SINGAPORE - The boss of the workers who died after an explosion at a Tuas workshop in February said at an inquiry hearing that he was about ready to give up on a problematic mixer machine on Feb 12 following a small fire.

On Friday (Sept 24), Mr Chua Xing Da, 37, the sole director and shareholder of Stars Engrg, said that he had decided then that if any other issues arose with the machine, he would replace it.

But on Feb 24, at about 11.20am, the explosion at a ground-floor industrial unit at 32E Tuas Avenue 11 killed three of his employees. Seven other workers were injured, including two from another company.

On Friday, Mr Chua was grilled about how he continued to use a mixer machine linked to the blast without a temperature sensor attached to its oil jacket, even though it had encountered several issues prior to the incident.

He said that the operating temperature of the mixer machine should be between 70 deg C and 160 deg C. As the fire clay - a material his company manufactured - was made at temperatures between 80 deg C and 100 deg C, he did not monitor the temperature inside the oil jacket.

State Counsel Kristy Tan questioned Mr Chua on this decision, saying: "You are assuming that because the temperature is at this range, the pressure (of the oil vapour in the oil jacket) will never increase... That is where your logic is extremely circular and built on assumptions."

She added: "Everything is built on the house of cards of assumptions and not on measurements."

Mr Chua's cross-examination came on the fifth day of public hearings by an inquiry into the causes and circumstances leading to the blast that killed three workers. The inquiry committee is chaired by Senior District Judge Ong Hian Sun.

The three workers - Mr Anisuzzaman Md, 29, Mr Subbaiyan Marimuthu, 38, and Mr Shohel Md, 23 - died from severe burns to 90 per cent of their bodies.

Star Engrg installs fire protection systems and also produces fire wrap, a material used to insulate water pipes and air-conditioning ducting systems against fire.

The mixer machine was used to mix several ingredients to make fire clay, which is used to make the fire wrap. It had nine heaters to heat oil in an oil jacket, a compartment that wrapped the mixer.

State Counsel Tan asked if a small fire that broke out on Feb 12 might have suggested to Mr Chua that the temperature was higher than he thought.

He replied that he thought it was a tape on the machine that had caught fire.

Asked to account for the white smoke emanating from the machine, Mr Chua said he thought this could have been steam.

Noting that he and the company's project engineer Lwin Moe Tun went on site to monitor the machine after the Feb 12 fire, Mr Chua said: "Would I risk my life for this?... If I thought there was something wrong, I would have replaced it."

The inquiry committee had earlier heard that the workers would work late into the night as their production was based on targets rather than hours.

Following a second fire that happened at about 8.40am on the day of the explosion, Mr Chua had asked Mr Marimuthu on the phone whether he knew how to change the heater on the mixer machine.

Mr Marimuthu had said he did not.

Mr Chua maintained that by this question, he intended for Mr Marimuthu to stop work, remove the faulty heater and wait for him to arrive.

State Counsel Tan pointed out that nothing in Mr Chua's witness statement stated that he explicitly called for production to halt.

She then postulated that if the faulty heater had been replaced, it would have set production back by hours. The workers would also have known that they would then have to work late into the night to meet the daily target.

"If Mr Marimuthu felt that the daily targets still had to be met... that would have given him pressure to use the mixer machine as is instead of replacing the heater," said State Counsel Tan.

A visibly upset Mr Chua wiped his eyes and responded: "I cannot agree."