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Following is a question by the Dr Hon Samson Tam and a written reply by the Secretary for Transport and Housing, Ms Eva Cheng, at the Legislative Council meeting today (December 10):
Question:
As there were a number of incidents of explosion in manhole in recent years, will the Government inform this Council:
(a) of the number of incidents of explosion in manhole in the past five years; the location, cause and resultant casualties (together with the number of staff of public utility organisations among them) of each incident, as well as the organisation to which the manhole belonged;
(b) whether it has studied in the past three years ways to how such incidents could be reduced; if so, of the study results and specific measures; if not, the reasons for that;
(c) whether it will assess the explosion risks of all manholes in Hong Kong; if it will, of the implementation timetable and related expenses; if not, the reasons for that;
(d) whether it has studied the feasibility of sealing off holes surrounding the pipelines connected to manholes, so as to prevent explosion caused by inflammable gas leaking into the manhole through such holes; if it has, of the results and whether it will legislate for mandatory enforcement by public utility organisations; if not, of the reasons for that;
(e) whether it has assessed the trend in explosion in manhole caused by power line failure in the past three years; if it has, of the details; if not, the reasons for that; and
(f) what measures are in place to enhance the occupational safety of staff of the Government and public utility organisations when they are working in the manholes?
Reply:
President,
(a) According to the records of the concerned Government Departments, there were six manhole explosion cases in the past five years. The details are attached (see Annex).
(b), (c) & (d) In May 2008, Highways Department completed a consultancy study "Prevention of Gas Explosion in Utility Manhole" ("the Study") to assess the risk of manhole explosions in public streets, through surveying a number of different types of manholes, and study the relevant preventive measures. The cost of the Study was around $600,000. The general findings on the risk of gas explosion in various types of utility manholes are as follows –
(i) the risk of explosive gas entering manholes for telecommunication facilities are generally higher given the large number of such manholes, their shallower depth of installation, and that the polyvinyl chloride ductings leading into these manholes are more susceptible to damage;
(ii) the risk of explosion in Towngas manholes is also relatively high owing to the possibility of leakage from Towngas pipes and fittings inside the manhole;
(iii) the risk of explosive gas entering sewer manholes is relatively low since the sewers are sealed. However, the risk still exists because sewage may produce explosive gas and sewer manholes have no ventilation;
(iv) the risk of explosion in drainage manholes is low since the connecting gullies provide ventilation;
(v) the risk of explosion in electricity manholes is low since they are filled and do not have underground power supply lines inside; and
(vi) the risk of explosion in water supply manholes is low since water pipes are sealed and there is no gap between the pipe and the manhole walls to allow explosive gas to enter.
The Study identified the following four measures to reduce the risk of gas explosion in manholes –
(i) sealing up ducts leading into manholes to prevent explosive gas from entering and accumulating inside manholes;
(ii) filling up the empty space inside manholes with bags of light-weight, flame-retardant materials to prevent excessive volume of explosive gas from accumulating;
(iii) ventilating the manholes by connecting them to vents or installing manhole covers with vent openings; and
(iv) installing restraints to manhole covers to prevent them from large displacement in case of an explosion.
The results of the Study have been presented and passed to the concerned Government departments as well as the utility undertakers and their relevant controlling authorities for follow-up actions. Utility undertakers have a common duty of care to ensure that their facilities are safe. As such, there is no plan at this stage for introducing new statutory requirements regarding the mandatory application of the above recommendations.
In addition to improving the safety of manholes, the Electrical and Mechnical Services Department (EMSD) has stepped up measures with a view to reducing the possibility of gas leakage. The Hong Kong China Gas Company (HKCGC) has since 2006 increased the number of routine leakage surveys for all underground medium pressure ductile iron (MPDI) pipes in Hong Kong from 3 times to 6 times per year. HKCGC also has a programme for replacing MPDI pipes with polyethylene pipes which are better in resisting gas leakage. Moreover, EMSD has strengthened regular inspections and surprise checks.
(e) According to the records, there has been no manhole explosion incident caused by power line failure in the past three years.
(f) Work safety in manholes is governed mainly by the Factories and Industrial Undertakings (Confined Spaces) Regulation (Cap. 59B) (the Regulation), administered by the Labour Department (LD). The Regulation sets out the safety requirements for working in confined spaces. These include requirements for risk assessment to be carried out by competent persons and for workers to undergo approved safety training. In enforcing the Regulation, LD conducts inspections of works at confined spaces, including drainage works. LD also conducts surprise inspections at night, when drainage works are commonly conducted, and launches special enforcement campaigns during the rainy seasons. A proprietor or contractor who contravenes the Regulation is liable to a maximum fine of $200,000, and to imprisonment for 12 months.
LD also promotes compliance with the Regulation through publications to provide practical guidance to duty holders. These include the "Code of Practice for Safety and Health at Work in Confined Spaces", "Safety Guide for Work in Manholes" and "Prevention of Gas Poisoning in Drainage Work". In addition, publicity and health talks are also regularly organised to enhance the occupational safety and health awareness of contractors and workers in such works.
Ends/Wednesday, December 10, 2008
Issued at HKT 16:25
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