Gas cooling.pdf - Industrial Fire Journal

fire environment in
appropriate under all circumstances! Firefighters who work to
become masters of their craft recognise that strategies, tactics,
and techniques must fit the problems presented by the incident.
Gas Cooling is the application of an appropriate amount of
water fog into the upper layer to reduce the temperature of the
gases.
Vapourisation of water in the upper layer reduces the
temperature of the hot gases, thermal load on the firefighters
working below, and potential for ignition. While this sounds simple
and fairly intuitive, this basic technique to control upper layer
hazards is frequently misunderstood.
Many firefighters in the United States believe that application of
water into the upper layer in a fog or spray pattern will result in
production of a large amount of steam which will fill the
compartment and make conditions untenable. In many cases this
is consistent with firefighters’ fireground experience. These
firefighters are sceptical of cooling the upper layer with the
application of water fog to improve conditions. The answer can be
found in a statement made by Floyd Nelson (1989, “In principle,
Ed Hartin, MS, EFO,
MIFireE, CFO
serves as Fire Chief
with Central
Whidbey Island Fire
& Rescue in
Washington (USA),
and is the owner of
CFBT-US, LLC.
Ed was co-author
of 3D Firefighting:
Techniques, Tips,
and Tactics, and he
delivers practical
fire dynamics
training
internationally and
across the US.
Figure 2:
short pulse.
Fire control tactics
It is essential to understand the interrelationship between
ventilation strategies such as tactical ventilation (removal of
smoke and introduction of air) and tactical anti-ventilation
(confinement and exclusion of air) and fire control.
It is fair to say that amongst fire services in the US offensive
firefighting involves aggressive use of tactical ventilation and direct
attack with high flow hoselines. In other parts of the world such as
Europe and Australia, use of tactical ventilation is limited or highly
controlled, and flow rates from hoselines are lower than those
typically used in the US.
While tactics vary, firefighters have often been taught not to put
water on smoke. These cautions were based on the need to put
water onto burning fuel for an effective direct attack and to limit
production of steam which could add to the upper layer and
worsen conditions for firefighters working at floor level. However,
what happens when the fire is shielded from direct attack?
Firefighters must advance their hoseline to the seat of the fire,
while working underneath the flammable upper layer. In a
ventilation controlled regime, the air introduced when the
firefighters made entry for fire attack can result in increased heat
release rate and rapid fire progression. How can this hazard be
mitigated?
Gas cooling as a fire control technique
First a qualifier, there are no universal solutions to control the
hazards presented by a compartment fire. Firefighters are often
presented with ideas such as positive pressure ventilation (PPV),
compressed air foam systems (CAFS), high pressure or ultra high
pressure water fog, and gas cooling. and see these technologies
or tactics as the solution. No one tactic or technique is
Figure 3: heating
and cooling
curves of smoke
and water.
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