combustible dust explosions

What was happened at the Imperial Sugar refinery northwest of Savannah, Georgia, on February 7, 2008, illustrates how dangerous combustible dust is if it is not treated properly.

In that accident, 14 people died and 38 others injured, including 14 people with serious and life-threatening burns.

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In this post, you are going to learn some important facts about combustible dust that you must take care of.

The purpose of this post is after reading this post, you will be able to take necessary actions to prevent similar explosion accidents from happening.

Combustible Dust Definition

We will start with the definition.

What is combustible dust actually?

There are several definitions we can find about that term, and here are some of them:

OSHA (Occupational Safety and Health Administration): combustible dust are fine particles that present an explosion hazard when suspended in air under certain conditions

CCOHS (Canadian Center for Occupational Health and Safety): combustible dust is any fine material that has the ability to catch fire and explode when mixed with air.

NFPA (National Fire Protection Agency): it is defined as dust particles that are 500 microns or smaller and present a fire or explosion hazard when dispersed and ignited in air.

WHMIS (Workplace Hazardous Materials Information System): it is defined as a mixture or substance that is in the form of finely divided solid particles that, upon ignition, is liable to catch fire or explode when dispersed in air

How Do Combustible Dust Explosions Occur?

Combustible dust explosions can occur if there are five (5) elements exist. If one of those five elements is unavailable, it will not occur.

Three elements (3) are called the fire triangle. Meanwhile, those five elements are called the dust pentagon.

  1. Fuel to burn
  2. Oxygen
  3. Ignition source
  4. Combustible dust dispersion in the air in a certain concentration
  5. Confinement of the combustible dust cloud

If you could control these elements, combustible dust explosions will not happen.

What are Examples of Combustible Dust?

Unfortunately, most people may not aware of the existence of combustible dust in their workplace. This situation is very dangerous since this can cause a severe accident.

Ideally, an effective hazard identification process can identify the existence of combustible dust along with its sources. But, in most cases, this does not happen.

If this is the case, then a combustible dust list will be definitely helpful.

In fact, OSHA has published a list of combustible dust that you can use as a reference.

Here they are:

Agricultural Products
Egg white
Milk, powdered
Milk, nonfat, dry
Soy flour
Starch, corn
Starch, rice
Starch, wheat
Sugar
Sugar, milk
Sugar, beet
Tapioca
Whey
Wood flour

Agricultural Dusts
Alfalfa
Apple
Beetroot
Carrageen
Carrot
Cocoa bean dust
Cocoa powder
Coconut shell dust
Coffee dust
Cornmeal
Cornstarch
Cotton
Cottonseed
Garlic powder
Gluten
Grass dust
Green coffee
Hops (malted)
Lemon peel dust
Lemon pulp
Linseed
Locust bean gum
Malt
Oat flour
Oat grain dust
Olive pellets
Onion powder
Parsley (dehydrated)
Peach
Peanut meal and skins
Peat
Potato
Potato flour
Potato starch
Raw yucca seed dust
Rice dust
Rice flour
Rice starch
Rye flour
Semolina
Soybean dust
Spice dust
Spice powder
Sugar (10x)
Sunflower
Sunflower seed dust
Tea
Tobacco blend
Tomato
Walnut dust
Wheat flour
Wheat grain dust
Wheat starch
Xanthan gum

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Carbonaceous Dust
Charcoal activated
Charcoal, wood
Coal, bituminous
Coke, petroleum
Lampblack
Lignite
Peat, 22%H20
Soot, pine
Cellulose
Cellulose pulp
Cork
Corn

Chemical Dusts
Adipic acid
Anthraquinone
Ascorbic acid
Calcium acetate
Calcium stearate
Carboxy-methylcellulose
Dextrin
Lactose
Lead stearate
Methyl-cellulose
Paraformaldehyde
Sodium ascorbate
Sodium stearate
Sulfur

Metal Dusts
Aluminum
Bronze
Iron carbonyl
Magnesium
Zinc

Plastic Dust
(poly) Acrylamide
(poly) Acrylonitrile
(poly) Ethylene
(low-pressure process)
Epoxy resin
Melamine resin
Melamine, molded
(phenol-cellulose)
Melamine, molded
(wood flour and
mineral-filled phenol-
formaldehyde)
(poly) Methyl acrylate
(poly) Methyl acrylate,
emulsion polymer
Phenolic resin
(poly) Propylene
Terpene-phenol resin
Urea-formaldehyde/
cellulose, molded
(poly) Vinyl acetate/
ethylene copolymer
(poly) Vinyl alcohol
(poly) Vinyl butyral
(poly) Vinyl chloride/
ethylene/vinyl
acetylene suspension
copolymer
(poly) Vinyl chloride/
vinyl acetylene
emulsion
copolymer

After knowing the list, what you should do is to identify the existence of these above lists, through the hazard identification process.

Cleaning

Combustible dust cleaning is an important aspect to prevent accumulation. This work should be done regularly on all work areas, including high surface areas such as ceiling, ducting, piping, and top of machinery.

Having a regular cleaning schedule is very important.

If you cannot do the cleaning work by yourself, you can ask a dust cleaning service company to do it for you. Such a company has well-trained workers and good procedures for doing that job.

Ignition Sources Control

Besides dust cleaning, ignition sources control is another important action that you have to do to prevent combustible dust explosions.

HSE.gov.uk has listed up ignition sources, that may come from:

  • Flames;
  • Direct fired space and process heating;
  • Use of cigarettes/matches etc;
  • Cutting and welding flames;
  • Hot surfaces;
  • Heated process vessels such as dryers and furnaces;
  • Hot process vessels;
  • Space heating equipment;
  • Mechanical machinery;
  • Electrical equipment and lights
  • Spontaneous heating;
  • Friction heating or sparks;
  • Impact sparks;
  • Sparks from electrical equipment;
  • Stray currents from electrical equipment
  • Electrostatic discharge sparks:
  • Lightning strikes.
  • Electromagnetic radiation of different wavelengths
  • Vehicles, unless specially designed or modified are likely to contain a range of potential ignition sources

To control the above ignition sources, HSE.gov.uk, has outlined the following countermeasures:

  • Select appropriate equipment for certain zone (hazardous area classification).
  • Use proper grounding or earthing for all the plant equipment
  • Avoid any surfaces above auto-ignition temperatures of flammable materials being handled
  • Provide lightning protection
  • Prohibit smoking and the use of matches or lighters
  • Avoid and control spark generation and static electricity
  • Replace damaged power cable immediately
  • Controls over activities that create intermittent hazardous areas, e.g. tanker loading/unloading