On Sep. 7, what looked like white smoke engulfed an MRT train at 9:50pm, forcing all passengers to disembark at City Hall MRT station.

The cause of the "smoke" was due to a refrigerant gas leak from the air conditioning system.

[caption id="" align="alignnone" width="464"] GIF from video sent by Mothership reader[/caption]

In response to a written parliamentary question, Acting Minister for Transport Chee Hong Tat said that all MRT trains are installed with "robust joints and corrosion-resistant pipes to minimise air conditioning refrigerant gas leaks".

Tanjong Pagar GRC Member of Parliament Joan Pereira asked what measures were in place to ensure that the aircon systems on the MRT trains were regularly maintained at a high standard and what was to be done to prevent future refrigerant gas leaks and other aircon malfunctions on the trains.

Chee also added that rail operators conduct preventive maintenance of aircon units and regularly check for signs of leaks. Aircon units on trains are also dismantled for thorough checks and replaced if necessary.

"Refrigerant gas leaks do occur, but these are rare incidents which do not pose public health risks."

MRT aircon serviced once every three weeks and six months

According to the SMRT website, the aircon system of the trains is serviced once every three weeks and additionally, once every six months.

Every three weeks, the service maintenance focuses on general preventive maintenance comprising "functional and visual checks of the aircon system".

Every six months, the service maintenance consists of detailed checks on aircon components.

In their Frequently Asked Questions, SMRT also answered why it "sometimes feels warmer" on the train. It is attributed to external factors such as longer stops at stations and higher passenger loads during peak hours that could lead to warmer conditions.

"When this happens, it will take longer for the space to cool down and for the temperature to return to the desired level," SMRT wrote.

Top photos via MCI/YouTube & Mothership reader