SINGAPORE - The Feb 24 explosion in a Tuas workshop that killed three workers could have been caused by insufficient oil being placed inside the mixer machine, said experts who investigated the cause of the blast.
Engineer Robert Shandro from Matcor Technology & Services told the inquiry committee on Monday (Oct 4) that the company's forensic investigations found a low level of oil that did not cover the machine's heaters could have resulted in the heaters being overheated to temperatures between 830 deg C and 1095 deg C.
This could have led to cracks forming on the oil jacket and its eventual rupture, the report by Matcor found.
The mixer machine in question was used by Stars Engrg to make an insulation material called fire wrap. The machine heated up oil in a jacket, which then heated ingredients, including potato starch, in the mixer component.
"The heat transfer will be through the air between the oil level and the bottom part of (the mixing component). Everybody knows air is a very bad conductor. So in this case, the equipment will (have to) heat up a lot to get the temperature you need," said Mr Shandro who gave evidence via video-link from France.
His colleague, Mr Ashley Ng, who also testified on Monday, concurred with the findings.
The explosion at the workshop unit at 32E Tuas Avenue 11 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 explosion is believed to have been caused when aerosols from the oil in the mixer machine were ignited.
The inquiry committee, chaired by Senior District Judge Ong Hian Sun, had earlier heard that Stars Engrg director Chua Xing Da did not make it a practice for the workers to monitor the temperature of the oil in the oil jacket each time the machine was used.
Mr Chua also testified earlier that he had decided to operate the machine as a "closed system", which meant all openings and vents were closed to prevent a loss of oil through evaporation.
Matcor's forensic investigations found grains on the inside of the heaters on the machine which indicated they had been exposed to temperatures between 830 deg C and 1,095 deg C.
These grains were formed through "a long process that happens when you heat the heaters for a long time", said Mr Shandro, when asked if they could have formed during the explosion.
The inquiry committee had earlier heard that a small fire had broken out on the machine at about 8.40am on the day of the explosion, and this was put out by one of the workers.
Workers in the workshop at the time were divided in their testimonies on whether they recalled hearing the machine being turned on again after the fire and prior to the explosion at about 11.20am.
Mr Shandro said on Monday that even with the machine turned off between those times, the high pressure in the oil jacket could have remained because of the closed system the machine was operated in.
"The temperature will be very hot because you don't have a very important exchange of temperature... The pressure will be maintained if you have good insulation and no leakage," said Mr Shandro, who confirmed that the machine had good insulation.