Silo Sensors and Instrumentation: Safety and Level Measurement for Powder Storage
5 min de lecture
ATEX regulations
Categories : Fiberglass Silo | Flexible Silo | IBC Containers | Metal Silo
By @ Stéphane BREXEL
The ATEX regulations, which stand for ATmosphères EXplosibles. They establish a common European framework to protect workers, determine the appropriate scale of installations, and impose design requirements on equipment used in hazardous areas.
What are the ATEX regulations?
The term ATEX stands for ‘ATmosphères EXplosibles’ (explosive atmospheres). An explosive atmosphere is a mixture of air (oxidiser) and flammable substances in the form of gases, vapours, mists or dusts, in which, once ignited, combustion spreads to the entire unburned mixture.
The regulations are based on two major European directives:
- Directive 2014/34/EU (ATEX 114): This applies to manufacturers and governs equipment and protective systems intended for use in ATEX zones.
- Directive 1999/92/EC (ATEX 153): This applies to employers and sets out the minimum requirements for improving the safety and health protection of exposed workers.
The mechanism of an explosion: The Explosion Hexagon
For an explosion to occur, six elements must be present simultaneously; these are often represented by the Explosion Hexagon:
- A combustible (gas, dust).
- An oxidiser (oxygen in the air).
- An ignition source (spark, flame, heat, static electricity).
- A concentration within the explosive range (between the LEL and the UEL).
- The suspension (for dust)
- A confined space (an aggravating factor that increases pressure effects).
Classification of ATEX Zones
Hazardous areas must be subdivided into zones according to the probability and duration of the presence of an explosive atmosphere.
For gases, vapours and mists:
- Zone 0: Permanent hazard or present for long periods (more than 1000 hours per year).
- Zone 1: Potential hazard, likely to occur during normal operation (between 10 and 1000 hours per year).
- Zone 2: Minimal, unlikely or short-term hazard (less than 10 hours per year).
For Dust:
- Zone 20: Permanent hazard (e.g. inside a silo).
- Zone 21: Potential hazard during normal operation.
- Zone 22: Minimal hazard (abnormal operation or short duration).
Marking and Equipment Categories
All equipment used in an ATEX zone must bear specific marking.
Equipment categories:
- Category 1: Very high level of protection, suitable for use in Zones 0/20, 1/21 and 2/22
- Category 2: High level of protection, suitable for use in Zones 1/21 and 2/22.
- Category 3: Standard level of protection, suitable for use only in Zones 2/22.
Interpretation of a typical marking (e.g. II 2 G Ex d IIB T4):
- II: Equipment group (surface industries)
- 2:Equipment category.
- G: Nature of the atmosphere (G for Gas, D for Dust).
- Ex d: Protection method (e.g. flameproof enclosure).
- IIB: Gas group.
- T4: Temperature class (indicates the maximum surface temperature, here 135°C).
| Zone Type | Nature of Hazard | Presence Frequency | Required Equipment Category | Equipment Group | Protection Method | Temperature Class |
|---|---|---|---|---|---|---|
| Zone 0 | Gases, vapors, mists | Permanent, long periods, or frequent (> 1000h/year) | Category 1 | Group II (Surface industries) | "Intrinsic Safety 'ia', Encapsulation 'm'" | T1 to T6 |
| Zone 1 | Gases, vapors, mists | Occasional during normal operation (10 to 1000h/year) | Category 2 (or 1) | Group II (Surface industries) | "Flameproof 'd', Increased Safety 'e', Intrinsic Safety 'ib', Oil Immersion 'o', Pressurized 'p', Powder Filling 'q'" | T1 to T6 |
| Zone 2 | Gases, vapors, mists | Accidental or short-term (upper 10h/year) | Category 3 (or 1 or 2) | Group II (Surface industries) | Concept 'n' (nA, nC, nR, nL, nP) | T1 to T6 |
| Zone 20 | Combustible dusts | Permanent, long periods, or frequent | Category 1 | Group II (Surface industries) | "Encapsulation 'm', Intrinsic Safety 'ia'" | Maximum surface temperature (e.g., T85°C) |
| Zone 21 | Combustible dusts | Occasional during normal operation | Category 2 (or 1) | Group II (Surface industries) | "Protection by Enclosure 't', Constructional Safety 'c', Liquid Immersion 'k'" | Maximum surface temperature |
| Zone 22 | Combustible dusts | Accidental or short-term | Category 3 (or 1 or 2) | Group II (Surface industries) | Protection by Enclosure 't' | Maximum surface temperature |
| Mines | Firedamp and coal dust | Risk related to underground works | Category M1 (very high level) or M2 (high level) | Group I | Cap lamps, mine-specific safety | N/A |
Advice from our experts
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