SINGAPORE - A chemist testifying for the company whose machine caused a blast that killed three workers in a Tuas workshop said he believed it did not have sufficient safety features.

Dr David Rose, regional director of Hawkins, a forensic investigation services company, said on Wednesday (Oct 6) that while Stars Engrg's mixer machine allowed users to detect the temperature in the oil jacket, he understood that it did not allow users to control it.

The inquiry committee looking into the blast heard that the company's sole director Chua Xing Da bought the machine on e-commerce site Alibaba, and had not made it a practice for workers to monitor the temperature in the machine's oil jacket.

"Monitoring temperature is all well and good, but it is actually controlling the temperature that is the important part," said Dr Rose, who added that "simple devices" like tumble dryers and deep fryers have safety thermostats that would allow the heaters to reset.

Last week, State Counsel Kristy Tan told Mr Chua that the machine's heaters could be automatically switched off at a certain temperature, but only if the jacket's temperature sensor was used at the oil jacket. Mr Chua said that he did not know about this.

The explosion on Feb 24 at the workshop unit at 32E Tuas Avenue 11 at around 11.20am injured 10 workers, including three - Mr Subbaiyan Marimuthu, 38, Mr Anisuzzaman Md, 29, and Mr Shohel Md, 23 - who later died in hospital of severe burns.

The inquiry committee on Tuesday heard chemical engineering expert Shaik Mohamed Salim's findings that the overpressured oil jacket could have caused a mechanical failure of the welded seams in the heating jacket. This, in turn, caused a sudden release of the oil from the oil jacket to form an aerosol.

The aerosol could have found an ignition source and caused the explosion outside of the machine, said Dr Shaik.

Dr Rose argued that the ignition took place inside the oil jacket, with a heating coil as a possible ignition source.

When asked, he said he did not have calculations to back up his claim because he did not at the time of his research think that it mattered where the ignition happened.

Senior District Judge Ong Hian Sun said on Wednesday that it was important, and asked Dr Shaik, who was present in court, if his theory still worked if the ignition source was a heating coil inside the machine.

Dr Shaik said that it was possible since the jacket had ruptured and opened.

"A culmination of the theories works," said Dr Rose.

The hearing continues on Thursday with more experts providing evidence.