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OCR for page 228
SESSION H: Fly PE0O~CE PETER
SESSION OBJECTIVES
Determine the fire performance parameters that need to be considered for specifying
matenals and on what they can be based.
PARTICIPANTS
Chair: Richard Gann, National Institute of Starboards arm Technology
Committee: Frederick Dryer, Princeton University
Howard Emmons, Harvard University
Patricia Tatem, Naval Research r~aborato~y
Participants: Toni Arnold, Federal Aviation Administration
Steven Beare, DuPont
Robert Buch, Dow Corning
Dougal Drysdale, University of Edinburgh
Sally Hasselbrack, Boeing Commercial Airplane Group
Vahid Motevalli, Worcester Polytechnic Institute
Thomas OhIemiller, National Institute of Standards and Technology
lames Quintiere, University of Maryland
Gus Sarkos Federal Aviation Administration
Usman Sorathia, Naval Surface Warfare Center
SESSION REPORT
Many of the session participants believed that the measures of fire performance of aircraft
interior materials should be consistent with an overall fire-hazard analysis.
Fire Performance Parameters
For current aircraft and materials, the Federal Aviation Administration (FAA) Technical
Center has demonstrated that the environment within a passenger cabin becomes untenable as
the Ore changes from localized to full-cabin in extent. Delaying this transition results in longer
time for evacuation. Should this determination hold for future aircraft, then the Federal Aviation
Administration goal of a 50 percent reduction in fire deaths could be achieved by using materials
228
OCR for page 229
Part 11- Workshop Summary
229
that further delay or even prevent ~flashover."' It must also be established that a lethal or
incapacitating atmosphere does not exist prior to flashover.
There are conditions that can lead to passengers being unable to evacuate: high
temperature, excessive thermal radiation (causing death by burns), and inhalation of toxic gases.
The length of exposure to these conditions could be increased by the formation of sufficient
amounts of smoke particles and aerosols so that vision is hindered and evacuation is impeded.
The potential for the production of corrosive smoke was not addressed. Corrosivity does not
affect life safely but may compromise the re-use of the aircraft.
The importance of each threat depends on the time frame for its manifestation relative
to the timing of other catastrophic events and the time needed for evacuation. Thus, the type of
fire determines which types of materials performance measures are valid. To illustrate this point,
the participants considered two classes of fire scenarios (post-crash, fuel fires and in-flight fires)
and their variations.
Plarze on the ground; e~cterr~al Velures; one or more holes ir' the fuselage; only flame
radiation enters. Interior materials are subjected to piloted radiation-induced ignition.2 Should
a seat or interior pane! begin burning, then the next important event is the subsequent ignition
and burning of adjacent entities. A mode! of the ignition and fire growth (especially of a
seat/assembly) and the transition to more extensive burning of these fire-hardened materials
would relate the discrete materials performance measurements to the system behavior. Some of
the important properties can be identified from existing knowledge. The mode! development
should be guided by and valida~ using real-scale tests.
The rate of heat release is the principal driver of fire growth. This can be measured using
a device such as the Cone Calorimeter. For low heat release rates, the oxygen depletion may
be too small, and an alternative measure based on, for example, CO/CO2 yield may be
necessary. Some participants noted concerns that any bench-scale device may produce artificial
phenomena that do not occur at real scale or may miss phenomena that do (e.g., pane! buckling
and delamination). These concerns will require some testing using larger samples and eventual
real-scale testing to resolve. It is important that typical values of the incident radiant flux be
obtained from real-scale testing.
According to participants, no current testing device has been shown to give a measure
of visual obscuration indicative of the real-scale fire. While the smoke-yield data can be related
to visual obscuration via a simple model, it is not yet understood how to use this data in a
meaningful way for fire scenarios expected for aircraft.
The radiant smoke toxicity apparatus (ASTM E-1678) measures yields of toxic products
that have been related to real-scale fires. In that apparatus, the samples are exposed as in this
fire scenario. Other toxic potency methods have not been related to real-scale fires. Analysis of
safety.
~ A more precise definition of the flashover phenomenon is needed to characterize properly the threat to life
2 While it is presumed that the aircraft interior materials will be fire-hardened, passengers' clothes and
carry-on items will be readily ignited by the high flux.
OCR for page 230
230
Improved Fire- aru] Smoke-Resistant Materials
compartment fires has shown that for combustibles of normal toxicity, heat is the initial threat
to life safety. Thus, the premium may well be on determining only if the smoke is of extreme
toxic potency.
An additional hazard is that exposure to the fire's hot upper gas layer may cause the
ceiling materials to melt, drip, or fall down. This could cause further ignition of interior
materials. There is no current measurement method to characterize the physical stability of the
installed panels.
Plane on the ground; external fuel fire; one or more holes in the~selage; flames arm
smoke eraer. In this case, the upper layer of the cabin is quickly vitiated, and thus the
decomposition of the exposed panels is different. This could result in a longer flame extension
from any burning materials, as well as smoke of higher toxicity, which results from less
complete combustion. In the case of vital upper layer, measurements from the above scenario
should be supplemented with the yield and flammability limits of the pyrolyzate. There is no
procedure for measuring pyrolyzate yield and flammability limits today. The external flames
would drive spread on the ceiling, while fire growth over the seats would likely be less
important.
Plan on the ground; e~cternai fuel Are; no holes in fuselage. The heating of the airplane
skin win eventually heat the back side of the interior wall panels, resulting in some degree of
aerobic pyrolysis. At the same time, there is a threat that the flames will burn through the
fuselage, resulting in a fire like the two types described above. Representing the former process
will require data on the pyrolysis rates under varying thermal stresses, as well as measurement
of the toxicity of the pyrolyzate. Since the fuel fires following a survivable crash have (to date)
heated only part of the fuselage, participants thought it likely that evacuating through one or
more doors would be practical. Thus, effective hull protection that stays in place could provide
ample egress time, and a comparison of the time to appreciable heating and degradation of the
wall panels with the time for evacuation is important. Measurement of the insulation system
quality is thus an important materials evaluation.
Plane in~?ight;fire starts within the cabin or lavatory. Participants regarded this as a
secondary problem. A small, accessible fire is quickly suppressed with hand-held extinguishers.
Plane in flight;fire starts ir' an inaccessible area (cargo hold or behind cabin liningsJ.
For such a fire, the tenability of the cabin would have to be maintained for up to 3 hours.
Should a suppression system not be installed or should it not work, this would require palette
containment materials and cabin isolation materials of extraordinary fire resistance. Fortunately,
the air leakage into the cargo hold could be made quite small, limiting the burning rate of the
combustibles. Research should be conducted to determine whether such materials are possible.
OCR for page 231
Part 11- Workshop Summary
231
The current test method for the cabin liners is very severe, involving resistance to an intense
burner impingement.
Due to increased use and complexity of electronic controls and systems, participants
thought that future planes will likely have more electrical cabling running behind the wall panels
and under the floors. There is always the potential for ignition in concealed spaces from an
electrical fault or an overheated wire. The nearby materials would be exposed to a sustained,
but small, hoe spot or flame. Participants thought the f~re-resistance of current materials is
probably adequate to survive this threat. Moreover, there has been a lot of work on materials
resistance to small ignition sources, so this may not be a research but an implementation issue.
Needed Development In Materials Evaluation and Characterization Methods
The above sections describe the need for characterization of the finished products in order
to enable evaluation of their appropriateness for use on board aircraft. A second series of
characterizations are those needed for guiding the development of new materials. Particinants
saw this as especially important in the early stages of exploration where only small tgram'
samples of the polymer may exist. Of particular importance is understanding how to promote
the formation of char during burning. Some present research includes experiments with the use
of techniques such as solid-state NMR for analyzing the partially combusted sample and its char.
Participants knew of no existing procedure for screening fire properties through tests on sub-
gram samples. However, research on thermogravimetry and differential scanning calorimetry
coupled with mass spectroscopy is investigating the relationship between rate of heat release and
ignition behavior. Participants foresaw a critical advance in the characterization of a material's
fire contribution when such an appraisal can be based on the molecular chemistry and thermal
embodiment of the product. Such relationships, based on fundamental understanding, will enable
efficient screening of new materials design.
~. . ~
At present, all materials properties are measured using "new" samples. Aircraft interior
products stay in service for years, undergoing wear and tear, frequent cleaning and maintenance,
and general aging. It is important that methods be developed for accelerated aging of new
materials and structures, so that tests may be conducted to ensure they will retain their desirable
Ore performance throughout their service life.
As noted above, participants said that several devices are needed to obtain the full
complement of data from burning materials for use in a hazard model. It would reduce the
burden of testing and increase the reliability of results if a single device were developed to
measure parameters such as heat release and smoke obscuration.
OCR for page 232
232
Imp roved Fire- and Smoke-Resistant Materials
Long-Term Research
Participants in the workshop session suggested the following areas for research on fire
performance of materials.
Develop methods for predicting fire performance of materials from chemical
structure.
Develop mesons for accelerating materials aging for predicting long-term
flammability.
Develop a verified computer mode} of ignition of and upward flame spread over
low-flammability seals and wall panels.
Develop accurate bench-scale methods to generate proper materials data.
Develop new, very small sample guidance methods.
Develop a validated two-dimensional or three-dimensional mode} of the evolution
of habitability of the cabin environment to identify key materials parameters.
Develop an understanding of flame spread in a vitiated upper layer and its impact
on ignition of fire-hardened seats and wall panels, as well as of clothing and carry
on items.
Representative terms from entire chapter:
aviation administration
