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Following is a question by the Hon Raymond Ho and a written reply by the Secretary for Transport and Housing, Ms Eva Cheng, at the Legislative Council meeting today (November 18):
Question:
According to the Secretary for Transport and Housing's reply to a written question raised by a Member of this Council on December 10 last year, there were six manhole explosion cases between 2003 and 2008. Among them, four involved manholes for telecommunication facilities. The Secretary pointed out that at the present stage, there was no plan for introducing new statutory requirements regarding the mandatory implementation of the recommendations of the consultancy study entitled "Prevention of Gas Explosion in Utility Manhole" (the Study). Yet, on August 11 this year, another manhole explosion occurred at the junction of Hong Ning Road and Shung Yan Street in Kwun Tong, which blew away five manhole covers. Three manholes for telecommunication facilities were involved in this accident which resulted in three persons being injured and admitted to hospital. In this connection, will the Government inform this Council:
(a) given that while the Government has advocated the relevant trades exercising self-discipline in implementing the recommendations of the Study, it has come to my knowledge that many manhole owners have yet to actually implement those recommendations, whether the Government will firmly require enterprises owning manholes to fulfil their corporate social responsibilities by expeditiously completing the risk assessment for their manholes on various streets within a specified period (e.g. in six months) and adopting appropriate improvement measures accordingly, thereby safeguarding public safety; and
(b) whether the Government will consider making reference to national standards such as the "Design Code for Communication Conduit and Passage Engineering" and the "Code of Construction and Acceptance for Communication Conduit Engineering", and enacting legislation to require the trades to seal the connecting conduits inside manholes, so as to prevent chain manhole explosions?
Reply:
President,
(a) 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). The Study has identified the following feasible measures to reduce the risk of explosion 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 recommended that the relevant government departments and utility companies should, in the light of actual needs, adopt the above precautionary measures for the type(s) of manholes under their purview. 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. In this regard, 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. Details are as follows:
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
Generally speaking, the risk of electricity manholes is relatively lower. Therefore, the Study has not specifically suggested the adoption of any measures for this type of manholes. Nonetheless, 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 Water Supplies Department (WSD) and Drainage Services Department (DSD), the drains provide ventilation which reduces the risk of accumulation of explosive gas in drainage system manholes. As for water pipes, they are sealed by design and there is no gap between the connecting points of pipes and manhole walls; and sewers also adopt a sealed design. Therefore, the explosion risk of these two types of manholes due to inflow of explosive gas is relatively lower. 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) installs 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. Moreover, 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. 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
According to the Office of the Telecommunications Authority (OFTA), telecommunication operators have adopted mitigation measures, for example by switching to employ manhole covers with ventilation holes and by surrounding PVC ducts with concrete for prevention of damages, to lower the risk of gas explosion in telecommunications manholes. The OFTA has, in September this year, set up a Joint Forum with representatives from the HyD, Fire Services Department, EMSD and telecommunication operators, with a view to studying the methodology of carrying out risk assessments and coordinating mitigation measures. The Joint Forum seeks to arrive at an acceptable approach and implementation timetable with telecommunication operators in half a year.
To conclude, 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.
(b) It is required by the national standards "GB50373 – Design Code for Communication Conduit and Passage Engineering" and "GB50374 – Code of Construction and Acceptance for Communication Conduit Engineering" that during and upon completion of the laying of communication conduits, and on entry into a structure or manhole, the openings in the conduits should be sealed to keep the debris off. These requirements are applicable to manholes for telecommunication facilities.
While there are no such statutory requirements in Hong Kong at present, some telecommunication operators have started to install plugs in their newly built conduits in manholes in recent years to seal those which are yet to be commissioned. In addition, as mentioned in part (a), OFTA set up a Joint Forum with the telecommunication operators and the departments concerned in September this year. It will actively study various feasible measures for mitigating the risk of explosion. Drawing reference from the national technical standards and standards of other regions (including the requirements of the above two national standards) as well as relevant experience, it will also formulate possible measures applicable to the actual situation in Hong Kong which can mitigate the risk of explosion in telecommunication manholes. At this stage, the Government has no plan to require utility companies to seal conduits in manholes through legislation.
Ends/Wednesday, November 18, 2009
Issued at HKT 17:21
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