United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/SR-95/167 February 1996
4>EPA Project Summary
Evaluation of the High Volume
Collection System (HVCS) for
Quantifying Fugitive Organic
Vapor Leaks
EricS. Ringler
Fugitive volatile organic compound
emissions associated with gas and/or
petroleum processing facilities have
historically been difficult and expen-
sive to measure accurately. A measure-
ments technique has recently been
developed that offers the potential for
providing an easy-to-use and cost-ef-
fective means to directly measure or-
ganic vapor leaks. The method, called
the High Volume Collection System
(HVCS), uses a high volume sampling
device and a portable flame ionization
detector (FID) for field analysis. The
HVCS can obtain direct measurements
of mass emission rates without the
need for tenting and bagging. This
study of HVCS method performance in-
cluded both field and laboratory test-
ing. Laboratory evaluation of HVCS
results closely matched EPA method
results with a difference in total mea-
sured emissions of only about 3%. In
one field test, the HVCS matched the
EPA estimate of total facility emissions
within about 4%. In the other field test,
the HVCS measured approximately 18%
more emissions than the EPA method.
However, the bias was present only
early in the test. Later in the test, after
efforts were made to identify and cor-
rect its source, HVCS bias was essen-
tially zero. With some physical and
procedural enhancements, the HVCS
may be offered to EPA for approval as
an acceptable alternative to the EPA
protocol bagging method with gas chro-
matographic analysis.
This Project Summary was developed
by EPA's National Risk Assessment
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
Fugitive emissions of methane and other
organic vapors from leaking pipelines,
valves, flanges, and seals associated with
natural gas, petroleum, and chemical pro-
duction and processing facilities are an
important source of methane and other
organic emissions to the atmosphere. Such
emissions have historically been difficult
and expensive to measure accurately. EPA
Reference Method 21, "Determination of
Volatile Organic Compound Leaks," de-
scribes instruments and procedures that
can be used to locate and assess the
magnitude of such leaks. However, Method
21 does not provide a direct measure of
the mass emission rate. According to the
current EPA protocol, the mass emission
rate is arrived at by associating plant/
component specific information and instru-
ment screening values (per Method 21)
with published EPA emission factors or
correlation equations. These emission fac-
tors and correlations were developed over
the last 15 years, based on field studies
at petroleum refineries, gas plants, and
Synthetic Organic Chemical Manufactur-
ing Industry plants. In these studies,
screening measurements based on
Method 21 were associated with direct
measurements of mass emissions ob-
tained by isolating leaking components and
measuring the pollutant concentration in a
-------
known flow of carrier gas (i.e., tenting and
bagging the leak).
A measurements technique has recently
been developed as a result of work spon-
sored by the Gas Research Institute. The
method, known as the High Volume Col-
lection System (HVCS), uses a high vol-
ume sampling device in front of a portable
flame ionization detector (FID) (Foxboro
OVA Model 108 portable FID). The HVCS
uses a battery-powered pump to draw air
across a leaking component at rates be-
tween 10 and 500 standard cubic feet per
hour (scfh1). Flows are metered using three
calibrated rotameters (100-1000, 10-50,
and 2-20 scfh). The FID is used to mea-
sure the hydrocarbon concentration in the
collected air. Hydrocarbon mass emission
rates are determined from the measured
airflow rates and hydrocarbon content in
the flow. The success of the method de-
pends on capturing all of the leaking gas
from a component in the flow entering the
sample inlet. The inlet is constructed to
enhance this capture (the inlet is shaped
like the mouthpiece of a snorkel). Diffuse
leaks from larger components (such as a
large flange) are captured by wrapping
the component in polyethylene wrap so
that the air flow passes over the entire
leaking surface. A flexible spring coil (toy
slinky) is used to prevent the wrapping
from obstructing the leak or inhibiting the
airflow across the component.
The HVCS was designed to obtain di-
rect measurements of mass emission rates
without the need for tenting and bagging
and offers the potential for providing an
easy-to-use and cost effective means to
measure organic vapor leaks from gas,
oil, and chemical industry sources. The
HVCS has the potential to provide accu-
rate and cost effective emissions data com-
pared to the current EPA protocol methods.
It provides a direct measurement of emis-
sions at the source and is simple and
inexpensive to operate. These capabilities
also provide the means to effectively evalu-
ate alternative inspection and maintenance
programs and select the program that pro-
vides maximum control and minimum cost.
Project Objectives and Scope
The purpose of this study was to com-
plete a detailed evaluation of HVCS
method performance over the wide range
of leak sizes, component types, and oper-
ating conditions characteristic of natural
gas production in the U.S. The focus of
this evaluation is direct comparisons of
HVCS results versus controlled leak rates
1 scfh = 0.0283 std m3/sec.
(laboratory) and EPA protocol "tent and
bag" method results (field). Consideration
is also given to the broader issue of
whether the HVCS can be used to accu-
rately determine total emissions from a
facility. The report presents results from
each of these points of view.
The study included both field and labo-
ratory testing. The field testing assessed
the accuracy of the HVCS method relative
to an EPA protocol emissions measure-
ments method. The goal was to challenge
HVCS performance over the range of leak
rates, component types and sizes, and
operating conditions characteristic of U.S.
natural gas production. A major focus of
the study was to develop performance
criteria for field use of the HVCS method.
This included identifying strengths and
weaknesses of the prototype HVCS sys-
tem, making recommendations for im-
provement, identifying conditions under
which best and worst HVCS performance
is achieved, and recommending proce-
dures for obtaining optimum results. The
laboratory testing was conducted to es-
tablish the accuracy and precision of the
EPA protocol (bagging) and HVCS meth-
ods compared to controlled leak rates.
This testing provided necessary support
to the field test results by examining the
performance of both methods under con-
trolled conditions. In the laboratory, many
of the sources of uncertainty associated
with field testing were eliminated; the most
important source is that the true leak rate
in the field is unknown.
A detailed Quality Assurance Project
Plan (QAPJP) was prepared, reviewed, and
approved, prior to beginning any actual
testing. This plan served as a guide
throughout the field testing and final data
analysis.
Summary of Testing and
Results
Laboratory testing was completed be-
fore the field testing and consisted of EPA
method and HVCS measurements on 134
constructed leaks (75 HVCS and 59 EPA)
representing a range of leak rates and
component types typical of natural gas
production. The EPA protocol vacuum
method was selected for the study based
on results of preliminary testing with both
EPA protocol methods. Field testing was
conducted at two gas production fields:
one in South Texas and one in West
Texas. A total of 135 paired EPA and
HVCS quantifications were obtained in the
field studies (56 in South Texas and 79 in
West Texas). The field sites were selected
to represent "typical" facilities where one
would expect to find leaking components.
This profile required an average facility
age of 15 or more years, moderate oper-
ating pressures (< 1000 psi2), low hydro-
gen sulfide levels, and no active leak
detection and repair program. The sites
had to contain a sufficient number of wells,
compressor stations, and other installa-
tions located in a small enough area to
permit cost effective screening and quan-
tification. Leaks were identified with soap
solution, and selected leaks were quanti-
fied by both the EPA and HVCS methods.
Gas composition was determined in the
field by gas chromatography (GC) for each
bag sample.
Laboratory Test Results
The EPA and HVCS methods were both
evaluated in laboratory studies. Since the
EPA method, like any measurement, is
subject to imprecision and bias, quantifi-
cation of these data quality indicators was
essential before the EPA method could
reliably be used in the field as a measure
of HVCS performance. Only limited con-
trolled testing of EPA protocol method per-
formance has been conducted previously,
and this did not include treatment of er-
rors associated with the total sampling
system, including the "bag" or component
enclosure.
The laboratory tests conducted for this
study were devised to represent "real
world" components and leak types so that
overall errors (including total sampling er-
rors) are represented. Actual pipeline com-
ponents were assembled in such a manner
that induced leak rates could be carefully
controlled and accurately metered against
a primary flow standard. Components
tested included a 2 in.3 gate valve, a 4 in.
threaded coupling, a 6 in. pipe flange, and
a 1/2 in. pump shaft. These represent
component types and sizes that are typi-
cally encountered at natural gas produc-
tion and processing facilities. Details of
the laboratory test bench setup and test
matrix are given in the QAPJP. Laboratory
test procedures were identical to the field
test procedures. Leak rates induced in the
laboratory study span 4 orders of magni-
tude and are representative of the range
of leaks likely to be encountered at actual
gas and oil production facilities. Induced
leak rates ranged from 0.02 to 20 stan-
dard liters per minute (slpm) (.04 to 40 Ib/
day as methane4).
Laboratory test results are summarized
in Table 1. Percentage differences are
2 1 psi = 6.89 kPa.
3 1 in. = 2.54 cm.
4 1 slpm = 2lb/day(thisconvertsthemetricstandard liter
per minute leak rate to the nonmetric pounds per day
mass equivalent of the principal gas, methane).
-------
Table 1.
Laboratory Results Summary
Method Bias
EPA Method Bias vs. Induced
HVCS Bias
HVCS Relative Bias
HVCS "True" Bias
Mean
(MVU)a
-7.4%
-8.3%
0.3%
-7.1%
Lower
95% Limit
-9.7%
-12.0%
-9.0%
-15.7%
Upper
95 % Limit
-5.0%
-4.3%
8.5%
0.5%
No.
55
32/55b
9/22b
9/22b
Difference in Total Emissions
EPA Method vs. Induced
HVCS Method vs. Induced
EPA vs. HVCS
Leak
(slpm)
96.1
175.1
25.1
(EPA)
Result
(slpm)
90.4
164.5
24.4
(HVCS)
Diff(%)
-5.9
-6.1
-2.8
No.
55
55
22
* MVU = Minimum variance unbiased.
b Summary results are calculated using only data that are unaffected by a bias caused by the position
of the FID probe in the HVCS exhaust., This bias was discovered during the laboratory study, and
measures were taken to prevent the bias from occurring during the field study.
used as the measure of bias in four cases:
(1) EPA results versus known leak rates,
(2) HVCS results versus known leak rates,
(3) HVCS versus EPA results (HVCS rela-
tive bias), and (4) HVCS versus bias cor-
rected EPA results (HVCS "True" bias).
The EPA bias correction is -7.4%, as de-
termined in these studies. HVCS "true"
bias is a useful measure of field perfor-
mance, since it compares the HVCS re-
sults to an estimate of actual emissions
(as estimated from the EPA method re-
sults), rather than relative to another mea-
surement (the EPA method).
Results are summarized in terms of a
minimum variance unbiased estimator of
the mean, lower 95%, and upper 95%
confidence interval limits. These summary
statistics were selected based on the natu-
ral log-normal distribution of the percent-
age difference used to measure bias.
In the laboratory study, the HVCS and
EPA methods gave very similar results
(relative bias is 0.3%). Both methods
showed a moderate negative bias (7 to
8%) compared to the known leak rates.
For the EPA method, the negative bias is
probably due to incomplete mixing in the
bag, so that outside air is taken up prefer-
entially to the leaking gas. For the HVCS
method, the negative bias is probably due
to incomplete leak capture, or failure of
the HVCS system to fully capture the leak-
ing gas in the slipstream of air pulled in
around the component. In the laboratory
study, the components were not fully en-
closed during HVCS sampling. In the field
study, however, components were thor-
oughly wrapped in polyethylene film dur-
ing HVCS sampling. This appeared to
improve leak capture.
To assess the ability of the HVCS to
quantify total facility emissions, total emis-
sions from all leaking components in the
laboratory test results may be viewed as
total facility emissions. The total induced
leak rate from all components tested by
the HVCS method was 175.1 slpm (84.6
Ib/day). The total leak rate measured by
the HVCS method was 164.5 slpm (79.5
Ib/day), for an overall difference of -6.1%.
The total induced leak rate from all com-
ponents tested by both the HVCS and
EPA methods was 26.1 slpm (54.0 Ib/
day). The total leak rate measured by the
EPA method was 25.1 slpm (52.0 Ib/day),
and the total leak rate measured by the
HVCS method was 24.4 slpm (50.5 Ib/
day). The overall difference between the
EPA and HVCS methods was -2.5%. The
total induced leak rate from all compo-
nents tested by the EPA method was 96.1
slpm (198.9 Ib/day). The total leak rate
measured by the EPA method was 90.4
slpm (187.1 Ib/day), for an overall differ-
ence of -5.9%.
Field Test Results
To locate leaks for the study, over
21,000 components were screened at two
gas production facilities located in sepa-
rate areas (South Texas, and West Texas).
Table 2 summarizes the number and type
of components screened and leaks found
at each location.
Table 3 summarizes the field study re-
sults using summary statistics as described
for the laboratory study.
At the South Texas site, measured leak
rates ranged from less than 0.01 to more
than 9 slpm as measured by the EPA
method. Some larger leaks were not mea-
surable by the EPA method. The HVCS
method measured leak rates up to 13
slpm. The average leak rate was about
1.2 slpm, with a median of 0.25 slpm.
Total measured emissions (EPA method)
were about 70 slpm, or about 140 Ib/day,
representing most of the leaks in two of
three gas fields served by the facility. There
appears to be a positive bias in the South
Texas field data compared to the labora-
tory results; however, a statistical com-
parison ("t" test) gives a probability that
the means are different by about only 65
to 75%. That is, given the variability in the
data, the means cannot be distinguished
with a very high level of statistical signifi-
cance. In terms of an inventory, the rela-
tive bias overstates the difference between
the two methods. Overall measured emis-
sions (final validated data only) are 58.2
slpm (about 120 Ib/day) for the HVCS
method and 55.8 slpm (about 115 Ib/day)
for the EPA method, an overall difference
of only 4%. The reason for the overstate-
ment is that small differences in measure-
ments of small leaks often yield large
percentage differences. The negative bias
observed in the laboratory studies was
probably eliminated by the additional
"wrapping" of components that was rou-
tinely performed in the field.
At the West Texas site, measured leak
rates ranged from less than 0.01 to more
than 20 slpm. The average leak rate was
about 1.2 slpm, with a median of 0.7 slpm.
Total measured emissions (EPA method)
amounted to about 130 slpm (about 260
Ib/day). Most of the measurements were
obtained in a gas processing plant (51/
79); the remainder were collected at well
heads and in a propane storage area.
There is a very significant positive HVCS
bias in the overall West Texas results.
The probability that the mean bias is the
same as in the laboratory studies is very
small (0.4%). The probability that the mean
bias is the same as in the South Texas
data is also small (0.9%). For the vali-
dated data, the HVCS method measured
a total of 93.9 slpm (194 Ib/day), while the
EPA method came up with only 79.2 slpm
(164 Ib/day). This difference in total emis-
sions is significant (18.6%) but not far
outside acceptable limits for field emis-
-------
Table 2. Component Screening and Leak Identification
South Texas
West Texas
Component
Flanges
Threaded Connectors
Tube Connectors
Valves
Open-End Lines
Miscellaneous
Screened
889
3733
931
1785
216
74
Leaks
0
12
3
25
8
11
Screened
1401
8010
982
2901
55
94
Leaks
1
11
0
79
0
7
Total
7628
59
13443
98
sions measurements. It is notable that the
bias occurred only early in the study. Be-
fore September 26, the difference in total
emissions was 47.1%, and after this date
the difference was essentially zero (-1.5%).
This is significant, as some operational
and procedural changes were made in
the field after September 26 in an attempt
to improve results.
The bias in the West Texas results was
immediately noted in the field. The field
crew conducted numerous quality control
and operational checks to determine the
source of the bias. The HVCS and bag
sampling apparatus were carefully leak-
checked, and additional flow calibrations
were performed. The OVA was calibrated
before and after each HVCS quantifica-
tion, using the same methane standards
used to calibrate the GC. Controlled leak
tests and other special tests were also
conducted in an attempt to isolate the
source of the bias.
After efforts early in the study failed to
eliminate the bias, a concentrated effort
was made on September 26 to isolate
and eliminate the bias, if possible. This
included controlled leak tests, equipment
checks and cleaning, and minor changes
in operating procedures. A hypothesis that
the apparent positive HVCS bias may have
actually been due to a negative bias
caused by dilution in the EPA sampling
apparatus was also investigated. Unfortu-
nately, this effort failed to identify and
explain the exact source of the bias; how-
ever, after this date, the bias was no longer
present in the results.
Two additional possibilities that could
explain the apparent HVCS bias were iden-
tified: (1) high background hydrocarbon
levels and (2) analytical bias of the OVA
versus the GC. Background hydrocarbon
concentrations can produce a positive
HVCS bias since the background concen-
tration is multiplied by the higher HVCS
flow rate to obtain the emission rate (i.e.,
the HVCS result is more strongly influ-
enced by background levels than the EPA
vacuum method, even though both use
the air surrounding the leaking compo-
nent as dilution gas). Note, however, that
observed background hydrocarbon con-
centrations were, in most cases, not suffi-
ciently high to have produced the observed
HVCS bias. Although both the GC and
the OVA use FID, an analytical bias could
result from differences in instrument de-
sign that make the OVA response sensi-
tive to sample contaminants, sample gas
composition, and possibly environmental
effects such as pressure. The possibility
that an analytical bias was present was
suggested by field efforts to identify the
source of the bias.
In addition to the possible effect of op-
erational changes that were implemented
after September 26 (the pump was cleaned
and an extension tube was added to the
EPA apparatus), the improvement in HVCS
results after September 26 may be re-
lated to a combination of two other fac-
tors. First, as part of efforts to determine
and eliminate the source of the bias, mea-
suring in areas with high background lev-
els was avoided after that date. Earlier in
the study, most of the measurements were
obtained from dense clusters of leaking
components where there were potentially
high background levels. At the South
Texas site, background levels were mini-
mal (samples were obtained in remote,
open areas and wind speeds were very
high). Second, the average leak rate after
September 26 ( 1.8 slpm) is larger than
the average leak rate before that date
(1.2 slpm). This would reduce an HVCS
bias related to background hydrocarbon
since such a bias is less significant for
larger leaks.
After the field studies, additional labora-
tory studies were conducted to confirm
the field tests that suggested an analytical
bias and to identify the source of the bias.
For these tests, five gas samples were
obtained in pressurized stainless steel
sample canisters from the West Texas
plant. The samples were collected pro-
gressively through the gas processing
stages and represent the areas in the gas
plant where leaks were quantified. In ad-
dition, the same OVA used in the study
was obtained for comparative tests with
the GC. The laboratory testing was de-
signed to compare the response of the
OVA and the GC under more controlled
conditions, to identify a contaminant in the
gas samples, and/or to identify an uniden-
tified compound that could have produced
the observed bias.
No evidence was found in the labora-
tory tests to confirm a positive analytical
bias of the OVA versus the GC. In addi-
tion, no contaminants or excess com-
pounds were identified that could have
produced such an analytical bias. The only
identified factors that were not investigated
in these tests are environmental; e.g., the
difference in atmospheric pressure due to
the high altitude of the West Texas site
(about 3500 ft5 above mean sea level
compared to near sea level elevations for
the laboratory and South Texas studies).
While the OVA response is known to be
sensitive to sample inlet pressure, this
should not effect the results since the
OVA was calibrated at the pressure at
which it was used.
Conclusions
As demonstrated in the laboratory study
and by the South Texas results, the HVCS
is capable of accurately quantifying fugi-
tive leaks over a wide range of leak sizes,
and component types and sizes. On the
other hand, the West Texas results re-
vealed an important limitation of the sys-
tem.
Laboratory evaluation of HVCS per-
formance was very favorable. The
HVCS results closely matched EPA
method results with a difference in
total measured emissions of only
about 3%. The HVCS also repro-
duced a wide range of known leak
rates with an average bias of-8.3%.
The negative bias is probably due
to incomplete leak capture. In the
laboratory tests, HVCS leak cap-
ture depended solely on the ability
' 1 ft = 0.3 m.
-------
Table 3.
Method Bias
Field Study Results Summary
Mean
(MVU)'
Lower
95% Limit
Upper
95% Limit
No.
South Texas HVCS Relative Bias 15.2%
South Texas HVCS "True" Bias 6.6%
West Texas HVCS Relative Bias - 44.5%
Overall
-3.6%
34.3%
29.8%
20.2%
56.7%
48
66
West Texas HVCS "True" Bias -
Overall
West Texas HVCS Relative Bias -
On or Before September 26
West Texas HVCS "True" Bias -
On or Before September 26
West Texas HVCS Relative Bias -
After September 26
West Texas HVCS "True" Bias -
After September 26
33.8%
67.0%
54.7%
5.7%
0.0%
24.4%
56.5%
44.9%
-0.4%
-7.3%
45.1%
84.8%
71.1%
18.6%
9.8%
66
40
40
26
26
Difference in Total Emissions
South Texas
West Texas - Overall
West Texas - On or
EPA
(slpm)
55.8
79.2
32.7
HVCS
(slpm)
58.2
93.9
48.1
Diff. (%)
+4.3
+ 18.6
+47.1
No.
48
66
40
Before September 26
West Texas - After
September 26
46.5
45.8
-1.5
26
MVU = Minimum variance unbiased.
of the HVCS to capture all of the
leaking gas in the slipstream of di-
lution air entering the HVCS inlet.
No enclosures were constructed to
shield components and direct gas
into the HVCS inlet.
The HVCS also performed very well
in the South Texas field study. The
HVCS matched the EPA estimate
of total facility emissions within
about 4%, similar performance to
that obtained in the laboratory stud-
ies. In the field, enclosures were
constructed to shield components
from wind and assist in directing
leaking gas into the HVCS inlet.
Early in the West Texas study, an
apparent positive bias was ob-
served in the HVCS results. On
and before September 26 (about
midway of the study), the HVCS
measured 47.1% more total emis-
sions than the EPA method. After
this date, no appreciable bias was
observed. After the entire study, the
HVCS measured 18.6% more emis-
sions from the facility than the EPA
method. The source of the early
study bias is unclear; however, re-
sults suggest that some operational
problems may have been overcome
as a result of efforts undertaken in
the field. Other factors that may
have contributed to the changed
results include (1) efforts that were
made to avoid sampling in areas
with potentially high background
concentrations that could cause a
positive bias in the HVCS results
and (2) the fact that average leak
rates were higher later in the study,
which would lessen the effect of
background interference on the
HVCS quantifications.
Overall, these results are within accept-
able limits for field emissions measure-
ments. With some physical and procedural
enhancements, the HVCS should offer an
acceptable alternative to the EPA protocol
bagging method with GC analysis.
Special precautions must be taken
to obtain accurate HVCS quantifi-
cations where there may be el-
evated background concentrations,
such as in confined areas, or where
there are dense clusters of leaking
components or very large leaks.
The simplest approach is to attempt
to quantify background levels with
the OVA and apply an appropriate
correction to the results. This must
be done very carefully since back-
ground levels in such areas have
been observed to range widely in
small areas and change very rap-
idly. An alternative method for de-
termining the background level has
been suggested that, in some in-
stances, could provide a useable
correction, even when background
levels cannot be practically mea-
sured. The limitation of this method
is that one must be certain that
changes in HVCS outlet concentra-
tion are due solely to changes in
HVCS flow; i.e., total leak capture
must be attained at all HVCS flows.
Improved HVCS flow capacity, con-
trol, and metering are needed to
enhance leak capture and provide
greater reliability and ease of use
in the field. With the current rota-
meter set-up, the capacity could be
doubled by simply increasing pump
capacity. Power requirements would
also be increased, but the unit could
still be battery-operated (a 12-V
pump could reach near 1000 scfh).
Much larger flows would require
more power, decreasing portability,
and the metering system would also
have to be modified substantially to
handle the higher flows. Increased
flow capacity would also increase
the size of leaks that could be quan-
tified without the need for a dilution
probe, or other alternative to ex-
tend the range of the portable hy-
drocarbon monitor. Enhanced leak
capture might also make it possible
to measure leaks from larger com-
ponents without the need for auxil-
iary bagging. This could decrease
the time required for each mea-
surement.
Increased range and enhanced sta-
bility of the portable hydrocarbon
monitoring device used with the
HVCS are also needed. The por-
table hydrocarbon monitor used with
the HVCS needs greater range and
reliability than the Foxboro OVA
Model 108 that is currently used.
The OVA's upper range is at 10,000
ppm, or 1%. This can be extended
to perhaps 15,000 ppm using the
-------
direct voltage output from the OVA;
however, precision rapidly deterio-
rates at this upper end. In the field,
Foxboro's dilution probe was used
to extend the quantification range,
with generally good results; how-
ever, the use of the dilution probe
adds a degree of complexity. The
OVA is also very sensitive to sam-
pling conditions, contaminants, bat-
tery levels, and other factors. The
OVA requires frequent calibration,
which adds significantly to the ex-
pense and level of uncertainty as-
sociated with its use in quantitative
applications. The OVA is very sen-
sitive to sample gas composition
since the detector is exposed to
the entire sample stream at once
and uses sample stream air as com-
bustion air for the FID. The OVA
exhibits varying responses to dif-
ferent hydrocarbons, and some-
times radical responses to
"contaminants" (water, dust, and
gases—e.g., excess hydrogen—
that affect the response of the FID).
Some research is needed to iden-
tify and test alternative analyzers
with greater range and stability than
the OVA. This might include infra-
red devices and electrochemical
sensors. In addition, there has
been some preliminary develop-
ment of a catalytic combustor that
would determine hydrocarbon con-
centration by stoichiometry, using
measurements of oxygen and car-
bon dioxide at the entrance to and
exit from the combustor.
The HVCS may have a very significant
role to play in applications where rapid,
cost effective, on-site leak quantifications
are important.
With the HVCS, a single operator
can quantify approximately 30
leaks per day. With the EPA bag-
ging method, approximately 10
leaks can be sampled per day with
additional time and expense re-
quired for GC analysis.
The HVCS could be very useful in
evaluating the effectiveness of dif-
ferent inspection and maintenance
programs, and determining the most
cost effective approach for main-
taining emissions below a given
level.
The HVCS would also be useful for
emissions inventory and compliance
testing activities related to federal
and state air permit requirements.
In addition, the HVCS may be valu-
able in evaluating the performance
of optical-sensing-based techniques
for determining fugitive emission
rates under real world conditions.
Such methods are currently under
development at EPA and may soon
be tested under actual site condi-
tions. For these tests, there will be
a need to independently determine
leak rates from multiple fugitive
sources as a basis for evaluating
the performance of the optical-sens-
ing-based methods.
-------
Eric S. Ringler is with Southern Research Institute, Chapel Hill, NC 27514.
Charles C. Masser is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of the High Volume Collection System
(HVCS) for Quantifying Fugitive Organic Vapor Leaks ," (Order No. PB96-
136395; Cost: $27.00, 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
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
National Risk Management
Research Laboratory (G-72)
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use
$300
EPA/600/SR-95/167
------- |