Questions

紓減電訊沙井氣體爆炸風險 Mitigating risk of gas explosion in telecommunications manholes

以下為立法會會議上盧偉國議員的提問和商務及經濟發展局局長蘇錦樑的書面答覆:

問題:

  鑑於近年電訊沙井內氣體爆炸的事故偶有發生,前電訊管理局於二○一○年三月委託顧問研究此問題,並於同年六月公布一套自願性的《紓減電訊沙井氣體爆炸風險的實施指引》(《指引》)。《指引》包含三項措施:(i)密封連接至沙井的管道,以防止易燃氣體進入沙井並在該處積聚;(ii)在沙井蓋加設疏氣孔,以防止易燃氣體在沙井內積聚;以及(iii)採用三合土保護塑膠管道,以防止管道損壞和防止易燃氣體進入沙井。然而,最近本人得悉,此等措施未被全面落實,而且經常有人為了防止污水積聚和蚊患而把沙井蓋的疏氣孔以膠貼密封,亦有沙井蓋的疏氣孔經常被泥塵堵塞,以致疏氣孔未能發揮作用。就此,政府可否告知本會:

(一)現時是否全港的電訊沙井已落實上述措施的至少一項;若是,該三項措施分別在多少百分比的電訊沙井中得到落實;若否,已落實其中一項措施的電訊沙井的數量及其佔總數的百分比為何,以及當局估計全港的電訊沙井將於何時完成落實至少一項措施;

(二)對於沙井蓋疏氣孔被人密封或被泥塵堵塞的問題,當局有否解決方案;若有,詳情為何;若否,當局如何紓緩有關的沙井的爆炸風險;及

(三)當局會否重新考慮參考國家標準《GB50373-通信管道與通道工程設計規範》及《GB50374-通信管道工程施工及驗收規範》,立法規定電訊業人士密封電訊沙井內的連接管道,以防止發生沙井內氣體連環爆炸的事故?

答覆:

主席:

(一)為減低在電訊沙井發生氣體爆炸的風險,前電訊管理局(即現時的通訊事務管理局辦公室,在下文統稱「通訊辦」)與有關的政府部門、固定網絡營辦商(固網商)、電力及煤氣公司於二○○九年九月成立工作組,並於二○一○年三月聘請顧問公司研究有關事宜。經諮詢工作組成員的意見及考慮顧問公司的建議後,通訊辦於二○一○年六月三十日發出《紓減電訊沙井氣體爆炸風險的實施指引》(《指引》)(註),要求固網商遵從相關規定。

  《指引》列出三項減低因沙井內積存易燃氣體而引致爆炸風險的紓減措施,即在沙井蓋加設疏氣孔、密封連接沙井管道的管口及用三合土封包連接沙井的管道。經詳細考慮後,工作組認為上述紓減措施應先在行人密集的街道實行,以減低行人因電訊沙井氣體爆炸而受傷的風險。該等街道的位置列於《指引》的附件六。固網商已按《指引》的要求,於二○一二年六月三十日前,在該等街道的7 600多口沙井實施上述其中至少一項的紓減措施。

  除上述7 600多口位於行人密集街道的沙井已實施至少一項的紓減措施外,《指引》亦要求固網商在其所有新建造的電訊沙井蓋加設疏氣孔,及在進行維修或提升工程時,以設有疏氣孔的新井蓋更換舊的井蓋。《指引》亦鼓勵固網商在他們其他的電訊沙井實施上述紓減措施。《指引》沒有指定全部電訊沙井完成紓減措施的時間表,然而固網商已陸續為他們的電訊沙井實施該等紓減措施。至二○一三年二月底為止,已實施紓減措施的電訊沙井數目及其佔全部電訊沙井數目的比例如下:

                  佔全部電訊沙井
紓減措施    電訊沙井數目    數目的百分比
----    ------    ------
在沙井蓋加設  約3 900口   約1‧5%
疏氣孔

密封連接沙井  約5 400口   約2‧1%
管道的管口

用三合土封包  約70 000口  約27‧7%
連接沙井的管道

(二)就沙井蓋疏氣孔被封上膠貼或被泥塵堵塞的問題,《指引》要求固網商在進行定期檢查時,清除阻塞沙井蓋疏氣孔的雜物,以確保疏氣孔發揮應有的功能。按《指引》的要求,每家固網商應每年抽樣檢查最少20%其位於上述行人密集街道的電訊沙井,及每兩年抽樣檢查最少5%其位於其他地方的電訊沙井。通訊辦亦會進行抽查,以確保固網商遵從《指引》內關於抽樣檢查的要求。通訊辦的抽查結果顯示,固網商符合《指引》內的要求。

(三)除在沙井蓋加設疏氣孔外,國家標準《GB50373-通信管道與通道工程設計規範》及《GB50374-通信管道工程施工及驗收規範》中所建議的密封管道和三合土封包管道方法亦已採納為《指引》所指定的紓減措施。固網商已按《指引》的要求,陸續為他們的電訊沙井實施該等紓減措施,以減低在電訊沙井發生氣體爆炸的風險。自《指引》於二○一○年六月三十日實施後,通訊辦至今沒有收到電訊沙井發生氣體爆炸的事故報告。鑑於《指引》運作良好,當局因而未有打算就有關紓減措施進行立法規管。

註:該指引可在tel_archives.ofca.gov.hk/en/report-paper-guide/guidance-notes/gn_201003.pdf下載。

 

Following is a question by Ir Dr Hon Lo Wai-kwok and a written reply by the Secretary for Commerce and Economic Development, Mr Gregory So, at the Legislative Council meeting:

Question:

     As there have been occasional incidents of gas explosion in telecommunications manholes in recent years, the former Office of the Telecommunications Authority appointed a consultant to study the matter in March 2010 and published in June of the same year a set of Implementation Guidelines on Mitigating the Risk of Gas Explosion in Telecommunications Manholes, which is voluntary in nature. The Guidelines include three measures: (i) sealing up ducts leading into manholes to prevent flammable gases from entering and accumulating inside manholes; (ii) retro-fitting manhole covers with vent holes to prevent flammable gases from accumulating in the manholes; and (iii) surrounding PVC ducts with concrete to prevent damages and flammable gases from entering manholes. However, I have recently learnt that these measures have not been implemented across the board, and that the vent holes of manhole covers cannot serve their purpose as some of them have often been sealed with plastic tapes to prevent accumulation of waste water and mosquito problems, while others have often been blocked by dust and debris. In this connection, will the Government inform this Council:

(a) whether, at present, at least one of the aforesaid measures has been implemented in all the telecommunications manholes in the territory; if so, of the respective percentages of telecommunications manholes in which each of the three measures has been implemented; if not, of the number of telecommunications manholes in which one of those measures has been implemented, and the percentage of such manholes in the total number of telecommunications manholes, and when, as estimated by the authorities, the implementation of at least one of the aforesaid measures in all the telecommunications manholes in the territory will be achieved;

(b) whether the authorities have any solution to the problem of vent holes in manhole covers being sealed off or blocked by dust and debris; if they have, of the details; if not, how the authorities mitigate the risk of explosion of the manholes concerned; and

(c) whether the authorities will consider afresh, making reference to the national standards "GB50373 - Design Code for Communication Conduit and Passage Engineering" and "GB50374 - Code of Construction and Acceptance for Communication Conduit Engineering", to enact legislation requiring members of the telecommunications industry to seal the connecting ducts in the telecommunications manholes, so as to prevent incidents of chained gas explosions in manholes?

Reply:

President,

(a) To minimise the risk of gas explosion in telecommunications manholes, the former Office of the Telecommunications Authority (now the Office of the Communications Authority, hereinafter collectively referred to as "OFCA") set up a Joint Forum in September 2009 with relevant government departments, fixed network operators (FNOs), power companies and the towngas company, and appointed a consultant in March 2010 to study the relevant issues. Having consulted the members of the Joint Forum and considered the recommendations of the consultant, OFCA issued the "Implementation Guidelines on Mitigating the Risk of Gas Explosion in Telecommunications Manholes" (the Guidelines) (Note) on June 30, 2010 for compliance by FNOs.

     The Guidelines set out three mitigation measures, namely installing vent holes in manhole covers, sealing up the ducts leading into manholes and surrounding the ducts leading into manholes with concrete, for minimising the risk of explosion caused by accumulation of flammable gases inside manholes. After careful consideration, the Joint Forum considered that priority should be given to the implementation of these mitigation measures in public streets of high pedestrian density to reduce the risk of injuries to pedestrians in the event of telecommunications manhole gas explosion incidents. A list of the locations of such public streets is at Annex 6 to the Guidelines. FNOs had, in accordance with the requirement of the Guidelines, implemented at least one of the mitigation measures in some 7 600 manholes in the aforesaid public streets by June 30, 2012.

     In addition to the 7 600 manholes or so located in public streets of high pedestrian density which have at least one of the mitigation measures implemented, the Guidelines require FNOs to install vented manhole covers for all their newly built telecommunications manholes, and replace the old manhole covers by new ones with vent holes during their maintenance or upgrading works. The Guidelines also encourage FNOs to implement the mitigation measures in their other telecommunications manholes. While the Guidelines do not specify a schedule for completing the implementation of the mitigation measures for all telecommunications manholes, FNOs have been implementing such measures in their telecommunications manholes. As at end February 2013, the numbers of telecommunications manholes with the mitigation measures implemented and their percentages in the total number of telecommunications manholes are as follows:

                                   Percentage in the
               Number of           total number of
Mitigation     telecommunications  telecommunications
measure        manholes            manholes
----------     -----------         -----------
Installing     about 3 900         about 1.5%
vent holes in 
manhole covers

Sealing up     about 5 400         about 2.1%
the ducts
leading into 
manholes

Surrounding    about 70 000        about 27.7%
the ducts 
leading into 
manholes with 
concrete

(b) Regarding the problem of vent holes in manhole covers being sealed with adhesive tapes or blocked by dirt and debris, the Guidelines require FNOs to clear the vent holes in manhole covers during their regular inspections in order to ensure the proper functioning of the vent holes. In accordance with the requirements of the Guidelines, each of the FNOs should conduct sample inspections of at least 20% of its telecommunications manholes located in the above mentioned public streets with high pedestrian density in every year, and conduct sample inspections of at least 5% of its telecommunications manholes located in other places in every two years. OFCA will also conduct sample checks to ensure that FNOs comply with the requirements in respect of sample inspections specified in the Guidelines. The result of OFCA's sample checks reveals that FNOs comply with the requirements of the Guidelines.

(c) In addition to installing vent holes in manhole covers, the measures of sealing up the ducts and surrounding the ducts with concrete as recommended in the national standards "GB50373 - Design Code for Communication Conduit and Passage Engineering" and "GB50374 - Code of Construction and Acceptance for Communication Conduit Engineering" were also adopted as mitigation measures specified in the Guidelines. FNOs have been implementing the mitigation measures in their telecommunications manholes in accordance with the requirements of the Guidelines to minimise the risk of occurrence of gas explosion in telecommunications manholes. Since the implementation of the Guidelines on June 30, 2010, OFCA has so far not received any incident report on gas explosion in telecommunications manholes. In view of the well-functioning of the Guidelines, the Administration has no plan to enact legislation to regulate the mitigation measures.

Note: The Guidelines can be downloaded attel_archives.ofca.gov.hk/en/report-paper-guide/guidance-notes/gn_201003.pdf .

 

立法會盧偉國議員 博士 工程師 (工程界)
Legislative Council Ir Dr Hon Lo Wai Kwok (Functional Constituency - Engineering)