presented to: by: date: federal aviation administration electric wire insulation study: flammable...
TRANSCRIPT
![Page 1: Presented to: By: Date: Federal Aviation Administration Electric Wire Insulation Study: Flammable Properties and Testing Methods Materials Working Group](https://reader035.vdocuments.mx/reader035/viewer/2022070308/551be289550346c3588b5e6e/html5/thumbnails/1.jpg)
Presented to:
By:
Date:
Federal AviationAdministrationElectric Wire
Insulation Study:
Flammable Properties and Testing Methods
Materials Working Group
Robert I. Ochs
10/20/2005
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Federal AviationAdministration
2Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Outline
1) Motivation
2) Current Regulations
3) Previous Work
4) Investigation
5) Testing Methods
6) Preliminary Findings
7) Questions
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Federal AviationAdministration
3Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Wire Insulation Flammability – Motivation
• Reinvestigation of flammability of materials contained within hidden areas of aircraft
• More stringent requirements for hidden area materials– Areas not accessible to flight crews for fire
extinguishment– Aim to limit the propensity of materials within these
areas to spread a flame to other areas of the aircraft
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Federal AviationAdministration
4Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Wire Insulation Flammability – Current Flammability Requirements
• Sixty-degree Bunsen burner test for electric wire/cable– Specified in Title 14 CFR 25.869– Appendix F to part 25 states:
• Insulation on electrical wire or cable installed in any area of the fuselage must be self-extinguishing when subjected to the 60° test specified in part I of appendix F
– Average burn length < 3 inches– Average flame time after removal < 30 seconds– Dripping flame time < 3 seconds
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Federal AviationAdministration
5Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Sixty-Degree Bunsen Burner Test – Description • Minimum of 3 specimens of each wire specification (make and size)
• Placed at an angle of 60° from the horizontal in a chamber free from drafts but providing sufficient oxygen for combustion
• Specimen length is 24”, flame application point is 8” from bottom end, held taught by counterweight over pulley
• Minimum temperature of hottest portion of flame no less than 1750 °F
• Hottest portion of flame must be applied to the flame application point
• Burn length recorded to nearest tenth of an inch
• Breaking of specimen is not considered a failure
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Federal AviationAdministration
6Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Sixty-Degree Bunsen Burner Test – Pros and Cons
• Advantages:– Simple configuration, operation, and data recording.– Shows relative performance when comparing
samples of similar sizes.
• Disadvantages– Cannot assess the performance of bundled wires,
effect of nearby burning materials (radiation heat transfer).
– Does not show a strong distinction between the best and worst performers, as shown by experimental testing (Cahill, 2004).
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Federal AviationAdministration
7Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Wire Insulation Flammability – Previous Experimental Study• Performed by FAA at WJHTC
• Investigation into the relevance and adequacy of the 60° Bunsen burner test, and the correlation with larger scale flammability tests
• Key findings:– 60° test showed little distinction between best and worst fire
performers – Intermediate scale testing showed better discrimination, and indicated
that materials that performed similarly in 60° test performed differently in intermediate scale tests
– Demonstrated the inadequacy of the 60° test, as some materials that passed the 60° test (and could be certified to be used in aircraft) were extremely poor performers in more realistic intermediate scale tests
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Federal AviationAdministration
8Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Wire Insulation Flammability – Previous Experimental Study
• Proved the necessity of developing new test methods for wire insulation that can: – Demonstrate the fire performance of wires and show
a strong distinction between good and bad performers
– Have the ability to scale-down and simulate the thermal processes and conditions experienced by aircraft wiring in actual fires
– Correlate with larger-scale tests – be repeatable, reproducible, easy to perform, bench
scale, etc…
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Federal AviationAdministration
9Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
About Wire Insulation• Purpose: to prevent contact of live electric conductors
• Composition: nonconductive materials with excellent dielectric properties
– Examples:• Plastics (polymeric materials)• Rubber• Glass• Oil
• For wiring applications, insulation needs to be flexible and resistant to fracture caused by mechanical stresses
• Almost all applications consist of wires insulated with polymeric materials, PVC blends being the most common application for low voltage systems
• Aircraft wiring is typically more fire resistant, as PVC/Nylon wiring was found to be very flammable
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Federal AviationAdministration
10Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Typical Aircraft Wiring
•DESIGNATION •COMPOSITION•M5086/1,2 •PVC/Nylon•M81381 •Aromatic Polyimide (KAPTON)•M22759/34 •Cross-Linked ETFE•M22759/80-92 •PTFE/Polyimide composite (TKT)•M22759/11 •TEFLON (PTFE)•M22759/18 •TEFZEL (ETFE)
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Federal AviationAdministration
11Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Polymer Combustion• Simultaneous physical and
chemical processes are occurring at the polymer surface
• Polymer decomposition requires large and continuous supply of thermal energy to evolve volatile molecules
• Analysis has shown that the rate of fuel generation is the rate limiting step, and is governed by the net rates of heat and mass transfer to and from the surface
From DOT/FAA/AR-05/14
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Federal AviationAdministration
12Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Quantifiable Fire Performance Parameters
• Pilot flame ignition tests– Burn length
– After flame time
– Burning debris flame time
• Radiant heat source + pilot flame ignition– Critical radiant heat flux
• O2 consumption calorimetry
– Heat release rate
– Total heat release
– Heat release capacity
– Temperature at peak heat release
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Federal AviationAdministration
13Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Pre-existing Fire Test Methods• Wire test methods:
– Riser test – vertical cable tray test
– Plenum test – Steiner tunnel test
– NASA STD-6001– 60° Bunsen burner
• Material test methods:– Radiant panel FPA– OSU– Cone calorimeter– PCFC
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Federal AviationAdministration
14Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
NASA STD-6001• Purpose: “to determine if a wire
insulation system, when exposed to an external ignition source, will self-extinguish and not transfer burning debris, which can ignite adjacent materials.”
• Test Criteria:– Wire insulation system at an internal
wire temperature of 257°F or max. operating temp. of wire
– Three standard sized samples of 20 gauge wire, 4 ft. length
– Burn lengths must be less than 6 inches for each sample
– For marginal samples, the configuration (wire bundles or the use of another gauge of wire) can cause a variation in the test results and must be addressed
– K-10 paper placed under the sample during testing must not ignite due to the transfer of burning debris
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Federal AviationAdministration
15Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Radiant Panel Test Apparatus – Description • Originally developed as ASTM E-648 to measure the critical radiant heat flux
of floor covering materials
• Utilizes a rectangular panel (gas fired or electric) as a radiant heat source
• Panel is at 30° angle from horizontal, thus providing an incident heat flux that decreases as the distance from the “zero position” increases
• Pre-mixed propane-air pilot flame is applied to “zero position,” where the incident heat flux is greatest
• Provides a good indication of the propensity of materials to propagate a flame when exposed to simulated fire conditions
• This test method was recently adopted by the FAA for fire testing of thermal/acoustic insulation materials, after it was determined that the vertical Bunsen burner test was inadequate
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Federal AviationAdministration
16Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Radiant Panel Test Apparatus – Considerations for Wire Testing • Preliminary work has shown that the sample configuration
and test criteria can affect results• Wires are not flat surfaces, hence the incident heat flux will
not be uniform across the sample surface• Wire thickness and mass will change results for wires of the
same type– Evolution of flammable molecules occurs at the material surface– For thicker wires, surface heat from the incident heat flux will diffuse
away from the surface, less heat will be available at the surface for polymer volatilization
• For multiple wire configurations, wire spacing will greatly affect the flame spread in the transverse direction– Difficult to make wires into a “sheet” material
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Federal AviationAdministration
17Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Radiant Panel Test Apparatus – Testing Criteria Options• Single or multiple wire samples
– If multiple wires• Size and method of bundling• Spacing between adjacent wires
• Flat or inclined test sample holder– 30° inclination provides same heat flux over length of the wires– Introduces a new buoyant convective flux into the equation
• Sample pre-heating– Pre-heating can reduce the effect of large sample sizes by reducing
the thickness temperature gradient– Pre-heat times need to be carefully determined, as longer pre-heat
times may result in off gassing of more flammable, volatile molecules that could be combusted, thereby reducing the apparent flammability of the material
• Pilot flame exposure time
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Federal AviationAdministration
18Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Results – Preliminary Radiant Panel Testing
• Individual wires– 12” long– Attached to rectangular
frame– 30 sec. flame exposure
• 2 different configurations
– Horizontal (heat flux “gradient”)
– 30-degree angle (parallel to panel, uniform heat flux)
00.5
11.5
22.5
33.5
44.5
PVC/Nylo
n
Gray R
iser
ETFE
X-linke
d ETFE
PTFE
PTFE/poly
imid
e/PTFE
Polyim
ide
Bur
n Le
ngth
, in. Horizontal
30-degree angle
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Federal AviationAdministration
19Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Microscale Combustion Calorimetry Tests
• PCFC was used to obtain data from various types of wires
• Testing independent of sample size, mass, geometry
• Heat release rate, heat release capacity, peak and total heat release, temperature at peak h.r. data was recorded for each wire type
• Micro scale test is simple to perform and can provide much data
• Data can be used to rank materials as more or less flammable
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Federal AviationAdministration
20Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Microscale Combustion CalorimetryHeat Release Rate vs. Temperature
0
100
200
300
400
500
600
700
800
900
0 100 200 300 400 500 600 700 800 900 1000
Temperature, Degrees C
Hea
t R
elea
se,
Wat
ts/g
ram
Riser Sheathing (PVC)
Riser 4-pair wires
ETFE
X-Linked ETFE
PTFEPTFE/Polyimide/PTFE
Polyimide
PVC/Nylon
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Federal AviationAdministration
21Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Comparison: 60° Test60-Degree Burn Length vs. Total Heat Release
0
2
4
6
8
10
12
14
16
0 5 10 15 20 25
Heat Release, kJ/g
Bur
n Le
ngth
, in.
PTFE/Polyimide/PTFE
Polyimide
X-linked ETFEETFE
Riser Sheathing
PVC/Nylon
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Federal AviationAdministration
22Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Comparison: Intermediate Scale
Int. Scale Burn Length vs. Total Heat Release
0
5
10
15
20
25
30
35
0 5 10 15 20 25
Total Heat Release, kJ/g
Bur
n Le
ngth
, in.
PTFE/Polyimide/PTFE
PolyimideX-linked ETFE
ETFE
Riser Sheathing
PVC/Nylon
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Federal AviationAdministration
23Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Comparison: Radiant Panel
Radiant Panel Burn Length vs. Total Heat Release
0
0.5
1
1.5
2
2.5
3
3.5
0 5 10 15 20 25
Total Heat Release, kJ/g
Rad
iant
Pan
el B
urn
Leng
th
PTFE/Polyimide/PTFE
PolyimidePTFE X-linked ETFE
ETFE
Riser Sheathing
PVC/Nylon
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Federal AviationAdministration
24Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Comparison: Radiant Panel
Radiant Panel Burn Length vs. Temperature @ Peak Heat Release
0
0.5
1
1.5
2
2.5
3
3.5
0 200 400 600 800 1000
Temperature, Deg. C.
Rad
iant
Pan
el B
urn
Leng
th, i
n. PVC/Nylon
Riser Sheathing ETFE
X-linked ETFEPTFE/Polyimide/PTFE
Polyimide
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Federal AviationAdministration
25Electric Wire Insulation StudyIAMFTWG, Atlanta – 10.20.2005
Summary
• Construction of an adjustable apparatus for the radiant panel test– Ability to vary the test configuration
• Single and bundled wires• Horizontal and inclined positions
• Further in-depth study of testing configuration effects on test results
• Discussions with working group members