Government engineers were aware of possible dangerous leaks from liquefied petroleum gas cylinders more than two weeks ago but delayed alerting the public until Tuesday, it emerged yesterday. Keith Whittle, the Electrical and Mechanical Services Department's chief engineer in gas utilisation, acknowledged department engineers had been conducting tests on gas tank regulators since last month but reached no conclusions. However, tests on a regulator found in To Kwa Wan last Friday confirmed there was a leakage problem, but the public was not alerted until Tuesday evening. Mr Whittle defended his department, saying a public warning could not have been issued last week because the conclusive tests were performed only on the following Monday and the results obtained on Tuesday morning. 'We conducted the test on Monday night and got the results back the next morning,' he said. 'The leakage was enough to cause concern and we decided we couldn't wait and so we told Shell to make the announcement immediately.' Shell announced on Tuesday that 20,000 regulators on gas tanks in Hong Kong and Macau could have loose screws that could result in leakage. Shell has replaced 1,742 regulators since Tuesday. The company said it could take up to a week to replace all the rest. All the regulators have the manufacturing dates September 1995 and March 1996, marked on them, and customers who find those dates on their tanks are to call 2436 6888 for immediate free replacement. Yesterday, Shell spokesman Alice Li Sin-man defended the company's delayed announcement. She said it was necessary to avoid public panic and to stock up replacement regulators. 'The report we got from the Japanese manufacturer on Friday was inconclusive and late in the evening,' she said. 'We wanted time to prepare because we did not have enough replacements.' She refused to name the Japanese company yesterday. But Albert Chan Wai-yip, the Democratic Party legislator, said public safety should always come first and criticised current laws for allowing gas supply companies too much freedom in conducting their own safety checks.