April 16, 2007 

TECHNICAL REPORT 

Fugitive Emissions Pilot Project: 

Measurement of Natural Gas Emissions from the 

Canadian Natural Gas Transmission and Distribution 

Industry 

PREPARED FOR: 

Canadian Energy Partnership for Environmental Innovation (CEPEI) 

75 Winbledon Road 

Guelph, Ontario 

N1H 7V7 

PREPARED BY: 

Clearstone Engineering Limited 

700, 900-6 Avenue S.W. 

Calgary, Alberta T2P 3K2 
i 

Executive Summary

A fugitive emission measurement program was conducted from 2004 to 2006 at a 

representative selection of natural gas transmission, storage and distribution facilities 

from across Canada. This was done as part of a fugitive emissions pilot project 

sponsored by CRESTech and included the development of a formal leak detection and 

measurement protocol aimed at providing reliable and consistent results. The objectives 

of this work were to improve the quality, coverage and compatibility of emission factors 

and average unit-specific component counts used to estimate fugitive methane 

emissions from the Canadian natural gas transmission, storage and distribution industry, 

and to calculate the uncertainty bounds associated with these industry-specific emission 

factors. 

The selected natural gas facilities were chosen, in consultation with the project 

sponsors, to provide increased data for the source categories estimated to contribute 

most to total uncertainty in the gas industry’s national GHG emissions inventory, while 

covering the range of operators, geographic locations, age, and type of facility or 

installation. Leak detection and measurement surveys were conducted at 149 facilities 

across the country including 121 distribution facilities (i.e., 50 regulator/gate stations, 20 

commercial meter sets, 18 farm taps, 30 residential meter sets and 3 industrial meter 

sets), 27 gas transmission facilities (i.e., 2 mainline block valves, 13 receipt/sales meter 

stations and 12 compressor stations) and 1 liquefied natural gas (LNG) storage facility. 

The results were combined with the data from a similar measurement program 

conducted in 1995/96 [1], as well as the results of several leak measurement programs 

sponsored by individual gas companies (i.e., Alliance Pipeline and Terasen). The 

combined data set represents emission survey results from 438 facilities located 

throughout British Columbia, Alberta, Saskatchewan, Manitoba, Ontario and Quebec 

and operated by the following study participants: Alta Gas, Atco Gas, Atco Pipelines, 

Duke Energy, Enbridge, Gaz Metro, Manitoba Hydro, TransCanada Pipelines and Union 

Gas. The leak measurement work was performed by Clearstone Engineering in all of 

these cases, with the exception of the 1995/96 study, which was performed jointly with 

Environment Canada. 

Before combing the results, some checks were performed to confirm that the data were 

all from the same population (i.e., that no statistically significant changes have occurred 

since the 1995/96 study). The combined results show that the leak-rate distribution for 

most component categories is highly skewed rather than normally distributed. As a 

result, much greater sample sizes are needed to accurately characterize the leak rate 

distribution than would be the case if the distributions were normal. 

While in most cases the new average emission factors have changed little from the 

current factors being used by the Canadian natural gas industry, in a few cases quite 

significant changes have occurred and the uncertainty limits on these factors have 

actually increased. In these cases, the developed emissions factors have been affected 

by a few particularly large leakers detected during the current study at different facilities. 

It could be argued that these data are outliers and should be excluded from the emission 

factor calculations. However, it has viewed that these extreme leaker results actually 

help to better delineate the full profile of the skewed distributions for the respective 

component categories. Accordingly, these extreme values were retained as valid points 

in the emissions distribution. 
ii

 

The uncertainties in the developed emission factors were determined based on a 95-

percent confidence interval in accordance with the IPCC (2000) Good Practice 

Guidance. This differs from the current practice in the United States where the US 

Environmental Protection Agency has been using a 90-percent confidence interval in 

GHG-related uncertainty analyses. 

Overall, the data collected during the 2005/06 field measurement campaign at a large 

selection of transmission, storage and distribution facilities has re-affirmed and 

highlighted a number of key findings from previous studies of fugitive emissions in the 

industry. No new trends or anomalies were detected in the compiled data. 

There were two LNG storage facilities included in the combined data set. Both facilities 

were relatively new but were operated by different companies and located in different 

provinces. Very little equipment at either facility was actually in LNG service, beyond a 

few fittings on the LNG spheres and vaporizers. Most of the equipment was in natural 

gas service and associated with the compressor units. There was insufficient data 

available to draw any meaningful conclusions regarding possible difference in fugitive 

emissions at LNG facilities; however, there was not indication of any differences. 

The component counts used to develop the emission factors were all prepared by 

Clearstone Engineering based on actual counts performed while at the facilities. In some 

cases operators also provided their own counts which were understood to have largely 

been derived from drawings rather than field counts. The results for smaller facilities 

such as distribution meter stations tended to agree well with the field counts; however, 

the company supplied counts for larger facilities often greatly understated the population 

of components determined from the field counts (i.e., by as much as an order of 

magnitude). This reflects the lack of detail shown on most types of drawings, particularly 

for third party packages such as compressors. As well, it highlights the need to improve 

the quality of component counts being compiled by some operators.. 
iii

Table of Contents

Executive Summary ........................................................................................................... i

List of Figures................................................................................................................... iv

List of Tables.................................................................................................................... vi

1.0 Introduction............................................................................................................1

2.0 Field Measurement Program.................................................................................2

2.1 Surveyed Facilities ............................................................................................2

2.2 Component Screening.......................................................................................4

2.3 Leak Rate Measurement ...................................................................................4

2.4 Component Counts ...........................................................................................4

3.0 Results ..................................................................................................................5

3.1 Average Emission Factors ................................................................................5

3.2 Default Component Counts .............................................................................10

4.0 Conclusions.........................................................................................................13

References......................................................................................................................14

Glossary..........................................................................................................................15

Appendix A: Average Emission Factors by Component Type .....................................19

Appendix B: Comparison of Average Emission Factors from Published Sources to 

Current Study by Component Type.................................................................................26

Appendix C: Leaker Data Distribution..........................................................................29

Appendix D: Cumulative Leak Contributions................................................................40

Appendix E: Default Component Counts and Confidence Intervals ............................46

Appendix F: Changes observed from 1995/1996 to 2005/2006 data sets...................51

Appendix G: Measured Emissions from 2005/2006 Field Campaign.......................56
iv

List of Figures

Figure A-1 Average Emission Factors – Centrifugal Compressor Seals .......................20

Figure A-2 Average Emission Factors – Reciprocating Compressor Seals...................20

Figure A-3 Average Emission Factors – Connector.......................................................21

Figure A-4 Average Emission Factors – Control Valve..................................................21

Figure A-5 Average Emission Factors – Controller........................................................22

Figure A-6 Average Emission Factors – Blowdown.......................................................22

Figure A-7 Average Emission Factors – Open-Ended Line ...........................................23

Figure A-8 Average Emission Factors – Orifice Meter...................................................23

Figure A-9 Average Emission Factors – Other Flow Meter............................................24

Figure A-10Average Emission Factors – Pressure Regulator ........................................24

Figure A-11Average Emission Factors – Pressure Relief Valve.....................................25

Figure A-12Average Emission Factors – Valve ..............................................................25

Figure B-1 Comparison of Average Emission Factors – All Equipment Components ...26

Figure B-2 Comparison of Average Emission Factors – Pressure Regulator, Connector 

and Other Flow Meter...................................................................................27

Figure B-3 Comparison of Average Emission Factors – Orifice Meter, Control Valve and 

Valve ............................................................................................................27

Figure B-4 Comparison of Average Emission Factors – Open-Ended Line, Controller 

and Pressure Relief Valve............................................................................28

Figure B-5 Comparison of Average Emission Factors – Blowdown, Centrifugal 

Compressor Seal and Reciprocating Compressor Seal...............................28

Figure C-1 Transmission Leaker Data Distribution – Centrifugal Compressor Seals ....30

Figure C-2 Transmission Leaker Data Distribution – Reciprocating Compressor Seals 30

Figure C-3 Transmission Leaker Data Distribution – Connector....................................31

Figure C-4 Transmission Leaker Data Distribution – Control Valve...............................31

Figure C-5 Transmission Leaker Data Distribution – Controller.....................................32

Figure C-6 Transmission Leaker Data Distribution – Blowdown....................................32
v

Figure C-7 Transmission Leaker Data Distribution – Open-Ended Line ........................33

Figure C-8 Transmission Leaker Data Distribution – Orifice Meter................................33

Figure C-9 Transmission Leaker Data Distribution – Pressure Regulator .....................34

Figure C-10 Transmission Leaker Data Distribution – Pressure Relief Valve .............34

Figure C-11 Transmission Leaker Data Distribution – Valve.......................................35

Figure C-12 Distribution Leaker Data Distribution – Centrifugal Compressor Seals ...35

Figure C-13 Distribution Leaker Data Distribution – Connector ..................................36

Figure C-14 Leaker Data Distribution – Control Valve ................................................36

Figure C-15 Distribution Leaker Data Distribution – Blowdown...................................37

Figure C-16 Distribution Leaker Data Distribution – Open-Ended Line.......................37

Figure C-17 Distribution Leaker Data Distribution – Pressure Relief Valve ................38

Figure C-18 Distribution Leaker Data Distribution – Pressure Regulator ....................38

Figure C-19 Distribution Leaker Data Distribution – Valve ..........................................39

Figure D-1 Cumulative Leak Contributions for Transmission Facilities – All equipment 

components..................................................................................................40

Figure D-2 Cumulative Leak Contributions – Transmission – Centrifugal Compressor 

Seals ............................................................................................................41

Figure D-3 Cumulative Leak Contributions – Transmission – Reciprocating Compressor 

Seals ............................................................................................................41

Figure D-4 Cumulative Leak Contributions – Transmission – Connector ......................42

Figure D-5 Cumulative Leak Contributions – Transmission – Controller Vent...............42

Figure D-6 Cumulative Leak Contributions – Transmission – Control Valve .................43

Figure D-7 Cumulative Leak Contributions – Transmission – Blowdown.......................43

Figure D-8 Cumulative Leak Contributions – Transmission – Open-Ended Line...........44

Figure D-9 Cumulative Leak Contributions – Transmission – Orifice Meter ..................44

Figure D-10 Cumulative Leak Contributions – Transmission – Pressure Relief Valve 45

Figure D-11 Cumulative Leak Contributions – Transmission – Valve .........................45
vi

List of Tables

Table 2-1 Scope of Survey.............................................................................................3

Table 3-1 Average Emission Factors for Gas Transmission and Distribution Facilities 

from the Combined Data Set..........................................................................7

Table 3-2 Comparison of Average Emission Factors (kg/h/source) from Published 

Sources to the 1995/1996 GTC/EC Study and the Combined Data Set........9

Table 3-3 Equipment Schedules for Gas Transmission Facilities. ...............................11

Table 3-4 Equipment Schedules for Gas Distribution Facilities....................................12

Table E-1 Confidence Limits on Equipment Schedules for Gas Transmission Facilities 

Based on 2005/2006 Measurement Campaign and Independent Company 

Studies Data Set. .........................................................................................46

Table E-2 Confidence Limits on Equipment Schedules for Gas Distribution Facilities 

and Meter/Regulation Stations Based on 2005/2006 Measurement 

Campaign and Independent Company Studies Data Set.............................48

Table E-3 Confidence Limits on Equipment Schedules for Gas Distribution Commercial 

and Residential Meter Sites Based on 2005/2006 Measurement Campaign 

Data Set. ......................................................................................................50

Table F-1 Comparison of Average Emission Factors for Gas Transmission Facilities. 51

Table F-2 Changes from 1995/1996 to 2005/2006 Gas Transmission Data Sets........52

Table F-3 Comparison of Average Emission Factors for Gas Distribution Facilities and 

Meter/Regulation Stations............................................................................53

Table F-4 Changes from 1995/1996 to 2005/2006 Gas Distribution Data Sets ...........54

Table F-5 Comparison of Average Emission Factors for Commercial and Residential 

Gas Distribution Sites...................................................................................55

Table F-6 Changes from 1995/1996 to 2005/2006 Commercial and Residential Gas 

Distribution Data Sets...................................................................................55

Table G-1 2005/2006 Measured Emissions by Facility Type........................................56

Table G-2 Top Twenty Leakers from 2005/2006 Emissions Survey.............................56
1 

1.0 Introduction 

The pilot measurement program comprised two parts. The first part was to develop a 

standard leak measurement protocol for detecting, measuring and classifying leaks at 

natural gas facilities. The second part, which is the focus of this document, was to apply 

the protocol at a representative sampling of natural gas transmission and distribution 

facilities to increase the current database of leak data for the industry and then use this 

information to develop improved emission factors and default unit-specific component 

counts. 

Leak detection and measurement data collected during the 2005/2006 field campaign at 

149 study participant facilities were combined with data collected during recent testing 

programs undertaken by independent companies1

 and with the data gathered for 

the1995/1996 GTC/EC study of Western Canadian natural gas facilities [1]. The 

combined data set was used to develop emission factors for estimating fugitive natural 

gas losses at Canadian gas transmission, storage and distribution facilities. 

A summary of the leak detection and quantification program is given in Section 2. 

Section 3 provides a summary of the results including the updated average emission, 

comparison of the developed factors to published data and average unit-specific 

component counts. The conclusions of the study are presented in Section 4. A graphical 

comparison of the emission factors, by component type, developed by the current study 

to those and developed by the 1995/1996 GTC/EC Study of Western Canadian natural 

gas facilities is given in Appendix A, along with the associated uncertainty bounds for 

each of the factors. Appendix B provides a graphical comparison of the average 

emissions to published factors. An examination of leaker data distribution profiles and 

cumulative leak contributions are available in Appendix C and Appendix D, respectively. 

Appendix E presents the confidence limits for the developed average unit-specific 

component counts. The changes in leak frequency and emission factors between the 

1995/1996 and 2005/2006 data sets are examined in Appendix F. Finally, Appendix G 

provides a summary of the total losses measured during the 2005/2006 field campaign 

and a listing of the top leaks encountered. 

 

1

 Data used with permission. 
2

2.0 Field Measurement Program 

The field measurement program was conducted from 2005 to 2006 at a selection of 

facilities which provided a uniform representation of the Canadian natural gas 

transmission, storage and distribution industry. This work comprised identifying all 

natural gas equipment leaks at each host facility, measuring the amount of emissions 

from each detected leak, developing equipment counts and estimating the amount of 

emissions from non-leaking sources. The work was completed in accordance with the 

Fugitive Emissions Measurement Protocol [2]. A component was considered to be 

leaking if it produced a screening value of 10,000 ppm or greater using a portable 

organic vapour analyzer when screened in accordance with US Environmental 

Protection Agency’s Method 21. 

2.1 Surveyed Facilities 

Facilities included in the study were selected by the industry participants and the project 

steering committee with the intent of providing a uniform representation of the Canadian 

natural gas transmission, storage and distribution system. Consideration was given to 

age, type, location and operator when selecting facilities. 

Measurement data collected during the study were combined with other similar leak data 

that were available and satisfied the basic requirements of the developed Leak 

Measurement Protocol. These additional data included the results of an industry 

sponsored leak measurement program conducted in Canada in 1995/96 [1] and several 

recent leak measurement campaigns sponsored by individual gas companies in Canada 

(namely, Alliance Pipeline and Terasen). Table 2-1 provides a summary of the compiled 

data sources along with the number and types of facilities that were surveyed in each of 

these cases. The combined data set represents survey results from 44 compressor 

stations, 33 sales and receipt meter stations, 47 block/control valve stations, which 

includes 6 border meter stations, 2 LNG storage facilities, 26 industrial meter sites, 56 

commercial meter sites, 111 residential meter sites, 28 farm taps and 94 regulation/gate 

stations. These facilities are located throughout British Columbia, Alberta, 

Saskatchewan, Manitoba, Ontario and Quebec and are operated by the following study 

participants: Alta Gas, Atco Gas, Atco Pipelines, Duke Energy, Enbridge, Gaz Metro, 

Manitoba Hydro, TransCanada Pipelines and Union Gas. 
3 

Table 2-1 Scope of Survey 

GAS DISTRIBUTION 

TOTAL Regulator / 

Gate 

Station 

Commercial 

Meter Set 

Farm 

Tap 

Residential 

Meter Set 

Industrial 

Meter Set 

Block / 

Control 

Valve 

Station1

Receipt 

/ Sales 

Meter 

Station1

Compressor 

Station1 Storage Facility1

Block / 

Control 

Valve 

Station 

2005/2006 Facilities Surveyed 

149 50 20 18 30 3 0 0 0 0 2 

Other Surveyed Facilities2

106 12 15 0 14 5 22 8 8 1 12 

TOTAL CURRENT STUDY 

255 62 35 18 44 8 22 8 8 1 14 

1995/1996 GTC/EC Study 

183 32 21 10 67 18 0 0 0 0 11 

COMBINED DATA SET 438 94 56 28 111 26 22 8 8 1 25 

1 Odourized transmission facilities are deemed to be in distribution service and are categorized as such for the purpose of developing ave2 Not all equipment surveyed at some facilities
4 

2.2 Component Screening 

Equipment components in pressurized natural gas service were screened for leaks in 

accordance with the methodology presented by the U.S. EPA [3] and following the 

methodology outlined in the Fugitive Emissions Measurement Protocol [2]. The types of 

components surveyed included connectors, valves, pressure relief devices, open-ended 

lines, blowdown vents (during passive periods), regulator and actuator diaphragms, flow 

meters, and compressor seal vents. 

Screening was conducted using ultrasonic leak detectors, bubble tests with soap 

solution and portable hydrocarbon vapour analyzers calibrated to methane (BascomTurner Gas Sentry CGI-201 and CGI-211). A screening value of 10,000 ppmv in the 

vicinity of the component was used at the leak definition. Component determined to be 

emitting based on qualitative screening techniques were also screened using 

quantitative screening techniques to verify the leak definition was exceeded. Identified 

leaking equipment components were marked with sequentially numbered tags indicating 

the source of the leakage. 

2.3 Leak Rate Measurement 

Emission rates were measured for all components determined to be leaking. The 

HiFlowTM Sampler was the primary instrument used to quantify emissions from leaking 

sources. However, flow through meters (i.e. rotary meter, diaphragm meter and 

rotameter) and velocity probes (i.e. hot wire anemometer, thermal dispersion 

anemometer, vane anemometer, and micro-tip vane anemometer) were also utilized 

when the source type and emission rate was appropriate. Section 4 of the Fugitive 

Emissions Measurement Protocol [2] outlines the leak measurement techniques applied. 

Data collection and reporting was done in accordance with the source classification 

scheme provided in Section 2 of the Protocol. 

2.4 Component Counts 

Detailed counts of the components in natural gas service for each facility surveyed were 

developed by Clearstone Engineering in accordance with the Fugitive Emissions 

Measurement Protocol. Independent component counts were provided by approximately 

half the operators. Count verification results showed significant differences between the 

two data sets for some facility types and highlighted some of the challenges related to 

obtaining an accurate component population: 

• Relying on piping and instrumentation drawings to develop equipment 

component counts can lead to a significant underestimation of the component 

population. P&IDs typically lack sufficient detail to develop an accurate count, 

details on packaged units are generally missing (particularly, for fuel gas system 

piping), and open-ended lines are not shown on drawings. 

• A systematic approach, such as that laid out in the Protocol, must be employed 

to avoid either missing equipment components or double counting. 
5

• Process knowledge and training is needed to recognize and exclude non-target 

service applications such as electrical conduit, coolant, heat medium and 

lubricating oil. 

• Facilities of the same type and size may have very different numbers of 

components due to differences in design practices and the number of trains 

present. 

Ultimately, only the Clearstone component counts were used to develop the average 

emission factors presented in the following section. Refer to Section 2.3 of the Fugitive 

Emission Measurement Protocol for a discussion of the component counting guidelines 

and basic component categories. 

3.0 Results 

Natural gas companies typically use average emission factors and estimated component 

populations to determine the amount of methane emitted at their facilities due to fugitive 

equipment leaks. This is done using the following relation: 

= ∑∑ ⋅ ⋅ i

j

j

ER EFi, j Ni X (1) 

Where: 

 ER is the total emission rate for the target source population 

 EF is the average emission factor 

 N is the number of sources (src) 

 X is the mass fraction of the target pollutant in the process fluid 

Updated average emission factors developed from the expanded leak measurement 

data set are presented in Section 3.1 below. Updated default unit-specific component 

counts are presented in Section 3.2; however, these values are derived from the 

2005/2006 and independent study measurement data only since the 1995/96 GTC/EC 

data set does not contain the detail required to evaluate the confidence limits on the 

component counts. 

Prior to combining the data sets, various statistical tests and quality assurance checks 

were performed on the data to ensure that they are representative of the same 

populations, to identify and deal with outliers and to harmonize component codes and 

database structures. Several comparisons were made between data from the current 

study (i.e., the 2005/2006 field campaign and recent independent company studies) and 

that from the 1995/1996 study. This included comparing the 95 percent confidence limits 

on the data sets, the data distributions and component populations. 

3.1 Average Emission Factors 

The average emission factors developed based on a statistical analysis of the total 

combined data set of leak measurement and component counts are presented in Table 

3-1 along with their 95 percent confidence limits. The previous study [1] of the Canadian 

natural gas transmission, storage and distribution industry concluded that fugitive 

equipment leaks are dependent on the industry sub-sector and component type. 

Consequently, emission factors developed in this study are classified accordingly. 

Following the Fugitive Emissions Measurement Protocol, odourized transmission 
6

facilities are deemed to be in distribution service as fugitive emissions from odourized 

transmission facilities are lower than their unodourized counterparts. Previous study has 

shown that components in gas transmission service tend to leak more, on average, than 

components in gas distribution service and that odourization of the distribution gas is 

likely an important factor [2]. 

The average emission factors represent the total amount of organic emission observed 

in each source category divided by the corresponding number of potential sources. 

Consequently, the factors account for emissions from both leaking and non-leaking 

sources. Emission rates for all leaking components were quantified using the methods 

described in the Fugitive Emission Measurement Protocol. Emissions from non-leaking 

equipment component were assigned the average non-leaking emission rates presented 

in the US EPA Protocol for Equipment Leak Emission Estimates [7]. 

The 95 percent confidence limits provide an indication of the variability of the compiled 

average emission factors. In general, the confidence interval is narrow when there were 

a large number of data points or the data were clustered around the mean. If the data 

showed a wide variability around the mean or there were few data points, the 95 percent 

confidence interval is wide. Comparing the confidence limits of two data sets provides a 

simple means of establishing if the data sets are from the same population. 

A comparison of the updated average emission factors to those developed from the 

1995/1996 study and to factors published for U.S. gas production [4], upstream oil and 

gas [5] and U.S. gas transmission systems [6] is presented in Table 3-2. 

An examination of the updated average emission factors for the Canadian natural gas 

transmission, storage and distribution industry shows that both the average emission 

factors and the 95 percent confidence limits have increased for a number of source 

categories. These changes to the average emission factors are attributed to the highly 

skewed emission rate distributions for leaking components and the inclusion of a few 

particularly big leakers detected during the current measurement program. Although 

most equipment components are considered non-leaking, those that do satisfy the leak 

definition contribute almost all the emissions. Furthermore, within the subset of leaking 

equipment components, the majority of emissions result from only a few big leakers. The 

top few leakers in each category, therefore, have a significant impact on the average 

emission rate. As a result of the highly skewed emission rate distributions encountered, 

sample sizes must be quite large to see the full range of emission rates. 

Additionally, the confidence limits for the 1995/96 data are believed to be artificially tight 

due to the use of published leak-rate correlations to estimate emissions for some of the 

leaks detected during that study (i.e., actual leak rate measurements were only 

performed on what appeared to be the greatest leakers at each site). 

Please refer to Appendix A for a graphical comparison of the average emission factors 

developed from 1995/1996 data to those from the 2005/2006 data sets and the 

combined data set, and to Appendix F for tabular summaries. Appendix B provides a 

graphical comparison of average emission factors to published sources. An examination 

of the leaker data distribution and cumulative leak contribution, both by component type, 

are provided in Appendix C and Appendix D, respectively. 
7

Table 3-1 Average Emission Factors for Gas Transmission and Distribution Facilities 

from the Combined Data Set. 

Gas Transmission Facilities 1 

95% Confidence Limits 

Source Number of 

Sources 

Leak 

Frequency 

Average 

Emissions 

(kg TOC/h/source) Lower Upper 

Compressor Seal – 

Centrifugal 2 103 64.1 1.269E+00 8.197E-01 1.718E+00

Compressor Seal – 

Reciprocating 2 167 40.1 1.073E+00 6.130E-01 1.533E+00

Connector 3 145829 0.9 4.471E-04 1.957E-04 6.985E-04

Control Valve 4 782 9.0 1.650E-02 1.082E-02 2.219E-02

Controller 5 50 90.0 2.371E-01 9.941E-02 3.747E-01

Station or Pressurized 

Blowdown System6 219 59.8 3.405E+00 0.000E-00 7.885E+00

Open-Ended Line 928 58.1 9.183E-02 5.395E-02 1.297E-01

Orifice Meter 7 185 22.7 4.863E-02 0.000E-00 1.066E-01

Other Flow Meter 8 443 1.8 9.942E-06 2.223E-07 1.966E-05

Pressure Regulator 816 7.0 7.945E-03 0.000E-00 1.882E-02

Pressure Relief Valve 612 31.2 1.620E-01 2.906E-02 2.950E-01

Valve 9 17029 2.8 4.131E-03 2.748E-03 5.514E-03

Gas Distribution Facilities and Meter/Regulation Stations 1 

95% Confidence Limits 

Source Number of 

Sources 

Leak 

Frequency 

Average 

Emissions (kg 

TOC/h/source) Lower Upper 

Compressor Seal – 

Centrifugal 2 Use Transmission Factor 

Compressor Seal – 

Reciprocating 2 Use Transmission Factor 

Connector 3 52051 0.9 8.227E-05 3.792E-05 1.266E-04

Control Valve 4 605 13.7 1.949E-02 1.127E-02 2.771E-02

Controller 5 25 84.0 3.997E-01 1.158E-01 6.836E-01

Station or Pressurized 

Blowdown System6 42 9.5 5.878E-03 0.000E-00 1.591E-02

Open-Ended Line 969 49.9 6.077E-02 3.086E-02 9.068E-02

Orifice Meter 7 142 17.6 3.011E-03 1.890E-03 4.131E-03

Other Flow Meter 8 348 2.0 7.777E-06 0.000E-00 1.752E-05

Pressure Regulator 1323 2.1 6.549E-04 0.000E-00 1.375E-03

Pressure Relief Valve 472 9.5 3.944E-03 0.000E-00 8.865E-03

Valve 9 9817 2.0 5.607E-04 1.892E-04 9.322E-04

TOC – Total organic compounds.
8

Gas Distribution Commercial and Residential Sites 

95% Confidence Limits 

Source Number of 

Sources 

Leak 

Frequency 

Average 

Emissions 

(kg TOC/h/source) Lower Upper 

Connector 3 8616 0.2 4.467E-06 8.226E-07 8.112E-06

Control Valve 4 8 0.0 1.006E-02 0.000E-00 2.466E-02

Open-Ended Line 642 72.1 8.355E-02 3.924E-02 1.279E-01

Orifice Meter 7 107 19.6 3.274E-03 1.919E-03 4.630E-03

Other Flow Meter 8 405 1.7 7.203E-06 0.000E-00 1.560E-05

Pressure Regulator 348 2.3 2.329E-05 2.410E-07 4.633E-05

Pressure Relief Valve 78 3.8 1.749E-03 0.000E-00 3.747E-03

Valve 9 1340 0.1 2.173E-06 1.753E-06 2.593E-06

TOC – Total organic compounds. 

1

 Includes two LNG storage facilities. Odourized transmission facilities are deemed to be in distribution 

service and have been categorized as such for the purpose of developing average emission factors. 2

 The Compressor Seal categories account for emissions from individual compressor seals (i.e., for a four 

cylinder reciprocating compressor unit there are four seals so the compressor seal emissions for the unit 

would be four times the factor in the table). 3

 Includes flanges, threaded connections and mechanical couplings. 

4

 Accounts for leakage from the stem packing and the valve body. Emissions from the controller and 

actuator are accounted for by the Instrument Controller and Open-Ended Line categories respectively. This 

factor applies to all valves with automatic actuators (including fuel gas injection valves on the drivers of 

reciprocating compressors). 5

 The Instrument Controller category accounts for emissions from pneumatic control devices that use natural 

gas as the supply medium. 6

 Accounts for leakage past a valve seat through an open vent line to the atmosphere. These vents are 

typically six inches or greater in diameter and are used to blowdown major process units or sections of 

pipeline. Small diameter open-ended lines such as those used to blowdown chart recorders, meter runs 

etc. are accounted for by the Open-Ended Line category. 7

 Accounts for emissions from the orifice changer. Emissions from sources on pressure tap lines etc. are not 

included in the factor (i.e., these emissions must be calculated separately). 8

 Accounts for emissions from other types of gas flow meters (e.g., diaphragm, ultrasonic, roots, turbine and 

vortex meters). 9

 Accounts for emissions from the stem packing and the valve body, and it applies to all types of block 

valves (e.g., butterfly, ball, globe, gate, needle, orbit and plug valves). Leakage past the valve seat is 

accounted for by the Open-Ended Line emission category. Leakage from the end connections is accounted 

for by the connector category (i.e., one connector for each end). 
9 

Table 3-2 Comparison of Average Emission Factors (kg/h/source) from Published Sources to the 1995/1996 GTC

Data Set. 

US Gas Production 2

Source Service

(VOC) (TOC) 

Upstream 

Oil & Gas 

Operations 

(TOC) 3

GRI Gas 

Transmission 

(TOC) 4

95/96 GTC/EC 

Study Gas 

Transmission 

(TOC) 

95/96 

GTC/EC 

Study Gas 

Distribution 

(TOC) 

95/96 

GTC/EC 

Study Gas 

Distribution 

- CR (TOC) 

Combin

Data G

Transmis

(TOC) 

Compressor Seal – Centrifugal G/V 0.042 0.20 0.80488 0.418 0.8139 - - 1.269 Compressor Seal – Reciprocating G/V 0.042 0.20 0.8 1.00 0.6616 - - 1.073 Connector G/V 0.00046 0.0011 0.00253 0.000372 0.0002732 0.0001098 0.00000678 0.000447Control Valve G/V 0.0075 0.200 0.04351 0.0203 0.01969 0.01969 - 0.01650 Controller G/V - - 0.1996 0.411 0.4618 0.4618 - 0.2371 Blowdown G/V - - - 0.669 0.9369 0.9369 - 3.405 Open-Ended Line G/V 0.014 0.022 0.001373 0.0284 0.08355 0.08355 0.08355 0.09183 Orifice Meter G/V - - - - 0.003333 0.003333 - 0.04863 Other Flow Meter G/V - - - - 0.00000906 0.00000906 0.00000906 0.000009Pressure Regulator G/V - - - - 0.003304 0.001915 0.00002198 0.007945 Pressure Relief Valve G/V 0.014 0.19 0.12096 0.0157 0.2795 0.01665 0.0002717 0.1620 Valve G/V 0.0075 0.200 0.04351 0.00220 0.00214 0.001109 0.00000333 0.004131 

G/V - Gas/Vapour - No data available or the source category does not apply to this industry sector. 1 Not all equipment was surveyed at some facilities. 2 U.S. EPA. 1985. [3] Table 9.1.2 3 Picard, D.J., B.D. Ross, and D.W.H. Koon. 1992. [5] Table 5, Page 49. 4 Adapted from; Hummel et al. 1996. [6] Table 4-15, page 51. 
10 

3.2 Default Component Counts 

To use the average emission factors presented in Table 3-1, the numbers of each of the 

different types of equipment components in each service category must be determined 

(see Section 2.4). In the absence of site-specific equipment component counts, 

however, the average equipment counts provided in Tables 3-2 and 3-3 may be used. 

These average counts were compiled by adding up the total number of each type of 

component at a particular type of facility and dividing by the number of such facilities 

surveyed. The industry-specific average component counts presented here are based on 

equipment component counts from 255 surveyed facilities, but data from the 1995/1996 

GTC/EC study is not included. 

Equipment schedules for residential meter sites, commercial meter sites, industrial meter 

sites, farm taps, district regulator stations and gate stations are presented on a per 

facility or per site basis. The amount of equipment at gas transmission facilities was 

found to vary widely from site to site. Refer to Appendix E where the upper and lower 

confidence limits on the component counts are provided. In an effort to manage the 

impact of this equipment variability, the schedules for meter stations are on a per meter 

run basis and compressor stations are on a per compressor unit basis. The amount of 

compressor yard station piping, excluding suction and discharge headers and valving for 

each unit, was found to be essentially independent of the number of compressor units 

[1]. Therefore, the total number of equipment components at a compressor station is 

determined by adding the components from yard piping to the components from each of 

the compressor units. If discharge coolers are used on site, the components from these 

must also be added. 
11 

Table 3-3 Equipment Schedules for Gas Transmission Facilities. 

Component Mainline Block Valve Receipt / Sales Meter Station 2 Reciprocating Compressor Unit 3 Centrifugal Compressor Unit 3 Compress

Station Ya

Piping 4 

Facilities Surveyed 1 13 168 25 29 21 Compressor Seal – Centrifugal - - - 2 - Compressor Seal – Reciprocating - - 4 - - Connector 200 33 256 502 950 Control Valve 0 6 0 1 5 13 Instrument Controller 0 0 0 0 1 Blowdown 0 - 1 1 4 Open-Ended Line 1 0 1 4 6 Orifice Meter - 0 1 0 2 Other Flow Meter 0 1 - 0 1 Pressure Regulator 2 1 2 5 15 Pressure Relief Valve 0 0 2 3 8 Valve 36 7 22 120 217 

1 Not all equipment at some facilities surveyed 2 Number of components per meter run 3 Number of components per compressor unit 4 Number of components per compressor station. For a station with 2 reciprocating compressor units, the total number of connect 2*256+985=1497 5 Number of components associated with discharge coolers at compressor stations. If the station has discharge coolers, add these 6 A zero value indicates a fractional value less than 0.5. Please refer to Appendix E for further discussion. 
12 

Table 3-4 Equipment Schedules for Gas Distribution Facilities. 

Distribution – Commercial 

and Residential Distribution Facilities 

Component 

Residential Meter Set 2

Commercial 

Meter Set 2

Farm 

Tap 2

Industrial 

Meter Set 

2

District 

Regulator 

Station 2

Gate 

Station 

2

Border 

Meter 

Station 

Mainline 

Block 

Valve 

Reciprocating 

Compressor 

Unit 3

Centrifug

Compres

Unit 3

Facilities Surveyed 1 44 35 18 15 32 30 6 22 2 12 Compressor Seal – Centrifugal - - - - - - - - - 2 Compressor Seal – Reciprocating - - - - - - - - 5 - Connector 48 82 48 111 181 353 381 142 163 430 Control Valve 0 6 0 0 0 1 2 1 1 1 5 Instrument Controller - - - - - 0 - 0 - - Blowdown - - - - - - - - 1 1 Open-Ended Line - - - - 0 0 4 1 4 5 Orifice Meter - 0 - 0 0 1 - 0 1 0 Other Flow Meter 1 2 0 1 0 1 1 0 - 1 Pressure Regulator 2 3 2 4 8 12 8 2 1 3 Pressure Relief Valve 0 1 2 0 2 3 3 1 2 2 Valve 8 14 13 26 40 64 62 33 20 83 

1 Not all equipment at some facilities surveyed 2 Number of components per meter set (for residential, commercial and industrial meter sets) or site (for district and gate stations) 

3 Number of components per compressor unit 4 Number of components per compressor station. For a station with 2 reciprocating compressor units, the total number of connect 2*256+985=1497 5 Number of components associated with discharge coolers at compressor stations. If the station has discharge coolers, add these 

6 A zero value indicates a fractional value less than 0.5. Please refer to Appendix E for further discussion. 
13 

4.0 Conclusions 

Updated average emission factors and average unit-specific component counts for the 

Canadian natural gas transmission, storage and distribution industry have been 

developed using data collected during leak detection and measurement programs 

conducted since 1995 at natural gas facilities throughout Canada. The confidence limits 

associated with these results are also provided and may be used, in accordance with 

IPCC Good Practice Guidance (2000), to help develop quantitative uncertainty estimates 

for emissions inventories. 

An analysis of the data collected during the 2005/2006 field measurement campaign has 

re-affirmed and highlighted a number of key findings from previous study of fugitive 

emissions in the industry: 

• Components satisfying the leak definition (i.e., those with screening values 

greater than 10,000 ppm) account for the vast majority of fugitive emissions at 

all facility types. Although non-leaking equipment components typically 

represent more than 98 percent of the component population, the contribution 

these components make to overall emissions is dwarfed by identified leakers. 

• The distribution of emission rates for equipment components is highly skewed 

for most component categories, indicating that component population is 

predominantly composed of non-leakers. The major exceptions are the 

compressor seal categories, which have relatively flat emission rate 

distributions. 

• Within the leaker subset of the component population, the distribution of 

emission rates is also highly skewed for all component categories. As a result, 

the top few leakers in each category have a significant impact on the average 

emission rate. Furthermore, a large sample population is required in order to 

define the shape of the emission rate distribution and see the full range of 

leakers. 

• Detailed, accurate component counts, ideally based on actual site surveys, are 

essential in developing emission inventories. The complexity of many facilities 

requires technicians both to be knowledgeable about the process and to follow a 

systematic approach such as that laid out in the Fugitive Emission Measurement 

Protocol. 
14

References

[1] Ross, B.D. and D.J. Picard. 1996. Measurement of Methane Emissions from 

Western Canadian Natural Gas Facilities – GTC Program #3 Environmental 

Technology Program. 

 [2] Clearstone Engineering Ltd. 2006. Canadian Energy Partnership for 

Environmental Innovation (CEPEI) – Fugitive Emissions Measurement Protocol. 

[3] U.S. EPA (Environmental Protection Agency). 1997. Method 21 – Determination 

of Volatile Organic Compound Leaks. Available at: 

www.epa.gov/ttn/emc/promgate/m-21.pdf. 

[4] U.S. EPA. 1985. Compilation of Air Pollutant Emission Factors – Volume I: 

Stationary Point and Area Sources. AP-42. Fourth Edition. 

[5] Picard, D.J., B.D. Ross, and D.W.H. Koon. 1992. A Detailed Inventory of CH4

and VOC Emissions from Upstream Oil and Gas Operations in Alberta. Volume 

III: Results of Field Validation Program. Prepared by Clearstone Engineering Ltd. 

for Canadian Petroleum Association. 

[6] Hummel et al. 1996. Final Draft. Methane Emissions from the Natural Gas 

Industry. Volume 8: Equipment Leaks. Prepared by Radian International LLC for 

Gas Research Institute and U.S. Environmental Protection Agency. 

[7] U.S. EPA. 1995. Protocol for Equipment Leak Emission Estimates. Publication 

No. EPA-453/R-95-017. Section 2. 

[8] Intergovernmental Panel on Climate Change. 2000. Good Practice Guidance and 

Uncertainty Management in National Greenhouse Gas Inventories. 
15

Glossary

Centrifugal Compressor 

Seal System 

A mechanical seal used to prevent the loss of process fluid 

past a rotating compressor shaft where the shaft 

penetrates the compressor housing. 

 

Connectors - A connector is any flanged or threaded connection, or 

mechanical coupling, but excludes all welded or backwelded connections. If properly installed and maintained, a 

connector can provide essentially leak-free service for 

extended periods of time. However, there are many factors 

that can cause leakage problems to arise. Some of the 

common causes include vibration, thermal stress and 

cycles, dirty or damaged contact surfaces, incorrect 

sealing material, improper tightening, misalignment, and 

external abuse. 

 

Control Valve A valve equipped with an actuator for automated operation 

to control flow, pressure, liquid level or other relevant 

process parameter. 

 

Leak Frequency The portion of a population of components that are 

determined to be leaking at the time of a leak detection 

survey. 

 

Open-ended Valves 

and Lines - 

An open-ended valve is any valve that may release 

process fluids directly to the atmosphere in the event of 

leakage past the valve seat. The leakage may result from 

improper seating due to an obstruction or sludge 

accumulation, or because of a damaged or worn seat. An 

open-ended line is any segment of pipe that may be 

attached to such a valve that opens to the atmosphere at 

the other end. 

Few open-ended valves and lines are designed into 

process systems. However, actual numbers can be quite 

significant at some sites due to poor operating practices 

and various process modifications that may occur over 

time. 

Some common examples of instances where this type of 

source may occur are listed below: 

• scrubber, compressor-unit, station and mainline 

blowdown valves, 

• supply-gas valve for a gas-operated engine starter (i.e., 

where natural gas is the supply medium), 

• instrument block valves where the instrument has been 
16

removed for repair or other reasons, and 

• purge or sampling points. 

 

Pneumatic Controller A mechanism activated by an analog or digital signal that 

regulates the escape of a supply medium (e.g., 

compressed air or natural gas) to move mechanical 

controls such as valves and levers. 

 

Pressure Regulator A device used for maintaining a constant outlet pressure at 

a predetermined set point. 

 

Pressure-Relief Valves - Pressure relief or safety valves are used to protect process 

piping and vessels from being accidentally over-pressured. 

They are spring loaded so that they are fully closed when 

the upstream pressure is below the set point, and only 

open when the set point is exceeded. Relief valves open in 

proportion to the amount of overpressure to provide 

modulated venting. Safety valves pop to a full-open 

positions on activation. 

When relief or safety valves reseat after having been 

activated, they often leak because the original tight seat is 

not regained either due to damage of the seating surface 

or a build-up of foreign material on the seat plug. As a 

result, they are often responsible for fugitive emissions. 

Another problem develops if the operating pressure is too 

close to the set pressure, causing the valve to "simmer" or 

"pop" at the set pressure. 

Gas that leaks from a pressure-relief valve may be 

detected at the end of the vent pipe (or horn). Additionally, 

there normally is a monitoring port located on the bottom 

of the horn near the valve. 

 

Reciprocating Compressor 

Packing Systems - 

Packings are used on reciprocating compressors to control 

leakage around the piston rod on each cylinder. 

Conventional packing systems have always been prone to 

leaking a certain amount, even under the best of 

conditions. According to one manufacturer, leakage from 

within the cylinder or through any of the various vents will 

be on the order of 1.7 to 3.4 m3

/h under normal conditions 

and for most gases. However, these rates may increase 

rapidly as normal wear and degradation of the system 

occurs. 

 

Standard Reference 

Conditions - 

Most equipment manufacturers reference flow, 

concentration and equipment performance data at ISO 

standard conditions of 15°C, 101.325 kPa, sea level and 

0.0 percent relative humidity. 
17

The following equation shows how to correct air 

contaminant concentrations measured in the exhaust to 3 

percent oxygen (15% excess air) for comparison and 

regulatory compliance purposes. To correct emission 

levels to 3 percent oxygen that are referenced to excess 

air levels other than 3 percent , use the following equation: 

 

Total Hydrocarbons - All compounds containing at least one hydrogen atom and 

one carbon atom, with the exception of carbonates and 

bicarbonates. 

 

Total Organic 

Compounds (TOC) - 

TOC comprises all VOCs plus all non-reactive organic 

compounds (i.e., methane, ethane, methylene chloride, 

methyl chloroform, many fluorocarbons, and certain 

classes of per fluorocarbons). 

 

Valves - There are three main locations on a typical valve where 

leakage may occur: (1) from the valve body and around 

the valve stem, (2) around the end connections, or (3) past 

the valve seat. Leaks of the first type are referred to as 

valve leaks. Emissions from the end connections are 

classified as connector leaks. Leakage past the valve seat 

is only a potential source of emissions if the valve, or any 

downstream piping, is open to the atmosphere. This is 

referred to as an open-ended valve or line. 

The potential leak points on each of the different types of 

valves are, as applicable, around the valve stem, body 

seals (e.g., where the bonnet bolts to the valve body, 

retainer connections), body fittings (e.g., grease nipples, 

bleed ports), packing guide, and any monitoring ports on 

the stem packing system. Typically, the valve-stem 

packing is the most likely of these parts to leak. 

 

Vented Emissions - Vented emissions are releases to the atmosphere by 

design or by operational practice, and may occur on either 

a continuous or intermittent basis. The most common 

causes or sources of these emissions are gas operated 

devices that use natural gas as the supply medium (e.g., 

compressor start motors, chemical injection and 

odourization pumps, instrument control loops, valve 

actuators, and some types of glycol circulation pumps), 

equipment blowdowns and purging activities, and venting 

of still-column off-gas by glycol dehydrators. 

 

Volatile Organic Any compound of carbon, excluding carbon monoxide, and 

x ppm(actual) 21 - O (actual)

21 - 3

ppm(3%)= 2
18

Compounds (VOC) - carbon dioxide, which participates in atmospheric chemical 

reactions. This excludes methane, ethane, methylene 

chloride, methyl chloroform, many fluorocarbons, and 

certain classes of per fluorocarbons. 
19 

Appendix A: Average Emission Factors by 

Component Type 

The figures in this appendix provide a graphical comparison of the average emission 

factors, by component type, developed based on the 1995/1996 GTC/EC data set, the 

2005/2006 data, which includes the independent company studies and factors 

developed from the combined data set. Each figure provides both whisker plots showing 

the average emission factor and the 95 percent confidence limits, and bar graphs 

indicating the number of surveyed sources. The bar graph scale is on the left axis and 

the average emission rate in kg/hr/source is on the right axis. 

The average emission factors for transmission facilities have increased for some 

categories and dropped for others. The most notable increases are in the factors for 

compressor seals, connectors, blowdowns and valves. In contrast, the distribution 

average emission factors, are virtually all lower than those from previous study. A tabular 

summary of change in the number of surveyed sources, leak frequency and average 

emission factors between the 1995/1996 and 2005/2006 data sets is provided in 

Appendix F. 

The whisker plots show the 95 percent confidence limits for each of the developed 

emission factors. In a number of instances, the confidence limits have become wider 

rather that tighter despite the larger sample population. In these cases, the relative 

increase in the sample variance was greater than the relative increase in the sample 

population. Examination of the leaker data shows that the top few largest leakers in each 

component category create a highly skewed emission rate distribution. Not only do these 

leakers introduce a great deal of variance into the data set, which accounts for the wider 

confidence limits, but they also have a significant impact on the average emission factor. 

Please refer to Appendix C for a discussion of the leaker data distribution. 
20

0

20

40

60

80

100

120

Transmission - Combined

Transmission - 2005/2006

Transmission - 1995/1995

Number of Sources

0

0.5

1

1.5

2

2.5

Average Emission Rate (kg/h/src)

Figure A-1 Average Emission Factors – Centrifugal Compressor Seals 

0

20

40

60

80

100

120

140

160

180

Transmission - Combined

Transmission - 2005/2006

Transmission - 1995/1995

Number of Sources

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Average Emission Rate (kg/h/src)

Figure A-2 Average Emission Factors – Reciprocating Compressor Seals 
21

0

20000

40000

60000

80000

100000

120000

140000

160000

Distribution - Combined

Distribution - 2005/2006

Distribution - 1995/1995

Distribution-CR - Combined

Distribution-CR - 2005/2006

Distribution-CR - 1995/1995

Transmission - Combined

Transmission - 2005/2006

Transmission - 1995/1995

Number of Sources

0

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

0.0008

0.0009

0.001

Average Leak Rate (kg/h/src)

Figure A-3 Average Emission Factors – Connector 

0

100

200

300

400

500

600

700

800

900

Distribution - Combined

Distribution - 2005/2006

Distribution - 1995/1995

Distribution-CR - Combined

Distribution-CR - 2005/2006

Transmission - Combined

Transmission - 2005/2006

Transmission - 1995/1995

Number of Sources

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

Average Leak Rate (kg/h/src)

Figure A-4 Average Emission Factors – Control Valve 
22

0

10

20

30

40

50

60

Distribution - Combined

Distribution - 2005/2006

Distribution - 1995/1995

Transmission - Combined

Transmission - 2005/2006

Transmission - 1995/1995

Number of Sources

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Average Leak Rate (kg/h/src)

Figure A-5 Average Emission Factors – Controller 

0

50

100

150

200

250

Distribution - Combined

Distribution - 2005/2006

Transmission - Combined

Transmission - 2005/2006

Transmission - 1995/1995

Number of Sources

0

2

4

6

8

10

12

14

16

Average Leak Rate (kg/h/src)

Figure A-6 Average Emission Factors – Blowdown 
23

0

200

400

600

800

1000

1200

Distribution - Combined

Distribution - 2005/2006

Distribution - 1995/1995

Distribution-CR - Combined

Distribution-CR - 1995/1995

Transmission - Combined

Transmission - 2005/2006

Transmission - 1995/1995

Number of Sources

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

Average Leak Rate (kg/h/src)

Figure A-7 Average Emission Factors – Open-Ended Line 

0

20

40

60

80

100

120

140

160

180

200

Distribution - Combined

Distribution - 2005/2006

Distribution - 1995/1995

Distribution-CR - Combined

Distribution-CR - 2005/2006

Distribution-CR - 1995/1995

Transmission - Combined

Transmission - 2005/2006

Transmission - 1995/1995

Number of Sources

0

0.05

0.1

0.15

0.2

0.25

0.3

Average Leak Rate (kg/h/src)

Figure A-8 Average Emission Factors – Orifice Meter 
24

0

50

100

150

200

250

300

350

400

450

500

Distribution - Combined

Distribution - 2005/2006

Distribution - 1995/1995

Distribution-CR - Combined

Distribution-CR - 2005/2006

Distribution-CR - 1995/1995

Transmission - Combined

Transmission - 2005/2006

Transmission - 1995/1995

Number of Sources

0

0.000005

0.00001

0.000015

0.00002

0.000025

0.00003

Average Leak Rate (kg/h/src)

Figure A-9 Average Emission Factors – Other Flow Meter 

0

200

400

600

800

1000

1200

1400

Distribution - Combined

Distribution - 2005/2006

Distribution - 1995/1995

Distribution-CR - Combined

Distribution-CR - 2005/2006

Distribution-CR - 1995/1995

Transmission - Combined

Transmission - 2005/2006

Transmission - 1995/1995

Number of Sources

0

0.005

0.01

0.015

0.02

0.025

Average Leak Rate (kg/h/src)

Figure A-10 Average Emission Factors – Pressure Regulator 
25

0

100

200

300

400

500

600

700

Distribution - Combined

Distribution - 2005/2006

Distribution - 1995/1995

Distribution-CR - Combined

Distribution-CR - 2005/2006

Distribution-CR - 1995/1995

Transmission - Combined

Transmission - 2005/2006

Transmission - 1995/1995

Number of Sources

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Average Leak Rate (kg/h/src)

Figure A-11 Average Emission Factors – Pressure Relief Valve 

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Distribution - Combined

Distribution - 2005/2006

Distribution - 1995/1995

Distribution-CR - Combined

Distribution-CR - 2005/2006

Distribution-CR - 1995/1995

Transmission - Combined

Transmission - 2005/2006

Transmission - 1995/1995

Number of Sources

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

Average Leak Rate (kg/h/src)

Figure A-12 Average Emission Factors – Valve 
26

Appendix B: Comparison of Average Emission 

Factors from Published Sources to 

Current Study by Component Type 

The figures in this appendix provide a graphical comparison of the average emission 

factors developed based on a statistical analysis of combined data set of leak 

measurement and component counts collected during several field measurement 

programs, to those from the 1995/1996 and the 2005/2006 data sets and to published 

sources. The 95 percent confidence intervals on the average emission factors developed 

for the Canadian natural gas transmission and distribution industry are incorporated via 

whisker plots. This comparison is presented in tabular form in Table 3-2. To illustrate the 

relative magnitude of the emission factors for various component categories, the first 

figure shows the average factors for all categories on a Cartesian scale. The following 

four figures offer the emission factor comparisons on log scales in order to expand the 

emission rate range for various component categories. 

0

1

2

3

4

5

6

Blowdown

Compressor Seal - Cent

Compressor Seal - Recip

Open-Ended Line

Controller

Pressure Relief Valve

Orifice Meter

Control Valve

Valve

Pressure Regulator

Connector

Other Flow Meter

Average Emission Factor (kg/h/src)

U.S. Gas Production [1] Upstream Oil and Gas Operations [2] GRI Gas Transmission [3]

1995/1996 Gas Transmission [4] 2005/2006 Gas Transmission Combined Gas Transmission

1995/1996 Gas Distribution [4] 2005/2006 Gas Distribution Combined Gas Distribution

1995/1996 Gas Distribution-CR [4] 2005/2006 Gas Distribution-CR Combined Gas Distribution-CR

Figure B-1 Comparison of Average Emission Factors – All Equipment Components 
27

0.000001

0.00001

0.0001

0.001

0.01

0.1

Pressure Regulator Connector Other Flow Meter

Average Emission Factor (kg/h/src)

U.S. Gas Production [1]

Upstream Oil and Gas Operations [2]

GRI Gas Transmission [3]

1995/1996 Gas Transmission [4]

2005/2006 Gas Transmission

Combined Gas Transmission

1995/1996 Gas Distribution [4]

2005/2006 Gas Distribution

Combined Gas Distribution

1995/1996 Gas Distribution-CR [4]

2005/2006 Gas Distribution-CR

Combined Gas Distribution-CR

Figure B-2 Comparison of Average Emission Factors – Pressure Regulator, Connector 

and Other Flow Meter 

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

Orifice Meter Control Valve Valve

Average Emission Factor (kg/h/src)

U.S. Gas Production [1]

Upstream Oil and Gas Operations [2]

GRI Gas Transmission [3]

1995/1996 Gas Transmission [4]

2005/2006 Gas Transmission

Combined Gas Transmission

1995/1996 Gas Distribution [4]

2005/2006 Gas Distribution

Combined Gas Distribution

1995/1996 Gas Distribution-CR [4]

2005/2006 Gas Distribution-CR

Combined Gas Distribution-CR

Figure B-3 Comparison of Average Emission Factors – Orifice Meter, Control Valve 

and Valve 
28

0.0001

0.001

0.01

0.1

1

Open-Ended Line Controller Pressure Relief Valve

Average Emission Factor (kg/h/src)

U.S. Gas Production [1]

Upstream Oil and Gas Operations [2]

GRI Gas Transmission [3]

1995/1996 Gas Transmission [4]

2005/2006 Gas Transmission

Combined Gas Transmission

1995/1996 Gas Distribution [4]

2005/2006 Gas Distribution

Combined Gas Distribution

1995/1996 Gas Distribution-CR [4]

2005/2006 Gas Distribution-CR

Combined Gas Distribution-CR

Figure B-4 Comparison of Average Emission Factors – Open-Ended Line, Controller 

and Pressure Relief Valve 

0.001

0.01

0.1

1

10

100

Blowdown Compressor Seal - Cent Compressor Seal - Recip

Average Emission Factor (kg/h/src)

U.S. Gas Production [1]

Upstream Oil and Gas Operations [2]

GRI Gas Transmission [3]

1995/1996 Gas Transmission [4]

2005/2006 Gas Transmission

Combined Gas Transmission

1995/1996 Gas Distribution [4]

2005/2006 Gas Distribution

Combined Gas Distribution

1995/1996 Gas Distribution-CR [4]

2005/2006 Gas Distribution-CR

Combined Gas Distribution-CR

Figure B-5 Comparison of Average Emission Factors – Blowdown, Centrifugal 

Compressor Seal and Reciprocating Compressor Seal 
29 

Appendix C: Leaker Data Distribution 

The figures in this appendix show the data distribution for leak measurements, sorted by 

source type, for the transmission and distribution industries. The percent of the leaker 

population is on the X-axis and the span of the leak rate measurements is on the Y-axis. 

Absolute emission rates can be inferred from the mean, standard deviation and 

confidence limits provided on each graph. These graphs only represent the emissions 

from identified leakers, and the statistical values provided on the graphs are for the 

leaking equipment component population rather than the entire population of leaking and 

non-leaking equipment components. The population of leaking equipment components 

at commercial and residential meter sets was not large enough to construct the 

corresponding figures for this industry sub-sector. 

The leak frequencies provided in Table 3-1 show that the component population, for 

most component categories, is composed predominantly of non-leaking equipment 

components. The overall leak frequency at the facilities surveyed is approximately 1.9 

percent. The distribution for most component types is very flat; therefore one is most 

likely to encounter non-leakers. The four exceptions to this are compressor seals, 

controllers, blowdowns and open-ended lines, all of which have leak frequencies 

exceeding 50 percent. 

The distributions of leaker emission rates, shown in the following figures, illustrate a 

highly skewed population for most component categories. The emission rates from the 

vast majority of components in the leaker population are small and there are only a few 

large leakers in the component category, typically representing only 1 to 2 percent of the 

population. These top few leakers in each category have a significant impact on the 

average emission rate. Again, the major exceptions are compressor seals and 

controllers, which have a flat distribution. For these component types, the likelihood of 

encountering a small leaker and large leaker is similar. 
30

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Transmission - Compressor Seal - Cent

Mean = 3.12E+00 (kg/h/src)

Standard Deviation = 3.05E+00 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 1.00E+00 (kg/h/src)

Figure C-1 Transmission Leaker Data Distribution – Centrifugal Compressor Seals 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Transmission - Compressor Seal - Recip

Mean = 4.31E+00 (kg/h/src)

Standard Deviation = 5.38E+00 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 1.76E+00 (kg/h/src)

Figure C-2 Transmission Leaker Data Distribution – Reciprocating Compressor Seals 
31

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Transmission - Connector

Mean = 7.27E-02 (kg/h/src)

Standard Deviation = 7.08E-01 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 5.29E-02 (kg/h/src)

Figure C-3 Transmission Leaker Data Distribution – Connector 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Transmission - Control Valve

Mean = 9.04E-02 (kg/h/src)

Standard Deviation = 1.75E-01 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 6.25E-02 (kg/h/src)

Figure C-4 Transmission Leaker Data Distribution – Control Valve 
32

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Transmission - Controller

Mean = 1.39E-01 (kg/h/src)

Standard Deviation = 1.59E-01 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 5.89E-02 (kg/h/src)

Figure C-5 Transmission Leaker Data Distribution – Controller 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Transmission - Blowdown

Mean = 1.16E+01 (kg/h/src)

Standard Deviation = 6.65E+01 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 1.74E+01 (kg/h/src)

Figure C-6 Transmission Leaker Data Distribution – Blowdown 
33

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Transmission - Open-Ended Line

Mean = 4.15E-01 (kg/h/src)

Standard Deviation = 1.16E+00 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 2.61E-01 (kg/h/src)

Figure C-7 Transmission Leaker Data Distribution – Open-Ended Line 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Transmission - Orifice Meter

Mean = 4.06E-01 (kg/h/src)

Standard Deviation = 1.16E+00 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 4.95E-01 (kg/h/src)

Figure C-8 Transmission Leaker Data Distribution – Orifice Meter 
34

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Transmission - Pressure Regulator

Mean = 1.67E-01 (kg/h/src)

Standard Deviation = 7.46E-01 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 2.44E-01 (kg/h/src)

Figure C-9 Transmission Leaker Data Distribution – Pressure Regulator 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Transmission - Pressure Relief Valve

Mean = 7.64E-01 (kg/h/src)

Standard Deviation = 3.36E+00 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 7.99E-01 (kg/h/src)

Figure C-10 Transmission Leaker Data Distribution – Pressure Relief Valve 
35

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Transmission - Valve

Mean = 2.23E-01 (kg/h/src)

Standard Deviation = 7.20E-01 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 9.37E-02 (kg/h/src)

Figure C-11 Transmission Leaker Data Distribution – Valve 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Distribution - Compressor Seal - Cent

Mean = 2.94E-01 (kg/h/src)

Standard Deviation = 1.53E-01 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 9.46E-02 (kg/h/src)

Figure C-12 Distribution Leaker Data Distribution – Centrifugal Compressor Seals 
36

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Distribution - Connector

Mean = 5.85E-03 (kg/h/src)

Standard Deviation = 5.32E-02 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 5.13E-03 (kg/h/src)

Figure C-13 Distribution Leaker Data Distribution – Connector 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Distribution - Control Valve

Mean = 8.16E-02 (kg/h/src)

Standard Deviation = 2.31E-01 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 6.90E-02 (kg/h/src)

Figure C-14 Leaker Data Distribution – Control Valve 
37

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Distribution - Blowdown

Mean = 5.58E-02 (kg/h/src)

Standard Deviation = 1.06E-01 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 1.04E-01 (kg/h/src)

Figure C-15 Distribution Leaker Data Distribution – Blowdown 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Distribution - Open-Ended Line

Mean = 2.48E-01 (kg/h/src)

Standard Deviation = 5.47E-01 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 2.34E-01 (kg/h/src)

Figure C-16 Distribution Leaker Data Distribution – Open-Ended Line 
38

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Distribution - Pressure Relief Valve

Mean = 2.40E-03 (kg/h/src)

Standard Deviation = 3.28E-03 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 1.18E-03 (kg/h/src)

Figure C-17 Distribution Leaker Data Distribution – Pressure Relief Valve 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Distribution - Pressure Regulator

Mean = 8.70E-03 (kg/h/src)

Standard Deviation = 2.08E-02 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 1.23E-02 (kg/h/src)

Figure C-18 Distribution Leaker Data Distribution – Pressure Regulator 
39

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Span

Percent of Components

Data Distribution for Distribution - Valve

Mean = 5.33E-03 (kg/h/src)

Standard Deviation = 1.41E-02 (kg/h/src)

95 Percent Confidence Limits = Mean +/- 2.47E-03 (kg/h/src)

Figure C-19 Distribution Leaker Data Distribution – Valve 
40

Appendix D: Cumulative Leak Contributions 

The following graphs for each equipment component type show the cumulative 

contribution of each leaking equipment component to emissions from that source 

category. When the leakers are ranked from largest to smallest, as on these graphs, it 

becomes apparent that the top 10 percent of leakers typically contribute approximately 

90 percent of the emissions. While this does vary somewhat by component category, the 

majority of the emissions in all component categories are contributed by a relatively 

small fraction of the leaking component population. Only the data from the surveyed 

transmission facilities are presented by way of example, as the cumulative leak 

contribution graphs for components at distribution facilities are analogous. 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Components

Percent of Emissions

Figure D-1 Cumulative Leak Contributions for Transmission Facilities – All equipment 

components 
41

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Components

Percent of Emissions

Figure D-2 Cumulative Leak Contributions – Transmission – Centrifugal Compressor 

Seals 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Components

Percent of Emissions

Figure D-3 Cumulative Leak Contributions – Transmission – Reciprocating 

Compressor Seals 
42

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Components

Percent of Emissions

Figure D-4 Cumulative Leak Contributions – Transmission – Connector 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Components

Percent of Emissions

Figure D-5 Cumulative Leak Contributions – Transmission – Controller Vent 
43

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Components

Percent of Emissions

Figure D-6 Cumulative Leak Contributions – Transmission – Control Valve 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Components

Percent of Emissions

Figure D-7 Cumulative Leak Contributions – Transmission – Blowdown 
44

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Components

Percent of Emissions

Figure D-8 Cumulative Leak Contributions – Transmission – Open-Ended Line 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Components

Percent of Emissions

Figure D-9 Cumulative Leak Contributions – Transmission – Orifice Meter 
45

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Components

Percent of Emissions

Figure D-10 Cumulative Leak Contributions – Transmission – Pressure Relief 

Valve 

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Percent of Components

Percent of Emissions

Figure D-11 Cumulative Leak Contributions – Transmission – Valve 
46 

Appendix E: Default Component Counts and Confidence Intervals 

The following tables present the default component count data and the 95 percent confidence limits (CL) on each vanumber of facilities or units surveyed. The 1995/1996 data set does not contain the detail required to evaluate confidcomponent counts; consequently, the counts presented are based on the 2005/2006 and independent company studAs has been noted, component counts can vary significantly based on a number of factors. The results of componen

facilities show that certain component categories may not be present at all facilities of a given type. In these cases a results. To avoid confusion associated with fractional activity factors, entries in the table have been rounded to genecases of fractional activity factors less than 0.5, a value of zero has been entered to indicate that the component mainfrequently at facilities of the given type. Since these fractional component types do not make a significant contributthe impact on large scale emission inventories is considered extremely small. 

Table E-1 Confidence Limits on Equipment Schedules for Gas Transmission Facilities Based on 2005/2006 Me

Campaign and Independent Company Studies Data Set. 

Component Receipt / Sales Meter Station Mainline Block Valve Reciprocating Compressor Unit Centrifugal Compressor Unit Compresso

Station Yard Piping 

Facilities Surveyed 168 13 25 29 21 

Average – – – 2 – Upper CL – – – – – 

Compressor Seal – Centrifugal Lower CL – – – – – 

Average – – 4 – – Upper CL – – 5 – – 

Compressor Seal – Reciprocating Lower CL – – 4 – – 

Average 33 200 256 502 950 

Connector Upper CL 46 317 347 576 1210 

Lower CL 20 84 165 429 689 
47

Table E-1 Confidence Limits on Equipment Schedules for Gas Transmission Facilities Based on 2005/2006 Me

Campaign and Independent Company Studies Data Set. 

Component Receipt / Sales Meter Station Mainline Block Valve Reciprocating Compressor Unit Centrifugal Compressor Unit Compresso

Station Yard Piping 

Average 0 0 1 5 13 

Control Valve Upper CL 0 1 2 6 22 

Lower CL 0 0 0 4 4 

Average 0 0 0 0 1 

Controller Upper CL 0 0 0 0 1 

Lower CL 0 0 0 0 0 

Average 0 0 0 1 4 

Blowdown Upper CL 0 0 0 1 5 

Lower CL 0 0 0 1 3 

Average 0 1 0 4 6 Upper CL 0 1 0 6 9 

Open-Ended Line Lower CL 0 1 0 3 3 

Average 0 – 1 0 2 

Orifice Meter Upper CL 0 – 1 0 4 

Lower CL 0 – 0 0 0 

Average 1 0 – 0 1 Upper CL 1 0 – 1 2 

Other Flow Meter Lower CL 1 0 – 0 0 

Average 1 2 2 5 15 Upper CL 1 5 3 6 20 

Pressure Regulator Lower CL 1 0 2 3 10 

Average 0 0 2 3 8 Upper CL 1 0 2 4 10 

Pressure Relief Valve Lower CL 0 0 1 2 5 

Average 7 36 22 120 217 

Valve Upper CL 9 53 27 140 289 

Lower CL 5 18 17 101 145 
48

Table E-2 Confidence Limits on Equipment Schedules for Gas Distribution Facilities and Meter/Regulation Sta

2005/2006 Measurement Campaign and Independent Company Studies Data Set. 

Component Industrial Meter Set Gate Station District Regulator Station Border Meter Station Mainline Block Valve Reciprocating Compressor Unit Centrifugal Compressor Unit Com

Stat

P

Facilities Surveyed 15 30 32 6 22 2 12 

Average – – – – – – 2 Upper CL – – – – – – – 

Compressor Seal – Centrifugal Lower CL – – – – – – – 

Average – – – – – 5 – Upper CL – – – – – – – 

Compressor Seal – Reciprocating Lower CL – – – – – – – 

Average 111 353 181 381 142 163 430 

Connector Upper CL 152 427 248 – 207 – 523 

Lower CL 70 280 113 – 77 – 336 

Average 0 2 1 1 1 1 5 

Control Valve Upper CL 1 3 1 – 3 – 6 

Lower CL 0 0 0 – 0 – 4 

Average – 0 – – 0 – – 

Controller Upper CL – 0 – – 0 – – 

Lower CL – 0 – – 0 – – 

Average – – – 0 – 1 1 

Blowdown Upper CL – – – – – – 1 

Lower CL – – – – – – 0 

Average – 0 0 4 1 4 5 

Open-Ended Line Upper CL – 1 1 – 1 – 8 

Lower CL – 0 0 – 0 – 2 

Average 0 1 0 – 0 1 0 

Orifice Meter Upper CL 0 1 0 – 0 – 1 

Lower CL 0 0 0 – 0 – 0 

Average 1 1 0 1 0 – 1 

Other Flow Meter Upper CL 2 1 0 – 1 – 1 

Lower CL 1 0 0 – 0 – 0 
49

Table E-2 Confidence Limits on Equipment Schedules for Gas Distribution Facilities and Meter/Regulation Sta

2005/2006 Measurement Campaign and Independent Company Studies Data Set. 

Component Industrial Meter Set Gate Station District Regulator Station Border Meter Station Mainline Block Valve Reciprocating Compressor Unit Centrifugal Compressor Unit Com

Stat

P

Average 4 12 8 8 2 1 3 

Pressure Regulator Upper CL 6 14 10 – 4 – 4 

Lower CL 2 10 5 – 1 – 1 

Average 0 3 2 3 1 2 2 Upper CL 1 3 2 – 3 – 3 

Pressure Relief Valve Lower CL 0 2 1 – 0 1 1 

Average 26 64 40 62 33 20 83 

Valve Upper CL 37 80 53 – 54 – 102 

Lower CL 15 49 27 – 13 – 64 
50

Table E-3 Confidence Limits on Equipment Schedules for Gas Distribution Commercial and Residential Meter 

2005/2006 Measurement Campaign Data Set. 

Component Residential Meter Set Commercial Meter Set 

Facilities Surveyed 44 35 

Average 48 82 

Connector Upper CL 69 100 

Lower CL 27 65 

Average 0 0 

Control Valve Upper CL 0 0 

Lower CL 0 0 

Average – 0 

Orifice Meter Upper CL – 0 

Lower CL – 0 

Average 1 2 

Other Flow Meter Upper CL 2 3 

Lower CL 1 1 

Average 2 3 

Pressure Regulator Upper CL 2 5 

Lower CL 1 2 

Average 0 1 Upper CL 0 2 

Pressure Relief Valve Lower CL 0 0 

Average 8 14 

Valve Upper CL 13 18 

Lower CL 4 10 
51

Appendix F: Changes observed from 1995/1996 to 2005/2006 data sets 

The tables in this appendix offer a comparison, by industry sub-sector, of the average emission factors and confiden

1995/1996 data set, the 2005/2006 measurement campaign and independent company studies data set and the comIn addition, tabular summaries of the magnitude of changes between the 1995/1996 study and subsequent measurenumber of sources encountered, leak frequencies and average emissions are provided. 

Table F-1 Comparison of Average Emission Factors (kg TOC/h/source) for Gas Transmission Facilities. 

Combined Data Set 2005/2006 Measurement Campaign + Independent Company Studies 1

Component 

Category

Number 

of 

Sources 

Average 

Emission 

Factor Upper CL Lower CL 

Number 

of 

Sources 

Average 

Emission 

Factor Upper CL Lower CL 

Number 

of 

Sources 

Ave

Em

Fa

Compressor Seal - Cent 79 1.617E+00 2.181E+00 1.053E+00 58 1.908E+00 2.634E+00 1.182E+00 21 8.13Compressor Seal - Recip 149 1.203E+00 1.714E+00 6.908E-01 113 1.375E+00 2.042E+00 7.074E-01 36 6.6Connector 145829 4.471E-04 6.985E-04 1.957E-04 100761 5.297E-04 8.928E-04 1.667E-04 45068 2.62Control Valve 782 1.650E-02 2.219E-02 1.082E-02 509 1.479E-02 1.911E-02 1.048E-02 273 1.96Controller 50 2.371E-01 3.747E-01 9.941E-02 33 1.181E-01 1.708E-01 6.532E-02 17 4.68Blowdown 219 3.405E+00 7.885E+00 0 117 5.556E+00 1.392E+01 0 102 9.36Open-Ended Line 928 9.183E-02 1.297E-01 5.395E-02 286 1.104E-01 1.827E-01 3.816E-02 642 8.35Orifice Meter 185 4.863E-02 1.066E-01 0 81 1.068E-01 2.386E-01 0 104 3.3Other Flow Meter 443 9.942E-06 1.966E-05 2.223E-07 177 1.131E-05 2.645E-05 0 266 9.03Pressure Regulator 816 7.945E-03 1.882E-02 0 687 8.770E-03 2.167E-02 0 129 3.55Pressure Relief Valve 612 1.620E-01 2.950E-01 2.906E-02 426 1.225E-01 2.520E-01 0 186 2.52Valve 17029 4.131E-03 5.514E-03 2.748E-03 10877 5.257E-03 7.366E-03 3.148E-03 6152 2.14
52

Table F-2 Changes from 1995/1996 to 2005/2006 Gas Transmission Data Sets 

Percent Change from 1995/1996 to 2005/2006 

Component Category 

Number of Sources 

Surveyed Leak Frequency Leaker Emission Factor 

Compressor Seal - Cent 176 -35 260 Compressor Seal - Recip 214 -63 462 Connector 124 -45 292 Control Valve 86 -60 19 Controller 94 -15 -70 Blowdown 15 -35 811 Open-Ended Line -55 -63 259 Orifice Meter -22 28 4519 Other Flow Meter -33 -79 554 Pressure Regulator 443 -68 743 Pressure Relief Valve 129 -76 100 Valve 77 -48 473 
53

Table F-3 Comparison of Average Emission Factors (kg TOC/h/source) for Gas Distribution Facilities and Me

Combined Data Set 2005/2006 Measurement Campaign + Independent Company Studies 1

Component 

Category

Number 

of 

Sources 

Average 

Emission 

Factor Upper CL Lower CL 

Number 

of 

Sources 

Average 

Emission 

Factor Upper CL Lower CL 

Number 

of 

Sources 

Ave

Em

Fa

Compressor Seal - Cent 24 1.223E-01 1.927E-01 5.191E-02 24 1.223E-01 1.927E-01 5.191E-02 – Compressor Seal - Recip 9 5.600E-04 1.789E-03 0 9 5.600E-04 1.789E-03 0 – Connector 52051 8.227E-05 1.266E-04 3.792E-05 43466 7.687E-05 1.258E-04 2.791E-05 8585 1.09Control Valve 605 1.949E-02 2.771E-02 1.127E-02 332 1.933E-02 2.875E-02 9.903E-03 273 1.96Controller 25 3.997E-01 6.836E-01 1.158E-01 8 2.544E-01 6.599E-01 0 17 4.68Blowdown 42 5.878E-03 1.591E-02 0 42 5.878E-03 1.591E-02 0 – Open-Ended Line 969 6.077E-02 9.068E-02 3.086E-02 327 1.606E-02 3.216E-02 0 642 8.35Orifice Meter 142 3.011E-03 4.131E-03 1.890E-03 38 2.182E-03 3.987E-03 3.771E-04 104 3.3Other Flow Meter 348 7.777E-06 1.752E-05 0 82 3.700E-06 7.634E-06 0 266 9.03Pressure Regulator 1323 6.549E-04 1.375E-03 0 954 1.218E-04 2.695E-04 0 369 2.03Pressure Relief Valve 472 3.944E-03 8.865E-03 0 378 7.860E-04 1.044E-03 5.283E-04 94 1.66Valve 9817 5.607E-04 9.322E-04 1.892E-04 7832 4.217E-04 4.629E-04 3.805E-04 1985 1.10
54

Table F-4 Changes from 1995/1996 to 2005/2006 Gas Distribution Data Sets 

Percent Change from 1995/1996 to 2005/2006 

Component Category 

Number of Sources 

Surveyed Leak Frequency Leaker Emission Factor 

Compressor Seal - Cent – – – Compressor Seal - Recip – – – Connector 406 17 -55 Control Valve 22 -12 8 Controller -53 -50 9 Blowdown – – – Open-Ended Line -49 -91 114 Orifice Meter -63 -48 -50 Other Flow Meter -69 -100 -100 Pressure Regulator 159 -75 -79 Pressure Relief Valve 302 -50 -98 Valve 295 -58 -81 
55

Table F-5 Comparison of Average Emission Factors (kg TOC/h/source) for Commercial and Residential Gas 

Combined Data Set 2005/2006 Measurement Campaign + Independent Company Studies 1

Component 

Category

Number 

of 

Sources 

Average 

Emission 

Factor Upper CL Lower CL 

Number 

of 

Sources 

Average 

Emission 

Factor Upper CL Lower CL 

Number 

of 

Sources 

Ave

Em

Fa

Connector 8616 4.467E-06 8.112E-06 8.226E-07 5846 3.469E-06 5.567E-06 1.371E-06 2770 6.57Control Valve 8 1.006E-02 2.466E-02 0 8 1.006E-02 2.466E-02 0 – Open-Ended Line 642 8.355E-02 1.279E-01 3.924E-02 642 8.35Orifice Meter 107 3.274E-03 4.630E-03 1.919E-03 3 1.925E-03 9.913E-03 0 104 3.3Other Flow Meter 405 7.203E-06 1.560E-05 0 139 3.700E-06 6.714E-06 6.861E-07 266 9.03Pressure Regulator 348 2.329E-05 4.633E-05 2.410E-07 246 2.383E-05 5.352E-05 0 102 2.19Pressure Relief Valve 78 1.749E-03 3.747E-03 0 72 1.872E-03 4.034E-03 0 6 2.7Valve 1340 2.173E-06 2.593E-06 1.753E-06 1081 2.100E-06 2.540E-06 1.660E-06 259 2.47

Table F-6 Changes from 1995/1996 to 2005/2006 Commercial and Residential Gas Distribution Data Sets 

Percent Change from 1995/1996 to 2005/2006 

Component Category 

Number of Sources 

Surveyed Leak Frequency Leaker Emission Factor 

Connector 111 -66 13 Control Valve – – – Open-Ended Line – – – Orifice Meter -97 -100 -100 Other Flow Meter -48 -100 -100 Pressure Regulator 141 -94 1747 Pressure Relief Valve – – – Valve 317 -100 -100 
56 

Appendix G: Measured Emissions from 2005/2006 

Field Campaign 

Emissions from fugitive equipment leaks identified and measured during the 2005/2006 

field campaign total 13,536 × 103

 m3/yr of lost product. The estimated value of these 

losses is $2,250,000 CDN/yr based on a natural gas value of $4.45 CDN/GJ. Table F-1 

provides a summary of the measured emissions by type of facility, while Table F-2 lists 

the top 20 leaks encountered during the survey, along with the volume and value of 

product lost. Both tables indicate the significant contribution compressor stations, both 

odourized and unodourized, make to the overall emissions from the Canadian natural 

gas transmission and distribution industry. Compressor stations account for 98 percent 

of overall leakage and all 20 of the top leakers encountered during the 2005/2006 

emission survey were located at compressor stations. 

Table G-1 2005/2006 Measured Emissions by Facility Type 

Facility Type Hydrocarbon Leak Rate 

(m3/hr) 

Contribution of Overall 

Leakage (%) 

Compressor Stations 1 1513.7 97.96 

Gate / Regulation Stations 14.61 0.95 

Block / Control Valve Stations 13.11 0.85 

Receipt / Meter Stations 3.66 0.24 

1

 Includes two LNG storage facilities. 

Table G-2 Top Twenty Leakers from 2005/2006 Emissions Survey 

Facility Type Process Unit Source 

Hydrocarbon 

Leak Rate 

(m3/hr) 

Value of Lost 

Product ($/yr) 

Compressor Stn. Station Blowdown Blowdown 656.2 $956,700 

Compressor Stn. Cyclone Separator Blowdown 121.7 $177,378 

Compressor Stn. Station Blowdown Pressure Relief 

Valve 35.7 $52,098 

Compressor Stn. Recip. Compressor Compressor Seal 28.8 $41,970 

Compressor Stn. Recip. Compressor Compressor Seal 28.8 $41,970 

Compressor Stn. Filter Unit Connector - Filter 

Cover 22.9 $33,392 

Compressor Stn. Recip. Compressor Compressor Seal 19.5 $28,475 

Compressor Stn. Recip. Compressor Compressor Seal 19.2 $28,025 

Compressor Stn. Station Fuel Gas 

Vent Blowdown 18.3 $26,640 

Compressor Stn. Cent. Compressor Compressor Seal 17.4 $25,367 

Compressor Stn. Compressor 

Blowdown Blowdown 15.9 $23,241 

Compressor Stn. Cent. Compressor Compressor Seal 15.8 $22,994 

Compressor Stn. Recip. Compressor Compressor Seal 14.0 $20,449 

Compressor Stn. Cent. Compressor Compressor Seal 12.8 $18,619 

Compressor Stn. Cent. Compressor Compressor Seal 12.1 $17,642 

Compressor Stn. Cent. Compressor Compressor Seal 11.7 $17,103 

Compressor Stn. Discharge Cooler Open-Ended Line 11.6 $16,939 

Compressor Stn. Recip. Compressor Compressor Seal 11.3 $16,403 

Compressor Stn. Cent. Compressor Compressor Seal 10.7 $15,545 

Compressor Stn. Cent. Compressor Compressor Seal 10.6 $15,435