On the fateful day of 28th June 2015 more than 500 people got injured in a fire accident at Color Play Asia Event which was organized at Formosa Fun Coast Water Park, Taipai, Taiwan. As per the spectators the fire erupted due to an accidental explosion of a colored theatrical powder thrown from the stage in front of about 1,000 people.

As per my understanding of the conditions and statements of people from the accidental site, the cause of the accident was "Dust Explosion".

Dust explosion is a rapid combustion of fine particles suspended in air, often but not always in an enclosed location. Dust explosions can occur at any place having dispersed powdered combustible material at high enough concentrations in the atmosphere or other oxidizing gaseous medium such as oxygen.

Dust explosions are the causes of frequent hazards in underground coal mines, grain elevators, and other industrial environments. Dust explosions are also commonly used by special effects artists, filmmakers and pyrotechnicians due to their spectacular appearance and ability to be safely contained under certain carefully controlled conditions.

There are four necessary conditions for a dust explosion:

1) A combustible dust
2) The dust is suspended in the air at a sufficiently high concentration
3) There is an oxidant (typically atmospheric oxygen)
4) There is an ignition source

If the rapid combustion takes place in a confined space, tremendous overpressures can build up, causing major structural damage and flying shrapnel. The sudden release of energy from a "detonation" can produce a shockwave, either in open air or in a confined space.

Many materials which are commonly known to oxidize and can generate a dust explosion are: coal, sawdust, and magnesium. However, many other organic materials can also be dispersed into a dangerous dust cloud, such as grain, flour, starch, sugar, powdered milk, cocoa, coffee, and pollen. Many powdered metals (such as aluminum, magnesium, and titanium) can form explosive suspensions in air.

The dust can arise from activities such as transporting grain, and grain silos have often exploded. Mining of coal leads to coal dust, and flour mills likewise have large amounts of flour dust as a result of milling. A gigantic explosion of flour dust destroyed a mill in Minnesota on May 2, 1878, killing 14 workers at the Washburn A Mill, and another 4 in adjacent buildings. A similar problem occurs in sawmills and other places dedicated to woodworking.

Although not strictly a dust, paper particles emitted during processing - especially rolling, unrolling, calendaring/slitting, and sheet-cutting - are also known to pose an explosion hazard. Enclosed paper mill areas subject to such dangers commonly maintain very high air humidity to reduce the chance of airborne paper dust explosions.

To support combustion, the dust must also consist of very small particles with a high surface area to volume ratio, thereby making the collective or combined surface area of all the particles very large in comparison to a dust of larger particles. Dust is defined as powders with particles less than about 500 micrometers in diameter, but finer dust will present a much greater hazard than coarse particles by virtue of the larger total surface area of all the particles.

In special effects pyrotechnics, lycopodium powder and non-dairy creamer are two common means of producing safe, controlled fire effects.

There are many sources of ignition, and a naked flame need not be the only one: over one half of the dust explosions in Germany in 2005 were from non-flame sources. Common sources of ignition include:

• electrostatic discharge
• friction
• electrical arcing from machinery or other equipment
• hot surfaces (e.g. overheated bearings)
• fire

However, it is often difficult to determine the exact source of ignition when investigating after an explosion. When a source cannot be found, ignition will often be attributed to static electricity. Static charges can be generated by external sources, or can be internally generated by friction at the surfaces of particles themselves as they collide or move past one another.

Below a certain value known as the lower explosive limit (LEL), there is simply insufficient dust to support the combustion at the rate required for an explosion. A combustible concentration at or below 25% of the LEL is considered safe. Similarly, if the fuel/air ratio increases above the upper explosive limit (UEL), there is insufficient oxidant to permit combustion to continue at the necessary rate.

Much research has been carried out in Europe and elsewhere to understand how to control these dangers, but dust explosions still occur. The alternatives for making processes and plants safer depend on the industry.

In the coal mining industry, a methane explosion can initiate a coal dust explosion, which can then engulf an entire mine pit. As a precaution, incombustible stone dust may be spread along mine roadways, or stored in trays hanging from the roof, to dilute the coal dust stirred up by a shockwave to the point where it cannot burn. Mines may also be sprayed with water to inhibit ignition.

Some industries exclude oxygen from dust-raising processes, a precaution known as "inerting". Typically this uses nitrogen, carbon dioxide, or argon, which are incombustible gases which can displace oxygen. The same method is also used in large storage tanks where flammable vapors can accumulate. Good housekeeping practices, such as eliminating build-up of combustible dust deposits that could be disturbed and lead to a secondary explosion, also help mitigate the problem.

Best engineering control measures include:

• Wetting
• Oxidant concentration reduction
• Deflagration venting
• Deflagration pressure containment
• Deflagration suppression
• Deflagration venting through a dust retention and flame-arresting device

The accident at Color Play Asia Event could have been averted, provided the above mentioned precautions should have been taken. Before organizing an event kindly think about such type of accidents and take the necessary precautionary steps to avoid them. Also use good quality colors to minimize the risk of Dust Explosion. To get such safe colors please click here.