But the driver of the CNG-fuelled bus died from complications arising from his burns four days later, a coroner's inquiry into his death in the August 2010 incident heard on Wednesday.
Mr Chan Beng San, then 56, had picked up the group of NSFs from Jurong Camp 1 at 6.45am on Aug 13, 2010.
He had ferried them to the Poyang Range at Old Lim ChuKang Road and the group alighted at 7.05am.
The group had smelled something similar to petrol or fuel when they boarded the bus earlier.
They alerted Mr Chan but he dismissed it and even suggested that some previous passengers could have brought durians onto the bus.
He then drove the bus away from the range. About 15 minutes later, the group, which had left some items behind in the bus, called Mr Chan's mobile phone for help.
It was answered by someone who told them that the bus had exploded.
Investigations also revealed that the explosion could have happened while Mr Chan was still in his driver's seat and the bus was on the move.
The explosion, which started at the front of the bus, was so great that all the seats in the bus were pushed backwards.
The windscreens were completely shattered and the roof above the door and the driver's seat were completely burned.
A witness who was driving along the same stretch of Old Lim Chu Kang Road spotted Mr Chan sitting on the road, a short distance away from the front of the burning bus.
The witness pulled him away from the bus to the side of the road and called the police.
When they arrived at the scene, officers found that Mr Chan could not speak and was disorientated.
He was rushed to the Singapore General Hospital by ambulance for treatment.
Complications
Mr Chan suffered burns on 39 per cent of his total body surface area. He underwent burns excision and skin grafting the next day.
But he faced complications such as acute renal failure and acute respiratory distress, in his recovery post-operation.
He died of broncho pneumonia on Aug 17.
Investigators later found a gas leak at a joint between the nut and the valve of some black tubing recovered from the rear left compartment of the bus.
There was also a part missing and this meant gas could have leaked out from the joint between the nut and the connector.
The gas had seeped into the passenger cabin of the bus and accumulated at the front of the bus, investigations showed.
An inspection of the bus also found a dashboard- mounted cigarette lighter near the driver's seat.
The court heard that the dashboard-mounted cigarette lighter wasn't part of the bus and that Mr Chan may have mounted it himself.
He was the only driver of the bus since its registration.
The eight CNG cylinders mounted on the roof of the bus were found intact.
The investigation report did not specify what sparked the ignition.
Design lapses
State Coroner Eddy Tham concluded that it was likely that CNG fuel had leaked at the joint of the tubing and had accumulated inside the bus.
An ignition of the leaked CNG fuel into the interior of the bus had resulted in the explosion at the front of the bus, followed by fire that went through the bus, he said.
He also said that the missing part on the tubing could have resulted in the gas leak.
The bus, owned by Sun-Gee Travel (SGT), was still under its one-year warranty.
Though its remaining 22 buses did not have missing parts, investigations by the Land Transport Authority (LTA) revealed that there were other several non-compliances to LTA's pre-registration approval standard in the design of the CNG buses.
The buses were impounded on Aug 24.
The bus manufacturer, Xiamen King Long, acknowledged that there were indeed lapses in their CNG bus design.
The 22 impounded buses were returned to SGT to be converted into diesel-powered ones in January last year. The licences for the buses were reinstated on July 25 last year.
Mr Chan's family members were not present in court during the inquiry.
They also declined to comment when The New Paper visited them at their home yesterday evening.
