Dangerous Dust Explosions.....

Any combustible material can burn rapidly when in a finely divided form. If such a dust is suspended in air in the right concentration, under certain conditions, it can become explosible. Even materials that do not burn in larger pieces (such as aluminum or iron), given the proper conditions, can be explosible in dust form.

Combustible dust are fine particles that present an explosion hazard when suspended in air under certain conditions. The force from such an explosion can cause employee deaths, injuries, and destruction of entire buildings.

A wide variety of materials that can be explosible in dust form exist in many industries. Examples of these materials include food (e.g., candy, sugar, spice, starch, flour, feed), grain, tobacco, plastics, wood, paper, pulp, rubber, pesticides, pharmaceuticals, dyes, coal, metals (e.g., aluminum, chromium, iron, magnesium, and zinc). These materials are used in a wide range of industries and processes, such as agriculture, chemical manufacturing, pharmaceutical production, furniture, textiles, fossil fuel power generation, recycling operations, and metalworking and processing which includes additive manufacturing and 3D printing.

How Dust Explosions Occur?

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In addition to the familiar fire triangle of oxygen, heat, and fuel (the dust), dispersion of dust particles in sufficient quantity and concentration can cause rapid combustion known as a deflagration. If the event is confined by an enclosure such as a building, room, vessel, or process equipment, the resulting pressure rise may cause an explosion. These five factors (oxygen, heat, fuel, dispersion, and confinement) are known as the “Dust Explosion Pentagon”. If one element of the pentagon is missing, an explosion cannot occur.

Prevention of Dust Explosions

To identify factors that may contribute to a explosion, a thorough hazard assessment should be carried out on:

 • All materials handled;

• All operations conducted, including by-products;

• All spaces (including hidden ones); and

• All potential ignition sources.

Taking these facts into account, the following measures are to be taken to prevent dust explosions in process industries where dust explosions mainly occur:

Good housekeeping is necessary to prevent accumulation and scattering of dust on the floor of the building;

Dust generating facilities should be improved by means of installment of the lid or a sealed structure so that dust is not scattered to the outside;

A metal separator must be installed at the crusher inlet to prevent sparks;
All dust generation facilities should be connected to the damping system, and if there is a risk of heat accumulation due to internal fixation, a thermometer should be installed;

If the gas used to calibrate the sensor differs from the actual measurement of the gas concentration, the manufacturer provides the correction value, and the user must apply the correction value to set the sensor sensitivity and alarm;  
Silos used in the production and storage of various resin products must be evaluated and monitored for the occurrence of gas concentrations at a normal time, due to process characteristics;

Oxygen concentrations must be lower than the explosion minimum concentration through the inclusion of inert gas, such as nitrogen. If a change in oxygen concentration is observed, it is considered to be a dangerous situation, and the operation should be immediately stopped until the problem is resolved;
High-speed operation valves, explosion pressure vents, and explosion suppression devices should be installed to protect against dust explosions.

Article by Dr.Yashoda Tammineni,

MSc, Ph.D.

HSE,HOD at NIFS