EPA-453/R-95-017

1995 Protocol for Equipment Leak

Emission Estimates

Emission Standards Division

U.S. ENVIRONMENTAL PROTECTION AGENCY

Office of Air and Radiation

Office of Air Quality Planning and Standards

Research Triangle Park, North Carolina 27711

November 1995
This report has been reviewed by the Emission Standards

Division of the Office of Air Quality Planning and Standards, the

EPA and approved for publication. Mention of trade names or

commercial products is not intended to constitute endorsement or

recommendation for use. Copies of this report are available

through the Library Services Office (MD-35), U.S. Environmental

Protection Agency, Research Triangle Park, North Carolina 27711;

from the Office of Air Quality Planning and Standards Technology

Transfer Network, U.S. Environmental Protection Agency, Research

Triangle Park, North Carolina 27711; or, for a fee, from the

National Technical Information Services, 5285 Port Royal Road,

Springfield, Virginia 22161.

Publication No. EPA-453/R-95-017
FOREWORD

The EPA’s protocol for estimating equipment leak emissions

is the result of detailed information gathering and data

analysis. The protocol was written to provide a thorough

understanding of acceptable approaches to generating process

unit-specific emission estimates. In preparing this document,

the EPA has encouraged knowledgeable individuals in industry and

the regulatory community to provide comments.

The EPA has put forth considerable effort to make this

document as comprehensive as possible. However, it should be

understood that not all details and topics pertaining to

equipment leaks could feasibly be included in this document.

Additionally, it should be understood that the procedures

presented in this document are not necessarily suitable for all

applications. There will be cases where it will be necessary for

the user of the document to make a professional judgement as to

the appropriate technical approach for collecting and analyzing

data used to estimate equipment leak emissions.

Additional data on equipment leak emissions continues to be

collected. It is the intent of the EPA to periodically update

this document after analysis of the data warrants such an

update. For example, data recently collected in the petroleum

industry has been used to revise the existing refinery

correlations, which are based on data collected in the

late 1970s. Furthermore, as new techniques for collecting and

analyzing data are developed, they will be included in updated

versions of this document.

Mention of any manufacturer or company name within this

document does not represent endorsement by the EPA.

i
TABLE OF CONTENTS

Section Page

FOREWORD .......................... i

1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . 1-1

2.0 DEVELOPMENT OF EQUIPMENT LEAK EMISSION ESTIMATES . . . . 2-1

2.1 Introduction . . . . . . . . . . . . . . . . . . . 2-1

2.2 General Information on the Approaches for

Estimating Equipment Leak Emissions . . . . . . . . 2-3

2.2.1 Equipment Leak Emission Estimation

Approaches . . . . . . . . . . . . . . . . . 2-3

2.2.2 Overview of Equipment Leak Data Collection . 2-6

2.3 Approaches for Estimating Equipment Leak

Emissions.................... 2-10

2.3.1 Average Emission Factor Approach..... 2-10

2.3.2 Screening Ranges Approach ........ 2-18

2.3.3 EPA Correlation Approach......... 2-24

2.3.4 Unit-Specific Correlation Approach.... 2-38

2.4 Special Topics ................. 2-44

2.4.1 Speciating Emissions........... 2-45

2.4.2 Using Response Factors.......... 2-46

2.4.3 Monitoring Instrument Type and Calibration

Gas . . . . . . . . . . . . . . . . . . . 2-51

2.4.4 Estimating Emissions for Equipment Not

Screened................. 2-51

2.4.5 Using Screening Data Collected at Several

Different Times ............. 2-52

2.4.6 Estimating VOC Emission Rates from Equipment

Containing Non-VOC’s........... 2-52

2.4.7 Estimating Equipment Leak Emissions of

Inorganic Compounds ........... 2-53

2.5 References ................... 2-54

3.0 SOURCE SCREENING . . . . . . . . . . . . . . . . . . . . 3-1

3.1 Introduction . . . . . . . . . . . . . . . . . . . 3-1

3.2 Monitoring Instruments . . . . . . . . . . . . . . 3-2

3.2.1 Operating Principles and Limitations of

Portable VOC Detection Devices . . . . . . . 3-2

ii
TABLE OF CONTENTS (Continued)

Section Page

3.2.2 Specifications and Performance Criteria of

Portable VOC Detection Devices . . . . . . . 3-4

3.2.3 Use of Monitoring Devices That Do Not Meet

EPA Reference Method 21 Requirements... 3-10

3.3 The Screening Program.............. 3-12

3.3.1 Identification of Equipment to be Screened 3-12

3.3.2 Procedure for Screening ......... 3-15

3.3.3 Data Handling .............. 3-25

3.4 References ................... 3-27

4.0 MASS EMISSION SAMPLING . . . . . . . . . . . . . . . . . 4-1

4.1 Introduction . . . . . . . . . . . . . . . . . . . 4-1

4.2 Sampling Methods . . . . . . . . . . . . . . . . . 4-2

4.2.1 Vacuum Method . . . . . . . . . . . . . . . 4-4

4.2.2 Blow-Through Method . . . . . . . . . . . . 4-8

4.3 Source Enclosure ................ 4-15

4.3.1 Valves.................. 4-15

4.3.2 Pumps and Agitators ........... 4-16

4.3.3 Compressors ............... 4-17

4.3.4 Connectors................ 4-17

4.3.5 Relief Valves .............. 4-18

4.4 Analytical Techniques.............. 4-18

4.4.1 Analytical Instrumentation........ 4-19

4.4.2 Calibration of Analytical Instruments . . 4-19

4.4.3 Analytical Techniques for Condensate... 4-21

4.4.4 Calibration Procedures for the Portable

Monitoring Instrument .......... 4-21

4.5 Quality Control and Quality Assurance Guidelines 4-21

4.5.1 Quality Control Procedures........ 4-22

4.5.2 Quality Assurance Procedures....... 4-25

4.6 References ................... 4-29

5.0 ESTIMATION OF CONTROL EFFICIENCIES FOR EQUIPMENT LEAK

CONTROL TECHNIQUES . . . . . . . . . . . . . . . . . . . 5-1

5.1 Introduction . . . . . . . . . . . . . . . . . . . 5-1

iii
TABLE OF CONTENTS (Continued)

Section Page

5.2 Equipment Modification Control Efficiency . . . . . 5-1

5.2.1 Closed-Vent Systems . . . . . . . . . . . . 5-2

5.2.2 Pumps . . . . . . . . . . . . . . . . . . . 5-2

5.2.3 Compressors . . . . . . . . . . . . . . . . 5-4

5.2.4 Pressure Relief Valves . . . . . . . . . . . 5-4

5.2.5 Valves . . . . . . . . . . . . . . . . . . . 5-5

5.2.6 Connectors . . . . . . . . . . . . . . . . . 5-5

5.2.7 Open-Ended Lines . . . . . . . . . . . . . . 5-6

5.2.8 Sampling Connections . . . . . . . . . . . . 5-6

5.3 Leak Detection and Repair Control Effectiveness . . 5-6

5.3.1 Approach for Estimating LDAR Control

Effectiveness . . . . . . . . . . . . . . . 5-8

5.3.2 Example Application of Approach ..... 5-57

5.4 References ................... 5-61

APPENDICES

A Example Calculations . . . . . . . . . . . . . . . . . . A-1

B Leak Rate Screening Value Correlation Development and

Revision of SOCMI Correlations and Emission Factors . . B-1

C Revision of Petroleum Industry Correlations and Emission

Factor . . . . . . . . . . . . . . . . . . . . . . . . . C-1

D Response Factors . . . . . . . . . . . . . . . . . . . . D-1

E Selection of Sample Size for Screening Connectors . . . E-1

F Reference Method 21 . . . . . . . . . . . . . . . . . . F-1

G Development of Leak Rate Versus Fraction Leaking

Equations and Determination of LDAR Control

Effectiveness . . . . . . . . . . . . . . . . . . . . . G-1

iv
LIST OF TABLES

Table Page

2-1 SOCMI Average Emission Factors ......... 2-12

2-2 Refinery Average Emission Factors........ 2-13

2-3 Marketing Terminal Average Emission Factors... 2-14

2-4 Oil and Gas Production Operations Average Emission

Factors..................... 2-15

2-5 SOCMI Screening Ranges Emission Factors..... 2-19

2-6 Refinery Screening Ranges Emission Factors . . . 2-20

2-7 Marketing Terminal Screening Ranges Emission

Factors..................... 2-21

2-8 Oil and Gas Production Operations Screening Ranges

Emission Factors ................ 2-22

2-9 SOCMI Leak Rate/Screening Value Correlations . . 2-26

2-10 Petroleum Industry Leak Rate/Screening Value

Correlations .................. 2-27

2-11 Default-Zero Values: SOCMI Process Units.... 2-33

2-12 Default-Zero Values: Petroleum Industry .... 2-34

2-13 10,000 and 100,000 ppmv Screening Value Pegged Emission

Rates For SOCMI Process Units.......... 2-36

2-14 10,000 and 100,000 ppmv Screening Value Pegged Emission

Rates For the Petroleum Industry ........ 2-37

3-1 Performance Criteria for Portable VOC Detectors . . 3-6

3-2 Portable VOC Detection Instruments ....... 3-11

3-3 Equipment Leak Emission Sources......... 3-13

3-4 Example Field Sheets For Equipment Screening Data 3-26

4-1 Calculation Procedures For Leak Rate When Using

the Vacuum Method . . . . . . . . . . . . . . . . . 4-9

4-2 Calculation Procedures For Leak Rate When Using

the Blow-Through Method............. 4-13

4-3 Example GC Calibration Data Sheet........ 4-20

v
LIST OF TABLES (Continued)

Table Page

4-4 Example Data Collection Form For Fugitive

Emissions Bagging Test (Blow-Through Method) . . 4-23

4-5 Example Data Collection Form For Fugitive

Emissions Bagging Test (Vacuum Method) ..... 4-24

4-6 Example Drift Test Report Form ......... 4-28

5-1 Summary of Equipment Modifications . . . . . . . . 5-3

5-2 Control Effectiveness For an LDAR Program At a

SOCMI Process Unit . . . . . . . . . . . . . . . . 5-9

5-3 Control Effectiveness For an LDAR Program At a

Refinery Process Unit.............. 5-10

5-4 Equations Relating Average Leak Rate to Fraction

Leaking at SOCMI Units ............. 5-46

5-5 Equations Relating Average Leak Rate to Fraction

Leaking at Refinery Units............ 5-47

5-6 Equations Relating Average Leak Rate to Fraction

Leaking At Marketing Terminal Units....... 5-48

5-7 Equations Relating Average Leak Rate to Fraction

Leaking At Oil and Gas Production Operating

Units...................... 5-50

5-8 Values Used in Example Calculation ....... 5-58

5-9 Example Calculation To Determine the Final Leak

Frequency Of SOCMI Gas Valves In a Monthly

Monitoring LDAR Program With a Leak Definition

of 10,000 ppmv ................. 5-60

vi
LIST OF FIGURES

Figure Page

2-1 Overview of Data Collection and Analysis

Approaches for Developing Equipment Leak

Emissions Inventory . . . . . . . . . . . . . . . . 2-4

2-2 SOCMI Correlations Relating Total Organic Compound

(TOC) Leak Rate to Screening Value:

0 - 1,000 ppmv ................. 2-28

2-3 SOCMI Correlations Relating Total Organic Compound

(TOC) Leak Rate to Screening Value:

1,000 - 1,000,000 ppmv ............. 2-29

2-4 Petroleum Industry Correlations Relating Total Organic

Compound (TOC) Leak Rate to Screening Value:

1,000 - 1,000,000 ppmv ............. 2-30

2-5 Petroleum Industry Correlations Relating Total Organic

Compound (TOC) Leak Rate to Screening Value:

1,000 - 1,000,000 ppmv ............. 2-31

3-1 Gate Valves................... 3-17

3-2 Globe Valves .................. 3-18

3-3 Lubricated Plug Valve.............. 3-19

3-4 Ball Valve and Butterfly Valve ......... 3-20

3-5 Weir-Type Diaphragm Valve and Check Valves . . . 3-21

3-6 Centrifugal Pumps................ 3-23

3-7 Spring-Loaded Relief Valve ........... 3-24

4-1 Sampling Train for Bagging a Source Using the

Vacuum Method . . . . . . . . . . . . . . . . . . . 4-5

4-2 Equipment Required for the Blow-Through Sampling

Technique.................... 4-10

5-1 SOCMI Gas Valve Average Leak Rate Versus Fraction

Leaking at Several Leak Definitions....... 5-11

5-2 SOCMI Light Liquid Valve Average Leak Rate Versus

Fraction Leaking at Several Leak Definitions . . 5-12

5-3 SOCMI Light Liquid Pump Average Leak Rate Versus

Fraction Leaking at Several Leak Definitions . . 5-13

vii
LIST OF FIGURES (Continued)

Figure Page

5-4 SOCMI Connector Average Leak Rate Versus Fraction

Leaking at Several Leak Definitions....... 5-14

5-5 Refinery Gas Valve Average Leak Rate Versus

Fraction Leaking at Several Leak Definitions . . 5-15

5-6 Refinery Light Liquid Valve Average Leak Rate

Versus Fraction Leaking at Several Leak

Definitions................... 5-16

5-7 Refinery Light Liquid Pump Average Leak Rate

Versus Fraction Leaking at Several Leak

Definitions................... 5-17

5-8 Refinery Connector Average Leak Rate Versus

Fraction Leaking at Several Leak Definitions . . 5-18

5-9 Marketing Terminal Gas Fittings Average Leak Rate

Versus Fraction Leaking at Several Leak

Definitions................... 5-19

5-10 Marketing Terminal Light Liquid Fittings Average Leak

Rate Versus Fraction Leaking at Several Leak

Definitions................... 5-20

5-11 Marketing Terminal Gas Others Average Leak Rate Versus

Fraction Leaking at Several Leak Definitions . . 5-21

5-12 Marketing Terminal Light Liquid Others Average Leak

Rate Versus Fraction Leaking at Several Leak

Definitions................... 5-22

5-13 Marketing Terminal Light Liquid Pumps Average Leak Rate

Versus Fraction Leaking at Several Leak

Definitions................... 5-23

5-14 Marketing Terminal Gas Valves Average Leak Rate Versus

Fraction Leaking at Several Leak Definitions . . 5-24

5-15 Marketing Terminal Light Liquid Valves Average Leak

Rate Versus Fraction Leaking at Several Leak

Definitions................... 5-25

5-16 Oil and Gas Production Gas Connectors Average Leak Rate

Versus Fraction Leaking at Several Leak

Definitions................... 5-27

viii
LIST OF FIGURES (Continued)

Figure Page

5-17 Oil and Gas Production Light Oil Connectors Average

Leak Rate Versus Fraction Leaking at Several Leak

Definitions................... 5-28

5-18 Oil and Gas Production Water/Oil Connectors Average

Leak Rate Versus Fraction Leaking at Several Leak

Definitions................... 5-29

5-19 Oil and Gas Production Gas Flanges Average Leak Rate

Versus Fraction Leaking at Several Leak

Definitions................... 5-30

5-20 Oil and Gas Production Light Oil Flanges Average Leak

Rate Versus Fraction Leaking at Several Leak

Definitions................... 5-31

5-21 Oil and Gas Production Gas Open-Ended Lines Average

Leak Rate Versus Fraction Leaking at Several Leak

Definitions................... 5-32

5-22 Oil and Gas Production Heavy Oil Open-Ended Lines

Average Leak Rate Versus Fraction Leaking at Several

Leak Definitions ................ 5-33

5-23 Oil and Gas Production Light Oil Open-Ended Lines

Average Leak Rate Versus Fraction Leaking at Several

Leak Definitions ................ 5-34

5-24 Oil and Gas Production Water/Oil Open-Ended Lines

Average Leak Rate Versus Fraction Leaking at Several

Leak Definitions ................ 5-35

5-25 Oil and Gas Production Gas Other Average Leak Rate

Versus Fraction Leaking at Several Leak

Definitions................... 5-36

5-26 Oil and Gas Production Heavy Oil Other Average Leak

Rate Versus Fraction Leaking at Several Leak

Definitions................... 5-37

5-27 Oil and Gas Production Light Oil Other Average Leak

Rate Versus Fraction Leaking at Several Leak

Definitions................... 5-38

5-28 Oil and Gas Production Water/Oil Other Average Leak

Rate Versus Fraction Leaking at Several Leak

Definitions................... 5-39

ix
LIST OF FIGURES (Continued)

Figure Page

5-29 Oil and Gas Production Gas Pumps Average Leak Rate

Versus Fraction Leaking at Several Leak

Definitions................... 5-40

5-30 Oil and Gas Production Light Oil Pumps Average Leak

Rate Versus Fraction Leaking at Several Leak

Definitions................... 5-41

5-31 Oil and Gas Production Gas Valves Average Leak Rate

Versus Fraction Leaking at Several Leak

Definitions................... 5-42

5-32 Oil and Gas Production Heavy Oil Valves Average Leak

Rate Versus Fraction Leaking at Several Leak

Definitions................... 5-43

5-33 Oil and Gas Production Light Oil Valves Average Leak

Rate Versus Fraction Leaking at Several Leak

Definitions................... 5-44

5-34 Oil and Gas Production Water/Oil Valves Average Leak

Rate Versus Fraction Leaking at Several Leak

Definitions................... 5-45

5-35 Marketing Terminals Light Liquid Pumps Average Leak

Rate Versus Fraction Leaking at Several Leak

Definitions................... 5-55

x
1.0 INTRODUCTION

This document is an update to the EPA equipment leaks

protocol document ("Protocol for Equipment Leak Emission

Estimates," EPA-453/R-93-026, June 1993). The purpose of this

document is the same as the original protocol document and

subsequent revisions- to present standard procedures for

estimating mass emissions from equipment leaks. However, this

document publishes the results of additional data collection and

analysis that has occurred since the original protocol and

subsequent revisions were published, and also expands on some of

the topics that were covered in the original protocol.

Some of the new features of the updated protocol are:

(1) New correlation equations, default zero emission rates,

and pegged emission rates for the petroleum industry that

replace the refinery correlations previously published

are presented. The correlations relate screening values

obtained using a portable monitoring instrument to mass

emissions.

(2) The document has been expanded to include emission

factors for marketing terminals and for oil and gas

production operations. The refinery emission factors

were not revised due to an unavailability of new data.

(3) Pegged emission rates for pegged readings at 10,000 ppmv

have been added for SOCMI process units.

(4) Several of the equations in this version of the protocol

have been revised by simplifying the symbols to more

clearly communicate the concept being conveyed.

(5) An adjustment has been added to the blow-through method

of calculating mass emissions. This adjustment more

accurately accounts for the total flow through the bag.

1-1
As with the original protocol document, this document

presents standard procedures for general use in generating

unit-specific emission estimates for permitting and inventories.

The document describes methodologies the EPA considers

appropriate for development of equipment leak emission estimates.

These methodologies are intended to assist States and industry in

their efforts to estimate equipment leak emissions.

The updated protocol is divided into five chapters and

several appendices. Chapter 2.0 describes how to estimate

equipment leak emissions. Chapter 3.0 describes collecting

screening data that can be used in the emission estimates.

Chapter 4.0 describes collecting unit-specific equipment leak

mass emissions data. Chapter 5.0 describes how to estimate the

control efficiencies of equipment leak control techniques. The

appendices support information contained in the chapters. Each

of these chapters and the appendices are briefly described below.

Chapter 2.0 presents the four approaches for estimating total

organic emissions from equipment leaks. These approaches are:

Average Emission Factor Approach;

Screening Ranges Approach;

EPA Correlation Approach; and

Unit-Specific Correlation Approach.

Additionally, several topics that are relevant to estimating

equipment leak emissions are addressed. These topics include

speciating equipment leak emissions of individual compounds from

an equipment piece containing a mixture, using response factors,

estimating emissions of volatile organic compounds, estimating

emissions of inorganic compounds, and other topics not

specifically related to any one of the four approaches.

Chapter 3.0 explains how to perform a screening survey at a

process unit. Requirements for the use of a portable monitoring

instrument are described. These requirements are based on the

EPA Reference Method 21. Additionally, in chapter 3.0, guidance

is provided on how to set up a screening program and how to

screen different types of equipment.

1-2
Chapter 4.0, explains how to collect equipment leak rate data

(bagging data) by enclosing individual equipment in a "bag" and

measuring mass emissions. These data can be used to develop

unit-specific leak rate/screening value correlations.

Chapter 4.0 details the rigorous steps that need to be followed

when collecting the bagging data to generate unit-specific

correlations. These steps are intended to ensure that the data

are of high quality.

Chapter 5.0, explains how to estimate the control efficiency

of equipment leak emission control techniques. The two primary

control techniques for reducing equipment leak emissions are

(1) equipment modifications (such as replacing a standard valve

with a sealless type) and (2) implementing a leak detection and

repair (LDAR) program. Control efficiencies for different

equipment leak modifications are summarized, and an approach for

estimating the control efficiency of any LDAR program is

provided.

Appendices A through G provide additional information

supporting the material in the chapters. Appendix A contains

detailed example calculations using the approaches described in

chapter 2.0. Appendix B documents how the SOCMI correlations and

emission factors were revised. Appendix B also serves as a

demonstration of how data can be analyzed to develop

unit-specific correlations. Appendix C presents the rationale

for the development of the petroleum industry correlations, as

well as the background for the development of marketing terminal

and oil and gas production operations emission factors.

Appendix D summarizes available data on response factors.

Appendix E provides guidance on how to collect representative

screening data for connectors. Appendix F contains a copy of the

EPA Reference Method 21. Finally, appendix G demonstrates how

LDAR control efficiencies presented in chapter 5.0 were

calculated.

1-3
2.0. DEVELOPMENT OF EQUIPMENT LEAK EMISSION ESTIMATES

2.1 INTRODUCTION

The purpose of this chapter is to describe the methods for

estimating mass emissions from equipment leaks in a chemical

processing unit. Four approaches for estimating equipment leak

emissions are presented:

Approach 1: Average Emission Factor Approach;

Approach 2: Screening Ranges Approach;

Approach 3: EPA Correlation Approach; and

Approach 4: Unit-Specific Correlation Approach.

General information on these approaches is presented in

section 2.2, and detailed information on applying each of the

approaches is presented in section 2.3. Included in section 2.3

are emission factors and leak rate/screening value correlations

for use in estimating emissions from equipment leaks in the

petroleum industry and the synthetic organic chemical

manufacturing industry (SOCMI). The SOCMI emission factors and

correlations were revised and introduced in the 1993 update of

this document. The refinery correlations that have been revised

and expanded to include the entire petroleum industry are

introduced in this document. Additionally, emission factors for

marketing terminals are introduced in this document. Emission

factors for gas plants that have been updated and expanded to

included oil and gas production operations are also introduced in

this document. The procedures in this document estimate

emissions of total organic compounds (TOC’s). However, special

procedures are also described for the purpose of estimating

volatile organic compounds (VOC’s). As defined by the EPA, VOC’s

2-1
include all organic compounds except those specifically excluded

by the EPA due to negligible photochemical activity.

After the four approaches have been discussed, topics that

are not specifically related to any particular approach, but are

relevant to how equipment leak emissions are estimated, are

addressed in section 2.4. These topics include:

Estimating emissions of individual compounds within a

mixture;

Using response factors when estimating emissions;

Considerations regarding the monitoring instrument used;

Estimating emissions of equipment not screened when other

equipment have been screened;

Using screening data collected at different times;

Estimating VOC emissions from equipment containing

organic compounds excluded from the EPA’s classification

of TOC’s; and

Estimating emissions from equipment containing inorganic

compounds.

Appendices A through E contain supporting documentation for

the material presented in this chapter. Appendix A contains

detailed example calculations that demonstrate the four

approaches for estimating equipment leak emissions, as well as

the topics discussed in section 2.4. Appendix B presents details

on how unit-specific correlations can be developed, and also

presents background information on the revision of the SOCMI

correlations and emission factors. Appendix C presents

background information on the development of average emission

factors and correlation equations for the petroleum industry.

Appendix D offers a detailed listing of available response

factors. Appendix E contains information on the minimum number

of connectors in a process unit that must be screened in order to

obtain a representative sample.

2-2
2.2 GENERAL INFORMATION ON THE APPROACHES FOR ESTIMATING

EQUIPMENT LEAK EMISSIONS

This section presents general information on the four

approaches for estimating equipment leak emissions. Each

approach is briefly described, and data requirements for each are

summarized. Additionally, background information is presented to

provide an historical overview of data collection and analysis on

emissions of VOC’s from equipment leaks.

2.2.1 Equipment Leak Emission Estimation Approaches

The four approaches described here can be used by any

chemical-handling facility to develop an inventory of TOC or VOC

emissions from equipment leaks. The approaches, in order of

increasing refinement, are: Average Emission Factor Approach,

Screening Ranges Approach, EPA Correlation Approach, and

Unit-Specific Correlation Approach.

In general, the more refined approaches require more data and

provide more accurate emission estimates for a process unit. In

the Average Emission Factor Approach and the Screening Ranges

Approach, emission factors are combined with equipment counts to

estimate emissions. To estimate emissions with the EPA

Correlation Approach, measured concentrations (screening values)

for all equipment are individually entered into general

correlations developed by the EPA. In the Unit-Specific

Correlation Approach, screening and leak rate data are measured

for a select set of individual equipment components and then used

to develop unit-specific correlations. Screening values for all

components are then entered into these unit-specific correlations

to estimate emissions.

Figure 2-1 is an overview of the data collection and analysis

required to apply each of the approaches. As can be seen from

this figure, all of the approaches require an accurate count of

equipment components by type of equipment (i.e., valves, pumps,

connectors, etc.). Additionally, for some of the equipment

types, the count must be further described by service (i.e.,

heavy liquid, light liquid, and gas).

2-3
2-4

Figure 2-1. Overview of Data Collection and Analysis

Approaches for Developing Equipment Leak

Emissions Inventory
Except for the Average Emission Factor Approach, all of the

approaches require screening data. Screening data are collected

by using a portable monitoring instrument to sample air from

potential leak interfaces on individual pieces of equipment. A

screening value is a measure of the concentration of leaking

compounds in the ambient air that provides an indication of the

leak rate from an equipment piece, and is measured in units of

parts per million by volume (ppmv). The procedures for

collecting screening data are presented in chapter 3.0.

In addition to equipment counts and screening data, the

Unit-Specific Correlation Approach requires bagging data.

Bagging data consist of screening values and their associated

measured leak rates. A leak rate is measured by enclosing an

equipment piece in a bag to determine the actual mass emission

rate of the leak. The screening values and measured leak rates

from several pieces of equipment are used to develop a

unit-specific correlation. The resulting leak rate/screening

value correlation predicts the mass emission rate as a function

of the screening value. Procedures for collecting bagging data

are described in detail in chapter 4.0.

Each of the approaches are applicable to any

chemical-handling facility. However, the EPA has developed more

than one set of emission factors and correlations, and the type

of process unit being considered governs which set must be used

to estimate emissions. Historical data collection on emissions

from equipment leaks in SOCMI, refineries, marketing terminals

and oils and gas production operations have yielded emission

factors and correlations for these source categories. Emission

factors and correlations for other source categories have not

been developed.

For process units in source categories for which emission

factors and/or correlations have not been developed, the factors

and/or correlations already developed can be utilized. However,

appropriate evidence should indicate that the existing emission

factors and correlations are applicable to the source category in

question. Criteria for determining the appropriateness of

2-5
applying existing emission factors and correlations to another

source category may include one or more of the following:

(1) process design, (2) process operation parameters

(i.e., pressure and temperature), (3) types of equipment used,

and (4) types of material handled. For example, in most cases,

SOCMI emission factors and correlations are applicable for

estimating equipment leak emissions from the polymer and resin

manufacturing industry. This is because, in general, these two

industries have comparable process design and comparable process

operation, they use the same types of equipment, and they tend to

use similar feedstock.

2.2.2 Overview of Equipment Leak Data Collection

Data on equipment leak emissions of organic compounds have

been collected from refineries, marketing terminals, oil and gas

production operations, and SOCMI process units. Emission factors

and correlations have been developed for the following equipment

types: valves, pumps, compressors, pressure relief valves,

connectors, flanges, and open-ended lines. An "others" category

has also been developed for the petroleum industry. For sampling

connections, an average emission factor has been developed that

estimates the typical amount of material purged when a sample is

collected. A brief history of the development of these factors

and correlations is presented below.

2.2.2.1 Refinery Assessment Study.1,2 In the late 1970s,

the EPA initiated the Petroleum Refinery Assessment Study, and

equipment leak data from 13 refineries were collected. In this

study, equipment was screened and the majority of sources that

had screening values over 200 ppmv were bagged. Bagged equipment

emission rates were reported as non-methane organic compound

emission rates. Average emission factors and correlations for

each equipment type were developed based on the screening and

bagging data collected in this study.

The Refinery Assessment Study included an investigation of

possible correlations between equipment leaks and process

variables. The only process variables found to correlate with

mass emission rates in a statistically significant manner were

2-6
(1) the phase of the process stream (service), and (2) the

relative volatility of liquid streams. This finding led to the

separation of data for valves, pumps, and pressure relief valves

by type of service. Three service categories were defined:

Gas/vapor - material in a gaseous state at operating

conditions;

Light liquid - material in a liquid state in which the

sum of the concentration of individual constituents with

a vapor pressure over 0.3 kilopascals (kPa) at 20 oC is

greater than or equal to 20 weight percent; and

Heavy liquid - not in gas/vapor service or light liquid

service.

2.2.2.2 Gas Plant Studies.3 A total of six gas plants were

screened in two studies: Four were screened by the EPA and two

by the American Petroleum Institute. Average emission factors

were developed, and information on the percentage of equipment

with screening values equal to or greater than 10,000 ppmv was

presented. The average factors include emissions of ethane and

methane, which are hydrocarbons but are not classified as VOC’s.

2.2.2.3 Revised Petroleum Industry Correlations and Emission

Factors. During the early-1990’s, new petroleum industry

equipment leak bagging data were collected and analyzed. The

Western States Petroleum Association (WSPA) and the American

Petroleum Institute (API) jointly commissioned the 1994 refinery

equipment leak report4 to evaluate fugitive emissions collected

from five petroleum refineries. The API also commissioned the

1993 marketing terminal equipment leak report,5 which included

bagging data from three marketing terminals, and, along with the

Gas Research Institute (GRI), jointly commissioned the 1993 and

1995 oil and gas production operations reports, which included

bagging data from 24 facilities.6,7 In addition to the bagging

data, screening data were also collected from 17 marketing

terminals8 and 24 oil and gas production facilities.6,7 Data

from gas/vapor, light liquid, and/or heavy liquid streams were

collected for these studies from non-flanged connectors, flanges,

open-ended lines, pumps, values, instruments, loading arms,

2-7
pressure relief valves, stuffing boxes, vents, compressors, dump

lever arms, diaphrams, drains, hatches, meters, and polished

rods.

A specific goal of the above studies was to collect high

quality data to enhance or replace the previously published

refinery correlations. As a result of the analyses discussed in

appendix C, the bagging data collected from refineries, marketing

terminals, and oil and gas production facilities during the

early-1990’s were combined to replace the previously published

refinery correlations with correlations applicable to the entire

petroleum industry. In addition, the new correlations apply

across all services for a given equipment type. The previously

published refinery correlations were specific to service and

equipment.

The screening data were used to develop average emission

factors for marketing terminals and for oil and gas production

operations. The average emission factors for oil and gas

production operations replace the gas plant factors published in

previous versions of this document and apply to light crude,

heavy crude, gas plant, gas production and off shore facilities.

No new screening data were available for refineries, therefore

the previously published refinery average emission factors remain

unchanged in this version of the protocol. Appendix C contains

more detailed information on how the new petroleum industry

correlations, marketing terminal emission factors, and oil and

gas production operations emission factors were developed.

2.2.2.4 Original SOCMI Average Emission Factors and

Correlations. In 1980, two studies were coordinated by the EPA

to collect data from SOCMI process units. These studies were the

24-Unit Study,9 and the Six-Unit Maintenance Study.10 In the

24-Unit Study, screening data were obtained from equipment

containing organic compounds at 24 individual chemical process

units representing a cross-section of the SOCMI. In the Six-Unit

Maintenance Study, bagging data were collected from six of the

process units within the 24-Unit Study to determine the effect of

maintenance on equipment leak emissions. Most of the bagging

2-8
data were collected from equipment with screening values above

1,000 ppmv. As part of the Six-Unit Maintenance Study,

correlations were developed for light liquid pumps, gas valves,

and light liquid valves.

The original SOCMI average emission factors were first

presented in the document "Fugitive Emission Sources of Organic

Compounds--Additional Information on Emissions, Emission

Reductions, and Costs."6 This document is referred to as the

Fugitive Emissions Additional Information Document (AID). In the

Fugitive Emissions AID, the data from the Refinery Assessment

Study were further analyzed to develop "leak/no leak" emission

factors. (A "leak" was defined as a screening value greater than

or equal to 10,000 ppmv.) With the exception of the factor for

gas valves, the original SOCMI average emission factors were

developed using (1) the leak/no-leak emission factors developed

from the Refinery Assessment Study data, and (2) the leak

frequencies from the SOCMI 24-Unit Study screening value data

set. This approach was based on statistical comparisons that

indicated that the most significant characteristic that

distinguished equipment in SOCMI facilities from that in

refineries was not the leak rate for a given screening value, but

rather the fraction of equipment that had screening values

greater than or equal to 10,000 ppmv.

Thus, the following equation was used to calculate the

original SOCMI average emission factors:

SOCMI Average Factor = (F × RLF) + (1 - F) × RNLF

where:

F = Fraction of sources from the 24-Unit Study that

screened greater than or equal to 10,000 ppmv;

RLF = Refinery leaking emission factor; and

RNLF = Refinery non-leaking emission factor.

For gas valves, the previously collected data suggested that

for a given screening value the leak rate at a SOCMI facility was

2-9
not statistically equivalent to the leak rate at a refinery.

Therefore, data from the Six-Unit Maintenance Study were used to

develop the gas valve average emission factor.

2.2.2.5 Revised SOCMI Emission Factors and Correlations. In

1987 and 1988, screening data were obtained from 19 ethylene

oxide and butadiene producers, and, in 1990, bagging data were

collected from 16 of these process units. Screening and bagging

data were collected from light liquid pumps, gas valves, light

liquid valves, and connectors. A specific goal of the program

was to bag equipment that had screening values less than

1,000 ppmv. The bagging data were combined with bagging data

previously collected in the Six-Unit Maintenance Study, and this

combined bagging data set was used to revise the SOCMI

correlations. Likewise, the new screening data were combined

with screening data previously collected in the 24-Unit Study,

and this combined screening data set was used with the revised

correlations to generate new SOCMI emission factors.

Appendix B.2 contains more detailed information on how the

revised SOCMI correlations and emission factors were developed.

2.3 APPROACHES FOR ESTIMATING EQUIPMENT LEAK EMISSIONS

In this section, each of the approaches for estimating

equipment leak emissions are discussed. The description of each

approach focuses on the basic method for estimating TOC

emissions. Each of the approaches are demonstrated in example

calculations contained in appendix A. Special topics at the end

of the chapter have been included to address how to estimate VOC

emissions when some of the organic compounds in the stream are

not classified as VOC’s and also how to speciate emissions for

individual chemicals from equipment containing a mixture.

2.3.1 Average Emission Factor Approach

One accepted approach for estimating emissions allows use of

average emission factors developed by the EPA in combination with

unit-specific data that are relatively simple to obtain. These

data include: (1) the number of each type of component in a unit

(valve, connector, etc.), (2) the service each component is in

(gas, light liquid, or heavy liquid), (3) the TOC concentration

2-10
of the stream (and VOC or HAP concentrations if speciation is to

be performed), and (4) the time period each component was in that

service. The average emission factors for SOCMI process units,

refineries, marketing terminals, and oil and gas production

operations are presented in tables 2-1, 2-2, 2-3, and 2-4

respectively. The SOCMI, marketing terminal, and oil and gas

production operations average emission factors predict total

organic compound emission rates, whereas the refinery average

factors predict non-methane organic compound emission rates.

Note that limited data has been collected on the leak rate of

agitators, and, until additional data are collected for emissions

from agitator seals, the average factor for light liquid pump

seals can be used to estimate emissions from agitators.

Although the average emission factors are in units of

kilogram per hour per individual source, it is important to note

that these factors are most valid for estimating emissions from a

population of equipment. The average factors are not intended to

be used for estimating emissions from an individual piece of

equipment over a short time period (i.e., 1 hour).

To estimate emissions using the Average Emission Factor

Approach, the concentration of TOC in weight fraction within the

equipment is needed because equipment with higher TOC

concentrations tend to have higher TOC leak rates. When using

the Average Emission Factor Approach, equipment should be grouped

into "streams" where all the equipment within the stream have

approximately the same TOC weight fraction.

To apply the average emission factors, use the following

equation to estimate TOC mass emissions from all of the equipment

in a stream of a given equipment type:

ETOC = FA × WFTOC × N

where:

ETOC = Emission rate of TOC from all equipment in

the stream of a given equipment type (kg/hr);

2-11
TABLE 2-1. SOCMI AVERAGE EMISSION FACTORS

Equipment type Service

Emission factora

(kg/hr/source)

Valves Gas

Light liquid

Heavy liquid

0.00597

0.00403

0.00023

Pump sealsb Light liquid

Heavy liquid

0.0199

0.00862

Compressor seals Gas 0.228

Pressure relief valves Gas 0.104

Connectors All 0.00183

Open-ended lines All 0.0017

Sampling connections All 0.0150

aThese factors are for total organic compound emission

rates.

bThe light liquid pump seal factor can be used to estimate the

leak rate from agitator seals.

2-12
TABLE 2-2. REFINERY AVERAGE EMISSION FACTORSa

Equipment type Service

Emission factor

(kg/hr/source)b

Valves Gas

Light liquid

Heavy liquid

0.0268

0.0109

0.00023

Pump sealsc Light liquid

Heavy liquid

0.114

0.021

Compressor seals Gas 0.636

Pressure relief valves Gas 0.16

Connectors All 0.00025

Open-ended lines All 0.0023

Sampling connections All 0.0150

aSource: Reference 2.

bThese factors are for non-methane organic compound

emission rates.

cThe light liquid pump seal factor can be used to estimate the

leak rate from agitator seals.

2-13
TABLE 2-3. MARKETING TERMINAL AVERAGE EMISSION FACTORS

Equipment type Service

Emission factor

(kg/hr/source)a

Valves Gas

Light Liquid

1.3E-05

4.3E-05

Pump seals Gas

Light Liquid

6.5E-05

5.4E-04

Others (compressors

and others)b

Gas

Light Liquid

1.2E-04

1.3E-04

Fittings (connectors

and flanges)c

Gas

Light Liquid

4.2E-05

8.0E-06

aThese factors are for total organic compound emission rates

(including non-VOC’s such as methane and ethane).

bThe "other" equipment type should be applied for any equipment

type other than fittings, pumps, or valves.

c"Fittings" were not identified as flanges or non-flanged

connectors; therefore, the fitting emissions were estimated by

averaging the estimates from the connector and the flange

correlation equations.

2-14
TABLE 2-4. OIL AND GAS PRODUCTION OPERATIONS AVERAGE EMISSION

FACTORS (kg/hr/source)

Equipment Type Servicea

Emission Factor

(kg/hr/source)b

Valves Gas

Heavy Oil

Light Oil

Water/Oil

4.5E-03

8.4E-06

2.5E-03

9.8E-05

Pump seals Gas

Heavy Oil

Light Oil

Water/Oil

2.4E-03

NA

1.3E-02

2.4E-05

Othersc Gas

Heavy Oil

Light Oil

Water/Oil

8.8E-03

3.2E-05

7.5E-03

1.4E-02

Connectors Gas

Heavy Oil

Light Oil

Water/Oil

2.0E-04

7.5E-06

2.1E-04

1.1E-04

Flanges Gas

Heavy Oil

Light Oil

Water/Oil

3.9E-04

3.9E-07

1.1E-04

2.9E-06

Open-ended lines Gas

Heavy Oil

Light Oil

Water/Oil

2.0E-03

1.4E-04

1.4E-03

2.5E-04

aWater/Oil emission factors apply to water streams in oil service

with a water content greater than 50%, from the point of origin

to the point where the water content reaches 99%. For water

streams with a water content greater than 99%, the emission rate

is considered negligible.

bThese factors are for total organic compound emission rates

(including non-VOC’s such as methane and ethane) and apply to

light crude, heavy crude, gas plant, gas production, and

off shore facilities. "NA" indicates that not enough data were

available to develop the indicated emission factor.

cThe "other" equipment type was derived from compressors,

diaphrams, drains, dump arms, hatches, instruments, meters,

pressure relief valves, polished rods, relief valves, and vents.

This "other" equipment type should be applied for any equipment

type other than connectors, flanges, open-ended lines, pumps, or

valves.

2-15
FA = Applicable average emission factor for the

equipment type (kg/hr/source);

FOR REFINERIES ONLY: The emission factor

"FA" must be adjusted to account for all

organic compounds in the stream because the

refinery factors are only valid for

non-methane organic compounds (percents up to

a maximum of 10 percent by weight methane are

permitted):

WFTOC

FA = FA × ;

WFTOC - WFmethane

WFTOC = Average weight fraction of TOC in the stream;

WFmethane = Average weight fraction of methane in the

stream; and

N = Number of pieces of equipment of the

applicable equipment type in the stream.

Note that the emission factor "FA" is defined differently for

refineries than for SOCMI, marketing terminals, or oil and gas

production operations when calculating TOC mass emissions. It is

necessary to adjust the "FA" term when applied to refineries,

because when the refinery factors were developed, the methane was

subtracted out of the organic total. Adjusting the "FA" term for

refineries is a way to correct for this. Two guidelines when

correcting the "FA" term when applied to refineries are as

follows:

The correction should only be applied to equipment

containing a mixture of organics and methane; and

The maximum correction for the methane weight fraction

should not exceed 0.10, even if the equipment contains

greater than 10 weight percent methane. (This reflects

that equipment in the Refinery Assessment Study1,2

typically contained 10 weight percent or less methane).

Thus, at a SOCMI process unit, if there were 100 gas valves

in a stream containing, on average, 90 weight percent TOC and

10 weight percent water vapor, emissions would be calculated as

follows:

2-16
ETOC = FA × WFTOC × N

= 0.00597 kg/hr/gas valve × 0.9 × 100 gas valves

= 0.54 kg/hr of VOC from gas valves in the stream

At a refinery, if there were 100 gas valves in a stream that,

on average, contained 80 weight percent non-methane TOC,

10 weight percent water vapor, and 10 weight percent methane

(thus, the TOC weight percent would be 90), emissions would be

calculated using the above equation as follows:

WFTOC

ETOC = FA × × WFTOC × N

WFTOC - WFmethane

= 0.0268 kg/hr/gas valve × (0.9/0.9-0.1) × 0.9 ×

100 gas valves

= 2.71 kg/hr of VOC from gas valves in the stream

If there are several streams at a process unit, the total TOC

emission rate for an equipment type is the sum of emissions from

each of the streams. The total emission rates for all of the

equipment types are summed to generate the process unit total TOC

emission rate from leaking equipment.

Assuming all of the organic compounds in the stream are

classified as VOC’s, the total VOC emission for each stream is

calculated as the sum of TOC emissions associated with each

specific equipment type in the stream. Section 2.4.6 discusses

an adjustment that can be made to predict the VOC emission rate

if some of the organic compounds in the stream are not classified

as VOC’s (such as methane and ethane).

As mentioned earlier, the average emission factors are not

intended to provide an accurate estimate of the emission rate

from a single piece of equipment. Rather, the average factors

are more appropriately applied to the estimation of emissions

from populations of equipment. Data indicate that the range of

possible leak rates from individual pieces of equipment spans

2-17
several orders of magnitude. As a result, the majority of total

emissions from a population of equipment at any given time will

normally occur from a small percentage of the total equipment.

The average emission factors account for the span of possible

leak rates, but, as a result, they are not necessarily an

accurate indication of the mass emission rate from an individual

piece of equipment.

Furthermore, the average emission factors do not reflect

different site-specific conditions among process units within a

source category. Site-specific factors can have considerable

influence on leak rates from equipment. Nevertheless, in the

absence of screening data, the average emission factors do

provide an indication of equipment leak emission rates from

equipment in a process unit.

2.3.2 Screening Ranges Approach

The Screening Ranges Approach (formerly known as the

leak/no-leak approach) offers some refinement over the Average

Emission Factor Approach, thereby allowing some adjustment for

individual unit conditions and operation. This approach is

included in this section primarily to aid in the analysis of old

datasets which were collected for older regulations that used

10,000 ppmv as the leak definition. This approach and the other

two remaining approaches require that screening data be collected

for the equipment in the process unit. The screening data are an

indication of leak rates. When applying this approach, it is

assumed that components having screening values greater than

10,000 ppmv have a different average emission rate than

components with screening values less than 10,000 ppmv.

This approach may be applied when screening data are

available as either "greater than or equal to 10,000 ppmv" or as

"less than 10,000 ppmv." Emission factors for SOCMI, refineries,

marketing terminals, and oil and gas production operations for

these two ranges of screening values are presented in tables 2-5,

2-6, and 2-7, and 2-8, respectively. As with the average

factors, the SOCMI, marketing terminal, and oil and gas

production operations screening range factors predict total

2-18
TABLE 2-5. SOCMI SCREENING RANGES EMISSION FACTORS

Equipment type Service

≥10,000 ppmv

Emission factor

(kg/hr/source)a

<10,000 ppmv

Emission factor

(kg/hr/source)a

Valves Gas

Light liquid

Heavy liquid

0.0782

0.0892

0.00023

0.000131

0.000165

0.00023

Pump sealsb Light liquid

Heavy liquid

0.243

0.216

0.00187

0.00210

Compressor

seals

Gas 1.608 0.0894

Pressure

relief valves

Gas 1.691 0.0447

Connectors All 0.113 0.0000810

Open-ended

lines

All 0.01195 0.00150

aThese factors are for total organic compound emission rates.

bThe light liquid pump seal factors can be applied to estimate

the leak rate from agitator seals.

2-19
TABLE 2-6. REFINERY SCREENING RANGES EMISSION FACTORSa

Equipment type Service

≥10,000 ppmv

Emission factor

(kg/hr/source)b

<10,000 ppmv

Emission factor

(kg/hr/source)b

Valves Gas 0.2626 0.0006

Light liquid 0.0852 0.0017

Heavy liquid 0.00023 0.00023

Pump sealsc Light liquid 0.437 0.0120

Heavy liquid 0.3885 0.0135

Compressor seals Gas 1.608 0.0894

Pressure relief

valves

Gas 1.691 0.0447

Connectors All 0.0375 0.00006

Open-ended lines All 0.01195 0.00150

aSource: Reference 6.

bThese factors are for non-methane organic compound emission

rates.

cThe light liquid pump seal factors can be applied to estimate

the leak rate from agitator seals.

2-20
TABLE 2-7. MARKETING TERMINAL SCREENING RANGES EMISSION FACTORS

Equipment

type Service

≥10,000 ppmv

Emission factor

(kg/hr/source)a

<10,000 ppmv

Emission factor

(kg/hr/source)a

Valves Gas

Light Liquid

NA

2.3E-02

1.3E-05

1.5E-05

Pump seals Light liquid 7.7E-02 2.4E-04

Other

(compressors

and others)b

Gas

Light liquid

NA

3.4E-02

1.2E-04

2.4E-05

Fittings

(connectors

and flanges)c

Gas

Light liquid

3.4E-02

6.5E-03

5.9E-06

7.2E-06

aThese factors are for total organic compound emission rates

(including non-VOC’s such as methane and ethane). "NA"

indicates that not enough data were available to develop the

indicated emission factor.

bThe "other" equipment type should be applied for any equipment

type other than fittings, pumps, or valves.

c"Fittings" were not identified as flanges or connectors;

therefore, the fitting emissions were estimated by averaging the

estimates from the connector and the flange correlation

equations.

2-21
TABLE 2-8. OIL AND GAS PRODUCTION OPERATIONS SCREENING RANGES

EMISSION FACTORS

Equipment type Serviceb

≥10,000 ppmv

Emission factor

(kg/hr/source)a

<10,000 ppmv

Emission factor

(kg/hr/source)a

Valves Gas

Heavy Oil

Light Oil

Water/Oil

9.8E-02

NA

8.7E-02

6.4E-02

2.5E-05

8.4E-06

1.9E-05

9.7E-06

Pump seals Gas

Heavy Oil

Light Oil

Water/Oil

7.4E-02

NA

1.0E-01

NA

3.5E-04

NA

5.1E-04

2.4E-05

Othersc Gas

Heavy Oil

Light Oil

Water/Oil

8.9E-02

NA

8.3E-02

6.9E-02

1.2E-04

3.2E-05

1.1E-04

5.9E-05

Connectors Gas

Heavy Oil

Light Oil

Water/Oil

2.6E-02

NA

2.6E-02

2.8E-02

1.0E-05

7.5E-06

9.7E-06

1.0E-05

Flanges Gas

Heavy Oil

Light Oil

Water/Oil

8.2E-02

NA

7.3E-02

NA

5.7E-06

3.9E-07

2.4E-06

2.9E-06

Open-ended lines Gas

Heavy Oil

Light Oil

Water/Oil

5.5E-02

3.0E-02

4.4E-02

3.0E-02

1.5E-05

7.2E-06

1.4E-05

3.5E-06

aThese factors are for total organic compound emission rates

(including non-VOC’s such as methane and ethane) and apply to

light crude, heavy crude, gas plant, gas production, and

offshore facilities. "NA" indicates that not enough data were

available to develop the indicated emission factor.

bWater/Oil emission factors apply to water streams in oil service

with a water content greater than 50%, from the point of origin

to the point where the water content reaches 99%. For water

streams with a water content greater than 99%, the emission rate

is considered negligible.

cThe "other" equipment type was derived from compressors,

diaphrams, drains, dump arms, hatches, instruments, meters,

pressure relief valves, polished rods, relief valves, and vents.

This "other" equipment type should be applied for any equipment

type other than connectors, flanges, open-ended lines, pumps, or

valves.

2-22
organic compound emissions, whereas the refinery screening range

factors predict non-methane organic compound emissions. Note

that there are not screening range factors for sampling

connections because emissions from sampling connections occur

when the line is purged, and, thus, are independent of any

screening value. Also, as with the average factors, the

screening range factors for light liquid pumps can be applied to

agitators.

The Screening Ranges Approach is applied in a similar manner

as the Average Emission Factor Approach in that equipment counts

are multiplied by the applicable emission factor. Also, for

refineries, the screening range emission factors must be adjusted

for methane in the equipment because when the refinery factors

were developed, the methane was subtracted out of the organic

total.

To calculate TOC emissions using the Screening Ranges

Approach, the following equation is used:

ETOC = (FG × NG) + (FL × NL)

where:

ETOC = TOC emission rate for an equipment type

(kg/hr);

FG = Applicable emission factor for sources with

screening values greater than or equal to

10,000 ppmv (kg/hr/source);

FOR REFINERIES ONLY: The emission factor "FG"

must be adjusted to account for all organic

compounds in the stream because the refinery

factors are only valid for non-methane

organic compounds (percents up to a maximum

of 10 percent by weight methane are

permitted):

WPTOC

FG = FG × ;

WPTOC - WPmethane

WPTOC = Average weight percent of TOC in the stream;

2-23
WPmethane = Average weight percent of methane in the

stream;

NG = Equipment count (specific equipment type) for

sources with screening values greater than or

equal to 10,000 ppmv;

FL = Applicable emission factor for sources with

screening values less than 10,000 ppmv

(kg/hr/source)

FOR REFINERIES ONLY: The emission factor

"FL" must be adjusted to account for all

organic compounds in the stream because the

refinery factors are only valid for

non-methane organic compounds (percents up to

a maximum of 10 percent by weight methane are

permitted):

WPTOC

FL = FL × ; and

WPTOC - WPmethane

NL = Equipment count (specific equipment type) for

sources with screening values less than

10,000 ppmv.

Assuming all of the organic compounds in the stream are

classified as VOC’s, the total VOC emission for each stream is

calculated as the sum of TOC emissions associated with each

specific equipment type in the stream. Section 2.4.6 discusses

an adjustment that can be made to predict the VOC emission rate

if some of the organic compounds in the stream are not classified

as VOC’s (such as methane and ethane).

The screening range emission factors are a better indication

of the actual leak rate from individual equipment than the

average emission factors. Nevertheless, available data indicate

that measured mass emission rates can vary considerably from the

rates predicted by use of these factors.

2.3.3 EPA Correlation Approach

This approach offers an additional refinement to estimating

emissions from equipment leaks by providing an equation to

predict mass emission rate as a function of screening value for a

particular equipment type. Correlations developed by the EPA

relating screening values to mass emission rates for SOCMI

2-24
process units and for petroleum industry process units are

presented in tables 2-9 and 2-10, respectively. Correlations for

the petroleum industry apply to refineries, marketing terminals

and oil and gas production operations. Figures 2-2 through 2-5

plot the correlations. Both the SOCMI and petroleum industry

correlations predict total organic compound emission rates.

Appendix B.1 contains additional information on the general

development of correlation equations. Additionally, appendix B.2

contains information about the development of the SOCMI

correlations and appendix C contains information about the

development of the petroleum industry correlations.

The EPA Correlation Approach is preferred when actual

screening values are available. Correlations can be used to

estimate emissions for the entire range of non-zero screening

values, from the highest potential screening value to the

screening value that represents the minimum detection limit of

the monitoring device. This approach involves entering the

non-zero, non-pegged screening value into the correlation

equation, which predicts the TOC mass emission rate based on the

screening value. Default zero emission rates are used for

screening values of zero ppmv and pegged emission rates are used

for "pegged" screening values (the screening value is beyond the

upper limit measured by the portable screening device).

Correlations for SOCMI are available for (1) gas valves;

(2) light liquid valves; (3) connectors; and (4) light liquid

pump seals. Correlations for the petroleum industry are

available for (1) valves; (2) connectors; (3) pumps; (4) flanges;

(5) open-ended lines; and (6) "others" (derived from instruments,

loading arms, pressure relief valves, stuffing boxes, and vents).

Limited bagging data for compressors and pressure relief

devices have been obtained at SOCMI plants. However, because

statistical tests performed as part of the Refinery Assessment

Study2 indicated that emissions from light liquid pumps,

compressors, and pressure relief valves could be expressed with a

single correlation, until additional data are collected, the

SOCMI equation for light liquid pump seals can be applied to

2-25
TABLE 2-9. SOCMI LEAK RATE/SCREENING VALUE CORRELATIONS

Equipment type Correlationa,b

Gas valves Leak rate (kg/hr) = 1.87E-06 × (SV)0.873

Light liquid valves Leak rate (kg/hr) = 6.41E-06 × (SV)0.797

Light liquid pumpsc Leak rate (kg/hr) = 1.90E-05 × (SV)0.824

Connectors Leak rate (kg/hr) = 3.05E-06 × (SV)0.885

aSV = Screening value in ppmv.

bThese correlations predict total organic compound emission

rates.

cThe correlation for light liquid pumps can be applied to

compressor seals, pressure relief valves, agitator seals, and

heavy liquid pumps.

2-26
TABLE 2-10. PETROLEUM INDUSTRY LEAK RATE/SCREENING VALUE

CORRELATIONSa

Equipment

type/service Correlationb,c

Valves/all Leak rate (kg/hr) = 2.29E-06 × (SV)0.746

Pump seals/all Leak rate (kg/hr) = 5.03E-05 × (SV)0.610

Othersd Leak rate (kg/hr) = 1.36E-05 × (SV)0.589

Connectors/all Leak rate (kg/hr) = 1.53E-06 × (SV)0.735

Flanges/all Leak rate (kg/hr) = 4.61E-06 × (SV)0.703

Open-ended lines/all Leak rate (kg/hr) = 2.20E-06 × (SV)0.704

aThe correlations presented in this table are revised petroleum

industry correlations.

bSV = Screening value in ppmv.

cThese correlations predict total organic compound emission

rates (including non-VOC’s such as methane and ethane).

dThe "other" equipment type was derived from instruments,

loading arms, pressure relief valves, stuffing boxes, and

vents. This "other" equipment type should be applied to any

equipment type other than connectors, flanges, open-ended

lines, pumps, or valves.

2-27
Figure 2-2. SOCMI Correlations relating total organic compound

(TOC) leak rate to screening value:

0 - 1,000 ppmv

2-28
Figure 2-3. SOCMI Correlations relating total organic compound

(TOC) leak rate to screening value:

1,000 - 1,000,000 ppmv

2-29
Figure 2-4. Petroleum Industry Correlations relating total

organic compound (TOC) leak rate to screening value:

1,000 - 1,000,000 ppmv

2-30
Figure 2-5. Petroleum Industry Correlations relating total

organic compound (TOC)leak rate to screening value:

1,000 - 1,000,000 ppmv

2-31
estimate emissions for compressor seals and pressure relief

valves in SOCMI process units. Because bagging data were limited

and the frequency of occurrence of some equipment types was

small, a correlation for an "other" equipment type was developed

for the petroleum industry correlations to apply to any equipment

type other than connectors, flanges, open-ended lines, pumps, or

valves.

Bagging data for agitator seals at petroleum industry and

SOCMI process units are unavailable at this time. Compared to

those equipment types that have correlations, agitators most

closely resemble light liquid pumps, and, for this reason, the

applicable light liquid pump correlation can be used to estimate

agitator emissions. Similarly, the SOCMI light liquid pump

correlation can be used to estimate emissions from SOCMI heavy

liquid pumps.

The "default-zero" leak rate is the mass emission rate

associated with a screening value of zero. (Note that any

screening value that is less than or equal to ambient

[background] concentration is considered a screening value of

zero.) The correlations mathematically predict zero emissions

for zero screening values. However, data collected by the EPA

show this prediction to be incorrect. Mass emissions have been

measured from equipment having a screening value of zero.

A specific goal when revising the SOCMI and petroleum industry

correlations was to collect mass emissions data from equipment

that had a screening value of zero. These data were used to

determine a default-zero leak rate associated with equipment with

zero screening values.

Table 2-11 lists the SOCMI default-zero leak rates and

table 2-12 presents the petroleum industry default-zero leak

rates for each of the equipment types with correlation equations.

These default-zero leak rates are applicable only when the

minimum detection limit of the portable monitoring instrument is

1 ppmv or less above background.

The portable monitoring device used to collect the

default-zero data was sufficiently sensitive to indicate a

2-32
TABLE 2-11. DEFAULT-ZERO VALUES: SOCMI PROCESS UNITS

Equipment type

Default-zero emission rate

(kg/hr/source)a

Gas valve 6.6E-07

Light liquid valve 4.9E-07

Light liquid pumpb 7.5E-06

Connectors 6.1E-07

aThe default zero emission rates are for total organic compounds

(including non-VOC’s such as methane and ethane).

bThe light liquid pump default zero value can be applied to

compressors, pressure relief valves, agitators, and heavy

liquid pumps.

2-33
TABLE 2-12. DEFAULT-ZERO VALUES: PETROLEUM INDUSTRY

Equipment type/service

Default-zero emission ratesa,b

(kg/hr/source)

Valves/all 7.8E-06

Pump seals/all 2.4E-05

Othersc/all 4.0E-06

Connectors/all 7.5E-06

Flanges/all 3.1E-07

Open-ended lines/all 2.0E-06

aDefault zero emission rates were based on the combined

1993 refinery and marketing terminal data only (default zero

data were not collected from oil and gas production

facilities).

bThese default zero emission rates are for total organic

compounds (including non-VOC’s such as methane and ethane).

cThe "other" equipment type was developed from instruments,

loading arms, pressure relief valves, stuffing boxes, vents,

compressors, and dump lever arms. This "other" equipment type

should be applied to any equipment type other than connectors,

flanges, open-ended lines, pumps, or valves.

2-34
screening value of 1 ppmv or less. In cases where a monitoring

instrument has a minimum detection limit greater than 1 ppmv, the

default-zero leak rates presented in tables 2-11 and 2-12 are not

applicable. For these cases, an alternative approach for

determining a default-zero leak rate is to (1) determine one-half

the minimum screening value of the monitoring instrument, and

(2) enter this screening value into the applicable correlation to

determine the associated default-zero leak rate.

The "pegged" emission rate is the mass emission rate

associated with a screening value that has "pegged" the meter on

the portable screening device (i.e. the screening value is beyond

the upper limit measured by the portable screening device). In

the case of a screening value pegged at 10,000 ppmv, a dilution

probe should be used to extend the upper limit of the portable

screening device to 100,000 ppmv. Thus, screening values can be

reported up to 100,000 ppmv before pegging the instrument and the

correlation equation can be used to estimate the mass emissions.

However, in the case of previously-collected data or in the

absence of a dilution probe, pegged readings of 10,000 ppmv are

sometimes reported. In such cases, the 10,000 ppmv pegged

emission rates can be used to estimate the mass emissions.

Table 2-13 presents the 10,000 ppmv and 100,000 ppmv pegged

emission rates for SOCMI process units and table 2-14 presents

the 10,000 ppmv and 100,000 ppmv pegged emission rates for

petroleum industry process units. These pegged emission rates

are to be used to estimate emissions when instrument readings are

pegged and a dilution probe is not used.

Assuming all of the organic compounds in the equipment are

classified as VOC’s, total VOC emissions for each equipment type

are calculated as the sum of emissions associated with each of

the screening values. Section 2.4.6 discusses a correction that

can be made to the predicted VOC emissions rate if some of the

organic compounds in the equipment are not classified as VOC’s

(such as methane and ethane).

To summarize the correlation approach, each equipment piece

with a screening value of zero is assigned the default-zero leak

2-35
TABLE 2-13. 10,000 PPMV AND 100,000 PPMV SCREENING VALUE PEGGED

EMISSION RATES FOR SOCMI PROCESS UNITS

Equipment type

10,000 ppmv pegged

emission rate

(kg/hr/source)a,b

100,000 ppmv pegged

emission rate

(kg/hr/source)a

Gas valves 0.024 0.11

Light liquid

valves

0.036 0.15

Light liquid pump

sealsb

0.14 0.62

Connectors 0.044 0.22

aThe SOCMI pegged emission rates are for total organic compounds.

bThe 10,000 ppmv pegged emission rate applies only when a

dilution probe cannot be used or in the case of

previously-collected data that contained screening values

reported pegged at 10,000 ppmv.

cThe light liquid pump seal pegged emission rates can be applied

to compressors, pressure relief valves, and agitators.

2-36
TABLE 2-14. 10,000 ppmv and 100,000 PPMV SCREENING VALUE PEGGED

EMISSION RATES FOR THE PETROLEUM INDUSTRY

Equipment

type/service

10,000 ppmv pegged

emission rate

(kg/hr/source)a,b

100,000 ppmv pegged

emission rate

(kg/hr/source)a

Valves/all 0.064 0.140

Pump seals/all 0.074 0.160c

Othersd/all 0.073 0.110

Connectors/all 0.028 0.030

Flanges/all 0.085 0.084

Open-ended lines/all 0.030 0.079

aThe petroleum industry pegged emission rates are for total

organic compounds (including non-VOC’s such as methane and

ethane).

bThe 10,000 ppmv pegged emission rate applies only when a

dilution probe cannot be used or in the case of

previously-collected data that contained screening values

reported pegged at 10,000 ppmv. The 10,000 ppmv pegged emission

rate was based on components screened at greater than or equal

to 10,000 ppmv; however, in some cases, most of the data could

have come from components screened at greater than 100,000 ppmv,

thereby resulting in similar pegged emission rates for both the

10,000 and 100,000 pegged levels (e.g., connector and flanges).

cOnly 2 data points were available for the pump seal

100,000 pegged emission rate; therefore the ratio of the pump

seal 10,000 pegged emission rate to the overall 10,000 ppmv

pegged emission rate was multiplied by the overall 10,000 ppmv

pegged emission rate to approximate the pump 100,000 ppmv pegged

emission rate.

dThe "other" equipment type was developed from instruments,

loading arms, pressure relief valves, stuffing boxes, vents,

compressors, dump lever arms, diaphrams, drains, hatches,

meters, and polished rods. This "other" equipment type should

be applied to any equipment type other than connectors, flanges,

open-ended lines, pumps, and valves.

2-37
rate. For all equipment with a non-zero screening value, the

screening value associated with each individual equipment piece

is entered into the applicable correlation to predict emissions.

It should be noted that each individual screening value must be

entered into the correlation to predict emissions for an

equipment piece. Do not average screening values and then enter

the average value into the correlation to estimate emissions.

Finally, each equipment piece with a screening value reported as

pegged is assigned the appropriate pegged emission rate.

2.3.4 Unit-Specific Correlation Approach

To develop unit-specific correlations screening value and

corresponding mass emissions data (i.e., bagging data) must be

collected from process unit equipment. (See chapter 4.0 for a

detailed discussion on the procedures for bagging equipment.)

The equipment selected for bagging should be screened at the time

of bagging. The mass emissions rate determined by bagging, and

the associated screening value, can then be used to develop a

leak rate/screening value relationship (i.e., correlation) for

that specific equipment type in that process unit. The

correlations must be developed on a process unit basis to

minimize the error associated with differing leak rate

characteristics between units.

If a unit-specific correlation is developed, as long as the

procedures for bagging discussed in chapter 4.0 are followed, it

is not necessary to demonstrate that the correlation is

statistically different from the EPA correlation for it to be

applied. However, before developing unit-specific correlations,

it may be desirable to evaluate the validity of the EPA

correlations to a particular process unit. As few as four leak

rate measurements of a particular equipment type in a particular

service can be adequate for this purpose. The measured emission

rates can be compared with the rates that would be predicted by

the EPA correlations to evaluate whether or not the EPA

correlations provide reasonable mass emission estimates. A

simple method of comparison is to determine if measured emission

rates are consistently less than or greater than what would be

2-38
predicted by the EPA correlation. If there is a consistent

trend, such as all of the measured leak rates being lower than

the rate predicted by the EPA correlation, the EPA correlation

may not provide reasonable emission estimates for the process

unit.

A more formal comparison is the Wilcoxon signed-rank test.

This test can be performed by comparing the logarithm of the

measured mass emission rates to the logarithm of the

corresponding rates predicted by the EPA correlation. The

absolute magnitude of the differences are then ranked (e.g., the

pair with the smallest difference is assigned a rank of 1, the

pair with the next smallest difference a rank of 2, etc.), and

the sum of the ranks associated with positive differences is

computed. For example, if four bags were measured and they each

predicted higher mass emission rates than the EPA correlation,

the value of the sum of the ranks associated with those pairs

with positive differences would equal:

1 + 2 + 3 + 4 = 10

On the other hand, if four bags were measured and three predicted

higher mass emission rates than the EPA correlation, but the one

with the greatest absolute difference predicted a lower rate than

the EPA correlation, then the sum of the positive ranks would

equal:

1 + 2 + 3 = 6. (Note: The sum of the negative ranks would

equal 4).

The value of the sum of the positive ranks can be compared to

given values on statistical tables to evaluate if there are

statistically significant differences between the measured rates

and the rates predicted by the EPA correlation.

However the comparison is performed, in cases where the EPA

correlations provide an adequate estimate of emissions, then the

potential increase in accuracy obtained by developing

2-39
unit-specific correlations may not be worth the effort.

Consideration should also be given to the typical screening value

measured at a process unit. If a process unit normally has very

low screening values, then the difference between the sum of unit

equipment leak emissions predicted by a unit-specific correlation

and the EPA correlation will likely be relatively small.

In developing new correlations, a minimum number of leak rate

measurements and screening value pairs must be obtained according

to the following methodology. First, equipment at the process

unit is screened so that the distribution of screening values at

the unit is known. Then, mass emissions data must be collected

from individual sources that have screening values distributed

over the entire range. The criteria for choosing these sources

is as follows. For each equipment type (i.e., valves, pumps,

etc.) and service (i.e., gas, light liquid, etc.), a random

sample of a minimum of six components should be chosen for

bagging from each of the following screening value ranges:

Screening Value Range (ppmv)

1 - 100

101 - 1,000

1,001 - 10,000

10,001 - 100,000

> 100,000

The requirement of six bags per screening value range is

based on the EPA experience with bagging components. There are

two primary reasons for the above requirement: (1) to be

confident in the representativeness of the data, and (2) to

accurately reflect the range of possible mass emission rates

associated with a given screening value. The importance of the

first reason is self-evident: The more data collected the better

the representativeness. The importance of the second reason is

that a given screening value does not necessarily have a "true"

emissions rate. For a single screening value, the mass emissions

may range over several orders of magnitude depending upon several

2-40
factors, including the equipment type (i.e., gate valve versus

ball valve versus plug valve, etc.) and operating parameters

(i.e., chemical handled, temperature, pressure, etc.). This

range of possible mass emission rates is accounted for when the

correlation is developed (see discussion on the scale bias

correction factor), and it is important to obtain enough data to

accurately reflect the range. If six sources are not available

in a particular screening value range, additional sources from

the nearest range should be tested so that a minimum of

30 emission rate/screening value pairs are obtained for each

source type. If 30 or more bags are collected, the process

unit-specific correlation can be used to estimate emissions

across the entire range of screening values (1 to

1,000,000 ppmv).

In some cases, it may be desirable to develop a correlation

with fewer than 30 bags. This can be accomplished by developing

a correlation that is not valid across the entire range of

screening values. Two alternatives are available: (1) to develop

a correlation valid for screening values ranging from 1 to

100,000 ppmv, or (2) to develop a correlation valid for screening

values ranging from 1 to 10,000 ppmv. These alternatives may be

preferable for process units with equipment that do not normally

have high screening values. An example of this type of process

unit is one that already has a leak detection and repair program

in place to prevent the release of odor-causing chemicals. At

this type of process unit, leaks may be quickly detected and

repaired.

For the first alternative, a minimum of 24 bags are required,

rather than 30, because sources with screening values greater

than 100,000 ppmv do not need to be bagged. Thus, a minimum of

six sources each should be chosen for bagging from each of the

screening ranges presented above except for the greater than

100,000 ppmv range. In the event that a source screens at

100,000 ppmv or greater, emissions can be estimated using

"pegged" emission rates shown in table 2-13 for SOCMI process

units, and in table 2-14 for petroleum industry process units.

2-41
For the second alternative, a minimum of 18 bags are

required, because sources screening greater than 10,000 ppmv do

not need to be bagged. Thus, a minimum of six sources should be

chosen for bagging from the 1 to 100 ppmv range, the 100 to

1000 ppmv range, and the 1,000 to 10,000 ppmv range. In the

event that a source screens at 10,000 ppmv or greater, emissions

can be estimated using the applicable greater than or equal to

10,000 ppmv pegged emission rate presented in table 2-13 for

SOCMI process units, or table 2-14 for petroleum industry process

units. An advantage of using the greater than or equal to

10,000 ppmv pegged emission rates is that several of the

available portable monitoring instruments have a maximum readout

of 10,000 ppmv, and to obtain a screening value from a source

screening at 10,000 ppmv, it is necessary to install a dilution

probe. However, if the greater than or equal to 10,000 ppmv

factor is used, installing a dilution probe is not necessary for

this alternative.

The above groupings and recommended number of sources are

given as guidelines. They are based on experience in measuring

leak rates and developing leak rate/screening value correlations.

Other source selection strategies can be used if an appropriate

rationale is given.

With mass emissions data and screening values, leak

rate/screening value correlations can be generated using the

following methodology. Least-squares regression analyses are

completed for each equipment type/service, regressing the log of

the leak rate on the log of the screening concentration,

according to:

Log10 (leak rate [in kg/hr]) = β0 + β1 × Log10 (SV)

where:

β0, β1 = Regression constants; and

SV = Screening value.

2-42
Note that the results are the same whether the base 10 or natural

logarithm are used (see appendix B). The equations presented

here are written assuming the base 10 logarithm is used. All

analyses should be conducted using logarithms of both the leak

rate and screening value because this type of data has been shown

to be log-normally distributed. A scale bias correction factor

(SBCF) is required in transforming the equation in the log-scale

back to the original units. The transformed equation is the

unit-specific correlation, and is expressed as:

where:

Leak rate = SBCF x 10β0 x SVβ1

Leak rate = Emission rate of TOC’s from the individual

equipment piece (kg/hr);

SBCF = Scale bias correction factor;

β0,β1 = Regression constants; and

SV = Screening value.

The SBCF is a function of the mean square error of the

correlation in log space. The greater the range of possible

emission rates for a given screening value, the greater the SBCF

will be. The purpose of the SBCF is to reflect this range when

transforming the correlation out of log space. When regressed in

log space, in general, approximately half of the data points will

lie above the correlation line and half will lie below it, and,

for a given screening value, the correlation will pass through

the mean log leak rate (i.e., the geometric mean). Thus, one way

of thinking of the correlation in log space is that it predicts

the geometric mean emissions rate across the range of screening

values. However, the geometric mean always underestimates the

arithmetic mean.

A simplified hypothetical example will help demonstrate this

point: For a screening value of 500,000 ppmv, three bagging data

points were obtained with mass emission rates of 0.1 kg/hr,

2-43
1 kg/hr, and 10 kg/hr. In log space, these emission rates

correspond to log10 (0.1) = -1, log10 (1) = 0, and

log10 (10) = 1, respectively. Thus, the geometric mean of these

three points is (-1+0+ 1)/3 = 0. Directly transforming this

geometric mean to normal space predicts an emission rate for a

screening value of 500,000 ppmv of 100 = 1 kg/hr, whereas the

arithmetic mean of the emission rates is

(0.1 + 1 + 10)/3 = 3.7 kg/hr. From this example, it can be seen

that the geometric mean underestimates the arithmetic mean.

Thus, if the correlation was directly transformed, it would

underestimate the true average emission rate associated with a

given screening value, and, for this reason, the SBCF is

necessary to transform the correlation out of log space.

In appendix B, additional details on developing a

process-unit specific correlation are presented. Appendix B also

contains information on development of the revised SOCMI

correlations.

2.4 SPECIAL TOPICS

There are several special topics relevant to estimating

equipment leak emissions that are not specific to any one of the

four approaches that have been described. These special topics

are discussed in this section:

Speciating emissions;

Using response factors;

Monitoring instrument type and calibration gas;

Estimating emissions for equipment not screened (when

other screening data are available);

Using screening data collected at several different

times;

Estimating VOC emission rates from equipment containing

organic compounds not classified as VOC’s (such as

methane and ethane); and

Estimating equipment leak emissions of inorganic

compounds.

2-44
Each of these topics above are addressed in the following

sections.

2.4.1 Speciating Emissions

For each of the four approaches for estimating equipment leak

emissions, the equations presented are used to estimate TOC

emissions for estimating equipment leak emissions. Often, in a

chemical-handling facility, material in equipment is a mixture of

several chemicals, and, in some cases, it may be necessary to

estimate emissions of a specific VOC in the mixture. The

following equation is used to speciate emissions from a single

equipment piece:

Ex = ETOC × (WPx/WPTOC)

where:

Ex = The mass emissions of organic chemical "x" from

the equipment (kg/hr);

ETOC = The TOC mass emissions from the equipment

(kg/hr) calculated from either the Average

Emission Factor, Screening Ranges, Correlation,

or Unit-Specific Correlation approaches;

WPx = The concentration of organic chemical "x" in the

equipment in weight percent; and

WPTOC = The TOC concentration in the equipment in weight

percent.

An assumption in the above equation is that the weight percent of

the chemicals in the mixture contained in the equipment will

equal the weight percent of the chemicals in the leaking

material. In general, this assumption should be accurate for

single-phase streams containing (1) any gas/vapor material, or

(2) liquid mixtures containing constituents of similar

volatilities.

If the material in the equipment piece is a liquid mixture of

constituents with varying volatilities, in certain cases this

assumption may not be correct. Whether or not the assumption is

valid for a liquid mixture of varying volatilities depends on the

physical mechanism of how the leakage occurs from the equipment.

2-45
If the physical mechanism is one in which the liquid "flashes"

before it leaks from the equipment, the leaking vapor may contain

a higher concentration of the more volatile constituents than is

contained in the liquid mixture. On the other hand, if the

mechanism is one in which the liquid material leaks from the

equipment and then evaporates, the assumption that the weight

percent of each constituent in the liquid will equal the weight

percent of each constituent in the vapor is valid. There are no

clear guidelines to determine what mechanism is taking place for

any given piece of equipment; for this reason, unless there is

information to suggest otherwise, it should be assumed that the

leaking vapor has the same concentrations as the liquid.

For those cases where it is suspected the leaking vapor will

have different concentrations than the liquid, engineering

judgement should be used to estimate emissions of individual

chemical species. An example might be equipment containing

material in two phases. Another hypothetical example is a case

where equipment contain a liquid mixture of two constituents with

one of the constituents having a very low vapor pressure and the

other a much higher vapor pressure. Leaks may occur from the

equipment such that the constituent with higher vapor pressure

volatilizes to the atmosphere, but the constituent with lower

vapor pressure is washed to the waste water treatment system

prior to volatilization.

2.4.2 Using Response Factors

A correction factor that can be applied to a screening value

is a response factor (RF) that relates the actual concentration

to the measured concentration of a given compound, using a

specific reference gas. As stated earlier, screening values are

obtained by using a portable monitoring instrument to detect

VOC’s at an equipment piece leak interface. An "ideal" screening

RF value is one that is equal to the actual concentration of

VOC’s at the leak interface. However, portable monitoring

instruments used to detect TOC concentration do not respond to

different TOC’s equally. (This is discussed in more detail in

chapter 3.0). To demonstrate this point, consider a monitoring

2-46
instrument calibrated using a reference gas. If the instrument

is calibrated correctly and is used to measure the concentration

of the gas with which it has been calibrated, it will indicate

the actual concentration. However, when used to measure other

gases for which the monitoring instrument is more or less

sensitive than the calibration gas, it will not indicate the

actual concentration. To correct for this, RF’s have been

developed. The RF is calculated using the equation:

RF = AC/SV

where:

RF = Response factor;

AC = Actual concentration of the organic compound (ppmv);

and

SV = Screening value (ppmv).

The value of the RF is a function of several parameters.

These parameters include the monitoring instrument, the

calibration gas used to calibrate the instrument, the compound(s)

being screened, and the screening value.

The correlations presented in this chapter have been

developed primarily from screening value/mass emission data pairs

collected from equipment containing compounds that had RF’s less

than three. Thus, for cases in which a calibrated instrument is

used to measure concentrations of a compound for which that

instrument has an RF of three or less, reasonably accurate

emission estimates can be obtained directly without adjusting the

screening value. However, for a case in which a compound has an

RF greater than three for the calibrated instrument, the

emissions estimated using the unadjusted screening value will

generally underestimate the actual emissions. The EPA recommends

that if a compound (or mixture) has an RF greater than three,

then the RF should be used to adjust the screening value before

it is used in estimating emissions.

2-47
A detailed listing of published RF’s is contained in

appendix D. These RF’s were developed by injecting a known

concentration of a pure compound into a monitoring instrument and

comparing that actual concentration to the instrument readout

(i.e., screening value).

As an example of applying a RF, consider chloroform. From

table D-2 in appendix D, it can be seen that the RF for

chloroform at an actual concentration of 10,000 ppmv is equal to

4.48 for a Foxboro OVA-108 monitoring instrument calibrated with

methane. Thus, when the actual concentration of chloroform is

10,000 ppmv, the instrument will read 10,000 ppmv divided by

4.48, which equals 2,230 ppmv. If the measured value for

chloroform was directly entered into the correlation, it would

tend to underestimate emissions. (Note that when the RF is less

than 1 the unadjusted screening value will tend to overestimate

actual emissions.)

The RF’s in appendix D are for pure compounds. Those RF’s

can be used to estimate the RF for a mixture using the equation:

where:

RFm = 1

n

i 1

xi/RFi

RFm = Response factor of the mixture;

n = Number of components in the mixture;

xi = Mole fraction of constituent i in the mixture; and

RFi = Response factor of constituent i in the mixture.

This equation is derived in appendix A.

An alternative approach for determining the RF of a pure

compound or a mixture is to perform analysis in a laboratory to

generate the data used to calculate a RF. The approach for

generating these data in the laboratory is described in

chapter 3.0. The approach involves injecting samples of a known

concentration of the material of interest into the actual

portable monitoring instrument used to obtain the screening

values and calculating the RF based on the instrument readout.

2-48
In general, calculating the RF by performing analysis on site

will give the most accurate RF information, since, among other

factors, RF’s have been shown to be a function of the individual

monitoring instrument.

Ideally, when using screening values to estimate equipment

leak emissions, the RF would be equal to 1, and, in this way, the

screening value would be the actual concentration. However,

because RF’s are a function of several parameters, this cannot

normally be achieved. Response factors can be used to correct

all screening values, if so desired. To evaluate whether a RF

correction to a screening value should be made, the following

three steps can be carried out.

(1) For the combination of monitoring instrument and

calibration gas used, determine the RF’s of a given

material at an actual concentration of 500 ppmv and

10,000 ppmv. (See appendix D; in some cases, it may not

be possible to achieve an actual concentration of

10,000 ppmv for a given material. In these cases, the

RF at the highest concentration that can be safely

achieved should be determined.)

(2) If the RF’s at both actual concentrations are below 3,

it is not necessary to adjust the screening values.

(3) If either of the RF’s are greater than 3, then the EPA

recommends an RF be applied for those screening values

for which the RF exceeds 3.

One of the following two approaches can be applied to correct

screening values:

(1) Use the higher of either the 500 ppmv RF or the

10,000 ppmv RF to adjust all screening values.

(2) Generate a response factor curve to adjust the

screening values.

A RF curve can be generated in one of two ways. The simplest

way is to assume that the RF value is a linear function of the

screening value. The first step to generate a line relating

screening value to RF is to convert the RF at the actual

concentration to the RF at the associated screening value. This

is done by dividing the RF by the actual concentration to get the

associated screening value. Thus, if, at an actual concentration

2-49
of 10,000 ppmv, an instrument has a RF of 5, this corresponds to

a screening value of 2,000 ppmv (i.e., 10,000 ppmv divided by 5).

This procedure is implemented at both actual concentrations of

10,000 ppmv and 500 ppmv, and a line is drawn between the RF’s at

each associated screening value. This line can then be used to

estimate the RF at any given screening value. (See appendix A

for a demonstration of this procedure.) The line should not be

extrapolated for screening values beyond the endpoints. For

these screening values, the endpoint RF should be applied.

For some materials, the RF is nonlinear as the screening

value increases. For these materials, RF’s at several screening

values can be estimated by collecting data in a laboratory, as

mentioned earlier. The RF/screening value relationship can then

be generated by fitting a curve through the data pairs.

When an RF is used, the screening value is multiplied by the

RF before mass emissions are estimated. Thus, if a screening

value is 3,000 ppmv and the associated RF is 4, then the

screening value must be adjusted to 12,000 ppmv (i.e., 3,000

multiplied by 4) before mass emissions are predicted.

It should be noted that if it is possible to calibrate the

monitoring instrument with the material contained in the

equipment that is being screened, the RF should equal 1. Thus,

theoretically, the screening values will equal the actual

concentration, and no RF adjustment will be necessary. If it is

necessary to apply RF’s, site personnel should use engineering

judgement to group process equipment into streams containing

similar compounds. All components associated with a given stream

can then be assigned the same RF, as opposed to calculating an RF

for each individual equipment piece.

2.4.3 Monitoring Instrument Type and Calibration Gas

When the correlations presented in section 2.3 were

developed, in general, for each of the source categories, the

data were collected using a specific type of monitoring

instrument calibrated with a specific calibration gas. The

correlations are intended to relate actual concentration to mass

emissions. For this reason, screening values obtained from any

2-50
combination of monitoring instrument and calibration gas can be

entered directly into the correlations as long as the screening

values are an indication of actual concentration. If the

screening values are not an indication of the actual

concentration, the guidelines set forth in the previous section

on RF’s can be applied to correct the screening values

(i.e., screening values should be adjusted if the RF is greater

than 3). Otherwise, it is not necessary to correct screening

values to account for the instrument type and calibration gas

that were used to develop the correlation curves developed by

the EPA.

2.4.4 Estimating Emissions for Equipment Not Screened

Often, screening data cannot be collected for all of the

equipment pieces in a process unit. In some cases, equipment are

difficult or unsafe to screen. Difficult or unsafe to screen

equipment must be included in the equipment counts. For these

equipment pieces, the average emission factors must be used to

estimate emissions.

In other cases, it is not possible to screen every equipment

piece due to cost considerations. This is particularly true for

connectors. Appendix E provides criteria for determining how

many connectors must be screened to constitute a large enough

sample size to identify the screening value distribution for

connectors. If the criteria in appendix E are met, the average

emission rate for connectors that were screened can be applied to

connectors that were not screened. It should be noted that if

connectors must be included in a leak detection and repair

program as part of an equipment leaks standard, then all

connectors must be screened. For equipment types other than

connectors, if they are not monitored, the Average Emission

Factor approach should be used to estimate emissions.

2.4.5 Using Screening Data Collected at Several Different

Times

When screening data is collected and used to estimate

emissions, the emissions estimate represents a "snapshot" of

emissions at the time the screening data were obtained. Over

2-51
time, it is possible that more screening data will be collected,

and that for individual equipment pieces, several screening

values will have been obtained at different time periods. For

example, if quarterly monitoring is performed on a valve, in an

annual period four screening values will be obtained from the

valve. The annual emissions from the valve should be calculated

by determining the emissions for each quarter based on the

operational hours for the quarter, and summing the quarterly

emissions together to arrive at emissions for the entire year.

See appendix A for an example of estimating emissions from an

equipment piece for which more than one screening value has been

obtained.

2.4.6 Estimating VOC Emission Rates from Equipment Containing

Non-VOC’s

Some organic compounds not classified as VOC’s can be

detected by the screening instrument. Because the compounds are

detected, the emissions associated with the screening value will

include emissions of the "non-VOC’s." The two key organic

compounds not classified as VOC’s are methane and ethane, but

other organic compounds not classified as VOC’s include methylene

chloride, 1,1,1-trichloroethane, and several chlorofluorocarbons.

An approach very similar to that outlined in section 2.4.1

(Speciating Emissions) is used to estimate VOC emissions from

equipment containing these non-VOC’s mixed with VOC’s.

Once TOC emissions have been estimated by using either the

Average Emission Factor, the Screening Ranges, the Correlation,

or the Unit-Specific Correlation approaches, the VOC emissions

from a group of equipment containing similar composition can be

calculated using the equation:

EVOC = ETOC × (WPVOC/WPTOC)

where:

EVOC = The VOC mass emissions from the equipment

(kg/hr);

ETOC = The TOC mass emissions from the equipment

(kg/hr) calculated form either the Average

2-52
Emission Factor, Screening Ranges, Correlation,

or Unit-Specific Correlation approaches;

WPVOC = The concentration of VOC in the equipment in

weight percent;

WPTOC = The TOC concentration in the equipment in weight

percent.

2.4.7 Estimating Equipment Leak Emissions of Inorganic

Compounds

The majority of data collected for estimating equipment leak

emissions has been for TOC’s or VOC’s and not for inorganic

compounds. Accordingly, the emission factors and correlations

presented in section 2.3 are not intended to be applied for the

used of estimating emissions of inorganic compounds. However, in

some cases, there may be a need to estimate equipment leak

emissions of inorganic compounds--particularly for those that

exist as a gas/vapor or for those that are volatile. Some

examples of inorganic compounds include sulfur dioxide, ammonia,

and hydrochloric acid.

The best way to estimate equipment leak emissions of

inorganic compounds would be to develop unit-specific

correlations as described in section 2.3.4. To do this, it would

be necessary to obtain a portable monitoring instrument that

could detect the inorganic compounds. If it is not possible to

develop a unit-specific correlation, but a portable monitoring

instrument (or some other approach) can be used to indicate the

actual concentration of the inorganic compound at the equipment

leak interface, then the "screening values" obtained with this

instrument can be entered into the applicable correlations

presented in section 2.3.3 to estimate emissions. Alternatively,

the equal to or greater than 10,000 ppmv, or the less than

10,000 ppmv emission factors could be applied. In the event that

there is no approach that can be used to estimate the

concentration of the inorganic compound at the leak interface,

then in the absence of any other data, the average emission

factors can be used.

2-53
2.5 REFERENCES

1. Radian Corporation. Assessment of Atmospheric Emissions from

Petroleum Refining: Volume 4. Appendices C, D, E. Prepared

for U.S. Environmental Protection Agency. Research Triangle

Park, NC. Publication No. EPA-600/2-80-075d. July 1980.

2. Wetherhold, R.G., L.P. Provost, and C.D. Smith (Radian

Corporation). Assessment of Atmospheric Emissions from

Petroleum Refining: Volume 3. Appendix B. Prepared for

U.S. Environmental Protection Agency. Research Triangle

Park, NC. Publication No. EPA-600/2-80-075c. April 1980.

3. DuBose, D.A., J.I. Steinmetz, and G.E. Harris (Radian

Corporation). Frequency of Leak Occurrence and Emission

Factors for Natural Gas Liquid Plants. Final Report.

Prepared for U.S. Environmental Protection Agency. Research

Triangle Park, NC. EMB Report No. 80-FOL-1. July 1982.

4. 1993 Study of Refinery Fugitive Emissions from Equipment

Leaks, Volumes I, II, and III, Radian DCN No. 93-209-081-02,

Radian Corporation, Prepared for Western States Petroleum

Association, Glendale, CA, and American Petroleum Institute,

Washington, D.C., 1994.

5. Development of Fugitive Emission Factors and Emission

Profiles for Petroleum Marketing Terminals, Volumes I and II,

API 4588, Radian Corporation, Prepared for American Petroleum

Institute, 1993.

6. Fugitive Hydrocarbon Emissions from Oil and Gas Production

Operations, API 4589, Star Environmental, Prepared for

American Petroleum Institute, 1993.

7. Emission Factors for Oil and Gas Production Operations,

API 4615, Star Environmental, Prepared for American Petroleum

Institute, 1995.

8. Letter from Robert Strieter, API, to David Markwordt,

U.S. EPA, regarding the submittal of gasoline distribution

facility fugitive equipment screening data. April 26, 1994.

9. Blacksmith, J.R., et al. (Radian Corporation.)

Problem-Oriented Report: Frequency of Leak Occurrence for

Fittings in Synthetic Organic Chemical Plant Process Units.

Prepared for U.S. Environmental Protection Agency. Research

Triangle Park, NC. Publication No. EPA-600/2-81-003.

September 1980.

10. Langley, G.J. and R.G. Wetherhold. (Radian Corporation.)

Evaluation of Maintenance for Fugitive VOC Emissions Control.

2-54
Prepared for U.S. Environmental Protection Agency. Research

Triangle Park, NC. Publication No. EPA-600/S2-81-080.

May 1981.

11. U.S. Environmental Protection Agency. Fugitive Emission

Sources of Organic Compounds - Additional Information of

Emissions, Emission Reductions, and Costs (section 2).

Research Triangle Park, NC. Publication

No. EPA-450/3 82-010. April 1982.

2-55
3.0 SOURCE SCREENING

3.1 INTRODUCTION

This chapter presents procedures for screening equipment

components with a portable volatile organic compound (VOC)

analyzer. When performing source screening, the portable

analyzer probe opening is placed at the leak interface of the

equipment component to obtain a "screening" value. The screening

value is an indication of the concentration level of any leaking

material at the leak interface. A screening value is not a

direct measure of mass emissions rate, but, as discussed in

chapter 2.0, can be entered into a mass emissions/screening value

correlation equation to estimate mass emissions.

This chapter is divided into two sections. The first section

provides a description of the portable analyzers that can be used

when conducting screening surveys. Operating principles of the

analyzers and performance criteria and specifications in the EPA

Reference Method 21 (the method describing the use of portable

VOC analyzers)1 are described, and the use of monitoring devices

that do not meet the EPA Reference Method 21 requirements is

discussed. The second section presents the protocol for

successfully conducting a screening program. This section

includes methods to identify components to be included in the

screening program, a discussion on the development of a

systematic approach for performing the screening survey, the

protocol for screening each of the equipment types, and

recommendations for collecting and handling data.

3-1
3.2 MONITORING INSTRUMENTS

A number of portable VOC detection devices have the potential

to measure the concentration level at the leak interface of

equipment. Any analyzer can be used, provided it meets the

specifications and performance criteria set forth in the EPA

Reference Method 21, section 3.0.1. Reference Method 21 is

included in this document as appendix F.

In general, portable VOC monitoring instruments are equipped

with a probe that is placed at the leak interface of a piece of

equipment. A pump within the instrument draws a continuous

sample of gas from the leak interface area to the instrument

detector. The instrument response is a screening value--that is,

a relative measure of concentration level. The screening value

is in units of parts per million by volume (ppmv). However, the

screening value does not necessarily indicate the actual total

concentration at the leak interface of the compound(s) being

detected because the sensitivity of instruments vary for

different compounds. As discussed in section 2.4.2, response

factors (RF’s) relate actual concentration of a compound to the

observed concentration from the detector. Before a monitoring

instrument is used, it must first be calibrated using a reference

gas containing a known compound at a known concentration.

Methane and isobutylene are frequently used reference compounds.

3.2.1 Operating Principles and Limitations of Portable VOC

Detection Devices

Monitoring instruments operate on a variety of detection

principles, with the three most common being ionization, infrared

absorption, and combustion. Ionization detectors operate by

ionizing the sample and then measuring the charge (i.e., number

of ions) produced. Two methods of ionization currently used are

flame ionization and photoionization. Each of these detector

types are briefly described below.

A standard flame ionization detector (FID) theoretically

measures the total carbon content of the organic vapor sampled,

but many other factors influence the FID readout. Although

carbon monoxide and carbon dioxide (CO2) do not produce

3-2
interferences, FID’s react to water vapor at a low sensitivity.

Furthermore, erratic readings may result if water condenses in

the sample tube. A filter is used to remove particulate matter

from the sample. Certain portable FID instruments are equipped

with gas chromatograph (GC) options making them capable of

measuring total gaseous non-methane organics or individual

organic components. Certain organic compounds containing

nitrogen, oxygen, or halogen atoms give a reduced response when

sampled with an FID, and the FID may not respond to some organic

compounds.

Photoionization detectors use ultraviolet light (instead of a

flame) to ionize organic vapors. As with FID’s, the detector

response varies with the functional group in the organic

compounds. Photoionization detectors have been used to detect

equipment leaks in process units in the SOCMI, especially for

certain compounds, such as formaldehyde, aldehydes, and other

oxygenated compounds, which will not give a satisfactory response

on a FID or combustion-type detector.

Nondispersive infrared (NDIR) instruments operate on the

principle of light absorption characteristics of certain gases.

These instruments are usually subject to interference because

other gases, such as water vapor and CO2, may also absorb light

at the same wavelength as the compound of interest. These

detectors are generally used only for the detection and

measurement of single components. For this type of detection,

the wavelength at which a certain compound absorbs infrared

radiation is predetermined and the device is preset for that

specific wavelength through the use of optical filters. For

example, if set to a wavelength of 3.4 micrometers, infrared

devices can detect and measure petroleum fractions, including

gasoline and naphtha.

Combustion analyzers are designed either to measure the

thermal conductivity of a gas or to measure the heat produced by

combustion of the gas. The most common method in which portable

VOC detection devices are used involves the measurement of the

heat of combustion. These detection devices are referred to as

3-3
hot wire detectors or catalytic oxidizers. Combustion analyzers,

like most other detectors, are nonspecific for gas mixtures. In

addition, combustion analyzers exhibit reduced response (and, in

some cases, no response) to gases that are not readily combusted,

such as formaldehyde and carbon tetrachloride.

3.2.2 Specifications and Performance Criteria of Portable VOC

Detection Devices

As previously stated, any portable analyzer may be used as a

screening device, provided it meets the specifications and the

performance criteria called for in the EPA Reference Method 21.

(See appendix F.) Reference Method 21 specifies the requirements

that must be met when a facility is collecting screening data to

comply with a regulation. The requirements of the EPA Reference

Method 21 are also applicable when screening data are collected

for the sole purpose of estimating emissions. When the

requirements of Reference Method 21 refer to a "leak definition,"

this is the screening value indicating that a piece of equipment

is leaking as defined in the applicable regulation. If screening

data are collected for the sole purpose of estimating emissions,

the equivalent to the "leak definition" concentration in the text

that follows is the highest screening value (i.e., 10,000 ppmv)

that the monitoring instrument can readout.

Reference Method 21 requires that the analyzer meet the

following specifications:1

• The VOC detector should respond to those organic

compounds being processed (determined by the RF);

• Both the linear response range and the measurable range

of the instrument for the VOC to be measured and the

calibration gas must encompass the leak definition

concentration specified in the regulation;

• The scale of the analyzer meter must be readable to

± 2.5 percent of the specified leak definition

concentration;

• The analyzer must be equipped with an electrically

driven pump so that a continuous sample is provided at a

nominal flow rate of between 0.1 and 3.0 liters per

minute;

3-4
• The analyzer must be intrinsically safe for operation in

explosive atmospheres; and

The analyzer must be equipped with a probe or probe

extension for sampling not to exceed .25 inch in outside

diameter, with a single end opening for admission of

sample.

Note that the suction flow rate span allowed by Reference

Method 21 is intended to accommodate a wide variety of

instruments, and manufacturers guidelines for appropriate suction

flow rate should be followed.

In addition to the above specifications, criteria for the

calibration gases to be used are specified. A minimum of two

calibration gases are required for analyzer performance

evaluation. One is a "zero" gas, which is defined as air with

less than 10 ppmv VOC; the other calibration gas, or reference

gas, uses a specified reference compound in an air mixture. The

concentration of the reference compound must approximately equal

the leak definition specified in the regulation. If cylinder

calibration gas mixtures are used, they must be analyzed and

certified by the manufacturer to be within ± 2 percent accuracy.

The shelf life must also be specified. Calibration gases can

also be prepared by the user as long as they are accurate to

within ± 2 percent.

The instrument performance criteria that each analyzer must

meet are presented in table 3-1 and discussed in greater detail

in the following sections.

3.2.2.1 Response Factor. The sensitivity of an analyzer

varies, depending on the composition of the sample and

concentration of VOC detected. The RF quantifies the sensitivity

of the analyzer to each compound. The RF is defined by:

An RF must be determined for each compound that is to be

RF = Actual Concentration of Compound

Observed Concentration from Detector

measured. Response factors may be determined either by testing

or from referenced sources. (The RF’s for many commonly screened

compounds are presented in appendix D.) The RF tests are

3-5
TABLE 3-1. PERFORMANCE CRITERIA FOR PORTABLE VOC DETECTORSa

Criteria Requirement Time interval

Instrument

response factor

Must be <10 unless

correction curve is

used

One time, before

detector is put in

service.

Instrument

response time

Must be ≤30 seconds One time, before

detector is put in

service. If

modification to sample

pumping or flow

configuration is made,

a new test is required.

Calibration

precision

Must be ≤10 percent

of calibration gas

value

Before detector is put

in service and at

3-month intervals or

next use, whichever is

later.

aSource: Reference 1.

3-6
required before placing the analyzer into service, but do not

need to be repeated. The RF for each compound to be measured

must be less than 10 for an analyzer to be acceptable for use in

a screening program. According to Reference Method 21, the RF

can either be measured in the laboratory using a prepared gas

concentration at 80 percent of the applicable leak definition, or

it can be taken from values published in the literature. When no

instrument is available that meets this criteria when calibrated

with the reference compound specified in the applicable

regulation, the available instrument may be calibrated with one

of the VOC’s to be measured. However, the analyzer RF must still

be less than 10 for each VOC to be measured.

As discussed in section 2.4.2, RF’s depend on several

parameters, including the compound, the screening value, the

monitoring instrument, and the calibration gas. In chapter 2.0,

guidance was provided on when and how to apply RF’s for

estimating emissions. Methods were presented on calculating an

RF for a given chemical at a screening value other than one for

which data were published. Methods were also presented for

calculating RF’s for mixtures.

In this chapter, several additional issues pertaining to RF’s

are discussed. These issues are (1) the consideration of RF’s

when selecting a monitoring instrument, (2) how laboratory

analysis can be performed to generate data to determine an RF for

a given compound, and (3) when laboratory analysis is

recommended.

Response factors contained in appendix D can be used as a

guide for selecting an appropriate monitoring device. If at the

applicable leak definition, the RF of an instrument is greater

than 10, that instrument does not meet Reference Method 21

requirements unless a substitute reference gas is used to

calibrate the instrument. For example, at a concentration of

10,000 ppmv, it can be seen that when screening equipment in a

process unit that contains cumene, an FID can be used (RF = 1.92

at an actual concentration of 10,000 ppmv), while the catalytic

oxidation detector cannot (RF = 12.49). Similarly, at a

3-7
concentration of 10,000 ppmv, neither of these devices respond to

carbon tetrachloride and, therefore, cannot be used unless

calibrated with a substitute VOC such that an RF of under 10 can

be calculated for this compound.

Response factors can be determined by laboratory analysis

using the following method. First, the analyzer is calibrated

using the reference gas. Then, for each organic species that is

to be measured, a known standard in air is obtained or prepared.

The concentration of the organic species should be at

approximately the leak definition value. This mixture is then

injected into the analyzer and the observed meter reading is

recorded. The analyzer is then "zeroed" by injecting zero air

until a stable reading is obtained. The procedure is repeated by

alternating between the mixture and zero air until a total of

three measurements are obtained. An RF is calculated for each

repetition and then averaged over the three measurements. This

procedure can be repeated at several different concentration

values. The data can then be used to generate a curve that

relates RF to screening value. (See appendix A.)

The most accurate method for estimating RF’s is to perform

laboratory analysis. This is particularly true because RF’s

vary, not just for the detector type, but also for each

individual instrument. However, in some cases, time and resource

constraints may require the use of published RF data.

Nevertheless, a limitation of the published data is that it is

typically specific to a pure compound for a single actual

concentration value, detector type, and calibration gas.

Additionally, although an RF for mixtures can be calculated as

described in section 2.4.2 (i.e., if an RF is known for each

individual compound), the most accurate RF for a mixture is

calculated by preparing known standards of air for the mixture

and injecting the standard into the analyzer as described

earlier.

3-8
3.2.2.2 Response Time. The response time of an analyzer is

defined as the time interval from a step change in VOC

concentration at the input of a sampling system, to the time at

which the corresponding concentration value is reached as

displayed on the analyzer readout meter. Response time is

determined by introducing zero air into the instrument sample

probe. When the meter reading has stabilized, the specified

calibration gas is injected. The response time is measured as

the time lapsed between switching to the calibration gas and the

time when 90 percent of the final stable reading is obtained.

This test is performed three times and the response time is

calculated as the average of the three tests. The response time

must be equal to or less than 30 seconds for the analyzer to be

acceptable for screening purposes.

The response time test is required before placing an analyzer

in service. The response time must be determined for the

analyzer configuration that will be used during testing. If a

modification to the sample pumping system or flow configuration

is made that would change the response time (e.g., change in

analyzer probe or probe filter, or the instrument pump), a new

test is required before the screening survey is conducted.

3.2.2.3 Calibration Precision. Calibration precision is the

degree of agreement between measurements of the same known value.

To ensure that the readings obtained are repeatable, a

calibration precision test must be completed before placing the

analyzer in service, and at 3-month intervals, or at the next

use, whichever is later. The calibration precision must be equal

to or less than 10 percent of the calibration gas value.

To perform the calibration precision test, three measurements

are required for each non-zero concentration. Measurements are

made by first introducing zero gas and adjusting the analyzer to

zero. The specified calibration gas (reference) is then

introduced and the meter reading is recorded. This procedure

must be performed three times. The average algebraic difference

between the meter readings and the known value of the calibration

gas is then computed. This average difference is then divided by

3-9
the known calibration value and multiplied by 100 to express the

resulting calibration precision as percent. The calibration

precision of the analyzer must be equal to or less than

10 percent of the calibration gas value.

3.2.2.4 Safety. Portable instruments to detect VOC

emissions from equipment leak sources are required to be used in

potentially hazardous locations such as petroleum refineries and

bulk gasoline terminals. The National Electrical Code requires

that instruments to be used in hazardous locations be certified

to be explosion-proof, intrinsically safe, or purged.

Hazardous locations are divided into three classes: Class I,

Class II, and Class III. Each class is divided into two

divisions (division 1 or 2) according to the probability that a

hazardous atmosphere will be present and also into seven groups,

depending on the type of hazardous material exposure: Groups A

through D are flammable gases or vapors, and groups E, F, and G

apply to combustible or conductive gases. Class I, division 1,

groups A, B, C, and D locations are those in which hazardous

concentrations of flammable gases or vapors may exist under

normal operating conditions. Class I, division 2, groups A, B,

C, and D locations are those in which hazardous concentrations of

flammable gases may exist only under unlikely conditions of

operation.

Any instrument considered for use in potentially hazardous

environments must be classified as intrinsically safe for

Class I, division 1 and class II, division 1 conditions at a

minimum. The instrument must not be operated with any safety

device, such as an exhaust flame arrestor, removed.

Table 3-2 lists several portable VOC detection instruments.

table 3-2 includes manufacturer, model number, pollutants

detected, principle of operation, and range. Note that

additional instruments, not listed here, may be available.

3.2.3 Use of Monitoring Devices That Do Not Meet EPA Reference

Method 21 Requirements

In some cases, a monitoring device may not be available that

meets all of the performance specifications of the EPA Reference

3-10
TABLE 3-2. PORTABLE VOC DETECTION INSTRUMENTS

Manufacturer Model no.

Pollutant(s)

detected

Principle of

operation

Range(ppm)

Bacharach Instrument Co.,Santa Clara, California

LTLV Sniffer

Combustible gasesCombustible gases

Catalytic combustionCatalytic combustion

0-100% LELa0-1,000 and 0-10,000

Foxboro,S. Norwalk, Connecticut

OVA-128OVA-108Miran IBX

Most organic compoundsMost organic compoundsCompounds that absorbinfrared radiation

FID/GCFID/GCNDIR

0-1,0000-10,000Compound specific

Health Consultants Detecto -

PAK III

Most organic compounds FID/GC 0-10,000

HNU Systems, Inc.Newton Upper Falls,Massachusetts

HW-101 Chlorinated hydrocarbons,

aromatics, aldehydes,ketones, any substancethat UV light ionizes

Photoionization 0-20, 0-200, 0-2,000

Mine Safety Appliances Co.,Pittsburgh, Pennsylvania

40 Combustible gases Catalytic combustion 0-10% and

0-100% LELa

Survey and Analysis, Inc.,Northboro, Massachusetts

On Mark Model 5 Combustible gases Thermal conductivity 0-5 and 0-100% LELa

aLEL = Lower explosive limit.

3-11
Method 21. For example, there are several cases (e.g., phosgene)

where the RF at 10,000 ppmv is greater than 10. An instrument

may meet all other requirements, but fail as a Reference

Method 21 instrument because it cannot meet the RF requirement.

If an instrument fails to meet Reference Method 21 requirements,

it can still be used for the purpose of estimating emissions if

its reliability can be documented.

Two primary steps must be taken to document the reliability

of an analyzer that fails to meet the Reference Method 21

requirements. First, a laboratory program must be undertaken to

demonstrate the response of the monitoring instrument to the

compounds being measured; that is, an instrument response curve

must be developed for the entire screening value range and

documented so that screening values taken in the field can be

adjusted to actual concentrations if necessary. Second, the

testing program must be sufficiently well-documented to

demonstrate how the instrument will be used when screening

equipment. For example, if the response time of the candidate

instrument exceeds the Reference Method 21 performance

specification, the test plan should reflect added screening time

at each potential leak point. Once this laboratory demonstration

has been completed and the screening value correction curve has

been established, the instrument may be used in a screening

program.

3.3 THE SCREENING PROGRAM

The goal of the screening program is to measure VOC

concentrations at seals, shafts, and other potential leak points.

All equipment to be included in the screening survey needs to be

identified before the screening program starts. A list of

equipment types that are potential sources of fugitive emissions

is provided in table 3-3.

3.3.1 Identification of Equipment to be Screened

The first step in the screening survey is to precisely define

the process unit boundaries. This is usually straightforward,

but occasionally multiple units may be built on the same pad and

share some common facilities. A process unit can be defined as

3-12
TABLE 3-3. EQUIPMENT LEAK EMISSION SOURCES

Equipment types

Agitator seals

Compressor seals

Connectors

Diaphrams

Drains

Dump lever arms

Flanges

Hatches

Instruments

Loading arms

Meters

Open-ended lines

Polished rods

Pressure relief devices

Pump seals

Stuffing boxes

Valves

Vents

Service

Gas/vapor

Light liquid

Heavy liquid

3-13
the smallest set of process equipment that can operate

independently and includes all operations necessary to achieve

its process objective. The exact basis for the unit definition

should be documented. A plot plan of the unit should be obtained

and marked with the appropriate boundaries.

The next step is to obtain a simplified flow diagram of the

process and note the process streams. The actual screening and

data collection can be done efficiently by systematically

following each stream. For example, a logical starting point

would be where one of the feed lines enters the process boundary.

The screening team would follow that line, screening all sources,

until the line terminates at the connectors of a reactor or

separation step. This approach offers the advantage of screening

groups of equipment with roughly the same composition of material

in the line. Screening would then continue on the outlet side of

the reactor or separation equipment. Minor loops, such as a

bypass around a control valve, pump, or heat exchanger, should be

screened on the initial pass. Larger loops of process equipment,

such as parallel passes and processing alternatives, are more

effectively treated as separate streams.

Each source should be uniquely identified to indicate that it

has been screened. For example, sources can be tagged. Tags can

consist of any form of weatherproof and readily visible

identification. Alternatively, a process unit can be considered

appropriately tagged if the unit has a system of identifying

markings with an associated diagram allowing easy location of

marked sources. Once all the equipment along the major streams

has been screened, the unit should be divided into a grid to

search for fittings missed on the initial survey. Consistent

with equipment leaks standards, equipment that is unsafe to

monitor or very difficult to access does not need to be included

in the survey. Documentation must be provided, however, to

substantiate the unsafe or confined nature of such equipment.

3-14
3.3.2 Procedure for Screening

Once the equipment to be screened has been identified, the

procedures outlined in the EPA Reference Method 21 to screen each

equipment type are followed.1 The probe inlet is placed at the

surface of the potential leak interface where leakage could

occur. (The potential leak interface is the boundary between the

process fluid and the atmosphere.) For equipment with no moving

parts at the leak interface, the probe should be placed directly

on the leak interface; for equipment with moving parts (e.g.,

pumps, compressors, and agitators), the probe should be placed

approximately 1 centimeter off from the leak interface. Care

must be taken to ensure that the probe is held perpendicular, not

tangential, to the leak potential interface; otherwise,

inaccurate readings will result. The probe must then be moved

along the interface periphery while observing the instrument

readout. If an increased meter reading is observed, slowly move

the probe along the interface where concentrations register until

the maximum meter reading is obtained. The probe inlet should be

left at this maximum reading location for approximately two times

the instrument response time. The maximum reading is recorded as

the screening value.

The instrument measurement may exceed the scale of the

instrument. This is referred to as a "pegged" readout. For

example, for several instruments, the highest readout on the

scale is 10,000 ppmv. For the purposes of generating an

emissions estimate, a dilution probe should be employed to

measure concentrations greater than the instrument’s normal range

unless average emission factors for greater than or equal to the

"pegged" readout are applied. It is important to note that

extending the measurement range necessitates the calibration of

the instrument to the higher concentrations.

Care should be taken to avoid fouling the probe with grease,

dust, or liquids. A short piece of Teflon® tubing can be used as

a probe tip extender and then can be snipped off as the tip

fouls. In areas with a noticeable particulate loading, this

tubing can be packed loosely with untreated fiberglass, which

3-15
acts as a filter. (Note that the instrument must also be

calibrated with this filter in place.) If a surface to be

screened is obviously dirty, hold the probe tip just over the

surface to avoid scooping up contaminants. Some fouling is

unavoidable, so it is recommended that the probe tip filter be

cleaned at least daily and any other filters on a weekly basis.

Normally, these filters can be cleaned by just tapping them

lightly on a table top, but if the deposits are wet and caked on,

they should be washed with an aqueous solution of soap and

alcohol. This solution also can be used to wash the probe and

transfer line periodically. Care should be taken to blow the

equipment dry before reuse.

This general procedure can be used to screen equipment such

as valves, connectors and flanges, pumps and compressors,

open-ended lines, and other potential sources of VOC leakage,

such as pressure relief devices, loading arms, stuffing boxes,

instruments, vents, dump lever arms, drains, diaphrams, hatches,

notes, or polished rods. The following sections describe the

location on each type of equipment where screening efforts should

be concentrated.

3.3.2.1 Valves. For valves, the most common source of leaks

is at the seal between the stem and housing. To screen this

source, the probe opening is placed where the stem exits the

packing gland and is moved around the stem circumference. The

maximum reading is recorded as the screening valve. Also, the

probe opening is placed at the packing gland take-up connector

seat, and the probe is moved along the periphery. In addition,

valve housings of multipart assemblies should be screened at the

surface of all points where leaks could occur. Figures 3-1

through 3-5 illustrate screening points for several different

types of valves.

3.3.2.2 Connectors and Flanges. For connectors, the probe

opening is placed at the outer edge of the connector - gasket

interface and the circumference of the connector is sampled. For

screwed connectors, the threaded connection interface must also

be screened. Other types of nonpermanent joints, such as

3-16
Rising Stem Type

 Nonrising Stem Type Packing Nut

Packing Gland

Packing

Disk or Wedge

Screen

Here

Stem

Packing Gland

Packing

Packing Out

Screen

Here

Disk or Wedge

3-17

Figure 3-1. Gate Valves
Manual Globe Valve

Stem

Packing

Gland

Packing

Screen

Here

Packing Nut

Screen

Here

Body

Seat

Disk

Stem

Body

Screen

Here

Packing

Globe Type Control Valve

3-18

Figure 3-2. Globe Valves

 through 
Plug

Screen Here

3-19

Figure 3-3. Lubricated Plug Valve
Ball Valve

Ball

Packing

Screen Here

Disk

Screen Here

Butterfly Valve

3-20

Figure 3-4. Ball Valve and Butterfly Valve
Diaphragm

Stem

Weir

Screen Here

Weir-Type Diaphragm Valve

Check Valves

Swing Check

Lift Check

Screen Here

Screen

Here

3-21

Figure 3-5. Weir-Type Diaphragm Valve and Check Valves
threaded connections, are sampled with a similar traverse.

3.3.2.3 Pumps, Compressors, and Agitators. Pumps,

compressors, and agitators are screened with a circumferential

traverse at the outer surface shaft and seal interface where the

shaft exits the housing. If the source is a rotating shaft, the

probe inlet is positioned within 1 centimeter of the shaft - seal

interface. If the housing configuration prevents a complete

traverse of the shaft periphery, all accessible portions must be

sampled. All other joints on the pump or compressor housing

where leakage could occur should also be sampled. Figure 3-6

illustrates screening points for two types of centrifugal pumps.

3.3.2.4 Pressure Relief Devices. The configuration of most

pressure relief devices prevents sampling at the sealing seat.

Because of their design and function, pressure relief devices

must be approached with extreme caution. These devices should

not be approached during periods of process upsets, or other

times when the device is likely to activate. Similarly, care

must be used in screening pressure relief devices to avoid

interfering with the working parts of the device (e.g., the seal

disk, the spring, etc.) For those devices equipped with an

enclosed extension, or horn, the probe inlet is placed at

approximately the center of the exhaust area to the atmosphere.

It should be noted that personnel conducting the screening should

be careful not to place hands, arms, or any parts of the body in

the horn. Figure 3-7 illustrates the screening points for a

spring-loaded relief valve.

3.3.2.5 Open-Ended Lines. Fugitive leaks from open-ended

lines are emitted through a regularly shaped opening. If that

opening is very small (as in sampling lines of less than 1 inch

in diameter), a single reading in the center is sufficient. For

larger openings it is necessary to traverse the perimeter of the

opening. The concentration at the center must also be read.

3-22
3-23

Screen Here

Moving Shaft

Screen Here

Stationary Casing

Vertical Centrifugal Pump

Horizontal Centrifugal Pump

Figure 3-6. Centrifugal Pumps
3-24

Tension Adjustment

Thimble

Disk

Nozzle

Alternate Screening

Area if Horn

Inaccessible

To Process

Horn

Screen Here

Spring

Figure 3-7. Spring-Loaded Relief Valve
3.3.3 Data Handling

To ensure that data quality is maintained, it is recommended

that data be recorded on prepared data sheets. The data

collected should include the following:

1. Monitoring instrument type and model number.

2. Operator’s name.

3. Date.

4. Component identification number (ID number). (If

permanent ID’s are not in place, assign ID’s as each

source is screened.)

5. Component type (i.e., valve, connector, open-ended line,

etc.)

6. Location/stream. (Provide brief description of where

the screened component is located and the composition of

material in the equipment.)

7. Service (i.e., gas, light liquid, or heavy liquid).

8. Number of hours per year the component is in service.

9. Screening value (ppmv).

10. Background concentration (ppmv).

11. Comments. If any explanation is required, it should be

noted in a "comments" section.

In some cases, it may be necessary or desirable to adjust the

screening values for RF. In these cases, the data sheet should

be designed to accommodate extra columns for RF and corrected

screening values. Table 3-4 provides an example data sheet that

may be used to log measurements taken during a screening program.

3-25
TABLE 3-4. EXAMPLE FIELD SHEETS FOR EQUIPMENT SCREENING DATA

Detector model no.Operator nameDate

Component

ID

Component

Type

Location/

Stream Service

Operating

hrs/yr

Screening

value

(ppmv)

Background

(ppmv) Comments

3-26
3.4 REFERENCES

1. Code of Federal Regulations, Title 40, Part 60, Appendix A.

Reference Method 21, Determination of Volatile Organic

Compound Leaks. Washington, DC. U.S. Government Printing

Office. Revised June 22, 1990.

3-27
4.0 MASS EMISSION SAMPLING

4.1 INTRODUCTION

This chapter describes the procedures for "bagging"

equipment to measure mass emissions of organic compounds. An

equipment component is bagged by enclosing the component to

collect leaking vapors. Measured emission rates from bagged

equipment coupled with screening values can be used to develop

unit-specific screening value/mass emission rate correlation

equations. Unit-specific correlations can provide precise

estimates of mass emissions from equipment leaks at the process

unit. However, it is recommended that unit-specific correlations

are only developed in cases where the existing EPA correlations

do not give reasonable mass emission estimates for the process

unit. The focus of the chapter is on bagging equipment

containing organic compounds, but similar procedures can be

applied to bag equipment containing inorganic compounds as long

as there are comparable analytical techniques for measuring the

concentration of the inorganic compound.

This chapter is divided into four sections. In section 4.2,

the methods for bagging equipment are discussed. Considerations

for bagging each equipment type are discussed in section 4.3. In

section 4.4, techniques used in the laboratory analysis of bagged

samples are discussed. Section 4.4 also includes a description

of a rigorous calibration procedure for the portable monitoring

device that must be followed. Finally, in section 4.5, quality

assurance and quality control (QA/QC) guidelines are provided.

4-1
4.2 SAMPLING METHODS

The emission rate from an equipment component is measured by

bagging the component--that is, isolating the component from

ambient air to collect any leaking compound(s). A tent

(i.e., bag) made of material impermeable to the compound(s) of

interest is constructed around the leak interface of the piece of

equipment. A known rate of carrier gas is induced through the

bag and a sample of the gas from the bag is collected and

analyzed to determine the concentration (in parts per million by

volume [ppmv]) of leaking material. The concentration is

measured using laboratory instrumentation and procedures. Mass

emissions are calculated based on the measured concentration and

the flow rate of carrier gas through the bag.

In some cases, it may be necessary to collect liquid leaking

from a bagged equipment piece. Liquid can either be dripping

from the equipment piece prior to bagging, and/or be formed as

condensate within the bag. If liquid accumulates in the bag,

then the bag should be configured so that there is a low point to

collect the liquid. The time in which the liquid accumulates

should be recorded. The accumulated liquid should then be taken

to the laboratory and transferred to a graduated cylinder to

measure the volume of organic material. Based on the volume of

organic material in the cylinder (with the volume of water or

nonorganic material subtracted out), the density of the organic

material, and the time in which the liquid accumulated, the

organic liquid leak rate can be calculated. Note that the

density can be assumed to be equivalent to the density of organic

material in the equipment piece, or, if sufficient volume is

collected, can be measured using a hydrometer. It should be

noted that in some cases condensate may form a light coating on

the inside surface of the bag, but will not accumulate. In these

cases, it can be assumed that an equilibrium between condensation

and evaporation has been reached and that the vapor emissions are

equivalent to total emissions from the source.

When bagging an equipment piece, the enclosure should be

kept as small as practical. This has several beneficial effects:

4-2
The time required to reach equilibrium is kept to a

minimum;

The time required to construct the enclosure is

minimized;

A more effective seal results from the reduced seal

area; and

Condensation of heavy organic compounds inside the

enclosure is minimized or prevented due to reduced

residence time and decreased surface area available for

heat transfer.

Two methods are generally employed in sampling source

enclosures: the vacuum method and the blow-through method. Both

methods involve enclosing individual equipment pieces with a bag

and setting up a sampling train to collect two samples of leaking

vapors to be taken to the laboratory for analysis. Both methods

require that a screening value be obtained from the equipment

piece prior to and after the equipment piece is enclosed. The

methods differ in the ways in which the carrier gas is conveyed

through the bag. In the vacuum method, a vacuum pump is used to

pull air through the bag. In the blow-through method, a carrier

gas such as nitrogen (or other inert gas) is blown into the bag.

In general, the blow-through method has advantages over the

vacuum method. These advantages are as follows.

(1) The blow-through method is more conducive to better

mixing in the bag.

(2) The blow-through method minimizes ambient air in the bag

and thus reduces potential error associated with

background organic compound concentrations. (For this

reason the blow-through method is especially preferable

when measuring the leak rate from components with zero

or very low screening values.)

(3) The blow-through method minimizes oxygen concentration

in the bag (assuming air is not used as the carrier gas)

and the risk of creating an explosive environment.

(4) In general, less equipment is required to set up the

blow-through method sampling train.

However, the blow-through method does require a carrier gas

source, and preferably the carrier gas should be inert and free

4-3
of any organic compounds and moisture. The vacuum method does

not require a special carrier gas.

Details of the sampling train of each of these bagging

methods are discussed in sections 4.2.1 and 4.2.2, respectively.

These sections also contain summaries of the steps of the

sampling procedure for each method. For both methods, the

approach described above for collecting and measuring liquid leak

rates can be utilized. In addition to the sampling descriptions

presented in the following sections, the quality control and

assurance guidelines presented in section 4.5 must also be

followed when bagging equipment.

4.2.1 Vacuum Method

The sampling train used in the vacuum method is depicted in

figure 4-1. The train can be mounted on a portable cart, which

can be moved around the process unit from component to component.

The major equipment items in the sampling train are the vacuum

pump used to draw air through the system, and the dry gas meter

used to measure the flow rate of gas through the train. In

previous studies that the EPA conducted, a 4.8-cubic feet per

minute Teflon® ring piston-type vacuum pump equipped with a

3/4-horsepower, air-driven motor was used. Other equipment that

may be used in the train includes valves, copper and stainless

steel tubing, Teflon® tubing and tape, thermometer,

pressure-reading device, liquid collection device, and air-driven

diaphragm sampling pumps. It also may be necessary to use

desiccant preceding the dry gas meter to remove any moisture.

The bag is connected by means of a bulkhead fitting and

Teflon® tubing to the sampling train. A separate line is

connected from the bag to a pressure-reading device to allow

continuous monitoring of the pressure inside the bag. If a

significant vacuum exists inside the bag when air is being pulled

through, a hole is made in the opposite side of the bag from the

outlet to the sampling train. This allows air to enter the bag

more easily and, thus, reduces the vacuum in the enclosure.

However, it is important to maintain a vacuum in the bag, since

VOC could be lost through the hole if the bag became pressurized.

4-4
This line should

be as short

as possible

Tent

Leaking

Valve

Cold Trap in Ice Bath

(Optional)

Dry Gas

Meter

Trap

Hg Manometer

Control

Valve

Filter

Small

Diaphragm

Pump Two-Way Valve

Sample Bag

Vacuum

Pump

Pressure

Reading

Device

4-5

Figure 4-1. Sampling train for bagging a source using the vacuum

method.
In practice, it has been found that only a very slight vacuum

(0.1 inches of water) is present in the bag during most of the

sampling, even in the absence of a hole through the bag wall.

Sufficient air enters around the seals to prevent the development

of a significant vacuum in the bag. A small diaphragm sampling

pump can be used to collect two samples into sample bags or

canisters, which are then transported to the laboratory for

analysis.

The diaphragm pump can also be used to collect a background

sample of the ambient air near the bagged component. The

concentration in the background bag is subtracted from the

average concentration in the sample bags when calculating the

leak rate. Often this correction is insignificant (particularly

for components with high leak rates or in cases where there is no

detectable volatile organic compound (VOC) concentration measured

by the portable monitoring device), and collection of a

background bag is optional. However, in some cases collection of

a background bag is important so that emission rates are not

biased high.

Any liquid that accumulates in the bag should be collected

using the approach described in section 4.2. Note that if there

is a concern that condensation will occur in equipment downstream

from the bag outlet, a cold trap can be placed as close to the

bag outlet as possible to remove water or heavy organic compounds

that may condense downstream. Any organic condensate that

collects in the cold trap must be measured to calculate the total

leak rate.

The flow rate through the system can be varied by throttling

the flow with a control valve immediately upstream of the vacuum

pump. Typical flow rates are approximately 60 liters per minute

( /min) or less. A good flow rate to use is one in which a

balance can be found between reaching equilibrium conditions and

having a high enough concentration of organic compounds in the

bag outlet to accurately measure the concentration in the

laboratory. As the flow rate is decreased, the concentration of

organic compounds increases in the gas flowing through the

4-6
sampling system. The flow rate should be adjusted to avoid any

operations with an explosive mixture of organic compounds in air.

It may also be possible to increase the flow rate in order to

minimize liquid condensation in the bag.

The flow rate should be set to a constant rate and kept at

that rate long enough for the system to reach equilibrium. To

determine if equilibrium conditions have been reached, a portable

monitoring device can be used to indicate if the outlet

concentration has stabilized.

It is not recommended that the vacuum method be used to

measure the leak rate from equipment that have low screening

values (approximately 10 ppmv or less), because considerable

error can be introduced due to the background organic

concentration in the ambient air that is pulled through the bag.

In summary, the vacuum sampling procedure consists of the

following steps.

(1) Determine the composition of material in the designated

equipment component, and the operating conditions of the

component.

(2) Obtain and record a screening value with the portable

monitoring instrument.

(3) Cut a bag from appropriate material (see section 4.3)

that will easily fit over the equipment component.

(4) Connect the bag to the sampling train.

(5) If a cold trap is used, immerse the trap in an ice bath.

(6) Note the initial reading of the dry gas meter.

(7) Start the vacuum pump and a stopwatch simultaneously.

Make sure a vacuum exists within the bag.

(8) Record the temperature and pressure at the dry gas

meter.

(9) Observe the VOC concentration at the vacuum pump exhaust

with the monitoring instrument. Make sure concentration

stays below the lower explosive limit.

(10) Record the temperature, pressure, dry gas meter

reading, outlet VOC concentration and elapsed time

every 2 to 5 minutes (min).

4-7
(11) Collect 2 gas samples from the discharge of the

diaphragm sampling pump when the outlet concentration

stabilizes (i.e., the system is at equilibrium).

(12) Collect a background bag (optional).

(13) Collect any liquid that accumulated in the bag as

well as in the cold trap (if used) in a sealed

container.

(14) Take a final set of readings and stop the vacuum

pump.

(15) Transport all samples to the laboratory, along with

the data sheet.

(16) Remove the bag.

(17) Rescreen the source with the portable monitoring

instrument and record.

Based on the data collected in the steps described above, mass

emissions are calculated using the equation presented in

table 4-1.

4.2.2 Blow-Through Method

The sampling train for the blow-through method is presented

in figure 4-2. The temperature and oxygen concentrations are

measured inside the bag with a thermocouple (or thermometer) and

an oxygen/combustible gas monitor. The carrier gas is metered

into the bag through one or two tubes (two tubes provide for

better mixing) at a steady rate throughout the sampling period.

The flow rate of the carrier gas is monitored in a gas rotameter

calibrated to the gas. Typical flow rates are approximately

60 /min or less. It is preferable to use an inert gas such as

nitrogen for the blow-through method so as to minimize the risk

of creating an explosive environment inside the bag. Also, the

carrier gas should be free of any organic compounds and moisture.

The pressure in the bag should never exceed 1 pound per square

inch gauge (psig).

The flow rate through the bag can be varied by adjusting the

carrier gas regulator. As mentioned in section 4.2.1, a good

flow rate to use is one in which a balance can be found between

reaching equilibrium conditions and having a high enough

4-8
TABLE 4-1. CALCULATION PROCEDURES FOR LEAK RATE WHEN USING THE

VACUUM METHOD

Leak Rate = 9.63 x 10-10 (Q)(MW)(GC)(P) ( + ρ)(VL)

(kg/hr) T + 273.15 16.67(t)

where:

9.63 x 10-10 = A conversion factor using the gas constant:

°K × 106 × kg-mol × min

;

× hour × mmHg

Q = Flow rate out of bag ( /min);

MWa = Molecular weight of organic compound(s) in

the sample bagc or alternatively in the

process stream contained within the equipment

piece being bagged (kg/kg-mol);

GCb = Sample bag organic compound concentration

(ppmv) minus background bag organic compound

concentrationc (ppmv);

P = Absolute pressure at the dry gas meter

(mmHg);

T = Temperature at the dry gas meter (°C);

ρ = Density of organic liquid collected (g/m );

VL = Volume of liquid collected (m );

16.67 = A conversion factor to adjust term to units

of kilograms per hour (g × hr)/(kg × min)

t = Time in which liquid is collected (min); and

aFor mixtures calculate MW as:

n n

= ∑ MWi Xi / ∑ Xi

i=1 i=1

where:

MWi = Molecular weight of organic compound i;

Xi = Mole fraction of organic compound i; and

n = Number of organic compounds in mixture. bFor mixtures, the value of GC is the total concentration of all

the organic compounds in the mixture.

cCollection of a background bag is optional. If a background bag

is not collected, assume the background concentration is zero.

4-9
Carrier

Gas

Source

Pressure

Regulator

Dessicant

Activated

Charcoal

Rotameter

1/4" Insulated

Teflon Tubing

Valve Stem

Tape or Adjustable Metal Band

Sample Port for Collecting Data on

- Temperature

- Hydrocarbon Concentration

- Oxygen Concentration

Foil or Tape or Compressed Foil

Mylar

Enclosure

(if needed)

(if needed)

R

R

4-10

Figure 4-2. Equipment Required for the Blow-Through

Sampling Technique
concentration of organic compounds in the bag outlet to

accurately measure the concentration in the laboratory.

Adjustments to the flow rate may also help minimize liquid

condensation in the bag. Any liquid that does accumulate in the

bag should be collected using the approach described in

section 4.2.

The carrier gas flow rate should be set to a constant rate

and kept at that rate long enough for the system to reach

equilibrium. In addition to the carrier gas flow through the

bag, some ambient air may enter the bag if it is not airtight.

The oxygen measurements are used to determine the flow of ambient

air through the bag. The oxygen measurements are also an

indication of the quality of the bagging procedure (the lower the

oxygen concentration the better). Once oxygen concentration

falls below 5 percent, the portable monitoring instrument is used

to check organic compound concentrations at several locations

within the bag to ensure that the bag contents are at steady

state.

Once the bag contents are at steady state, two gas samples

are drawn out of the bag for laboratory analysis using a portable

sampling pump. It may also be necessary to collect a background

bag sample, particularly if the source had screened at zero and

if there is still a detectable level of oxygen in the bag.

However, collection of a background bag is optional.

In summary, the blow-through method consists of the

following steps, which assume nitrogen is used as the carrier

gas.

(1) Determine the composition of the material in the

designated equipment component, and the operating

conditions of the component.

(2) Screen the component using the portable monitoring

instrument.

(3) Cut a bag that will easily fit over the equipment

component.

4-11
(4) Connect tubing from the nearest nitrogen source to a

rotameter stand.

(5) Run tubing from the rotameter outlet to a "Y" that

splits the nitrogen flow into two pieces of tubing and

insert the tubes into openings located on either side of

the bag.

(6) Turn on the nitrogen flow and regulate it at the

rotameter to a constant rate and record the time.

(7) After the nitrogen is flowing, wrap aluminum foil around

those parts of the component where air could enter the

bag-enclosed volume.

(8) Use duct tape, wire, and/or rope to secure the bag to

the component.

(9) Put a third hole in the bag roughly equidistant from the

two carrier gas-fed holes.

(10) Measure the oxygen concentration in the bag by

inserting the lead from an oxygen meter into the

third hole. Adjust the bag (i.e., modify the seals

at potential leak points) until the oxygen

concentration is less than 5 percent.

(11) Measure the temperature in the bag.

(12) Check the organic compound concentration at several

points in the bag with the portable monitoring

instrument to ensure that carrier gas and VOC are

well mixed throughout the bag.

(13) Collect samples in sample bags or canisters by

drawing a sample out of the bag with a portable

sampling pump.

(14) Collect a background bag (optional).

(15) Remove the bag and collect any liquid that

accumulated in the bag in a sealed container. Note

the time over which the liquid accumulated.

(16) Rescreen the source.

Table 4-2 gives equations used to calculate mass emission rates

when using the blow-through method. An adjustment is provided

for the leak rate equation in table 4-2 to account for the total

flow through the bag. This adjustment is recommended and

represents an improvement over previous versions

4-12
TABLE 4-2. CALCULATION PROCEDURES FOR LEAK RATE

WHEN USING THE BLOW-THROUGH METHOD

where:

Leak Rate

(kg/hr)













1.219 x 10 5 (Q) (MW) (GC)

T 273.15

(ρ) (VL)

16.67 (t)

x 











106ppmv

106ppmv GC

1.219 x 10-5 = A conversion factor taking into account the gas

constant and assuming a pressure in the tent of

1 atmosphere:

oK × 106 × kg-mol

;

m3

Q = flow rate out of tent (m3/hr);

= N2 Flow Rate ( /min) × [0.06 (m3/min)]

1 - [Tent Oxygen Conc. (volume %)/21] ( /hr)

MWa = Molecular weight of organic compounds in the

sample bag or alternatively in the process

stream contained within the equipment piece

being bagged (kg/kg-mol);

GCb = Sample bag organic compound concentration

(ppmv), corrected for background bag organic

compound concentration (ppmv);c

T = Temperature in tent (oC);

ρ = Density of organic liquid collected (g/m );

VL = Volume of liquid collected (m );

16.67 = A conversion factor to adjust term to units of

Kilograms per hour (g × hr)/(kg × min); and

t = Time in which liquid is collected (min).

aFor mixtures calculate MW as:

n n

= ∑ MWi Xi / ∑ Xi

i=1 i=1

where:

MWi = Molecular weight of organic compound i;

4-13
TABLE 4-2. CALCULATION PROCEDURES FOR LEAK RATE

WHEN USING THE BLOW-THROUGH METHOD

(Continued)

Xi = Mole fraction of organic compound i; and

n = Number of organic compounds in mixture.

bFor mixtures, the value of GC is the total concentration of all

the organic compounds in the mixture.

cCollection of a background bag is optional. If a background bag

is not collected, assume the background concentration is zero.

To correct for background concentration, use the following

equation:

where:

GC

(ppmv) SB TENT

21

x BG

SB = Sample bag concentration (ppmv);

TENT = Tent oxygen concentration (volume %); and

BG = Background bag concentration (ppmv)

4-14
of this document for quantifying mass emissions from the blow

through method.

4.3 SOURCE ENCLOSURE

In this section, choosing a bagging material and the

approach for bagging specific equipment types are discussed. An

important criteria when choosing the bagging material is that it

is impermeable to the specific compounds being emitted from the

equipment piece. This criteria is also applicable for sample gas

bags that are used to transport samples to the laboratory. A bag

stability test over time similar to the Flexible Bag Procedure

described in section 5.3.2 of the EPA method 18 is one way to

check the suitability of a bagging material.1 After a bag has

been used, it must be purged. Bags containing residual organic

compounds that cannot be purged should be discarded. Mylar®,

Tedlar®, Teflon®, aluminum foil, or aluminized Mylar® are

recommended potential bagging materials. The thickness of the

bagging material can range from 1.5 to 15 millimeters (mm),

depending on the bagging configuration needed for the type of

equipment being bagged, and the bagging material. Bag

construction for individual sources is discussed in

sections 4.3.1 through 4.3.5. For convenience, Mylar® will be

used as an example of bagging material in the following

discussions.

4.3.1 Valves

When a valve is bagged, only the leak points on the valve

should be enclosed. Do not enclose surrounding flanges. The

most important property of the valve that affects the type of

enclosure selected for use is the metal skin temperature where

the bag will be sealed. At skin temperatures of approximately

200 oC or less, the valve stem and/or stem support can be wrapped

with 1.5- to 2.0-mm Mylar® and sealed with duct tape at each end

and at the seam. The Mylar® bag must be constructed to enclose

the valve stem seal and the packing gland seal.

When skin temperatures are in excess of 200 oC, a different

method of bagging the valve should be utilized. Metal bands,

wires, or foil can be wrapped around all hot points that would be

4-15
in contact with the Mylar® bag material. Seals are then made

against the insulation using duct tape or adjustable metal bands

of stainless steel. At extremely high temperatures, metal foil

can be used as the bagging material and metal bands used to form

seals. At points where the shape of the equipment prevent a

satisfactory seal with metal bands, the foil can be crimped to

make a seal.

4.3.2 Pumps and Agitators

As with valves, a property of concern when preparing to

sample a pump or agitator is the metal skin temperature at areas

or points that are in contact with the bag material. At skin

temperatures below 200 oC, Mylar® plastic and duct tape are

satisfactory materials for constructing a bag around a pump or

agitator seal. If the temperature is too high or the potential

points of contact are too numerous to insulate, an enclosure made

of aluminum foil can be constructed. This enclosure is sealed

around the pump and bearing housing using silicone fabric

insulting tape, adjustable metal bands, or wire.

The configuration of the bag will depend upon the type of

pump. Most centrifugal pumps have a housing or support that

connects the pump drive (or bearing housing) to the pump itself.

The support normally encloses about one-half of the area between

the pump and drive motor, leaving open areas on the sides. The

pump can be bagged by cutting panels to fit these open areas.

These panels can be made using thicker bagging material such as

14-mm Mylar®. In cases where supports are absent or quite

narrow, a cylindrical enclosure around the seal can be made so

that it extends from the pump housing to the motor or bearing

support. As with the panels, this enclosure should be made with

thicker bagging material to provide strength and rigidity.

Reciprocating pumps can present a somewhat more difficult

bagging problem. If supports are present, the same type of

two-panel Mylar® bag can be constructed as that for centrifugal

pumps. In many instances, however, sufficiently large supports

are not provided, or the distance between pump and driver is

relatively long. In these cases, a cylindrical enclosure as

4-16
discussed above can be constructed. If it is impractical to

extend the enclosure all the way from the pump seal to the pump

driver, a seal can be made around the reciprocating shaft. This

can usually be best completed by using heavy aluminum foil and

crimping it to fit closely around the shaft. The foil is

attached to the Mylar® plastic of the enclosure and sealed with

the duct tape.

In cases where liquid is leaking from a pump, the outlet

from the bag to the sampling train should be placed at the top of

the bag and as far away from spraying leaks as practical. A low

point should be formed in the bag to collect the liquid so that

the volume of the liquid can be measured and converted to a mass

rate.

4.3.3 Compressors

In general, the same types of bags that are suitable for

pumps can be directly applied to compressors. However, in some

cases, compressor seals are enclosed and vented to the atmosphere

at a high-point vent. If the seals are vented to a high-point

vent, this vent line can be sampled. A Mylar® bag can be

constructed and sealed around the outlet of the vent and

connected to the sampling train. If the high-point vents are

inaccessible, the vent lines from the compressor seal enclosures

can be disconnected at some convenient point between the

compressor and the normal vent exit. Sampling is then conducted

at this intermediate point. In other cases, enclosed compressor

seals are vented by means of induced draft blowers or fans. In

these cases, if the air flow rate is know or can be determined,

the outlet from the blower/fan can be sampled to determine the

emission rate.

4.3.4 Connectors

In most cases, the physical configurations of connectors

lend themselves well to the determination of leak rates. The

same technique can be used for a connector whether it is a

flanged or a threaded fitting. To bag a connector with a skin

temperature below 200 oC, a narrow section of Mylar® film is

constructed to span the distance between the two flange faces or

4-17
the threaded fitting of the leaking source. The Mylar® is

attached and sealed with duct tape. When testing connectors with

skin temperatures above 200 oC, the outside perimeter of both

sides of the connector are wrapped with heat-resistant insulating

tape. Then, a narrow strip of aluminum foil can be used to span

the distance between the connection. This narrow strip of foil

can be sealed against the insulating tape using adjustable bands

of stainless steel.

4.3.5 Relief Valves

Relief devices in gas/vapor service generally relieve to the

atmosphere through a large-diameter pipe that is normally located

at a high point on the process unit that it serves. The "horns"

can be easily bagged by placing a Mylar® plastic bag over the

opening and sealing it to the horn with duct tape. Because may

of these devices are above grade level, accessibility to the

sampling train may be limited or prevented. It is sometimes

possible to run a long piece of tubing from the outlet connection

on the bag to the sampling train located at grade level or on a

stable platform.

As discussed previously in section 3.0, the purpose of

pressure relief devices makes them inherently dangerous to

sample, especially over a long period of time. If these

equipment are to be sampled for mass emissions, special care and

precautions should be taken to ensure the safety of the personnel

conducting the field sampling.

4.4 ANALYTICAL TECHNIQUES

The techniques used in the laboratory analysis of the bagged

samples will depend on the type of processes sampled. The

following sections describe the analytical instrumentation and

calibration, and analytical techniques for condensate. These are

guidelines and are not meant to be a detailed protocol for the

laboratory personnel. Laboratory personnel should be well-versed

in the analysis of organic compound mixtures and should design

their specific analyses to the samples being examined.

Also discussed is the calibration protocol for the portable

monitoring instrument. When bagging data are collected, it is

4-18
critical that the screening value associated with mass emission

rates is accurate. For this reason, a more rigorous calibration

of the portable monitoring instrument is required than if only

screening data are being collected.

4.4.1 Analytical Instrumentation

The use of analytical instrumentation in a laboratory is

critical to accurately estimate mass emissions. The analytical

instrument of choice depends on the type of sample being

processed. Gas chromatographs (GC’s) equipped with a flame

ionization detector or electron capture detector are commonly

used to identify individual constituents of a sample. Other

considerations besides instrument choice are the type of column

used, and the need for temperature programming to separate

individual constituents in the process stream with sufficient

resolution. For some process streams, total hydrocarbon analyses

may be satisfactory.

4.4.2 Calibration of Analytical Instruments

Gas chromatographs should be calibrated with either gas

standards generated from calibrated permeation tubes containing

individual VOC components, or bottled standards of common gases.

Standards must be in the range of the concentrations to be

measured. If cylinder calibration gas mixtures are used, they

must be analyzed and certified by the manufacturer to be within

± 2 percent accuracy, and a shelf life must be specified.

Cylinder standards beyond the shelf life must either be

reanalyzed or replaced.

Field experience indicates that certified accuracies of

± 2 percent are difficult to obtain for very low-parts per

million (ppm) calibration standards (< 10 ppm). Users of

low-parts per million calibration standards should strive to

obtain calibration standards that are as accurate as possible.

The accuracy must be documented for each concentration standard.

The results of all calibrations should be recorded on

prepared data sheets. Table 4-3 provides an example of a data

collection form for calibrating a GC. If other analytical

instruments are used to detect the organic compounds from liquid

4-19
TABLE 4-3. EXAMPLE GC CALIBRATION DATA SHEET

Plant ID

Instrument ID

Analyst Name

Date Time

Certified

Gas Conc.

(ppmv)

Instrument

Reading

(ppmv) Comments

4-20
samples, they should be calibrated according to standard

calibration procedures for the instrument.

4.4.3 Analytical Techniques for Condensate

Any condensate collected should be brought to the laboratory

sealed in the cold trap flask. This material is transferred to a

graduated cylinder to measure the volume collected. If there is

enough volume to make it feasible, the organic layer should be

separated from the aqueous layer (if present) and weighed to

determine its density. If water-miscible organic compounds are

present, both the aqueous and organic phases should be analyzed

by GC to determine the total volume of organic material.

4.4.4. Calibration Procedures for the Portable Monitoring

Instrument

To generate precise screening values, a rigorous calibration

of the portable monitoring instrument is necessary. Calibrations

must be performed at the start and end of each working day, and

the instrument reading must be within 10 percent of each of the

calibration gas concentrations. A minimum of five calibration

gas standards must be prepared including a zero gas standard, a

standard approaching the maximum readout of the screening

instrument, and three standards between these values. If the

monitoring instrument range is from 0 to 10,000 ppmv, the

following calibration gases are required:

A zero gas (0-0.2 ppm) organic in air standard;

A 9.0 ppm (8-10 ppm) organic in air standard;

A 90 ppm (80-100 ppm) organic in air standard;

A 900 ppm (800-1,000 ppm) organic in air standard; and

A 9,000 ppm (8,000-10,000 ppm) organic in air standard.

The same guidelines for the analysis and certification of the

calibration gases as described for calibrating laboratory

analytical instruments must be followed for calibrating the

portable monitoring instrument.

4.5 QUALITY CONTROL AND QUALITY ASSURANCE GUIDELINES

To ensure that the data collected during the bagging program

is of the highest quality, the following QC/QA procedures must be

followed. Quality control requirements include procedures to be

4-21
followed when performing equipment leak mass emissions sampling.

Quality assurance requirements include accuracy checks of the

instrumentation used to perform mass emissions sampling. Each of

these QC/QA requirements are discussed below.

4.5.1 Quality Control Procedures

A standard data collection form must be prepared and used

when collecting data in the field. Tables 4-4 and 4-5 are

examples of data collection forms for the blow-through and vacuum

methods of mass emissions sampling, respectively.

In addition to completing the data collection forms, the

following guidelines need to be adhered to when performing the

bagging analysis:

Background levels near equipment that is selected for

bagging must not exceed 10 ppmv, as measured with the

portable monitoring device.

Screening values for equipment that is selected for

bagging must be readable within the spanned range of

the monitoring instruments. If a screening value

exceeds the highest reading on the meter (i.e., "pegged

reading"), a dilution probe should be used, or in the

event that this is not possible, the reading should be

identified as pegged.

Only one piece of equipment can be enclosed per bag; a

separate bag must be constructed for each equipment

component.

A separate sample bag must be used for each equipment

component that is bagged. Alternatively, bags should

be purged and checked for contamination prior to reuse.

A GC must be used to measure the concentrations from

gas samples.

Gas chromatography analyses of bagged samples must

follow the analytical procedures outlined in the EPA

method 18.

To ensure adequate mixing within the bag when using the

blow-through method, the dilution gas must be directed

onto the equipment leak interface.

To ensure that steady-state conditions exist within the

bag, wait at least five time constants (volume of bag

dilution/gas flow rate) before withdrawing a sample for

recording the analysis.

4-22
TABLE 4-4. EXAMPLE DATA COLLECTION FORM FOR FUGITIVE EMISSIONS

BAGGING TEST (BLOW-THROUGH METHOD)

Equipment Type Component ID

Equipment Category Plant ID

Line Size Date

Stream Phase (G/V, LL, HL) Analysis Team

Barometric Pressure

Ambient Temperature Instrument ID

Stream Temperature Stream Pressure

Stream Composition (Wt %) ,

, ,

Time Bagging Test Measurement Data

Initial Screening (ppmv) Equipment Piece Bkgd.

Background Bag Organic Compound Conc. (ppmv)a

Dilution Gas Flow Rate ( /min)

Sample Bag 1 Organic Compound Conc. (ppmv)

O2 Concentration (volume %)

Bag Temperature (°C)

Dilution Gas Flow Rate ( /min)

Sample Bag 2 Organic Compound Conc. (ppmv)

O2 Concentration (volume %)

Bag Temperature (°C)

Condensate Accumulation: Starting Time Final Time

Organic Condensate Collected (m )

Density of Organic Condensate (g/m )

Final Screening (ppmv) Equipment Piece Bkgd.

aCollection of a background bag is optional. However, it is

recommended in cases where the screening value is less than

10 ppmv and there is a detectable oxygen level in the bag.

4-23
TABLE 4-5. EXAMPLE DATA COLLECTION FORM FOR FUGITIVE EMISSIONS

BAGGING TEST (VACUUM METHOD)

Equipment Type Component ID

Equipment Category Plant ID

Line Size Date

Stream Phase (G/V, LL, HL) Analysis Team

Barometric Pressure

Ambient Temperature Instrument ID

Stream Temperature Stream Pressure

Stream Composition (Wt %) ,

, ,

Time Bagging Test Measurement Data

Initial Screening (ppmv) Equipment Piecea Bkgd.

Background Bag Organic Compound Conc. (ppmv)b

Dry Gas Meter Reading ( /min)

Sample Bag 1 Organic Compound Conc. (ppmv)

Vacuum Check in Bag (Y/N) (Must be YES to collect sample.)

Dry Gas Meter Temperaturec (°C)

Dry Gas Meter Pressurec (mmHg)

Dry Gas Meter Reading ( /min)

Sample Bag 2 Organic Compound Conc. (ppmv)

Vacuum Check in Bag (Y/N) (Must be YES to collect sample.)

Dry Gas Meter Temperaturec (°C)

Dry Gas Meter Pressurec (mmHg)

Condensate Accumulation: Starting Time Final Time

Organic Condensate Collected (m )

Density of Organic Condensate (g/m )

Final Screening (ppmv) Equip. Piecea Bkgd.

aThe vacuum method is not recommended if the screening value is

approximately 10 ppmv or less.

bCollection of a background bag is optional.

cPressure and temperature are measured at the dry gas meter.

4-24
The carrier gas used in the blow-through method of

bagging should be analyzed by GC before it is used, and

the concentration of organic compounds in the sample

should be documented. For cylinder purge gases, one

gas sample should be analyzed. For plant purge gas

systems, gas samples should be analyzed with each

bagged sample unless plant personnel can demonstrate

that the plant gas remains stable enough over time to

allow a one-time analysis.

The portable monitoring instrument calibration

procedure described in section 4.4.4 should be

performed at the beginning and end of each day.

4.5.2 Quality Assurance Procedures

Accuracy checks on the laboratory instrumentation and

portable monitoring device must be performed to ensure data

quality. These checks include a leak rate check performed in the

laboratory, blind standards to be analyzed by the laboratory

instrumentation, and drift checks on the portable monitoring

device.

4.5.2.1 Leak Rate Check

A leak rate check is normally performed in the laboratory by

sampling an artificially induced leak rate of a known gas. This

can clarify the magnitude of any bias in the combination of

sampling/test method, and defines the variance in emissions

estimation due to the sampling. If the result is outside the

80 to 120 percent recovery range, the problem must be

investigated and corrected before sampling continues. The

problems and associated solutions should be noted in the test

report.

Leak rate checks should be performed at least two times per

week during the program. The leak rate checks should be

conducted at two concentrations: (1) within the range of 10

multiplied by the calculated lower limit of detection for the

laboratory analytical instrument; and (2) within 20 percent of

the maximum concentration that has been or is expected to be

detected in the field during the bagging program.

To perform a leak rate check, first induce a known flow rate

with one of the known gas concentrations into a sampling bag.

4-25
For example, this can be done using a gas permeation tube of a

known organic compound constituent. Next, determine the

concentration of the gas using a laboratory analytical instrument

and compare the results to the known gas concentration.

If the calculated leak rate is not within ± 20 percent of

the induced leak rate, further analysis should be performed to

determine the reason.

Areas that can potentially induce accuracy problems include:

Condensation,

Pluggage,

Seal of bag not tight (leakage),

Adsorption onto bag, and

Permeation of bag.

The results of all accuracy checks should be recorded on prepared

data sheets.

4.5.2.2 Blind Standards Preparation and Performance

Blind standards are analyzed by the laboratory

instrumentation to ensure that the instrument is properly

calibrated. Blind standards must be prepared and submitted at

least two times per week during the program. The blind standards

are prepared by diluting or mixing known gas concentrations in a

prescribed fashion so that the resulting concentrations are

known. The analytical results should be within ± 25 percent of

the blind standard gas concentration. If the results are not

within 25 percent of the blind standard concentration, further

analyses must be performed to determine the reason. Use of blind

standards not only defines the analytical variance component and

analytical accuracy, but it can serve to point out equipment

malfunctions and/or operator error before questionable data are

generated.

4.5.2.3 Drift Checks

Drift checks need to be performed to ensure that the

portable monitoring instrument remains calibrated. At a minimum,

drift checks must be performed before and after a small group of

components (i.e., two or three) are bagged. Preferably, drift

4-26
checks should be performed on the screening instrument

immediately before and after each component is bagged. These

checks should be performed by analyzing one of the calibration

gases used to calibrate the portable monitoring instrument. The

choice of calibration gas concentration should reflect the

anticipated screening value of the next component to be

monitored. For example, if a component had previously screened

at 1,000 ppmv and been identified for bagging, the calibration

standard should be approximately 900 ppmv.

Drift check data must be recorded on data sheets containing

the information shown in the example in table 4-6. If the

observed instrument reading is different from the certified value

by greater than ± 20 percent, then a full multipoint calibration

must be performed (see section 3.2.4.1). Also, all those

components analyzed since the last drift check must be retested.

Drift checks should also be performed if flameout of the

portable monitoring instrument occurs. Using the lowest

calibration gas standard (i.e., approximately 9 ppmv standard),

determine the associated response on the portable monitoring

instrument. If the response is not within ± 10 percent of the

calibration gas concentration, a full multipoint calibration is

required before testing resumes.

4-27
TABLE 4-6. EXAMPLE DRIFT TEST REPORT FORM

Plant ID

Instrument ID

Analyst Name

Date

Standard

Gas Conc.

(ppmv) Time

Measured

Conc.

(ppmv)

%

Errora

ID Number of

Component Bagged

Since Last Test

a% Error = Certified Conc. - Measured Conc. * 100

Certified Conc.

4-28
4.6 REFERENCES

1. Code of Federal Regulations, Title 40, Part 60, Appendix A.

Reference Method 21, Determination of Volatile Organic

Compound Leaks. Washington, DC. U.S. Government Printing

Office. Revised June 22, 1990.

4-29
5.0 ESTIMATION OF CONTROL EFFICIENCIES FOR

EQUIPMENT LEAK CONTROL TECHNIQUES

5.1 INTRODUCTION

In this chapter, control techniques for reducing equipment

leak emissions are described. There are two primary techniques

for reducing equipment leak emissions: (1) modifying or

replacing existing equipment, and (2) implementing a leak

detection and repair (LDAR) program.

Modifying or replacing existing equipment is referred to in

this chapter as an "equipment modification." Examples of

equipment modifications include installing a cap on an open-ended

line, replacing an existing pump with a sealless type, and

installing on a compressor a closed-vent system that collects

potential leaks and routes them to a control device. In

section 5.2, possible equipment modifications for each of the

equipment types are briefly described. Also, the estimated

control efficiency is presented for each equipment modification.

An LDAR program is a structured program to detect and repair

equipment that is identified as leaking. The focus of this

chapter is LDAR programs for which a portable monitoring device

is used to identify equipment leaks from individual pieces of

equipment. In section 5.3, an approach is presented for

estimating the control effectiveness of an LDAR program.

5.2 EQUIPMENT MODIFICATION CONTROL EFFICIENCY

Controlling emissions by modifying existing equipment is

achieved by either installing additional equipment that

eliminates or reduces emissions, or replacing existing equipment

with sealless types. Equipment modifications for each equipment

type are described in the following sections. A separate section

5-1
is included on closed-vent systems, which can be installed on

more than one type of equipment. Equipment modifications that

can be used for each equipment type are summarized in table 5-1.

Table 5-1 also contains an approximate control efficiency for

each modification.

5.2.1 Closed-Vent Systems

A closed-vent system captures leaking vapors and routes them

to a control device. The control efficiency of a closed-vent

system depends on the percentage of leaking vapors that are

routed to the control device and the efficiency of the control

device. A closed-vent system can be installed on a single piece

of equipment or on a group of equipment pieces. For use on

single pieces of equipment, closed-vent systems are primarily

applicable to equipment types with higher potential emission

rates, such as pumps, compressors, and pressure relief devices.

5.2.2 Pumps

Equipment modifications that are control options for pumps

include routing leaking vapors to a closed-vent system

(as discussed in section 5.2.1), installing a dual mechanical

seal containing a barrier fluid, or replacing the existing pump

with a sealless type.

5.2.2.1 Dual Mechanical Seals. A dual mechanical seal

contains two seals between which a barrier fluid is circulated.

Depending on the design of the dual mechanical seal, the barrier

fluid can be maintained at a pressure that is higher than the

pumped fluid or at a pressure that is lower than the pumped

fluid. If the barrier fluid is maintained at a higher pressure

than the pumped fluid, the pumped fluid will not leak to the

atmosphere. The control efficiency of a dual mechanical seal

with a barrier fluid at a higher pressure than the pumped fluid

is essentially 100 percent, assuming both the inner and outer

seal do not fail simultaneously.

If the barrier fluid is maintained at a lower pressure than

the pumped fluid, a leak in the inner seal would result in the

pumped fluid entering the barrier fluid. To prevent emissions of

the pumped fluid to the atmosphere, a barrier fluid reservoir

5-2
TABLE 5-1. SUMMARY OF EQUIPMENT MODIFICATIONS

Equipment type Modification

Approximate

control

efficiency

(%)

Pumps Sealless design

Closed-vent system

Dual mechanical seal with

barrier fluid maintained at a

higher pressure than the pumped

fluid

100a

90b

100

Compressors Closed-vent system

Dual mechanical seal with

barrier fluid maintained at a

higher pressure than the

compressed gas

90b

100

Pressure relief

devices

Closed-vent system

Rupture disk assembly

c

100

Valves Sealless design 100a

Connectors Weld together 100

Open-ended

lines

Blind, cap, plug, or second

valve

100

Sampling

connections

Closed-loop sampling 100

aSealless equipment can be a large source of emissions in the

event of equipment failure.

bActual efficiency of a closed-vent system depends on percentage

of vapors collected and efficiency of control device to which

the vapors are routed.

cControl efficiency of closed vent-systems installed on a

pressure relief device may be lower than other closed-vent

systems, because they must be designed to handle both

potentially large and small volumes of vapor.

5-3
system should be used. At the reservoir, the pumped fluid can

vaporize (i.e., de-gas) and then be collected by a closed-vent

system.

The actual emissions reduction achievable through use of

dual mechanical seals depends on the frequency of seal failure.

Failure of both the inner and outer seals could result in

relatively large releases of the process fluid. Pressure

monitoring of the barrier fluid may be used to detect failure of

the seals, allowing for a quick response to a failure.

5.2.2.2 Sealless Pumps. When operating properly, a

sealless pump will not leak because the process fluid cannot

escape to the atmosphere. Sealless pumps are used primarily in

processes where the pumped fluid is hazardous, highly toxic, or

very expensive, and where every effort must be made to prevent

all possible leakage of the fluid. Under proper operating

conditions, the control efficiency of sealless pumps is

essentially 100 percent; however, if a catastrophic failure of a

sealless pump occurs, there is a potential for a large quantity

of emissions.

5.2.3 Compressors

Emissions from compressors may be reduced by collecting and

controlling the emissions from the seal or by improving seal

performance. Shaft seals for compressors are of several

different types--all of which restrict but do not eliminate

leakage. In some cases, compressors can be equipped with ports

in the seal area to evacuate collected gases using a closed-vent

system. Additionally, for some compressor seal types, emissions

can be controlled by using a barrier fluid in a similar manner as

described for pumps.

5.2.4 Pressure Relief Valves

Equipment leaks from pressure relief valves (PRV’s) occur as

a result of improper reseating of the valve after a release, or

if the process is operating too close to the set pressure of the

PRV and the PRV does not maintain its seal. Emissions occurring

from PRV’s as a result of an overpressure discharge are not

considered to be equipment leak emissions. There are two primary

5-4
alternatives for controlling equipment leaks from pressure relief

devices: use of a rupture disk (RD) in conjunction with the PRV,

or use of a closed-vent system.

5.2.4.1 Rupture Disk/Pressure Relief Valve Combination.

Although they are also pressure relief devices, RD’s can be

installed upstream of a PRV to prevent fugitive emissions through

the PRV seat. Rupture disk/pressure relief valve combinations

require certain design constraints and criteria to avoid

potential safety hazards, which are not covered in this document.

If the RD fails, it must be replaced. The control efficiency of

the RD/PRV combination is assumed to be 100 percent when operated

and maintained properly.

5.2.4.2 Closed-Vent System. A closed-vent system can be

used to transport equipment leaks from a pressure relief device

to a control device such as a flare. The equipment leak control

efficiency for a closed-vent system installed on a pressure

relief device may not be as high as the control efficiency that

can be achieved by installing a closed-vent system on other

equipment types. This is because emissions from pressure relief

devices can be either high flow emissions during an overpressure

incident or low flow emissions associated with equipment leaks,

and it may be difficult to design a control device to efficiently

handle both high and low flow emissions.

5.2.5 Valves

Emissions from process valves can be eliminated if the valve

stem can be isolated from the process fluid. Two types of

sealless valves are available: diaphragm valves and sealed

bellows valves. The control efficiency of both diaphragm and

sealed bellows valves is virtually 100 percent. However, a

failure of these types of valves has the potential to cause

temporary emissions much larger than those from other types of

valves.

5.2.6 Connectors

In cases where connectors are not required for safety,

maintenance, process modification, or periodic equipment removal,

emissions can be eliminated by welding the connectors together.

5-5
5.2.7 Open-Ended Lines

Emissions from open-ended lines can be controlled by

properly installing a cap, plug, or second valve to the open end.

If a second valve is installed, the upstream valve should always

be closed first after use of the valves to prevent the trapping

of fluids between the valves. The control efficiency of these

measures is assumed to be essentially 100 percent.

5.2.8 Sampling Connections

Emissions from sampling connections occur as a result of

purging the sampling line to obtain a representative sample of

the process fluid. Emissions from sampling connections can be

reduced by using a closed-loop sampling system or by collecting

the purged process fluid and transferring it to a control device

or back to the process. The closed-loop sampling system is

designed to return the purged fluid to the process at a point of

lower pressure. A throttle valve or other device is used to

induce the pressure drop across the sample loop. The efficiency

of a closed-loop system is assumed to be 100 percent.

Alternatively, in some cases, sampling connections can be

designed to collect samples without purging the line. If such a

sampling connection is installed and no emissions to the

atmosphere occur when a sample is collected, then the control

efficiency can be assumed to be 100 percent.

5.3 LEAK DETECTION AND REPAIR CONTROL EFFECTIVENESS

An LDAR program is designed to identify pieces of equipment

that are emitting sufficient amounts of material to warrant

reduction of the emissions through repair. These programs are

best applied to equipment types that can be repaired on-line,

resulting in immediate emissions reduction, and/or to equipment

types for which equipment modifications are not feasible. An

LDAR program is best suited to valves and pumps, and can also be

implemented for connectors.

For other equipment types, an LDAR program is not as

applicable. Compressors are repaired in a manner similar to

pumps; however, because compressors ordinarily do not have a

spare for bypass, a process unit shutdown may be required for

5-6
repair. Open-ended lines are most easily controlled by equipment

modifications. Emissions from sampling connections can only be

reduced by changing the method of collecting the sample (since by

definition equipment leak emissions are the material purged from

the line), and cannot be reduced by an LDAR program. Safety

considerations may preclude the use of an LDAR program on

pressure relief valves.

In this section, an approach is presented that can be used

to estimate the control effectiveness of any given LDAR program

for light liquid pumps, gas valves, light liquid valves, and

connectors. The approach is based on the relationship between

the percentage of equipment pieces that are leaking and the

corresponding average leak rate for all of the equipment. In

this approach, the three most important factors in determining

the control effectiveness are: (1) how a "leak" is defined,

(2) the initial leak frequency before the LDAR program is

implemented, and (3) the final leak frequency after the LDAR

program is implemented. The leak definition (or action level) is

the screening value at which a "leak" is indicated if a piece of

equipment screens equal to or greater than that value. The leak

frequency is the fraction of equipment with screening values

equal to or greater than the leak definition.

Once these three factors are determined, a graph that plots

leak frequency versus mass emission rate at several different

leak definitions is used to predict emissions preceding and

subsequent to implementing the LDAR program. In this way the

emissions reduction (i.e., control effectiveness) associated with

the LDAR program can be easily calculated.

A general description of the approach is provided in the

subsections below. This is followed by an example application of

the approach. The approach has been applied to determine the

control effectiveness at Synthetic Organic Chemical Manufacturing

Industry (SOCMI) and refinery process units for the following

LDAR programs: (1) monthly LDAR with a leak definition of 10,000

parts per million by volume (ppmv), (2) quarterly LDAR with a

leak definition of 10,000 ppmv, and (3) LDAR equivalent to that

5-7
specified in the proposed hazardous organic National Emission

Standard for Hazardous Air Pollutants (NESHAP) equipment leaks

negotiated regulation.1 Tables 5-2 and 5-3 summarize the

estimated control effectiveness for the three LDAR programs

mentioned above at SOCMI process units and refineries,

respectively. It should be noted that, to calculate the control

effectiveness values presented in tables 5-2 and 5-3, assumptions

were made that may not necessarily be applicable to specific

process units. For example, the control effectiveness values in

the tables are based on the assumption that the emission rate

prior to implementing the LDAR program is the emission rate that

would be predicted by the average emission factor. The best way

to calculate the effectiveness of an LDAR program is by

collecting and analyzing data at the specific process unit.

5.3.1 Approach for Estimating LDAR Control Effectiveness

As previously stated, the key parameters for estimating the

control effectiveness of an LDAR program are the leak definition,

the initial leak frequency, and the final leak frequency. The

leak definition is a given part of an LDAR program. It can

either be defined by the process unit implementing the program or

by an equipment standard to which the process unit must comply.

After the leak definition is established, the control

effectiveness of an LDAR program can be estimated based on the

average leak rate before the LDAR program is implemented, and the

average leak rate after the program is in place.

Figures 5-1 through 5-4 are graphs presenting mass emission

rate versus leak frequency for SOCMI-type process units at

several leak definitions for gas valves, light liquid valves,

light liquid pumps, and connectors, respectively. Figures 5-5

through 5-8 are graphs presenting mass emission rate versus leak

frequency for refinery process units at several leak definitions

for gas valves, light liquid valves, light liquid pumps, and

connectors, respectively. Figures 5-9 through 5-15 are graphs

presenting mass emission rate versus leak frequency for gas

fittings, light liquid fittings, gas others, light liquid others,

light liquid pumps, gas valves, and light liquid valves, for

5-8
TABLE 5-2. CONTROL EFFECTIVENESS FOR AN LDAR PROGRAM AT A SOCMI PROCESS UNIT

Equipment type and

service

Control effectiveness (%)

Monthly monitoring

10,000 ppmv leak

definition

Quarterly monitoring

10,000 ppmv leak

definition HON reg neg

a

Valves - gas 87 67 92

Valves - light liquid 84 61 88

Pumps - light liquid 69 45 75

Connectors - all

b

b 93

a Control effectiveness attributable to the requirements of the proposed hazardous

organic NESHAP equipment leak negotiated regulation are estimated based on equipmentspecific leak definitions and performance levels.

b Data are not available to estimate control effectiveness.

5-9
TABLE 5-3. CONTROL EFFECTIVENESS FOR AN LDAR PROGRAM AT A REFINERY PROCESS UNIT

Equipment type and

service

Control effectiveness (%)

Monthly monitoring

10,000 ppmv leak

definition

Quarterly monitoring

10,000 ppmv leak

definition HON reg neg

a

Valves - gas 88 70 96

Valves - light liquid 76 61 95

Pumps - light liquid 68 45 88

Connectors - all

b

b 81

a Control effectiveness attributable to the requirements of the proposed hazardous

organic NESHAP equipment leak negotiated regulation are estimated based on equipmentspecific leak definitions and performance levels.

b Data are not available to estimate control effectiveness.

5-10
Figure 5-1. SOCMI Gas Valve Average Leak Rate Versus Fraction

Leaking at Several Leak Definitions.

5-11
Figure 5-2. SOCMI Light Liquid Valve Average Mass Emission

Rate Versus Fraction Leaking at Several Leak

Definitions

5-12
Figure 5-3. SOCMI Light Liquid Pump Average Leak Rate Versus

Fraction Leaking at Several Leak Definitions

5-13
Figure 5-4. SOCMI Connector Average Leak Rate Versus Fraction

Leaking at Several Leak Definitions.

5-14
Figure 5-5. Refinery Gas Valve Average Leak Rate Versus

Fraction Leaking at Several Leak Definitions

5-15
Figure 5-6. Refinery Light Liquid Valve Average Leak Rate

Versus Fraction Leaking at Several Leak

Definitions

5-16
Figure 5-7. Refinery Light Liquid Pump Average Leak Rate

Versus Fraction Leaking at Several Leak

Definitions

5-17
Figure 5-8. Refinery Connector Average Leak Rate Versus

Fraction Leaking at Several Leak Definitions

5-18
Figure 5-9. Marketing Terminal Gas Fittings Average Leak Rate

Versus Fraction Leaking at Several Leak

Definitions

5-19
Figure 5-10. Marketing Terminal Light Liquid Fittings Average

Leak Rate Versus Fraction Leaking at Several Leak

Definitions

5-20
Figure 5-11. Marketing Terminal Gas Others Average Leak Rate

Versus Fraction Leaking at Several Leak

Definitions

5-21
Figure 5-12. Marketing Terminal Light Liquid Others Average

Leak Rate Versus Fraction Leaking at Several Leak

Definitions

5-22
Figure 5-13. Marketing Terminal Light Liquid Pumps Average Leak

Rate Versus Fraction Leaking at Several Leak

Definitions

5-23
Figure 5-14. Marketing Terminal Gas Valves Average Leak Rate

Versus Fraction Leaking at Several Leak

Definitions

5-24
Figure 5-15. Marketing Terminal Liquid Light Valves Average

Leak Rate Versus Fraction Leaking at Several Leak

Definitions

5-25
marketing terminal process units. Figures 5-16 through 5-34

present mass emission rate as a function of leak frequency for

connectors, flanges, open-ended lines, others, pumps, and valves

at oil and gas production operations. Using these figures, for a

given leak definition, the leak rate before and after the LDAR

program is implemented, along with the corresponding control

effectiveness, can be determined by plotting the initial and

final leak frequency on these graphs. Tables 5-4, 5-5, 5-6, and

5-7 present equations for the lines in each of the SOCMI,

refinery, marketing terminal, and oil and gas production

operations, and graphs, respectively. Appendix G describes the

approach that was used to develop the equations.

Figure 5-35 provides guidance on how to determine the

initial and final leak frequencies. This figure is a simplified

graphical presentation on how the leak frequency will change

after an LDAR program is implemented. When generating the

figure, it was assumed that all equipment pieces are monitored at

the same time. Each occurrence of equipment monitoring is

referred to as a "monitoring cycle," and it is assumed that equal

time periods lapse between monitoring cycles.

From figure 5-35, it can be seen that there is an immediate

reduction in leak frequency after the LDAR program is

implemented, and then the leak frequency will oscillate over

monitoring cycles. This oscillation occurs because between

monitoring cycles a certain percentage of previously non-leaking

equipment will begin to leak. There are four key points on the

graph presented in figure 5-35. These key points are:

Point X - initial leak frequency;

Point Y - leak frequency immediately after monitoring

for and repairing leaking equipment (i.e., immediately

after a monitoring cycle);

Point Z - leak frequency immediately preceding a

monitoring cycle; and

Point F - average leak frequency between monitoring

cycles (final leak frequency).

5-26
Figure 5-16. Oil and Gas Production Gas Connectors Average Leak

Rate Versus Fraction Leaking at Several Leak

Definitions

5-27
Figure 5-17. Oil and Gas Production Light Oil Connectors

Average Leak Rate Versus Fraction Leaking at

Several Leak Definitions

5-28
Figure 5-18. Oil and Gas Production Water/Oil Connectors

Average Leak Rate Versus Fraction Leaking at

Several Leak Definitions

5-29
Figure 5-19. Oil and Gas Production Gas Flanges Average Leak

Rate Versus Fraction Leaking at Several Leak

Definitions

5-30
Figure 5-20. Oil and Gas Production Light Oil Flanges Average

Leak Rate Versus Fraction Leaking at Several Leak

Definitions

5-31
Figure 5-21. Oil and Gas Production Gas Open-Ended Lines

Average Leak Rate Versus Fraction Leaking at

Several Leak Definitions

5-32
Figure 5-22. Oil and Gas Production Heavy Oil Open-Ended Lines

Average Leak Rate Versus Fraction Leaking at

Several Leak Definitions

5-33
Figure 5-23. Oil and Gas Production Light Oil Open-Ended Lines

Average Leak Rate Versus Fraction Leaking at

Several Leak Definitions

5-34
Figure 5-24. Oil and Gas Production Water/Oil Open-Ended Lines

Average Leak Rate Versus Fraction Leaking at

Several Leak Definitions

5-35
Figure 5-25. Oil and Gas Production Gas Other Average Leak Rate

Versus Fraction Leaking at Several Leak

Definitions

5-36
Figure 5-26. Oil and Gas Production Heavy Oil Other Average

Leak Rate Versus Fraction Leaking at Several Leak

Definitions

5-37
Figure 5-27. Oil and Gas Production Light Oil Other Average

Leak Rate Versus Fraction Leaking at Several Leak

Definitions

5-38
Figure 5-28. Oil and Gas Production Water/Oil Other Average

Leak Rate Versus Fraction Leaking at Several Leak

Definitions

5-39
Figure 5-29. Oil and Gas Production Gas Pump Average Leak Rate

Versus Fraction Leaking at Several Leak

Definitions

5-40
Figure 5-30. Oil and Gas Production Light Oil Pumps Average

Leak Rate Versus Fraction Leaking at Several Leak

Definitions

5-41
Figure 5-31. Oil and Gas Production Gas Valves Average Leak

Rate Versus Fraction Leaking at Several Leak

Definitions

5-42
Figure 5-32. Oil and Gas Production Heavy Oil Valves Average

Leak Rate Versus Fraction Leaking at Several Leak

Definitions

5-43
Figure 5-33. Oil and Gas Production Light Oil Valves Average

Leak Rate Versus Fraction Leaking at Several Leak

Definitions

5-44
Figure 5-34. Oil and Gas Production Water/Oil Valves Average

Leak Rate Versus Fraction Leaking at Several Leak

Definitions

5-45
TABLE 5-4. EQUATIONS RELATING AVERAGE LEAK RATE TO FRACTION LEAKING AT SOCMI UNITS

Equipment type

Leak definition

(ppmv) Equations

a

Gas valve 500 ALR = (0.044 × LKFRAC) + 1.7E-05

1000 ALR = (0.050 × LKFRAC) + 2.8E-052000 ALR = (0.057 × LKFRAC) + 4.3E-055000 ALR = (0.068 × LKFRAC) + 8.1E-05

10000 ALR = (0.078 × LKFRAC) + 1.3E-04

Light liquid valve 500 ALR = (0.047 × LKFRAC) + 2.7E-05

1000 ALR = (0.053 × LKFRAC) + 3.9E-052000 ALR = (0.061 × LKFRAC) + 5.9E-055000 ALR = (0.077 × LKFRAC) + 1.1E-04

10000 ALR = (0.089 × LKFRAC) + 1.7E-04

Light liquid pump 500 ALR = (0.095 × LKFRAC) + 3.1E-04

1000 ALR = (0.11 × LKFRAC) + 4.6E-042000 ALR = (0.13 × LKFRAC) + 6.7E-045000 ALR = (0.20 × LKFRAC) + 1.4E-03

10000 ALR = (0.24 × LKFRAC) + 1.9E-03

Connector 500 ALR = (0.047 × LKFRAC) + 1.7E-05

1000 ALR = (0.060 × LKFRAC) + 2.5E-052000 ALR = (0.073 × LKFRAC) + 3.5E-055000 ALR = (0.092 × LKFRAC) + 5.4E-05

10000 ALR = (0.11 × LKFRAC) + 8.1E-05

aALR = Average leak rate (kg/hr per source) and LKFRAC = leak fraction.

5-46
TABLE 5-5. EQUATIONS RELATING AVERAGE LEAK RATE TO FRACTION LEAKING AT REFINERY UNITS

Equipment type

Leak definition

(ppmv) Equation

a

Gas valve 500 ALR = (0.11 × LKFRAC) + 8.8E-05

1000 ALR = (0.13 × LKFRAC) + 1.4E-04

10000 ALR = (0.26 × LKFRAC) + 6.0E-04

Light liquid valve 500 ALR = (0.038 × LKFRAC) + 2.0E-04

1000 ALR = (0.042 × LKFRAC) + 2.8E-04

10000 ALR = (0.084 × LKFRAC) + 1.7E-03

Light liquid pump 500 ALR = (0.20 × LKFRAC) + 1.3E-03

1000 ALR = (0.23 × LKFRAC) + 2.0E-03

10000 ALR = (0.43 × LKFRAC) + 1.2E-02

Connector 500 ALR = (0.014 × LKFRAC) + 1.3E-05

1000 ALR = (0.017 × LKFRAC) + 1.8E-05

10000 ALR = (0.037 × LKFRAC) + 6.0E-05

aALR = Average leak rate (kg/hr per source) and LKFRAC = leak fraction.

5-47
TABLE 5-6. EQUATIONS RELATING AVERAGE LEAK RATE TO FRACTION

LEAKING AT MARKETING TERMINAL UNITS

Equipment

Type

Leak

Definition

(ppmv) Equationa

Gas

Connector

500 ALR = (0.017 × LKFRAC) + 5.3E-06

1000 ALR = (0.017 × LKFRAC) + 5.3E-06

2000 ALR = (0.034 × LKFRAC) + 5.9E-06

5000 ALR = (0.034 × LKFRAC) + 5.9E-06

10000 ALR = (0.034 × LKFRAC) + 5.9E-06

Light

Liquid

Connector

500 ALR = (0.0021 × LKFRAC) + 7.0E-06

1000 ALR = (0.0028 × LKFRAC) + 7.1E-06

2000 ALR = (0.0042 × LKFRAC) + 7.1E-06

5000 ALR = (0.0058 × LKFRAC) + 7.2E-06

10000 ALR = (0.0065 × LKFRAC) + 7.2E-06

Gas Other 500 ALR = (0.0018 × LKFRAC) + 3.1E-05

1000 ALR = (0.0021 × LKFRAC) + 4.0E-05

2000 ALR = (0.0023 × LKFRAC) + 4.8E-05

5000 ALR = (0.0029 × LKFRAC) + 8.4E-05

10000 ALR = 1.2E-04

Light

Liquid

Other

500 ALR = (0.019 × LKFRAC) + 2.1E-05

1000 ALR = (0.022 × LKFRAC) + 2.2E-05

2000 ALR = (0.025 × LKFRAC) + 2.2E-05

5000 ALR = (0.034 × LKFRAC) + 2.4E-05

10000 ALR = (0.034 × LKFRAC) + 2.4E-05

Light

Liquid Pump

500 ALR = (0.014 × LKFRAC) + 9.6E-05

1000 ALR = (0.018 × LKFRAC) + 1.2E-04

2000 ALR = (0.029 × LKFRAC) + 1.6E-04

5000 ALR = (0.051 × LKFRAC) + 2.1E-04

10000 ALR = (0.077 × LKFRAC) + 2.4E-04

5-48
TABLE 5-6. EQUATIONS RELATING AVERAGE LEAK RATE TO FRACTION

LEAKING AT MARKETING TERMINAL UNITS (CONTINUED)

Equipment

Type

Leak

Definition

(ppmv) Equationa

Gas Valve 500 ALR = (0.0012 × LKFRAC) + 8.9E-06

1000 ALR = (0.0017 × LKFRAC) + 9.2E-06

2000 ALR = (0.0017 × LKFRAC) + 9.2E-06

5000 ALR = (0.0017 × LKFRAC) + 9.2E-06

10000 ALR = 1.3E-05

Light

Liquid

Valve

500 ALR = (0.0045 × LKFRAC) + 9.5E-06

1000 ALR = (0.0052 × LKFRAC) + 9.8E-06

2000 ALR = (0.0077 × LKFRAC) + 1.1E-05

5000 ALR = (0.013 × LKFRAC) + 1.2E-05

10000 ALR = (0.023 × LKFRAC) + 1.5E-05

aALR = Average leak rate (kg/hr per source)

LKFRAC = Leak fraction.

5-49
TABLE 5-7. EQUATIONS RELATING AVERAGE LEAK RATE TO FRACTION

LEAKING AT OIL AND GAS PRODUCTION OPERATION UNITS

Equipment

Type

Leak

Definition

(ppmv) Equationa

Gas

Connector

500 ALR = (0.016 × LKFRAC) + 7.7E-06

1000 ALR = (0.018 × LKFRAC) + 8.0E-06

2000 ALR = (0.020 × LKFRAC) + 8.5E-06

5000 ALR = (0.023 × LKFRAC) + 9.4E-06

10000 ALR = (0.026 × LKFRAC) + 1.0E-05

Light Oil

Connector

500 ALR = (0.016 × LKFRAC) + 7.7E-06

1000 ALR = (0.021 × LKFRAC) + 8.3E-06

2000 ALR = (0.022 × LKFRAC) + 8.6E-06

5000 ALR = (0.025 × LKFRAC) + 9.2E-06

10000 ALR = (0.026 × LKFRAC) + 9.7E-06

Water/Oil

Connector

500 ALR = (0.013 × LKFRAC) + 7.8E-06

1000 ALR = (0.014 × LKFRAC) + 7.9E-06

2000 ALR = (0.016 × LKFRAC) + 8.3E-06

5000 ALR = (0.023 × LKFRAC) + 9.4E-06

10000 ALR = (0.028 × LKFRAC) + 1.0E-05

Gas Flange 500 ALR = (0.043 × LKFRAC) + 1.1E-06

1000 ALR = (0.051 × LKFRAC) + 1.8E-06

2000 ALR = (0.059 × LKFRAC) + 2.6E-06

5000 ALR = (0.075 × LKFRAC) + 4.7E-06

10000 ALR = (0.082 × LKFRAC) + 5.7E-06

Light Oil

Flange

500 ALR = (0.037 × LKFRAC) + 9.4E-07

1000 ALR = (0.046 × LKFRAC) + 1.2E-06

2000 ALR = (0.055 × LKFRAC) + 1.6E-06

5000 ALR = (0.068 × LKFRAC) + 2.1E-06

10000 ALR = (0.073 × LKFRAC) + 2.4E-06

5-50
TABLE 5-7. EQUATIONS RELATING AVERAGE LEAK RATE TO FRACTION

LEAKING AT OIL AND GAS PRODUCTION OPERATION UNITS

(CONTINUED)

Equipment

Type

Leak

Definition

(ppmv) Equationa

Gas

Open-Ended

Line

500 ALR = (0.037 × LKFRAC) + 4.1E-06

1000 ALR = (0.039 × LKFRAC) + 5.0E-06

2000 ALR = (0.045 × LKFRAC) + 7.5E-06

5000 ALR = (0.051 × LKFRAC) + 1.2E-05

10000 ALR = (0.055 × LKFRAC) + 1.5E-05

Heavy Oil

Open-Ended

Line

500 ALR = (0.012 × LKFRAC) + 4.3E-06

1000 ALR = (0.015 × LKFRAC) + 4.9E-06

2000 ALR = (0.020 × LKFRAC) + 6.0E-06

5000 ALR = (0.030 × LKFRAC) + 7.2E-06

10000 ALR = (0.030 × LKFRAC) + 7.2E-06

Light Oil

Open-Ended

Line

500 ALR = (0.030 × LKFRAC) + 3.8E-06

1000 ALR = (0.032 × LKFRAC) + 4.7E-06

2000 ALR = (0.036 × LKFRAC) + 6.7E-06

5000 ALR = (0.040 × LKFRAC) + 9.7E-06

10000 ALR = (0.044 × LKFRAC) + 1.4E-05

Water/Oil

Open-Ended

Line

500 ALR = (0.030 × LKFRAC) + 3.5E-06

1000 ALR = (0.030 × LKFRAC) + 3.5E-06

2000 ALR = (0.030 × LKFRAC) + 3.5E-06

5000 ALR = (0.030 × LKFRAC) + 3.5E-06

10000 ALR = (0.030 × LKFRAC) + 3.5E-06

Gas Other 500 ALR = (0.055 × LKFRAC) + 1.8E-05

1000 ALR = (0.061 × LKFRAC) + 3.1E-05

2000 ALR = (0.066 × LKFRAC) + 4.5E-05

5000 ALR = (0.078 × LKFRAC) + 8.2E-05

10000 ALR = (0.089 × LKFRAC) + 1.2E-04

5-51
TABLE 5-7. EQUATIONS RELATING AVERAGE LEAK RATE TO FRACTION

LEAKING AT OIL AND GAS PRODUCTION OPERATION UNITS

(CONTINUED)

Equipment

Type

Leak

Definition

(ppmv) Equationa

Heavy Oil

Other

500 ALR = (0.0011 × LKFRAC) + 2.1E-05

1000 ALR = (0.0011 × LKFRAC) + 2.1E-05

2000 ALR = 3.2E-05

5000 ALR = 3.2E-05

10000 ALR = 3.2E-05

Light Oil

Other

500 ALR = (0.053 × LKFRAC) + 3.4E-05

1000 ALR = (0.058 × LKFRAC) + 4.4E-05

2000 ALR = (0.067 × LKFRAC) + 6.4E-05

5000 ALR = (0.075 × LKFRAC) + 8.6E-05

10000 ALR = (0.083 × LKFRAC) + 1.4E-04

Water/Oil

Other

500 ALR = (0.066 × LKFRAC) + 2.5E-05

1000 ALR = (0.066 × LKFRAC) + 2.5E-05

2000 ALR = (0.066 × LKFRAC) + 2.5E-05

5000 ALR = (0.066 × LKFRAC) + 2.5E-05

10000 ALR = (0.069 × LKFRAC) + 5.9E-05

Gas Pump 500 ALR = (0.027 × LKFRAC) + 1.1E-04

1000 ALR = (0.052 × LKFRAC) + 2.3E-04

2000 ALR = (0.052 × LKFRAC) + 2.3E-04

5000 ALR = (0.074 × LKFRAC) + 3.5E-04

10000 ALR = (0.074 × LKFRAC) + 3.5E-04

Light Oil

Pump

500 ALR = (0.071 × LKFRAC) + 7.9E-05

1000 ALR = (0.079 × LKFRAC) + 1.5E-04

2000 ALR = (0.082 × LKFRAC) + 1.9E-04

5000 ALR = (0.10 × LKFRAC) + 5.1E-04

10000 ALR = (0.10 × LKFRAC) + 5.1E-04

5-52
TABLE 5-7. EQUATIONS RELATING AVERAGE LEAK RATE TO FRACTION

LEAKING AT OIL AND GAS PRODUCTION OPERATION UNITS

(CONTINUED)

Equipment

Type

Leak

Definition

(ppmv) Equationa

Gas Valve 500 ALR = (0.070 × LKFRAC) + 9.1E-06

1000 ALR = (0.076 × LKFRAC) + 1.1E-05

2000 ALR = (0.083 × LKFRAC) + 1.4E-05

5000 ALR = (0.092 × LKFRAC) + 1.9E-05

10000 ALR = (0.098 × LKFRAC) + 2.5E-05

Heavy Oil

Valve

500 ALR = (0.0013 × LKFRAC) + 7.8E-06

1000 ALR = (0.0013 × LKFRAC) + 7.8E-06

2000 ALR = (0.0013 × LKFRAC) + 7.8E-06

5000 ALR = 8.4E-06

10000 ALR = 8.4E-06

Light Oil

Valve

500 ALR = (0.059 × LKFRAC) + 9.4E-06

1000 ALR = (0.069 × LKFRAC) + 1.2E-05

2000 ALR = (0.075 × LKFRAC) + 1.4E-05

5000 ALR = (0.083 × LKFRAC) + 1.7E-05

10000 ALR = (0.087 × LKFRAC) + 1.9E-05

Water/Light

Oil Valve

500 ALR = (0.022 × LKFRAC) + 8.1E-06

1000 ALR = (0.022 × LKFRAC) + 8.1E-06

2000 ALR = (0.064 × LKFRAC) + 9.7E-06

5000 ALR = (0.064 × LKFRAC) + 9.7E-06

10000 ALR = (0.064 × LKFRAC) + 9.7E-06

aALR = Average leak rate (kg/hr per source)

LKFRAC = Leak fraction.

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The initial leak frequency is the fraction of sources

defined as leaking before the LDAR program is implemented. The

initial leak frequency is point X on figure 5-35. The lower the

leak definition, the higher the initial leak frequency. At a

process unit, the initial leak frequency can be determined based

on collected screening data. If no screening data are available,

the initial leak frequency can be assumed to be equivalent to the

leak frequency associated with the applicable average emission

factor. However, if a process unit already has some type of LDAR

program in place, the average emission factor may overestimate

emissions.

On figures 5-1 through 5-34, the average emission factor for

each equipment type is plotted as a horizontal line. From this

line, an initial leak frequency can be determined for any of the

leak definitions. For example, on figure 5-1, which is for gas

valves, the SOCMI average emission factor equals

0.00597 kilograms per hour (kg/hr). For a leak definition of

500 ppmv, this average emission factor corresponds to a fraction

leaking of approximately 0.136. Similarly, for a leak definition

of 10,000 ppmv, the average emission factor corresponds to a

fraction leaking of 0.075. These points are determined by

finding the intersection of the SOCMI average emission factor

line and the applicable leak definition line and reading off the

corresponding fraction leaking. Alternatively the fraction

leaking associated with the average factor can be calculated

using the equations in tables 5-4, 5-5, 5-6, and 5-7.

The leak frequency immediately after a monitoring cycle is

Point Y on figure 5-35. After an LDAR program is implemented for

a given time period, point Y will reach a "steady-state" value.

As presented in figure 5-35, point Y depends on two key factors:

(1) the percentage of equipment successfully repaired after being

identified as leaking, and (2) the percentage of equipment that

was repaired for which leaks recurred. Two simplifying

assumptions when calculating point Y are: (1) that leaking

equipment is instantaneously repaired, and (2) that the recurring

leaks will occur instantaneously after the equipment is repaired.

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5-55

Figure 5-35. Simplified Graphical Presentation of Changes in

Leak Frequency After Implementation of an LDAR

Program 
Based on these assumptions the value for point Y is calculated

using the following equation:

Yi = Zi - (FR × Zi) + (FR × Zi × R)

where:

Yi = Leak fraction immediately after monitoring cycle i;

Zi = Leak fraction immediately preceding monitoring cycle

i (note that Z1 equals point X.);

R = Fraction of repaired sources for which a leak

immediately recurs; and

FR = Fraction of leaking sources successfully repaired.

Point Z on figure 5-35 is the leak frequency immediately

preceding equipment monitoring. After an LDAR program is

implemented for a given time period, point Z will reach a

"steady-state" value. To go from point Y to point Z on

figure 5-35, the occurrence rate is added to point Y. The

occurrence rate equals the percentage of initially nonleaking

equipment that starts to leak between monitoring cycles. Use the

following equation to go from point Y to point Z:

Zi+1 = Oc × (1 - Yi)+Yi

where:

Zi+1 = Leak fraction immediately preceding monitoring

cycle i + 1;

Oc = Fraction of nonleaking sources which will leak in

the time period between monitoring cycles

(i.e, occurrence rate); and

Yi = Leak fraction immediately after monitoring cycle i.

After several monitoring cycles, the leak frequency will be

found to approximately oscillate between points Y and Z. The

average value of these two "steady-state" values is the final

leak frequency. This is point F on figure 5-35. The final leak

frequency is the average percent of sources that are still

leaking after an LDAR program has been implemented.

Once the initial and final leak frequencies are determined,

they can be entered into the applicable equation from table 5-4

5-56
or table 5-5 to calculate the associated average leak rates at

these leak frequencies. Based on the initial leak rate and the

final leak rate, the control effectiveness for an LDAR program

can be calculated. The control effectiveness is calculated as:

Eff = (ILR-FLR)/ILR × 100

where:

Eff = Control effectiveness (percent);

ILR = Initial leak rate (kg/hr/source); and

FLR = Final leak rate (kg/hr/source).

5.3.2 Example Application of Approach

As previously mentioned, the approach described in

section 5.3.1 was applied to estimate the control effectiveness

for three types of LDAR programs: (1) monthly inspection with a

leak definition of 10,000 ppmv, (2) quarterly inspection with a

leak definition of 10,000 ppmv, and (3) a program complying with

the requirements specified in the proposed hazardous organic

NESHAP equipment leaks negotiated regulation.1 Details of these

calculations are presented in appendix G. As an example of

applying the approach, the control effectiveness for gas valves

at a SOCMI process unit implementing a monthly LDAR program with

a leak definition of 10,000 ppmv is presented in the following

paragraphs.

Table 5-8 presents the SOCMI gas valve occurrence rate,

recurrence rate, unsuccessful repair rate, and initial leak

frequency. (See appendix G for details on how each of these

parameters were determined.) Using the values presented in

table 5-6 and the approach presented in section 5.3.1, the LDAR

control effectiveness can be calculated. Note that figure 5-9 is

also based on monthly monitoring of gas valves in a SOCMI process

unit with a leak definition of 10,000 ppmv, and it is referred to

in this example demonstration.

For gas valves with a leak definition of 10,000 ppmv, the

initial leak frequency is 7.5 percent. This initial leak

frequency value is taken from figure 5-1, by finding the value of

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TABLE 5-8. VALUES USED IN EXAMPLE CALCULATIONa

Source Category: SOCMI

Equipment Type: Gas Valves

LDAR Program: Monthly Monitoring with a Leak Definition

of 10,000 ppmv

Occurrence Rate: 1.00%

Recurrence Rate: 14%

Unsuccessful Repair Rate: 10%

Initial Leak Frequency:b 7.5%

aSee appendix F for information on how the occurrence rate,

recurrence rate, and unsuccessful repair rate were determined.

bBased on the SOCMI average emission factor for gas valves.

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the fraction leaking at the intersection of the SOCMI average

factor line and the 10,000-ppmv leak definition line. The

initial leak rate for this leak frequency is the SOCMI gas valve

average emission factor, which equals 0.00597. After the LDAR

program is implemented and monitoring occurs on a monthly basis,

the steady-state leak frequency immediately after monitoring (see

point Y6 on figure 5-35) equals 0.29 percent. The steady-state

leak frequency prior to monitoring (see point Z6 on figure 5-35)

equals 1.29 percent. This gives an average of 0.79 percent as

the final leak frequency (see point F on figure 5-35). The

calculations performed to determine the final leak frequency are

shown in table 5-9. Once the estimated gas valve final leak

frequency is determined, the associated leak rate can be found

using figure 5-1 or the gas valve equation for a leak definition

of 10,000 ppmv listed on table 5-4. The corresponding leak rate

associated with the final leak frequency of 0.79 percent at a

leak definition of 10,000 ppmv is 0.00075 kg/hr. Thus, the

control effectiveness of a monthly LDAR program with a leak

definition of 10,000 ppmv for gas valves is:

= (0.00597-0.00075)/0.00597 × 100

= 87 percent.

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TABLE 5-9. EXAMPLE CALCULATION TO DETERMINE THE FINAL LEAK FREQUENCY OF SOCMI GAS VALVES

IN A MONTHLY MONITORING LDAR PROGRAM WITH A LEAK DEFINITION OF 10,000 PPMV

a

Starting parameters Resulting parameters

1. Leak definition:

= 10,000 ppmv

2. Leak occurrence (Oc):

= 1.00 percent

3. Leak recurrence (R):

= 14 percent

4. Successful repair rate (FR):

= 90 percent

5. Initial leak frequency (Point X):

= 7.5 percent

1. Steady-state leak frequency after

monitoring (Point Y

6):

= 0.29 percent

2. Steady-state leak frequency immediately

prior to monitoring (Point Z

6):

= 1.29 percent

3. Final leak frequency (Point F)

b:

= 0.79 percent

Calculations

Monitoring cycle

Leak frequency after

monitoring: Point Y

i

(percent)

c

Leak frequency prior to

monitoring: Point Z

i

(percent)

d

123456

e

1.700.610.360.310.290.29

7.502.671.601.361.301.29

aRefer to Figure 5-4 for graphical presentation of all points identified in this table.bFinal Leak Frequency equals the average of the prior to monitoring and after monitoring

steady-state leak frequencies.

c

Y

i = Z

i - (FR * Z

i) + (FR * Z

i * R)

d

Z

i + 1 = Oc * (1 - Y

i)+Y

i

eAfter the sixth monitoring cycle, the values for Y

i and Z

i reach steady-state.

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5.4 REFERENCES

1. National Emission Standards for Hazardous Air Pollutants for

Source Categories; Organic Hazardous Air Pollutants from the

Synthetic Organic Chemical Manufacturing Industry and Seven

Other Processes. Subpart H--Equipment Leaks. Federal

Register. Vol. 57, No. 252, pp 62765-62785. Washington,

DC. Office of the Federal Register. December 31, 1992.

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