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Regarding ATEX, the term “explosive atmosphere” is vital for determining whether a particular environment is classified as an ATEX Zone. Therefore, knowing the definition of an explosive atmosphere and specific explosive atmosphere regulations is useful. In this blog, we will explain this definition. We will also provide additional information about these areas and the corresponding circumstances.

The definition

Explosive atmospheres are defined as atmospheres that contain a mixture of air and combustible substances under atmospheric conditions, in which the combustion can spread to the unburned mixture after ignition. Some ignition sources are difficult to detect, for example, static electricity.

Such combustible substances in the form of:
  • Gases
  • Vapors
  • Mists
  • fibers

Important to know is that if we speak of an explosive atmosphere, the area is classified as an ATEX zone. ATEX regulations, or “explosive atmosphere regulations”, apply in these zones and are covered by the corresponding ATEX directive.

Another important term that this definition contains, are the so called “atmospheric conditions”. When can you exactly speak of those conditions? We will explain this in the next paragraph

What are Atmospheric conditions?

So for an area to be classified as an explosive atmosphere and to fall within ATEX regulations, most of the time, there must be spoken of atmospheric conditions. There are several essential variables regarding atmospheric conditions in the context of ATEX. These variables are the temperature, the oxygen in the air, and the air pressure of the corresponding area.

Atmospheric conditions meet the following requirements:
  • The presence of oxygen levels of 21 ±1% in the air
  • A temperature that lies between –20 °C and +60 °C ( -4 degrees and 140 degrees)
  • Air pressure between 0.8 and 1.1 bar

When working with substances under non-atmospheric conditions, usually, the area is not classified as an explosive atmosphere. Therefore this area does not fall within ATEX regulations. However, in many situations, the decision can still be made to classify those areas as ATEX zones based on a risk analysis.

When is an explosive atmosphere identified?

As noted in the last paragraph, atmospheric conditions are not completely determinative for defining explosive atmospheres. The definition partially gives away when an area is labeled as an explosive atmosphere, but exceptions exist. Next to this, it is important to not immediately exclude specific installations from having an ATEX certification due to the following examples:

  • When an installation has an operating temperature of 70 °C, the first insight is that we cannot speak of atmospheric conditions. However, when starting and warming up, the installation temperature temporarily falls within the range of atmospheric conditions. Therefore, an explosive atmosphere is present, and an ATEX certification for the installation may be appropriate.
  • A nitrogen tank does not contain enough oxygen to fall under atmospheric conditions. However, the inertisation of this tank is essential in this case. Namely, the method of inertisation and the reliability of this process determine whether the area is defined as an ATEX zone.

Explosive atmospheres: potential causes

Explosion danger can arise from the presence of different combustible substances. Here are some examples of substances that can potentially form explosion danger:

  •  Gases and vapors: alcohol, acetylene (for example, in a workshop), biogas, hydrogen sulfide, hydrogen gas (as a result of charging batteries or generated by electrolysis, natural gas, LPG).
  • Powders: combustible dust (diameter size is less than 0.5mm), polymers, granulate dust, dust coming from wood, foodstuffs, pigments, etc.
  • Mists: combustible mists can form an explosive atmosphere. These are flammable liquids with high and low flash points that can be released under pressure. Combustible mists can be created by atomizing a liquid or cloud formation during vapor cooling. Most of the time, a risk analysis is done to determine ATEX Zones regarding combustible mists.

Why explosive atmospheres are important

It is crucial to know whether your company’s working environment is classified as an explosive atmosphere. If an explosive atmosphere is identified, ATEX equipment must be used within that environment. Next to this, several rapidly flammable combustible substances should be taken into account. Rapid flammability means that vapors immediately arise when these substances are released, which can result in an enormous explosion in the presence of an ignition source.

Examples of such substances are:
  • Acetone
  • Alcohol
  • Isopropyl alcohol
  • Ethanol
  • Gasoline

When these substances are present or worked with in your environment, close attention must be paid, and adequate measures must be taken to ensure safety.

We hope you have learned more about “explosive atmospheres.” Please look at our blog page for more information about ATEX, explosion safety, and other related subjects. For any questions or remarks, please get in touch with us at

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