[American Institute of Aeronautics and Astronautics 43rd AIAA Aerospace Sciences Meeting and Exhibit...

American Institute of Aeronautics and Astronautics

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A Research Plan for Fire Prevention, Detection, and Suppression in Crewed Exploration Systems

Gary A. Ruff* and David L. Urban.† NASA Glenn Research Center, Cleveland, Ohio, 44135

and

Merrill K. King‡ NASA Headquarters, Washington, D.C., 20546

Fire is a particularly critical danger in future extraterrestrial vehicles and habitats on long-range, long-duration missions since, unlike in most scenarios here on Earth, escape is not an option and the fire department will not be coming. In such vehicles and habitats, the first line of defense lies in determining the ignitability and flammability of candidate materials under reduced and microgravity conditions and at appropriate oxygen mole fractions and then using this information to help select materials to be used in these vehicles and habitats. If, despite our efforts to prevent a fire, one does occur, our next line of protection is fast and reliable detection of such occurrences (with minimum false positives) and definition of their locations. After a fire and its location have been identified, we must have reliable means of extinguishing this fire as quickly as possible with as little impact to the mission and crew as possible. Finally, post-fire cleanup, toxicology of fire products and products of the interaction of the flame with the extinguishant, and virtual simulation training of the crew in fighting fires are also important areas which must be addressed by the research plan presented in this paper.

I. Introduction The Vision for Space Exploration announced by President George W. Bush on January 14, 2004 directed NASA to achieve the long-term goal of sending humans back to the Moon and then on to Mars. The amount of knowledge that must be gained and the number of technologies that must be developed before such missions can occur are certainly formidable. The performance standards required for these technologies are, in many cases, well beyond those used on the International Space Station and the Space Shuttle and will stretch our current knowledge of living and working in space. Many of the challenges are aimed at ensuring the health and safety of the crew during the entire mission. Fire Prevention, Detection, and Suppression (FPDS) is one of the technology development areas identified within the Life Support and Habitation element of the Exploration System Missions Directorate (ESMD). The overarching goal for work in the FPDS area is to enhance crew health and safety on exploration missions by reducing the likelihood of a fire, or, if one does occur, minimizing the risk to the mission, crew, or system. This paper presents the initial draft of the research plan that will define technologies and methodologies to be developed in the areas of fire prevention and material flammability, fire signatures and detection, fire suppression and response, and development and analysis of fire scenarios. In each of these areas, products or deliverables that are required for use in future exploration spacecraft and habitats by the ESMD have been identified. These deliverables may be hardware, design requirements, data for trade studies, test procedures, data libraries, or recommendations for fire response procedures depending on the area. To realize these deliverables, this plan will incorporate areas of combustion science, fire safety engineering, risk assessment, and failure analysis. Implementing the plan will require a coordinated effort from numerous researchers as well as fire safety professionals. * FPDS Element Lead, NASA John H. Glenn Research Center/MS 77-5, AIAA Associate Fellow. † Branch Chief, Microgravity Combustion Branch, NASA John H. Glenn Research Center/MS 77-5, AIAA Member ‡ FPDS Program Element Manager, NASA Headquarters, AIAA Fellow.

43rd AIAA Aerospace Sciences Meeting and Exhibit10 - 13 January 2005, Reno, Nevada

AIAA 2005-341

This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.


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A. Current Status of Spacecraft Fire Safety Systems and Procedures Any discussion of fire prevention practices and/or detection and suppression systems for exploration systems

must begin by defining what is being or has been used on spacecraft. Of particular interest are areas where knowledge has been gained since the design of the systems on the ISS and STS Shuttle that could impact the design of next-generation systems. While the technologies to be developed in this plan are not intended for use on the ISS and STS, lessons learned from the fire detection and suppression system aboard these systems are relevant and will be identified.

1. Fire Prevention and Material Flammability

Existing material flammability acceptance test methods have been in place with little revision since the early days of manned spaceflight. The criteria applied in these acceptance tests were developed more from a phenomenological basis than the quantification of the risk of a fire. At this time, material flammability characterization used in support of selection or rejection of materials for use in spacecraft is based on NASA-STD-6001: Flammability, Odor, Offgassing, and Compatibility Requirements and Test Procedures for Materials in Environments that Support Combustion1. The Upward Flame Propagation test (Test 1) is conducted in a normal gravity environment with the ambient conditions (gas composition and pressure) set equal to that of the worst-case environment to which the material will be exposed. As shown in Fig. 1, a vertical strip of material typically 5 cm wide, 33 cm long and of the worst-case thickness is ignited at the bottom and the flame spread up the strip is measured. A material fails Test 1 if it burns more than 15 cm or drips flaming debris on a piece of K-10 paper placed 20 cm below the sample. While this may represent a worst-case scenario on Earth, research conducted in microgravity has shown clearly that the ignition behavior and flame spread rate for any given material is quite different under low- and microgravity conditions at various imposed (ventilation) velocities (including zero cross-flow) than under the buoyancy-driven convection conditions naturally present in the upward spread tests.2-4 Accordingly, the results of the NASA-STD-6001 Test 1 do not map quantitatively to those in the low- or partial-gravity environment of an exploration vehicle or habitat. A second test (Test 2) uses a standard oxygen-consumption cone-calorimeter to provide quantitative data on ignition delay times and burning rates of materials. However, the parameters measured by this test are also buoyancy dominated so their relationship to reduced gravity behavior is uncertain. 2. Fire Detection

In terms of fire detection, there is not unanimity as to the best system between the Russian and U.S. modules of the ISS and the Space Shuttle. The Shuttle and the Russian modules of the ISS use ionization-based smoke detectors while photoelectric smoke detectors are used on the U.S. modules. (A photograph of the STS smoke detector is shown in Fig. 2 while the ISS photoelectric detector is shown in Fig. 3) However, the Comparative Soot Diagnostic (CSD) experiment, which flew in the Glovebox on STS-75, provided data concerning the performance of NASA’s smoke detectors in microgravity and provided particle size information for three types of solid smoke particulate. The most important finding of CSD was that for liquid smoke aerosols, the microgravity performance of the space shuttle (STS) smoke detector was substantially reduced from that in normal gravity. It was hypothesized that this performance difference was due to extended growth of the liquid smoke particulate in low-gravity due to the enhanced residence times in high smoke concentration regions. These findings have considerable implications for the design of smoke detectors exploration vehicles but were unavailable when the design studies were performed to select the smoke detectors on the STS or ISS.

Figure 1. Experimental configuration for the Upward Flame Propagation test (Test 1). The specimen is 33 x 5 cm and the “worst-case” thickness. A chemical igniter is used if the O2 mole fraction is less than 50%. Otherwise, a silicone igniter is used.


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3. Fire Suppression The Space Shuttle currently uses a Halon-based suppressant with portable extinguishers available for crew use and a fixed Halon delivery system within the avionics bays. The U.S. modules of the ISS utilize portable CO2 extinguishers, shown in Fig. 4, while the Russian modules use portable water-based foam extinguishers. The U.S. CO2 extinguishers are charged with 2.7 kg of CO2 gas at a pressure of 5.9 MPa at 21 deg C. The design requirement is that when discharged, the CO2 could reduce the O2 concentration in an International Standard Payload Rack (ISRP) (approximately 0.73 m x 0.97m x 1.75m with a useable volume of 1.6 m3) by 50% within 60 sec. This is based on the requirements of the NFPA 12 regulations that require a CO2 concentration of 50% be achievable when extinguishing smoldering fires and 34% for flaming combustion.5 (NFPA 12 also requires that the 50% concentration for smoldering fires be held for 20 minutes to ensure the fire is extinguished.) Little has been done to determine which of these approaches is most effective in suppressing a fire and least invasive in terms of post-fire toxicology and cleanup.

II. Assumptions To develop a plan for fire-safe design of spacecraft, assumptions

must be made about (1) the definition and schedules for the exploration missions and (2) the most likely fire scenarios in the vehicles/habitats used on these missions. Without these definitions, the solution-space for the design of any fire protection system is simply too large to apply a rational design strategy. Our current understanding of these underlying assumptions is discussed below.

A. Development Spirals for the Crew Exploration Vehicle The primary goal of this plan is to deliver products that will ensure the fire safety of exploration vehicles and

habitats to the Exploration Systems Mission Directorate. The current requirements for these systems can be found in the definitions and schedule for the development spirals of the Crew Exploration Vehicle. The spiral definitions and schedule are as shown in Table 1, defined as of September 10, 2004.

The objective of the spiral development strategy is to allow maturing technologies to be incorporated into the

Figure 2. Brunswick Defense™ smoke detector used in the NASA shuttle fleet. The inlet is on the right and the gas is expelled out the small plate on the top.

Figure 3. Allied Signal/Honeywell light-scattering smoke detector used in the ISS. The near IR laser beam emerges from the enclosure into the top assembly (A) and is reflected by two mirrors (one visible at top right (B)) and is then reflected back to the sensors in the enclosure (C). One sensor detects the forward scattered light and is referenced by another sensor that looks directly at the incident beam.

Figure 4. Portable CO2 fire extinguisher used on the U.S. modules of the ISS. The orange jacket provides thermal protection because the extinguisher gets cold during discharge. The straight nozzle is shown in the front pocket of the jacket.


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Table 1. Definition and Schedule of CEV Development Spirals

Spiral Definition Duration Schedule0 Unmanned CEV flight -- 20111 Lunar-capable CEV in Low Earth Orbit -- 20142 Moon Landing Extended Stay 4 - 14 days 2015-20203 Moon Landing Long Stay 60 - 90 days 2020+4 Human Exploration to Mars Vicinity 1 - 2 years 2025+5 Mars Landing Short Stay TBD 2030+

*Spirals 1-3 are for a crew of 4 - 6 persons

design of a vehicle more gradually by identifying a desired capability without defining the end state requirements. The requirements are then refined through system demonstration and risk management. While seemingly ideal for the development of spacecraft, the technology lead time is still significant. For example, as currently planned, a Design Readiness Review (DRR) would be held six years prior to deployment of a flight system. However, according to the current schedules, one year of concept development and definition of requirements, one year of technology development and about two years of system development and verification precedes the DRR. Therefore, there is a total of about 10 years between the initial concept development and deployment of a new vehicle. The initial concept requirements for Spiral 1 were developed late in 2004 so we are already into the concept refinement and technology development phases. For new FPDS technologies to be incorporated into the Spiral 1 CEV, they would have to be sufficiently mature by 2008 at the latest. The concept definition for Spiral 2 would have to begin in 2009-2010 for it to be deployed about 2020. While there is time for new FPDS technologies to impact these spirals, this schedule can only be met by the aggressive implementation of a focused research plan with both short and long-term objectives. Furthermore, it must make use of all the tools available including testing in ground-based reduced-gravity facilities, modeling, and where absolutely necessary, flight experiments.

B. Use of Existing Flight Hardware Because of the spiral development schedule, the maturity of the design for the Combustion Integrated Rack and

associated experimental inserts (Multi-User Droplet Combustion Apparatus (MDCA) and the Flow Enclosure Accommodating Novel Investigations in Combustion of Solids (FEANICS)), the time required to develop new inserts, and the limited flight opportunities to get experiments on board the ISS, the first course choice for any new fire safety investigations requiring space experiments must be to use or to be based on existing experimental concepts. Therefore, we have taken the approach of re-vectoring existing flight science projects to address specific questions required to deliver products in the three focus areas (fire prevention and material flammability, fire detection, and fire suppression and response). The re-vectoring of flight experiments is difficult because of the unique requirements each experiment places on the design and operation of the CIR but it is required to obtain critical data and verifications that cannot be obtained in ground-based reduced gravity facilities. While the detailed requirements for these experiments are still being formulated and will undergo peer review when completed, this plan describes the programmatic needs that the end products from these experiments must fulfill.

C. Pre-specified Flight Opportunities The use of existing flight hardware also imposes schedule constraints because the hardware has been scheduled

to fly on specific shuttle flights. Therefore, not only must the experiments make use of hardware that is partially designed (completely, in some cases) but it would also be beneficial for the experiments to be developed in time to maintain these flight opportunities. Table 2 shows a schedule of hardware availability and flight opportunities as currently planned (December 2004). Given the uncertainty surrounding the Return-to-Flight, these dates are tentative and are likely to change. However, the targets remain and expeditious development of the FPDS experiments only increases the likelihood that they will be ready at the earliest flight opportunity.

III. FPDS Deliverables The research plan in the Fire Prevention, Detection, and Suppression sub-element is based on deliverables that,

when incorporated into the design philosophy and functional design of exploration vehicles and habitats will quantitatively reduce the likelihood of a fire and reduce the extent and degree of equipment damage should a fire occur. These products have been developed through a series of workshops focusing on spacecraft fire safety. The most recent workshops were held in 20016, 20037, and 2004; the first workshop was held in 19868. At each of these workshops, input was obtained from designers and operators of current spacecraft (STS and ISS) and was used to formulate the products required for exploration systems. (Even though no formal requirements have been stated by


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the Exploration Systems Mission Directorate, the issues and concerns will undoubtedly be similar to those expressed by the designers and operators of current spacecraft, with the major exception that partial gravity performance will also be important for lunar and Martian operations.) Several other reports that overview and recommend spacecraft fire safety needs have been prepared and these also provided input to this plan.9-11 The needs identified from these workshops and reports consisted of suggestions for flight hardware and experiments, ground-based test techniques and matrices, design rules, and data bases in various areas of fire safety. The entire FPDS research program will be focused on developing the knowledge base and technology solutions to produce these deliverables.

A. Fire Prevention and Material Flammability 1. Normal gravity material flammability test to evaluate reduced gravity flammability

Existing material flammability acceptance test methods have been in place with little revision since the early days of manned spaceflight. The criteria applied in these acceptance tests were developed more from a phenomenological basis than quantification of the risk of a fire. Microgravity testing has identified that some materials become more flammable (as evidenced by a lower limiting oxygen index) in a reduced gravity convective flow than under normal gravity conditions2 indicating that this test may not be conservative in all cases, although the actual margin of safety is unknown. The deliverable from this effort will be a standardized test (or tests) that can be conducted in normal gravity to accurately assess material flammability in low and partial gravity levels. An acceptance criterion will be developed that is traceable to fire behavior in reduced gravity. The accuracy of this normal-gravity analog must be verified by in-space tests.

2. Material flammability assessment in candidate atmospheres for exploration transit vehicles and habitats

One design parameter that will determine much of the design and operational philosophy for exploration vehicles will be the composition of the atmosphere and ambient pressure for the habitable volume. The atmosphere of previous spacecraft has ranged from 100% O2, 34.5 kPa for Mercury, Gemini, and Apollo missions to standard air (21% O2/79% N2, 1 atm) for ISS and STS. (Atmospheric conditions prior to EVA were different from the standard cabin atmosphere.) These design points are shown in Fig. 5 and generally lie along the normoxic equivalent line, i.e., having the same O2 partial pressure as 100 kPa, 21% O2 by volume.12 In order to maintain O2 partial pressure along the normoxic line, the %O2 increases as the total pressure decreases. Yet, it is the mole fraction of oxygen that drives the susceptibility of materials to fire. The increased material flammability of these conditions is critical in terms of fire initiation and suppression.

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Figure 5. Design space for cabin atmosphere and pressure and O2 concentration. Space suit pressure is 29.6 kPa (4.3 psia); R is the bends (Tissue) ratio. At a bends (tissue) ratio of R=1.4, 4.5% of the population will experience symptoms of decompression sickness.12

Table 2. Flight Hardware Availabilty (FHA) and Space Flight Opportunities for FPDS Experiments (as of December 2004)

FHA On-OrbitCombustion Integrated Rack May-05 May-07

FLEX May-05 May-07FEANICS-1 Jul-07 Jan-08FEANICS-2 Jul-07 Jan-08FEANICS-FPDS TBD 2010

MSGSAME Jan-06 Jul-06

ExpressDAFT-1,2 Sep-03 Dec-04DAFT 3,4 Sep-03 Jul-05

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As evidenced by the range of atmospheres that have been used, there is no optimum atmosphere for space vehicles with each mission requiring a detailed evaluation of the mission. Various trade studies have indicated significant advantages associated with operation at total pressures considerably lower than one atmosphere. For example, Fig. 5 shows the design space obtained from one of these studies.12 The hypoxic boundary represents the partial pressure of O2 below which human activity is impaired because of lack of oxygen. The pre-breathe lines represent the duration required for pre-breathe before an EVA. A bends ratio of R = 1.4 is assumed and represents the ratio of the partial pressure of N2 in the blood to the ambient (EVA suit) pressure. At higher ratios, more of the population would experience symptoms of decompression sickness. The vertical line at a 30% volume of O2 is the limit imposed by material flammability because it was concluded in this study that below 30% O2, there are still a sufficient number and variety of materials that can be used based on their flammability and ability to pass Test 1. Obviously, the remaining design space for exploration atmospheres is rather small and, as designs develop, there will be pressure to move it to even higher O2 concentrations. If, indeed, the oxygen mole fraction is raised relative to Earth ambient, testing of all candidate materials at the selected mole fraction will be a critical part of the FPDS activities.

An early assessment of material flammability in candidate atmospheres would provide additional information to be factored into the selection process. While it is not set, it will most likely fall into the range shown in Fig. 5 above. Therefore, the deliverable from this task will be a quantitative assessment of the effect of high O2 mole fractions at lower ambient pressures on the flammability of a set of typical spacecraft materials. This assessment will be done at various gravity levels so that design trade-offs can be made for various exploration missions using the appropriate level of gravity. 3. Definition of realistic fire scenarios for exploration spacecraft and habitats

The science of fire protection engineering in terrestrial applications has developed considerably since the specifications were written for either the STS or ISS. Not only do we better understand the mechanisms of ignition, flame spread and fire growth, we now possess better computational models that can be used to predict the development and outcomes of the fires. These tools have been developed to evaluate terrestrial fire safety issues such as the suitability of material flammability criteria, the design of fire detection and suppression systems, and the adequacy of fire response strategies and protocols to provide a quantifiable level of fire protection. Even though an equivalent evaluation and assessment is required by designers of exploration spacecraft and habitats, these tools have not been applied in a systematic way to analyze fire scenarios in microgravity and partial gravity environments. When coupled with the knowledge of flame spread and fire development in reduced gravity, these tools can be tailored to evaluate various fire scenarios relevant for exploration spacecraft and habitats and yield practical information upon which design and operational decisions can be based. At the very least, it would provide a rational methodology to assess what information is known about fires in reduced gravity and what data is required to adequately define a fire scenario.

B. Fire Signatures and Detection 4. Advanced detection system for gaseous and particulate pre-fire and fire signatures

Smoke detectors on the ISS have proven to be sensitive to dust and have produced numerous false alarms. As such, there is an immediate need for new fire detector technology that eliminates nuisance alarms. This problem will only be exacerbated on long-duration exploration missions in both transit vehicles and surface habitats. The spacecraft fire detection system developed in this work should be able to (1) detect a fire with minimal false or nuisance alarms, (2) minimize the time from the beginning of a pyrolysis or pre-fire event to the time an alarm sounds, (3) indicate to the crew the location of the fire, and (4) identify the source of the fire from the measured signature. The tasks required to accomplish this goal include sensor development and verification, development of the logic to allow a distributed network of sensors to assist in locating and assessing a fire, and quantification of fire and pre-fire signatures in reduced gravity. The Spacecraft Fire Safety Program at NASA GRC has funded the development of micro-chemical sensors for combustion gases and particulates. However, this is only one of several candidate technologies that could satisfy this need. An experimental evaluation of several sensor prototypes in both normal and reduced gravity should be conducted so that relevant data is available for use in a trade study.

5. Verified models of the transport of contaminants, smoke, and combustion gases throughout the habitable volume

of a spacecraft or habitat The effectiveness of even the most refined and exotic sensor will be reduced unless it is located in the right place

and the time required for the contaminant to reach a detectable level at that location is known. If a distributed network of sensors is used, the number of sensors in the system will undoubtedly be limited and the design goal will


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be to minimize the number of sensors required to provide adequate protection. The deliverable in this task is a validated computer model for the large-scale transport of smoke and combustion products within a habitable volume that can be used to evaluate fire detector location and activation. This tool would be linked to vehicle models for incorporation of this analysis into the structural design process. It will also be used to support the development of a realistic crew training tool to be discussed in Deliverable 7.

C. Fire Suppression and Response 6. Design rules for suppressant system including effectiveness of suppressants, required concentrations, and

dispersion methods Carbon dioxide was selected as the fire suppressant on the ISS primarily because of its use in terrestrial

applications. The objective of this work is to develop rational data and guidelines for the design of fire suppression systems in microgravity, as well as the Lunar and Martian partial gravity environments. On-going projects in the Spacecraft Fire Safety Program at NASA GRC are evaluating the effectiveness of suppressants in ground-based reduced gravity facilities. These projects have resulted in new data that can direct future work but they also indicated the need for continued assessment of suppressant effectiveness in microgravity (experiments in space and ground-based facilities). Extinguishing agents to be evaluated include but are not limited to CO2, N2, He, water mist, and micro-encapsulated water.

7. Simulations of fire and fire-response scenarios for system evaluation and crew training

Effective fire detection systems and suppression techniques are only as good as the training the crew receives to use them. Efficient use of the learned skills and the tools provided under what most likely will be a very tense and confusing situation is required to minimize equipment damage and limit the contamination of the cabin atmosphere either by combustion products or the fire extinguishing agent. Performing such a simulation in a cabin mock-up on Earth is pointless because the fire and fluid transport will be dominated by buoyancy and will behave very differently than in a reduced-gravity environment. The objective of this deliverable is to provide a virtual reality (VR) simulation in which the crew can experience a realistic fire scenario during ground-based training. Additionally, this simulation could be used to evaluate fire response scenarios to evaluate crew response relative to their capabilities and task demands.

IV. Formulation of the Program Plan The deliverables listed above constitute the anticipated outcome of the FPDS element. The researchers in the

Microgravity Combustion and Reacting Systems Branch at NASA Glenn Research Center have formed teams associated with each of these areas to address how the existing suite of funded projects can be utilized to achieve these deliverables. The overall research plan will proceed through integration of ground-based testing, analytical and numerical modeling which will permit use of the ground-based testing to predict space-based results, and limited space-based testing to verify these procedures. The specific requirements for the space-based experiments are not outlined in this plan. Instead, the plan identifies the overall research objectives required to meet the programmatic needs and a set of tasks that could be used to achieve that objective.

A. Fire Prevention and Material Flammability The tasks that must be accomplished to deliver the products identified in Section III are identified in this section.

The philosophy of these tasks is to understand existing material flammability testing and procedures, determine if there are normal gravity tests from which we can deduce reduced gravity flammability, and measure quantities that will allow us to numerically model the behavior of flammable materials and eventually fires in reduced gravity. This philosophy can be translated directly into the primary tasks listed below (1) better understand what the existing test methods tell us in terms of material flammability in reduced gravity, (2) develop new test methodologies and/or acceptance criteria for existing tests that give a direct indication of the material flammability in reduced gravity, and (3) measure quantities for fires in reduced gravity that, through the application of performance-based fire safety analysis tools, can be used to evaluate material flammability and fire dynamics in reduced gravity environments. A detailed discussion of each of these areas is beyond the scope of this paper but some important work that can give the flavor for the tasks can be identified.


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Objective 1: Evaluate existing test methods to determine if current test results can be made more quantitative or relevant to reduced-gravity flammability

As described in Section II, NASA-STD-6001 Test 1 is used to screen materials for acceptability in spacecraft. The Material and Processes Technical Information System database (MAPTIS-II) contains the results of this test for a wide variety of materials.§. The usefulness of this test lies primarily in the extensive experience that has been gained applying this method for various types of materials. As previously discussed, the relation between the test results and actual flammability in reduced gravity is unclear. It was assumed that this test is conservative (meaning that materials that pass Test 1 will not propagate a flame in reduced gravity) because a strong buoyant flow is created that pre-heats the sample. However, Olson2 has shown that a material can be more flammable in reduced gravity at a velocity lower than that imposed by natural convection in normal gravity. More over, some charring foams will not propagate an upward flame but will burn downwards. If Test 1 is over-conservative, it could eliminate materials from use that would not sustain a flame in reduced gravity. Material selection based on incorrect criteria can only increase overall system mass and complexity which could have direct implications for the feasibility of exploration missions. Several of the tasks required to gain a better understanding of existing test methods and what they imply about flammability in reduced gravity are:

1. Evaluate the NASA-STD-6001 Test 1: Upward Flame Propagation test configuration and upward

flame propagation in normal and reduced gravity facilities as required to better quantify and interpret test results.

2. Obtain property data for various simple materials as well as other representative materials using cone calorimetry and other standard tests for use in ignition and flame spread models.

3. Model Test 1 and compare results with experimental results of Task 1. 4. Use this model to evaluate the effect of reduced gravity on flame spread on the candidate material.

Some of this work is currently being performed with encouraging results. For example, Coutin et al.13 are

performing detailed experiments and simulations of an upward flame spread (Test 1) configuration to attempt to translate the result from normal-gravity to microgravity. (PI: Professor S. Buckley, Univ. of California – San Diego) Specifically, they are measuring the experimental flame stand-off distance to extract an experimental mass transfer number, a material-related parameter that could be used to assess the potential of a material to sustain co-current flame spread. This parameter could then be measured from Test 1 and provide a relative ranking of material flammability. Recently, Feier et al.14 have performed an experimental and theoretical investigation of upward flame spread over thin solids and found that the spread rates are proportional to p1.8g where p is the ambient pressure and g is the gravity level. The significance of this work is that using this scaling, it may be possible to simulate upward flame spread rates in partial gravity by conducting tests in normal gravity but at a reduced ambient pressure. This work is continuing to establish the limitations of this scaling, the functional relationship for sample width, and the effect of observed unsteady growing modes for upward flame spread.

Objective 2: Develop and verify new normal gravity test methodologies that relate directly to reduced- gravity flammability

A normal-gravity flammability test that provides information pertinent to the ignition, flame spread, and burning rate (heat release) of various candidate materials under reduced or microgravity conditions is strongly desired because there are a very large number of materials that must be characterized over a wide range of possible ambient atmospheres and we simply cannot run all of these test points under reduced gravity or microgravity. The general method of attack which we are developing to solve this problem is to select a limited number of materials and test them in various candidate ground tests as well as under microgravity conditions to calibrate/verify models and scaling hypotheses that could relate the ground test results and the microgravity test results. The following tasks are planned to achieve this result:

1. Identify candidate test methods that provide results that can be related to reduced-gravity flammability. 2. Evaluate these methods for a variety of materials to develop repeatable test procedures and confidence

in the general applicability of the results. 3. Conduct verifications of these test methods using experiments in normal gravity, ground-based

reduced-gravity facilities, and modeling.

§ The MAPTIS-II database can be accessed at http://maptis.nasa.gov/index.html


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4. If necessary, conduct space flight experiments to verify the conclusions drawn from the results of the normal gravity tests.

In 2001, the Bioastronautics Spacecraft Fire Safety Program funded a joint project between NASA Glenn

Research Center and NASA White Sands Test Facility (PI: Dr. S. Olson (GRC) and Dr. H. Beeson (WSTF)). The objective of this work is to develop the Earth-Based Equivalent Low Stretch Apparatus (ELSA) that could be a normal gravity analog for many characteristics of reduced gravity fires.15 The hypothesis here is that the material ignition, flame spread, and burning rate characteristics will be the same under normal gravity, reduced gravity, and microgravity conditions at equal stretch rates. (For steady flames, flame stretch is defined as the tangential velocity gradient at the flame surface. It has been postulated that the flame spread rates measured in two (or more) different experiments may be identical if the surface velocity gradients are identical (all other factors such as free-stream oxidizer concentration and solid fuel material remaining the same).16) If experimentally validated, the normal gravity test results at a stretch rate that is equal to the expected stretch rate for given forced flow conditions (ventilation flow) at reduced gravity or microgravity to accurately predict ignition and flame spread at those conditions. The low stretch rates in normal gravity are obtained using an inverted-cone geometry with the sample burning in a ceiling fire (stagnation flow) configuration as shown in Fig. 6. Parameters being measured in the ELSA apparatus include ignition delay times, mass loss rates, limiting stretch rates, critical heat flux for ignition, and toxic product generation rates. Results to date have verified the scaling of these parameters with stretch rate -- which of these parameters are actually representative of reduced gravity behavior must be verified. Other possible ground-based tests are also being examined, such as the Forced Ignition and Spread Test (FIST), with models being developed to relate normal gravity test results to results under various g-level and flow conditions. Again, space flight testing will be required to verify these models. At some point, a standard ground-based test will be defined and incorporated into NASA-STD-6001.

Objective 3: Investigate the need for and develop a screening test to characterize materials in terms of their susceptibility to smolder initiation and transition to flaming.

In 2001, a workshop was held in Cleveland, Ohio to identify research needs in spacecraft fire safety. One of the high-priority outcomes from the Fire Prevention and Material Flammability working group was the need to understand the implications of non-flaming and smoldering combustion in microgravity with respect to ISS engineering materials. (At the time, only relevance to ISS was being considered although this issue will also exist for the CEV and other extended-mission vehicles and habitats.) Current NASA standard flammability test techniques do not take smoldering combustion into account so this data would fill this apparent gap. Tasks to be accomplished to fill this need include:

1. Propose and develop a normal gravity test to screen materials for smoldering. 2. Perform reduced gravity tests to verify the relation between the screening test and reduced-gravity

smoldering. 3. Evaluate smoldering of materials at ambient conditions that are relevant for exploration vehicles and

habitats. 4. Define design rules for material selection and stowage that preclude the initiation of sustained

smoldering reactions in reduced gravity. A flight definition project was funded in 2001 by the Spacecraft Fire Safety program of the Bioastronautics

Initiative titled “Two-Dimensional Smoldering and Transition to Flaming in Microgravity” (PI: Professor Carlos Fernandez-Pello, University of California-Berkeley). The objective of this project was to continue the investigations on smoldering in microgravity begun by the Microgravity Smoldering Combustion (MSC) flight project but to examine the conditions by which a smoldering fire may transition to a flaming fire in microgravity. This work is

Figure 6. Concept of ELSA apparatus, showing fuel sample suspended above radiant cone heater and oxidizer flow jet. The enclosure reflects the WSTF Controlled Atmosphere Cone Calorimeter facility.15


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continuing but is being re-cast to address the most relevant features of the FPDS program as well as developing a normal gravity screening method materials that smolder, similar to the NASA-STD-6001 Test 1 for the upward spread of flaming fires.

Objective 4: Assess material flammability at total pressure and O2 mole fraction combinations of exploration atmospheres

As discussed in Section III, the low pressure, high O2 mole fraction combinations that reduce the time required for EVA pre-breath result in strongly increased flammability. Therefore, a detailed evaluation of the trade-offs is required for each exploration mission scenario. The selection of the ambient conditions for any phase of an exploration mission determines to a large degree the protocol that must be followed to assess the flammability of materials used in that mission, the requirements for the fire detection system, and the amount and type of suppressant that is required to suppress a fire. This product derived from this task will provide input to the requirements/systems analysis teams on the flammability of materials in atmospheres being considered for use in exploration spacecraft and habitats.

B. Fire Signatures and Detection In this section, the research objectives and tasks in the area of fire signatures and detection are presented. The

research to be performed can be divided into three major areas, namely (1) sensor development, (2) quantification of fire signatures, and (3) modeling of smoke and contaminant transport. The primary objective of each of these areas and a short description of each is given below. Objective 1: Develop suitable sensors for spacecraft applications

The sensors being considered in this program for use as advanced fire detectors include both particulate sensors and gas sensors. The types of particulate sensors being developed include those that simply detect the presence of particles and others that could yield information on the range of particle sizes, i.e., particle classifiers. Two types of gas sensors are also being evaluated. These are (1) species-specific sensors, i.e., those that respond to a known gaseous compound such as CO or CO2, and (2) electronic nose technology that responds to many compounds that can then be identified through training. Achieving this objective will require both the scientific objective of developing sensors having the required properties and operating characteristics as well as packaging this suite of sensors into a useful device.

1. Develop packaged sensors for ground-based testing. 2. Develop a flight-ready sensor package for continued evaluation in ground tests and potential

incorporation into space flight experiments for verification. 3. Develop an advanced fire detector and/or detector strategy suitable for use in exploration vehicles and

habitats. Species-specific sensor development has been funded through the Spacecraft Fire Safety Program of the

Bioastronautics Initiative since 2001 with the joint funding of the Aviation Safety Program at NASA Glenn Research Center. This has resulted in a suite of particulate and gas sensors that have demonstrated excellent rejection of false positives while maintaining sensitivity to actual fires. These sensors have been packaged for use in reduced-gravity testing that will be conducted during 2005. The development of electronic nose technologies has recently been funded through the Microgravity Combustion Science program. This technology is also being developed at the Jet Propulsion Laboratory for environmental monitoring and will be evaluated for suitability in fire detection as well.

Objective 2: Quantification of Fire Signatures

If Objective 1 is thought of as developing the tools, Objective 2 can be thought of as evaluating and verifying that the tools perform as required. Specifically, the fire signatures to be quantified will depend on the sensors intended to detect the fire. Three major tasks have been identified that make use of the sensors developed in Objective 1 as they become available. The outcome of this work is a database of fire signatures in exploration environments that can guide the development of advanced fire detectors to coincide with the spiral development of the CEV. The tasks that will be implemented include:

1. Evaluation of signatures in normal gravity from practical materials to quantify products and the effect of heating rate, method, etc.


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2. Perform ground-based micro-and partial-gravity testing to determine if there are quantifiable differences from the normal gravity results.

3. Develop a normal-gravity analog for reduced gravity fire signatures. 4. Quantify fire signatures during a space experiment to verify the accuracy of the signatures.

Work in this area was funded in the 1999 and 2002 Microgravity Combustion Science NRAs. The Smoke Aerosol Measurement Experiment (SAME) (PI: Dr. David L. Urban, NASA-GRC) is being prepared to conduct a test in the ISS Microgravity Science Glovebox to extend the CSD concept mentioned in Section I to provide in situ particle size information for several smoke aerosols (solid and liquid). This data will further quantify the differences in the particle size and quantify the particulate pre-fire signatures of relevant spacecraft materials (Kapton™ and Teflon™, for example). This data will be used to guide the development of optimized smoke detectors.

A ground investigation funded in 2002 (PI: Dr. Randall L. VanderWal, NCMR) has the objective of quantifying the gaseous fire signatures from various materials in normal gravity and determining if the transient nature of these signatures are changed in reduced gravity. The tests are planned for NASA’s Reduced Gravity Aircraft and will make use of the advanced fire detectors developed for Objective 1 as well as other analytical diagnostics. Objective 3: Development of a computational model of smoke and contaminant transport

The effectiveness of even the most refined and exotic sensor will be reduced unless it is located in the right place and the time required for the contaminant to reach a detectable level at that location has been quantified. If a distributed network of sensors is used, the number of sensors in the system will undoubtedly be limited and the design goal will be to minimize the number of sensors required to provide adequate protection. The outcome of this objective is a validated computer model for the large-scale transport of smoke and combustion products within a habitable volume that can be used to evaluate fire detector location and activation. This is also a primary deliverable in the FPDS element and a co-objective with the Advanced Environmental Monitoring and Control (AEMC) element. This will be accomplished through the following tasks.

1. Develop models for detector activation that can be incorporated into codes for smoke and contaminant

transport. 2. Calibrate models for forced convection in reduced gravity using ground-based reduced gravity

facilities. 3. Evaluate detector location and activation scenarios in reduced gravity using the models developed in

Tasks 1 and 2.

In the 2001 and 2002 Microgravity Combustion Science NASA Research Announcements, several projects were selected to work on various aspects of this objective. Funding has recently been set in place and the projects are being coordinated to align with these goals, particularly with regard to experimental verifications of the models.

Objective 4: Evaluation of emerging technologies in sensor development

One of the primary features of the spiral development concept is that new technologies can be incorporated into a design as they are matured. Early spirals will be based largely on existing technology. Technologies that are currently in the early stages of development may make significant contributions to later spirals. Advances in sensor technology such as miniaturization, reduced power requirements, development of wi-fi interfaces, and improved sensitivity all may significantly impact the fire detection and response technologies in future spacecraft and habitats. This technology development program must stay in touch with these advances and, where appropriate, create new tasks to continue or hasten the development of promising technologies.

C. Fire Suppression and Response Our understanding of the processes involved in microgravity fire suppression, particularly with regard to the

practical technology for fire extinguishment, is very limited. In general, fire suppression in microgravity has only been investigated in small scale experiments using idealized geometries. Nevertheless, the Shuttle and ISS both have portable fire extinguishers for use by the crew. Carbon dioxide is currently used as the fire suppressant in the U.S. modules and the planned Japanese and ESA modules of the International Space Station (ISS). (The Russian modules use hand-held water-based foam extinguishers, similar to those used on the Mir space station.)

Before CO2 was selected as the fire suppressant on the ISS, trade studies were performed (Opfell17 and Panzarella and Lewis18, for example) to evaluate potential suppressants. The criteria used to evaluate various extinguishing agents and techniques included (1) effectiveness against potential fires; (2) reliability; (3)


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maintainability of the suppressant system; (4) weight of the system; (5) required post-fire cleanup; (6) toxicity of the suppressant and products of its interaction with the fire; and (7) collateral damage caused by use of the suppressant. While the effectiveness of the suppressant to extinguish a fire is a necessary condition for selection of a fire suppressant on board a spacecraft, it is not a sufficient condition, as evidenced by the design considerations listed above. The design features that will be addressed by FPDS research program are the determination of the effectiveness for different suppressants, defining deployment options and procedures, and quantifying the potential concentrations of the suppressant and post-suppression products in the atmosphere. The data in these areas required to perform rational trade studies and make informed design decisions will be obtained by achieving the objectives discussed below.

Objective 1: Determine suppressant effectiveness in reduced gravity

A large number of variables are involved in quantifying suppressant effectiveness including: type of suppressant, type of fuel (phase and composition), atmospheric composition (O2 and diluent concentrations), fuel geometry, flow velocity, and method of agent dispersion. As such, there is a large amount of data available for normal gravity conditions for a wide range of suppression agents, fuels, configurations, etc. How this data relates to effectiveness in low- and partial-gravity behavior is unknown so the number of variables again increases. Therefore, the approach taken to achieve this objective is to evaluate suppressant effectiveness in reduced gravity using a geometry which is amenable to detailed computational analysis. A droplet geometry is appropriate because of the considerable knowledge and simulation capabilities that have been developed through the Microgravity Combustion Science program over the years. These tests are currently being planned for the Flame Extinguishment experiment (FLEX) to be conducted in the Multi-user Droplet Combustion Facility (MDCA) on the ISS. The investigations of fire suppression experiments and modeling (Tasks 2 and 3) will continue while the flight experiment is being developed and performed.

Coupled with this experiment will be experiments in ground-based reduced gravity facilities and modeling efforts that will evaluate difference suppressants, fuels, and configuration. For example, several recent studies have been conducted19-22 that have dealt with the effectiveness of various gaseous agents (CO2, N2, He, Ar, CF3H, and CF3Br) on diffusion flame extinguishment in low gravity both through experiments and computation. However, we still require data from long-duration reduced gravity experiments to verify some of the conclusions from these investigations. Based on this discussion, the tasks that will be used to achieve this objective are:

1. Baseline reduced gravity tests using a simplified geometry that is amenable to detailed computational analysis.

2. Conduct tests in ground-based facilities using similar suppressants in a range of configurations. 3. Model fire suppression in these configurations to extend the reduced-gravity test matrices.

The outcome from this work will be data on the concentrations of various agents required to suppress a wide

range of configurations in reduced gravity. The space flight data will provide validation for the conclusions drawn from the investigations performed in ground-based reduced gravity facilities.

Objective 2: Characterize large-scale agent deployment in reduced-gravity

While certainly coupled to agent effectiveness, this objective is focused on the delivery of the agent and how it interacts with the local structures to arrive at the location of the fire. We anticipate that a combination of small scale validation experiments and large-scale flow simulations will be required to achieve this objective. The flow models will most likely be those that are developed for smoke and contaminant transport to maintain consistency of the computational tools that are developed within the program. In 2002, several projects were selected by the Microgravity Combustion Science program that will conduct the small-scale experiments on agent deployment in reduced gravity that will provide some of the data that will be used to verify the sub-models of the simulations. One challenging portion of this objective will be to conduct tests for code validation. By nature, these should use a relatively large scale facility but would have to be performed in reduced gravity if actual agents because they would settle in normal gravity. Alternatively, a neutrally-buoyant surrogate agent could be used for code validation tests. These details will be considered and worked out as this work progresses. The tasks described above can be summarized as follows:

1. Incorporate simplified reduced-gravity suppression models into rack and module-scale flow simulation

codes. 2. Computationally evaluate agent deployment strategies.


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3. Perform code validation tests in reduced gravity using a relevant geometry.

Objective 3: Verify suppressant system design rules through reduced-gravity testing of relevant fuels and/or geometries

The successful completion of Objectives 1 and 2 will yield data and analysis tools that can be used to design fire suppression systems for exploration vehicles and habitats. The extension of these computational models to the suppression of fires on realistic solid materials would be possible but the reduced-gravity validation would still be lacking. Such a space flight test could be conducted, probably in the FEANICS insert in the Combustion Integrated Rack but would require considerable advanced planning so that the capabilities were incorporated into the insert. These requirements and the impact on the FEANICS development effort are currently being assessed. Assuming this path is feasible and selected, the tasks for this objective would be follows:

1. Extend the models to address other fuels and geometries. 2. Conduct reduced gravity tests to verify suppressant performance using relevant fuels/geometries.

D. Definition and Evaluation of Fire Scenarios The implementation of this research area brings together the capabilities developed in all of the other three areas.

It is listed as a separate area because of its importance and last because it draws on activities performed in all of the other areas. However, these tasks are performed concurrently with those in the other areas, helping to define test requirements and conditions while drawing on the most current data to better quantify and refine the fire scenarios and definition of design fires. A detailed discussion of the probabilistic risk assessment and performance-based fire protection engineering procedures that will be applied in this area are beyond the scope of this paper; however, these activities should be used to guide research needs and aid in the development of tests, tests conditions, and protocols.

Objective 1: Apply performance-based fire safety analyses to quantify fire scenarios and response strategies

As discussed in Section III, identification of the most probable fire scenarios is required to define rational fire protection strategies. Previous studies11,23-25 have also made use of fire scenarios and these will serve as starting points for this analysis and these will serve as starting points for this analysis. This task will be performed concurrently with those in the other area because of their inherent synergy. For example, while designing the tests for Objective 2 in the Fire Prevention and Material Flammability area, we will examine various scenarios that might lead to ignition and burning of materials and develop an understanding of the most critical output parameters that dictate the severity of a potential fire. Using this information, we can establish rational pass/fail criteria for existing or new tests that can be directly linked to the flammability of the material in reduced gravity. Likewise, knowledge of the types of fires that are most probable could significantly impact the selection of a suppression agent, deployment strategy, and response procedure. Once this has been accomplished, we will develop a list of material and ambient composition combinations which need to be tested and proceed with these tests. The specific tasks required to perform this analysis have yet to be defined; however, they are intertwined with many of the objectives and tasks in the previous areas.

Objective 2: Create realistic visualizations of fire response strategies to aid in assessment and crew training

This objective would be achieved by combining the computational tools previously discussed to create a unique tool that provides a realistic simulation of fire scenarios and response on an exploration vehicle or habitat. The fire suppression simulations previously described would be incorporated into the smoke and contaminant transport models to include the transport of suppression agent throughout the module upon deployment of a fire extinguisher. Simultaneously with the development of the computational tools previously described, a separate effort will be conducted to allow virtual reality visualizations of the results of the simulations. The benefits of this task would be to assess fire response strategies based on what the crew would actually experience during the event. Concepts of human factors engineering could then be used to further develop the response. This could impact the location and design of safety and fire response equipment, crew communications, and fire response procedures. Using these visualizations, VR crew training modules could then be developed that would better prepare the crew to address a fire emergency during a long-duration mission. These tasks are summarized below:

1. Incorporate fire suppression simulations from Objective 2 into flow simulations with smoke and

contaminant transport models from the Fire Signature and Detection work area. 2. Use the flow simulations to evaluate fire response strategies for relevant fire scenarios defined in the

fire Prevention and Material Flammability areas.


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3. Produce virtual reality visualizations of these simulations to improve response evaluation and crew training.

V. Schedule and Program Status At this time, we have approximately 40 tasks (extramural and intramural) directed toward fire safety on

exploration vehicles and habitats. We are in the process of mapping these to the tasks and deliverables identified in this plan and will use this information to define technology gaps which we will fill in future selections of research and technology programs. In some cases, we have parallel approaches bring pursued toward a specific goal: down-selection of some of these efforts will be made when appropriate. Deliverables, in the form of hardware, software, and/or information (e.g., data libraries) have been defined along with a timetable for the first few years of many of these efforts. Where possible, the work of several on-going projects will be coordinated to better address the program needs.

A detailed schedule for all of the tasks identified in this plan will be developed as we examine each of the research objectives in more detail. However, a preliminary schedule for the deliverables of this program is shown in Table 3. Based on the development spirals defined in Table 1, Spiral 1 technologies must be set by approximately 2008 while those for Spiral 2 will be set in the 2009-2014 time-frame, depending on the pace of the development. The pace of the development of the FPDS products is rapid but must keep in step with the planned pace of the development spirals. As these are adjusted, we will modify our plans and schedules to provide the products that will have the largest impact on the health and safety of the exploration crew.

VI. Summary and Concluding Remarks This paper constitutes the first draft of the research and technology development plan for the Fire Prevention,

Detection, and Suppression element. It has been developed through the input of individuals from various NASA centers including GRC, MSFC, JSC, and WSTF, the National Institute for Standards and Technology, Research Partnership Centers, combustion and fire safety researchers in academia, and others working in the fire safety industry. This input has been received through several workshops that focused entirely on research needs in spacecraft fire safety as well as other meetings and forums over the last few years. The products and many of the proposed tasks have been presented to the microgravity combustion science research communities involved with all aspects of fire safety with many of the comments incorporated into the tasks. Other input and comments collected will be used to help formulate detailed plans for research tasks that were only mentioned in this plan.

In the next few months, this plan will undergo both internal and external reviews during which the objectives and tasks will undoubtedly be modified. Additional details specifying how existing funded projects map to these tasks will be added as well as process and logic diagrams for many of the work areas. The current goal is to produce and baseline a document that will (a) define a tactical plan to deliver the FPDS products, (b) identify areas that are not currently being addressed by on-going research, and (c) provide a means to define requirements and evaluate proposed FPDS research. The ultimate goal is to ensure crew health and safety on exploration missions by reducing the risk of fire and giving them tools that would allow them to continue the mission should a fire occur.

References 1National Aeronautics and Space Administration Technical Standard 6001, “Flammability, Odor, Offgassing, and

Compatiblity Requirements and Test Procedures for Materials in Environments That Support Combustion”, 1998. 2Olson, S.L. “Mechanisms of Microgravity Flame Spread Over a Thin Solid Fuel: Oxygen and Opposed Flow Effects,”

Comb. Science and Tech., Vol. 76, 1991, pp. 233-249.

Table 3. Preliminary milestone schedule for delivery of FPDS productsDate

Fire Prevention and Material FlammabilityIdentification of effective candidate ground-based tests 2Q FY06Acceptance cirteria for reduced gravity flammability 4Q FY07Reduced gravity verification of normal gravity flammability tests 4Q FY08Definition of a normal gravity test technique 3Q FY09

Fire Signatures and DetectionQuantification of the ISS background particulate size distribution 2Q FY05Quantification of the size distribution of prefire pyrolysis particulate 4Q FY06Reduced gravity tests of suite of gas and particulate sensors 3Q FY06Database of fire and pre-fire signature in microgravity 2Q FY07Advanced fire detector suite 4Q FY08Verified models of smoke and contaminant transport in microgravity 3Q FY08

Fire Suppression and ResponseQuantification of suppressant effectiveness in microgravity 4Q FY07Design rules for suppressant system design and operation 3Q FY08Reduced gravity verification of suppressant system performance 4Q FY10

Visualizations of Fire ScenariosRealistic visual representations of fire environment 4Q FY06VR Fire response module for analysis of scenarios and crew training 2Q FY09

Deliverable


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3McGrattan, K.B., Kashiwagi, T., Baum, H.R., and Olson, S.L. Olson, .Combust. Flame, Vol. 106, 1996, pp. 377-391. 4Prasad, K., Olson, S.L., Nakamura, Y., and Kashiwagi, T.; "Effect of Wind Velocity on Flame Spread in Microgravity",

Proceedings of the Combustion Institute, V. 29, pp 2553-2560, July 2002. 5NFPA 12: Standard on Carbon Dioxide Extinguishing Systems. National Fire Protection Association, Quincy,

Massachusetts, 2000. 6Ruff, G. A. (ed.), Research Needs in Fire Safety for the Human Exploration and Utilization of Space: Proceedings and

Research Plan, NASA CP-2003-212103, April 2003. 7Sacksteder, K. (ed.), Seventh International Workshop on Microgravity Combustion and Chemically Reacting Systems,

NASA CP-2003-212376, June 2003. 8Margle, J.M. (ed.), Spacecraft Fire Safety, NASA CP-2476, Aug. 1987. 9Apostolakis, G.E.; Catton, I.; Paulos, T.; Paxton, K.; and Jones, S., “Findings of a Review of Spacecraft Fire Safety Needs,”

NASA CR-189181 (UCLA ENG 92-19), 1992. 10Youngblood, W. N. and Vedha-Nayagam, M., “Advanced Spacecraft Fire Safety: Proposed Projects and Program Plan,”

NASA CR-185147, 1989. 11Reuther, J. J., “Definition of Experiments to Investigate Fire Suppressants in Microgravity,” NASA CR 185295, 1990. 12Lange, K. E., Duffield, B. E., Jeng, F. F., and Campbell, P. D., "Exploration Spacecraft and Space Suit Internal Atmosphere

Pressure and Composition," 2005 Bioastronautics Investigators' Workshop, Galveston, Texas, January 2005. 13Coutin, M., Rangwala, A. S., Torero, J. L., and Buckley, S. G. “Material Properties Governing Co-current Flame Spread:

The Effect of Air Entrainment,” Seventh International Workshop on Microgravity Combustion and Chemically Reacting Systems, NASA CP-2003-212376, June 2003, pp. 205-208.

14Feier, I. I., Kleinhenz, J., T’ien, J. S., Ferkul, P. V., and Sacksteder, K. R. “Pressure Modeling of Upward Flame Spread Rates in Partial Gravity,” 43rd AIAA Aerospace Sciences Meeting and Exhibit, AIAA-2005-0716, January 2005, Reno, NV.

15Olson, S. L., Beeson, H., and Haas, J. P., “An Earth-Based Equivalent Low Stretch Apparatus to Assess Material Flammability for Microgravity and Extraterrestrial Fire-Safety Applications,” Seventh International Workshop on Microgravity Combustion and Chemically Reacting Systems, NASA CP-2003-212376, June 2003, pp. 213-216.

16Wichman, I. S., "Flame Spread in an Opposed Flow with a Linear Velocity Gradient," Combustion and Flame, Vol. 50, 1983, pp. 287-304.

17Opfell, J., “Fire Detection and Fire Suppression Trade Study,” Allied-Signal Aerospace Co. 85-22472, Rev. 1, 1985. 18Panzarella, L. N., Jr., and Lewis, P., “Crew Lock/Hyperbaric Chamber FDS Fire Suppressant Selection Trade Study,”

McDonnell Douglas (Houston) Memorandum A96-J753-STN-M-LP-900070, 1990. 19Hamins, A., Bundy, M., Puri, I. K., McGrattan, K., and Park, W. C., “Suppression of Low Strain Rate Nonpremixed Flames

by an Agent,” NASA/CP-2001-210826, 2001, pp. 101-104. 20Ruff, G. A., Hicks, M., and Pettegrew, R., “Assessment of CO2, N2, and He as Suppressant Agents in Microgravity,” Spring

Meeting of the Western States Section/The Combustion Institute, Davis, CA, March 2004. 21Katta, V. R., Takahashi, F., and Linteris, G. T., “Suppression of Cup-Burner Flames Using Carbon Dioxide in

Microgravity,” Combust. Flame, Vol. 137, 2004, pp. 506-522. 22Takahashi, F., Linteris, G. T., and Katta, V. R., “Suppression Characteristics of Cup-Burner Flames in Low Gravity,”

AIAA-2004-0957, 42nd AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, January 2004. 23Sheridan, J. G., “A Systems Analysis of Fire Suppression Methods for the U.S. Space Station,” AFIT/GSO/AA/87D-5,

December 1987. 24Sribnik, F., Birbara, P. J., Faszcza, J. J., and Nalette, T. A., “Smoke and Contaminant removal System for Space Station,”

SAE Paper 901391, 20th Intersociety Conference on Environmental Systems, Williamsburg, VA, July 9-12, 1990; also SP-829 – Space Station Environmental/Thermal Control and Life Support Systems.

25Heard, A., “International Space Station Probabilistic Risk Assessment Fire Analysis,” presented at the Seventh International Workshop on Microgravity Combustion and Chemically Reacting Systems, June 2003.

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