In Singapore, Potato starch powder has been identified as the source of an explosion at an industrial building in Tuas on Wednesday (Feb 24), which left seven injured and three workers dead.
Commissioner for Workplace Safety and Health (WSH) Silas Sng on Thursday stated that preliminary investigations have found that the incident at 32E Tuas Avenue 11 was caused by “a combustible dust explosion”, and that the dust in this was “potato starch in powder form”.
Stars Engrg- the company at the site – uses potato starch powder to manufacture its products, said Mr. Sng.
Potato starch powder – or other dust particles, including commonly available ones such as sugar or flour – can be an explosion hazard.
THE “DUST EXPLOSION PENTAGON”
The Ministry of Manpower (MOM) circular was issued by the Occupational Safety and Health Division in July 2015. According to this, fine particles can combust when all five elements of a “dust explosion pentagon” are present:
(Graphic: MOM)
Mr. Sng, who is also director of the Occupational Safety and Health Division also said that “It is a known scientific fact that … materials in powder form can be explosive when it is dispersed over the air. Especially when they are in an enclosed environment … with a source of ignition, you get an explosion, as you see in this case here.”
According to the MOM circular, such dust explosions happen “often but not always in an enclosed location” – the fine particles that are suspended in air experience “rapid combustion”. What differentiates dust explosions from fires associated with a mass of solid material is the size of the combustible surface area.
“A mass of solid combustible materials will burn relatively slowly due to the limited surface area exposed to the air. However, when the same solid is split into a fine powder and dispersed as suspended particles in the air in the form of a dust cloud, the result will be quite different”.
“In this case, the surface area exposed to the air is much larger, and if ignition occurs, the whole of the cloud may burn very rapidly. This results in a rapid release of heat and gaseous products, causing pressure to rise.”
THINGS THAT ARE COMBUSTIBLE IN DUST FORM
Materials that are combustible in dust form 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.
(Source: MOM)
HOW TO PREVENT DUST EXPLOSION
According to Mr. Sng, “Over time, the dust can accumulate in the environment, especially if the ventilation or the housekeeping is inadequate.”Combustible dust can be generated when the powder is transferred, for example from a bag into a mixer. As such, dust control is one of the measures recommended to minimize fire risks.
The MOM circular suggests having local exhaust ventilation systems that “can capture clouds of dust effectively to prevent unnecessary dispersion of combustible dust where people are at work”.
The ministry also recommended housekeeping and maintenance of a dust collection system and filters, with vacuuming or wet cleaning methods favored over sweeping methods as “sweeping would tend to cause more dispersion of dust particles.”
Such a system can be implemented at suitable locations where materials are loaded, unloaded, or transferred, while “taking care not to have an extensive ducting network, which can cause burning materials to spread following an explosion” within the ventilation system, it said.
To prevent ignition, MOM stated that flame-proof equipment or non-sparking tools should be used in areas where combustible powders are being handled.
Operators should also ensure effective bonding and grounding of powder handling units to prevent the build-up of electrostatic charges, which may lead to ignition when inadvertently discharged.
Inert gases such as nitrogen can be used to reduce or eliminate the presence of oxygen in the atmosphere.
MOM recommended other measures as well, such as providing explosion relief to safely vent the energy in the event of an explosion, installing detectors for sparks or glowing materials, and isolating areas handling combustible dust from other parts of the workplace.
On top of providing training and refresher courses on combustible dust hazards, employers must also equip workers with the right personal protective equipment such as fire-retardant clothing and safety shoes.
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