=
gE
£
g
e e {3.0
Py
Sr ro] 2
z
é t 28
° f 28
+246 834 1.914 2,994 4,074

; CO and sensor SA response to coal fire
for experiment No 4

25

&
a
So |
8 e 7 ‘0.60
= i
5h g |
2 Ss 0.58
o 0.56
-246 834 1,914 2,994 4,074
TIME, s
Figure 7: CO and sensor SB response to coal fire
POC for experiment No 4

teristics to the diesel exhaust and coal combus-
tion products indicate a capability for sensor SA in
combination with a CO sensor to discriminate a
mine fire from diesel emissions.

A'smoke sensor alarm value is defined for this
analysis as-the average sensor output signal less
ten standard deviations from the prefire ambient
condition. The mean value for sensor SA and SB
is given in Table 2, and the standard deviation for
SA and SB is listed for each experiment in Table
4. The alarm times, based’ upon the defined vari-
ation from the sensor's mean value in ambient
conditions, for smoke sensors SA and SB, as well
as the optical density relative to the pre-fire
ambient environment are shown in Table 5. The
optical density, D, is calculated from equation (1)
with Ip defined as the measured optical transmis-
sion through the air in the presence of diesel
emissions. The CO alert time was determined by
the CO cell of the diesel discriminating mine fire
sensor. Since the fires in these experiments did
not produce CO concentrations of 10 ppm above
ambient, a comparison is made with the CO alert
value of 5 ppm. Smoke sensor SA, with an instan-

taneous optical measurement, alarmed earlier -

than the diffusion mode point type smoke sensor
-SB, which alarmed earlier than the diffusion mode
CO sensor alert time. A comparison of these
alarm times, with the time for onset of flaming
combustion and the smoke transport time in
Table 1, shows that the smoke sensor SA
detected the coal fire in its smoldering stage for
each experiment, whereas the CO alert occurred

in the coal flaming combustion stage for experi-
ment Nos 2 - 4. The average optical density of the
smoke sensor SA’s alarm relative to the diesel
environment for experiment Nos. 2 - 4 was 0.0025
m’; for sensor SB it was 0.012 m", and for the CO
sensor it was 0.024 m". These values are to be
compared with an optical density of 0.022 m*
which corresponds to a mine fire smoke sensor
alarm value. At an optical density of 0.022 m* the
visibility in the smoke is less than 36 m based
upon visibility studies (Rasbash, 1975). Smoke
sensor SA’s signal had decreased sensor SB’s
signal at an average 28.1 pct From its prefire
signal, and smoke average of 11.8 pct from its pre
- fire signal at an optical density of 0.022 m rela-
tive to the diesel environment for experiment Nos
2-4. Sensor SA's significant response to a slowly
developing fire, yet its ability to mask the diesel
emissions, demonstrates that a smoke sensor
with sensor SA’s response characteristics is a
candidate for a diese! discriminating fire sensor.

In the transition associated with the starting of
the diesel engine in experiment Nos 2 - 4, sensor
SA's signal reached minimum values which were
19.2, 5.7, and 4.7 pct decreased from the
ambient, respectively before increasing, and
before the CO alert value of 5 ppm was reached.
In the transition from the steady diesel emission
environment to the growth of POC associated
with coal combustion in these experiments
sensor SA’s signal had decreased 38.0 25.4 and
26.5 pct from the ambient value in the diesel
emissions at the 5-ppm CO alert value. This
greater response of SA to the coal fire POC at a
CO value of 5 ppm than to the diesel emissions
before the CO reached 5 ppm is a discriminating
response characteristic of SA between diesel
exhaust and a coal fire’s POC. This property of
the magnitude of the response of SA and its
simultaneous occurrence with a 5 ppm CO alert
value is significant for discriminating a coal: fire
from diesel exhaust.

The rate of increase in diesel emissions asso-
ciated with starting the engine was much greater
than the POC rate of increase associated with the
coal combustion. in experiment No. 4 the average
rate of increase in CO associated with the diesel
engine's startup was 0.0716 ppm/s, and the
average rate of rise in CO associated with the coal
combustion was 0.00141 ppm/s. For the slowly
developing coal fires in these experiments,
sensor SA’s signal had a small rate of increase, or
remained constant, or continued to decrease for
Experiment Nos. 2, 3, and 4, respectively when the
5 ppm CO alert was reached. However, the signif-
icant reduction in SA’s signal, between 25.4 and
38.0 pct for experiment Nos. 2 - 4, had occurred in
the case of coal combustion as compared to the
diesel engine's startup. This indicates a combus-
tion of SA and a CO sensor is a possible candidate
for early mine fire detection of a slowly developing
coal fire in a diesel environment.


20 4.05

4.00
3.95

{3.90
43.85

SA, V

3.80

43.76

3.70

-9,046 8,646

Figure 2: CO and sensor SA response to diesel
emissions for experiment No 4

Bob das
esr i 3
ee 7°"
© oak 432
Sia 3.0

300 400 500

: Sensor SA and light monitor response to
diesel emissions for experiment No 2

20 0.95
woen 0.90
yeh
0.85
€
B 1ap 0.20 >
= 3
8 ae 0.75
40.70
4r 0.65
A 0.60
-9,846 9,446 -9,046 ~8,646
TIME, s

: CO and sensor SB response to diese!
emissions for experiment No 4

99.0

4.08

da
S 98.5 00
= 50.0 7298
g
— 3.90 >
B s70 305 Z|
Eee 3s Z
= cost 2% vane monitor 3.80
SB seof =88 ors
95.5 3.70

9,846 -9,446 —-9,046 -8,646

TIME, s

Figure 4: Sensor SA and light monitor response to
diesel emissions for experiment No 4

three experiments. The response of the light
monitor to the diesel emissions was quite
different for experiment Nos. 2 and 4. Figure 5
shows the response of SA and the light monitor
for experiment No. 2. In experiment No. 2, the
light monitor's output signal followed that of
sensor SA with a characteristic dip in response to
the initial surge of the diesel emissions. The differ-
ence in the light monitor's response between the
experiments can be attributed to the emissions of
the locomotive in experiment No. 4 which were
absent from experiment No. 2.

There is a difference in optical wavelength
between the light monitor and sensor SA. The
light monitor operates in the visible, and SA oper-
ates in the infrared. The optical scattering and

Exp. Time,s
CO (Sppm)/ CO (10ppm)
2. 28 NA
3 40 690
4 () 32

Table 3: Lag time of CO alert and alarm times rela-
tive to time of minimum in SA

absorption properties of the diesel emissions as a
function of the light wavelength also differentiates
the response of optical sensor SA from ionization
sensor SB. Sensor SB responds to smoke partic- .
ulate number more effectively than particulate
diameter.

The decrease in smoke sensor SA's signal
followed by a signal increase in response to the
diesel emissions while the measured CO
increased was a characteristic of the diesel's
performance in experiments 2-4. SA’s signal
reversal occurred prior to the CO reaching its alert
value. The lag time between sensor SA's
minimum and the CO alert and alarm times asso-
ciated with a 5 and 10 ppm diesel emission CO
rise above ambient is listed in table 3.

Acombination of the optical smoke sensor, SA,
and the CO sensor signal characteristics.provides
the basis for a distinguishing signature for diese}
emissions. This characteristic is to be compared
with the response of smoke sensor SA and the CO
sensor to a slowly developing coal fire.

The response of smoke sensors SA and SB to
the coal fire POC in the presence of diesel emis-
sions for experiment No. 4 is shown in Figures 6 -
7. The sensors respond continuously to a change
in the POC associated with the increase in the
measured CO concentration. Smoke sensors SA
and SB respond similarly to the fire, as apposed
to their characteristically different response to the
diesel emissions in Figures 2 and 3.

The expected time of arrival of the POC asso-
ciated with smoke and flame generation is indi-
cated in Figures 6 - 7.

Although it is not possible to infer the response
of sensor SA to a variable diesel output from
these data, the distinct sensor response charac-


Exp. SA,Volt SB,Volt
1 0.014 0.0028
2 0.009 0.0026
_3 0.018 0.0033
4 0.010 0.0028

Table 4: Standard deviation of pre-fire background
‘signal :

25

E 20 4
8
z2
So 18F 4
=
= NO
E tof — cco 4
2
&
3
2 5
fet
8
°
246 834 1,914 2,994 4,074
TIME, s

Elgure 8: Response of diesel discriminating mine
fire sensor SC

The response of SA and SB to POC in experi-
ment No. 1 without diesel emissions resulted in
an alarm at an optical density significantly less
than the relative optical density at which alarms
occurred in experiment Nos. 2 - 4. A factor which
could effect this, is the absence of pulverized coal
in experiment No. 1. This effects the CO and
smoke production. The optical density at which
an alarm occurs in this case shows the advantage
of a smoke sensor over a CO sensor for early fire
detection.

Figure 8 shows the response of sensor SC to
the slowly increasing coal fire of experiment No.
4. The value CCO, which is the excess CO
produced by the fire, did not reach zero because
of the high ratio of CO to NO. The average diesel
CO and NO were 17 and 1 ppm above ambient.
The rate in rise in CO associated with the fire is
0,00141 ppm/s. At this rate of rise, the CO
reaches an alert value of 5 ppm above back-
ground in 1 hour. The value of CCO in figure 8
shows some nonsteady characteristics, but no
significant rise to indicate a fire. The rate of rise in
the CO is offset by the decrease in the value of
CCO. This indicates sensor SC would be more
appropriate for an increase in CO from a more
rapidly developing fire than considered in this
experiment.

Conclusions

For the one coal fire experiment with no diesel
equipment, and the three experiments with diesel
equipment operating in a steady state mode, the
optical path smoke sensor alarmed earlier than
the diffusion mode ionization smoke sensor. Both
smoke sensors alarmed earlier than the diffusion
mode CO sensor and at an optical density less
than 0.022m". .

A commercial diesel discriminating fire sensor
based upon the ratio of CO to NO failed to detect
a slowly increasing coal fire with a CO production
rate of 0.00141 ppm/s. It was shown that the tran-
sient emissions associated with starting the diesel
could be discriminated from a slowly developing
coal fire with a combination of an optical path
smoke sensor and a CO sensor. This involved the
interpretation of the rate of change of the smoke
sensor's signal associated with diesel emissions
as a characteristic to be differentiated from that
associated with increasing POC from developing
coal combustion. This result is limited to the
experimental conditions considered. Future
research must focus on a decision making
process, such as a neutral network, which can be
applied to fire sensor response from a wide
variety of fire and diesel emission conditions.

Acknowledgment

The authors acknowledge the miners who
maintain Safety Research Coal Mine at the Pitts-
burgh Research Laboratory for their assistance in
preparation of the experiments.

References

* CFR, Code of Federal Regulations, Title 30, part
75.351 a 3.1, Atmospheric Monitoring System, July
1997 a, p, 478.

* CFR, Code of Federal Regulations, Title 30, part
75.344. a 2. ii, Compressors, July 1997b, p. 478.

+ Edwards, J.C. and Friel, G.F, (1996) “Comparative
mine Evaluation of Carbon Monoxide and
Smoke Sensors,” USBM R1 9622, 11 pp

* Litton, C.D. Conti. R.S. Tabacchi, J.G., and Grace, R.,
(1998) “Evaluation of a Nitric-Oxide ‘Compen-
sated Carbon Monoxide Fire Sensor", USBM IC
9339, 10 pp.

* Rasbash, D.J., (1975), “Sensitivity Criteria for Detec-
tors Used to Protect Life” Fire International, v.5, no.
40, pp 30 - 49.

Sensor SA Sensor SB CO =5 ppm
Exp. | Alarm time,s. D,m" Alarm time,s |__D, m* Alert time,s |_D,m"*
1 2178 0.00084 2550 0.0044 NA. : NA
2 1484 0.0026 2072 0,0099 3690 0.032
3 1984 0.0026 2954 0.015 3009 0.016
4 1788 0.0023 2904 0.011 4047 0.023

Table 5: Smoke sensor and CO alarm times


Mine Fire Detection in the Presence

Paper presented at the 8th U.S. Mine Ventilation
Symposium, Rolla, Missouri. The Editor acknowledges
the University of Missouri - Rolla for permission to
reproduce this paper.
by J.C. Edwards, R.A. Franks, G.F Friel, C.P Lazzara, and J.J.
Opferman Pittsburgh Research Laboratory National Institute for
Occupational Safety and Health Pittsburgh, U.S.A.
NEES
A series of four coal combustion experiments was
conducted at the National Institute for Occupational Safety and
Health's (NIOSH) Pittsburgh Research Laboratory (PRL) in the
Safety Research Coal Mine (SRCM) to evaluate the response
of fire sensors to a small 0.61 m square smoldering coal fire
which transitions to flaming combustion in the presence of
diese! emissions. An optical path smoke sensor alarmed
earlier than a point type diffusion mode ionization smoke
sensor, which alarmed prior to a CO alert value of 5 PPM
above ambient. The presence of steady state diesel emis-
sions resulted in a decrease in the optical smoke sensor
analog output voltage signal by less than 1.4 pct for the three
coal fire experiments in which a diesel engine was operating,
whereas the ionization smoke sensor output decreased
between 10.8 and 26.7 pct after the initial surge of the diesel
engine. A commercial diesel discriminating fire sensor did not
alarm for a fire in the one experiment for which it was used.

The results of the experiments demonstrated that an optical
path smoke sensor might be used to detect a coal fire under
the experimental conditions considered of starting a diesel

engine followed by a slowly developing coal fire.
EA

Introduction

Mine fire detectors as a part of an atmospheric
mine monitoring system are used to monitor
temperature and products - of - combustion
(POC). Alarm and alert values are based upon
temperature, CO concentration, and smoke
optical. density. Carbon monoxide and smoke
sensor capability has been previously evaluated
(Edwards and Friel, 1996) for in-mine diesel fuel
fire conditions. In those experiments, the
measurements were made in an ambient back-
ground of fresh air. With the introduction of diesel

- powered equipment in an increasing number of
underground coal mines, the capability of mine
fire detectors to discriminate a coal fire from diesel
particulate and CO emissions.is a concern for

of Diesel Emissions

adequate underground mine fire protection. The
change in the atmospheric CO concentration or
optical density must now be referenced to a
changing background of diesel emissions. There
are several approaches to resolve this problem. If
the CO is selected as the signature of interest, one
method is to differentiate the CO produced by the
fire from that produced by the diesel engine with a
second POC signature which would be absent
from the fire POC. A commercial diesel discrimi-
nating fire sensor compares the relative CO to NO
ratio. This method relies upon a historical trend
analaysis of the CO associated with the NO
produced by the diesel engine under different
operating conditions. Evaluation of this tech-
nology was made for a rapidly developing coal fire
(Litton, et al., 1993). A second approach is to
examine the rate of change in CO production as a
‘stand alone POC signature. The rate of change in
CO historically collected for a diesel engine can be
used to differentiate the diesel from a fire based
upon the rate of CO change associated with fire
growth. A third approach to the problem is to
Gifferentiate particulate emissions of the diesel
from that of the fire with smoke sensors. This
method relies upon geometric properties such as
the smoke particulate size and shape, and a phys-
ical property such as its index of refraction. Optical
and ionization smoke sensors: will respond differ-
ently to smoke. An optical sensor is generally
more responsive to larger particles associated
with smoldering combustion, whereas an ioniza-
tion sensor is more responsive to smaller particles
associated with flaming combustion. The charac-
teristic response of a smoke sensor to diesel emis-
sions is to be investigated.

The objective of this research is to investigate a
fire detection method to discriminate a coal fire
from diesel emissions. As part of the development
of a mine fire detection strategy for discriminating
amine fire from diesel exhaust, a series of coal fire
experiments was conducted in the National Insti-
tute for Occupational Safety and Health (NIOSH),
Pittsburgh Research Laboratory's (PRL) Safety
Research Coal Mine (SRCM) to evaluate the
response of fire sensors to.a slowly developing
coal fire in the presence of diesel exhaust. These
experiments provide an opportunity to evaluate
the response of standard CO and smoke mine
fire sensors, a commercial gas descriminating fire
sensor, and a commercial optical smoke sensor
to a slowly developing coal fire which could result
from frictional heating of coal in an underground


coal mine. The different response characteristics
of an ionization and an optical smoke sensor to
diesel exhause and smoke from an incipient coal
fire will provide guidance for future development
of mine fire diese! descriminating sensors and
strategies. The intent of using a slowly increasing
coal fire is to demonstrate the capability of early
and reliable mine fire detection.

Experimental procedure

The coal fire detection experiments in-the pres-
ence of diesel engine exhause were conducted in
the mine entry and room section of the SRCM
shown in Figure 1. Room 10, in which the fire
zone is located, has an average height and width
of 2.0 m and 3.9 m, and F-Butt has an average
height and width of 1.9 m and 4.5 m. The brattice
at Room 10 and B-Butt was adjusted to regulate
the air flow in Room 10 and F-Butt. Air quantity
measurements were made at the fire zone and
near the end of F-Butt 7,6 m downwind of sensor
station S2. A hot wire anemometer was used to
make five point time averaged linear air velocity
measurements. There was significant variation in
the airflow over the cross section of the fire zone in
room 10 because of the right angle split 18.4 m
upwind of the fire station at B-Butt and because of
the lack of thermal equilibrium in the airflow due to
a temperature variation between B-Butt and F-Butt
along Roorn 10. Near station S2, the air was trans-
ported 117 m along a straight entry and thermal
equilibrium with the mine entry surface was estab-
lished. The air quantity measurements at the fire
zone and near the end of F-Butt are denoted by
Q,, and Q, respectively. The fire source consisted
of 10 - 15 kg of Pittsburgh seam coal with diameter
less than 6 cm distributed uniformly over a pan
0.61 m on each side. Less than 1 kg of pulverized
coal! dust was distributed over the coal for experi-
ments 2 - 4 to enhance the smoldering combus-
tion. Heating of the coal was provided with five 60
ohm electrical strip heaters connected in parallel.
Electrical power was supplied incrementally to the
heaters over a maximum range of 1 to 2 kW. Table
1 shows the experimental air quantity conditions
as well as the time of first observation of smoke
production, (Smoke) and flaming combustion,
(Flame), at the fire source. The increase in air
quantity, Q, /Q, > 1, is due to leakage into F-Butt
around brattice curtains along F-Butt from a
parallel airway which was connected by a bore-
hole to the surface. The smoke expected transport
time T, from the fire to station S2 is estimated from
the accessible entry volume and the measured
volumetric flow rates, and is shown in Table 1. For
experiment No. 1, there was no diesel in the entry;
for experiment Nos 2 - 4, there was a diesel scoop
operational in F-Butt 79 m upwind of sensor
‘station S2. In experiment No. 4 there was also a
diese! locomotive operational in F-Butt approxi-
mately 15 m upwind of the diesel scoop. Diffusion
mode CO sensors were located at stations S 1

—_— Time, s
Exp | Q,,m*/s | Qy,m*/s | Smoke} Flame] T,
1 4.52 5.31 240 4490 | 244
2 2.64 4.71 300 2520 | 348
3 3.73 5.72 945 3000 | 362
4 2.91 4.63 540 2640 | 330

Table 1: Experimental conditions

148m 10

Figure 1: Plan view of mine section

and S 2. The sensors were mounted with the diffu-
sion tube inlet approximately 0.8 m from the rib,
and 0. 41 m from the roof.

‘Two smoke sensors were positioned at station
S2. One sensor, SA, sampled over a path, and the
other SB, at a point. Sensor SA was a commer-
cially available optical type sensor with a trans-
mitter and receiver. The receiver was positioned
at S2 near one rib of the entry, and the transmitter
was positioned near the opposite rib at a distance
of 9.5 m upwind from the receiver. The optical
path length was 9.65 m. Sensor SB was a
commercially available diffusion mode ionization
type mine smoke sensor. It was positioned at
entry midwidth at S2 with the smoke inlet the
same 0.41 m distance from the entry roof as the
CO sensors. The analog voltage output from the
smoke sensors provided an indirect measure of
the smoke intensity.

Alight obscuration monitor consisting of a light
source and a photovoltaic cell separated by a
distance of 1 meter was mounted mid-height at
S2 with its optical path transverse to the airflow
and parallel to the entry floor. The attenuation in
the light by the smoke was measured by the
voltage output from the photovoltaic cell. The
smoke optical density D is defined by :

D= tL logio () mt (1)

where the light intensity I is directly propor-
tional to the voltage, I is the intensity in ambient
air, and L, equal to 1.0 m in this application, is the
optical path length.

As part of the fire monitoring system for exper-
iment No. 4, a commercial discriminating mine
fire sensor (SC) was located at station S2._ at entry
midwidth with its diffusion tube inlet port 0.41
from the entry roof. This sensor, which operates in
the diffusion mode, contains two chemical cells.
One cell detects CO, and the other cell detects


NO. Based upon a historic collection of data over
a 2 hour period, the sensor through an internal
processor associates CO with NO produced by
the operational diesel equipment. Any subse-
quent changes in the ratio of CO to NO deter-
mines the excess CO produced by the fire.

Prior to each experiment, the sensors were
calibrated. The diesel engines were moved into
the entry after the sensor calibration and ventila-
tion measurements. Their presence in the entry
increased the entry’s aerodynamic resistance
which would be expected to reduce the airfiow.
Data from each of the fire sensors was collected
in a realtime mode and transmitted to an above
ground mine monitoring computer. The data
collection occurred every 2 seconds.

Results

At station S2, the CO reached an alert value of
5 ppm above ambient for experiments Nos. 2 - 4,
and the smoke optical density reached an alarm
value of 0.022 m' for all four experiments. A CO
concentration of 5 ppm above ambient is desig-
nated the alert value for a CO sensor when used
as part of a.coal mine atmospheric mine moni-
toring system (CFR, 1997 a). An optical density of
0.022m" is designated a smoke sensor alarm
value (CFR, 1997b) when used at an under-
ground coal mine compressor station: These
values are relative to the prefire airflow conditions
which include the diesel emissions.

Table 2 shows the average background values
of smoke detectors SA and SB, and the light
transmission measured by the optical light
monitor before the diesel emissions and before
the fire. The pre-fire values are averages within a
5 minute time period before the heating of the
coal. Startup of the diesel engine resulted in a
surge in diesel emissions -with a transient less
than 5 minutes in duration before the emissions
settled into a steady production rate. The pre-fire
analog signal of sensor SA in the presence of
diesel emissions decreased by less than 1,4 pct
from its value in clear air, whereas sensor SB’s
signal decreased between 10.8 and 26.7 pct.

The CO sensors at Stand S2 were used to
determine the POC transport time, T,, listed in
‘Table 2 based upon the time difference in a 1 ppm
tise in the CO above the ambient value when the
fire was initiated. These values are augmented by
the expected transport time from the. fire to S1.
The measured values of T,, exceed the expected

values T,, in Table 1. This is due to the dispersion
ofthe fire POC through turbulent transport along
the airway and dilution due to leakage into the
airway around brattices which block rooms
connected to parallel airways. This effect is
partially offset by the increased air velocity in the
entry due to leakage. Measured and predicted
values of the transport time are in closer agree-
ment in experiments 2 and 3 than in experiments
1 and4 due to the greater use of pulverized coal
dust in experiments 2 and 3 to produce increased
quantities of CO. An increased CO production
rate will reduce the effect of concentration reduc-
tion due to dispersion for a given airflow rate. In
experiment No. 1, no pulverized coal was used
and in experiment no 4, half as much was used in
comparison with experiment Nos. 2 and 3. The
new ambient values for SA and SB in the diesel
environment were achieved only after quite
different transient responses to the onset of the
diesel emissions. An examination of the response
of SA and SB to the diesel emissions is shown in
Figures 2 and 3 for experiment No 4. The diesel
emissions are tracked by the CO measurement in
Figures 2 and 3. The maximum rate of increase in
CO was 0.127 ppm/s' with an average rate of
0.0716 ppm/s over the 320 second period from
-9,574 s to -9,254 s. These times are relative to
initial heating of the coal at zero time. Figure 2
shows that SA responds rapidly to the onset of
diesel emissions when the diesel engines were
started, as it would to a fire, but returns to an equi-
librium value slightly offset from its prediesel
ambient value.

Smoke sensor SB, as shown in Figure 3,
responds to the diesel emissions, but its output
signal has an asymptotic signal decrease to a
new equilibrium value. The new equilibrium volt-
ages for sensors SA and SB, 15 minutes after the
sensors detect the diesel emissions are offset 3.0
and 24.8 pct, respectively from the prediesel
emissions voltages. Figure 4 shows a compar-
ison of the response of sensor SA and the light
monitor. The light monitor's new equilibrium value
is offset 1.1 pct from the prediesel value. Over the
subsequent 2.7 hour period before ignition of the
coal fire, these equilibrium values for the sensors
shift to offset values of 1.2, 26.7 and 2.0 pct from
the prediesel conditions for SA, SB, and the light
monitor, respectively.

The dip in the output signal of sensor SA below
its final equilibrium value in response to the diesel
emissions was a characteristic of SA during all

SA, volt ‘SB, volt Time,s
Exp. No.| Pre-diesel | Pre-fire Pre-diesel | Pre-fire Pre-diesel | Pre-fire tn
1 NA 4.025 NA 0.914 NA 96.28 859
2 3.991 3.935, 0.897, 0.800 98.59 97.49 405
3 3.997 3.951 0.913. 0.780 99.6 99.39 426
4 4.010 3.959 0.899 0.659 98.6 96.6 646

NA = not available
Table 2: Smoke sensor and light transmission