EN 12874 STANDARD

TESTING AND CERTIFICATION
Functional testing proving the capacity of an arrester is the only guarantee of arrester performance. Arresters should be tested to guarantee that they meet a recognized standard such as EN 12874.

VAPOUR COMPOSITION
For the purposes of arrester selection, the Maximum Experimental Safe Gap (MESG) gas classification has been used

IDENTIFICATION OF PROTECTIVE SYSTEMS AND EXPLOSION GROUPS ACC. TO EN 12874 - BASED ON MESG (Maximum Experimental Safe Gap)

(I)	(=> 1.1)	[mm]
IIA	>0.9	[mm]
IIB1	0.9 =>s=>0.85	[mm]
IIB2	0.85 > s => 0.75	[mm]
IIB3	0.75 > s => 0.65	[mm]
IIB	0.65 > s => 0.5	[mm]
IIC	< 0.5	[mm]

OPERATING PRESSURE
Arresters must not be installed in systems with an operating pressure exceeding that for which the arrester has been tested.

LIMITS OF USE

Explosion Group Chart

IIA

Acetone Acrylonitrile Ammonia Benzene Butylene 1-Butanol (butyl alcohol) 2-Butanol (secondary butyl alcohol) Cyclohexane N-Butyl acetate Isobutyl acetate Ethane Ethanol (ethyl alcohol) Ethyl acetate Ethyl acrylate Ethylene dichloride Gasoline Heptanes Hexanes Isoprene Methane (natural gas) Methyl acrylate Methylamine

Methyl ethyl ketone Methyl mercaptan 3-Methyl-1-butanol (isoamyl alcohol) Methyl isobutyl ketone 2-Methyl-1-propanol (isobutyl alcohol) 2-Methyl-2-propanol (tertiary butyl alcohol) Naphtha (petroleum ether) N-Propyl acetate Octanes Pentanes 1-Pentanol (amyl alcohol) Propane 1-Propanol (propyl alcohol) 2-Propanol (isopropyl alcohol) Propylene Styrene Toluene Turpentine Vinyl acetate Vinyl chloride Xylenes

IIB3

Acetaldhyde
Cyclopropane
Diethyl ether
Dimethylhydrazine
Ethylene
Hydrogen sulfide
* Methanol (methyl alcohol)
Methyl mercaptan
Unsymmetrical dimethylhydrazine (UDMN)

IIC

Butadiene
Ethylene oxide
Hydrogen
Manufactured gases containing more
than 30% hydrogen (by volume)
Propylene oxide
Propyl nitrate