Issue 88: Aircraft Hangar High Expansion Foam Incident
By Samuel S. Dannaway, PE, FSFPE
On Wednesday January 8, 2014, at Eglin Air Force Base
near Valparaiso, Florida, a civilian contractor lost his life after
entering the King Hangar in which the high expansion foam (HEF) system
had activated. According to the investigation report:1
The entire hangar floor was covered with
approximately 17 ft (5 m) of HEF (High Expansion Foam) engulfing all but
the very top of the vertical fins of the A-10, F-16 and three F-15
The deceased, age 31, and three other contractor
employees, entered the hangar as they "were ‘curious’ to see the foam”.
At some point, they became immersed in foam. The cause of death was not
published. It may have resulted from extreme disorientation caused when
immersed in the foam.
The investigation reported three findings. This article will focus on
issues raised with finding #3 related to mitigation measures to
"greatly reduce the potential for similar incidents …” Specifically,
this article will address measures related to the design and criteria.
The system activated at 11:24 am. The accidental system operation was
the result of a hangar wet pipe sprinkler waterflow alarm switch
activation after a valve in the inspector's test froze and burst,
causing a flow of water.
Because of this incident, and several other accidental system
operations in hangars worldwide, the Air Force is conducting a global
review of existing hangar HEF systems.
Not all accidental system discharges are caused by the operation of a
sprinkler waterflow switch. In addition to the waterflow switch, there
are two other common causes of accidental discharges. The first is
operation of the manual foam release station and the second is a fault
with the HEF control panel or its field devices.
The manual release station can be the culprit in a system release
that is either accidentally or maliciously intended. Accidental
releases, caused by bumping into or hitting the release station, can be
mitigated by the use of a tamper proof cover. Many years ago, an AFFF
system discharged when a sailor mopping the floor struck the release
station. The use of a double-action station can limit accidental
operation. Air Force guidance2 requires a tamperproof cover on the release station, which is, in effect, a dual-action function.
Accidental operation of the manual release station can also occur
when it is mistaken for a fire alarm system manual station. The station
color and signage requirements in Air Force guidance2 distinguish
foam release stations from fire alarm pull stations. Personnel must be
routinely instructed on actions to take in the event of a fire and the
situations that indicate the need for operation of the foam system
The problem with HEF control panel faults is more controversial. The
environment in hangars is often not controlled, and temperature and
humidity may at times fall outside of the listed ranges of fire alarm
system electronics. Additionally, water wreaks havoc with fire alarm
systems when it gets into raceways and devices, and water in hangars is a
fact of life. Rain happens; roofs leak.
Another issue is that addressable fire alarm system control units may
not be stable enough to control fire suppression discharge. The Air
National Guard has come to a similar conclusion3 about addressable systems. The requirements for hangar protection call for a conventional releasing panel.
15.6.2. The HEF panel shall be a non-addressable unit having an
output capability, which emulates the inputs on a zone-by-zone basis.3
Air Force guidance2
requires equipping waterflow alarm switches with a retard feature to
minimize the chance of pressure surges causing switch activation. The
guidance also requires surge arrestors on sprinkler and foam systems to
reduce the impact of pressure surges.
Foam discharge can also be accidentally initiated if an unsuspecting
sprinkler technician operates the inspector’s test not realizing that
foam discharge will occur. To mitigate this, designs can incorporate a
plug in the wet pipe sprinkler test connection outlet with warning
signage at each test valve.
To protect high value aircraft, one must detect and deliver fire
suppression agent quickly and efficiently. Losses can be substantial in
an aircraft hangar containing several F-22s, at a price of $150 million
each, F-35s at $200 million, or a B-2 bomber at $800 million.
FM Data Sheet 7-93N4 cites Federal Aviation Administration
testing in which failure of aircraft fuselage skin occurs within 45
seconds of a flammable liquid fire exposure. A Naval Research Lab Study,5
reported damage to aircraft adjacent (30 feet [9 m] away) to an
aircraft involved in a fuel spill fire would likely not occur if total
time to suppression (detection time + activation time + suppression
time) is less than 110 seconds. This need to suppress the fire quickly
must be balanced against the possibility for false activations.
One could use optical (flame) detectors and arrange the sequence of
operations so automatic HEF discharge only occurs with one or more flame
detectors activating in conjunction with the sprinkler waterflow alarm.
Flame detectors will not cause any increase in detection time beyond
that already expected with ceiling sprinklers. To convert HEF systems to
manual activation only will only solve the problem with waterflow
switch activation, while placing high value/mission essential aircraft
Another, more significant change would be to change the system from
HEF to AFFF using Navy style grate nozzles. This system has the benefit
of not producing inundating blankets of foam, but does bring with it
increased costs in terms of higher water flow rates and water storage
quantity, trench drains, and the possible need to deal with AFFF
The loss of life in the Eglin incident is unfortunate and tragic and
correctly serves to highlight the need to address accidental HEF system
activations. However, it should not result in removal high expansion
foam from the design toolbox.
Samuel Dannaway is with S. S. Dannaway Associates, Inc.
Weaver, R. "Commander Directed Investigation Findings and Conclusions
Concerning Eglin AFB Accidental High Expansion Foam Discharge and
Fatality," Eglin Air Force Base, Florida (undated.)
"Engineering Technical Letter (ETL) 02-15: Fire Protection Engineering
Criteria - New Aircraft Facilities," Air Force Civil Engineer Support
Agency, Tyndall AFB, FL, 2002.
Anon, "Air National Guard Design Policy ANG ETL 01-1-1, 2004.
FM Data Sheet 4-7N, Low Expansion Foam Systems, FM Global, Norwood, MA, 2013.
Scheffey, J., et al., "Aircraft Hangar Fire Suppression System Design
Study," NRL/MR/6180-00-8464, Naval Research Laboratory, Washington, DC,
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