker Liu Ngan-fong, 41, died instantly when the 6.5kg slab of concrete fell from the residential block behind her stall on Tung Choi Street and hit her head on Tuesday. The incident was simply the 'tip of the iceberg', the chairman of the Institute of Surveyors membership committee, David Chan Wah-wai, said yesterday. 'It is a very difficult situation . . . but the Buildings Department should carry out inspections on all buildings, issue statutory orders and follow up promptly on complaints,' Mr Chan said. At present, a two-to-three year wait was common for a check-up, he said. The institute's chairman, Kenneth Chan Jor-kin, said high-density districts like Mongkok, Causeway Bay and Wan Chai should be immediately targeted for inspection. The Buildings Department implemented voluntary inspections in April 1997, but this largely amounted to leaflets being distributed to the public. A total of 22 inspections were conducted in April and May.