Fire Detection in MicrogravityPrepared by: Lt Paul Konyha & Lt Jennifer SchutzenhoferFires: Microgravity vs. Earth• Non-convecting purely diffusive environment• No bouyant flow-- heated gases don’t rise– Example: Candle Experiment•O2supply dependent on STS/ISS ventilation fans• CO orders of magnitude higher-- more toxic • Flammable material still present after fire is extinguished• Hemispherical flamesSTS/ISS Detection Designs• CURRENT (STS)– Ionization detection, Freon-1301 bottles, and hand-held Halon-1301 extinguishers – NASA requirements: Each payload must monitor SOH-- multiple sensors• FUTURE (STS/ISS)– SECOND GENERATION HALON REPLACEMENTS: Flame-Ex & Halon 1211– FIRESCAPE: Images invisible flames of alcohol & hydrogen fires-- sees through smoke– SOLID-SOLID HYBRID GAS GENERATORConcluding Remarks• Need more data on microgravity combustion• Ground-based scientists will have to adopt new approaches to space combustion phenomena• Each component will continuously need to be monitored for overheat conditions• Combination of new technologies utilized– Portable extinguishers will continue to be used in manned area so 2nd generation Halon replacements are a given– Solid-solid hybrid gas generators likely since the pros far outweighed the cons– FIRESCAPE will possibly be an asset on the launch pad but not relevant to STS or ISSReferences• http://liftoff.msfc.nasa.gov/shuttle/usmp4/science/combust.html• http://microgravity.grc.nasa.gov/fcarchive/combustion/edmps/scmedmp.html• http://quest.arc.nasa.gov/shuttle/ask/living• http://science.msfc.nasa.gov/newhome/headlines/msad12jul97_1.htm• http://science.msfc.nasa.gov/newhome/headlines/msad08jul97_1.htm• http://www.floridatoday.com/space/explore/releases/1996b/n96200.htm• http://www.ksc.nasa.gov/shuttle/technology/sts-newsref/sts-caws.html#sts-fire• http://www.lerc.nasa.gov/WWW/RT1996/6000/6711u.htm• http://www.mainstream-engr.com/chemical.html• http://www.microgravity.com/combustion.html• http://nextstep.com/stepback/cycle10/122/fire.htmlFire Detection in MicrogravityASEN 5519Prepared by: Lt Paul Konyha & Lt Jennifer SchutzenhoferOverview• Background• NASA Requirements• Current STS Fire Detection System• Micro-gravity Fire Experiments• Future Designs/ISS• ConclusionFires: Microgravity vs. Earth• No bouyant flow-- heated gases don’t rise– Example: Candle wax consumed 5 times more slowly• Entire candles melt in 2 min due to increased downward heat conduction• Surface tension of liquid wax prevents fire extinctionFires in Microgravity• Non-convecting, purely diffusive environment–O2supply dependent on STS/ISS ventilation fans– CO orders of magnitude higher-- more toxic • Flammable material still present after fire is extinguished• Hemispherical flamesAir Flow Dependency in Space• Quiescent (no airflow) environment– Materials burn more slowly than on Earth• Low-speed airflow (2-8 inches/sec)– Materials more flammable than on Earth– Flame front which propagates into wind stronger due to increased O2supply & no convection• Lesson: Turn off ventilation to suppress firesFire Detection & Suppression Methods• Detection Methods: IR, UV, ion, particle• Detection Approach: centralized, distributed, or a combination• Suppression Methods: CO2, N2, H2O, halon– Water & foam not suitable for space habitats • Suppression Approach: centralized, distributed, portable, or a combination• Bottom Line: remove oxidizer or fuel or else remove heat req’d for combustion to occur• Cleanup Options: sorption, conversion, vent to spaceNASA Requirements• All payloads shall output SOH data at 1 Hz continuously• Must identify fire potential while reducing possibility of false alarms• Multiple sensors of more than one type – 2 temperature and 2 current sensors• Fire potential defined: 2 or more sensors of any type have out-of-tolerance conditionsCurrent STS Fire Detection/Suppression• Ionization detection: sense levels of smoke concentrations and trigger alarms• Avionics bays fire suppression – Freon 1301 (bromotrifluoromethane) extinguisher bottle• Crew cabin fire suppression– Hand-held fire extinguishers with Halon-1301 (monobromotrifluoromethane)Microgravity Combustion Experiments• Droplet Combustion Experiment (STS-94)– Researches the dynamics of burning drop of fuel in space– Scientists compare the effects that a supporting fiber has on a droplet with a free-floating droplet– Following image shows ignition of vapor cloud around the droplet and the outline of the fiberDroplet Combustion ExperimentMicrogravity Combustion Experiments• Comparative Soot Diagnostics Experiment– Designed to compare the effectiveness of an ionization detector vs. an infrared light-scattering detector in micro-gravity– Light-scattering detector more sensitive to smoke particulate samples than the ionization detectorMicrogravity Combustion Experiments• The Structure of Flameballs– Why fires keep burning and what makes them go out?• The Laminar Soot Experiment– Soot re-radiates fire’s heat as visible light & infrared warmth--formed faster in space• Candle Flames in Microgravity– Studies candle flame behavior in spaceDroptower ExperimentFuture Design Possibilities• Solid-solid hybrid gas generator – Pros: • Replaces ozone depleting Halon 1301• Agents drastically cooler than conventional gas generators• Significantly smaller and lighter• Single storage vessel as a solid• Acceptable atmosperhic & toxicological properties– Cons:• Clean-up can be problem in space/contained environmentFuture Design Possibilities• Second-generation Halon replacements– Flame-Ex, triflouroiodomethane, Halon 1211, & perfluorohexane– Pros:• Increased application density for comparable agent amounts• More effective than most chemicals as total flooding agent– Cons:• Less effective than Halon 1301 as total flooding agent• Toxicity info and atmospheric impact studies incomplete• High manufacturing costs• Has not yet received EPA SNAP approvalFuture Design Possibilities•FIRESCAPE– Images invisible flames of alcohol & hydrogen fires– Sees through smoke & finds origin of visible fires– Pros:• First affordable commercial product for fire imaging• Used like binoculars-- no moving parts/easy to operate• Firefighters can remain at safe distance while finding invisible fires• Low purchase