SMRT inspects tunnel cross-passage doors after metal cladding incident

SINGAPORE – Rail operator SMRT has inspected all cross-passage doors in tunnels – meant to prevent the spread of fire and smoke from one track tunnel to another – and reinforced the outer layers of doors with structural issues.

It conducted the checks after an incident on Sept 10, 2025 when a metal layer came loose from a tunnel door between Expo and Changi Airport stations on the East-West Line, and fell on the left side of the rail track.

An investigation report on the incident was published on Aug 21 by the Transport Safety Investigation Bureau (TSIB), which falls under the Transport Ministry.

SMRT told The Straits Times it is working with the Land Transport Authority (LTA) to carry out renewal works for these doors, particularly those on the older North-South, East-West and Circle Lines.

The TSIB report said thin and flat objects like the metal cladding can pose a hazard to train operations and even lead to a train derailment.

No one was injured in the incident, which took place from 5.57pm on Sept 10, 2025, when the captain of a train travelling from Expo to Changi Airport stations reported that he heard a thumping sound.

Later, the train captain of an eastbound train and the station manager of Expo station – who was onboard to investigate the sound – checked the tracks.

At 6.13pm, the station manager sent a photo of the object to the control centre.

The station manager of Tanah Merah station then boarded the next train bound for Changi Airport station to check the tracks. At about 6.26pm, he informed the control centre that there was a metal object on one of the running rails and that it was not safe for the train to proceed.

The control centre closed the track between Expo and Changi Airport stations at 6.30pm before routing the train back to Expo station and getting passengers to alight from the train.

The object was later removed.

The investigation found that the affected door was open when the metal cladding got detached, although cross-passage doors must be closed during normal train operations.

While the bureau was unable to pin down the reason for the door opening, it surmised that either the strike plate – a part of the door frame that the latch engages to lock the door – was damaged, or that the lockset of the affected door was loose.

Metal cladding not secured properly

The bureau found that SMRT did not know about the wind load requirements for the doors, which were set by rail asset owner LTA.

The 15 cross-passage doors along the Changi Airport branch on the East-West Line connecting Tanah Merah, Expo, and Changi Airport were installed in 2001.

According to LTA, these doors have to withstand a differential pressure of +/-2,000Pa due to the piston effect which causes air to flow in a confined space when a train approaches a door. Pa is a measure of air pressure.

The affected door from which the metal cladding fell off was replaced by SMRT in 2016. However, the rail operator was unaware of the wind load requirements and believed it was a “straightforward one-to-one replacement” of the door with no modification involved.

LTA said the document containing design specifications for cross-passage doors was made available online since 2010, and that it was the rail operators’ responsibility to see the document. But LTA added that it was unable to locate records informing rail operators of the document.

The bureau, in its report, said rail operators were not obligated to access and review materials uploaded online, unless specifically required to do so by LTA.

It also felt that it may not be a “reasonable expectation” for rail operators to request documents from LTA even if they were not published online.

This is because LTA should “clearly communicate” its requirements and expectations to rail operators, instead of assuming that they will proactively request for documents that they may not know about.

As for the affected door, the metallic frame structure and paper honeycomb filling were glued between two metallic claddings or outer layers. The bureau found no evidence that the claddings were secured via mechanical fasteners or welding.

The investigation team doubted that metal-to-metal glueing would provide the structural strength needed to withstand the wind loads experienced by such doors. It was likely that the glue bonding the cladding to the door frame had deteriorated.

The strike plate was also damaged, possibly because its mounting screws were inserted wrongly and of the incorrect length. The incorrect type of screws were also used.

SMRT carried out inspections on these doors every six months, but did not check for the splitting or peeling of metal cladding.

It also only recorded defects that could not be rectified during the inspection, while those fixed during the inspection were not reported.

A strike plate is a metal piece on a door frame that secures the door latch or bolt.

As a result, there was no way to determine whether the screws securing the affected door’s lockset or strike plate had ever been replaced or removed, after the new door was installed in 2016.

The bureau concluded that opportunities to identify recurrent issues across these doors were missed, even though they might have prompted closer monitoring or troubleshooting.

The last two inspections of these doors on Jan 27 and July 24, 2025 did not record any defect on the affected door.

Limitations of track detection system

While there is a track circuit detection system in place to detect metallic foreign objects that lie across both left and right running rails, the metal cladding in this incident rested only on the left running rail. As such, it did not generate an alarm to alert the control centre.

The front of each train is also equipped with an obstacle deflector about 105mm above the running rails, to activate the train’s emergency braking system when a sufficiently large foreign object is detected.

In this incident, the door cladding was flat and only 1mm thick, and could not trigger the train’s emergency braking system.

Hence, it remained undetected when five trains drove past, before the train captain heard the thumping sound at 5.57pm.

The bureau said the early detection of such foreign objects could reduce operational safety risks while preventing minor incidents from escalating into serious accidents.

It added that it would be “desirable” for technologies to be used to allow the identification of such objects on tracks, to which SMRT responded that it is exploring ways to detect thin flat objects on tracks such as mounting suitable sensors on trains.

After the incident, SMRT mandated the recording of all defects identified during inspections – whether or not they are resolved on-site.

It also made sure to carry out monthly sampling checks on the maintenance records for these doors to ensure proper compliance.

LTA also sent an e-mail to rail operators on July 20, 2026, to inform them that specifications of critical infrastructure – including cross-passage doors – are available online and provided a link to access them.

Responding to The Straits Times’ queries, Lam Sheau Kai, president of SMRT trains, said: “We acknowledge the findings of the TSIB investigation report and take this matter seriously.”

Noting that cross-passage doors undergo regular maintenance and inspections, he said this is the first occurrence of such an incident.

Lam added that following the incident, SMRT has enhanced its inspection regime to include checks on door claddings and worked with LTA to include wind-load specifications into the door replacement criteria.

TSIB is the air, marine and rail accidents and incidents investigation authority in Singapore. It aims to promote transport safety by carrying out independent investigations into air, marine and rail accidents and incidents. The safety investigations do not seek to apportion blame or liability.