Residential Nuisance Source Characteristics for Smoke Alarm Testing by vev19514

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									Thomas G. Cleary
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899 U.S.A.


Residential Nuisance Source Characteristics for Smoke Alarm Testing
Abstract
Nuisance scenario tests were performed in the manufactured home used in the Home
Smoke Alarm fire test series.        The scenario selections were based on what are
commonly thought to be causes of residential nuisance alarms, and were designed to
mimic normal activities (i.e. no intentional food burning, with the exception of toasted
bread.) The bulk of the scenarios were related to cooking activities including: frying,
deep-frying, baking, broiling, boiling, and toasting. In addition, cigarette smoking and
candle burning were included.          Smoldering fire scenarios were examined for
comparative purposes. Aerosol concentrations, temperature, humidity, flow velocity
and analog output from several photoelectric, ionization and carbon monoxide sensors
were gathered.    It was observed that nuisance alarms in residential settings were
affected by the properties of the aerosol produced, its concentration, the location of an
alarm relative to the source, and the air flow that transports smoke to an alarm. This
study provides a detailed set of data that can be used to address several issues involving
nuisance alarms and reinforces current suggested practices.


Introduction
Smoke alarms are susceptible to alarming when exposed to non-fire aerosols.              In
residential settings, this typically involves cooking activities or transient, high humidity
conditions (i.e., “show steam”).     The objective of this research, performed as part of
the Home Smoke Alarm project [1], was to develop a basis for standard residential
nuisance source testing. The approach taken was to define a set of nuisance scenarios,
replicate the events that cause nuisance alarms, and quantify the important variables
that cause nuisance alarms.        Translating the results to a set of nuisance source
conditions reproducible in a suitable test-bed (i.e., a test room or the fire
emulator/detector evaluator) would allow for more comprehensive detector
performance testing.


Experimental
Nuisance scenario tests were performed in the manufactured home used in the Home
Smoke Alarm fire test series [1]. The selections were based on what are commonly
thought to be causes of residential nuisance alarms, and scenarios were designed to
mimic normal activities (i.e. no intentional food burning, with the exception of toasted
bread). No consideration was given to the probability of occurrence for any given
scenario; the objective was to gather data on a number of scenarios. The bulk of the
scenarios were related to cooking activities including: frying, deep-frying, baking,
broiling, boiling, and toasting.             Cigarette smoke and candles were included.
Smoldering fire scenarios (smoldering polyurethane foam, beech wood blocks and
cotton wick) were examined for comparative purposes.


A schematic of the manufactured home is shown in Figure 1. Its exterior dimensions
were 20.1 m long and 4.2 m wide, with and interior ceiling that was pitched from the
centerline height of 2.4 m to a height of 2.1 m at the long exterior walls. The dark
shaded areas were closed off. During these tests, all external doors and windows were
closed. Most scenarios were repeated with and without a floor fan blowing air from the
master bedroom into the kitchen/living room area.


Aerosol concentrations, temperature, humidity, flow velocity and analog output from
photoelectric, ionization and carbon monoxide sensors were gathered. Figure 1 shows
the approximate ceiling location of all the measurement positions. Details of the
measurement are given in NIST TN 1455 [1].


Two portable aerosol instruments were used to gather aerosol number and mass
concentrations during the tests. Number concentration was recorded with a TSI model
3007 portable condensation particle counter (CPC)*. This instrument is capable of


*
 Certain commercial equipment are identified in this paper in order to accurately describe the
experimental procedure. This in no way implies recommendation by NIST
                         A
                                  C
                                      B     D
                                                   E
                                                        F
                                                             G




Figure 1. Schematic of the test home.


counting particles greater than 10 nanometers up to concentrations of 5x105
particles/cm3 with an uncertainty of 10% of the reading. The upper concentration limit

of the instrument is insufficient for many fire and nuisance conditions so the air sample
was diluted with a fixed amount of clean air prior to entering the CPC resulting in an
approximate 20 to 1 dilution ratio of the sample. The dilution ratio for each test was
obtained by measuring undiluted and diluted background room aerosol prior to the start
of the test. The uncertainty in the dilution corrected number concentration is estimated
to be 12%. A TSI model 8520 “Dustrak” portable aerosol mass monitor was used to
gather the aerosol mass concentration.      This device consists of a light scattering
photometer that analyzes the laser light scattered at an angle of 90o from particles
flowing through the device. Its default calibration is set to the respirable fraction of
standard ISO 12103-1 A1 test dust. It has a range from 0.001-150 mg/m3. The
effective particle size measurement range is 0.1 µm up to 10 µm. The device can be
calibrated for any aerosol with scattering properties different from the test dust
provided the true mass concentration is determined. Here, the default calibration was
used, so any given mass concentration measurement reported are relative to an
equivalent mass of test dust. Since the device in not calibrated to each of the aerosols
produced in the nuisance tests, the uncertainty in the measurement in not determined.
However, the results are proportional to the mass concentration and correspond directly
to the scattering signal strength of photoelectric detectors with an equivalent amount of
aerosol in its sensing region.


Seven dual photo/ion smoke alarms were modified at NIST to provide continuous
analog output of photoelectric, ionization, carbon monoxide, and temperature sensor
values [1]. Each detector was calibrated in the FE/DE with the cotton wick smoke, and
the sensor values are presented in engineering units of extinction coefficient (m-1),
volume fraction of CO, and temperature in Celsius.           The positions of the sensor
packages are indicated on Figure 1 and represented in the results by the letters A-G.
Carbon monoxide and temperature sensor data are not presented here. All of the data
collected in this test series is available in the NIST Report of Test FR 4019 [2].


The time to reach photoelectric and ionization alarm points was determined from ion
and photoelectric sensor calibration test data, and estimated alarm sensitivities
appropriate for the FE/DE cotton wick smoke.          Estimated high, medium and low
sensitivities for both photoelectric and ionization alarms in terms of extinction
coefficient and obscuration are given in Table 1.         These values cover the range
expected for residential smoke alarms for each sensor type.


  Sensor               High sensitivity       Medium sensitivity      Low sensitivity
                       m-1, (%/ft)            m-1, (%/ft)             m-1, (%/ft)
  Photoelectric
                       0.05, (1.5)            0.083, (2.5)            0.117, (3.5)
  Ionization
                    0.016, (0.5)           0.033, (1.0)         0.050, (1.5)
Table 1. Alarm sensitivity for photoelectric and ionization sensors


Results and Analysis
The results presented here are for selected tests showing the time to alarm for each
photoelectric and ionization sensor at the three sensitivity levels, and the aerosol mass
and number concentration at a central ceiling level location. Location E only had an
                              600




                                                                                                                                                   Number Concentration (particles/cm )
                                                                                                  300                                      1 107




                                                                                                                                                   3
                                    (A)           PE low
Time to Alarm Threshold (s)

                                                  PE mid                                                (B)




                                                                     Mass Concentration (mg/m3)
                              500                                                                                               Mass
                                                  PE high                                         250
                                                  Ion low                                                                       Number
                              400                 Ion mid                                         200
                                                  Ion high
                              300
                                                                                                  150                                      5 106

                              200
                                                                                                  100
                              100
                                                                                                  50
                               0
                                      A   B     C   D   E    F   G                                 0                                       0
                                                                                                         0    120   240   360     480    600
                                              Alarm Location
                                                                                                                    Time (s)

                              600




                                                                                                                                                     Number Concentration (particles/cm )
                                                                                                  300                                      5 106




                                                                                                                                                   3
                                    (C)
Time to Alarm Threshold (s)




                                                 PE low                                                 (C)

                                                                     Mass Concentration (mg/m3)
                              500                PE mid                                           250
                                                 PE high                                                                                   4 106
                                                                                                                                  Number
                              400                ION low
                                                 ION mid                                          200                             Mass
                                                                                                                                               6
                                                 ION high                                                                                  3 10
                              300
                                                                                                  150
                                                                                                                                               6
                              200                                                                                                          2 10
                                                                                                  100
                              100                                                                                                              6
                                                                                                                                           1 10
                                                                                                  50
                               0
                                      A   B     C D     E    F   G                                 0                                       0
                                                                                                         0    100 200 300      400 500   600
                                              Alarm Location
                                                                                                                    Time (s)



Figure 2. Results for toasting bread. Figures labeled A and B are for the test with
no fan, and figures labeled C and D show repeated test results with the fan on.


ionization smoke sensor. Nominal repeat tests are shown without the floor fan on
(labeled A and B) and with the floor fan turned on (labeled C and D.)


The toasted bread results are shown in Figure 2. The toaster with two slices of bread
was placed on the counter to the left of the range. It was turned on at time = 0 and
turned off 250 s later. With no fan flow, the ionization alarms tended to reach their
threshold levels before photoelectric alarm. The time to reach the threshold increased
as the distance of the toaster from the alarms increased. The number concentration
reached its peak before the mass concentration began to rise, and started to fall before
the mass concentration peak was reached.                                                          With the fan turned on, fewer alarm
thresholds were met, and contrary to the no fan case, some photoelectric alarm
thresholds were reached before the ionization thresholds, and at some locations the
                              800                                                                     100                                       1 10
                                                                                                                                                       7




                                                                                                                                                               Number Concentration (particles/cm )
                                    (A)




                                                                                                                                                           3
                                                                                                            (B)
Time to Alarm Threshold (s)

                              700




                                                                         Mass Concentration (mg/m3)
                              600                                                                     80

                              500                                                                                 Number
                                                                                                      60
                              400                                                                                 Mass                                 6
                                                              PE low                                                                            5 10
                              300                             PE mid                                  40
                                                              PE high
                              200                             ION low
                                                              ION mid                                 20
                              100                             ION high
                               0
                                      A     B     C D     E    F   G                                   0                                        0
                                                                                                             0    100 200   300 400 500       600
                                                Alarm Location
                                                                                                                         Time (s)


                              700




                                                                                                                                                           Number Concentration (particles/cm )
                                                                                                      30                                        5 106




                                                                                                                                                           3
                                    (C)
Time to Alarm Threshold (s)




                              600                                                                           (D)
                                                                         Mass Concentration (mg/m3)
                                                                                                      25
                                          PE low                                                                  Number                        4 106
                              500         PE mid
                                          PE high                                                     20          Mass
                              400                                                                                                                      6
                                          ION low                                                                                               3 10
                                          ION mid                                                     15
                              300         ION high                                                                                                     6
                                                                                                                                                2 10
                              200                                                                     10
                                                                                                                                                       6
                              100                                                                                                               1 10
                                                                                                       5
                               0
                                      A     B     C D     E    F   G                                   0                                        0
                                                                                                             0    100 200 300       400 500   600
                                                Alarm Location
                                                                                                                         Time (s)



Figure 3. Results for frying hamburgers (A and B – fan off, C and D - fan on)


ionization alarms never reached their low threshold.                                                                     The number and mass
concentration trends were similar to the no fan case, but the levels were lower.

Three 110 g frozen hamburgers were fried in an aluminum skillet pan on an electric
range. With no fan flow, all locations reached photoelectric and ionization alarm
thresholds, most within 100 s of one another. The photoelectric sensor closest to the
electric range reached a threshold first. The number and mass concentration increased
steadily after 350 s. With the fan on, no ionization alarm thresholds were reached, and
photoelectric alarm thresholds were reached at all locations they were present except
location A. The number and mass concentration started to increase at 150 s and the
mass concentration showed brief sharp increases periodically.
                              1500




                                                                                                                                                                                        Number Concentration (particles/cm )
                                                                                                                         10                                                5 106




                                                                                                                                                                                        3
                                     (A)
                                                                                                                                      (B)
Time to Alarm Threshold (s)




                                                                         Mass Concentration (mg/m3)
                                                                                                                              8               Number                       4 106
                              1000                                                                                                            Mass
                                                                                                                                                                                    6
                                                              PE low                                                          6                                            3 10
                                                              PE mid
                                                              PE high                                                                                                               6
                               500                                                                                            4                                            2 10
                                                              ION low
                                                              ION mid
                                                              ION high                                                        2                                            1 10
                                                                                                                                                                                    6



                                 0
                                       A   B    C     D   E     F   G                                                         0                                             0
                                                                                                                                  0         200   400     600   800 1000 1200
                                               Alarm Location
                                                                                                                                                        Time (s)




                                                                                                                                                                                                                               Number Concentration (particles/cm )
                              1500                                                                                            10                                                5 106




                                                                                                                                                                                                                      3
                                     (C)                                                                                               (D)
Time to Alarm Threshold (s)




                                                                                                 Mass Concentration (mg/m3)
                                                                                                                                  8                                             4 106
                              1000                                                                                                                Number
                                                                                                                                  6               Mass                          3 10
                                                                                                                                                                                              6


                                           PE low
                                           PE mid                                                                                                                                             6
                                                                                                                                  4                                             2 10
                               500         PE high
                                           ION low
                                                                                                                                                                                              6
                                           ION mid                                                                                2                                             1 10
                                           ION high
                                 0                                                                                                0                                             0
                                       A   B     C D     E    F     G                                                                  0     200 400 600 800 1000 1200
                                               Alarm Location
                                                                                                                                                          Time (s)




Figure 4. Results for pizza cooking (A and B – fan off, C and D - fan on)


A small (158 g) frozen cheese pizza was cooked on a pan in the oven. To begin, the
oven was pre-heated to 350 oF, the pizza was placed in the oven, then baked. The oven
door was opened twice during baking time to check the pizza. After 630 s, the oven
broiler element was turned on and the door was left slightly open. Figure 4 shows the
results for the pizza cooking tests. With the fan off, all locations reached an ionization
threshold, and only one location reached a photoelectric threshold.                                                                                                  The number
concentration results show three spikes at the time the oven door was being opened.
The mass concentration doesn’t start to increase significantly until about 900 s. With
the fan on, only one location reached an ionization alarm threshold, and it was at a
location some distance from the oven. The number concentration showed three spikes
due to the door opening, but both the number concentration and mass concentration
were lower compared to the fan off case.
                              1600




                                                                                                                                                                              Number Concentration (particles/cm )
                                                                                                                                                                  6
                                                                                                              60




                                                                                                                                                                      3
Time to Alarm Threshold (s)                                                                                                                                2 10
                                                                                                                       (B)




                                                                            Mass Concentration (mg/m3)
                                                                 PE low
                                                                 PE mid                                       50
                              1200                                                                                                 Number
                                                                 PE high
                                     (A)                         ION low                                      40                   Mass
                                                                 ION mid
                               800                               ION high                                                                                         6
                                                                                                              30                                           1 10


                                                                                                              20
                               400
                                                                                                              10
                                0
                                      A     B    C    D   E      F   G                                         0                                           0
                                                                                                                   0    200 400 600 800 1000 1200 1400
                                                Alarm Location
                                                                                                                                      Time (s)




                                                                                                                                                                      Number Concentration (particles/cm )
                                                                                                              50                                           2 106




                                                                                                                                                                      3
                              2000
                                                                                                                       (D)

                                                                                 Mass Concentration (mg/m )
                                     (C)
                                                                            3
Time to Alarm Threshold (s)




                                                                                                              40
                                                                                                                             Number
                              1500
                                                                                                                             Mass
                                                                                                              30
                                                                                                                                                           1 106
                              1000         PE low
                                           PE mid                                                             20
                                           PE high
                               500         ION low
                                           ION mid                                                            10
                                           ION high

                                0                                                                              0                                           0
                                      A     B     C D     E    F     G                                             0         400      800    1200   1600
                                                Alarm Location                                                                        Time (s)




Figure 5. Results for smoldering wicks (A and B – fan off, C and D - fan on)


The cotton smolder smoke was generated with the staged wick ignition device [3]
placed on the floor in the living room area. After an initial delay of 30 s, 8 sets of 4
wicks were ignited with 12 s delay times between sets. With no fan flow, ionization
alarm thresholds were reached at all locations. Photoelectric alarm thresholds were
reached at the locations nearest the source first, then much later at locations further
from the source (Location B did not have a working photoelectric alarm during this
test.) The number and mass concentration began to increase around 150 s, and steadily
increased during the test. With the fan on, the two ionization alarms closest to the
smoldering wicks reached thresholds, followed by the locations further from the source.
Only two locations reached photoelectric alarm thresholds. The number and mass
concentration began to increase around 150 s. The mass concentration steadily
                              1500




                                                                                                                                                                                   Number Concentration (particles/cm )
                                                                                                           100                                                         1 106




                                                                                                                                                                                   3
                                     (A)
Time to Alarm Threshold (s)

                                                                                                                                   (B)




                                                                      Mass Concentration (mg/m3)
                                                                                                                      80                                               8 105
                              1000
                                                                                                                                           Number                              5
                                                                                                                      60                                               6 10
                                            PE low                                                                                         Mass
                                            PE mid                                                                                                                             5
                               500          PE high                                                                   40                                               4 10
                                            ION low
                                            ION mid                                                                                                                            5
                                                                                                                      20                                               2 10
                                            ION high
                                0
                                       A   B     C D     E    F   G                                                        0                                           0
                                                                                                                               0        200 400 600 800 100012001400
                                               Alarm Location
                                                                                                                                                  Time (s)




                                                                                                                                                                                                                          Number Concentration (particles/cm )
                                                                                                                           50                                              1 106




                                                                                                                                                                                                                 3
                              1500
                                                                                                                                    (D)


                                                                                              Mass Concentration (mg/m3)
Time to Alarm Threshold (s)




                                                                                                                           40                                              8 105
                                     (C)
                              1000                                                                                                            Number
                                                                                                                                                                                         5
                                                                                                                           30                                              6 10
                                                                                                                                              Mass
                                           PE low                                                                                                                                        5
                                           PE mid                                                                          20                                              4 10
                               500         PE high
                                           ION low                                                                                                                                       5
                                           ION mid                                                                         10                                              2 10
                                           ION high
                                0                                                                                              0                                           0
                                       A   B     C D     E    F   G                                                                 0    200 400 600 800 100012001400
                                               Alarm Location                                                                                        Time (s)




Figure 6. Results for smoldering wood (A and B – fan off, C and D - fan on)


increased during the test, while the number concentration rate of rise started to decrease
after 200 s.

Wood smoke was produced by placing eight 3.5 cm by 2.0 cm by 1.0 cm beech wood
blocks on a 750 W electric hot plate. The hot plate was located on the living room
floor, and at the beginning of the test the hot plate was turned on. For the fan off case,
the photoelectric alarms reached their thresholds before the ionization alarms at all
locations. The number and mass concentration started to increase between 500 s and
600 s, and both increased steadily until the hot plate was turned off at 1200 s. For the
case with the fan on, all locations that have photoelectric alarms reached threshold
values, and ionization alarms closest to the source reached threshold values. Results
were similar to the no fan case. The number concentration started to increase at about
500 s, while the mass concentration started to increase at 700s; the concentration levels
were below the no fan case.


Conclusions
The results presented for nuisance source tests and comparative smoldering tests here
display several characteristics related to nuisance alarms.          Nuisance alarms in
residential settings from typical cooking activities, smoking or candle flames were
affected by the properties of the aerosol produced and its concentration, the location of
an alarm relative to the source, and the air flow that transported smoke to an alarm.
These conclusions hold for the additional tests from this series [1].           Threshold
adjustment to lower sensitivities reduced the number of nuisance alarms in some cases,
but in others, the rate of smoke production was so great, that all threshold levels were
reached in a short period of time. With ventilation air flow, dilution of the aerosol as it
was dispersed throughout the home tended to reduce the smoke levels below alarm
threshold values. This study provides a detailed set of data that can be used to address
several issues involving nuisance alarms and reinforces current suggested practice of
moving alarms as far away from cooking appliances as practical. Additionally, the
results are being programmed into the fire emulator/detector evaluator to reproduce the
nuisance source conditions, which will allow for more comprehensive detector
performance testing.


References
[1]    Bukowski, R., Peacock, R., Averill, J., Cleary, T., Bryner, N., Walton, W., Reneke,
       P., and Kuligowski, E., “Performance of Home Smoke Alarms,” Natl. Inst. Stand.
       Technol., Techical Note 1455, 2003.

[2]    Cleary, T., “Home Smoke Alarm Project, Alarm Responses to Nuisance Sources,”
       Natl. Inst. Stand. Technol., Report of FR 1419, 2003.

[3]    Cleary, T., Donnelly, M., and Grosshandler, W., “The Fire Emulator/Detector
       Evaluator: Design, Operation, and Performance,” 12th International Conf. on
       Automatic Fire Detection AUBE ’99, Gaithesburg, MD, USA , pp. 312-323, 2001.

								
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