Updated emission standards to control pollution caused by off-road vehicles and construction machinery would apply to new imports but not to equipment already in the city, under an Environment Bureau proposal. Some lawmakers had argued for equipment of a certain age to be phased out, but environmental officials said it was impractical to place a blanket limit on the lifespan of machines such as excavators, tractors, cranes and airport vehicles, whose purpose and durability vary greatly. Officials also insisted that while emissions from such machinery and vehicles accounted for some 8 per cent of the city's nitrogen oxide and suspended particles, they believed new measures could help to lower the health risks to workers using or working with the machines. The proposal will be introduced to the legislature next year. If passed, it would go into effect in April. It is estimated that under the new emission standards, which are based on the European Union rules, most such equipment will be at least 60 per cent cleaner than it would have been before the relevant Euro standards took effect in 1995. Under the proposal, all 15,000 such items of equipment already in the city could be registered with the Environmental Protection Department to be exempted from the new rules within six months after the law is passed. The machinery would be issued labels spelling out status and specifications. Kenneth Chan Ka-lok, from the Civic Party, said that while he supported the general direction of the proposed regulations, he was also concerned about the lifespan of the polluting equipment, which some officials said could be 20 years. "We just can't have an illusion that we should give up fighting for mandatory retirement just because some say their machines are in good shape," he said. However, Andrew Lai Chi-wah, deputy director of environmental protection, defended the proposal, saying the equipment was so diverse that setting lifespan limits was not pragmatic. "We believe most of the machines will be replaced in several years," he said. He also asserted that there would be no difficulties in sourcing equipment abroad because major exporters of the machines in the United States, Europe, Japan and China were also upgrading their emission standards.