United States
Environmental Protection
Agency
Environmental Sciences
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S3-84-093 Nov. 1984
&EPA Project Summary
Evaluation of Trained Visible
Emission Observers for Fugitive
Emission Opacity Measurement
Thomas H. Rose
The stack of a visible emission
training school smoke generator was
modified to emit white or black smoke
in a horizontal direction near ground-
level to simulate fugitive emissions.
Trained smoke observers measured the
opacity of these simulated fugitive
emissions against a dark terrestrial
background and under clear sky lighting
conditions. They measured both black
and white emissions generated at four
different opacities--! 5, 20, 30, and 40%.
The observers also measured the same
opacity of smoke plumes emitted from
an unmodified training school smoke
generator. These vertical-flow smoke-
stack plumes were evaluated against a
sky background to provide reference
data on the observers ability to measure
the opacity of conventional stack
plumes under the same clear sky
lighting conditions used for the fugitive
plume tests.
The observers measured opacities of
white fugitive emissions with
accuracies similar to the conventional
stack emissions when opacities were in
the range of 15 to 20%. As opacity
increased, however, the observers
increasingly underestimated opacity.
At 40% opacity, observer measure-
ments were lower on average by about
8% opacity. The opacities of black
fugitive emissions were underesti-
mated at all opacity levels. Opacity was
lower on average by 5% opacity at the
15% opacity level and by 11 % opacity at
the 40% opacity level. It was also
observed that for both black and white
simulated fugitive emission plumes, the
observers sensitivity to changes in
opacity levels declined relative to the
conventional vertical stack plumes.
This Project Summary was developed
by EPA's Environmental Sciences Re-
search Laboratory. Research Triangle
Park, NC, to announce key findings of
the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Many types of airborne participates
and aerosols are not emitted from
conventional vertical stacks. Instead,
these emissions may come from win-
dows, roof monitors, vents, conveyor
belts, hoppers, storage piles, construction
sites, roads, and a variety of other sources.
Often these unconfined emissions origi-
nate close to the ground and move with
the wind in a horizontal direction. Unlike
conventional smokestack plumes that are
viewed against the sky, these emissions
are usually viewed against a darker
terrestrial background. This study was
designed to determine the biases, if any,
introduced when certified Method 9
smoke observers measure opacities of
horizontal-flow, ground-level emissions
Experimental Design
Smoke Generators
Two smoke generators were used Both
generators were originally designed for
training smoke observers, however, for
the study one was modified to provide
horizontal emissions near ground level
This was achieved by raising the stack
only partially to a horizontal position and
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placing an elbow between the lower
vertical stack element and the upper
horizontal stack element The elbow was
caulked and shimmed to prevent leaks.
This method of generating horizontal
emissions was selected after it was
determined that the plume would remain
uniform in both vertical and horizontal
axes through the transmissometer and at
the emission point. The determination
consisted of viewing the white plume
against a black velvet background at close
range and the black plume against a
white background The appearances of
both plumes were uniform along both
axes To further simulate the fugitive
nature of horizontal emissions, a 12-
mch-wide board was used to block an
observer's view of the stack end
The other smoke generator was set up
in the conventional manner, with the
stack upright to emit a vertical plume
Observers
The observers selected for the study
were six inspectors from a state agency
and two air pollution personnel from local
contractors Each participant possessed a
current Method 9 certification and a past
record of accurate smoke reading, as
evidenced by hisabilitytocertifypromptly
at a smoke school. The Method 9
certification procedure is described in the
Federal Register. The participants ranged
in age from 26 to 38 years old, with an
average age of 31. Three possessed
college degrees, three had associate
degrees, and the other two had some
education beyond high school. Their
experience at reading visible emissions
ranged from one to eight years, with an
average of 4.1 years.
Observer Tests
Both black and white simulated (hori-
zontal-flow) fugitive emissions were
measured under clear sky conditions.
Black and white conventional (vertical-
flow) plumes were also measured under
clear sky conditions to confirm the
observers' abilities to assign unbiased
opacity values to conventional plumes.
The opacity levels selected for the study
were 40, 30, 20, and 15 percent. For
each opacity level, the observers were
required to read for 12 minutes. Within
that 12-minute period there was a period
of just over six minutes of steady opacity
smoke. The average of 24 consecutive
readings by an observer during this six-
minute period was the EPA Method 9
evaluation of the smoke opacity. The
observers were shown the same opacity
levels from each generator but in random
order. They were given no review of
emission opacities prior to testing and
were given no instructions except how to
complete the test form and to read on
signal. Smoke opacity measurements
were recorded on computer compatible
data forms in bound books. Th3 observers
were instructed by a pre-recorded tape to
read at 15-second intervals to assure
Method 9 compatibility and standardiza-
tion of the time reference. At the same
time, the data logger made a reference
mark on the transmissometer strip chart
record.
Results
To observe the effect smoke color and
mode of emission had upon the observers,
opacity measurements were plotted
against actual transmissometer values. A
slope of 1.00 would show equal sensitivity
between observer and transmissometer
to opacity changes.
Panel (averaged observer) opŁ
measurements of conventional s
plumes (white and black), under blue
conditions and observed against a
background, agreed closely w
transmissometer opacity measuremt
over the range of opacity levels. Slope
1.17 and 1.01 were calculated for
white and black smoke, respectiv
Thus, the observers showed on aver
an ability to correctly measure the opa
of normal plumes with little bias.
Measurements of simulated (honz
tal-flow) fugitive emissions for wl
plumes on a clear day (Figure 1) revea
no systematic difference (bias) betw<
observers and transmissometer readu
for opacities around 15-20%. At hig
opacities, however, an increas
negative observer bias was seen (Fig
1). At 40% opacity, this bias resultec
observer panel readings around
opacity lower than transmissome
values. For black emission lower obsen
30-
20-
10-
Mean ± 95%
Confidence Interval
Regression Line
10
20
30
Transmissometer
% Opacity
40
50
60
Figure 1. Observer opacity evaluations versus transmissometer measured opacities o
simulated white fugitive plumes viewed against a terrestrial background on a clea,
day.
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panel measurements were seen at all
opacity levels (Figure 2). At 1 5% opacity,
measurements were 5% opacity low; at
40% opacity, they were 11 % opacity low.
Overall, observer sensitivity to opacity
changes, as evidenced by the slopes of
the curves, declined for both the white
and black (horizontal-flow) fugitive
plumes. The change in observer
measured per change in transmissome-
ter measured opacities declined
from near 1.0 for the conventional (verti-
cal-flow) plume measurements to 0.62
and 0.77 for the white and black simu-
lated (horizontal-flow) fugitive plume
measurements, respectively.
Conclusions and
Recommendations
The panel of smoke observers
measured the opacities of simulated
white (horizontal-flow)fugitive emissions
with accuracies similar to (vertical-flow)
plume opacity measurements when
opacity levels were around 15-20%. As
opacities increased, however, the panel
increasingly underestimated them. They
were lower on average by about 8%
opacity at the 40% opacity level.
Opacity measurements for black
fugitive emissions were underestimated
at all opacity levels. At 15% opacity, the
observers measured the simulated
fugitive emissions 5% opacity low, and at
40% opacity they measured them 11%
opacity low.
Observer panel sensitivity to opacity
changes was less for simulated (horizon-
tal-flow) fugitive emissions than for
conventional smokestack plumes. The
change in panel opacity measurement
per change in transmissometer opacity
measurement declined from near 1.00
for the conventional smokestack plumes
to 0.62 and 0.77 for the white and black
(horizontal-flow) fugitive plumes, respec-
tively.
It is recommended that controlled tests
of observer and transmissometer opacity
measurements of simulated black and
white fugitive emissions be conducted for
other environmental lighting conditions,
e.g., on an overcast day. It is also recom-
mended that a lower opacity level around
5 or 10% be included in the tests.
Mean + 95%
y Confidence Interval
Transmissometer
% Opacity
Figure 2. Observer opacity evaluations versus transmissometer measured opacities of
simulated black fugitive plumes viewed against a terrestrial background on a clear
day.
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Thomas H. Rose is with Eastern Technical Associates, Raleigh, NC 27658.
William D. Conner is the EPA Project Officer (see below}.
The complete report, entitled "Evaluation of Trained Visible Emission Observers
for Fugitive Emission Opacity Measurement," (Order No. PB 85-115 152, Cost:
$8.50, subject to change) will be available only from-
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at.
Environmental Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park. NC 27711
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