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How balloons can bring a train to a halt

NO LAUGHING MATTER: Posters like this one have recently been put up at North East Line stations. A train disruption happened on April 6 last year due to an aluminium-foil balloon causing an electrical fault.


    Oct 16, 2015

    How balloons can bring a train to a halt

    DID you know that your shiny, metallic helium balloons could disrupt MRT train services?

    It is no laughing matter if your Minion or Minnie Mouse balloon flies up and away. Posters have recently been put up at stations on the North East Line (NEL) to remind commuters to hold on tightly to their balloons.

    In the poster, train operator SBS Transit explains: "If (the balloons) get caught in the overhead power lines, they can cause a power trip and bring train services to a halt."

    SBS Transit told The Straits Times (ST) that it decided to put up the posters two months ago after a train disruption happened on April 6 last year.

    In that incident, train services on the NEL were disrupted for close to an hour in both directions between Farrer Park and Boon Keng stations due to a power trip.

    Investigations by the Land Transport Authority showed that a passenger accidentally released an aluminium-foil helium balloon which slipped into the tunnel at Boon Keng station when the platform screen doors were opened.

    The balloon then came into contact with an electrical insulator of the overhead catenary system - the power supply system installed on the ceiling of the train tunnel - and caused an electrical fault.

    Said Liew Ah Choy, a professor from the National University of Singapore's electrical and computer engineering department: "The aluminium foil is an electrical conductor, and when it comes into contact with the live overhead wires, a short circuit occurs. This would then trigger the circuit breakers to trip, to prevent further damage to the electrical equipment."

    Meanwhile, SBS Transit's senior vice-president of corporate communications Tammy Tan told ST: "There has not been a (recurrence) of the April 2014 incident, but prevention is better than cure and the posters have been put up as a precautionary measure."

    The 16-station NEL is the only MRT line here powered by overhead catenary systems instead of a power-supplying rail on the ground, so the posters are put up only in NEL stations.

    But the posters can be hard to spot, as several stations have just two or three of them put up along the platform. A few commuters who frequent the Clarke Quay station told ST they saw the posters only in recent weeks.

    While incidents of balloons causing power trips are usually rare here, they happen more often in cities like Hong Kong, where there are signs telling people not to take balloons into train stations.

    According to a Hong Kong magazine, the ban was started in 1996, when a Minnie Mouse balloon floated into a tunnel during the rush hour period. The resulting short circuit halted all trains between Admiralty and Quarry Bay - both interchange stations - for 1½ hours and affected 100,000 commuters.