methods for characterizing artificial smoke generators for
TRANSCRIPT
Presented to:
By:
Date:
Suppression, Detection and Signaling Research and Applications Symposium (SUPDET)
Matthew E. Karp
September 2019
Methods for Characterizing Artificial
Smoke Generators for Standardizing
Inflight Smoke Detection Certification
Overview
– Section 1 Background
– Section 2 Methods and test equipment
– Section 3 Potential parameters
– Section 4 Conclusions
2
Test Apparatus
Section 1
Background
• Federal Aviation Administration (FAA) regulations require that a commercial
aircraft cargo compartment smoke detection system must provide visual
indication to the flight crew within one minute after the start of a fire 1.
• Further FAA guidance states that the smoke detection certification test is
designed to demonstrate that the smoke detection system will detect a
smoldering fire that produces a small amount of smoke 2.
• In an attempt to eliminate the frequency of false alarms, the FAA issued a
Technical Standard Order to adopt the Minimum Performance Standards of
smoke detector equipment, which includes criteria for resisting alarms from
nuisance sources such as water vapor, insecticide aerosols, dust and light 3.
3
1 Title 14 Code of Federal Regulations (CFR) Part 25.858, 2/10/1998
2 Federal Aviation Administration Advisory Circular 25-9A
3 TSO C1e, 8/19/2014
Section 1
Background Continued
• Due to health and safety concerns – artificial smoke generators are used for
inflight certification testing
• Aerosols created by artificial smoke generators must have similar size
distributions and light scattering characteristics in order for the false alarm
resistant smoke detectors to alarm
• standardizing the artificial smoke generators for the total quantity of aerosol
production, rate of aerosol production and repeatability of aerosol production
is necessary to ensure the reliability and integrity of the inflight smoke
detection certification test
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Section 2
Methods and Test Equipment
• Testing is conducted in an environmental chamber
that is capable of simulating ambient conditions that
are typical to flight
• Blue and infrared, light scattering measurement
(LSM)
• Scanning mobility particle sizer (SMPS)
• 6 vertically aligned light obscuration meters
• Four aircraft manufacturer’s smoke generators and
settings are tested and compared
– Annotated as: MFR 1a, MFR 1b, MFR 1c, MFR 2a,
MFR 2b, MFR 3, and MFR 4
• Vane anemometers characterize smoke transport
5
Test Apparatus
Method
• A smoke generator is turned on to produce an
aerosol for 60 seconds to best represent the test
procedures outlined in 14 CFR 25.858
• Light obscuration and light scattering
measurements are taken through the entire test
• SMPS measurements are taken at 210 seconds
• Additionally, size distributions and light scattering
characteristics from smoke created by smoldering
foam, smoldering wood, and lithium-ion battery
thermal runaway vent-gas are measured and
compared to aerosols produced by the smoke
generators
6
Altitude Chamber
Smoke Transport
• A cone is connected to the
smoke generator’s chimney
• Attached to the cone is a vane
anemometer to measure the
volumetric flow rate
• The volumetric flow rate is
directly correlated with
chimney heat output
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Siemens Cerberus with Volumetric Flow
Rate Cone
Vane
anemometer
Cone
Chimney
Smoke Generators
• Theatrical smoke generators use an inert gas to
propel mineral oil into a heat exchanger, where
the solution is vaporized to create smoke.
• The theatrical smoke exits through a chimney
incorporated with heaters to create a thermally-
buoyant plume
• Important variables of smoke generators
– Gas propellant
– Gas propellant pressure
– Chimney heater temperature
– Mineral oil characteristics
• Viscosity and refractive index
8
Simplified Smoke Generator
Schematic
Inert Gas Regulator
Mineral Chimney Stack
Oil and Heaters
Heat Exchanger
Nozzle
Mie Scattering Theory
• Mie Scattering Theory governs light
scattering by sub-micron particles
• A simplified approximation of Mie Scattering
Theory is given by van de Hulst [4]
𝑸 = 𝟐 −𝟒
𝒑𝐬𝐢𝐧 𝒑 +
𝟒
𝒑𝟐(𝟏 − 𝐜𝐨𝐬 𝒑 )
• Where Q is the efficiency factor of scattering
𝒑 =𝟒𝝅𝒂 𝒏 − 𝟏
λ
Blue Scattering Intensity
IR Scattering Intensity
0 0.2 0.4 0.6 0.8 1
0
0.5
1
1.5
2
2.5
3
3.5
4
0
2
4
0 0.25 0.5 0.75 1
Effi
cie
ncy
Fac
tor
of
Scat
teri
ng
Diameter, µm
This shows that the scattering intensity is
a function of
n, Refractive index of the particle
a, radius of the particle
λ, Wavelength of the incident lightMaxwell’s Equation plotted using 470nm and 850nm
wavelengths, refractive index 1.5
[4] van de Hulst, H. C. (1957). Light scattering by small particles.
New York: John Wiley and Sons. ISBN 9780486139753.
Electromagnetic Radiation
Scattering Measurement (LSM)
• Two LEDs
– 470nm blue LED forward
scattering angle of 135°
– 850nm IR LED forward
scattering angle of 135°
• Measurements used to calculate:
– Percentage of blue to blue and IR
light scattering intensity
– Utilize van de Hulst
approximation to characterize
very small particles
LEDs
Silicon
Detectors
45°
Smoke
Electromagnetic Radiation Scattering
Measurement (LSM)
Scanning Mobility Particle Sizer (SMPS)• How does the SMPS work?
– An impactor removes large particles and
measures flow.
– A neutralizer creates a well-characterized
charge distribution on the particles.
– Inside a Differential Mobility Analyzer
(DMA), the charged particles experience
an electrical field that separates particles
based on their electrical mobility and
outputs a monodisperse aerosol.
• Electrical mobility is inversely related to
particle size
– The condensation particle counter (CPC)
counts the monodispersed particles as
they exit the DMA.
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Co
nce
ntr
atio
n
DiameterSMPS Output
SMPS Simplification
• Particle characterization
– LSM
– SMPS
• Light obscuration
– Transient obscuration
– Steady state obscuration
– Repeatability
• Ambient environment
• Smoke transport
LSM and Vane Anemometer Cone
Section 3
Potential Parameters
MFR 1
MFR 2
MFR 3
MFR 4
Smoldering Foam
Lithium Batteries
Smoldering Wood
0
100
200
300
400
0 0.25 0.5 0.75 1G
eo
met
rica
l Me
an D
iam
ete
r, n
m% Blue Signal
Particle Size - LSM and SMPS
• Smoke generators used by airline
manufacturers are capable of
producing an aerosol that is
comparable to particles from certain
smoke sources
• There is a strong negative correlation
between the percentage of blue to
blue and IR light scattering intensity
and geometric mean diameter for
individually sourced particles
• Strong correlation diminished when
comparing particles from multiple
sources with varying refractive
indexes
LSM %blue signal vs SMPS diameter
Time vs light obscuration
Various manufacturer smoke generator settings
Light ObscurationTransient
Obscuration
Steady State
Obscuration
• Transient Obscuration
– Initial 60 seconds
– Characterizes rate of aerosol
production
• Steady State Obscuration
– After 120 seconds when the
aerosol fully mixes
– Characterizes total aerosol
production
• Repeatability
– Relative deviation between tests
over 10 second increments
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120 140 160 180
Ob
scu
rati
on
, %/f
t
Time, s
MFR 1a MFR 1b MFR 1c MFR 2a MFR 2b
MFR 3 MFR 4 foam wood
Transient Obscuration
Time vs light obscuration
Used to determine transient light obscuration
• Transient obscuration characterizes the rate of aerosol production
• The data points represent the time to surpass the marked light obscuration threshold
• The steeper the curve, the more rapid the aerosol production rate
• The highest point on the curve represents the maximum light obscuration reached
• There is a range of aerosol production rates used for smoke detection certification testing
MFR 1b
MFR 2b
MFR 3
MFR 1a
MFR 1c
MFR 4
MFR 2a
0 10 20 30 40 50 60
0
20
40
60
80
100
120
0
25
50
75
100
0 20 40 60%
ob
s/ft
Time, s
Steady State Obscuration
Time vs light obscuration
Used to determine steady state light obscuration
• Steady state obscuration characterizes the total aerosol production
• Tests conducted in a 7.8m3 vessel
• The average steady state obscuration is 32 %/ft with a standard deviation of 17 %/ft
• There is a range of total aerosol production used for smoke detection certification testing
– Two perspectives• This is ok, because of the varying
size of aircraft cargo compartments
• This is not ok, because a fires beginning does not discriminate against aircraft size
6
23
25
30
32
49
64
0 20 40 60 80
MFR 1a
MFR 2a
MFR 3
MFR 1b
MFR 2b
MFR 1c
MFR 4
Steady State Obscuration, %/ft
Repeatability
• The percent deviation of light obscuration per foot between a minimum of three tests over 10 second increments are calculated to determine test repeatability
• The initial 10 seconds are the least repeatable and arguably the most significant portion of certification testing
• The first 10 seconds have an average of 24% deviation between tests from an individual smoke generator
Time vs percent deviation
Used to determine repeatability
5, 24%
15, 15%
25, 9%35, 7%
45, 7%
55, 7%
0
10
20
30
40
50
0 20 40 60
Perc
ent
Dev
iati
on
Time, s
MFR 1a MFR 1b MFR 2a MFR 2b
MFR 3 MFR4 Average
Ambient Environment and
Steady State Obscuration
Steady State Light Obscuration by Ambient
Temperature
• Positive correlation between
ambient temperature and the
total aerosol production
• The significance of the
ambient temperature on a
smoke generator’s aerosol
production varies by smoke
generator and setting 32.128.4
22.621.7
48.828.4
30.216.6
27.225.1
10.05.5
0 20 40 60
MFR 2b 30C 101kPaMFR 2b 10C 101kPa
MFR 2a 30C 101kPaMFR 2a 10C 101kPa
MFR 1c 30C 101kPaMFR 1c 10C 101kPa
MFR 1b 30C 101kPaMFR 1b 10C 101kPa
MFR 1b 30C 69.7kPaMFR 1b 10C 69.7kPa
MFR 1a 30C 69.7kPaMFR 1a 10C 69.7kPa
Steady State Light Obscuration, %/ft
Ambient Environment and
Steady State Obscuration
Steady State Light Obscuration by Ambient
Pressure
• Weak negative correlation
between ambient temperature
and the total aerosol
production
• Increasing the ambient
pressure can, but does not
always, decrease the total
aerosol production 48.8
49.6
30.2
27.2
16.6
23.9
5.6
10.0
0 20 40 60
MFR 1c 30C 101kPa
MFR 1c 30C 69.7kPa
MFR 1b 30C 101kPa
MFR 1b 30C 69.7kPa
MFR 1b 10C 101kPa
MFR 1b 10C 69.7kPa
MFR 1a 30C 101kPa
MFR 1a 30C 69.7kPa
Steady State Light Obscuration, %/ft
Smoke Transport
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• Volumetric flow rate characterizes
the smoke transport
• The volumetric flow rate is directly
correlated with chimney heat output
• There is a range of volumetric flow
rates used for smoke detection
certification testing
– Previous large scale testing has
shown that detection time is
significantly reduced by
increasing volumetric flow rate
Volumetric flow rate
Comparison volumetric flow rate of various smoke
generator settings with Siemens Cerberus and Aviator 440
13
13
13
13.2
16.8
16.8
19.4
MFR 2a
MFR 2b
MFR 3
MFR 1a
MFR 1b
MFR 1c
MFR 4
Volumetric Flow Rate, ft3/min
• Smoke generators are capable of producing an
aerosol with similar particle size distributions and
light scattering characteristics to real smoke sources
• There is a measurable difference between the total
aerosol production, rate of aerosol production and
smoke plum velocity between smoke generators
used by major airline manufacturers for certification
testing
• A smoke generator’s aerosol production can vary
with the ambient temperature range associated with
a typical aircraft flight profile
Section 4
Conclusions
Contact Information
- Matthew Karp
- Research Engineer
- FAA ANG-E211 Systems Fire Protection
- Phone: 609-485-4538
- Email: [email protected]
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