The type of gas in the system determines its gas
grouping and therefore predetermines the type of
arrestor element required. The element must be
designed to accommodate the specific gas group that
could possibly ignite and propagate in the system. The
more explosive gases require the flame cell to absorb
the heat more quickly and efficiently. The International
Electrotechnical Commission (IEC) groups gases
and vapors into Groups IIA through IIC categories
depending on a number of factors including the
Maximum Experimental Safe Gap (MESG) of the gas.
The National Electrical Code (NEC) groups gases into
A, B, C, D and G.M. categories.
Maximum Experimental Safe Gap (MESG)
WArninG
!
Verify that the detonation flame arrestor
being installed has the appropriate gas
group rating for your process. This
information is included in the nameplate
attached to the element housing. Do not
remove or alter this nameplate.
The Maximum Experimetal Safe Gap (MESG) is the
measurement of the maximum gap between two
equatorial flanges on a metal sphere that prevents 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. See Table 2 for MESG information.
Turbulence in Piping System
Elbows, tees, pipe expansions and/or contractions,
spiral wound vapor hoses, valves, orifice plates
and similar devices will contribute to turbulent flow.
Turbulent flow enhances mixing of the combustible
gases, greatly increasing the combustion intensity.
This can result in increased flame speeds, higher
flame temperatures and higher flame front pressures
than would occur in normal flow conditions. The
likelihood for developing detonations via Deflagration
to Detonation Transition (DDT) is enhanced by
turbulent flow conditions.
Pipe Length
Extended lengths of pipe allow the flame to advance
into more severe states of flame propagation such
as high pressure deflagration and detonations.
Enardo Detonation Flame Arrestors are not limited by
pipe length.
Flow restrictions at Protected Side of
the Arrestor; Pressure Piling
When flame propagation occurs, unburned and
pressurized flammable vapors are forced through the
detonation flame arrestor into the protected (cold)
side piping. Restrictions close to the protected (cold)
side of the arrestor will restrict the passage of the
unburned flammable vapors causing pressurization to
occur inside the crimped passages of the detonation
flame arrestor element assembly. This pressurization
can result in flame passage through the arrestor to the
protected side during a flame propagation event.
WArninG
!
For maximum safety, avoid bends
and flow obstructions within 10 pipe
diameters but not less than 3 meters
on the protected (cold) side of the
detonation flame arrestor.
Maximum initial Operating Pressure and
Fundamental Burning Velocity
The Maximum Initial Operating Pressure of the
detonation arrestor is indicated on the product
nameplate in absolute pressure units. This is the
maximum allowable pressure that is allowed at the
instant the flowing velocity of the process vapors drops
to a value to or less than the fundamental burning
velocity of that particular flammable vapor stream.
When the flowing velocity drops to this level, any flame
in the system can propagate back toward the fuel
source. High pressure deflagrations and detonations
can occur more easily at higher system operating
pressures than at pressures near atmospheric.
Elevated pressures compress the system vapors
and can cause the flame propagation to become
more intense.
5
Enardo DFA Series
Outside North
America Only
