Pile-drivers will be gradually barred from urban areas within the next three years and replaced by quieter hydraulic hammers. Environmentalists said the move was welcome but should be speeded up. Amendments to the Noise Control (Amendment) Bill 1997 will be introduced to the Legislative Council on April 9. Restrictions will phase out the use of three types of noisy hammers - diesel, pneumatic and steam - in built-up areas by 2000. They produce noise levels of 103 to 106 decibels. Hydraulic hammers are two to nine decibels quieter. A spokesman for Planning Environment and Lands said the change would be phased in over four six-month intervals. The construction industry supported the phased change, which will still allow diesel hammers in rural areas. But Patrick Chan Wing-tung, the Secretary-General of the Construction Association, warned that the move would increase total building costs by up to 10 per cent. Hong Kong has about 100 pile-drivers. The only market left for them would be Vietnam or Africa, and contractors have already begun negotiating with companies in Vietnam.