On February 25, 2021, the day after the fire broke out at No. 11, 32E Tuas Avenue, SCDF personnel inspected the damage to the Tuas Industrial Building. (Photo: Gaya Chandramohan)

Singapore: An explosion occurred in an industrial building in Tuas on Wednesday (February 24), killing three workers and injuring seven others. Potato starch powder has been identified as the source of the explosion.

Workplace Safety and Health Commissioner (WSH) Silas Sng said on Thursday that a preliminary investigation found that the 32E Tuas Avenue 11 incident was caused by a "combustible dust explosion."

He added that the dust in this case is powdered potato starch. Mr. Sng said that the company Stars Engrg on site uses potato starch powder to manufacture its products.

As of Thursday night, five injured workers were still in the hospital in critical condition, and two others had been discharged.

CNA explains that potato starch powder-or other dust particles, including common dust particles such as sugar or flour-can be explosive.

According to the Ministry of Manpower (MOM) notice issued by the Department of Occupational Safety and Health in July 2015, when all five elements of the "dust explosion pentagon" are present, fine particles will burn: fuel (combustible dust), air , Dispersion, restriction and ignition source.

"It is a well-known scientific fact that... materials in powder form can explode when dispersed in the air," said Mr. Sng, who is also the director of the Occupational Safety and Health Department.

"Especially when they are in a closed environment... when there is an ignition source, an explosion occurs, as you can see here," he added.

The MOM notice stated that in this type of dust explosion-"frequently but not always in enclosed places"-fine particles suspended in the air experience "rapid combustion."

The difference between a dust explosion and a fire associated with a large amount of solid materials is the size of the combustible surface area.

"A large number of solid combustibles burn relatively slowly due to the limited surface area exposed to the air. However, when the same solid is divided into fine powders and dispersed in the air in the form of dust clouds in the form of suspended particles, the result will be completely Different," Mom said in the circular.

"In this case, the surface area exposed to the air is much larger, and if ignition occurs, the entire cloud may burn very quickly. This will cause the rapid release of heat and gas products, leading to an increase in pressure."

Combustible items in the form of dust

According to the MOM announcement, combustible materials in the form of dust include organic matter, such as sugar, corn starch, flour, peat, soot, and cellulose pulp.

Various types of chemical particles are also combustible, including ascorbic acid (vitamin C) and sulfur.

Metals such as aluminum, bronze, magnesium, and zinc can also catch fire in powder form, as can plastics such as resins, melamine, and polymers.

How to prevent dust explosion

The WSH commissioner explained on Thursday that combustible dust is generated when powder is transferred, for example from a bag to a mixer.

"Over time, dust can accumulate in the environment, especially if ventilation or housekeeping is insufficient," Mr. Sng said.

Therefore, dust control is one of the recommended measures to reduce the risk of fire.

The announcement of the Ministry of Manpower recommends having a local exhaust ventilation system, which "can effectively capture dust to prevent unnecessary spread of combustible dust when people are working."

MOM stated that such systems can be implemented in suitable locations for loading, unloading or transferring materials, while “be careful not to have an extensive network of pipes in the ventilation system, which will cause the burning materials to spread after the explosion”.

The Ministry also recommends cleaning and maintenance of the dust collection system and filter. Vacuum or wet cleaning methods are better than cleaning methods. "Sweeping will cause more dust particles to disperse," it said.

To prevent fire, the Ministry of Manpower stated that fire-proof equipment or non-sparking tools should be used in areas where combustible powder is handled.

The operator should also ensure the effective connection and grounding of the powder handling unit to prevent the accumulation of electrostatic charge, which may cause fire when unintentionally discharged.

Inert gases such as nitrogen can be used to reduce or eliminate the presence of oxygen in the atmosphere.

MOM also recommends other measures, such as providing explosion relief to safely discharge energy in the event of an explosion, installing spark or luminescent material detectors, and isolating areas handling combustible dust from other parts of the workplace.

In addition to providing training and refresher courses on combustible dust hazards, employers must also equip workers with appropriate personal protective equipment, such as fire-resistant clothing and safety shoes.

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