Combustible Dust and Its Hazard (How Fire Generated)

How is fire produced?

The fire is the reaction that occurs when you have a combustible material, in this case dust, oxygen and an ignition source, combined in suitable proportions to maintain the initial combustion

What is a Deflagration?

It occurs when the combustion or fire zone advances rapidly (0.5 to 1 m / sec), generating large amounts of heat. The gas expansion also creates a pressure wave. Both heat and pressure generated can cause serious damage to people and structures.

How does a detonation occur?

When the shock wave from the explosion travels faster than the speed of sound a detonation occurs. This can happen when the explosion occurs in enclosed areas such as pipes or buildings. Detonations are usually very destructive and difficult to control once begun.

When structures or closed containers are affected due to the blast, it is said that an explosion has occurred. One factor that greatly affects the risk of dust explosion is how easily the material can agglomerate or form clumps. Agglomeration is usually seen in humid environments.

How is the primary explosion generated?

It is the result of creating a fire in a confined space, where the rapid change in temperature causes a rapid change in pressure, resulting in a shock or pressure wave.

In the case of combustible dusts, the explosion, requires the presence of all these factors to occur

1. Ignition sources

2. Fuel

3. Source of oxygen or oxidizing material

4. Dispersion

5. Containment or confinement

What is Dispersion?

It is the effect of moving a cloud of dust from one place to another either by mechanical processes (transport, ventilation, vibration) or as the result of a primary explosion.

               

Secondary explosion

The combination of the fire elements within an enclosed structure provides the conditions for the flame to quickly spread, creating enough pressure to move any dust from work surfaces. This movement of dust is enough to create chain reactions that result in subsequent or secondary explosions.

Minimum Explosive Concentration

It is the minimum dust concentration needed to sustain the process of deflagration of a dust sample in a laboratory test.

Auto Ignition Temperature

It is the temperature at which dust combustion starts only due to the effect of temperature increase with no other source of ignition present. Auto-ignition temperature for the same material, may be different between a cloud and a thin layer of dust

Deflagration index (K _st)

This value is used to estimate the dust behavior of a particular material during a deflagration. The higher the value of K _st the more severe the explosion can be.

List of Materials with the Potential to Generate combustible dusts

Plastic Vinyl acetylene Poly vinyl acetate Poly propylene Molded Pulp Poly Acrylamide Poly ethylene Co-polymer Poli Acrylonitrile Epoxy or phenolic resin Ethylene Co-polymer Poly methyl acrylate Polymer Emulsion poly vinyl alcohol Melamine and its resin Poly vinyl butyral Urea-formaldehyde Poly vinyl chloride (PVC) Terpene phenol resin

Chemical Industry Adipic acid Sulfur Sodium stearate Ascorbic acid Carboxymethylcellulose Lactose Calcium acetate Dextrin Methylcellulose Anthraquinone Calcium stearate Paraformaldehyde Sodium Ascorbate Lead stearate Metal Aluminum Iron Carbonyl Zinc Bronze Magnesium

Food Garlic Alfalfa Cotton Rice starch Corn starch Wheat starch Sugar Cocoa powder Coffee Coconut shell Lemon peel Onion powder Spice powder Potato starch Sunflower Gluten Locust bean gum Xanthan gum Rice flour Oatmeal Peanut Flour

Rye flour Cornmeal Potato flour Wheat flour Lemon Malt Apple Peach Mixed tobacco snuff Potato Parsley (dried) Rice powder Wheat grain dust Walnut Powder Soybean Powder Beet Linseed Seeds of raw cassava Sunflower Seeds Semolina Tomato Carrot

Agricultural products Rice starch Cellulose Milk Powder Corn Starch Cork Dry skim milk Wheat starch Egg white Corn Sugar Soybean meal Whey Beet sugar Wheat flour Tapioca Barley Lactose

Carbon Products Activated carbon Coca-cola Carbon black Bituminous coal Petroleum coke Pulp Charcoal Pine soot Oil Cellulose Lignin       Chemical  Dust