Tuas blast inquiry: How the mixer machine that exploded and killed 3 works

A fire investigation team at the site of the incident at 32E Tuas Avenue 11 on Feb 25, 2021. PHOTO: LIANHE ZAOBAO

SINGAPORE - Used to produce a clay-like material for a fire protection product, the mixer machine used by Stars Engrg was of key interest during the inquiry.

It was purchased by company director Chua Xing Da in August 2019 through the Alibaba online platform, and is manufactured by Laizhou Keda, a company in China.

The machine was delivered to Stars Engrg around October 2019, and was installed on a platform at the Tuas workshop on June 12 last year.

It had a capacity of 1,000 litres and weighed over 3,000kg.

The main parts are the mixing compartment and the oil jacket, surrounding the front and back of the mixing compartment.

The jacket is filled with thermic oil, which is heated so it can heat the mixing compartment.

At the bottom of the oil jacket are nine heaters, with rods that heat the oil.

In the mixing compartment, rotating blades mix water and other ingredients, including potato starch and boric acid.

It produces a clay-like substance used in the production of fire protection wrap that is assembled, sold and used by Stars Engrg in its projects.

Attached to the oil jacket are three pipes - two at the top on the front and back of the machine, and a third at the base.

The pipe at the top of the back was meant for pouring oil into the jacket, while the bottom pipe was used to drain the oil out.

The other pipe on the top and front of the jacket was where a dip stick could be inserted to gauge the amount of oil inside.

There are also three fixtures on the machine where temperature sensors were meant to be placed.

Two were at the front and back of the machine on the oil jacket, the third was on the side of the machine on the mixing compartment.

Two temperature sensors were attached to the control panel.

One measured the temperature in the oil jacket, the other the temperature in the mixing compartment.

However, Stars Engrg did not attach the sensors to the fixtures, and would drop either of the sensors into the mixing compartment to measure the temperature of the water being heated inside.

Workers had welded the bottom corners of the machine, and had also welded a metal base plate to the bottom of the oil jacket to address leaks that were found.

Following the blast, the machine was found to have ruptured at the bottom.

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