p.1 

OAR Box 1168 

Prepped by Ollie Stewart 

Document Number: 

65) ll-A-3 

Docket Number: 

A-89-10 

Printed 4/29/2008 11:23.18 AM Sheet 65 of 131 
P-2 . 

I/O. * 

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&ERA 

United States Office of Air Quality 

Environmental Protection Planning and Standards 

Agency Research Triangle P=>* wr •>-»->. . 

EPA-450/3-88-010 

October 1988 

Air 

Protocols for 

Generating 

Unit-Specific 

Emission Estimates 

for Equipment 

Leaks of VOC and 

VHAP 

A-89-10 

II-A- 3 

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P.3 

* * , 

PROTOCOLS FOR GENERATING UNIT-SPECIFIC 

EMISSION ESTIMATES FOR 

EQUIPMENT LEAKS OF VOC AND HAP 

U. S. Environmental Protection Agency 

Office of Air and Radiation 

Office of Air Quality Planning and Standards 

Emission Standards Division 

Research Triangle Park, NC 27711 

October 1988 
P.4 

TABLE OF CONTENTS 

Section Page 

List of 

Figures v 

List of 

Tables vi 

GLOSSARY ..vi i 

FOREWORD xi 

1.0 INTRODUCTION .1-1 

2.0 DEVELOPMENT OF EMISSION ESTIMATES .2-1 

2.1 Introduction 2-1 

2.2 Use of the EPA's Average Emission Factors. 2-1 

2.3 The Leak/No-Leak Approach 2-4 

2.4 Application of Stratified Emission Factors .. . 2-8 

2.5 Leak Rate/Screening Value Correlations . 2-9 

2.6 Unit-Specific Correlations 2-13 

2.6.1 Generation of Mass Emissions Data 2-13 

2.6.2 Development of Leak Rate/Screening Value 

Correlations. 2-15 

2.6.3 Statistical Considerations of Leak Rate/Screening 

Value Correlations 2-16 

2.6.3.1 Graphical Comparison of EPA vs. Other 

Correlations 2-16 

2.6.3.2 Statistical Comparison of EPA vs. Other 

Correlations 2-23 

2.6.3.3 Other Statistical Analyses 2-23 

2.6.4 Generation of Emission Estimates 2-24 

2.6.5 Statistical Considerations for the Predicted 

Emission Estimate . . 2-24 

3.0 SOURCE SCREENING 3-1 

3.1 Screening Survey Procedures. ... . 3-1 

3.2 Monitoring Instrument 3-3 

3.2.1 Operating Principles and Limitations of Portable 

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

3.2.2 Performance Criteria and Evaluation for Portable 

VOC Detectors 3-5 

3.2.2.1 Response Factor . 3-7 

3.2.2.2 Response Time. . 3-8 

3.2.2.3 Calibration Precision. ......... . 3-9 

3.2.2.4 Safety 3-9 

3.2.3 Monitoring Devices For Difficult Situations ... . 3-10 

in 
P.5 

TABLE OF CONTENTS 

(cont'd.) 

Section Page 

3.3 Screening Procedures 3-12 

3.3.1 Calibration Procedures 3-12 

3.3.2 Procedure for Screening Equipment 3-12 

3.4 Data Handling 3-19 

3.5 Calibration Procedures For Quality Assurance . 3-22 

4.0 MASS EMISSIONS SAMPLING 4-1 

4.1 Vacuum Method 4-1 

4.2 Blow-Through Method. 4-6 

4.3 Source Enclosure 4-10 

4.3.1 Valves 4-12 

4.3.2 Pumps and Agitators 4-13 

4.3.3 Compressors 4-14 

4.3.4 Flanges . 4-15 

4.3.5 Relief Valves 4-15 

4.4 Accuracy Checks . 4-16 

4.5 Analytical Techniques. 4-16 

4.5.1 Analytical Instrumentation 4-16 

4.5.2 Calibration 4-17 

4.5.3 Analytical Techniques for Condensate. ...... . 4-17 

4.5.4 Quality Control for Analytical Techniques 4-18 

5.0 REFERENCES 5-1 

Appendix A - Reference Method 21 

Appendix B - Response Factors 

Appendix C - Calculations of Mass Emission Rates 

Appendix D - Leak Rate/Screening Value Equations 

Appendix E - Selection of Sample Size for Flange Screening 

Appendix F - Determination of Emission Rates for Default Zero Screening Values 

Appendix G - Development of a Default Emission Rate for Equipment That Does 

Not Screen Above the Background Concentration 

iv 
P.6 

LIST OF FIGURES 

Figure

 s Page 

2-1 Strategy for Estimating Emissions from Equipment Leaks 2-2 

2-2 Modeled relationship-leak rate vs. OVA for valves in gas service . 2-17 

2-3 Log,Q leak rate vs. log,0 OVA reading for pump seals 2-18 

2-4 Log,Q leak rate vs. log,0 OVA reading for valves-gas service . . . 2-19 

2-5 Log,Q leak rate vs. log,0 OVA reading for valves-liquid service. . 2-20 

2-6 Comparison of SOCMI and refinery leak rate correlations. ...... 2-22 

3-1 Gate valves 3-14 

3-2 Globe valves 3-15 

3-3 Lubricated plug valve. . 3-16 

i 

3-4a Ball valve 3-17 

3-4b Butterfly valve 3-17 

3-5a Weir type diaphragm valve 3-18 

3-5b Check valves ...... . 3-18 

3-6a Vertical centrifugal pump 3-20 

3-6b Horizontal centrifugal pump. . . 3-20 

3-7 Spring loaded relief valve 3-21 

4-1 Sampling train for baggable sources of hydrocarbon emissions using 

a diaphragm. 4-2 

4-2 Mylar plastic sample bag 4-4 

4-3 Equipment required for the blow-through sampling technique ... . 4-7 

4-4 Tent construction around the seal area of a vertical pump 4-11 

wmmimmm 
P.7 

LIST OF TABLES 

Table Page 

2-1 Average Emission Factors for Fugitive Emissions 2-3 

2-2 Leaking and Non-Leaking Emission Factors for Fugitive Emissions 

(kg/hr source) 2-6 

2-3 Estimate of "Uncontrolled" Fugitive Emissions for a Hypothetical 

Case . 2-7 

2-4 Stratified Emission Factors for Equipment Leaks 2-10 

2-5 Estimate of Fugitive Emissions Using Stratified Emission Factors 

for a Hypothetical Case 2-11 

3-1 Fugitive Emission Sources 3-2 

3-2 Performance Criteria for Portable VOC Detectors 3-6 

3-3 Portable VOC Detection Instrument Performance Specifications. . . 3-11 

3-4 Example Data Sheet 3-23 

4-1 Calculation Procedure for Tented Leak Rate 4-8 

B-l Response Factors with 95% Confidence Intervals Estimated 

at 10,000 ppmv Response B-l 

B-2 Tested Compounds Which Appear to be Unable to Achieve an 

Instrument Response of 10,000 ppmv at any Feasible 

Concentration B-7 

D-1 Prediction Equations for Nonmethane Leak Rate for Valves, Flanges, 

and Pump Seals in SOCMI Processes . D-1 

vi 
P.8 

GLOSSARY 

Censored source - a source whose screening value is known to be above 

100,000 ppmv but whose actual screening value is unknown. 

Emission factor - the per component mass emission rate applicable to 

populations of sources, not individual component measurements. 

Inaccessible source - a component which cannot be reached because it is 

beyond the reach of a 6-foot ladder. 

Leak definition - monitoring instrument reading selected as the trigger value 

for initiating some action such as maintenance; e.g., 10,000 ppmv is the 

leak definition used by EPA. 

Leak frequency - the percentage of sources (a particular equipment type and 

service) determined to be leaking based upon a chosen leak definition. 

Leak rate - see mass emissions rate. 

Leaking emission factor - the per component mass emission rate associated with 

the population of sources with screening concentrations at or above the 

leak definition. 

Leaking source - a source whose screening concentration is greater than or 

equal to 10,000 ppmv. 

Mass emissions rate - the quantity of volatile organic compound(s) released to 

the atmosphere in terms of total mass per unit time. 

Monitoring instrument - portable hydrocarbon analyzer meeting the performance 

specifications given in Method 21. 

Non-leaking emission factor - the per component mass emission rate associated 

with the population of sources with screening concentrations less than 

the leak definition. 

Non-emitting source - a source whose screening value is 0 ppmv; a zero 

emission rate is assumed. 

Non-leaking, emitting source - a source whose screening concentration is 

greater than 0 ppmv but less than 10,000 ppmv. 

Screening value - raw monitoring instrument reading. 

Screening concentration - the screening value (raw instrument reading) 

corrected by the appropriate response factor. 

Unsafe-to-monitor equipment - equipment that exposes monitoring personnel to 

an immediate danger while screening the equipment. 

vii 
P.9 

EF = average emission rate per source 

EF, = average emission rate per leaking source 

EF2 = average emission rate per non-leaking emitting source 

X-,. = measured emission rate for the ith leaking source 

X2i = measured emission rate for the ith non-leaking emitting source 

Xp = average measured emission rate for non-leaking emitting sources 

N, = number of leaking sources 

N« = number of non-leaking emitting sources 

N3 = number of non-emitting sources 

N = total number of sources (including inaccessible sources) 

n, = number of bagged leaking sources 

np = number of bagged non-leaking emitting sources 

2 

s2 = estimate of the variance of the emission rates of the non-leaking 

emitting sources 

n2 

= £ (X2i - X2 )

2 /(n2 - 1) 

y,. = measured emission rate for the ith leaking source 

y?. = measured emission rate for the ith non-leaking emitting source 

/, . = predicted emission rate for the ith leaking source screened 

131 <100,000 ppmv 

/,. . = measured emission rate for ith censored source lbi 

y, = average predicted emission rate for leaking sources 

y2 = average predicted emission rate for non-leaking emitting sources 

y, = average predicted emission rate for leaking sources screened 

13 <100,000 ppmv 

y,. = average measured emission rate for censored sources 

N. = number of leaking sources screened, <100,000 ppmv 

1 a 

N,. = number of censored sources 

n1 h = number of bagged censored sources 'lb 

= \ 

N 

2 

s , = variance of the predicted emission rates of the leaking sources 

1 

d 

1-1 

- s (yu - y1)

2/(N1 - i) 

vm 
P.10 

'yz 

Via 

variance of the predicted emission rates of the leaking sources 

screening <100,000 ppmv 

N2 

£ (y2i - y2)

2/(N2 - i) 

variance of the predicted emission rates of the leaking sources 

screening <100,000 ppmv 

N la 

5

ylb 

" f = 1

( y lai - *l.> /<N

ia - » 

= variance of the measured emission rates of the censored sources 

'lb 

" -ftfolbl " *lb> ^ ni b " *>• 

The symbol t is the value of the normal deviate corresponding to the 

desired confidence probability. If the number of bagged sources, n, is 

greater than or equal to 50 then the value of t approaches 1.96. If the 

sample size is less than 50, the percentage points may be taken from Student's 

t table with (n-1) degrees of freedom. The t distribution holds exactly only 

if the emission rates are normally distributed. Moderate departures from 

normality do not affect it greatly. 

ix 
P.11 

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, EPA has encouraged industry experts and trade association 

representatives to comment on the document's content. Chief among these 

contributors has been the Chemical Manufacturers Association (CMA), who 

has written a guidance document similar to this EPA protocol. 

The CMA document is consistent with this guide. Both documents present 

acceptable approaches to generating emission estimates. Minor differences 

that exist between the two documents should not affect the acceptability of 

the emission estimates, provided the approaches to generating acceptable 

emission estimates are thoroughly understood. The CMA protocol includes 

a provision for the addition of bagging data from a single process unit to 

the EPA correlation curves to modify the leak rate/screening value 

correlation. While the EPA agrees with the technical premise that additional 

data could be added to the existing database, the Agency believes that, for 

practical reasons, this approach could create interpretation problems for 

control agencies. Therefore, the Agency does not support this approach. 

Currently, EPA is working with CMA to expand the existing database of 

equipment screening and bagging data. Ultimately, the Agency will consider 

the addition of the data currently being collected to the existing database. 

This effort may provide a better understanding of the magnitude of equipment 

leaks and appropriate controls for them. The EPA will consider appropriate 

modifications to this protocol when additional data collected during this 

interim period are analyzed. 

xi 
P.12 

1.0 INTRODUCTION 

The purpose of this document is to present standard protocols for 

estimating mass emissions from equipment leaks. The EPA's interest in 

developing standard protocols is to assist states and industry in their 

efforts to estimate equipment leak emissions. Emission estimates are being 

developed for a variety of purposes, including permitting, inventories, and 

for the Superfund Amendments and Reauthorization Act (SARA). 

The EPA previously developed equipment leak emission factors in previous 

work supporting standards. These factors represented emissions from typical 

facilities and were used to develop industry-wide emission estimates. The 

EPA's standards-setting process will continue to rely upon the average 

emission factors for industry-wide estimates. However, those estimates do not 

yield the accuracy that facilities are looking for today; therefore, there is 

now a need for more accurate emission estimating techniques. 

Recognizing that the significance of our protocols is in providing a 

consistent approach to data collection and emissions estimates, EPA believes 

there is need for certain minimal requirements in any protocol. Our desire is 

to develop standard protocols for general use in generating unit-specific 

emission estimates for permitting and inventories. 

This document describes methodologies the EPA considers appropriate for 

development of unit specific emission estimates for equipment leaks of organic 

compounds: volatile organic compounds (VOC) and volatile hazardous air 

pollutants (VHAP). Estimates generated using this protocol would be specific 

only to process units (or groups of sources) for which an estimate was made. 

EPA has made provision for extending such estimates beyond the limits of that 

group of sources. 

Five methods for estimating emissions from equipment leaks from a 

specific chemical processing unit are included in the protocol: 

o Average emission factor method; 

o Leak/no-leak emission factor method; 

o Three-strata emission factor method; 

o Application of EPA correlations; and 

o Development of new correlations. 

1-1 
P.13 

They range from simply applying accurate equipment counts to the EPA's average 

emission factors to the more complex project of developing unit-specific 

correlations of mass emission rates and screening values. 

All methods start with obtaining an accurate identification and count of 

equipment to be included in the emission estimate. The equipment counts can 

simply be used with the EPA's previously developed emission factors. The next 

step in complexity and refinement is the use of a portable organic analyzer to 

find the number of leaking and nonleaking sources. Leaking and nonleaking 

emission factors previously developed by the EPA can then be applied to 

generate the emission estimate. 

A final refinement in a method employing discrete emission factors is 

that of applying emission factors to represent three different ranges of 

screening values. This has been called the stratified emission factor 

approach, or the three-strata approach. Applying the stratified emission 

factors requires more rigorous measurement of organic vapor concentrations 

with a portable instrument because actual concentration readings must be 

recorded instead of noting whether a piece of equipment is classified as 

leaking or not leaking. 

The remaining two methods make use of correlation equations relating mass 

emissions to organic concentrations measured with a portable organic analyzer. 

The EPA's previously developed correlations are offered for use, and finally, 

if a process unit's emissions are statistically different from those 

represented by the EPA's correlations, provision is made for development of 

correlations specifically for that process unit. 

Guidance and recommendations are offered for statistical analyses and for 

gathering the data required to execute the methods. The information is 

provided in the following major sections of this protocol: 

o Section 2.0 Emission Estimate Development; 

o Section 3.0 Source Screening; 

o Section 4.0 Mass Emissions Sampling. 

1-2 
P.14 

Section 2.0 details the types of data needed for making emissions estimates 

and how that data is to be applied. Sections 3.0 and 4.0 offer more detail on 

collection of data using a portable organic analyzer and using a technique 

known as "bagging," in which an enclosure is made around a potential leak 

point and emissions are actually measured. Additional reference material is 

included in the Appendices. 

j? 

1-3 
P.15 

2.0 DEVELOPMENT OF EMISSION ESTIMATES 

2.1 INTRODUCTION 

In this section, five methods for estimating VOC and VHAP emissions from 

equipment leaks in chemical processing units are described. The methods 

increase in complexity and in the amount of data collection and analysis 

required. However, all five methods require some data collection, data 

analysis, and/or statistical evaluation. The five estimation methods and the 

options available for collecting and analyzing the data are shown in 

Figure 2-1. As the flow chart shows, the methods increase in rigorousness and 

complexity. The first method, the average factor method, is the least complex 

and demanding and the last method, developing site specific correlations, is 

the most complex and demanding. The end product of each of the procedures 

described is an emissions inventory for equipment leaks by type of equipment 

and by service (i.e., light liquid, gas, heavy liquid). 

2.2 USE OF THE EPA'S AVERAGE EMISSION FACTORS 

All of the methods require an accurate count of equipment components by 

type of equipment and by service. The most basic approach for estimating 

emissions merely requires application of average emissions factors developed 

by EPA to the equipment counts for the unit. EPA's average emission factors 

are shown in Table 2-1. The product of the emission factor and the number of 

equipment components yields the emission rate per source type, and the 

emission rates for all source types are summed to generate the unit-specific 

emission estimates. 

The method EPA used for development of emission factors for individual 

equipment leak emission sources was described in reports on the Petroleum 

Refinery Assessment Study. ' In this study, "screening" data were gathered 

using a portable organic vapor analyzer, and mass emissions were measured by 

enclosing individual pieces of equipment with bags or tents and measuring the 

organic material emitted. 

These data permitted the development of leak rate/screening value 

correlations and emission factors for sources in petroleum refineries. 

15 Subsequently, EPA coordinated the SOCMI 24-unit Study, a study of 24 

individual chemical process units representing a cross-section of the SOCMI 

2-1 

MBt 
P.16 

Count Equipment Components 

(by type and service) 

6-

Apply Average Emission Factors 

and 

Composite Total Emissions 

inventory Section 2.2 

Conduct Complete Screening 

Survey 

(Response Factor Adjustment 

Optional) 

6-

Apply Leak/No Leak Emission 

Factors and 

Composite total Emissions 

Inventory Section 2.3 

oApply Three Strata Emission 

and 

Composite Total Emissions 

^ Inventory Section 2.4 

6-

*n Adjust Screening 

Value to 

OV A/Methane Format 

Bag Components for Each 

Equipment Type and Service 

Develop Individual 

Correlations 

Compare Statistically 

to Existing Correlations 

Apply New Correlation 

and Composite Total 

Emissions 

Apply EPA OVA 

Correlations to 

Screening Values 

Above trie Default 

Zero Screening Value 

Apply Default.Zero 

Emission Rate to 

Screening Values 

8eiow the Oefault 

Zero Screening Value 

Inventory 

Composite 

Total 

Emissions 

Section 2.S 

Inventory Section 2.6 

Figure 2-1. Strategy for Estimating Emissions from 

Equipment Leaks 

2-2 
PJ * J 

TABLE 2-1. AVERAGE EMISSION FACTORS FOR FUGITIVE EMISSIONS 

Equipment Service 

Emission Factor 

(kg/hr/source) 

P.17 

Valves 

Pump Seals 

Compressor Seals 

Pressure Relief Seals 

Flanges 

Open-Ended Lines 

Sampling Connections 

Gas 

Light Liquid 

Heavy Liquid 

Light Liquid 

Heavy Liquid 

Gas/Vapor 

Gas/Vapor 

All 

All 

All 

0.0056 

0.0071 

0.00023 

0.0494 

0.0214 

0.228 

0.104 

0.00083 

0.0017 

0.0150 

2-3 
P.18 

population, and a six-unit Maintenance Study. As a result of these chemical 

process unit studies, leak rate/screening value correlations and emission 

factors were generated for valves in gas/vapor service in SOCMI. Leak 

rate/screening value correlations were also generated for light liquid valves 

and light liquid pumps in SOCMI, but industry average emission factors were 

not developed. 

2.3 THE LEAK/NO-LEAK APPROACH 

The second method offers some refinement over the average emission factor 

method, thereby allowing some adjustment to individual unit conditions and 

operation. This method and all the remaining methods require screening of all 

equipment to be included in the inventory using a portable analyzer. 

Equipment that is dangerous to screen may be omitted from the set of equipment 

components to be screened. Their emission rates may be estimated using the 

EPA's average factors presented in Table 2-1. 

Insulated equipment can be considered difficult-to-monitor equipment. 

The decision to remove insulation to facilitate screening is left to 

individual judgement. If insulation is not removed, the insulated component 

is assumed to leak at the same rate as a similar uninsulated component. 

For flanges, a reduced number of components may be screened. Appendix E 

describes how to select the sample size for flanges. In compiling screening 

values for use in this technique (or any of those that follow), a response 

factor may be applied to correlate the screening values measured for the 

chemical in the line to the screening values observed in calibrating the 

instrument to another chemical. For a discussion of response factor 

adjustment, see Section 3.2.2.1. 

The leak/no-leak approach to estimating emissions is based on the 

assumption of only two emission rates and two populations of equipment 

components: sources that "leak" (with screening concentrations greater than 

or equal to 10,000 ppmv) and sources that do not "leak" (with screening 

concentrations less than 10,000 ppmv). 

The basis of this approach is as follows: when a group of sources leak, 

they leak at a certain emission rate on the average. Similarly, as a group, 

non-leaking sources have, on the average, a certain mass emission rate 

2-4 
P.19 iBI 

associated with them. Thus, the overall emission estimate for a population of 

emission sources consists of two components: leaking source emissions and 

non-leaking source emissions. 

Table 2-2 presents leaking and non-leaking emission factors previously 

determined by EPA for equipment leaks. EPA generated leaking and non-leaking 

emission factors using: 1) emission factors generated from empirical 

screening distribution data and leak rate/screening value correlations, 2) the 

leak frequencies associated with the emission factors, and 3) the percent of 

mass emissions associated with the leaking sources. The detailed procedure 

for generating leaking and non-leaking emission factors has been previously 

13 published in the "Additional Information Document" (AID) for fugitive 

emission sources of organic compounds and is also described in a document 

16 entitled "Emission Factors for Equipment Leaks of VOC and HAP." 

The application of the leak/no-leak approach for estimating emissions is 

shown in the following example for a hypothetical chemical process unit. 

Table 2-3 presents the data for this hypothetical process unit needed to 

apply the leak/no-leak procedure for estimating emissions. The first column 

shows the number of sources in the process unit by source type. The second 

column shows the number of sources with screening values greater than or equal 

to 10,000 ppmv (i.e., leaking sources). The percentage of sources leaking is 

shown in the third column. The emission estimates for this hypothetical 

process unit can then be computed using the leaking and non-leaking emission 

factors in Table 2-2. For example, three of the 47 pump seals in light liquid 

service were found to be leaking. Using the leak/no-leak approach, the 

emission estimate is generated: 

(0.437 kg/hr/source)(3) + (0.012 kg/hr/source)(47-3), 

or 1.84 kg/hr. The emission estimate per source for pumps in light liquid 

service could then be computed by dividing the unit-specific emission estimate 

by the equipment count. The last column in Table 2-3 shows the annual 

emission estimates by source type for the hypothetical unit. 

While this examplejllustrates how total VOC emissions per source type 

are calculated, a similar procedure can be used to estimate emissions for a 

particular species in the line. For example, consider this same hypothetical 

case where the light liquid pumped contained 20 weight percent of Compound A. 

2-5 

u*MM 
P.20 

TABLE 2-2. LEAKING AND NON-LEAKING EMISSION FACTORS FOR 

FUGITIVE EMISSIONS (kg/hr source) 

Equipment 

Valves 

Pump Seals 

Compressor Sealse 

Pressure Relief Valves 

Flanges 

Open-Ended Lines 

Service 

Gasa 

LLb 

HLC 

LL 

HL 

Gas 

Gas 

All 

All 

Leaking 

(>10,000 ppm) 

Emission Factor 

0.0451 

0.0852 

0.00023d 

0.437 

0.3885 

1.608 

1.691 

0.0375 

0.01195 

Non-leaking 

(<10,000 ppm) 

Emission Factor 

0.00048 

0.00171 

0.00023 

0.0120 

0.0135 

0.0894 

0.0447 

0.00006 

0.00150 

The leaking and nonleaking emission factors for valves in gas/ 

vapor service are based upon the emission factors determined for 

gas valves in ethylene, cumene, and vinyl acetate units during the 

SOCMI Maintenance Study. References 8 and 15. 

LL - light liquid service. 

CHL - heavy liquid service. 

Leaking emission factor assumed equal to non-leaking emission 

factor since the computed leaking emission factor (0.00005 kg/hr/ 

source) was less than non-leaking emission factor. 

eEmission factor reflects existing control level of 60 percent 

found in the industry; control 1s through the use of barrier 

fluid/degassing reservo1r/vent-to-flare or other seal leakage 

capture system. 

2-6 
P.21 

TABLE 2-3. ESTIMATE OF "UNCONTROLLED" FUGITIVE 

EMISSIONS FOR A HYPOTHETICAL CASE 

Source 

Pump Seals 

Light Liquid 

Heavy Liquid 

Valves 

Gas/Vapor 

Light Liquid 

Heavy Liquid 

Pressure Relief Val 

Gas/Vapor 

Open-Ended Lines 

Compressor Seals 

Number 

Screened 

47 

3 

625 

1180 

64 

ves 

31 

278 

4 

Sampling Connections 70 

Flanges 2880 

Number 

Leaking 

3 

1 

19 

13 

0 

1 

9 

0 

-

20 

Percent 

Leaking 

6.4 

33.3 

3.0 

1.1 

0 

3.2 

3.2 

0 

-

0.7 

Computed 

Emission Estimate 

(per Source) 

kg/hr/source 

0.0391 

0.1385 

0.0018 

0.0026 

0.00023 

0.0978 

0.0018 

0.0894 

0.0150 

0.00032 

Annual 

Emissions 

Mg/yr 

16.1 

3.6 

10.1 

27.2 

0.1 

26.6 

4.5 

3.1 

9.2 

8.1 

aBased on values from Table 2-2, using EE = [LEF * PCL + NLEF * (100-PCL)]/100 

where 

EE = Emission Estimate (per Source) 

LEF = Leaking Emission Factor 

NLEF = Non-leaking Emission Factor 

PCL = Percent of sources found leaking 

This hypothetical process unit is assumed to be in continuous operation, so 

it operates for 8,760 hours per year. Batch or campaign processes may 

operate fewer hours per year, so the annual emissions would be prorated to 

account for the hours the equipment contained the chemical. 

2-7 

IHS! iuxiat 
P.22 

The emission estimate for Compound A for light liquid pumps is computed by 

applying the weight percent (20 percent in this case) to the emission estimate 

generated above: 

(0.20)(1.84 kg/hr) = 0.368 kg/hr. 

As another example, consider the hypothetical case where the light liquid 

pumped contained only 80 weight percent VOC and Compound A accounted for 

20 percent by weight. The emission estimate for Compound A for light liquid 

pumps is computed as: 

(0.2/0.8)(1.84 kg/hr) = 0.460 kg/hr 

In other words, compound A accounts for one-fourth of the total VOC emissions 

of 1.84 kg/hr. As before, emissions per source can be determined by dividing 

the estimate by the number of components involved. Emission factor estimates 

calculated in this manner may then be applied to the equipment counts (where 

the material in the process line contained 20 weight percent of compound A) to 

estimate emissions of compound A for that specific process unit. 

2.4 APPLICATION OF STRATIFIED EMISSION FACTORS 

Another approach to generating emission estimates involves a refinement 

of the leak/no-leak approach discussed above. The leak/no-leak approach is 

based on two emission rates and two populations (i.e., leaking and non-leaking 

sources). The stratified emission factor approach, on the other hand, is 

based on several population and emission factors spanning several discrete 

screening value ranges. 

Screening values in the EPA SOCMI data base are distributed widely from 

0 ppmv to over 100,000 ppmv. The mass emissions are correspondingly 

distributed. The stratified emission factor approach for estimating emissions 

segments this distribution into discrete intervals to account for different 

ranges of screening values. The following ranges are used: 

o 0 -. 1,000 ppmv; 

o 1,001 - 10,000 ppmv; and 

o over 10,000 ppmv. 

Using data gathered during previous EPA studies, emission factors for 

each screening value range have been generated. These stratified emission 

factors represent the leak rates measured during fugitive emissions testing. 

2-8 
P.23 

Their development incorporated the statistical methods used by the EPA in 

developing other emission factors. The emission factor for each discrete 

interval is presented in Table 2-4 by equipment type and service. 

This method requires that screening of all equipment (except that which 

is hazardous to screen) be conducted in accordance with methods described in 

Section 3 of this report. All screening values must be recorded according to 

the applicable ranges. Then, as with the leak/no-leak approach, the total 

emission estimate is generated by applying the number of components in each 

screening value range to the appropriate emission factor and summing each 

subtotal. An example of this procedure, shown in Table 2-5, illustrates how 

to implement the stratified emission factor approach. 

2.5 LEAK RATE/SCREENING VALUE CORRELATIONS 

Mathematical correlations offer an additional refinement to estimating 

emissions from equipment leaks by providing a continuous function over the 

entire range of screening values instead of discrete intervals. The EPA has 

published correlations relating screening values to mass emissions rates. As 

shown in Appendix D, there are four correlations which can be applied to all 

equipment types and services. The EPA's correlations are based upon OVA 

measurements taken using Method 21. The instrument was calibrated to methane 

(see Method 21). Screening value measurements used with these published 

correlations should be in this same format. For example, if a TLV instrument 

calibrated to hexane were used to gather screening data, the data must be 

transformed to represent measurements gathered using an OVA, calibrated to 

methane, before using the published correlations. If a detector fails to meet 

Method 21 specifications or published transformations are not available, an 

instrument response curve must be developed to relate screening values to 

actual concentrations in the appropriate format (OVA/methane). Development of 

this screening value correction curve should be done in the laboratory before 

the detector is used in the field. 

Another correction factor that can be applied to Method 21 and 

non-Method 21 instruments is the response factor. For many compounds, the 

instrument response is non-linear with increasing screening value. In terms 

of the basic leak/no-leak approach described in a previous section, a single 

2-9 
P.24 

TABLE 2-4. STRATIFIED EMISSION FACTORS FOR EQUIPMENT LEAKS 

(kg/hr/source) 

Source 

Compressor seals 

Pump seals 

Valves 

Flanges, connections 

Pressure relief devices 

Open-ended lines 

Service 

Gas/vapor 

Light liquid 

Heavy liquid 

Gas/vapor 

Light liquid 

Heavy liquid 

All 

Gas/vapor 

All 

Emission Factors (kg/hr/source) for 

Screening Value Ranqes, ppmv 

0-1,000 1,001-10,000 Over 10,000 

0.01132 

0.00198 

0.00380 

0.00014 

0.00028 

0.00023 

0.00002 

0.01H 

0.00013 

0.264 

0.0335 

0.0926 

0.00165 

0.00963 

0.00023 

0.00875 

0.279 

0.00876 

1.608 

0.437 

0.3885 

0.0451 

0.0852 

0.00023 

0.0375 

1.691 

0.01195 

2-10 

 
TABLE 2-5. ESTIMATE OF FUGITIVE EMISSIONS USING STRATIFIED EMISSION FACTORS FOR A HYPOTHETICAL CASE 

Source 

Number 

Screened 

Number of Sources Screening (ppmv) 

0-1,000 1,001-10,000 Over 10,000 

Computed Emission Estimate 

per Source Type8 per Source 

(Kg/hr) (Kg/hr/source) 

Compressor seals 

Gas/vapor 

Pump seals 

Light liquid 

Heavy liquid 

Valves 

Light liquid 

Heavy liquid 

Flanges 

Pressure relief devices 

Gas/vapor 

Open-ended lines 

47 

3 

1,180 

64 

2,880 

31 

278 

32 

1 

1,020 

63 

2,600 

25 

236 

12 

1 

147 

1 

160 

5 

33 

20 

1 

9 

0.298 

2.20 

3.37 

0.427 

0.0745 

3 

1 

3 

0 

1.776 

0.485 

2.81 

0.01472 

0.0378 

0.1616 

0.00238 

0.00023 

0.00076 

0.1087 

0.00154 

aBased on emission factors from Table 2-2, where EE = (NLj * SEFj) + (NL2 * SEF2) + ... 

EE = Emission Estimate 

NLj, NL2, etc. = Number leaking in 1st range (0-1,000), Number leaking in 2nd range (1,001-10,000), etc. 

SEF,, SEF2, etc. = Stratified emission factor for 1st range, stratified emission factor for 2nd range, etc. 

Computed Emission Estimate per source = Computed Emission Estimate per Source Type/Number Screened. 
P.26 

point response factor adjustment at the leak definition of 10,000 ppm is 

adequate. If, however, the correlations are to be used, the best estimate of 

screening concentration over the entire range is needed. Therefore, a 

correction for non-linear response must be made. This can be accomplished in 

the laboratory by generating a response curve. 

The flow chart in Figure 2-1 shows a separate treatment of "zero" 

screening values. The function describing the correlation of leak rate and 

screening value becomes discontinuous for zero and near zero values. The 

correlation function mathematically predicts zero emissions for zero readings 

on the portable instrument. Empirically speaking, however, the EPA's data 

shows this prediction to be incorrect. Mass emissions have been measured from 

equipment showing no screening concentration above zero. The reason for this 

involves the detector accuracy. In the Refinery Assessment Study mass 

emissions corresponding to a screening value of 200 ppm or less could not be 

quantified because the accuracy limit of the detector was 200 ppm. To handle 

this discontinuity at the low end of the correlation, the EPA has derived a 

"default zero" screening value (8 ppm) and an associated mass emission rate 

for the screening values between zero and that default zero reading. These 

"default zero" values and emission rates shown below were derived as shown in 

Appendix F from mass emissions data gathered in chemical plants and the 

published leak rate/screening value correlations shown in Appendix D: 

Equipment Type/Service 

Valves, gas 

Valves, light liquid 

Flanges 

Pumps and all other components 

These emission factors should be applied to equipment components screening 

between 0 and 8 ppm. The published correlations would be applied to all 

screening concentrations above 8 ppm. The total emissions estimate for 

equipment leaks is generated by totaling emissions estimates for all "default 

zeroes" and adding that total to the total estimates generated using the 

correlations. Appendix G presents an alternative methodology for generating 

unit-specific default zero emission rates. 

2-12 

"Default Zero' 

Screening Value, 

8 

8 

8 

s 8 

ppm 

Zero Screening 

Value Emission 

Rate (kg/hr/source) 

0.000033 

0.000451 

0.000093 

0.000039 
2.6 UNIT-SPECIFIC CORRELATIONS 

A process unit may develop its own correlations if leak rates are 

statistically different from EPA's rates. The steps involved in generating a 

unit-specific emissions estimate using correlations developed specifically for 

that unit are: 

1. Gathering of mass emission data and calculation of mass emission 

rate (leak rate); 

2. Development of leak rate/screening value correlations; 

3. Statistical consideration of leak rate/screening value correlations; 

4. Application of leak rate/screening value correlation to the 

empirical screening data; and 

5. Prediction of emissions. 

These steps are discussed individually in the following sections. 

2.6.1 Generation of Mass Emissions Data 

After complete screening of the process unit is done for all source types 

(except possibly flanges), selected sources can be bagged to measure the mass 

emission rate. The sources selected for mass emission measurement should be 

rescreened at the time of bagging. The mass emission rate determined by 

bagging and the rescreening value can then be used to validate the application 

of EPA's correlations to the process unit. Alternatively, the measurements 

can be used in development of leak rate/screening value relationships for that 

specific unit. The screening value can be affected by the portable screening 

instrument used and the gas used to calibrate the instrument. The EPA leak 

rate/screening value correlations are based on data gathered using an OVA 

instrument calibrated with methane. 

If other instruments or calibration gases are used, then the screening 

value should be adjusted (using theoretical or empirical correction factors) 

to be equivalent to values measured using an OVA calibrated with methane prior 

to any comparisons to the EPA equations. Instrument readings above the 

saturation point of the detector must be bagged to quantify the emission rate. 

The amount of leak rate testing (bagging) that should be done depends on 

the objective of the data collection. If one wishes to check the fit of EPA 

published equations to a particular process unit, as few as four leak rate 

measurements of a particular source type in a particular service may be 

2-13 

sou 
P.28 

,••> 

adequate. If it is desirable to develop new equations, 30 leak rate 

measurements should be obtained. Because of the inherent variability of leak 

rate/screening data, it is difficult to detect differences between 

correlations with fewer than 30 data pairs. However, the statistical goal is 

to generate estimates that are within 50 percent of the mean value with 95 

percent confidence. If this statistical goal can be achieved with fewer data 

pairs, then fewer data pairs are acceptable. 

Consider a hypothetical process unit having a large population of sources 

with screening values well distributed over the range of 0 to 100,000+ ppmv. 

To develop statistically valid leak rate/screening value correlations, mass 

emissions data must be collected from individual sources that have screening 

values distributed over the entire range. For each source type (i.e., valves, 

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

six sources 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 

If the maximum response of the screening instrument is 100,000 ppmv, then 

20 or all (whichever is less) of the sources screened at 100,000 ppmv should 

be bagged. If six sources are not available in a particular screening value 

range, additional sources from the nearest range should be tested. If 

screening values greater than 10,000 ppmv are not found in the process, the 

following five groups can be used: 

1 - 100 ppmv 

101 - 300 ppmv 

301 - 1,000 ppmv 

1,001 - 3,000 ppmv 

3,001 - 10,000 ppmv 

2-14 
P.29 

Similar groupings can be developed if all sources in the unit screen less than 

1,000 ppmv. 

If a statistical determination is made that estimates within 50 percent 

of the mean value with 95 percent confidence can be achieved with fewer than 

30 data pairs, the following bagging strategies are recommended: 

SCREENING VALUE TOTAL NUMBER OF LEAK RATE MEASUREMENTS 

RANGE (ppmv) 4 8 12 20 

1-10 0 2 2 3 4 

10.1 - 1,000 1 2 4 

1,001 - 10,000 1 2 4 

10,001 - 100,000 2 2 3 4 

> 100,000 2 2 4 

These 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 equations. Other source selection 

strategies can be used if an appropriate rationale is given. 

2.6.2 Development of Leak Rate/Screening Value Correlations 

With appropriate mass emission data and screening values, leak 

rate/screening value correlations can be generated. Least-squares regression 

analyses are done for each source type/service, regressing the logarithm of 

the nonmethane leak rate on the logarithm of the screening concentration, 

according to 

Log (leak rate) = B +.B, Log (screening concentration), 

where 

B , B, = model parameters. 

All analyses should be done using logarithms of both the leak rate and 

screening concentration. Confidence intervals should be calculated for the 

estimated equation (Reference 19, pages 28-31). A scale bias correction 

factor (Reference 20) is required in transforming the equation in the 

log-scale back to the original units. A statistician should be consulted 

unless one is familiar with this type of analysis. Bagged sources whose 

screening values are known to be above 100,000 ppmv but whose actual screening 

2-15 
P.30 

values are unknown should not be used to fit the regression line described 

above. For those sources censored at 100,000 ppmv and which were not bagged, 

leak rates should be estimated from the average leak rate for those censored 

sources that were bagged. 

2.6.3 Statistical Considerations of Leak Rate/Screening Value Correlations 

The predictive equations resulting from the least-squares regression 

analyses discussed above must be statistically evaluated. 

If new correlation equations are developed; they must be shown to be 

i 

statistically different from the existing correlations developed during the 

refinery and SOCMI studies. If the new correlations are statistically 

different from the existing correlations, the new correlations may be used in 

the development of the unit-specific emission estimates for that specific 

class of sources. If not, the EPA's correlations should be used. The 

correlations can be compared graphically or mathematically. 

2.6.3.1 Graphical Comparison of EPA vs. Other Correlations. If enough 

data are collected to develop a process specific leak rate/screening equation, 

then this equation should be compared to the published EPA equation. The 

EPA's predictive equation should be used unless the equation developed for the 

specific process unit is found to give significantly different estimates. 

This comparison can be done graphically by drawing the process specific 

equation on a graph of the EPA equation. Figure 2-2 (from Reference 14, 

page 66) is an example of such a graph. 

A graphical comparison may also be made by plotting the leak 

rate/screening data from the process on a log-scale plot of the EPA equations. 

The log scale is preferred so that linear comparisons can be made. Figures 

2-3 through 2-5 (from Reference 14, pages 57-62) show such plots of the EPA 

equations. The leak rate/screening value measurements used to develop the 

equations are also shown on the plots. These plots were developed from draft 

versions of the correlations. The correlations were refined when censored 

sources were included in modeling the leak rate/screening value relationships. 

Only small differences exist between the old and new models (see Reference 8, 

pages 14-18). 

2-16 
ro 

i 

CO 

. O 

T3 

0.08-

0.07-

0.06-

0> 0.05 -

0.04-

(0 

DC 

co 

CD 

_ l 

" O 

CD 

V. 0.03 -

0.02-

0.01-

0 -

x 

/ / 

/ / 

y 

/ 

/ 

(95% Confidence Limits of the Mean) / 

T T T 

20,000 40,000 60,000 80,000 

Maximum Screening Value (ppmv) 

— i 

100,000 

Figure 2-2. Modeled relationship - leak rate vs. OVA for valves i n gas service. 
ro 

• —• 

00 

• • • 

CD 

< - 9 

CO 

CC 

-.rC 

CO 

CD 

- J 

CD 

C 

CO 

c <m9 

CD 

s cz 

o 

2 

D) 

O 

1 -

- 1 -

- 2 -

- 3 -

- 4 -

- 5 -

T 

1.5 

Legend: o = 1 Observations 

D = 2 Observations 

A = 3-10 Observations 

oo 

2.0 

T" 

2.5 3.0 

1 ^ 

3.5 4.0 4.5 5.0 5.5 6.0 

Log Mean OVA Reading 

Figure 2-3. Log1 0 leak rate vs. logio

 0V A

 reading for pump seals. 
0 -

Legend: • = 1 Observations 

• = 2 Observations 

A = 3-10 Observations 

0 = 11-14 Observations 

ro 

i 

vo 

<D 

CO 

cr 

CO 

CD 

CD 

C 

CO 

JZ 

CB 

c 

o 

cn 

o 

1 -

- 2 -

- 3 -

- 4 -

- 5 

• ••• i 

• 

• • 

• 

• 

• 

• • 

t— • 

• •• > • ^+f v^* 

• • • 

» • • • 

• ••* • 

• 

• 

• 

• 

• 

• A 

• A 

• * -

OA 

• • 

• • • A 

•••• A 

• 

••• 

• • 

• 

• 

o 

• • 

• 

• • 

• • 

• • 

• • 

- 6 -

—I— 

1.25 1.75 2.25 2.75 3.25 3.75 4.25 4.75 5.25 5.75 

Log Mean OVA Reading 

Figure 2-4. LogjQ leak rate vs. logj 0 OVA reading for valves in gas service. 
I 

ro 

o 

CD 

CO 

CC 

XL 

CO 

CD 

CD 

C 

CO 

- C 

*-9 

CD 

C 

o 

CD 

O 

0 -

- 1 -

- 2 -

- 3 -

Legend: • = 1 Observations 

• = 2 Observations 

A = 3-10 Observations 

- 5 -

- 6 

0.0 1.0 1.5 2.0 

" T " 

2.5 3.0 

T " 

3.5 

" T " 

4.5 

~T~ 

0.5 4.0 5.0 5.5 6.0 

Log Mean OVA Reading 

Figure 2-5. Login leak rate vs. log^g OVA reading for valves in liqui d service. 
A-i 

If the points fall on both sides of the line representing the equation 

and are within the range of data points used to develop equations, then it is 

reasonable to use the published equations for estimating emissions from the 

process. Statistical tests, such as the Wilcoxon Paired Replicate Rank test 

(Reference 21, pages 401-403) can be used to aid in the decision of 

reasonableness of the equations. 

As an example, Figure 2-6 (from Reference 14, page 79) shows two 

comparisons of equations developed by EPA from Petroleum Refineries to the 

SOCMI equations. The first comparison (valves in gas service) shows the 

refinery equation consistently estimates greater leak rates throughout the 

curve. The confidence limits for the two equations do not overlap. For this 

comparison, it is obvious that different equations are required for the two 

different types of process units. 

A second example of graphical comparison is shown in Figure 2-6 for 

valves in light-liquid service. In this case the refinery equation estimates 

greater leak rates than the SOCMI equation, but the refinery equation is 

within the confidence bands for the SOCMI equation. The SOCMI equation falls 

below the lower confidence band for the refinery equation for valves screening 

greater than 30,000 ppmv. The comparison is not as clear as the valves in gas 

service. Since there were about 300 data pairs used to develop the SOCMI 

equation, it should be used to develop estimates for SOCMI units. 

For comparisons of process specific equations to the EPA equations there 

will usually be fewer data sets used to develop the specific equations. This 

will result in much wider confidence bands for the process specific equations. 

If 30 pairs of data are selected, the upper confidence band should be less 

than a factor of two greater than the upper confidence band predicted by the 

equation. 

The form of the graph can be modified to facilitate the comparison of the 

equations. If most of the sources screen less than 10,000 ppmv, the equations 

can be graphed on a scale from 0 to 10,000 ppmv. The equations can also be 

graphed on a log-scale to make the comparisons linear. However, the 

scale-bias correction factors would not be incorporated if the comparisons are 

made in this way. Therefore, this type of comparison is not recommended. 

2-21 

..PU,.—--""—-«—^TM—•^^^"•—"iii^^i^—^-^•—TMTM^ " 
P.36 

if) 

n 

_ j 

CO 

a> 

_i 

•o 

a> 

o 

•5 

<x> 

a . 

20,000 40,000 60,000 80,000 

Maximum TLV Sniffer Reading (ppmv) 

Valves-Gas 

100,000 

CO 

n 

_ i 

JC 

(0 

<D 

_l 

T3 

<0 

->m 

u 

20,000 40,000 60,000 80,000 100,000 

Maximum TLV Sniffer Reading (ppmv) 

Valves-Light Liquid 

Dotted lines are 90% confidence bounds for the "Refinery" model 

Dashed lines are 95% confidence bounds for the SOCMI model 

Figure 2-6. Comparison of SOCMI and refinery leak rate correlations. 

. 2-22 
2.6.3.2 Statistical Comparison of EPA vs. Other Correlations. A more 

formal approach to comparing leak rate/screening value equations is to use 

statistical tests to compare the parameters estimated by the equations. The 

important parameters of the leak rate/screening value equations (developed on 

a log-scale) are the following: 

1) the intercept (Bo); 

2) the slope (Bl); 

3) the standard error (Se). 

Statistical tests for the slope and intercept are also available (Reference 

19, page 24-33). 

Ninety-five percent confidence intervals for the slope and intercept were 

developed for each of the SOCMI leak rate/screening value equations 

(Reference 8, pages 24-25). For example, the slope of the equations for 

valves in gas service using the OVA was estimated to be 0.693. The 95 percent 

confidence interval for this slope is given as 0.53 to 0.85. If a slope 

estimated from a particular SOCMI process unit is within this confidence 

interval, then the EPA equation provides a reasonable slope for a predictive 

equation. If the slope estimate is outside the confidence interval for the 

EPA correlation, the confidence interval for the slope estimated by the 

unit-specific equation must be evaluated. Reference 19 indicates how to make 

these evaluations. 

A statistical test to compare the standard errors for two equations can 

be done using an F-test (Reference 20, page 31 or Reference 21, pages 

111-116). Since the standard error is the key component of the scale-bias 

correction factor, this comparison of standard errors will also serve as a 

comparison of the scale bias correction factors incorporated in the two 

correlations. 

2.6.3.3 Other Statistical Analyses. There are other types of 

statistical analysis that can be used in the development, evaluation, and 

comparison of leak rate/screening value equations. A General Linear Models 

analysis of the leak/rate screening value data (Reference 20, Chapter 2) can 

be used to develop equations and to test for different leak rate/screening 

relationships for different groups of data. This approach was used in 

Reference 14 (pages 51-53) to evaluate differences between the cumene, 

ethylene, and vinyl acetate units. 

2-23 

sssa 
P.38 

.A 

2.6.4 Generation of Emission Estimates 

The generation of the emission estimate using correlations developed for 

specific process units makes use of the empirical screening data and the leak 

rate/screening value correlations. The leak rate/screening value correlations 

are applied to the screening data to calculate predicted emission rates. 

Emission rates are estimated for all emitting sources (including those 

sources which were bagged) by: 

Predicted emission rate = exp [B + B, log (screening concentration)] 

x (scale bias correction factor) 

B and B, are the coefficient estimates either published by EPA 

(Appendix D) or developed from a linear regression analysis, if site specific 

correlations are used. The results presented in arithmetic scale are adjusted 

to represent mean emission rates using the scale bias correction factor. 

The sum of the individual predicted leak rates represents the total mass 

emission estimate for a given type of source and service being considered. An 

emission estimate per source can be derived by averaging the total emission 

estimate over the number of sources in the distribution. 

2.6.5 Statistical Considerations for the Predicted Emission Estimate 

This section presents formulas for calculating the 95 percent confidence 

intervals for the predicted emission estimate. For clarity, formulas for 

calculating the emission estimate per source and total emission estimate are 

presented also. Definitions for the formulas are presented in the Glossary. 

For the Averaae Emission Rate Per Leaking Source (EE,): 

N, 

£ Y EE, without censoring = i=l li , 

N

i 

with a 95 percent confidence interval of: 

EE, + tsvl 

( N l i

I / 2 

2-24 
P.39 

EE,, with censoring =

 Nla Yla + NlbYlb , 

with a 95 percent confidence interval of: 

EEl±^^Nla s al2

 + ^lb-l[N l b s ] 2

)

1 / 2 

N

l

 n lb 

For the Average Emission Rate Per Non-leaking Emitting source (EFg): 

EE, = i^l

 Y2i , 

N2 

with a 95 percent confidence interval of: 

:2 EE, ± tsv2 

( N2 )'/2 

For the Average Emission Rate Per Source (EE) 

EE = ¥ E 1 + N 2

E E 2 , 

Nj + Ng + N3 -

with 95 percent confidence intervals of: 

EE ± t {[NjS j IF + [N2sy 2] > without censoring. 

2 + [N2 sy 2 ]2 }1 / 2 

Total Emissions + N x EE (use the EE confidence limits above multiplied by N) 

Nj + N2 + N3 

2-25 
P.40 

APPENDIX A 

REFERENCE METHOD 21 
P.41 

MITKOD 21—DRnMIHATIOR OF VOUTOl 

OROAJIIC COMPOUNDS LEAKS 

1. Applicability and Principle. 

1.1 Applicability. This method applies to 

the determination of volatile organic com. 

pound (VOC) leaks from process equipment 

These sources include, but are not limited 

to. valves, fiances and other connection*, 

pumps and compressors, pressure relief devices, process drains, open-ended valves 

pump and compressor seal system degassing 

vents, accumulator vessel vents, agitator 

seals, and access door seals. 

1.2 Principle. A portable instrument la 

used to detect VOC leaks from individual 

sources. The Instrument detector type ts not 

specified, but it must meet the specifications and performance criteria contained in 

Section 3. A leak definition concentration 

based on a reference compound Is specified 

ln each applicable regulation. This procedure Is Intended to locate and classify leaks 

only, and Is not to be used u a direct measure of mass emission rates from individual 

sources. 

2. Definition*. 

2.1 Leak Definition Concentration. The 

local VOC concentration at the surface of a 

leak source that indicates that a VOC emission (leak) Is present. The leak definition Is 

an instrument meter reading based on a reference compound. 

2.2 Reference Compound. The VOC species selected as an instrument callbratloa 

basis for specification of the leak definition 

concentration. (For example: If a leak definition concentration Is 10,000 ppmv ss 

methane, then any source emission that results ln a local concentration that yields a 

meter reading of 10.000 on an instrument 

calibrated with methane would be classified 

as a leak. In this example, the leak definition is 10.000 ppmv, and the reference compound is methane.) 

2.3 Calibration Oos. The VOC compound 

used to adjust the instrument meter reading 

to a known value. The calibration gas Is usually the reference compound at a concentration approximately equal to the leak definition concentration. 

2.4 No Detectable Emiuion. The local 

VOC concentration at the surface of a leak 

source that indicates that a VOC emission 

(leak) Is not present. Since background VOC 

concentrations may exist, and to account 

for instrument drift and Imperfect reproducibility, a difference .between the source 

surface concentration and the local ambient 

concentration is determined. A difference 

based on meter readings of less than a concentration corresponding to the minimum 

readability specification indicates that a 

VOC emission (leak) is not present. (Por example, if the leak definition in a regulation 

la 10.000 ppmv, then the allowable increase 

in surface concentration versus local ambient concentration would be SOO ppmv based 

on the instrument meter readings.) 

2.5 Response Factor. The ratio of the 

known concentration of a VOC compound 

to the observed meter reading when measured using an instrument calibrated with 

the reference compound specified in the application regulation. 

2.t Calibration Precision. The degree of 

agreement between measurements of the 

same known value, expressed ss the relative 

percentage of the average difference between the meter readings and the known 

concentration to the known concentration. 

2.7 Retponte Time. The time interval 

from a step change In VOC concentration at 

the input of the sampling system to the 

Ume at which 90 percent of the corresponding final value Is reached as displayed on 

the instrument readout meter. 

I Apparatus. 

II Monitoring Instrument 

3.1.1 Specifications. 

a. The VOC Instrument detector shall respond to the compounds being processed. 

Detector types which may meet this requirement include, but ara not limited to, 

catalytic oxidation, flame lonixatloa infrared absorption, and photolonlsatioa 

b. The Instrument shall be capable of 

measuring the leak definition concentration 

specified In the regulation, 

c The scale of the Instrument meter shall 

be readable to ±S pereent of the specified 

leak definition concentration. 

d. The instrument shall be equipped with 

a pump ao that a continuous sample Is provided to the detector. The nominal sample 

(low rate shall be H to 3 Uters per minute. 

e. The instrument shall be intrinsically 

nfe tor operation in explosive atmospheres 

is defined by the applicable UJ&A. standards (e.g.. National Electrical Code by the 

National Fire Prevention Association). 

3.1.2 Performance Criteria, 

a. The Instrument response factors for the 

indlvidal compounds to be measured must 

be less than 10. 

b. The instrument response time must be 

equal to or less than 30 seconds. The response time must be determined for the instrument configuration to be used during 

testing. 

c. The calibration precision must be equal 

to or less than 10 percent of the calibration 

gas value. 

d. The evaluation procedure for each parameter is given ln Section 4.4. 

3.1.3 Performance Evaluation Requirement*. 

a. A response factor must be determined 

for each compound that Is to be measured, 

either by testing or from reference sources. 

The response factor tests are required 

before placing the analyzer into service, but 

do not have to be repeated as subsequent Intervals. 

b. The calibration precision test must be 

completed prior to placing the analyzer Into 

service, and at subsequent 3-month Intervals 

or at the next use whichever Is later. 

c. The response time test is required prior 

to placing the Instrument into service. If a 

modification to the sample pumping system 

or flow configuration is made that would 

change the response time, a new test Is required prior to further use. 

3.2 Calibration Oate*. The monitoring 

Instrument is calibrated in terms of parts 

per million by volume (ppmv) of the reference compound specified in the applicable 

regulation. The calibration gases required 

for monitoring and instrument performance 

evaluation are a zero gaa (air. less than 10 

ppmv VOC) and a calibration gas ln air mixture approximately equal to the leak definition specified ln the regulation. If cylinder 

calibration gas mixture are used, they must 

be analysed and certified by the manufacturer to be within ±2 percent accuracy, and 

a shelf life must be specified. Cylinder 

standards must be either reanalyzed or replaced at the end of the specified shelf life. 

Alternately, calibration gases may be prepared by the user according to any accepted 

gaseous standards preparation procedure 

that will yield a mixture accurate to within 

±2 percent. Prepared standards must be replaced each day of use unless it can be demonstrated that degradation does not occur 

during storage. 

Calibrations may te performed using a 

compound other than the reference compound If a conversion factor Is determined 

for that alternative compound so that the 

resulting meter readings during source surveys can be converted to reference compound results. 

4. Procedures 

4.1 Pretest Preparations. Perform the instrument evaluation procedures given in 

Section 4.4 if the evaluation requirements of 

Section 3.1.3 have not been met. 

A-l 
P.42 

4.2 Calibration Procedures. Assemble 

and start up the VOC analyzer according to 

the manufacturer's Instructions. After the 

appropriate warmup period and zero internal calibration procedure, introduce the 

calibration gas into the Instrument sample 

probe. Adjust the instrument meter readout 

to correspond to the calibration gas value. 

Non.—If the meter readout cannot te adJusted to the proper value, a malfunction of 

the analyzer is indicated and corrective actions are necessary before use. 

4.3 Individual Source Surveys. 

4.3.1 Type I—Leak Definition Based on 

Concentration. Place the probe inlet at the 

surface of the component Interface where 

leakage could occur. Move the probe along 

the interface periphery while observing the 

instrument readout. If an increased meter 

reading ts observed, slowly sample the interface where leakage la indicated until the 

m.Timnm meter reading is obtained. Leave 

the probe inlet at this maximum reading location for approximately two times the instrument response time. If the maximum 

observed meter reading la greater than the 

leak definition In the applicable regulation, 

record and report the results as specified In 

the regulation reporting requirements. Examples of the application of this general 

technique to specific equipment types are: 

a. Valves—The moat common souree of 

leaks from valves Is at the seal between the 

stem and housing. Place the probe at the 

Interface where the stem exists the parking 

gland and sample the stem circumference. 

Also, place the probe at the interface of the 

packing gland take-up flange seat and 

sample the periphery. In addition, survey 

valve housings of multipart assembly at the 

surface of all Interfaces where a leak couid 

occur. 

b. Flanges and Other Connections—Por 

welded flanges, place the probe at tbe outer 

edge of the flange-gasket interface and 

sample the circumference of the flange. 

Sample other types of nonpermanent Joints 

(such aa threaded connections) with a similar traverse. 

c. Pumps and Compressors Conduct a circumferential traverse at the outer surface 

of the pump or compressor shaft and seal 

Interface. If the source la a rotating shaft, 

position the probe Inlet within 1 cm of the 

shaft seal Interface for the survey. If the 

housing configuration prevents a complete 

traverse of the shaft periphery, cample all 

accessible portions. Sample all other Joints 

on the pump or compressor housing where 

leakage could occur. 

d. Pressure Relief Devices The configuration of most pressure relief devices prevents 

sampling at the sealing seat interface. Por 

those devices equipped with an enclosed extension, or horn, place the probe Inlet at approximately the center of the exhaust are* 

to the atmosphere. 

e. Process Drains—For open drains, pi^. 

the probe inlet at approximately the center 

of the area open to the atmosphere. por 

covered drains, place the probe at the sur 

face of the cover Interface and conduct a at. 

ripheral traverse. 

f. Open-Ended Lines or Valves—Place the 

probe inlet at approximately the center of 

the opening; to the atmosphere. 

g. Seal System Degassing Vents and Accumulator Vents—Place the probe inlet at approximately; the center of the opening to 

the atmosphere. 

h. Access; Door Seals-Place the probe 

inlet at the'surface of the door seal interface and conduct a peripheral traverse. 

4.3.2 Type II—"No Detectable Emission" 

Determine the local ambient concentra! 

tion around the source by moving the probe 

inlet randomly upwind and downwind at a 

distance of > one to two meters from tbe 

source. If ah Interference exists with this 

determination due to a nearby emission or 

leak, the local ambient concentration may 

be determined at distances closer to tat 

source, but ln no caae shall the distance bt 

less than 2ft centimeters. Then move tbs 

probe inlet to the surface of the souree and 

determine the concentration described in 

4.3.1. The difference between these concentrations determines whether there are no 

detectable emissions, Record and report tht 

results as specified by the regulation. 

Por those cases where the regulation require*- a specif lc device Installation, or that 

specified vents be ducted or piped to a control device, the existence of these conditions 

shall be visually confirmed. When the regulation also requires that no detectable emissions exist, visual observations and «"»p"ig 

surveys are required. Examples of this technique are: 

(a) Pump or Compressor Seals—If appUcable. determine the type of shaft seal Preform a survey of the local area ambient 

VOC concentration and determine if detectable emiasions exist as described above. 

(b) Seal System Degassing Vents. Accumulator Vessel Vents. Preasure Relief DevicesIf applicable, observe whether or not the 

applicable ducting or piping exists. Alas, determine tf any sources exist In the ducting 

or piping where emissions could occur prior 

to the control device. If the required ducting or piping, exists and there are no sourest 

where the emissions could te vented to ths 

atmosphere prior to the control device, then 

lt la presumed that no detectable rmlwtans 

are present. If there are sources ln the ducting or piping where emissions could bs 

vented or sources where leaks eould occur, 

the ««wpniig surveys described In this paragraph shall te used to determine If detectable emiasions! exist. 

A-2 
P.43 

4,3.3 Alternative Screening Procedure. A 

screening procedure based on the formation 

0( bubbles in a soap solution that is sprayed 

0n s potential leak source may be used for 

those sources that do not have continuously 

moving parts, that do not have surface temperatures greater than the boiling point or 

[ess than the freezing point of the soap solution, that do not have open areas to the atmosphere that the soap solution cannot 

bridge, or that do not exhibit evidence of 

liquid leakage. Sources that have these conditions present must be surveyed using the 

instrument techniques of 4.3.1 or 4.3.2. 

Spray a soap solution over all potential 

leak sources. The soap solution may be a 

commercially available leak detection solution or may be prepared using concentrated 

detergent and water. A pressure sprayer or 

$ squeeze bottle may te used to dispense the 

solution. Observe the potential leak sites to 

determine if any bubbles are formed. If no 

bubbles are observed, the source Is presumed to have no detectable emissions or 

leaks as applicable. If any bubbles are observed, the instrument techniques of 4.3.1 or 

4.3.2 shall te used to determine if a leak 

exists, or if the source h u detectable emissions, as applicable. 

4.4 Instrument Evaluation Procedures. At 

tne beginning of the Instrument performance evaluation test, assemble and start up 

tne Instrument according to the manufacturer's Instructions for recommended 

warmup period and preliminary adjustments. 

4.4.1 Response Factor. Calibrate the instrument with the reference compound as 

specified in the applicable regulation. Por 

each organic species that Is to be measured 

during individual source surveys, obtain or 

prepare a known standard ln air at a concentration df approximately 80 percent of 

the applicable leak definition unless limited 

by volatility or exploslvlty. In these cases, 

prepare a standard at 90 percent of the 

saturation concentration, or 70 percent of 

the lower explosive Umit respectively. Introduce this mixture to the analyser and 

record the observed meter reading. Introduce sero .sir until a stable reading la obtained. Make a total of three measurements 

by alternating between the known mixture 

and sero sir. Calculate the response factor 

for each repetition and the average response factor. 

Alternatively, tf response factors have 

been pubUshed for the compounds of interest for the instrument or detector type, the 

response factor determination Is not required, and existing results may te referenced. Examples of pubUshed response factors for flame ionization and catalytic oxidation detectors are included ln Section 9. 

4.4.2 Calibration Precision. Make a total 

of three measurements by alternately using 

zero gaa and the specified caUbration gas. 

Record the meter readings. Calculate the 

average algebraic difference between the 

meter readings and the known value. Divide 

this average difference by the known calibration value and mutiply by 100 to express 

the resulting caUbration precision as a percentage. 

4.4.3 Response Time. Introduce zero gas 

Into the Instrument sample probe. When 

the meter reading has stabilized, switch 

quickly to the specified caUbration gas. 

Measure the time from switching to when 

90 percent of the final stable reading is attained. Perform this test sequence three 

times and record the results. Calculate the 

average response tune. 

5. Bibliography. 

5.1 DuBose, D.A., and G.E. Harris. Response Factors of VOC Analyzers at a Meter 

Reading ot 10.000 ppmv for Selected Organic Compounds. U.S. Environmental Protection Agency, Research Triangle Park. N.C. 

PubUcation No. EPA 600/2-61-051. September 1981. 

5.2 Brown, O.E., et aL Response Factors 

of VOC Analyzers Calibrated with Methane 

for Selected Organic Compounds. VS. Environmental Protection Agency. Research Triangle Park. N.C. PubUcation No. EPA 600/ 

2-81-022. May 1981. 

5.3 DuBose, DA., et al Response of Portable VOC Analysers to Chemical Mixtures, 

U.S. Environmental Protection Agency. Research Triangle Park. N.C. PubUcation No. 

EPA 600/2-81-110. September 1981. 

A-3 
P.44 

APPENDIX B 

RESPONSE FACTORS 

This appendix presents response factors estimated 

for a 10,000 ppmv detector reading. These 

response factors were previously reported in 

References 4 and 6. They can be used to determine 

whether or not a concentration is above or below 

10,000 ppmv. The response factors may or may not 

be accurate at other concentrations. 
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TABLE B-l. RESPONSE FACTORS WITH 95% CONFIDENCE INTERVALS ESTIMATED AT 10.000 PPMV RESPONSE (cont'd.) 

00 

ro 

CAS No.« 

109-73-9 

13952-84-6 

75-64-9 

123-72-8 

107-92-6 

109-74-0 

75-1-50 

108-90-7 

67-66-3 

25167-80-0 

1 

108-41-8 

95-49-8 

106-43-4 

95-48-7 

4170-30-0 

98-82-8 

110-82-7 

108-93-0 

108-94-1 

110-83-8 

108-91-8 

123-42-2 

Compound Name 

Butyl amIne, NButylamine, SecButyl amine, TertButylbenzene, TertButyraidehyde, NButyrlc acid 

Butyronltrll e 

Carbon disulfide 

Chioroacetaldehyde 

Chlorobenzene 

Chloroethane 

Chloroform 

Chlorophenol, 0-

Chloropropene, 1 -

Chloropropene, 3-

Chlorotoluene, MChlorotoluene, OChlorotoluene, PCresol, OCrotonal dehyde 

Cumene 

Cyclohexane 

Cyclohexanol 

Cyclohexanone 

Cyclohexene 

Cyclohexylamlne 

Oecane 

Dlacetone alcohol 

Dlacetyl 

D1chloro-l-propene, 2,3 -

Volatlllt y 

Class 

LL 

LL 

LL 

HL 

LL 

HL 

LL 

LL 

LL 

LL 

G 

L 

HL 

LL 

LL 

LL 

LL 

LL 

S 

LL 

LL 

LL 

HL 

LL 

LL 

LL 

HL 

HL 

LL 

LL 

Response 

0.69 

0.70 

0.63 

1.32 

1.29 

0.80 

0.52 

9.10 

0.38 

5.38 

9.28 

4.56 

0.67 

0.80 

0.48 

0.48 

0.56 

6.96 

1.25 

1.87 

0.47 

0.85 

1.50 

0.49 

0.57 

0.09 

1.45 

1.54 

0.75 

OVA 

Factor Confidence 

0.53. 

0.58. 

0.58, 

0.89, 

1.07, 

0.38, 

0.40 , 

B 

5.73, 

0.32. 

I 1.87, 

5.19 , 

1.72, 

0.61 , 

0.72 , 

0.45, 

0.42, 

0.52, 

0.70, 

0.82, 

1.10, 

0.39, 

0.65, 

0.97, 

0.42, 

0.42, 

N 0.05, 

0.96, 

1.25, 

0.56, 

Intervals 

0.98 

0.87 

0.70 

2.20 

1.61 

3.14 

0.74 

16.20 

0.47 

26.40 

20.00 

27.20 

0.73 

0.90 

0.51 

0.55 

0.61 

1.45 

2.24 

3.71 

0.58 

1.20 

2.76 

0.57 

0.86 

>100.00 

2.48 

1.92 

1.09 

Response 

2.02 

1.56 

1.95 

2.30 

10.70 

1.47 

3.92 

5.07 

0.88 

3.90 

18.30 

0.87 

1.24 

0.91 

1.06 

1.17 

4.36 

0.70 

7.04 

2.17 

1.38 

0.16 

0.98 

3.28 

1.75 

TLV 

Factor 

B 

I 

I 

P 

B 

I 

I 

I 

B 

B 

B 

I 

1 

. 

Confidence Intervals 

1.14. 

0.77, 

1.42, 

0.96, 

6.53. 

0.62 , 

1.87, 

3.08, 

0.77, 

1.58, 

6.50, 

0.69, 

1.08, 

0.40, 

0.33, 

0.77, 

0.40, 

0.62, 

1.59. 

1.78. 

1.28, 

0.07, 

0.44. 

2.25. 

1.14. 

4.97 

5.24 

2.91 

12.80 

17.60 

3.48 

12.60 

9.79 

1.00 

14.10 

51.50 

1.16 

1.42 

7.47 

>100.00 

1.77 

47.40 

0.80 

>100.00 

2.74 

1.48 

0.35 

5.93 

5.12 

3.18 
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B-4 
TABLE B-l. RESPONSE FACTORS WITH 95$ CONFIDENCE INTERVALS ESTIMATED AT 10,000 PPMV RESPONSE (cont'd.) 

oo 

i 

tn 

CAS No.» 

77-75-8 

98-83-9 

110-91-8 

98-95-3 

79-24-3 

75-52-5 

25332-01-4 

109-66-0 

123-38-6 

79-09-4 

71-23-8 

115-07-1 

75-56-9 

110-86-1 

100-42-5 

79-34-Sc 

108-88-3 

71-55-6 

79-00-5 

79-01-6 

96-18-4 

Compound Name 

Methylpentynol 

Methyl styrene, AMorphollne 

Nitrobenzene 

Nltroethane 

Nltromethane 

Nltropropane 

Nonane-N 

Octane 

Pentane 

Plcollne, 2-

Propane 

Propionaldehyde 

Propionic acid 

Propyl alcohol 

Propyl benzene, NPropylene 

Propylene oxide 

Pyridine 

Styrene 

Tetrachloroethane, 1,1,1.2 -

Tetrachloroethane, 1,1,2,2 -

Tet rach1oroethylene 

Toluene 

Trichlorobenzene, 1,2,4-

TrIchloroethane, 1,1,1 -

Trlchloroethane, 1,1,2-

Trlchloroethylene 

Trlchloroprppane, 1,2,3-

Volatlllt y 

Class 

LL 

LL 

LL 

HL 

LL 

LL 

LL 

LL 

LL 

LL 

LL 

G 

LL 

LL 

LL 

LL 

G 

LL 

LL 

LL 

LL 

LL 

LL 

LL 

HL 

LL 

LL 

LL 

LL 

OVA 

Response Factor Confidence 

1.17 

13.90 

0.92 

1.40 

3.52 

1.05 

1.54 

1.03 

0.52 

0.43 

0.55 

1.14 

1.30 

0.93 

0.51 

0.77 

0.83 

0.47 

4.22 

4.83 

7.89 

2.97 

0.39 

1.21 

0.80 

1.25 

0.95 

0.96 

B 

I 

0 

I 

0.71 , 

9.50, 

0.67, 

1.20. 

3.03. 

0.80, 

0.94, 

0.89, 

0.42, 

0.38, 

0.46, 

1.00, 

1.03, 

0.77, 

0.45, 

0.44, 

0.74, 

0.40, 

3.45, 

1.24, 

5.01 , 

1.71 , 

0.36, 

0.50, 

0.72, 

1.05, 

0.83, 

0.64, 

Intervals 

2.48 

21.50 

1.40 

1.65 

4.15 

1.48 

2.98 

1.21 

0.66 

0.50 

0.72 

1.32 

1.70 

1.16 

0.58 

2.66 

0.95 

0.55 

5.27 

>100.00 

13.80 

6.11 

0.43 

2.94 

0.90 

1.50 

1.09 

1.78 

Response 

3.42 

2.59 

0.01 

3.45 

7.60 

2.02 

11.10 

2.11 

0.63 

1.18 

0.60 

1.71 

5.08 

1.74 

1.74 

1.15 

1.16 

6.91 

25.40 

2.68 

0.47 

2.40 

3.69 

3.93 

1.99 

TLV 

Factor 

B 

I 

I 

P 

D 

B 

I 

B 

B 

D 

I 

Confidence Intervals 

1.83. 

0.64, 

0.00, 

1.56. 

1.91 . 

1.17, 

3.13, 

1.68. 

0.57, 

1.08, 

0.59. 

1.11 , 

0.73, 

1.06, 

0.15, 

0.69, 

1.03, 

3.14. 

8.06. 

0.79, 

0.32, 

1.81, 

2.77. 

2.68, 

1.27, 

8.54 

10.50 

82.80 

13.00 

>100.00 

4.47 

>100.00 

2.75 

0.70 

1.29 

0.69 

3.06 

>100.00 

3.50 

20.30 

2.46 

1.34 

22.50 

>100.00 

>100.00 

0.68 

3.35 

5.16 

6.32 

3.82 
TABLE B-l. RESPONSE FACTORS WITH 95% CONFIDENCE INTERVALS ESTIMATED AT 10,000 PPMV RESPONSE (cont'd.) 

CAS No.* Compound Name 

Volatilit y 

Class 

OVA 

Response Fvector Confidence Intervals 

TLV 

Response Factor Confidence Intervals 

121-44-8 Trlethylamlne 

108-05-4 Vinyl acetate 

75-01-4 Vinyl chloride 

Vinyl propionate 

75-35-4 Vlnylldene chloride 

106-42-3 Xylene, PXylene, M95-47-6 Xylene, OLL 

LL 

G 

LL 

LL 

LL 

LL 

LL 

0.51 

1.27 

0.84 

1.00 

1.12 

2.12 

0.40 

0.43 

0.40, 

0.95, 

0.61, 

0.57, 

0.87, 

1.71, 

0.36, 

0.28, 

0.70 

1.82 

1.38 

1.74 

1.52 

2.68 

0.46 

0.85 

1.48 

5.91 

1.06 

1.21 

2.41 

7.87 

5.87 

1.40 

0.96. 

1.26, 

0.59, 

0.46, 

1.82, 

3.49, 

0.91. 

0.61. 

2.76 

>100.00 

4.60 

3.20 

3.35 

24.90 

>100.00 

9.33 

I 

cn 

^CAS numbers refer to the Chemical Abstracts Registry numbers of specific chemicals.'Isomers, or mixtures of chemicals. 

G = Gas; LL - light liquid ; HL = heavy liquid 

I = Inverse estimation method 

D = possible outliers in data 

N = narroa range of data 

X = no data available 

B = 10,000 ppmv response unachievable 

P = suspect points eliminated 

2 
P.51 

TABLE B-2. TESTED COMPOUNDS WHICH APPEAR TO JE UNABLE TO ACHIEVE AN INSTRUMENT 

RESPONSE OF 10,000 PPMV AT ANY FEASIBLE CONCENTRATION 

Instrument 

CASb 

75-1-50 

56-23-5 

--

--

--

--

1221 

98-01-1 

1660 

98-95-3 

108-95-2 

--

a OVA 

Compound Name 

Acetyl-1-propanol, 3-

Carbon disulfide 

Carbon tetrachloride 

Dichloro-1-propanol, 2,3 

Dichloro-2-propanol, 1,3 

Diisopropyl benzene, 1,3 

Dimethylstyrene, 2,4 

Freon 12 

Furfural 

Methyl-2,4-pentanediol,2 

Monoethanolamine 

Nitrobenzene 

Phenol 

Phenyl-2-propanol, 2-

CASb 

98-86-2 

--

74-86-2 

79-10-7 

100-52-7 

100-47-0 

98-88-4 

100-44-7 

56-23-5 

67-66-3 

4170-30-0 

98-82-8 

108-93-0 

--

--

--

--

64-18-6 

1221 

98-01-1 

115-11-7 

--

98-83-9 

1660 

108-95-2 

--

--

100-42-05 

2860 

TLV 

Compound Name 

Acetophenone 

Acetyl-1-propanol, 3-

Acetylene 

Acrylic acid 

Benzaldehyde 

Benzonitrile 

Benzoyl chloride 

Benzyl chloride 

Butyl benzene, TertCarbon tetrachloride 

Chloroform 

Crotonaldehyde 

Cumene 

Cyclohexanol ^ 

Dichloro-1-propanol, 2,3 

Dichloro-2-propanol, 1,3 

Diisopropyl benzene, 2,4 

Dimethylstyrene, 2,4 

Formic acid 

Freon 12 

Furfural 

Isobutylene 

Methyl-2,4-pentanediol 

Methylstyrene, AMonoethanolamine 

Phenol 

Phenyl-2-propanol, 2-

Propylbenzene, NStyrene 

Tetrachloroethy1ene 

OVA and TLV are two portable hydrocarbon analyzers that have been used in 

previous studies of fugitive emissions. Operating with a flame ionization 

detector (FID), OVA measures nonmethane hydrocarbon emissions; TLV measures 

total hydrocarbon emissions. 

3CAS numbers refer to the Chemical Abstracts Registry numbers of specific 

chemicals, isomers, or mixtures of chemicals. 

B-7 
P.52 

APPENDIX C 

CALCULATION OF MASS EMISSION RATES 
P.53 

APPENDIX C 

The calculation of emission rates is illustrated below for VOC: 

E = E + E 

T V L 

where Ey = total VOC emission rate, lb/hr, 

E. = condensed organic liquid component of the VOC emission rate, 

lb/hr, and 

Ew = vapor component of the VOC emission rate, lb/hr. 

The emission rate of the vapor component is calculated from the following 

equation: 

F ..

 QPM A (Cs-Ca> 

tv - K T 

where K =5. 6 x 10" , a factor incorporating conversion factors and 

standard temperature and pressure, 

Q = flow rate of gas through the sample train, actual cubic 

feet/minute, 

P = sampling system pressure at the dry gas meter, psia, 

M. = molecular weight of the air/VOC mixture, 

C = concentration of VOC in the gas sample from the sampling 

train, ppm by weight, 

C = concentration of VOC in the ambient air, ppm by weight, and 

T = sampling system temperature at the dry gas meter, R. 

The emission rate of the organic condensate component, E., is determined 

from the following equation: 

c 0-1 V 

fcL " t 

C-1 
P.54 

where E^ = organic condensate rate, lb/hr, 

V = volume of condensate collected, ml, and 

t = time over which the sample was collected, min. 

This calculation assumes an average density of 0.75 g/cc for the organic 

condensate. 

These equations can be modified as necessary to provide for 

water-miscible compounds and to express emissions in terms of compounds other 

than hexane. 

C-2 
P.55 

APPENDIX D 

LEAK RATE/SCREENING VALUE EQUATIONS 
TABLE D-1. PREDICTION EQUATIONS FOR NONMETHANE LEAK RATE FOR 

VALVES, FLANGES, AND PUMP SEALS IN SOCMI PROCESSES 

SOURCE TYPE INSTRUMENT LEAST - SQUARES EQUATION1 

NUMBER 

OF DATA 

PAIRS 

CORRELATION 

COEFFICIENT 

(r) 

STANDARD 

DEVIATION 

OF ESTIMATE 

Valves* 

Gas Service OVA NMLK = 1.68 (10~5) (MXOVA)0-69 3 99 0.66 0.716 

Light Liquid Service OVA NMLK = 3.74 (IO"4) (MXOVA)0*

47 129 0.47 0.902 

o 

I i Flanges OVA NMLK = 3.731 (IO*5) (MXOVA)0"

82 52 0.77 0.520 

Pump Seals' OVA NMLK = 1.335 (IO"5) (MXOVA)0,89 8 52 0.81 0.650 

NMLK = Nonmethane leak rate (lb/hr) 

MXOVA = Maximum screening value (ppmv) OVA instrument 

Source: Langley, G. J., and R. G. Wetherold (Radian Corporation) 1981. Evaluation of Maintenance for 

Fugitive VOC Emissions Control. EPA-600/52-81-080. pp. 54-56. 

'Source: Wetherold, R.G., L.P. Provost, and CD . Smith (Radian Corporation). Assessment of Atmospheric 

Emissions from Petroleum Refining: Volume 3. Appendix B. (Prepared for U.S. Environmental 

Protection Agency.) Research Triangle Park, North Carolina. Publication No. EPA-600/2-80-075c. 

'NMLK is given in units of lb/hr. The units may have to be changed for reporting purposes. 
P.57 

APPENDIX E 

SELECTION OF SAMPLE SIZE FOR FLANGE SCREENING 
APPENDIX E 

SELECTION OF SAMPLE SIZE FOR SCREENING FLANGES AND OTHER CONNECTORS 

In estimating emissions for a given process unit, all equipment 

components must be surveyed for each class of components. For example, all 

valves in gas/vapor service must be screened to establish the number of 

components in each of the given ranges of screening values. The one exception 

to this "total component screening" criterion is the category of flanges and 

other connectors. In typical process units, flanges and other connectors 

represent the largest count of individual equipment components, making it 

costly to screen all components. The purpose of this appendix is to present a 

methodology for determining how many flanges or other connectors must be 

screened to constitute a large enough sample size to identify the actual 

screening value distribution of flanges and other connectors in the entire 

process unit. Please note that the sampling is to be a random sampling 

throughout the process unit. 

The basis for selecting the sample population to be screened is the 

probability that at least one "leaking" flange will be in the screened 

population. The "leaker" is used as a representation of the complete 

distribution of screening values for the entire class of sources. The 

following binomial distribution was developed to approximate the number of 

flanges and other connectors that must be screened to ensure that the entire 

distribution of screening values for these components is represented in the 

sample: 

n > N * [1 - (1 -p)1/D ] (E-1) 

where D may be taken as (fraction of leaking flanges) * N and p > 0.95. 

Currently available data gathered for flanges in VOC service in chemical 

process units show an estimated 2.09 percent flanges leaking. The EPA 

recommends starting with the factor 0.0209 for the fraction of leaking 

flanges, since the actual leak frequency for flanges in a chemical process 

unit probably will not be known prior to the selection of a sample size for 

screening. A larger sample size will be required for units exhibiting a lower 

fraction of leaking flanges and other connectors. If a lower leak frequency 

E-1 

. 
P.59_ 

for a process unit is known or can be estimated, it may be substituted into 

the equation above in place of 0.0209. 

After 'n' flanges have been screened, an actual leak frequency should be 

calculated as follows: 

Leaking Frequency = Number of leaking flanges (£.2) 

Then, the confidence level of the sample size can be calculated using the 

following equation, based upon a hypergeometric distribution: 

p _ . (N-D')l (N-n)! 

Y

 ~

 L N! (N-D'-n)! (E-3) 

where N = Total population of flanges and other connectors 

n = Sample size 

D, _ Number of leaking flanges and connectors * N 

n 

If 'p' calculated in this manner is less than 0.95, then a less than 

95 percent confidence exists that the screening value distribution has been 

properly identified. Therefore, additional flanges/connectors must be 

screened to achieve a 95 percent confidence level. The number of additional 

flanges required to satisfy the requirement for a 95 percent confidence level 

can be calculated by solving Equation (E-1) again, using the leak frequency 

calculated in Equation (E-2), and subtracting the original sample size. After 

this additional number of flanges/connectors have been screened, the revised 

fraction of leaking components and the confidence level of the new sample size 

(i.e., the original sample size plus the additional flanges/connectors 

screened) should be recalculated using Equation (E-3). The Agency requires 

sufficient screening to achieve a 95 percent confidence level, until a maximum 

of 50 percent of the total number of flanges and other connectors in the 

process unit have been screened. The EPA believes that 50 percent of the 

total flange/connector population is a reasonable upper limit for a sample 

size. If half of the total number of flanges and other connectors are 

screened, no further flange screening is necessary, even if a 95 percent 

confidence level has not been achieved. 

E-2 
P.60 

APPENDIX F 

DETERMINATION OF EMISSION RATES FOR 

DEFAULT ZERO SCREENING VALUES 
P.61 

APPENDIX F 

DETERMINATION OF EMISSION RATES FOR 

DEFAULT ZERO SCREENING VALUES 

In developing emission estimates using correlations, the emissions 

associated with zero screening values are estimated using default emission 

rates. Due to their logarithmic form, the correlations estimate zero 

emissions for zero screening values. Field testing, however, indicates that 

there are finite emissions associated with equipment screening at the 

background concentrations. To account for these emissions in the protocol, 

EPA has established some default zero screening values and their associated 

emission rates based on data gathered during the SOCMI Maintenance Study. 

Twelve data pairs for valves in gas/vapor service were bagged to 

determine mass emissions during the Maintenance Study. The mass emission 

rates for these twelve sources were averaged to establish the emission rate 

for gas/vapor valves screening at 0 ppm above the background level. This 

average emission rate is 0.000033 kilograms per hour per source. Using the 

S0CMI/0VA correlation for gas/vapor valves shown in Appendix D and this 

emission rate, the "default zero" screening value was established (8 ppm). 

All components screening at or below this default screening value are assumed 

to have an emission rate equal to the default zero emission rate. 

No mass emissions data for zero screening values were available for 

equipment components other than valves in gas/vapor service. The default zero 

emission rates for all equipment types and services were established using the 

correlations shown in Appendix D and the default zero screening value (8 ppm-) 

calculated from the gas/vapor valves bagging data. 

Equipment Type/Service 

Valves, gas 

Valves, light liquid 

Flanges 

Pumps and all other components 

"Default Zero" 

Screening Value, DDm 

8 

8 

8 

s 8 

Zero Screening 

Value Emission 

Rate (kg/hr/source) 

0.000033 

0.000451 

0.000093 

0.000039 

F-l 
P.62 

APPENDIX G 

DEVELOPMENT OF A DEFAULT EMISSION RATE 

FOR EQUIPMENT THAT DOES NOT SCREEN ABOVE THE 

BACKGROUND CONCENTRATION 

Text adapted from Guidance for Estimating Fugitive Emissions, published by the 

Chemical Manufacturers Association. 
APPENDIX G 

DEVELOPMENT OF A DEFAULT EMISSION RATE FOR EQUIPMENT 

THAT DOES NOT SCREEN ABOVE THE BACKGROUND CONCENTRATION. 

If bagging data for equipment components that do not screen above 

background do not exist, the EPA default emission rates in Appendix F 

should be used to estimate emissions from these sources. If a process unit 

intends to develop its own default zero emission rates, it must bag samples 

from each equipment type (e.g., gas/vapor valves, light liquid valves) for 

which it plans to determine default zero emission rates. If bagging data 

exist, the first step in developing a default emission rate is to adjust 

for the background concentration by subtracting the background bag from the 

source bag; that is, calculate 

h • LRs,1 -

 LRB,i 

where LRC . = leak rate from source bag i 

s, i 

LRp . = leak rate from background bag i 

Next, take the logarithm of the data and add a constant (if necessary) 

to avoid taking the logarithm of a nonpositive X.. The following procedure 

is used: 

Case 1: If all of the data are positive, y. = log(Xi) 

Case 2: If all of the data are nonnegative with at least one zero, 

y / - log(Xi +C ) 

where C = largest power of 10 less than the smallest nonzero value of 

X (e.g., if the smallest nonzero value of X is 8 x 10" , 

then C = 1 x 10"*). 

Case 3: If some of the data are negative, the smallest value (Kl) is 

first subtracted from each observation in the data set (note that Kl is a 

negative number). This results in all nonnegatives, with at least one zero 

value. Then K2 is added to each observation in the set, where K2 = largest 

power of 10 less than the smallest nonzero value of the updated nonnegative 

data set. Hence, the logarithmic expression used is 

y. = log(Xi + C) where C = K2-K1 

G-l 
P.64 

The average, standard deviation, and scale bias correction factor (SBCF) 

are calculated for the Y. as follows: 

_ n 

n i-l

 1 

2

 n - 2 

- S' =_] _ y (y.-y)Z 

n-1 ^ 1 

i-l 

SBCF = g [(lnlO)2 (S2/2)] 

where g(t) = 1 + (n-1) t + (n-l)3t

2 + (n-l)5t3 + ... 

n n22!(n+l) n33!(n+l)(n+3) 

(Approx. 10-15 terms required to obtain accuracy of + 10" ) 

The estimate of emissions for components screening below the lower 

limit of detection (LLD) for the screening instrument, (EF,*), is then: 

EFj* = max [(10ySBCF)-C, 0] 

where C = 0 for Case 1, and previously stated for Case 2 and Case 3. 

A statistical test is used to compare the calculated EF,* with the 

established 'default zero' in Appendix F. The results of this test 

determine which value (EF,* or 'default zero') is used to represent 

emissions for components screening below the LLD. The test involves two 

cases: 

G-2 
P.65 

••> *-AA* ^ 

Case A: If EFj^'Default zero', then use EF,* if 

3W< y+t(.95, n-l)V S.yn 

E F U L = 10 SBCF < 'Default zero' 

(Use 'Default zero' if EFUL > 'Default zero') 

Case B: If EF,* > 'Default zero', then use EF,* if 

y-t(.95, n-l)Vs^n 

EFLL = 10 SBCF > 'Default zero' 

(Use 'Default zero' i f EFLL < 'Default zero') 

A confidence interval for EF, can be calculated as: 

y+tj(.975, n-lj\fs?/n y-tj(.975, n-ll^S 2/ ^ 

(10 SBCF, 10 SBCF) 

Note: This interval should only involve the nonnegative region. In the 

case where the above computation includes negative values, it should 

be truncated to zero. 

G-3 
P.66 

" - N -*>&••

 1 rt 

TECHNICAL REPORT DATA 

(Please read Instructions on the reverse before completing) 

.. REPORT NO. 3. RECIPIENT'S ACCESSION NO. 

4. TITLE AND SUBTITLE 

Protocols for Generating Unit-Specific Emission 

Estimates for Equipment Leaks of VOC and HAP 

5. REPORT OATE 

October 1988 

6. PERFORMING ORGANIZATION CODE 

7. AUTHOR(S) 8. PERFORMING ORGANIZATION REPORT NO. 

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT NO. 

11. CONTRACT/GRANT NO. 

68-02-4378 

12. SPONSORING AGENCY NAME AND ADDRESS 

Office of Air and Radiation 

Office of Air Quality Planning and Standards 

U.S. Environmental Protection Agency 

Research Triangle Park, North Carolina 27711 

13. TYPE OF REPORT AND PERIOD COVERED 

Final 

14. SPONSORING AGENCY CODE 

15. SUPPLEMENTARY NOTES 

16. ABSTRACT 

EPA has developed a Protocol for Generating Unit-Specific Emission Estimates fir 

Equipment Leaks of VOC and VHAP. The protocol provides several methods for estimating 

emissions from equipment leaks. These methods range from the application of average 

emission factors for the equipment component inventory to the use of bagging data for 

generating unit-specific leak rate/screening value correlations. In addition, the 

protocol provides technically sound methods of source screening and mass emissions 

sampling (bagging). The document will help facitilies generate accurate plant-specific 

equipment leak emissions. 

17. 

a. 

KEY WORDS AND DOCUMENT ANALYSIS 

DESCRIPTORS b.lOENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group 

18. DISTRIBUTION STATEMENT 

Unlimited distribution 

19. SECURITY CLASS (This Report) 

Unclassified 

2 1 . NO. OF PAGES 

110 

20. SECURITY CLASS (Thispage) 

Unclassified 

22. PRICE 

EPA Form 2220-1 (Rev. 4-77) PREVIOU S EDITIO N IS OBSOLET E 
3.0 SOURCE SCREENING 

This section presents protocols and methodologies for conducting 

screening of equipment components with a portable organic analyzer. The 

overall survey procedure is presented to give the perspective of a unit^wide 

screening plan. In addition, screening protocols are given for the different 

equipment types. The selection of an appropriate portable monitoring 

instrument is discussed and a section on data handling is also included. 

3.1 SCREENING SURVEY PROCEDURES 

For development of a unit-specific emission estimate, the concentration 

of organic materials at seals, shafts, and other potential leak points must be 

measured. In preparing to screen all equipment in a unit, all equipment to be 

included in the emission estimate unit needs to be identified. A listing of 

equipment types that are potential sources of fugitive emissions is given in 

Table 3-1. 

The first step in the screening survey is to define precisely the process 

unit boundaries. This is usually quite straightforward, but occasionally 

multiple units may be built on the same pad and share some common facilities. 

A process unit can be defined as the smallest set of process equipment which 

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 most systematically by following each stream. For instance, 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 flanges of a reactor or separation step. 

Screening would then continue on the outlet side of the reactor or separation 

equipment. Minor loops like 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 

3-1 

•MiiiiaJ^HI ^

 ! "" " 
P.68 

TABLE 3-1. FUGITIVE EMISSION SOURCES 

Equipment Types 

Pump seals 

Compressor seals 

Valves 

Pressure relief devices 

Sampling connections 

Flanges, screwed connections, etc. 

Open-ended lines 

Drains, vents, doors 

Agitator seals 

Service 

Gas/vapor 

Light liquid 

Heavy liquid 

3-2 
P.69 

effectively treated as separate streams. If the emission estimate is being 

generated in support of control strategies for individual chemical compounds, 

this approach offers the advantage of screening groups of equipment components 

with roughly the same composition of materials in the line. 

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. The unit survey is completed when all sources in the 

unit have been either screened or identified as a nonhydrocarbon fitting. 

Leakless equipment and equipment not in VOC (or VHAP) service should not be 

included in the screening survey. Equipment documented as inaccessible should 

be included in the survey; such equipment must be screened annually under 

regulations for fugitive emissions. 

Consistent with equipment leaks standards for hazardous air pollutants, 

unsafe-to-monitor equipment do not need to be included in the survey. 

Documentation must be provided, however, to substantiate the unsafe nature of 

such equipment. 

3.2 MONITORING INSTRUMENT 

A number of portable VOC detection devices are capable of measuring leaks 

from process units. These devices operate on a variety of principles, the 

three most common being ionization, infrared absorption, and combustion. Any 

analyzer can be used provided it meets the specifications and performance 

criteria set forth in EPA Reference Method 21. Reference Method 21 is 

included in this document as Appendix A. Any analytical instruments are 

permitted provided they are shown to measure the organic compounds of 

interest and the results are related to EPA's data base generated using a 

flame ionization detector, calibrated to methane. Analytical instruments 

referenced to compounds other than methane must develop response factors to 

relate screening values to concentration. This will allow use of many 

instruments that cannot be calibrated with methane. 

3-3 
P.70 

3.2.1 Operating Principles and Limitations of Portable VOC Detection Devices 

Ionization detectors operate by ionizing the sample and then measuring 

the charge (number of ions) produced. Two methods of ionization currently 

used are flame ionization and photoionization. 

A standard flame ionization detector (FID) usually measures the total 

carbon content of the organic vapor sampled. Although carbon monoxide and 

carbon dioxide do not produce interferences, FID analyzers do react to water 

vapor, although at a low sensitivity. Furthermore, if water condenses in the 

sample tube, erratic readings may result. A filter is used to remove 

particulate matter from the sample. When equipped with options, certain 

portable FID instruments are capable of measuring total gaseous nonmethane 

organics or individual organic components. Certain organic compounds 

containing nitrogen, oxygen, or halogen atoms when sampled with an FID give a 

reduced response; and some organics may not give any response at all. For 

this reason, it is necessary to develop response factors for each compound 

that is to be measured. Response factors are discussed in Section 3.2.2.1. 

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 leaks in process units used in the synthetic organic 

chemical manufacturing industry, especially for certain compounds such as 

formaldehyde that will not give a response on an FID or combustible detector. 

Nondispersive infrared (NDIR) instruments operate on the principle of 

light absorption characteristics of certain gases. NDIR instruments are 

usually subject to interference because other gases such as water vapor and 

carbon dioxide may also absorb light at the same wavelength as a compound of 

interest. These detectors are generally used only for the detection and 

measurement of single components. For the detection and measurement of single 

components, the wavelength at which a certain compound absorbs infrared 

radiation is predetermined and the device is preset for that specific 

wavelength by using 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. 

3-4 
P.71 

Combustion analyzers are designed either to measure the thermal 

conductivity of a gas or to measure the heat produced by combusting the gas. 

The most common method used in portable VOC detection devices is measuring the 

heat of combustion. These devices are referred to as hot wire detectors or 

catalytic oxidizers. Combustion analyzers, like most other detectors, are 

nonspecific for gas mixtures. In addition, combustion analyzers exhibit 

reduced response (in some cases, no response) to gases that are not readily 

combusted, such as formaldehyde and carbon tetrachloride. 

3.2.2 Performance Criteria and Evaluation for Portable VOC Detectors 

As previously stated, any portable VOC detector may be used as a 

screening device directly provided it meets the performance criteria specified 

in Reference Method 21 (see Appendix A) . Although this approach has been 

shown to be applicable to many organics, it cannot be universally applied. 

Facilities may need to develop an appropriate method for testing inorganic and 

some organic compounds. A discussion of the performance criteria and detector 

evaluation procedure is presented below and summarized in Table 3-2. 

In addition to the performance criteria, Reference Method 21 also 

requires that the analyzer meet the following specifications: 

o The VOC detector shall respond to those organic compounds being 

processed (determined by the response factor). 

o The analyzer shall be capable of measuring the leak definition 

specified in the regulation (i.e., 10,000 ppmv or "no detectable 

limit"). 

o The scale of the analyzer shall be readable to +5 percent of the 

specified leak definition concentration. 

o The analyzer shall be equipped with a pump so that a continuous 

sample is provided at a nominal flow rate of between 0.5 and 3.0 

liters per minute. 

o The analyzer shall be intrinsically safe for operation in explosive 

atmospheres. 

Also, criteria for the calibration gases to be used are specified. Two 

or more calibration gases are required for analyzer performance evaluation. 

One is a zero gas which is air with less than 10 ppmv VOC. The other 

calibration gases, or reference gases, use reference compounds in air 

mixtures. The concentration of the reference gas should represent the range 

3-5 

IMHHI asm 
P.72 

TABLE 3-2. PERFORMANCE CRITERIA FOR PORTABLE VOC DETECTORS' 

Criteria Requirement Time Interval 

Instrument response 

factor 

Instrument response 

time 

Calibration precision 

Must be <10 unless 

correction curve is 

used. 

Must be <30 seconds 

Must be <10% of 

calibration gas value 

One time, before detector 

is put in service. 

One time, before detector 

is put in service. If 

modification to sample 

pumping or flow configuration is made, a new test 

is required. 

Before detector is put in 

service and at 3-month 

intervals or next use, 

whichever is later. 

Source: Reference Method 21. 

3-6 
of responses measured. For the purpose of developing unit-specific emission 

estimates, a reference gas for the appropriate range should be used. 

3.2.2.1 Response Factor. The sensitivity of an analyzer varies, 

depending on the composition of the sample and concentration detected. The 

response factor (RF) helps to quantify the sensitivity for each compound. The 

response factor is defined by: 

D . c^ri-nv Actual concentration of compound 

Kesponse r-acior = observed concentration from detector 

It is important to note that the response factor may be used as a guide 

to selecting an appropriate monitoring device. For example, from the data 

presented in Appendix B, it can be readily seen that in screening equipment in 

a process unit containing cumene, an FID can be used (RF = 1.87) directly, 

with no correction for response factor; while the catalytic oxidation detector 

cannot (RF has no value). Similarly, from the same data, neither of these 

devices would be capable of detecting leaks from a source containing carbon 

tetrachloride if response factor adjustments are not used. 

Using response factors as a general guide to analyzer applicability is 

especially important when dealing with chemical mixtures, since many process 

streams in industrial plants are composed of mixtures of chemicals. One EPA 

study concluded that analyzer response factors for a chemical mixture fall 

5 

between the responses expected for the pure components. Therefore, if 

desired, an interpolated or weighted average can be used to predict the 

response for mixtures based on known responses for individual chemicals. If 

sufficient information on pure components is not available or if desired, the 

response factor of a mixture for a specific instrument may be determined 

experimentally in the laboratory. Such results should be well documented. 

For further information see EPA-600/2-81-110, Response of Portable VOC 

Analyzers to Chemical Mixtures, and EPA-600/2-8-051, Response Factors of VOC 

A 

Analyzers at a Meter Reading of 10,000 ppmv for Selected Organic Compounds. 

Response factors also may be used to correct screening value measurements 

gathered to estimate emissions when using an emission factor approach (e.g., 

leak/no-leak approach or three-strata approach). If using leak rate/screening 

value correlations, however, a standard curve covering the entire range of 

3-7 
P.74.. 

screening values measured must be used. A response factor must be determined 

for each compound that is to be measured, either by testing or from reference 

4 5 6 

sources. ' ' An analyzer's response factor for individual compounds to be 

measured must be less than 10 at or near the concentrations defining emission 

factors (e.g., 1,000 and 10,000 ppmv) to be acceptable. The response factor 

tests are required before placing the analyzer in service, but do not have to 

be repeated at subsequent intervals. 

Response factors can be determined by 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. 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 is 

obtained. A response factor is calculated for each repetition and then 

averaged over the three measurements. 

Alternately, if response factors have been published for the compounds of 

interest for the combination of detector and calibration gas desired, the 

response factor determination is not required, and existing results may be 

referenced. Results of a study developing response factors of FID (Foxboro 

OVA-108 and 0VA-128) and catalytic oxidation (J. W. Bacharach TLV Sniffer) 

4 

analyzers are presented in Table B-l of Appendix B. These response factors 

can be used when determining if a screening concentration is above or below 

10,000 ppmv. The values are for pure organic chemicals only. Table B-2 of 

Appendix B presents tested compounds that appear unable to achieve an 

instrument response of 10,000 ppmv at any feasible concentration unless 

A 

response factors are used. These single response factors are adequate for 

response factor adjustments when using one of the emission factor approaches 

for estimating emissions. When applying correlations, however, an accurate 

correction for the non-linear response of an instrument is needed. Response 

factors must be evaluated at several concentrations to establish a correction 

curve for use in translating instrument readings. 

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 

3-8 
sampling system, to the time at which 90 percent of the corresponding final 

value is reached as displayed on the analyzer readout meter. The response 

time must be equal to or less than 30 seconds. The response time must be 

determined for the analyzer configuration that will be used during testing, 

and the response time test is required before placing an analyzer in service. 

If a modification to the sample pumping system or flow configuration is made 

that would change the response time, a new test is required before further 

use. 

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 three-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, a total of three measurements 

is required for each nonzero 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. 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 the known calibration value and multiplied by 100 to 

express the resulting calibration precision as percent. 

3.2.2.4 Safety. Portable instruments to detect VOC emissions from 

equipment leak sources are required to be used in 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 

3-9 
P.76 

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 

flammables may exist only under unlikely conditions of operation. 

As of 1982, five manufacturers produced portable VOC detection 

instruments that are certified to be intrinsically safe. Table 3-3 lists 

these manufacturers, approved instrument model numbers, instrument 

certification categories, and performance specifications. Additionally, newer 

instruments may be available that meet the performance requirements for 

generating emission estimates. 

3.2.3 Monitoring Devices For Difficult Situations 

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

the performance specifications of Method 21. For example, there are several 

cases (e.g., phosgene) where the response factor at 10,000 ppmv is greater 

than ten (10). The instrument may meet all other requirements, but fails as a 

Method 21 instrument because it cannot meet the response factor requirement. 

The instrument can still be used to estimate emissions from equipment leaks, 

provided the instrument is shown to be sufficiently reliable in providing data 

that can be related to EPA's data collected using an OVA calibrated to 

methane. 

Several steps must be taken initially to document the viability of a 

device that fails to meet the Method 21 requirements. First, a laboratory 

program must be undertaken to demonstrate the response of the monitoring 

instrument to the compounds being measured. This response must be documented. 

The second step involves relating the instrument response (i.e., screening 

value) to actual concentrations, or in other words, developing an instrument 

response curve. The screening value 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. Third, the testing 

program should be sufficiently well documented to demonstrate how the 

instrument will be used in screening equipment. (For example, if the response 

time of the candidate instrument exceeds the Method 21 performance 

specification, the test plan should reflect added screening time at each 

potential leak point to be screened. Once this laboratory demonstration has 

been completed and the screening value correction curve has been established, 

the screening can begin. 

3-10 
TABLE 3-3. PORTABLE VOC DETECTION INSTRUMENT PERFORMANCE SPECIFICATIONS 

Manufac ture r Model No. 

Pollutant(s) 

Detected 

Principle of 

Operation 

Range 

(ppm) Certification 

Bacharach Instrument Co. , 

Santa Clara, California 

Combustible gases Catalytic 

Combustion 

0-100Z LEL Intrinsically safe. Class I, 

Division 1, Groups C and D 

TLV Sniffer Combustible gases Catalytic 0-1,000 and Intrinsically safe. Class I, 

Combustion 0-10,000 Division 1, Groups C and Di and 

Class I, Division 2, Groups A 

and B 

Foxboro, 

S. Norwalk, Connecticut 

0VA-128 Total hydrocarbons FID/GC 0-1,000 Intrinsically safe. Class I, 

Division 1, Groups A, B, C and D 

OVA-108 Total hydrocarbons FID/GC 0-10,000 Intrinsically safe. Class I, 

Division 1, Groups A, B, C and D 

CJ 

I 

HNU Systems, Inc. 

Newton Upper Falls, 

Massachusetts 

Mine Safety Appliances Co. 

Pittsburgh, Pennsylvania 

Survey and Analysis, Inc., 

Northboro, Massachusetts 

PI-101 

40 

On Mark 

Model 5 

Chlorinated hydrocarbons, 

aromat ics, aldehydes, 

ketones, any substance 

which UV light ionizes 

Combustible gases 

Combustible gases and 

vapors 

Photoionization 

Catalytic 

Combustion 

Thermal 

Conductivity 

0-20, 

0-200. 

0-2,000 

0-10X and 

0-100X LEL 

0-5 and 

0-100X LEL 

Intrinsically safe. Class I, 

Division 2, Groups A, B, C and D 

Intrinsically safe, Class I, 

Division 1, Group D; and Class I, 

Division 2, Groups A, B, and C 

Intrinsically safe. Class I, 

Division 1, Groups A, B, C and D 
E-TBL. 

3.3 SCREENING PROCEDURES 

3.3.1 Calibration Procedures 

Pretest procedures to be followed include calibration of the monitoring 

instrument. The VOC analyzer should be assembled and started up according to 

the manufacturer's instructions. After the appropriate warm-up period and zero 

internal calibration procedure, the calibration gas is introduced into the 

sample probe. The instrument meter readout is then adjusted to correspond to 

the calibration gas value. If the meter readout cannot be adjusted to the 

proper value, a malfunction of the instrument is indicated and corrective 

measures should be taken before use. 

3.3.2 Procedure for Screening Equipment 

The mechanics of the screening operation outlined in Reference Method 21 

are summarized in the following discussion. The probe inlet is placed at the 

surface of the leak interface where leakage could occur. (The leak interface 

is the boundary between the process fluid and the atmosphere.) Care must be 

taken to ensure that the probe is held perpendicular, not tangential, to the 

leak 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 leakage is indicated 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. For 

example, the reading may exceed 10,000 ppmv when using an OVA analyzer. For 

the purposes of generating an emission estimate, these higher readings also 

must be recorded. A dilution probe should be employed to allow measurement of 

concentrations greater than the instrument's normal range. The OVA can be 

equipped with a dilution probe that permits measurement of concentrations up 

to 100,000 ppmv. It is important to note that extending the measurement range 

also necessitates the calibration of the instrument to the higher 

concentrations. 

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

even liquids. A short piece of Teflon tubing can be used as a probe tip 

3-12 
P.79 

extender and snipped off as the tip fouls. In areas with a noticeable 

particulate loading, this tubing can be packed with untreated fiberglass to 

act 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 sintered steel 

filter be cleaned at least daily and the side-pack filter on a weekly basis. 

Normally, these filters can be cleaned by just rapping them lightly on a table 

top, but if the deposits are wet and caked on, washing with an aqueous 

solution of soap and alcohol is recommended. This can also 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, 

flanges, pumps and compressors, pressure relief devices, and other potential 

sources of VOC leakage such as process drains and open-ended lines or valves. 

For valves, the most common source of leaks is at the seal between the 

stem and housing. To screen this source, the probe is placed where the stem 

exits the packing gland. The probe is moved around the stem circumference. 

The maximum reading is recorded as the screening value. Also, the probe is 

placed at the packing gland take-up flange 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. 

For flanges, the probe is placed at the outer edge of the flange-gasket 

interface and the circumference of the flange is sampled. For screwed 

flanges, the threaded connection interface must also be screened. Other types 

of nonpermanent joints, such as threaded connections, are sampled with a 

similar traverse. 

Pumps and compressors are screened with a circumferential traverse at the 

outer surface of the pump or compressor shaft and seal interface where the 

shaft exits the housing. If the source is a rotating shaft, the probe inlet 

is positioned within 1 cm 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 

3-13 

j H B 
P.80 

Screen 

Here 

PtekiBf aut 

Screen 

Here 

Figure 3-lb. Non-rising stem type. 

Figure 3-la . Rising stem type. 

Figure3-1. Gate valves. 

3-14 
P.81 

Ptekisf am 

Screen 

Here 

Body 

Uu 

Figure 3-2a. Manual Globe Valve 

Screen 

Here 

Packing 

L P Duk 

Figure 3-2b. Globe type control valve 

Figure 3-2. Globe valves. 

3-15 
P.82 

Screen 

Here 

Figure 3-3. Lubricated plug valve. 

3-16 
Screen 

Here 

Figure 3-4a. Ball valve. 

Screen 

Here 

Oiik 

Figure 3-4b. Butterfly valve. 

Figure 3-4. 

3-17 
P.84 

Oiaehragm 

Screen 

Here 

Figure 3-5a. Weir type diaphragm valve 

Screen 

Here 

Figure 3-5. 

Figure 3-5b. Check valves, 

3-18 
compressor housing where leakage could occur should also be sampled. 

Figure 3-6 illustrates screening points for two types of centrifugal pumps. 

Agitator seals should be screened in a similar manner. 

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. Again, only the probe should be placed in 

the horn; personnel conducting the screening should not place hands, arms, or 

any parts of the body into the horn. Figure 3-7 illustrates the screening 

points for a spring-loaded relief valve. 

Fugitive leaks from most other sources such as process drains, open-ended 

lines or valves, and seal system degassing vents and accumulator vents, are 

emitted through a regularly shaped opening. If that opening is very small (as 

in sampling lines of less than one inch diameter), a single reading in the 

center is sufficient. For larger openings (like a six inch drain mouth), it 

is necessary to traverse the perimeter of the opening. The concentration at 

the center must also be read. For even larger sources (like a wash-up drain 

grate), a grid of readings should be taken on about six inch centers. For 

access door seals, the probe inlet is placed at the surface of the door seal 

for the peripheral traverse. For all of these types of equipment, it is the 

maximum value that is recorded as the screening concentration. 

3.4 DATA HANDLING 

To handle the screening data uniformly, it is recommended that data be 

recorded on prepared data sheets. The data collected should include the 

following: 

1. Date. 

2. Hydrocarbon detector type. 

3. Source identification. (If permanent ID'S are not in place, assign 

ID's consecutively as each source is screened. The first source 

screened is assigned ID1, the second source screened, ID2, and so 

on.) 

3-19 

SXMM 
P.86 

Meviaf ibsh 

Figure 3-6a. Vertical centrifugal pump. 

Figure 3-6b. Horizontal centrifugal pump 

Figure 3-6. 

3-20 
P.87 

Screen 

Here 

Figure 3-7. Spring loaded relief valve. 

3-21 
P.88_ 

4. Screening value recorded in ppmv. 

5. Source type (i.e., type of valve, pump, compressor, flange, etc.) 

6. Service. For example, gas, light liquid, and heavy liquid. Liquids 

are classified based on their most volatile component present at 

20 weight percent or more. If the components have a total vapor 

pressure equal to or greater than 0.04 psi at 20 C, the material 

(containing greater than or equal to 20 percent VOC) is classified 

as a light liquid; if not, it is classified as a heavy liquid. 

Classification is based upon the actual process conditions, not 

ambient conditions. 

7. Comments. If any explanation is required, it should be noted in a 

"comments" section. An example data sheet is given in Table 3-4. 

In some cases, it may be necessary or desirable to adjust the screening 

values for response factor. In these cases, the data sheet should be designed 

to accommodate extra columns for response factor and corrected screening 

values. 

3.5 CALIBRATION PROCEDURES FOR QUALITY ASSURANCE 

Calibration procedures must be used for quality control to ensure the 

collected data are of high quality and can be compared to the data already 

gathered by EPA. 

Each screening instrument should be checked for calibration before each 

use and readings from these checks recorded. As an example, instruments 

should be calibrated each morning before use and before use in the afternoon. 

The calibration should also be checked periodically (such as during breaks in 

the daily testing schedule) to ensure that calibration has not drifted. The 

instruments should be calibrated if the reading is off by more than +5% on the 

high standard, or +20 on the low standard. If more than one instrument is 

being used at one process unit, the calibration readings for all instruments 

must be recorded. 

3-22 
TABLE 3-4. EXAMPLE DATA SHEET 

oo 

i 

ro 

NvO 

|Hydrocarbon Detector| Source | Screening Value | Process | | Primary | 

Date | Type | ID j (ppmv) J Unit j Service j Material j Comments 

1 I I I I 1 1 
P.90 

SECTION 4.0 

MASS EMISSIONS SAMPLING 

The process of measuring organic concentrations at potential leak points 

of equipment when combined with the EPA's leaking and non-leaking emission 

factors gives a good estimate of the leak rate from a process unit. More 

rigorous procedures may be used to determine the mass emission rate more 

accurately. Measuring mass emission rates requires source enclosure combined 

with sampling of the gas in the enclosure. The dilution or vacuum method is 

the preferred technique for sampling the emissions from sources that can be 

enclosed. An alternate sampling technique is the blow-through method which is 

usually used for sources with very large leak rates (in excess of the vacuum 

pump capacity). An important step in either of these methods, however, is 

source enclosure, a procedure called bagging. 

4.1 VACUUM METHOD 

In the past, the method preferred for sampling leaks from baggable 

sources has been the dilution or vacuum method. The sampling train used in 

this method is shown in Figure 4-1. 

The train can be mounted on a portable cart, which can be easily moved 

around the process unit from source to source. 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 EPA conducted, a 4.8 CFM Teflon-ring piston type 

vacuum pump equipped with a 3/4-horsepower air-driven motor was used. Low 

pressure air (-100 psig) is available at or near most process units. An 

example of a suitable dry gas meter is a Rockwell Model 1755 Test Gas Meter 

12 with a Number 83 Test Index. Other equipment that EPA used in the train 

includes Whitey valves, copper and stainless steel tubing, Teflon tubing, 100 

cc glass airtight syringe, thermometers, mercury and water manometers, a cold 

trap, and an air-driven diaphragm sampling pump. 

The leak source is shown as a valve in Figure 4-1. However, the same 

sampling train can be used for all equipment to be sampled using the vacuum 

technique. As described in Section 4.3, the size and shape of the enclosure 

(tent) around the potential leak point is adjusted to fit the particular shape 

4-1 

E2BB 
Magnehelic 

i 

ro 

This line should 

be as short 

as possible 

Tent 

J " l| J L | A Cold Trap 

L_| L r§J (Ice toth) 

Leaking 

Valve 

Trap 

Vacuum Pump 

DryGas 

Meter 

Sample Bag 

Small 

Diaphragm 

Pump Two Way Valve 

Figure 4-1. Sampling train for baggable sources of hydrocarbon emissions using a diaphragm. 
and operating condition of the equipment. When the full sampling train is 

connected, the vacuum pump is able to maintain a maximum flow rate of 

approximately 2.5 cubic feet per minute (0.001 cubic meters per second). 

The tent is connected by means of a bulkhead fitting and Teflon tubing to 

the sampling train. A separate line is connected from the tent to a 

magnahelic to allow continuous monitoring of the pressure inside of the tent. 

If a significant vacuum exists inside the tent when air is being pulled 

through, a hole is made in the opposite side of the tent from the outlet to 

the sampling train. This allows air to enter the tent more easily and thus 

reduces the vacuum in the enclosure. In practice, it has been found that only 

a yery slight vacuum (0.1 inches H-0) is present in the tent during most of 

the sampling, even in the absence of a hole through the tent wall. Sufficient 

air enters around the seals to prevent the development of a significant vacuum 

in the tent. Sample bags are used to collect gas samples and transport them 

to the laboratory for analysis. As with the tent material, sample bags must 

be constructed of material that is impermeable to hydrocarbons so that the 

process components are contained within the sample bag. Mylar plastic, 

Teflon, and Tedlar are materials well suited to this function. A typical 

sample bag is shown in Figure 4-2. 

A cold trap is placed in the system to condense water and heavy organics, 

thus preventing condensation in downstream lines and equipment. The cold trap 

can be simply a 500 ml flask in an ice bath placed as close as possible to the 

tent. While not always necessary, this ice bath cold trap is very effective 

in preventing condensation in the remainder of the sampling train and in the 

gas sample bag. Any organic condensate that collects in the cold trap must be 

measured for later use in calculating total leak rates. On some streams the 

use of a cold trap is critical. 

The flow rate through the system can be varied by throttling the flow 

with a control valve immediately upstream of the vacuum pump. As the flow 

rate is decreased, the concentration of hydrocarbon increases in the gas 

flowing through the sampling system. This allows considerable flexibility in 

avoiding operations with an explosive mixture of hydrocarbon in the air. If 

an explosive mixture is present, the blow-through method should be used. 

4-3 
P.93 

Figure 4-2. Mylar plastic sample bag, 

4-4 
In summary, the vacuum sampling procedure consists of the following 

steps: 

• Obtain and record a screening value with the portable hydrocarbon 

detector, 

• Enclose the source in a tight shroud, 

• Connect the tent to the sampling train, 

• Immerse the cold trap in an ice bath, 

• Note the initial reading of the dry gas meter, 

• Start the vacuum pump and a stopwatch simultaneously, 

• Record the temperature and pressure at the dry gas meter, 

• Observe the VOC concentration at the vacuum pump exhaust with the 

hydrocarbon detector, 

• Record the temperature, pressure, dry gas meter reading, outlet VOC 

concentration and elapsed time eyery 2 to 5 minutes, 

• Fill a gas sample bag from the discharge of the Teflon-lined 

diaphragm pump when the outlet VOC concentration stabilizes (i.e., 

the system is at equilibrium), 

§ Fill another bag with ambient air near the tent area to detect 

* 

the background VOC concentration, 

• Take a final set of readings and stop the vacuum pump, 

• Remove, seal, and transport the cold trap is to the laboratory 

along with the two bag samples and the data sheet, 

• Remove the tent, 

• Rescreen the source with the portable hydrocarbon detector and 

record. 

All of the above data and any pertinent comments should be recorded in a 

permanent laboratory notebook. 

* 

This bag sample may be omitted in favor of the hydrocarbon detector 

reading if the background VOC concentration is less than 5 percent of the 

lower limit of the screening range (i.e., <50 ppm for the 1,000 to 10,000 ppm 

class). When bagging a "zero" screening value component, it is extremely 

important to take a background bag. Data obtained without a background bag 

will bias emission factors on the high side unless this correction is made. 

4-5 
P.95 

4.2 BLOW-THROUGH METHOD3 

Blow-through refers to blowing nitrogen through a flexible tent to create 

a constant VOC concentration inside the tent. Nitrogen is metered into the 

tent through 1 or 2 polyvinyl chloride tubes. The temperature and oxygen 

concentrations are measured inside the tent with a platinum-RTD.thermocouple 

and an oxygen/combustible gas monitor. The flow of nitrogen is monitored in a 

gas rotameter calibrated to nitrogen. The nitrogen passes though activated 

charcoal and drierite to remove any organics and;moisture. The pressure in 

the tent never exceeds 1 psig. Figure 4-3 illustrates the equipment required 

for the blow-through method. 

At least two OVA (Foxboro 108 Organic Vapor1Analyzer ) measurements are 

made inside the tent, each measurement at two or more differing nitrogen flow 

rates to increase accuracy. [The OVA must be attached to a dilution probe and 

calibrated to nitrogen-diluted gases to allow its use in the nitrogen 

atmosphere in the tent.] The OVA readings are converted to emission rates of 

VOC via response factors for the OVA; the calculation is shown in Table 4-1. 

Alternatively, gas samples from the tent can be collected with a portable 

sampling pump and transported to a lab for chemical speciation and 

concentration measurement. The calculation in Table 4-1 is also applicable 

for concentrations measured in this manner (except that the response factor is 

set equal to 1). 

The oxygen concentration is also measured to determine the total gas flow 

rate through the tent. However, oxygen concentration is also used to rate the 

quality of the tent, and except for a few extremely difficult situations, VOC 

concentrations are not measured until the oxygen concentration in the tent is 

reduced below 5%. 

Air can replace nitrogen as a dilution gas if the hydrocarbon 

concentration is not expected to be high enough to cause an explosive 

atmosphere inside the tent. However, calculations based on air tent data must 

assume a nominal tent leakage rate, i.e., extra flow through the tent due to 

air entering the tent that is not metered through the tubing. 

Safety has been a key factor in the development of this procedure. Over 

400 valves have been tented with this technique without incident. Nitrogen is 

aText adapted from Chemical Manufacturers Association, Guidance for Estimating 

Fugitive Emissions, July, 1987. 

4-6 
I 

Pressure 

Plant Regulator 

Nitrogen •>— • 

(or Air) 

Activated 

Charcoal 

1/4" Insulated Teflon 

Tubing 

Valve Stem 

Tape or Adjustable Metal Band 

Sample Port for Collecting Oata on 

— Temperature 

— Hydrocarbon Concentration 

— Oxygen Concentration 

Tape or Compressed Foil 

Figure 4-3. Equipment required for the blow-through sampling technique. 
TABLE 4-1. CALCULATION PROCEDURES FOR TENTED LEAK RATE 

Tent rate _ 4.836 x IO"5 (QHMWHOVAHRF) 

(lb/hr) " T + 460 

where 

Q = flow rate into tent in cubic meters/hour 

N, flow rate in liters/minute m3 m.-ll4./% = 2 I-Q QC m -minute-. 

, ,tent oxvoen concentration in %>

 L ' liter-hour-1 

i - l 21 ) 

MW* = molecular weight of gas in pounds/pound-mole 

T = temperature in tent in °F 

OVA = instrument reading minus background reading, in vppm 

RF** = response factor for leaking gas relative to calibration gas 

_5 

4.836 x 10 = a conversion factor taking into account the gas constant and 

assuming a pressure in the tent of 1 atmosphere 

* 

For mixtures: 

gas molecular weight = (mole fraction-gas 1)(molecular weight-gasl) + 

(mole fraction-gas 2)(molecular weight-gas 2) + ... 

** 

For mixtures: 

gas response factor = (mole fraction-gas 1)(response factor-gas 1) + 

(mole fraction-gas 2)(response factor-gas 2) + ... 

where response factor is calculated at the OVA concentration. For liquid 

mixtures, a detailed analysis based on vapor-liquid equilibrium must be done 

to use OVA concentrations. 

4-8 
used as a dilution gas instead of air to prevent an explosive atmosphere 

within the tent. All of the instruments used are battery-operated and 

approved for Class I, Division I use. In summary, the blow-through method 

consists of the following steps: 

o Interview the unit operator to determine the composition of the 

material in the designated equipment component (in weight or volume 

% ) , and the operating conditions of the component. 

o Screen the component by placing a Tygon nozzle on the end of the 

Foxboro/Century OVA (Organic Vapor Analyzer), holding the end of the 

nozzle within 1 centimeter of the leak interface, and recording the 

highest concentration seen on the OVA readout. 

o Cut a tent from appropriate material (see section 4.3 - Source 

Enclosure) that will easily fit over the equipment component. 

o Connect tubing from the nearest low pressure nitrogen station to a 

rotameter stand, which includes a regulator, dessicant, activated 

charcoal, and a rotameter in series. 

o Run tubing from the rotameter outlet to a "Y" that splits the 

nitrogen flow into two pieces of tubing. Insert the tubes into 

openings located on either side of the tent. 

o Turn on nitrogen at the utilities station and regulate it at the 

rotameter to approximately 40 liters/minute. 

o After the nitrogen is flowing, wrap aluminum foil around those parts 

of the equipment component where air could enter the tent-enclosed 

volume. 

o Use duct tape, wire, and/or rope to secure the tent to the 

component. 

o Put a third hole in the tent roughly equidistant from the two 

nitrogen-fed holes. 

o Measure the oxygen concentration in the tent by inserting the lead 

from an 0» meter into the third hole. Adjust the tent (add 

additional tape, foil, rope, etc.) until the 02 concentration is 

less than 5%. 

o Measure the temperature in the tent with a platinum-RTD 

thermocouple. 

o Calibrate the OVA to methane or hexane at a known concentration in 

nitrogen using the OVA dilution probe. Remember to correct for the 

dilution before inserting the OVA concentration reading into the 

calculation in Table 4-1. 

4-9 
o Check the VOC concentration at several points in the tent with the 

OVA to insure that the tent contents are at steady state. 

o Measure the hydrocarbon VOC concentration in the tent with the OVA 

at three different nitrogen flow rates. Typically the flow rates 

will be 40, 30 and 20 liters/minute if there is no OVA response at 

the higher rates (i.e., the mass leak rate from the component is 

very low). After each adjustment of the nitrogen flow, check the 0? 

concentration to ensure it stays below 5%. Alternatively, collect 

samples in Tedlar or aluminized sample bags by drawing sample out of 

the bag with a portable sampling pump. 

o Remove the tent and any plugs from the component and collect any 

condensate on the inside of the tent in a plastic graduated 

cylinder. Record the amount collected and the elapsed time the tent 

was on the component. 

o If there is liquid dripping from the component, collect the drips 

for a timed period which produces enough collected material for 

accurate volume measurement. Record the amount in the report, but 

do not add it to the vapor leak rate. 

4.3 SOURCE ENCLOSURE 

To measure the leak rate from any given fitting accurately, it is 

necessary to isolate that fitting from the ambient air. This is accomplished 

by an enclosure (or tent) formed around the leak source. Appropriate tent 

material must be selected, so that the substances found in the process fluid 

are contained within the tent. For example, because polyethylene is permeable 

to hydrocarbons, it is an inappropriate tent material. By comparison, Mylar 

plastic (polyethylene terephthalate) is well suited to this function as it 

does not absorb significant amounts of hydrocarbons, it is very tough, and it 

has a high melting point (250°C). Other suitable materials are Tedlar (PVF 

film) and Teflon (fluorocarbon resin). For convenience, Mylar will be used as 

an example of tent material in the following discussions. The thickness of 

the tent material can range from 1.5 to 15 mil depending on the type of 

equipment being bagged. A typical tent is shown in Figure 4-4. The 

enclosures should be kept as small as practical. This has several beneficial 

effects: 

o the time required to reach equilibrium is kept to a minimum, 

o the time required to construct the enclosure is minimized, 

o a more effective seal results from the reduced seal area, and 

•10 
,fpr»H_Mi-.i,-« •-•-•>•jr^i'---**-'-

P.1 

Surgical 

tubing 

pressure tap 

Outlet 

to 

pump 

Figure 4-4. Tent construction around the seal area of a vertical pump. 

4-11 
_EL2.. 

o condensation of heavy hydrocarbons inside the enclosure is minimized 

or prevented due to reduced residence time and decreased surface 

area available for heat transfer. 

Tent construction for individual sources is discussed in the sections 4.3.1 

through 4.3.5. 

4.3.1 Valves 

The most important property of the valve that affects the type of 

enclosure (tent) selected for use is the metal skin temperature of the area 

enclosed by the tent and around which the seal is made. 

At skin temperatures of 400°F or less, the valve stem and/or stem support 

can be wrapped with 1.5-2.0 mil Mylar and sealed at each end and at the seam 

with duct tape. A leak-tight seal is not required when the vacuum method of 

leak measurement is used. Actually, it is better to allow for some areas of 

incomplete sealing to provide access for air being drawn through the tent by 

the vacuum pump in.the sampling train. 

Two bulkhead fittings are then attached to the Mylar tent. One is for 

the water manometer or differential pressure gauge connection, and the other 

is for the line to the sampling train. If, after starting the sampling, a 

vacuum greater than 0.1 inches of water is found to exist in the tent, a hole 

can be added on the side of the tent opposite the outlet to the sampling 

train. This provides an additional entrance for the dilution air, and reduces 

the vacuum in the tent while sampling. The Mylar tent must be constructed to 

enclose the valve stem seal and the packing gland seal. 

When skin temperatures are in excess of 400°F, other methods of tenting 

the valves can be used. In one method, adjusted metal bands or wires are 

wrapped around all hot points that are in contact with the Mylar tent 

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 wrapped around the 

valve leak area. In a previous study, seals were made using adjustable metal 

bands. At points where the shape of the equipment prevented a satisfactory 

seal with metal bands, the foil was crimped to make a seal. It was necessary, 

in some of these instances, to use a relatively high capacity vacuum pump to 

insure a constant inflow of air through all seal areas. 

4-12 
Mixed-phase valve leaks are enclosed with the same type of tent described 

above. The rate of leakage of liquid is measured by collecting it over a 

measured length of time. A low point is formed in the tent to collect the 

liquid so its volume can be measured and converted to a mass rate. The total 

mass leak rate can then be estimated by adding the liquid mass leak rate to 

the gas mass leak rate. 

4.3.2 Pumps and Agitators 

As with valves, the property of most concern when preparing to sample a 

pump or agitator is the metal skin temperature at areas or points that are in 

contact with the tent material. 

At skin temperatures below 400°F, Mylar plastic and duct tape are 

satisfactory materials for constructing a tent around a pump or agitator seal. 

The vast majority of centrifugal pumps in VOC service have a housing or 

support that connects the pump drive (or bearing housing) to the pump itself. 

The two supports normally enclose about half of the area between the pump and 

drive motor, leaving open areas on the sides. It is usually a relatively 

simple matter to cut panels to fit these remaining open areas. In a previous 

study, the panels were cut from 14 mil Mylar. Bulkhead fittings for the 

outlets to the water manometer and sampling train are placed through one Mylar 

panel and sealed. An opening (hole, bulkhead fitting) is made in the opposing 

panel, if necessary, to allow easier flow of dilution air into the enclosure 

around the seal. 

In many horizontal pumps, there is a line from the bottom of the lower 

metal support to a drain. This line serves as a drain for coolant, sealant, 

and/or process liquid leaking from the pump seal. This line (and all other 

lines from the enclosure) should be sealed off to avoid drawing air and 

hydrocarbon vapors from the drain back up to the sealed enclosures. If there 

is no liquid flowing through this drain line, it can be plugged off. If 

liquid is going to the drain, a short length of hose or tubing can be attached 

to the end of the drain line and looped upward to form an effective liquid 

seal. 

In the 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. This enclosure can be made of 14 mil Mylar, 

since this thickness provides considerable strength and rigidity. 

4-13 

O B 
P.4 

Reciprocating pumps present a somewhat more difficult tenting problem. 

If supports are present, the same type of two-panel Mylar tent 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 similar to 

that used for centrifugal pumps 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 made 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 

duct tape. 

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 insulating tape, adjustable metal bands, or wire. 

In cases where liquid and vapors are leaking from a pump, the enclosures 

described above for valves can be used. The outlet from the tent to the 

sampling train is placed at the top of the enclosure and as far away from 

spraying leaks as practical. Thus, entrainment of the liquid into the 

sampling train (and cold trap) is avoided. The rate of leakage of liquid is 

measured by collecting it over a measured length of time. A low point is 

formed in the tent to collect the liquid so its volume can be measured and 

converted to a mass rate. The total mass leak rate can then be estimated by 

adding the liquid mass leak rate to the gas mass leak rate. 

4.3.3 Compressors 

In general, the same types of tents that are suitable for pumps can be 

directly applied to compressors. The construction and application of these 

enclosures have been described in the preceding discussions of pump sampling 

and will not be repeated in this section. 

Compressors generally handle light gases, and in many cases, the seals 

are enclosed. The seal enclosures are vented to the atmosphere at a 

high-point vent or may be vented to the blowdown/flare system. 

If the seals are vented to a high-point vent, this vent Hn e can be 

sampled. A Mylar bag can be constructed and sealed around the outlet of the 

4-14 
P.5 

vent and connected to the sampling train. The leak rate from the vented 

compressor seals is then measured using the normal flow-through method. 

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 done at 

this intermediate point. 

When enclosed compressor seals are vented by means of induced draft 

blowers or fans, the outlet from the blower/fan can be sampled. In a previous 

study, a pitot tube was used to determine the air flow rate. A sample of 

the outlet air was taken and returned to the laboratory for methane and 

nonmethane hydrocarbon analysis. Ambient air samples were taken around the 

compressor seal enclosure area at the same time and were analyzed for 

hydrocarbon content. The compressor seal leak rate was determined from the 

knowledge of air flow rate, its hydrocarbon content, and the hydrocarbon 

content of the ambient air. 

4.3.4 Flanges 

In most cases, the physical configurations of flanges lend themselves 

well to the determination of leak rates. For small to moderately large leaks 

from flanges with metal skin temperatures up to about 400°F, a narrow section 

of Mylar film can be used to span the open distance between the two flange 

faces of the leaking source. The Mylar is attached and sealed to each flange 

with duct tape. Connections (bulkhead fittings) for the water manometer and 

sampling train are attached to the Mylar. 

When testing flanges with skin temperatures above 400°F, the outside 

perimeter of both sides of the flange connection are wrapped with asbestos 

insulating tape. Then, a narrow strip of aluminum foil can be used to span 

the opening between the flange faces. This narrow strip of material can be 

sealed against the asbestos 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 which 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 many of these devices are high above grade, accessibility to the 

4-15 

•IH 
P.6 

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. And as discussed 

previously in the section on screening, 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 ACCURACY CHECKS 

An accuracy check is normally performed in the laboratory by sampling an 

artificially induced leak rate of a known gas. This effectively points out 

any bias in the test methods and defines the variance component due to 

sampling. If the result is outside the 80 percent to 120 percent recovery 

range, the problem should be investigated and corrected before sampling 

continues. The problems and associated solutions should be noted in the test 

report. 

4.5 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, calibration, analytical techniques for condensate, 

and quality control. These are guidelines for the field sampling team and are 

not meant to be a detailed protocol for the laboratory personnel. Laboratory 

personnel should be well versed in the analysis of hydrocarbon mixtures and 

should design their specific analyses to the samples being examined. 

4.5.1 Analytical Instrumentation 

The selection of analytical instrumentation is critical to identification 

of individual organics in the sample. The instrument of choice depends on the 

type of sample being processed. Organic components of the streams of some 

process units may produce widely differing responses with an FID. For this 

reason, more comprehensive analyses by gas chromatography must be performed to 

identify individual components. FID gas chromatographs or electron capture 

gas chromatographs are commonly used to identify individual components of a 

sample. Other considerations besides instrument choice are the type of column 

used, and whether or not temperature programming is necessary to separate out 

4-16 
P.7 

individual components of the process stream with sufficient resolution. An 

example of a gas chromatograph that has been used in previous studies is the 

Hewlett Packard 573-A Dual FID Gas Chromatograph.12 

For some process streams such as ethylene and cumene, total hydrocarbon 

analyses are satisfactory. The response of the FID to these compounds is 

similar; therefore an instrument such as the Byron Total Hydrocarbon Analyzer 

(THC) can be calibrated with a single representative hydrocarbon. This 

instrument has an FID and resolves samples with methane and nonmethane 

components. The emission streams can then be analyzed for the total 

hydrocarbon content with reasonable accuracy. 

4.5.2 Calibration 

Proper calibration of both the laboratory and field instruments for the 

wide range of organic species is different. Each instrument must be 

calibrated with the appropriate species each day it is used. 

Calibration of the portable hydrocarbon detector should be done with 

standards of hexane in air. A hexane standard of approximately 2,000 ppmv is 

available in a bottle supplied and certified to +2 percent by the 

manufacturer. Higher concentrations than this may lead to problems involving 

condensation at ambient temperatures. Lower concentrations must be generated 

by dilution. 

The total hydrocarbon analyzer can be calibrated with the same hexane 

standard. The standard is related to an NBS propane standard by measuring the 

concentration of the NBS standard using the total hydrocarbon analyzer after 

the analyzer has been calibrated with the hexane standard. 

The gas chromatograph is calibrated with either gas standards generated 

from calibrated permeation tubes containing individual VOC components or 

bottled standards of common gases. 

4.5.3 Analytical Technioues for Condensate 

Any condensate collected by the ice bath in the sampling train 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. 

Both the aqueous and organic phases should be analyzed by gas chromatography 

if water-miscible organic compounds are present. 

4-17 

iiBH^HHlHI|^^^^^HH-^^^^^^^^^^^^^BBB^^iHi^^^KU 
P.8 

4.5.4 Oualitv Control for Analytical Technioues 

Blind standards should be prepared and submitted for analysis. The blind 

standards are prepared by diluting or mixing primary standards in a prescribed 

fashion so that the resulting concentrations are known. The calculated 

concentrations and the analytical results should be logged into a laboratory 

notebook. If the results are not within 25 percent of the certified level, 

further analyses must be performed to determine the reason. Such a procedure 

not only defines the analytical variance component and analytical accuracy, 

but it serves to point out equipment malfunctions and/or operator error before 

many data are affected. 

4-18 
1 . * . 

' 1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

P.9 

SECTION 5.0 

REFERENCES 

Code of Federal Regulations, Title 40, Part 60, Appendix A. Reference 

Method 21, "Determination of Volatile Organic Compound Leaks." 

Harris, G.E. and G.J. Langley. (Radian Corporation.) Detailed Screening 

Plan for Fugitive Emissions from SOCMI Process Units. (Prepared for U. 

S. Environmental Protection Agency.) Research Triangle Park, N.C 

December 1979. 

Joseph, G.T. and M. Peterson. (Northrop Services, Inc.) APTI Course 

S1.417 Controlling VOC Emissions from Leaking Process Equipment Student \ 

Guidebook. (Prepared for U.S. Environmental Protection Agency.) Research 

Triangle Park, N.C. Publication No. EPA-450/2-82-01. 1982. 

U. S. Environmental Protection Agency. Response Factors of VOC Analyzers 

at a Meter Reading of 10,000 ppmv for Selected Organic Compounds. 

Publication No. EPA-600/2-81-051. 1981. 

U. S. Environmental Protection Agency. Response of Portable VOC 

Analyzers to Chemical Mixtures. Publication No. EPA-600/2-81-110. 1981. 

Brown, G.E., et al. (Radian Corporation.) Response Factors of VOC 

Analyzers Calibrated with Methane for Selected Organic Compounds. 

(Prepared for U. S. Environmental Protection Agency.) Research Triangle 

Park, N.C. Publication No. EPA-600/2-81-022. September 1980. 

Anastas, M.Y., and H.J. Belknap. (PEDCo Environmental, Inc.) Summary of 

Portable VOC Detection Instruments. (Prepared for U. S. Environmental 

Protection Agency.) Washington, D.C. Publication No. EPA-340/1-80-010. 

March 1980. 

Langley, G.J., and L.P. Provost. (Radian Corporation.) Revision of 

Emission Factors for Nonmethane Hydrocarbons from Valves and Pump Seals 

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