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Understanding what an ‘explosive atmosphere’ means is key when identifying whether a space should be classified as an ATEX Zone or hazardous area. It is, therefore, beneficial to understand both the definition of an explosive atmosphere and the regulations that pertain to it.

In this article, we aim to clarify this definition. Additionally, we will furnish further details about such environments and the particular conditions associated with them.

Explosive Atmospheres: The Definition

An explosive atmosphere is defined as a mixture of air and combustible substances in atmospheric conditions, where combustion can spread to the entire mixture after ignition. Some sources of ignition, like static electricity, can be difficult to detect.

  • Gases
  • Vapors
  • Mists
  • Dusts

It’s important to note that the duration an explosive atmosphere is present leads to the classification of the area as an ATEX zone. The ATEX regulations, referred to as “explosive atmosphere regulations,” are applicable in these zones and are specified by the relevant ATEX directive, in this instance, directive 153.

The term “atmospheric conditions” is a central concept when it comes to explosive atmospheres. So, what are these atmospheric conditions exactly?

What are Atmospheric conditions?

For an area to be classified as an explosive atmosphere under ATEX regulations, it typically must exhibit certain atmospheric conditions. These conditions are determined by several essential factors:

  • The temperature
  • The oxygen content in the air
  • The atmospheric pressure of the area

Atmospheric conditions are defined by the following parameters:

  • Oxygen levels of approximately 21 ±1% in the air.
  • A temperature range between –20 °C and +60 °C (-4 °F to 140 °F).
  • Atmospheric pressure ranging from 0.8 to 1.1 bar.

When substances are managed under conditions that do not align with these parameters, the area is usually not classified as an explosive atmosphere and, thus, does not adhere to ATEX regulations. However, a risk assessment may lead to the classification of such areas as ATEX zones regardless of these standard conditions.

No Atmospheric Conditions, Still An Explosive Atmosphere?

Atmospheric conditions alone do not fully determine the classification of explosive atmospheres. The existing definition guides the identification of explosive atmospheres but acknowledges exceptions. It is crucial not to prematurely dismiss the need for ATEX certification in certain installations, as demonstrated by the following:

  • Installations operating at 70  °C are typically outside the range considered atmospheric. Nonetheless, during start-up or warm-up phases, temperatures may briefly fall within the atmospheric range, potentially creating an explosive atmosphere and necessitating ATEX certification.
  • Nitrogen tanks, generally lacking sufficient oxygen, might not be classified under atmospheric conditions. However, the significance of the tank’s inertisation process cannot be understated. The inertisation method and its dependability are pivotal in determining if the space qualifies as an ATEX zone, along with additional safety measures.

Real-World Cases of Explosive Environments

Explosive hazards can emerge from various combustible materials. Below are examples of such substances that may pose an explosion risk:

  • Leaking Pipes: Particularly at flange connections, gases and vapors such as alcohol, acetylene (often used in workshops), biogas, hydrogen sulfide, hydrogen gas (produced during battery charging or by electrolysis), natural gas, and LPG can escape and create hazardous conditions.
  • Dust Accumulation: Inadequate housekeeping can lead to accumulations of combustible dust particles smaller than 0.5mm in diameter. Sources of such dust include polymers, granulate materials, wood, food products, and pigments.
  • Vaporization – Mists: Flammable mists, capable of forming explosive environments, arise from the vaporization of liquids with both high and low flash points, especially when released under pressure. Such mists may result from the atomization of liquids or cloud formation during the cooling of vapors. Typically, a risk assessment is conducted to identify ATEX Zones for areas prone to combustible mists.

We trust this information has enhanced your understanding of ‘explosive atmospheres.’ For further insights on ATEX, explosion safety, and related topics, please visit our blog. Should you have any inquiries or comments, do not hesitate to reach us at

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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