Following the trend of Internet celebrities’ “fire control skills”, firefighters remind: beware of dust explosions!

Review expert: Zhou Hongzhi, senior experimenter and master's supervisor at the School of Physics and Optoelectronic Engineering, Beijing University of Technology

Recently, “fire control” has become popular on social media due to its cool transitions and presentation effects.

With a flick of the arm, flames instantly ignited. The cool picture and the timely music triggered heated discussions among netizens and a large number of imitations.

Is fire control really safe? What is the dust produced during flash combustion? Why should we be wary of dust explosions?

01 Fire Control Technique: Ghost Paper and Flour (or Rosin Powder)

It is understood that the internet celebrity's "fire control technique" requires the use of "ghost paper" and flour (or rosin powder), both materials pose great safety hazards.

Ghost Paper:

There are many ways to make "ghost paper". The most commonly used one is to use a tougher base paper, coated with tung oil or other drying oil to make a kind of oil paper.

This kind of paper is often used in magic shows and movie special effects. Ghost paper burns rapidly when exposed to open flames, causing a large temperature difference around the paper. Due to the rapid rise in the high heat of the paper itself, the paper flies up.

Flour (or rosin powder):

In the art of fire control, we can see that when paper ignites and flies up, if it encounters combustible dust, a large fireball will be produced, causing a momentary explosion. This is the effect of a dust explosion .

02 Dust Explosion

Dust has always been around us, but there has never been an explosion. So where does the dust explosion come from?

We often see such a small scientific experiment: the performer lights a candle in a sealed plastic bag, and then blows flour (starch, milk powder) into the plastic bag. When the powder encounters the candle flame, it suddenly explodes, causing the plastic bag to fly into the air. This is the best demonstration of dust explosion.

What is a dust explosion? A dust explosion is when combustible dust reaches a certain concentration in the air and burns rapidly under the action of an ignition source. If the space is small enough, an explosion will occur. The reasons are:

When a dust cloud is formed, the contact area with the air is greatly increased because the combustibles are tiny;

The dust is small in size and has a low ignition point, which can easily trigger a chain combustion reaction;

When tiny dust particles burn, due to the fast speed and high temperature, their volume will expand rapidly, usually reaching tens to hundreds of times their own volume.

In certain environments, such as flour mills, milk powder factories, and starch factories, when a dust explosion occurs, the shock wave of the initial explosion will lift up the deposited dust in other areas, forming a dust cloud and triggering a secondary explosion . The scope and power of the secondary explosion are often much greater than the initial explosion.

Why does dust explode?

The dusts that are generally more prone to explosion accidents include aluminum powder, zinc powder, ferrosilicon powder, magnesium powder, iron powder, aluminum processing grinding powder, various plastic powders, intermediates of organic synthetic drugs, wheat flour, starch, sugar, sawdust, dyes, bakelite ash, milk powder, tea powder, tobacco powder, coal dust, plant fiber dust, etc.

When these materials reach a certain density in the air, they may deflagrate and cause an explosion.

Dust explosion principle Source: Beijing Fire Department

The reason why the dust of these materials is prone to explosion and combustion is that they contain strong reducing agents such as H, C, N, S, etc. When they coexist with peroxides and explosive dusts, they decompose and produce a large amount of gas by oxidation reaction, or a small amount of gas but releases a large amount of combustion heat.

Flour explosion moment Source: Beijing Fire Department

Dusts that are usually not likely to cause explosions include soil, sand, iron oxide, abrasive materials, cement, quartz dust, and dust similar to that after combustion. The chemical properties of dusts of these substances are relatively stable, so they are not easy to burn. However, if these dusts are generated in oil mist and combustible gases such as CO, CH4, and coal gas, they are also prone to explosions.

Are there conditions for dust explosion?

Combustion-supporting gas : A certain oxygen content is the basis for dust combustion.

Combustible dust : Dust that can undergo oxidation reaction with combustion-supporting gas and burn when reaching a certain concentration.

Ignition Source : A heat source that reaches the ignition point of the dust, such as an open flame.

Dust cloud : A cloud of combustible dust suspended in the air that reaches a sufficient air concentration.

Confined space : The dust cloud is confined to a relatively small or even confined space.

Dust explosion moment Source: Beijing Fire Department

Judging from the shooting scenes of fire control techniques, there are residential areas, rooftops of shopping malls, as well as indoors, outdoors, parks, cultural relics and ancient buildings. Once the flour or rosin powder reaches a certain concentration and encounters an open flame, coupled with a closed space and sufficient oxygen in the air, it is very easy to cause a dust explosion. Once an explosion occurs, the impact is unimaginable.

Flour explosion principle Source: Beijing Fire Department

Fire Tips

Dust explosions are chemical reactions that react quickly and are highly destructive. Once they occur, they often cause significant casualties! There are many ways to be cool, and flow is far less important than your own safety!