Technical Documentation: Fire Detectors used in hazardous areas
P-DET/EX/RCE/PM5/GKa/110995 8 Autronica Fire and Security AS
The table below shows the relation between temperature grades, equipment
surface temperature, and gas ignition temperature.
Temperature grades T1 T2 T3 T4 T5 T6
Max. surface temperature °C 450 300 200 135 100 85
Gas min. ignition temperature °C 450 300 200 135 100 85
Note that maximum surface temperature must not, at any occasion (even with
fault) exceed the igniting temperature of the actual gas.
The table below shows the relationship between different gas groups and
allowed igniting energy.
Gas-group IIA IIB IIC
Igniting Energy in µ Joule 200 60 20
NOTE that values given for igniting energy are limits, and therefore safety
factors must be introduced. Values may be selected from the CENELEC norm
EN-50020.
In order to calculate igniting energy, the following two equations are actual:
Energy stored in a capacitor (capacitance) is: E
C
= ½ C U
2
Energy stored in a coil (inductance) is: E
L
= ½ L I
2
Where: E
C
and E
L
are energies in Joules.
C is capacitance in Farads.
U is voltage in Volts.
L is inductance in Henry.
I is current in Ampere.
Note that wires represents both capacitance and inductance, and this phenom-
ena must be taken into consideration for long wire installations at the hazardous
side of zenerbarriers.
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