THOUSANDS of passenger lifts in Hongkong's commercial, industrial and residential high-rises have no system to warn of over-loading. An Electrical and Mechanical Services Department engineer said last night that passenger lifts installed before 1969 did not have to include an over-loading warning device. Michael Yeung Kok-fai, of the department's legislation and enforcement division, said there were 20,000 to 30,000 buildings with such lifts. ''Of course we recommend owners install over-loading mechanisms, but we haven't got the power to force them,'' he said. Wong Man-wing, services manager of Schindler Lifts - the world's second largest lift manufacturer - said about 10 per cent of the territory's passenger lifts were manufactured and installed before 1969. ''In those days having an over-load device built into the lift wasn't compulsory according to required regulations and standards. ''We now advise building owners to either replace their old lifts with modern ones or put over-loading devices into the existing lifts. ''Although many owners follow our recommendations . . . many risk accidents to save money by not modernising,'' he said. ''The old lifts can be kept safe with proper and careful maintenance, but the risks of not having safety devices are a very high price to pay for short-term financial benefit,'' Mr Wong added. Under regulations outlined in the Lift and Escalator Safety Ordinance, lifts installed after 1969 must include over-loading devices. All such lifts must be checked at least once a month and receive more stringent checks annually and after five years of use. Regulations require monthly checks to be carried out by ''competent lift workers'' who have either completed a four-year apprenticeship or have an equal amount of practical lift work experience. The more detailed annual and five-yearly safety checks are completed by lift engineers who gain this qualification through four years' experience, having a higher certificate in electrical or mechanical engineering and passing written and oral exams. Mr Wong said his company checked its lifts at least twice a month as well as annually and after five years. Lift engineers test the maximum carrying capacity of lifts before installation by using a dead weight equal to the desired capacity with a safety factor added on. ''For example if a 1,000 kilogram capacity is required, we make sure the lift's maximum capacity is 25 per cent higher at 1,250 kg. We test the brakes at that weight but set the overload device to signal overload at 1,000 kg. We would then post, inside the lift, 1,000 kg as the maximum weight capacity,'' he said. Speed is also a factor with the average passenger lift travelling at between 1.75 to 2 metres per second. Lift technology has changed rapidly over the years and according to Mr Wong the improving technology may cause safety problems if engineers are not trained in the use of the latest equipment. ''It is vital engineers are aware of the latest equipment and techniques involved in lift manufacturing so they can locate and fix any potential problems.''