SINGAPORE - When workers raised concerns after a leak was found on a mixer machine, their boss Chua Xing Da thought it was a "small thing".

And even after it caught fire, he tried to persuade a concerned worker that it was not dangerous.

That worker, along with two others, later died as a result of an explosion linked to the machine.

On Thursday (Sept 23), Mr Chua, 37, the sole director and shareholder of Stars Engrg, testified before an inquiry committee looking into the explosion.

The blast happened at around 11.20am on Feb 24, at the workshop situated on the first floor of the building at 32E Tuas Avenue 11.

A total of 10 workers, including eight employed by Stars Engrg, were injured in the blast.

Three of them died from severe burns that covered 90 per cent of their bodies shortly after they were taken to hospital.

They were Stars Engrg employees Anisuzzaman Md, 29, Subbaiyan Marimuthu, 38, and Shohel Md, 23.

At the State Courts on Thursday, Mr Chua testified before the committee chaired by Senior District Judge Ong Hian Sun, giving the background of the company and its work.

He was the fifth witness to testify since the inquiry hearings began on Monday (Sept 20).

The four witnesses who previously testified were current and past employees of the company, including one of the workers who survived the blast.

Stars Engrg is a fire protection company that made an insulation called fire wrap.

Its production involved using a mixer machine to create a clay-like material, by heating up water and mixing it with ingredients including potato starch.

The machine, purchased via online platform Alibaba, was installed at the Tuas workshop in June last year.

It used nine heaters to heat oil in an oil jacket compartment that wrapped the mixer.

When it was used on Aug 8 last year, a heater emitted a spark and smoke.

Smoke was again observed from the machine by workers on Aug 28 and Sept 21.

A leak at the corner of the machine was found by workers on Sept 28.

All these incidents were reported by the workers to Mr Chua, but the leak was not immediately dealt with.

On Oct 12, workers again raised concerns to him about the leak, saying it appeared to be bigger.

But Mr Chua told the inquiry that he did not think of examining the cause of the leak at the time.

"I thought this was a small thing," he said.

He told the workers to repair the machine by welding it, and said he thought he had adequate experience and knowledge to operate and maintain the machine because Stars Engrg has "experience in big motors and hydraulic machineries".

Mr Chua claimed that he supervised the repairs either in person or through calls and messages.

"I would not have been the person carrying out the repairs, as I had many things to do as the director of Stars," he told the committee.

Smoke was again seen emanating from the machine on Jan 8 this year.

On Feb 12, a fire broke out at the corner of the machine, but was put out by the workers.

One of them, Mr Marimuthu, raised concerns that the machine was dangerous.

Mr Chua said that when he found out about this, he tried to alleviate Mr Marimuthu's fears and messaged him: "Actually this fire not come from the machine... U thinking the machine very dangerous but actually no."

On the morning of Feb 24, at about 8.40am, another fire broke out at the machine and was again put out by the workers.

Mr Marimuthu, who was at the workshop, later spoke to Mr Chua over the phone four times within 15 minutes from about 10am to 10.15am.

Mr Chua told the inquiry that he did not instruct any of the workers to continue operating the machine, and had told Mr Marimuthu to drain the oil and wait for him to arrive at the workshop.

At about 11.15am, Mr Marimuthu sent a photo of a damaged heater from the machine to the company's engineer, Mr Lwin Moe Tun.

Less than 10 minutes later, the explosion happened.

The force of the blast blew out the window panels in the building, caused the rear wall of the workshop to collapse, and ripped a large hole in the adjoining wall of the unit.

Mr Marimuthu and seven of his colleagues were taken to hospital with burn injuries.

He died along with Mr Anis and Mr Shohel shortly after.

Mr Chua said that after the incident, Mr Lwin Moe Tun told him he was scared and wanted to delete the messages and photo of the damaged heater he had received from Mr Marimuthu.

Mr Chua said he did not instruct him to delete it, but said "ok".

Mr Lwin Moe Tun deleted the same material from Mr Marimuthu's phone, before handing it over to Mr Chua, who then handed it over to the police.

However, the police forensics team managed to recover the photo.

Mr Chua said he had been trying to get a new machine from the same company in China after the Feb 12 fire.

He added that he felt then that the manufacturer Laizhou Keda was reputable, and expected that the machine would have few frills to deal with.

"My thinking is that it's like an oil fryer with everything built in, and you don't have to monitor the oil temperature," he said.

A key area raised during the inquiry is the use of the machine and whether the amount of oil poured into the oil jacket was adequate.

Statements from the workers and Mr Chua have thus far indicated it may not have been operated as intended by the manufacturer, with inconsistencies regarding the use of the temperature sensors during production and trials.

Mr Chua will continue to testify and answer questions from the committee on Friday (Sept 24).

The first tranche of hearings will last till Oct 8, while the second tranche is expected to be from Nov 15 to 19.

Other witnesses expected to present their statements in the coming days include the other workers who were injured, as well as investigators from the Singapore Civil Defence Force and Ministry of Manpower.