--- title: 'Explosive Atmosphere' url: 'https://hazardex.com/ex-atmosphere' markdown: 'https://hazardex.com/ex-atmosphere.md' date: '2026-09-14' description: "Dust⤵️ \_Hybrid⤵️ Explosive Gas Atmosphere . . 'mixture with air, under atmospheric conditions, of flammable substances in the form of gas or vapour which, after ignition, permits self-sustaining flame propagation.' EN 60079-0 define the standard ambient atmosphere as: Temperature: –20 …" taxonomy: category: - docs --- # Explosive Atmosphere [](#) [ Hazardex ](https://hazardex.com/) Explosive Atmosphere [Dust⤵️](#dust) [Hybrid⤵️](#hybrid) ## Explosive Gas Atmosphere . . 'mixture with air, under atmospheric conditions, of flammable substances in the form of gas or vapour which, after ignition, permits self-sustaining flame propagation.' [EN 60079-0](https://hazardex.com/reference#en60079) define the standard ambient atmosphere as: - Temperature: –20 °C to 60 °C; - Pressure: 80 kPa (0,8 bar) to 110 kPa (1,1 bar); and - air with normal oxygen content, typically 21 % v/v. Outside these conditions the standards do not generally apply although they can be used for 'special' assessments or considerations. Note. This applies to the atmosphere, **not** the operating conditions of any equipment. ![Gas Triangle](https://hazardex.com/user/images/expl-gas.svg)The traditional ignition triangle shows the 3 parts which are required to be present[1](#fn:1) for an explosion to occur. The protection methods detailed in the [EN 60079-0](https://hazardex.com/reference#en60079) standards are designed to remove at least one of those parts, the exception being [Ex d](https://hazardex.com/protection/ex-d) flameproof[2](#fn:2). 1. **Fuel** can be Dust or Gas/vapour, Although the purists would argue Gas and vapour are different, within the context of [Hazardous Areas](https://hazardex.com/hazardous-areas) the terms generally are interchangeable. For convenience the term Gas is generally used to mean both Gas and Vapour. 2. The **ignition** source can be a [hot surface](https://hazardex.com/define/hot-surface) or energy from a [spark](https://hazardex.com/define/spark), they are different and need to be considered separately. 3. **Air (Oxygen):** The [60079 standards](https://hazardex.com/reference#en60079) refer to Normal Temperature and Pressure (NTP), it is assumed that Air/Oxygen is always present (unless of course removed by a protection technique). Locations where enriched or depleted Oxygen exists e.g. Waste digesters or extremes of pressure scenarios are special cases and strictly speaking outwith the scope of any conventional protection methods, more detailed risk assessments need to be conducted and standard product certification becomes invalid. --- [Gas⤴️](#gas) [Hybrid⤵️](#hybrid) [🔝](#top) ## Explosive Dust Atmosphere . . 'mixture with air, under atmospheric conditions, of flammable substances in the form of dust, fibres or flyings which, after ignition, permits self-sustaining propagation.' **Combustible Dust:** 'Finely divided solid particles, 500 μm or less in nominal size, which may be suspended in air, may settle out of the atmosphere under their own weight, may burn or glow in air, and may form explosive mixtures with air at atmospheric pressure and normal temperatures' **Combustible Flyings**solid particles, including fibres[3](#fn:3), greater than 500 μm in nominal size, which may be suspended in air, may settle out of the atmosphere under their own weight, can burn or glow in air, and may form explosive mixtures with air at atmospheric pressure and normal temperatures ![Dust Pentagon](https://hazardex.com/user/images/expl-dust.svg)This includes dust and grit as defined in ISO 4225 and the term solid particles is intended to address particles in the solid phase and not the gaseous or liquid phase, but does not exclude a hollow particle. Although the ignition triangle is widely used and is a perfectly good representation, perhaps a better depiction for dust would be the ignition pentagon. Dust lying around might be a fire or health hazard but is generally not considered an explosive atmosphere, unless disturbed. For an explosive atmosphere to form there must be **Dispersion** but also some form of **Confinement** to achieve explosive concentrations. However, a dust cloud can be its own confinement with varying concentrations as dust generally does not disperse as evenly as a gas cloud. --- [Dust⤴️](#dust) [Gas⤴️](#gas) [🔝](#top) ## Hybrid Explosive Atmosphere 'Mixture of flammable substances in different physical states[4](#fn:4). Thankfully this is not a common occurrence but occasionally exists in the chemical industry when areas are zoned for gas and dust. As virtually no equipment is actually certified for a hybrid mixture this can create problems and additional risk assessments will generally need to be carried out. Older equipment may be marked for **GD**, but unless it specifies conditions for a Hybrid atmosphere in the Type Certificate it must be interpreted as **Gas or Dust *not* Gas and Dust**. Prior to the publishing of EN 60079-31 (2009) [EX d Flameproof](https://hazardex.com/protection/ex-d) was the goto solution for dust certification and its use was often misunderstood[5](#fn:5). Newer equipment certified to standards released after 2014 should conform to the tighter restrictions on labelling implemented for this very reason. Equipment certified to current standards will have separate lines in the certification label for Gas (**G**) and Dust (**D**) with a third (**GD**) specifically for Hybrid mixture if covered by the certification. If both gas and dust are present in a 'Hybrid' Atmosphere assessment, particularly of equipment protection methods, gets much more complicated. Very little equipment certification covers a Hybrid environment and specialist assistance should be sought regarding equipment choice. --- Notes --- 1. To be pedantic if the fuel is Acetylene, then external Oxygen (Air) does not need to be present as Acetylene creates it own oxygen to mainatain combustion if ignited. [↩](#fnref1:1) 2. Flameproof (Ex d) protection method allows the explosion to happen and contains it, preventing propagation outside the device [↩](#fnref1:2) 3. Fibres or Flyings are log thin particles, examples of which include rayon, cotton (including cotton linters and cotton waste), sisal, jute, hemp, cocoa fibre, oakum, and baled waste kapok. [↩](#fnref1:3) 4. Where Gas and Dust could be present e.g. Methane & Coal dust. [↩](#fnref1:4) 5. Dust is not compatible with the flamepath and see [EX d Flameproof](https://hazardex.com/protection/ex-d#ex-d-and-dust) for more information. [↩](#fnref1:5) [🔝](#top) [ ](https://hazardex.com/hazardous-areas) [](https://hazardex.com/define) --- ## Navigation - Parent: [Hazardex](https://hazardex.com/index.md) - Previous: [Hazardous Areas](https://hazardex.com/hazardous-areas.md)