SINGAPORE - Four people were taken to hospital after a gas leak at a building in Jurong on Friday (Jan 26).

The Singapore Civil Defence Force (SCDF) said in a Facebook post that it was alerted to an incident of an ammonia leak at 1, Fishery Port Road, at about 11.40am.

The building houses Ben Foods, a food distribution company that does food trading, packing and wholesale operations.

It is housed in a multi-temperature warehouse, according to its website.

"The leak in a first-floor chiller room was shut off by the company and its staff were evacuated prior to SCDF's arrival," said SCDF.

SCDF decontaminated three people by washing them down with water. They were taken to Ng Teng Fong General Hospital in a conscious and stable condition.

Another worker who was exposed to the ammonia vapour did not want to be sent to the hospital. But by late afternoon, she experienced breathlessness and sought medical attention from SCDF, bringing the total number of those taken to hospital to four.

Mr Salim Anwar, a 68-year-old finance and administration manager at NCS Cold Stores, the building adjacent to Ben Foods, told The Straits Times that he could already smell the ammonia in the air when he reached his workplace at 8.30am.

"At about 10.30am, the smell became unbearable. My eyes felt very painful, like they were getting pricked," he said.

He called the company's engineering department, which said it was looking into the problem. It also asked him to get everyone to evacuate the building.

Mr Fauzan Tahir, 30, a delivery driver for Ben Foods, was on his way back to get a second batch of goods when his boss called him to tell him not to enter the building.

"My supervisor said there was an ammonia gas leak. I've been waiting outside since 1pm," he told ST at 3.15pm.

He and his fellow delivery driver colleagues have not received word on when the building will be reopened.

As of 3.45pm, SCDF officers were still at the scene of the gas leak, where a slight stench remained in the air.

SCDF said in an update at 3.39pm that SCDF's HazMat (Hazardous Materials) Specialists have picked up low levels of ammonia in the immediate perimeter outside the affected building with detectors.

The HazMat Specialists, who wore protective suits, detected a leak within the ceiling of the chiller room worked to access the concealed ammonia piping.

In another update at 9.05pm, SCDF said it had traced the source of the ammonia leak to a main distribution pipe.

"The pipe is not easily accessible as it is installed within a metal plate ceiling and further concealed by layers of insulation materials."

SCDF had already shut off the main supply line and several control valves, confining the area of operations to a chiller room and part of the loading/unloading bay.

Although the concentration of ammonia vapour within the affected area had diminished considerably in the last three hours, SCDF officers deployed three water curtains within the premises as a precautionary measure.

"This is to suppress any residual ammonia vapours which may escape beyond the affected area," it said. "It is expected to be an extended operation."

About 100 workers from the premises were evacuated prior to SCDF's arrival.

The neighbouring premises are not affected.

ST has contacted Ben Foods for more information.

In July last year, 11 workers were taken to hospital after being exposed to a chemical leak at a wafer fabrication plant in Kallang Way.

In September 2016, seven people were taken to hospital after a chlorine gas leak from an indoor storage facility in Pioneer.