Suppressant Performance Evaluation in a Baffle-Stabilized Pool Fire.
Suppressant Performance Evaluation in a
Baffle-Stabilized Pool Fire.
Grosshandler, W. L.; Donnelly, M. K.; Charagundla, S.
R.; Presser, C.
Halon Options Technical Working Conference.
Proceedings. HOTWC 1999. April 27-29, 1999,
Albuquerque, NM, 105-116 pp, 1999.
Sponsor:Department of Defense, Washington, DC
halon alternatives; pool fires; fire suppression;
aircraft fires; fire tests
The amount of a gaseous agent required to extinguish
fires in full-scale engine nacelles varies greatly with
the geometry of the test fixture and the manner in which
the flame is stabilized. It has been observed that if
the test is designed to allow fuel to collect behind
obstacles in the vicinity of a hot surface, a
significantly higher mass of agent is necessary for
sustained suppresssion. The superior performance of
chemically acting agents, such as CF3Br and CF3I,
relative to a hydrofluorocarbon alternative like HFC-125
is also accentuated in some of these tests. Full-scale
testing carried out by the Navy using two different
fixtures, each meant to simulate fires in the F/A-18
engine nacelle, has led to different conclusions
regarding the amount and relative performance of both
HFC-125 and solid propellant gas generator (SPGG) fire
suppressants. The complexity and unpredictability of
full-scale tests can be traced to two factors: flame
stabilization and agent mixing. Flame stability is
governed by local geometry, surface temperature, and
fuel and air flow patterns. Flame extinction will occur
if the agent is entrained into the flame zone in
sufficient concentration, if the fuel and air flows are
disrupted enough by the agent discharge process, or by a
combination of the two effects. Entrainment and
localized flame stretch are, in turn, controlled by the
way the fire suppression system is designed and by the
location of the fire relative to the discharge nozzle.
Hirst and Sutton developed a wind tunnel to explore the
impact of step height, air flow, and pressure on the
blow-out of a jet fuel pool fire stabilized behind a
backward facing step. Hirst et al. studied the
suppression of these types of fires using various
halons, and concluded that a liquid pool burning in a
flow behind an obstacle is the most difficult fire to
extinguish. This was born out in full-scale tests done
later. Experiments by Hamins et al., in cooperation
with Walter-Kidde Aerospace, were conducted in a wind
tunnel scaled down from the earlier work by Hirst to
examine the performance of HFC-125 and HFC-227ea.
Investigations at the Air Force Research Laboratory as
part of the Next-Generation Program (NGP) sought to
determine the detailed structure, during suppression, of
a non-premixed methane/air flame stabilized behind a
step. The changing character of the flame with step
height and air velocity was examined, along with the
amount of Halon 1301 required to suppress the flame as a
function of the flow parameters and injection interval.