5
EN-DFA Series
North America
Only
Maximum Experimental Safe Gap (MESG)
The MESG is the measurement of the maximum gap
between two equatorial flanges on a metal sphere that
will prevent a flame from being transmitted from the
sphere to the surrounding flammable mixture. MESG
is dependent on gas composition. The stoichiometric
mixture (the ideal air/fuel ratio for the most efficient
combustion) is used to determine the minimum MESG
for a given gas.
Maximum Initial Operating Pressure, p
0
Detonation flame arrestors tested at p
TB
(pressure
before ignition) are suitable for operational pressures
p
0
≤ p
TB
in the same or smaller pipe size when the
application is limited to mixtures with an MESG equal
to or greater than that tested. See Table 5 for maximum
initial operating pressure limits, p
0
. If p
0
is exceeded
at the time of ignition, there is a risk of the flame
arrestor being unable to stop the flame front and flame
transmission through the flame arrestor is possible.
Table 2.
Warning Label Information
INFORMATION
DESCRIPTION
DET
I
ndicates product is a Detonation Flame Arrestor
2
Tested for unstable detonation without restriction
L
u
/D = n/a
The ratio of pipe length (between the potential ignition source and the flame arrestor) and pipe diameter. It indicates unlimited
BC: b
Indicates the flame arrestor is for short-time burning not to exceed 1 minute
Ex. G IIA
Indicates the arrestor is rated for use in Explosion Group IIA vapors
Ex. G IIB3
Indicates the arrestor is rated for use in Explosion Group IIB3 vapors
T
o
Indicates maximum operational temperature of flame arrestor
P
o
Indicates maximum operational pressure of flame arrestor
Table 3.
Marking Plate Information
MARKING PLATE FIELD
MARKING
MODEL No.
Per order, ex. EN-DFA-1206/IIA-C4R-2
Flange Size and Rating
Per order, ex. 3 in CL150
Max Pressure (P
o
)
Appropriate value from Table 5
Lowest MESG
Appropriate value from Table 4
Gas Group
IIA or IIB3, per order
Direction of Flow
Bi-directional. If product ordered with (1) temperature sensor, flow arrow will be added to unit
Serial Number
Per order
EU-Type Examination Certificate
Based on unit ordered
Date of Manufacture
Date of manufacture
Customer Tag Number
Based on customer request
Table 4.
Maximum Experimental Safe Gap (MESG)
NATIONAL ELECTRIC CODE
(NEC)
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION (IEC)
MESG
TEST GAS LIST
In.
mm
Group D
Group IIA
> 0.035
> 0.90
Propane
Group C
Group IIB3
≥ 0.026
≥ 0.65
Ethylene
Group B
Group IIC
< 0.020
< 0.50
Hydrogen
Table 5.
Maximum Initial Operating Pressure P
o
EXPLOSION GROUP
CONNECTION SIZE
P
O
In.
mm
psia
kPa a
IIA
2 to 6
50 to 150
17.7
122.3
IIA
8 to 12
200 to 300
16.9
116.3
IIB3
2 to 12
50 to 300
17.2
118.3
