SINGAPORE: The Bishan MRT tunnel flooding incident was "entirely preventable", said the Land Transport Authority (LTA), as it concluded investigations into the Oct 7 incident.
The flooding, which disrupted train services for more than 20 hours, might not have happened had the SMRT team responsible for the maintenance of the Bishan storm water sump pit and pump system carried out their duties, said LTA in a news release on Tuesday (Dec 5) summarising its investigation findings.
The probe revealed that existing flood protection measures at the Bishan tunnel portal were "designed to be more than adequate" to handle the Oct 7 rainfall, the authority said, adding that measures such as a high-capacity sump pit and three complementary high-capacity pumps "have safeguarded the Bishan tunnel portal entrance for over 30 years without incident".
LTA said that the individual components of the Bishan storm water pump system were not defective and that that there are three possible scenarios why it failed to work:
- The lowest “stop” float switch was likely impeded by accumulated silt and sludge in the storm water sump pit, which prevented the storm water sump pumps from activating;
- The highest “alarm” float switch, which is wired independently from the other four float switches, could have been impeded by floating debris in the storm water sump pit, which prevented the SMRT Operations Control Centre from being alerted of rising water levels in the pit; and/or
- The SMRT crew that conducted corrective maintenance for the storm water pump system on Jul 13 may have failed to switch the pump controls back to “automatic” mode after work was done.
However, whether it was one of these three scenarios or a combination of them that led to the incident "cannot be established definitively", said LTA, as the exact conditions cannot be recreated following immediate remedial works.
"Nonetheless, all three possible failure scenarios could only arise as a result of a lack of proper maintenance, audits and supervision," it added.
The release also stated how a separate and independent investigation by SMRT found that team responsible for preventive maintenance works on the sump pit and pump system "had not been carrying out the required works on the purported maintenance dates, and in fact, falsified maintenance records".
"SMRT has accepted full responsibility for the incident and disciplined the staff found responsible," said LTA.
It also reiterated that together with the transport operator, it has "enhanced the robustness and resilience" of flood protection measures at Bishan MRT station and other tunnel portals, which are how trains get from above ground to underground.
Earlier on Tuesday, Transport Minister Khaw Boon Wan announced the formation of an LTA-PUB committee to look into tunnel flood prevention and study long-term measures.