ATEX is named after the French “ATmosphère EXplosible”

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.

For more information please see:

www.europa.eu.int/comm/enterprise/atex

UK – Dangerous Substances and Explosive Atmospheres Regulations 2002

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 where an explosive atmosphere is present continuously or for long periods

• Zone 1 – An area where an explosive atmosphere is likely to to occur in normal operation

• Zone 2 – An area where an explosive atmosphere is not likely to occur in normal operation

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 vapours, 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 autoignition 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
Toluene
Benzene
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 explosion protection
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 sourounds the ignition source so that an arc from inside the housing cannot ignite the surrounding combustable atmosphere