Space Based Fires & Suppression Systems

John W. Thomas
1 April 2013
Fire prevention in Space
Low-gravity/Microgravity Fire Characteristics
Fire Detection Technology / Detection in Microgravity
False Alarms
Fire Response
Fire Suppression Technology / Suppression in Microgravity
Post Fire Actions
Fire Safety for Payloads
Fire Safety needs for Beyond Earth Orbit
Fire Safety in partial gravity
NASA’s fire-safety record is excellent,
longer future missions (Moon, Mars, Asteroids)
increase the possibility of fires occurring and minimize mission
termination options
NASA’s primary goals as of this point have been based upon
minimizing flammable materials and eliminating sources of ignition
Research needs to be done in the suppression of fires in microgravity
and low-gravity environments
It is especially important to detect and suppress these fire incidents
when they occur in the contained crew environments
Even though there are strict safety policies in place fire incidents are
possible during any space mission
Fire Prevention in Space
The first thing done in space fire prevention is to
eliminate one of the three-fire causing factors
(fuel, oxygen and ignition energy). This method of
prevention isn’t perfect so detection and
suppression systems are always needed.
 Space fire suppression and detections systems
follow standards set for transportation systems
and aircraft.
 Spacecraft and Aircraft have similar fire issues
 Confined spaces, hostile outside environment
 And restricted mass, volume and power availability for
these fire intervention methods.
Low-Gravity/Microgravity Fire
Considered to be combustion in a
non-buoyant environment
 Flammability and flame-spread rate in
microgravity are particularly sensitive
to atmospheric flow.
 Flames propagate poorly in truly quiescent
conditions, but they are enhanced vigorously by
low-rate atmospheric flows (velocities up to
about 20cm/s).
 Some burning plastic materials may induce flow
to continue combustion through the action of
boiling and vapor-jet ejection.
Low-Gravity/Microgravity Fire
This environment diminishes the
effectiveness of the fire suppressant as it
effects the buoyancy and natural convective
flows of the typical agents used
 It changes the flammability characteristics of
the materials used and it also effects the
dispersal of suppressants
 Microgravity tends to complicate post-fire
clean up
 No single method currently used works
against all the different possible fire
scenarios onboard a space craft
Fire Detection Technology
The most reliable and original method of
detecting fires onboard a spacecraft is by the
crew itself.
 In the first manned space missions this was the only
way to detect fires.
However, modern spacecraft tend to have
sections of the craft that are inaccessible and
complex and therefore often require
additional automated systems.
There are several types of automated
sensors aboard spacecraft and they use
differing fire “signatures” to determine a fire
Fire Detection Technology
Some of the types of fire “signatures” are acoustic
waves, combustion gasses, light, particulates (smoke),
pressure rise, temperature rise and other radiation.
 Most current spacecraft have automated early fire
warning systems that detect smoke using lightscattering or ionization-current interruption.
 The US Space Shuttle achieves this with nine aspirating
ionization-current interruption detectors.
 The U.S., European, Japanese, and Italian segments of the
International Space Station (ISS) have detectors in each module
that sense smoke through photoelectric light-beam obscuration
and scattering.
 The ISS uses a variety of these specific detectors with some set
up as area or spot detectors and others within air-ducts and
aspirating detectors.
Fire Detection Technology
Fire Detection in Microgravity
Burning tests of PMMA
in microgravity done
PMMA - Poly (methyl
methacrylate) (Developed
in 1928, bought to market
in 1933 by Rohm and
Haas Company under the
trademark Plexiglas).
Fire Detection in Microgravity
There was a shuttle based project called
Comparative Smoke Diagnostics (CSD)
that examined particulate emissions
from typical well established pyrolysis of
fire events in microgravity.
 The sources in this experiment included a
burning candle and four overheated materials.
 Paper (Flaming in some tests), silicone, rubber
and polytetrafluoroethylene-insulated wires and
polymide –insulated wires.
Fire Detection in Microgravity
CSD Experiment
 Near Field
○ Within the same chamber as the smoke generation
○ Smoke particulates collected on thermophoretic grids for later
analysis and total smoke density is measured by laser-light
 Far Field
○ In a separate chamber connected by a pumped hose line with
smoke detector response determined for a Shuttle (STS) detector
and a prototype ISS detector used in parallel.
Fire Detection in Microgravity
Fire Detection in Microgravity
From the CSD project the response of the ISS and
STS detectors can be seen.
 The ionization detector is more sensitive to relatively
small particles and is good for detecting a flaming
 The photoelectric detector is more sensitive to
relatively large particles and good for detecting
smoldering fires.
 Additionally in microgravity smoke particles tend to
agglomerate into larger groups due to the lack of
buoyant motion.
 This study suggests that the ISS detector should be
a good replacement for fire detection in space as it
responds faster in microgravity.
Fire Detection in Microgravity
Fire Detection Using Atmospheric
An additional source of early warning in the case of a
fire event is the rate of buildup of atmospheric
 This particularly includes carbon monoxide concentrations.
Due to changes in the flame-zone temperature in
microgravity environments the combustion and
quantity of gaseous combustion products will differ
than that of combustion in normal gravity conditions.
 Some early studies on smoldering in low-gravity
indicated an increased quantity of light-gas
production but this could be due to the scale and
conditions used in the experiment as it has not been
observed in later tests.
Fire Detection Using Atmospheric
The ISS uses continuous atmospheric
sampling for air-quality monitoring. This has
the potential to detect the buildup of carbon
monoxide as the confirmation of a fire event.
 Multiple-gas sensing is being considered for
more effective interpretation of fire
signatures, rather than the currently used
single-gas sampling.
 In ground tests combined CO/CO2 detectors have
been shown to have the ability to distinguish between
non-flaming fires, flaming fires and non-fire events.
Fire Detection from Flame Radiation
Originally the ISS was set to have flameradiation sensors in the end cones for
overall monitoring of the open spaces of
the different modules.
 The need for conserved mass and
electrical power eliminated this type of
detector from the ISS design.
 The European Space Agency (ESA) is
continuing to develop these flame
detectors as a supplemental fire
detection technology.
False Alarms
False alarms can cause needless interruptions and
waste suppressant in automatic systems and they can
erode the confidence in the detection system.
A study done by Cleary and Grosshandler reported that
false alarms in aircraft cargo compartments are 100
times more frequent than actual fire events.
NASA has had a better record with less than 20 false
alarms or detector failures recorded during time of the
Shuttle’s operation
During this time only five potential fire-causing events
consisting of component overheating or electrical short
circuits occurred.
For these five incidents the fire “signature” was not
strong enough to cause a smoke detector to actuate
and the crew was able to identify and correct the issue.
Fire Response
In the event of a verified fire alarm, the automated or manual
crew response is to first isolate the affected zone where the
fire is present and then to remove the power and local or
general air circulation. The assumption in this case is that
without forced ventilation flow the fire in microgravity will not
Research has shown that in most fire situations quiescent
flames do self-extinguish.
 This implies that a minimum atmospheric flow rate is necessary in low
gravity to maintain fire propagation (and conversely to ensure extinction).
 Limiting flows for relatively flammable materials are very low.
 Self-induced flows may be sufficient to continue combustion.
U.S. investigators in a series of experiments on the MIR
space station found that a candle would continue to burn in a
quiescent environment for several minutes.
 This shows that the removal of air flow upon fire detection is a necessary
response but it is not always adequate for the control of the initial fire.
Fire Suppression Technology
While fire events onboard spacecraft may be
rare during regular space operations, fire
suppression technology must be made
available for the security and safety of the
crew and the mission integrity.
 Human-crew spacecraft have always been
equipped with some way of fire
 The Mercury and Gemini spacecraft a water
gun that was used for food reconstitution
was designed for the secondary purpose of
an emergency fire extinguisher
Fire Suppression Technology
In the Apollo missions there was a dedicated fire
extinguisher available that generated a stable
water-gas mixture propelled by an inert Freon
and nitrogen gas mixture.
 The Shuttle and it’s payload bay lab had
extinguishers that were charged with Halon 1301
 Portable fire extinguishers have nozzles suitable for
streaming discharge into open spaces or insertion through
cover ports for flooding discharge within racks.
 The shuttle also has a fixed, remotely operated Halon
1301 system, for use during critical periods, such as reentry when the mobility of the crew is limited.
Fire Suppression Technology
Fire Suppression Technology
Fire Suppression Technology
Astronaut Marsha Ivins performing a Zero G evaluation of orbiter fire
extinguishers while onboard the KC-135
Fire Suppression Technology
 The
non-Russian segments of the ISS
have portable fire extinguishers
charged with carbon dioxide. No
centralized fixed system is planned.
 The Russian segment of the ISS has
water-foam extinguishers based upon
technology already in service in other
Russian spacecraft.
Fire Suppression in Microgravity
Currently the key concern is to discern either the
minimum quantity of suppressant needed or the
minimum oxygen concentration needed to ensure
 The current studies base the minimum requirements
for carbon dioxide as a flame suppressant in spacecraft
upon the resulting oxygen concentration in the flames
 The ISS suppression system reduces the ambient
oxygen concentration to half of its original in less than
60 seconds while increasing the carbon dioxide to a
minimum of 50%.
 The National Fire Protection Association (NFPA)
standard 12 permits a minimum concentration of 34%
carbon dioxide for flooding suppression systems.
Fire Suppression in Microgravity
Fire Suppression in Microgravity
The results from the experiments that went
into the previous table emphasize the strong
fire-enhancing actions of low flows in
As an extinguisher carbon dioxide can not only
work as an oxygen diluter but also though
thermal effects by reducing the temperature of
the fuel surface and in the flame zone.
Due to the minimal nature of this temperature
reduction, the approach to determining the
minimum amount of suppressant is to define
the minimum amount needed to dilute the
oxygen for guaranteed fire suppression.
Fire Suppression in Microgravity
PMMA surface temperature
at the rear stagnation point
as a function of mass flow
rate of oxygen.
 Results from this
experiment showed that
increasing the sample
temperature made the
flame more difficult to
extinguish by suppressant
than those that were not
Fire Suppression in Microgravity
PMMA samples in flowing
oxidizer after flames became
stable in the low-gravity
At the higher velocities the
flame does not wrap
completely around the
Results of this show the
interdependence of the flow
velocity and the flame
intensity and structure on the
suppressant performance
Halon Phase-out and Replacement
CF3Br - Bromotrifluoromethane
By international protocol the manufacture
and production of Halon 1301 is now
 Halon 1301 acts as a stratoshperic ozone
layer depleter.
 A Chemical agent that inhibits combustion
by chemical reactions to remove free
radicals from the reaction zone.
 Many Halon replacements have great
Halon Phase-out and Replacement
Halon Phase-out and Replacement
HFC-227ea – Heptafluoropropane
 Is a highly regarded Halon replacement but
it requires about twice the discharge quantity
as Halon 1301
Suppression of Oxygen-Generator Fires
February 1997 – Russian Space Station Mir
 A chemical fire resulted from a failed Vika oxygen
 Fortunately no one was hurt and it did little overall
 Module and atmospheric cleanup took several days
The Vika Oxygen Generator
 It uses solid canisters of lithium perchlorate (LiClO4) and
it burns these to create gaseous oxygen
 Lithium perchlorate decomposes at around 400 Degrees
Celsius to form lithium chloride and oxygen
 It has the highest oxygen to weight and oxygen to volume
ratio of all perchlorates except beryllium diperchlorate
which happens to be highly toxic and expensive
Suppression of Oxygen-Generator Fires
Astronaut Jay Apt looking at a solid-fuel oxygen generator like the one that
caught fire on Mir.
Suppression of Oxygen-Generator Fires
Chemical Oxygen Generators are not used in most of the
The Russian segment has one as a backup oxygen
In ground tests it was shown that water based foam (the
extinguishers used in the Mir incident) is the most
effective agent to extinguish these types of fires.
The foam must be applied directly to the surface of the
generating cassette.
The carbon dioxide extinguishers used by the rest of the
ISS modules has been shown to be ineffective against
these fires. In some cases they have actually enhanced
the fire.
Other Agents for Spacecraft Fire
Nitrogen is used as an alternative to Halon and
carbon dioxide in small, inhabited modules of space
craft (ISS airlock)
 It is less effective than the other methods but is inert,
easily available and non-toxic
Water-based mists and foams are also used.
 The Russian segment will continue to use the Mir-type
aqueous foam suppression system
 The foam penetration is different in low gravity compared
to normal gravity. The foam sticks to surfaces and
successfully smothers the fires
 Obvious disadvantages of non-gaseous agents are their
removal from the atmosphere and other surfaces once the
fire has been contained. Also accidental release of these
agents can cause serious damage to other systems in the
Other Agents for Spacecraft Fire
Experimental results in the
effect of several diluent
atmospheres on
microgravity flame-spread
and flame-extinction limits.
 As can be seen from this
about half the required
carbon dioxide is needed
to accomplish flameextinction than nitrogen
Pressure Reduction and Venting
for Extinguishment
Venting the Atmosphere in the event of an
uncontrollable fire event is possible on the
 The U.S. Laboratory Module has a vent/relief
valve that is designed to reduce pressure
Two scenarios merit this action
 For fire suppression the module is
depressurized to a limit of 6.9 kPa in 10 minutes
 For hazardous atmosphere removal the module
is depressurized to a limit of 2.8 kPa in 24 hr.
Pressure Reduction and Venting
for Extinguishment
Experiments done in low-gravity have
looked into the effects of depressurization
and the final pressure on the suppression
of a fire
 These experiments suggest that if a fire is
to be controlled by depressurization, the
pressure in the module in question must be
decreased as rapidly as possible
 This induces high velocities and limits the flame
zone heating
 Slow depressurization might lead the final
pressure to lower limits and complicate the
suppression efforts.
Pressure Reduction and Venting
for Extinguishment
PMMA cylinder ignited
along its axis with
atmospheric crossflow
This figure is a combination
of the experimental data
and analytical results
Notable is that low-gravity
suppression is much more
difficult with increasing fuel
Extinction appears to be
most difficult around a flow
of 10cm/s
Post-fire Actions
Burned material remains hot in the non-convective
microgravity environment this means that embers may
reignite if prematurely exposed to fresh air
 Atmospheric revitalization is necessary to remove even
trace quantities of fire and suppressant contamination
 This may tax the environmental controls and require the use of
portable air-breathing equipment for extended periods of time
Despite all of the clean up when normal conditions are
restored there will be trace amounts of toxic and corrosive
aftereffects of the fire on the equipment, systems and
After the discharge of the Halon systems in the Shuttle
the mission was terminated and all of the post-cleanup
was done groundside.
Fire Safety For Payloads
One of the most serious concerns for fire
safety in the ISS and onboard the STS
missions are the payloads
 Payloads can be anything from furnaces,
energetic experiments and sensitive biological
There are currently many proposed
methods for fire detection in payload areas
 Parameter monitoring (continuous monitoring for
fire signatures)
 Automated air-cooling shutoff for preventing
Fire Safety For Payloads
A proposed ISS payload safety system
is the Combustion Integrated Rack
 Common facility to provide the majority of
chamber, power, diagnostics, flow and
control for combustion –experiment
 Uses the standard ISS smoke detector and
internal cooling-air flow
Fire Safety Needs for Beyond
Earth Orbit
Can be broken into two phases
 Travel / Transit Phase
○ Assumed unpowered and without gravity
○ Fire safety on these long term missions is
○ Amounts of suppressant and spare
atmosphere is limited
 Surface Base / Habitat Phase
○ Systems and the crew are exposed to the
local gravity which will be greater than
microgravity but less than Earth
Fire Safety in Partial Gravity
Even less is known about the exact effects
of partial gravity upon fire characteristics
(0.01 to 0.6 g)
 Flights on the KC-135 give a short period
of time in which to analyze this
 From the studies that have been done, it
seems that from the fuels tested that
flammability range increases to a maximum
between normal-gravity and microgravity
Fire Safety in Partial Gravity
These studies also show that flame spread
also increases to a maximum at this partial
 The increase in flammability and flame
spread are thought to be caused by the
generation of optimum buoyant flow
velocities at this low yet finite convective
 This effect is similar to the effect that was
observed during the low-velocity forced airflow experiments in microgravity.
Fire Safety in Partial Gravity
Fire Safety in Partial Gravity
Fire prevention in space is usually done by
limiting the possible sources of ignition.
Fire Characteristics are quite different in
microgravity as it is a non buoyant
Fire detection in microgravity is vastly different
than fire detection in normal gravity as the
smoke particulates can act as liquid droplets
under quiescent conditions.
Detectors currently used in microgravity use
light obscuration and ionization-current
False alarms are a serious issue in
space as they can cancel missions
 Responding to fires in microgravity as
soon as they start is very important as
low air flow rates can accelerate the
flame spread.
 Not all quiescent flames in microgravity
Fire suppression technology in microgravity
meet different requirements than
suppressants that are used in normal
 The most efficient way to extinguish flames
in microgravity is by smothering rather than
 All post fire cleanup for the shuttle missions
was done Earth-side. This however, isn’t
possible for space stations.
Fire response and detection systems need
to be greatly improved for microgravity
environments, especially as the shuttle
detectors seemed not to function during
their fire incidents.
 Many of the studies examined here show
data that conflicts with itself. More funding
needs to be given to NASA to study the
effects of microgravity and partial gravity
on fire characteristics in order to build a
better knowledge base about this topic.
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Image References

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