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If you ask someone whether they know what an explosion is, almost everyone will confidently respond with a “yes”.

But do they know the definition of an explosion? When we dive deeper into the term, we will notice that there are different kinds of explosions that do not necessarily need to be harmful and can occur in different ways.

In this blog, we will elaborate on various topics regarding this subject.

The definition of an explosion

Let’s start by defining this concept: a sudden and violent release of pressure waves. When thinking about explosion effects, most people immediately will think about something violent and harmful, but they are not necessarily always violent or destructive. For instance, the explosions in a car’s combustion engine are pretty helpful, aren’t they?

The following factors determine the violence of an explosion:

  • The amount of available energy
  • The location of the explosion
  • How quickly the reaction happens

In the context of ATEX, explosions are seen as something very negative, because they cause damage and injury. In the next paragraph, we will inform you about the different types of outbursts.

Gas and dust explosions

The main criterion for distinguishing between different outbursts is whether we can speak of a gas or dust explosion. Gas explosions are caused by a mixture of gas and oxygen, which results in an explosive atmosphere. An ignition source within this explosive atmosphere can cause a combustion reaction, resulting in an explosion.

However, a dust explosion typically occurs a bit differently. The first outburst is usually very small but will result in an immense dust cloud that raises an enormous explosion. This process will then happen a second time, with higher intensity.

Different types

There are two different types of explosions: chemical and physical blasts. Both types have other characteristics, but ATEX Directives do not cover them both. Let’s go more into depth.

Physical Explosion: Common?

A physical explosion can be defined as the sudden restoration of the equilibrium between two pressure differences. Examples of this are an exploding bicycle tire or a balloon that pops. Important to know is that physical explosions are not covered by ATEX regulations but by pressure equipment rules. Physical outbursts can be subdivided into two categories:


So what is a thermal explosion definition? This phenomenon occurs when a boiling, liquid, or solid substance comes into contact with a cold liquid. The consequence of this contact is rapid evaporation of the liquid, causing high pressures. For example, when molten iron comes into contact with water, voluminous steam arises, causing increased pressure in the area.


A BLEVE, or “Boiling liquid expanding vapor explosion,” is caused by the sudden evaporation of gas condensed into a liquid substance. For example, consider an LPG tank containing propane, an explosive material. If the tank catches fire, the liquid evaporates, and this results in the increase of gas in the tank, which increases the pressure. Eventually, the tank ruptures and the contents of the tank are released. The released cloud of gas is ignited, and explosion fire is seen. This ignition looks like a bomb exploding and falls under the other type of explosion: chemical explosions.

Concluding on this: the rupture of the tank is a physical explosion, but the ignition of the released gases afterward is a chemical explosion—more about this in the next paragraph.

Chemical Explosions

These types of outbursts are caused by exothermic chemical reactions, such as decomposition reactions (Dynamite blowing up/ TNT), exothermic combustion reactions (gas, dust, and mist exploding), run-away reactions (uncontrolled polymerization), and so forth. Because of the chemical reaction, often a fire explosion is seen. Chemical blasts can also be subdivided based on the reaction’s speed. They can be categorized as deflagration or detonation.


Deflagrations are less devastating outbursts than detonations because the increase of the explosion’s pressure is maximally ten times. So when the ambient pressure lies at 1 bar, a maximum pressure of 10 bar is reached when a particular object blows up. Deflagrations procreate relatively slowly and, therefore, are somewhat less devastating.


A detonation means that the explosion takes place very quickly, to be a little more exact: faster than the speed of sound. This means the pressure can be increased up to 100 times, so 100 bar can be reached at an ambient pressure of 1 bar. To give some perspective: a few boilers, barrels, or even buildings can withstand a force of 100 bar. An example of a detonation is the Beirut explosion of ammonium nitrate in 2020. However, detonation can also provide safety, for example, when a controlled explosion occurs, a method for preventing the ignition of a suspected explosive device. Concluding on this, detonations most of the time should be prevented, but detonation is also used to avoid danger.

Common causes of explosions

Explosions have many different causes; for instance, think about ignition, hot work, and pressurizing containers/tanks. In addition to this, cleaning objects like tanks and barrel bottles can also cause outbursts. Therefore it can be helpful to know the most common causes of explosions to prevent them.

Below, we have provided a table with a selection of common causes retrieved from a dataset covering 1998 to 2009.

Cause of the explosion Number of incidents (1998-2009)
Using an ignition source 75
Hot work 53
Being involved in or assisting explosive activities 50
Feeding, filling and pressurizing objects 48
Working near/on a barrel containing highly flammable / explosive substances 43
Switching an object on or off, or lighting it 19
Cleaning a container, barrel, bottle etc. 19

As you can see, using an ignition source is the most common cause of an explosion. The term “Hot work” is also worth discussing because this is also an important cause. Hot work refers to any activity or process that generates a source of ignition. In particular, an open ignition source. Examples of hot work are soldering, welding and cutting.

The consequences

In most cases, the consequences of an explosion are enormous. Explosions can cause human injury or even death. Next to this, an explosion, most of the time, leaves severe damage to the environment. To give an insight into how deadly explosions are, we consulted a dataset that measured the average number of victims per year from 1998 to 2009. The average number of victims of explosions during this period was 28, with two deaths. From this, we can conclude that explosions are hazardous and should be prevented at any cost.

Explosive atmospheres

Explosive atmospheres, also called ATEX zones, are essential for this subject because there is a risk of explosion in these atmospheres, and specific regulations apply.

For example, the use of explosion-proof equipment is mandatory in ATEX zones. Explosive atmospheres are areas characterized by explosion danger because flammable substances are present.

An example of an explosive atmosphere is the area surrounding an oil storage tank. It is also essential to know that explosions can occur in non-ATEX zones.


As we have read, the consequences of an explosion are significant: a pressure wave, fire, and heat radiation are released. These consequences often have devastating effects on people, installations, and buildings. The amount of damage caused by an explosion depends on the amount of flammable substances and other circumstances, such as the location (indoor or outdoor). From this, we can conclude that preventing explosions is of high importance. Therefore, we have provided three ways of prevention.

  • Preventing explosive atmospheres. This can be done by replacing flammable substances with non-flammable substances or ventilating rooms to avoid leakage.
  • Preventing ignition sources in explosive atmospheres. The explosions must be controlled if ignition sources in explosive atmospheres can not be stopped. This can, for instance, be done by using explosion protections. Ignition sources in explosive atmospheres can be prevented by utilizing explosion proof lighting, such as ATEX lighting.
  • The application of explosion protections, like rupture discs or a dust filter.

We hope that you learned a little bit more today on this subject. Please look at our other blogs for more info and knowledge about safety, ATEX, and other topics. For any questions or quotations, please don’t hesitate to contact us at

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