Towngas' underground pipes are safe according to a leakage survey, the Electrical & Mechanical Services Department says.

A comprehensive probe was launched after the leak and explosion in Ngau Tau Kok on April 11. It involved the company's nine survey teams and was audited by the department's on-site inspections through random sampling.

It found:

* minute leakage at three locations - the junction of Wong Chuk Hang and Nam Long Shan Roads on Hong Kong Island, Prince Edward Road West in Kowloon and Lai Yiu Street in Kwai Chung. Leakage was due to pipe corrosion, and replacement has been completed;

* minute leakage was detected in 30 of more than 200,000 pipe joints, and been rectified; and,

* 18 above-ground installations where minute leakage was detected, and repaired.

The department will monitor the company's safety management system and review its maintenance programme. Measures to further enhance gas safety are being explored.