The ATEX directive consists of two EU directives describing what equipment and work environment is allowed in an environment with an explosive atmosphere. ATEX derives its name from the French title of the 94/9/EC directive: Appareils destinés à être utilisés en ATmosphères EXplosibles

Since July 1st 2003 it has been mandatory under European law, that all equipment for use in a potentially explosive atmosphere must conform to specific safety standards. Many manufacturing processes, including biodiesel production, generate potentially explosive atmospheres.

European Directive 137 – The protection of workers from potentially explosive atmospheres – makes it mandatory under European law to assess for an explosion risk and classify the area accordingly.

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The following information is intended as a guide only. Determination of appropriateness of equipment is the responsibility of the organisation/user.

A professional risk assessment determines hazardous area zones. EN 60079-10 is the european standard for determining the classification of hazardous areas, giving guidance on determining the area classification and recommendations for detailing the zones on drawings.

  • Zone 0: An area in which an explosive gas atmosphere is present continuously or for long periods
  • Zone 1: An area in which an explosive gas atmosphere is likely to occur in normal operation
  • Zone 2: An area in which an explosive gas atmosphere is not likely to occur in normal operation and, if it occurs, will only exist for a short time
Zone Description Equipment Category
(gases & vapours) (dusts)
Zone 0 Zone 20 An area where an explosive atmosphere is present continuously or for long periods Category 1
Zone 1 Zone 21 An area where an explosive atmosphere is likely to to occur in normal operation Category 2
Zone 2 Zone 22 An area where an explosive atmosphere is not likely to occur in normal operation Category 3

Classification of Gases and Dusts

Gases and dusts are classified according to their ignition properties.

For gases and vapors, the gas group (explosion group) is determined according to:

  • MESG – maximum experimental safe gap (IEC 60 079-1A)
  • MIC – minimum ignition current ratio relative to methane (IEC 60 079-3)

The dangerousness of the gases increases from gas group IIA to IIC.

Temperature class is based on the auto-ignition temperature of the material.

Gas group Temperature class
T1 T2 T3 T4 T5 T6
I Methane
IIA Acetone Ethanol Diesel fuel Acetaldehyde
Methane Cyclohexane Aircraft fuel
Ethane n-butane Fuel oil
Propane n-butyl alcohol n-hexane
Methanol Propan-2-ol Heptane
Acetic acid
IIB Coal gas (Town gas) Ethylene Ethylene glycol Ethyl methyl ether
Ethylene oxide Hydrogen sulphide
Propan-1-ol Tetrahydrofuran (THF)
IIC Hydrogen Acetylene Carbon disulphide
Explosion group MESG MIC ratio relative to methane
IIA >0.9mm >0.8
IIB 0.5 – 0.9mm 0.45 – 0.8
IIC <0.5mm <0.45

MESG – Experimental vessel has an aperture of length 25mm from the inside to the outside of the vessel. Width (gap) is adjustable. MESG is the maximum gap that an internal ignition of an explosive mixture is not propagated to the exterior.

Temperature class Max surface temperature Ignition temperatures Temperature class
IEC/EN of equipment of flammable substance NEC 500-3
NEC 505-10 °C °C CEC 18-052
T1 450 >450 T1
T2 300 >300 ≤ 450 T2
280 >280 ≤ 300 T2A
260 >260 ≤ 280 T2B
230 >230 ≤ 260 T2C
215 >215 ≤ 230 T2D
T3 200 >200 ≤ 300 T3
180 >180 ≤ 200 T3A
165 >165 ≤ 180 T3B
160 >160 ≤ 165 T3C
T4 135 >135 ≤ 200 T4
120 >120 ≤ 135 T4A
T5 100 >100 ≤ 135 T5
T6 85 >85 ≤ 100 T6

Temperature class relates to all parts of equipment that can come into contact with potentially explosive atmosphere.

Method of protection Ex Marking Protection principle
Flameproof enclosure d Contains explosion & prevents flame propagation
Increased safety e No arcs, sparks, or hot surfaces
Nonsparking n No arcs, sparks, or hot surfaces
Intrinsic safety i Limited energy of spark & surface temperature
Oil immersion o Ignition source kept constantly immersed in oil
Pressurised enclosure p Protective gas contains ignition source
Sand filling q Fine ground filling surrounds the ignition source so that an arc from inside the housing cannot ignite the surrounding combustable atmosphere