|Fire Suppression Systems using Total Flooding
Systems working on a total flooding principle apply an
extinguishing agent to an enclosed space in order to achieve
a concentration of the agent (volume percent of the agent
in air) adequate to extinguish the fire. These types of
systems may be operated automatically by detection and related
controls or manually by the operation of a system actuator.
This is true for any gaseous total flooding agent irrespective
of its mechanism of extinguishment.
|1. Chemical effects - inhibition by halogen atoms. Bromine,
iodine and chlorine atoms can act catalytically, each atom
participating multiple times to scavenge important free radicals
from the combustion gases. Bromine and chlorine are both much
more potent than fluorine in this regard. Fluorine also reacts
with free radicals but forms strong chemical bonds. Thus,
fluorine atoms react only once and are then “consumed.”
|2. Physical effects - thermal. The addition of any non-reactive
gas to a flammable gas mixture leads to a reduction in flame
temperature by virtue of the fact that the heat liberated
by the reaction of oxygen molecule with a fuel species must
be distributed into a larger heat sink. The rate of the combustion
chemical reactions decreases rapidly with reductions in temperature.
If the concentration of added inert gas is high enough the
flame chemistry becomes too slow to propagate. The potency
of an inert gas agent is related directly to the heat capacity
of the gas composition.
|3. Physical effects - dilution. Addition of a third gas
to a fuel-air mixture has the effect of reducing the collision
frequency of the oxygen and fuel species. This leads to a
reduction in chemical reaction rates. The magnitude of the
effect, however, is relatively minor compared to chemical
inhibition or thermal effects.
In the case of inert gas agents for fire suppression,
the extinguishing effects are entirely physical. In the
case of halons the chemical inhibition effects are most
important. For example the extinguishing mechanisms of halon
1301 has been reported to be a combination of 80% chemical
effects and 20% physical effects. 5 In the case of hydrofluorocarbons
the extinguishing effects are predominantly physical with
some (estimate at about 10 to 15%) chemical effects.”
Total flooding is the most common system application of
halons and has been employed for the protection of volumes
containing essential electronics, machinery spaces on ships,
aircraft engines and cargo bays, enclosed process modules
in the oil and gas industry and both crew and engine compartments
on military armored vehicles.