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Following is a question by the Hon Cheung Hok-ming and a written reply by the Secretary for Transport and Housing, Ms Eva Cheng, at the Legislative Council meeting today (November 4):
Question:
It has been reported that recently incidents of explosion in manholes occurred one after another, which has aroused public concern about the safety of manholes, and the Highways Department is conducting an inspection of all the manholes in Hong Kong. It has also been reported that the risk level of explosion in manholes depends mainly on the amount of explosive gases accumulated as well as the types of pipes used in manholes. Among such risks, the highest is that of explosive gas entering manholes for telecommunication facilities, and the risk of explosion in Towngas manholes is also relatively high. In this connection, will the Government inform this Council:
(a) when the Highways Department is expected to complete the inspection of all the manholes in Hong Kong; among the manholes of which inspection has been completed so far, of the number of those with very high risk of explosion, as well as the districts in which they are located;
(b) whether it has considered further enhancing the safety equipment provided to persons entering and working in manholes, with a view to reducing the chances of accidents;
(c) of the details of the current safety standards stipulated for the materials for various types of pipes to be used in manholes; and whether it will focus on manholes with relatively high risk of gas explosion, and examine upgrading the safety standards of the materials for the pipes used in such manholes; if it will not, of the reason for that;
(d) what new measures are in place to reduce the accumulation of explosive gases, such as methane, in manholes; and
(e) whether it will consider formulating an explosion risk classification table for all the manholes in Hong Kong and making it available for public inspection?
Reply:
President,
(a) To more thoroughly assess the systemic explosion risk of manholes on public roads and to study the relevant preventive measures, the Highways Department (HyD) completed a consultancy study entitled "Prevention of Gas Explosion in Utility Manhole" (the Study) in May 2008. The Study concluded that amongst the risk of gas explosion for the manholes of various public utilities, the risk level of manholes for town gas and those for telecommunication facilities is relatively higher. But the actual risk of individual manholes is closely related to their design, installation and surrounding environment (e.g. whether there are sources of flammable gas nearby). Given the unique nature of different types of manholes in terms of their operation, maintenance and safety, different types of manholes are put under the regulatory control of different authorities/departments. The Study under the HyD focused on the examination of the overall explosion risk and the preventive measures for different types of manholes, and its purpose was not to comprehensively inspect all manholes in Hong Kong. The crucial point, however, is that the measures for improvement of safety and reduction of risks and accidents suggested by the Study were being implemented and followed up. Details in this regard are set out in parts (c) and (d) of the reply below. As regards the general safety inspections for different types of manholes, they are conducted by the relevant authorities/departments according to other established procedures.
(b) Work safety in manholes is mainly governed by the Factories and Industrial Undertakings (Confined Spaces) Regulation (the Regulation) administered by the Labour Department (LD). The Regulation sets out the safety requirements for working in confined spaces, including requirements for risk assessments to be carried out by competent persons and for workers to undergo approved safety training. On enforcement, the LD conducts routine inspections of the working conditions in confined spaces as well as surprise checks at night. Any proprietor or contractor who contravenes the Regulation is liable to a maximum penalty of a fine of $200,000 and imprisonment for 12 months.
The LD also seeks to enhance safety awareness of the trade on working in confined spaces through a variety of promotion and publicity activities, including:
- publications, such as 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", to provide relevant duty holders with practical guidance for promotion of strict compliance with the Regulation;
- announcement in the Public Interest on television and radio as well as mini-dramas on radio;
- roving exhibitions; and
- health talks.
(c)&(d) At present, the materials for the ducts and valves installed in different types of manholes comply with the relevant safety standards. The Study has also identified the following feasible measures to reduce the risk of explosive gas accumulating inside manholes:
- sealing up ducts leading into manholes to prevent explosive gas from entering and accumulating inside manholes;
- filling up the empty space inside manholes with bags of light-weight and flame-retardant materials to prevent excessive volume of explosive gas from accumulating;
- enhancing the ventilation of the manholes by connecting them to vents or installing manhole covers with vent openings; and
- installing restraints on manhole covers to prevent them from substantial displacement in case of an explosion.
The Study also recommended that the relevant government departments and utility companies should, in the light of actual need, adopt the above precautionary measures for the type(s) of manholes under their purview. The HyD has passed the relevant information of the Study to other relevant government departments, public utilities and regulatory authorities for reference and follow-up action.
Cable manholes
Based on the recommendations of the Study, the HyD has completed the improvement works for all its cable manholes. To reduce the risk of gas explosion, empty space inside the manholes is filled up with bags of light-weight and flame-retardant materials to prevent excessive accumulation of explosive gas.
Electricity manholes
Local power companies usually lay their underground electricity cables using direct burial method under soil instead of wiring through underground ducts. Therefore, the chance of flammable gas entering the electricity manholes is low. The two power companies also conduct inspections of their respective manholes to ensure safety. The Electrical and Mechanical Services Department (EMSD) monitors the progress of their work.
Manholes for drainage and water supply facilities
On manholes under the management of the Drainage Services Department (DSD) and Water Supplies Department (WSD), the drains provide ventilation which reduces the risk of gas accumulation in drainage manholes. On the other hand, water pipes are sealed and there is no gap between pipes and manhole walls to allow entry of explosive gas into water supply manholes. Nonetheless, the DSD will continue to carry out preventive cleaning for its sewers and manholes regularly to further prevent and reduce the risk of explosive gas (such as methane) from accumulating.
Town gas manholes
The Hong Kong and China Gas Company Limited (HKCG) is installing restraints on the covers of its manholes (where necessary) to prevent substantial displacement of the covers in case of an explosion, as recommended in the Study. It is expected that the improvement works will be completed by end 2009. Moreover, the HKCG has implemented a series of measures to reduce the possibility of gas leakage from town gas pipes. The HKCG has since 2006 increased the number of routine leakage surveys for all underground medium pressure ductile iron (MPDI) pipes in Hong Kong from three to six times per year, while the EMSD has stepped up regular inspections and surprise checks. The HKCG has also drawn up annual programmes for replacing MPDI pipes with polyethylene pipes which perform better in preventing gas leakage.
Manholes for telecommunication facilities
The Office of the Telecommunications Authority has set up a Joint Forum comprising representatives from the fixed network operators, the HyD, EMSD and Fire Services Department with a view to identifying specific measures and implementation plans for mitigating the risk of gas explosion in telecommunications manholes. The Joint Forum meets regularly to co-ordinate the development of mitigation measures and risk assessments. The aim is to work out a set of guidelines or code of practice on risk mitigation of gas explosion for compliance by the relevant fixed network operators.
(e) The Study has assessed the relative risks of gas explosion for different types of manholes and proposed specific preventive measures. Accordingly, the relevant entities have taken corresponding measures to further reduce the risk of their facilities. The relevant authorities and departments do not consider there is a need to formulate an explosion risk classification table covering individual manholes.
Ends/Wednesday, November 4, 2009
Issued at HKT 12:26
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