United States
            Environmental Protection
            Agency
            Office of Air Quality
            Planning and Standards
            Research Triangle Park NC 27711
EPA-450/3-86-002
January 1986
            Air
&EPA
Emission Factors
For Equipment Leaks
Of VOC And HAP

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                                        EPA-450/3-86-002
Emission Factors for Equipment Leaks
                of VOC and  HAP
                         Prepared by:

                       Radian Corporation
                3200 E. Chapel Hill Road/Nelson Highway
                  Research Triangle Park, NC 27709
                       Under EPA Contract
                        No. 68-02-3889
                                           *"«*
                      230 South Dearborn Street
                      Chicago, Illinois
              U.S. ENVIRONMENTAL PROTECTION AGENCY
                    Office of Air and Radiation
               Office of Air Quality Planning and Standards
               Emission Standards and Engineering Division
              Research Triangle Park, North Carolina 27711

                        January 1986

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                                        DISCLAIMER

This report has been reviewed by the Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, and approved for publication as received from the Radian Corporation. Approval does
not signify that the content necessarily reflect the views and policies of the U.S. Environmental Protection
Agency, nor does mention of trade names or commercial products constitute endorsement or recommenda-
tion for use. Copies of this report are available from the National Technical Information Services, 5285 Port
Royal Road, Springfield, Virginia 22161.

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                                TABLE  OF CONTENTS


                                                                       Page

 LIST OF TABLES	       y

 LIST OF FIGURES	      v1

 Section 1.0 - OVERVIEW	     l_l

 Section 2.0 - FUGITIVE EMISSION SOURCES  	     2-l

     2.1  VALVES	         2_3

     2.2  PUMPS	                                           0  ,
                              	     £-0

     2.3  COMPRESSORS	     2_10

     2.4  RELIEF DEVICES	     2_n

     2.5  OPEN-ENDED VALVES AND LINES 	     2-15

     2.6  SAMPLING SYSTEMS	       2_15

     2.7  FLANGES AND OTHER CONNECTORS	    2-17

Section 3.0 -  EMISSION FACTORS	      3.!

     3.1  STUDIES CONSIDERED IN SOCMI  EMISSION FACTOR DEVELOPMENT      3-1
          3.1.1  Petroleum Refining Assessment Study.                  ? 9
          3.1.2  Four Unit EPA Study	        	    ," =
          3.1.3  EPA 6-Unit Study	        	    ,"?
          3.1.4  DuPont  Study	.'.'.'	    35
          3.1.5  Exxon Cyclohexane Study. .	    *%
          3.1.6  EPA 24-Unit Study	!  !  ! !	    35
          3.1.7  Maintenance Study	'	    3 6
          3.1.8  Analysis  Report and Revision
                    of SOCMI Emission  Factors  	    3.7
          3.1.9  German  Studies  on Fugitive  Emissions !  	    37
          3.1.10  Union Carbide Study	              	    3 «
          3.1.11  Analysis  of Allied HOPE Unit  Data.'	    7 q
          3.1.12  SCAQMD  Study	,  [	    ?'|
          3.1.13  Coke  Oven By-product  Recovery and	
                    Gas  Plant Studies	    3_10

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                         TABLE OF CONTENTS (CONTINUED)

                                                                      Page
     3.2  ERA'S CHOICE OF DATA FOR SOCMI EMISSION FACTORS	    3-10
     3.3  EMISSION FACTOR DEVELOPMENT	          3.12
          3.3.1  Detailed Procedural Method	'.'.'.'.    3-12
          3.3.2  Statistical Considerations	      3-14
          3.3.3  Leak/No-Leak Approach	 . .  .    3-17
                 3.3.3.1  Generation of Leaking and
                              Nonleaking Emission Factors	    3-19
                 3.3.3.2  Computation of Average Emission Factors.    3-20
     3.4  EMISSION FACTORS PRESENTED IN THE AID	    3-22
     3.5  EXAMPLE HYPOTHETICAL CASE	    3.27
Section 4.0 - EMISSION REDUCTION 	    4_!
     4.1  OVERVIEW OF TECHNIQUES	    4_j
     4.2  LEAK DETECTION AND REPAIR (LDAR)	    4.2
     4.3  SUMMARY OF EMISSION REDUCTIONS 	    4.7
Section 5.0 - LIST OF REFERENCES	    5_!
                                      IV

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                                LIST OF TABLES
Table                                                                 Page
 3-1      FUGITIVE EMISSION STUDIES IN THE AID	     3.3
 3-2      LEAK FREQUENCIES AND EMISSION FACTORS:
               REFINING ASSESSMENT STUDY	     3.4
 3-3      LEAKING AND NONLEAKING EMISSION FACTORS FOR
               FUGITIVE EMISSIONS (kg/hr/source)	     3-21
 3-4      AVERAGE EMISSION FACTORS FOR FUGITIVE EMISSIONS
               IN SOCMI	     3.23
 3-5      LEAK FREQUENCIES BY PROCESS  FOR EQUIPMENT
               IN 24  SOCMI UNITS	     3.28
 3-6      ESTIMATE OF "UNCONTROLLED" FUGITIVE  EMISSIONS  FOR
               A HYPOTHETICAL CASE	     3_2g
 4-1      LDAR INPUTS AND  COMPUTED REDUCTIONS  FOR
               SOCMI/MONTHLY  MONITORING  	     4.4
 4-2      LDAR MODEL  RESULTS  FOR SOCMI VALVES  AND PUMPS  	     4.5
 4-3      CONTROL LEVELS FOR  SOCMI  FUGITIVE  EMISSIONS:
               NSPS AND CTG	     4.8

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                                LIST OF FIGURES

Figure                                                                Page
 2-1      Estimated Emissions by Source Subcategories of SOCMI .  .     2-2
 2-2      Diagram of a Gate Valve	     2-5
 2-3      Diagrams of Valves with Diaphragm Seals	     2-7
 2-4      Diagram of a Double Mechanical Seal
               (a)  Back-to-back Arrangement 	     2-9
               (b)  Tandem Arrangement 	     2-9
 2-5      Simple Single-stage Reciprocating Compressor 	     2-12
 2-6      Pressure Relief Valve in a Basic RD/PRV Combination. .  .     2-13
 2-7      Schematics of Closed Purge Sampling Systems	     2-16
 3-1      Cumulative Distribution: Cumene Gas Valves 	     3-13
 3-2      Cumulative Mass Emissions Distribution:
               Cumene Gas Valves	     3-15
 3-3      Cumulative Distribution of Total Emissions by Screening
               Values - Comparison of Confidence Intervals ....     3-18
 3-4      Comparison of Emission Factors: Gas Valves 	     3-25
 3-5      Comparison of Emission Factors: Light Liquid Valves
               and Pumps	     3-26
 4-1      Schematic Diagram of the LDAR Model	     4-3
                                       vl

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 GLOSSARY


 Average emission factor  - the per component mass emission rate applicable to
     populations of sources, not individual component measurements.

 Leak definition - the monitoring instrument reading selected as the trigger
     value for initiating some action such as maintenance; e.g., 10,000 DDRIV
     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 values at or above the leak
     definition.

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  values less than the leak
     definition.

Screening value -  monitoring instrument  reading generally given in
     concentration units; e.g.,  ppmv.
                                     vn

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                                 1.0  OVERVIEW

     One of  the first major  efforts  in the field  of  fugitive hydrocarbon
emissions was the  Joint  Refinery Study initiated by the  Los Angeles County
APCD, the California State Department  of  Public  Health,  and the U. S. Public
Health Service  in  August 1955.  Additional studies were  made subsequent to
this original work.   But it was not  until  the mid- to  late-1970's  that a
renewed interest was sparked by two events.
     The Clean Air Act, originally passed in 1970, laid out the groundwork for
the  U.  S.  Environmental  Protection Agency  (EPA)  to  set  standards  of
performance for newly constructed, modified, or  reconstructed sources of air
pollution which may endanger  the public health or welfare.   Since these  New
Source Performance Standards  (NSPS) were to be promulgated  for  a  large  number
of industries or industry segments, a ranking was developed in accordance with
the 1977 amendments so that  those  industries with the highest  potential  for
impacting public  health  would  be  examined first.  The  Synthetic Organic
Chemical Manufacturing Industry (SOCMI) was placed  first on  the Priority  List
of industry  categories  as the  single  most significant contributor  to  air
pollution.
     Around this same time,  an  extensive  study of atmospheric emissions from
petroleum refining  was  conducted.   The study was  initiated  to  evaluate
existing and developing refining emissions control  technologies and  to  assess
the potential impact of atmospheric emissions from refining on the surrounding
environment. As the program  began,  fugitive emissions (i.e.,  emissions  from
various types of equipment such as valves, pumps, compressors, pressure relief
devices, and connectors)  were found to  be a large (if not  the largest)  source
of hydrocarbon emissions from refining. As a result, the scope of the Refining
Study was expanded to include  the  quantification of fugitive emissions. This
particular objective was given added emphasis as a result of the Clean Air Act
and its emissions  offsets regulations, which  require  emission factors  for
evaluating  compliance.
     Subsequent to the refinery assessment, EPA's  research  group conducted
additional  studies in chemical  plants.   Twenty-four separate chemical  units
                                    1-1

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were evaluated.  Of these units, six were studied more closely for the effec-
tiveness of  emission  control  techniques.  These  new data, coupled  with  a
review of data from other studies, were  compiled  into  an Additional  Informa-
tion Document  (AID) on  fugitive emissions of VOC  in SOCMI.  The AID details
EPA's conclusions about how to estimate emissions  and emissions reductions for
fugitive emissions of VOC.
     The concepts behind fugitive emissions  and their  control  are  relatively
simple;  however,  the  understanding  of fugitive  emissions  data is  quite
complex.  Not  surprisingly, the  estimates of emissions,  emission reductions,
and costs  still  draw  the bulk  of comments  and questions from  regulatory
personnel as well as  industry representatives.   This document addresses  the
development of emission factors for fugitive VOC emissions (or equipment leaks
of VOC).  The comments and questions most often raised are given below with  a
brief  response.   Detailed  responses  are  contained  in  the   substantial
literature generated by EPA to support the  fugitive emission standards.

1.   My emissions are  already low because of OSHA  regulations.   Why,  then, are
     there also environmental  emissions standards  for equipment leaks?

     Environmental emissions  standards for  equipment  leaks  have different
purposes from  OSHA  regulations.   Indeed,  they may even  result in  different
environmental benefits.  Environmental standards  focus  on reducing  the  total
quantity of emissions, in this case VOC emissions, to the atmosphere.  On the
other  hand,  OSHA  regulations,   unlike environmental  standards, do not
necessarily limit mass emissions directly.   OSHA regulations permit control  of
emission sources by substitution of  chemicals with  less hazardous  materials,
process  modifications,  worker  rotation,   process  or  worker  isolation,
ventilation  controls,  or modification of work  practices.  Such  control
measures are focused on reducing occupational exposure  (as  a concentration),
not necessarily reducing mass emissions of VOC to  the atmosphere.
     The  idea  of workplace  concentration  reduction  is the  key to OSHA
regulations.   It  is   often  thought  that  OSHA  regulations  result  in
concentrations in the  workplace well  below  10,000  ppmv, the  concentration
                                    1-2

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level used to identify leaking components under the environmental  regulations.
An important distinction is that environmental standards call for measurement
of VOC concentration  at the leak  interface,  not in the  surrounding  area.
Field studies have shown that the concentration of VOC decreases exponentially
with increasing distance from the leak interface.  Thus, a leak determined  at
the interface will rarely  be seen  at  a  distance  only 20 cm from the  surface
and yet  substantial  quantities of  VOC  may be emitted  from such a  leak.
Dispersion and dilution of the VOC into the surrounding area mask the severity
of emissions  from  the leak.  As a  result,  while OSHA regulations may well
reduce the concentration of VOC in  the workplace,  they  do  not  guarantee that
the total mass emissions from leaks are also reduced.

     I already control  my  emissions under the Control Techniques Guideline.
     Am I subject to more environmental  standards for equipment leaks?

          There are several  environmental  regulatory programs in existence:
National  Ambient Air  Quality Standards  (NAAQS),  State  Implementation Plans
(SIP's),  National  Emission Standards for Hazardous Air  Pollutants (NESHAP's),
and  New  Source Performance  Standards (NSPS's).   All  of  these  types of
regulations work toward meeting the goals of the Clean Air Act.
     The control techniques  guideline documents  (CTG)  are  presentations  of
what is  considered  by EPA to  be  "reasonably  available control technology"
(RACT).  RACT-based environmental  regulations are established by States  to
correct  existing  air  pollution problems,  focusing on existing  sources   in
particular.  The control techniques discussed in the CTG for SOCMI fugitive
emission sources are  completely consistent  and compatible  with standards  set
under other environmental programs.  The resultant control levels may vary due
to differences in the frequency of monitoring or  the use of  equipment control
techniques.
     RACT-based standards  would not be  duplicative with standards set  under
other  environmental  programs.   NSPS's  are  applicable  only  to   newly
constructed, modified,  or  reconstructed  facilities.   Since  they  apply to  new
facilities, the requirements of NSPS  are generally more stringent than those
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of RACT-based standards set for existing facilities.  In the case of fugitive
emissions control, for example, NSPS-based standards would require monitoring
of equipment more frequently than required under RACT-based standards.
     Similarly, NESHAP's are established for all facilities, new or existing.
Again,  the  difference  between requirements  of NESHAP's  and  RACT-based
standards is  basically the degree  of stringency.   NESHAP's  require more
frequent monitoring than RACT-based standards  for  fugitive emission  sources.
Furthermore,  NESHAP's  often require  the  use  of  control  equipment  where
RACT-based standards may only  require work  practices such as leak detection
and repairs.  Since NESHAP's are  applicable  to existing  sources,  as well as
new sources, their more stringent requirements would need to be met,  in excess
of RACT-based standards for existing sources.
     In terms  of emissions estimates,  process units  complying with  the
RACT-based standards presented  in the  CTG  would indeed exhibit  lower emissions
than would be presented by the simple use of the SOCMI emission  factors.   As
shown in Table 4-3 of this document varying degrees of emission reduction are
achievable under the different  standards (NSPS, NESHAP, CTG).  Emissions from
process units complying with the CTG  can be  estimated by applying  the  proper
efficiency to the estimated uncontrolled emissions.
2.   Emissions from my process unit are lower than the SOCMI factors indicate.
     I control the  emissions  by looking for  leaks,  sometimes smelling for
     them.  Why should my unit be covered by these standards?

     The chemical  industry  is comprised of  numerous  processes producing  a
large number of chemicals.  Each process unit may by itself  emit a  relatively
small amount of VOC;  however,  the  total  amount of VOC from  the  industry  is
significant.  Therefore, individual processes or units are not exempted.
     EPA recognizes the wide variability of leak percentages on a unit process
basis throughout the industry.  Of the 24 units surveyed in the 24-unit study,
15 demonstrated overall  leak  frequencies for valves in  gas/vapor  and light
liquid services of  less  than  2 percent.   Environmental  standards,  therefore,
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provide  alternatives  for units that exhibit  low-leak characteristics.  For
example, an owner  or  operator of a process unit may  elect  to comply with a
performance limit  of  2  percent leaking valves.   In such a  case,  the  routine
leak detection and repair  practices  required  by the basic  rule would  not  be
followed.  Instead, the process unit would be screened (using Reference Method
21) on an  annual  basis  to  demonstrate  that the unit does indeed  demonstrate
the low  leak characteristics of less than 2 percent of valves leaking.
     EPA selected  this  value based upon  cost and  emissions  analyses  which
showed that  monthly leak  detection  and repair for  valves  is not  a  cost
effective  control  technique  for  process  units exhibiting  very  low  leak
characteristics.   These  characteristics may result from the  nature of  the
chemicals processed, tight plant design, or enhanced maintenance.

     Fugitive emissions from my process unit are lower than  estimated using
     SOCMI factors.   I  have verified the  low leak rates by  measuring the
     concentration and flow rate at the ventilation outlet.

     It may well be true that actual  fugitive emissions from any given process
unit are lower than the  emissions  estimated using  the average SOCMI emission
factors.   The SOCMI factors, however, are applicable to the  industry at large,
and should be applied to any individual unit  where the leak  frequencies for
equipment have not been established  by a rigorous  application  of Reference
Method 21.  Concentration and ventilation flowrates give an indication of  the
magnitude  of  fugitive  emissions;  they would not  necessarily provide  an
accurate estimate  of  total  VOC fugitive emissions.   For process  units that
would have ventilation  outlets,  all  potential sources of fugitive  emissions
are not generally enclosed in the building.  Also, large buildings  that  house
chemical  process units  are  not  generally  air  tight;  therefore,  some VOC may
not be accounted for in the ventilation air.
     Furthermore,  the  evaluation of fugitive emissions from an enclosed
building represents a complex measurement problem.   All emission points from
the building  would need to be  measured  simultaneously for  3  hours  to
constitute an emissions test.  This is the only way  to ensure  that  all
emissions from non-vented  sources  would be  accounted for.   Since fan  curves
                                      1-5

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are inaccurate for emissions measurements, EPA flow measurement methods would
need to be employed.  These methods require obstruction-free ducting on either
side of the fan,  a situation not always found in  ventilation  applications.
Finally, when  applied  to the estimation  of hazardous air  pollutants,  the
analytical  techniques  used  must be  capable of  speciation of  organic
constituents.   Common detectors  are not always adequate for this task.
     Concentration and ventilation flow rate could indicate that emissions are
lower than estimated by SOCMI factors.  This technique, however, would not be
sufficient  to  prove  that  emissions  are  low.  There is  an acceptable
alternative to estimating emissions.  Conducting a rigorous  Method  21  survey
would lead  to computing percent  leaking  values  (leak  frequency)  for all
equipment types.  These values could  then  be used  to  construct  unit-specific
overall  emission factors using "leaking" and "nonleaking" emission  factors as
described in  Section  3.3.3.   Using such a  procedure  would  develop  emission
factors consistent  with the  vast amount of fugitive VOC  emissions  data
gathered  to date.  The  unit-specific  emission  factors, applied  to  the
equipment counts for  the process unit,  lead to the overall  estimate  of VOC
emissions.  As noted in this document, pre-survey maintenance would  invalidate
the results of the survey and estimates.

3.   It is  not  appropriate  to use petroleum refinery  test data to  determine
     SOCMI emission factors.

     The development of VOC emission factors for  equipment leaks is  founded on
the concept that  equipment leaks VOC  at  the same rate  regardless  of the
industry or process unit.  Total  emissions or average  emission rates may vary,
however,  based  upon the relative percentage of leaks  found in different
process units.   In  developing VOC emission  factors for  equipment  leaks  in
SOCMI, EPA  examined  and  considered every study available.  This  evaluation,
explained  in  the AID,  makes it  clear that  the  data contained  in  the
Maintenance Study  and 24-Unit Study  are  not the  sole source  of data on
fugitive  emissions.   Numerous studies  have  been  conducted  and these were
reviewed  in the AID,  pointing out both strengths  and weaknesses associated
with each  study.   To gain maximum utility  of the  data from these  studies,
interpretation of  the  data  is required, drawing  upon  the strong points of  a

                                      1-6

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study while considering its weaknesses.  This evaluation and interpretation of
the data was done in the context of the whole base of fugitive emissions work;
it was  not done just  for isolated studies.   Based upon this  review and
analysis,  it was determined that the relevant data  from  different  studies  had
to be  merged and transformed  to provide  a useful  method  for estimating
emissions.  One  of  the most  important studies was the  Petroleum Refining
Assessment.
     The Petroleum Refining Assessment was  an enormous study of VOC  emissions
from all facets of refining.  A major  goal  of the work  was  the investigation
of fugitive emissions  and  the  development  of emission factors that  could  be
used to estimate fugitive VOC emissions.  The research program, therefore, was
designed to gather data that would lend itself to generation of such factors.
As a result, the mass  emissions data collected  during the Petroleum Refining
Assessment represent the best  available data on VOC emissions from  fugitive
emission sources.  Mass emissions data were gathered  on sources in  chemical
units to evaluate the effects of maintenance on emissions.  The data were  not
collected  with emission  factor development as the  primary  goal;  therefore,
these mass emissions data  do  not  represent the highest quality data on mass
emission of VOC from fugitive emission sources.
     The work done in petroleum refineries  and subsequent studies  in chemical
process units indicated that actual mass emissions  (as  described  by emission
factors) are related  to the number of leaking components  compared  to the
number of  non-leaking components.  The mass emissions data  from the  Petroleum
Refining Assessment served  as  the basis of emission  factor development for
fugitive VOC  sources  in  SOCMI.  Recognizing  that  leak frequencies  for
equipment  in  SOCMI  were  different  from those  reported  in the Refining
Assessment, EPA  used  leak  frequency  data   for  SOCMI  to weight  the mass
emissions data from the Petroleum Refining Assessment in generating  the SOCMI
average emission factors.   This procedure  is detailed in the AID  and in this
report.   In the AID, EPA compared the  emission  factors  generated using this
approach with the  factors  developed as part of  the  study  of maintenance
effects in chemical  units.   The factors were found to  be similar except in the
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case of gas/vapor service valves.  Therefore, the chemical  unit data were used
to generate the emission factor for valves in gas/vapor service.

4.   Using average  SOCMI  emission factors overestimates emissions  from my
     process unit,  because  of  the inherent nature of  the  chemicals I use,
     their volatility, their value, etc.

     In gathering data on the SOCMI, EPA sampled a number of vastly different
chemical  process  units.   Characteristics of  individual  chemicals  were
considered in selecting the  process  units  sampled during the 24-Unit Study.
Hi-volume,  low-priced  chemicals  were  included,  as   were  lower-volume,
higher-priced chemicals.  Chemicals  with  widely divergent  volatilities were
included  along  with  chemicals  that  are  particularly  odoriferous.   Not
surprisingly, the frequencies of leaks found  ranged from nearly zero to thirty
percent.  Leak frequencies provide an  indication  of  the relative quantity of
mass emissions and  it is  apparent from this  range of  leak  frequencies  that
fugitive  emissions  from some  units  will  be  higher  and some  lower than
estimates based on the SOCMI factors.  The mass emissions estimates generated
by EPA using the average SOCMI emissions factors represent an  average that  is
applicable to  industry-wide  emissions estimates.   Without conducting  a
rigorous Method 21 survey to determine the leak frequency (thereby generating
average emission  factors  based on the leak/no-leak  factor  components),  the
average SOCMI emission  factors  stand as  the  best estimators of  fugitive  VOC
emissions currently available.

5.   I have measured  emission rates  for some sources in my  plant.  Why  aren't
     these measurements better than the estimates EPA supports?

     The  emission factors  supported  by EPA are based  upon  a  vast amount of
data gathered  on fugitive  VOC  emission  sources  using  rigorous sampling
protocols.   The   factors  for  each equipment  type  have  been  developed
considering two types of  data:  leak frequency data and mass emissions  data.
The entire distribution of mass  emissions from  each  class of  sources  has  been
                                    1-8

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considered.  For example, 76 individual measurements of mass emission from gas
valves were taken across the distribution of screening  values  (i.e.,  analyses
measurements)  to  develop a  mass emissions correlation  to be  applied  to
screening  data.   Similar distributions of  mass  emissions measurements  are
necessary  for  each equipment  type to  develop the  correlations used  in
generating average emissions factors.
     Furthermore, the correlations represent only  part  of what goes into the
emissions  factors.  Screening  data  (i.e,  screening values for all  equipment
components are  needed  to ensure that  the  entire  distribution of screening
values is  included in emission factor development.
     Limited,  isolated  measurements  of emission rates  for "some"  sources,
therefore, are not representative of the entire distribution of sources in the
process unit.  Only by  considering  the entire  distribution can the emission
factor be representative.

6.   How do I estimate emissions for my plant...
           (A) if I have no data?
           (B) if I have some measurements?
           (C) if I have done a rigorous Method  21  survey?

     For process units  where no emissions data are  available,  estimates of
fugitive VOC emissions should  be made  using equipment  counts  and the  typical
average emission  factors developed  for  SOCMI.  The development of  these
factors given  in this  document,  was  explained  in  the Additional  Information
Document (AID) for VOC equipment leaks.
     In some cases, isolated  emission  rate  measurements may have been  made.
These measurements serve to give the  owner or operator  a "sense"  of  the
quantity of  mass  emissions  that might  be emitted from  the process  unit.
Again, however,  the  average  SOCMI  factors must be  employed  to  estimate
emissions  when  only  isolated mass emissions measurements have  been  made.
Isolated measurements do not  represent  the  entire  distribution of  screening
values and mass emission rates present in a process unit.
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      The  alternative  to  using  the  average  SOCMI  factors  is  to employ complete
 leak  frequency data  gathered  using a  rigorous  Method  21  survey on  all
 equipment types.   In  so  doing,  the leak/no-leak  approach described within can
 be  used to estimate emission factors for the specific process unit  screened.
 The resultant  "custom" emission factors would then be applied  to  the equipment
 counts  for the  specific process  unit  to  derive  the  total  fugitive  VOC
 emissions estimate  for the process  unit.  This procedure  is illustrated  for  an
 example case in Section  3.5.
      The  initial  step in generating surrogate emission  factors  is to use a
 rigorous  Method  21 survey on  all  sources  in the  process unit.   Method  21
 survey  is the  promulgated method  developed  by  EPA that   is used  to  monitor
 equipment for  leaks.   "Rigorous" means  that  all  sources  must be  screened  and
 that  no  maintenance  of  sources should  be conducted prior to screening.
 Conducting  maintenance  immediately prior to  conducting the Method  21  survey
 would bias  the leak frequencies generated  and thus invalidate the subsequent
 emissions estimates based upon the  leak frequencies.
      Emissions estimated in  this manner should  be  reviewed on a continual,
 i.e., annual,  basis.  For example,  as time passes, the leak frequencies  noted
 for  individual  equipment types  in  a process unit  may  change.   An  annual
 testing using  a  rigorous  Method  21  survey  would  ensure that  emissions
 estimates made using  "custom" emission factors would remain  representative of
 the process unit.

 7.    I am not  interested in  total  VOC emissions.  How do  I  estimate  emissions
     of a specific pollutant?

     The  estimates of VOC emissions represented  by the average SOCMI emission
 factors are total VOC emissions.  In many instances, only one component  in the
VOC stream is of interest and the estimate of emissions need  only reflect the
 specific  pollutant.   In  order to  reflect  compound-specific emissions,  the
estimates,  (or emission  factor)  should  be  apportioned  to reflect the  single
compound  (or component) of interest.  As illustrated in Section 3.5, a simple
mass fraction approach can be  applied; that  is,  for  equipment in VOC  service
                                      1-10

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containing X weight  percent  of the compound of interest, the emission  factor
could  be apportioned  by X/100 to  reflect emissions  of only the  single
compound.

8.   The control costs associated with leak detection  and repair are too  high,
     particularly  in light of  low emissions reduction.

     EPA based  its estimates of cost on cost  data  gathered from industrial
sources during  standards development  activities.  The  time  estimates  used for
equipment monitoring  (i.e.,  screening)  and for repair (of valves)  were based
on  information  supplied  by industry.  Cost and  cost effectiveness analyses
were conducted  for control of  individual  equipment types and for  complete
process units.  The costs  of regulatory alternatives  for equipment  types  were
judged to  be reasonable.  Likewise,  for   process units  considered on  the
average, the costs were found to be reasonable.
     EPA recognized, however,  that  not  all process  units could be considered
the model unit  average SOCMI norm, described  by model  equipment  counts and
average  SOCMI  emission  factors.   There are  tools  to  examine  regulatory
alternatives, as applied  to  an entire industry.  Therefore,  EPA  considered
alternative  control   options   for   those   situations  where  costs   became
unreasonable with  respect  to the amount of emissions controlled.   An example
of alternative standards allowed by  EPA is the 2  percent leaking  performance
limit for valves.  In its analysis of regulatory alternatives, EPA  determined
that the costs of  control  for  process units with  less  than  1  percent leaking
valves were too high for the relatively small  emissions  reductions  achievable
by routine leak detections and repair (monthly).  To allow  for variability in
measurements, EPA provided a  limit of 2  percent leaking.  As evidenced by data
gathered during the 24-Unit Study, there are  process  units  which  exhibit low
leak characteristics.  Owners or operators  of such units could opt  for meeting
a 2 percent (or lower) performance limit of leaking  valves,  as demonstrated by
an annual Method 21 performance test.
                                     1-11

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                         2.0   FUGITIVE  EMISSION  SOURCES

      The  term fugitive  emissions  used in the  context  of volatile  organic
 compounds  (VOC)  refers to leaks from  equipment such  as valves, pumps,  com-
 pressors,  etc.   The term  fugitive emissions,  also called  equipment leaks,
 means the  loss  of VOC through  the sealing  mechanism separating the  process
 fluid (contained  in  the  equipment)  from the  atmosphere.
      Fugitive emissions  are  generally  more  diffuse than most point sources of
 emissions,  especially  when considering the  collective  emissions  from widely
 dispersed  equipment  within a processing  plant.   As noted  by  the  emissions
 estimates  presented  in  Figure  2-1,  fugitive emissions  contribute a  large
 proportion  of VOC emissions  from the  chemical  industry  overall (about 35 per-
 cent).1
      As with  process-related sources,  fugitive emissions sources  are  readily
 identifiable  pieces  of  equipment  within  a   processing  plant.   But a  major
 difference  is in  the number  of  sources found in  any given process  unit.  While
 there may be only a  few  process-related sources  within  a process unit  (e.g., a
 reactor train and associated distillation columns  for purification),  there can
 be  hundreds or  thousands of valves, pumps,  flanges,  compressors,  and other
 fugitive emission sources within a process unit.  And while  fugitive  emissions
 on  a  per component basis can  be small, the  collective total  of emissions from
 all fugitive sources within  a process unit can be large.
      No single control technique is applicable  to  the control  of  all  types of
 equipment leaks.  Neither is a  single emission limit universally applicable to
 equipment leaks.   Rather,  each  type  of  fugitive  emission  source must  be
 considered  individually  in  establishing  appropriate,  applicable  control
 techniques.  Equipment controls, operational practices,  and work practices are
 all valid approaches to  reducing or eliminating VOC emissions from equipment
 leaks, depending on the equipment type.
     Chemical process plants  are comprised  of  numerous  major  equipment  com-
ponents such as reactors,  accumulators, storage tanks,  distillation columns,
condensers,  and  heaters.   There is also a large  class of ancillary equipment,
                                      2-1

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ro

ro
                                                     Organic Chemical Hanufacturing

                                                            544  Gg/yr (100X)
Process Sources

1
1
Reactor Operations
i
i _J 	
Air Oxidation
Processes
110 Gg/yr
(2M)

Reactor
Processes0
32 Gg/yr
(61)


Distillation
Operations
140 Gg/yr
(261)
                                                                                          Non-Process Sources
                                                                             Equipment
                                                                               Leaks
                                                                              189 Gg/yr

                                                                                (351)
  Storage of
Organic Liquid:
   47 Gg/yr
Secondary
 Sources0
 26 Gg/yr
             •Estimates for process emissions sources  estlMted using best available Information from current standards
                                   (25 October 1982).
                                       Figure 2-1.    Estimated Emissions by Source  Subcategories of  SOCMI2

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 most  of which  involves  the  transport  of chemicals  and  control  of  chemical  flow
 through the  process  unit.   These  components  include:
           -  Valves
           -  Pumps
           -  Compressors
           -  Pressure Relief  Devices
           -  Open-Ended Valves or Lines
           -  Sampling Connections
           -  Flanges and Other Connectors
 These ancillary  items of equipment  are  fugitive emission  sources.

 2.1   VALVES

      The valve is one of the  most basic, common elements  found  in the  chemical
 plant.   Valves are  available  in  numerous designs for widely varying applica-
 tions:   gate,  globe,  control, plug, ball,  check, and  relief.   Most  of these
 valve designs  (check and relief  valves excepted)  have a valve stem  which
 operates to  restrict or to  open the valve  for fluid  flow.  Typically the stem
 is sealed by a packing  gland  or 0-ring  to  prevent  leakage of process fluid to
 the atmosphere.   Packing glands  are the most commonly used sealing mechanism
 for valves,  and  a wide  variety of packing materials are available to suit most
 operational  requirements of temperature, pressure, and compatibility.  Because
 of design and  materials limitations, 0-rings are  much less  common  as  the
 sealing  mechanism for valves  in chemical plants.
      With  time and prolonged  use,  the packing or  sealing  0-ring in the  valve
 can fail.  To eliminate the VOC  leakage resulting  from the seal failure, the
 valve  packing  and seals must be  replaced or the  valve  body  repaired  or
 replaced.  Leak  detection and repair  methods  are  effective means  of reducing
 the leakage  of VOC from this  class  of sources in  a plant.  Basically,  a leak
detection  and  repair (LDAR)  program  is a  systematic  program  of  routinely
monitoring individual sources  (in this case,  valves)  to identify those sources
which are leaking.   Those leaking sources  would then be targeted  for repair
 For different source types or industries,  the definition of a leak may vary
 For the purpose of this document,  the leak definition is a screening value
 greater than or equal to 10,000 ppmv read  on a portable organic compound
 analyzer, in accordance with Method 21.
                                     2-3

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 (i.e., elimination  of the  "leak")  and for subsequent follow-up monitoring to
 ensure that the repair had indeed been effective in eliminating the leak.
     Maintenance or repair techniques can range from simple,  on-line  mainten-
 ance to  complex techniques.   Some basic  types of maintenance  that  can be
 performed on a valve while it remains in-place and in service are:
          (1)  tightening or replacement of bonnet bolts,
          (2)  tightening of packing gland nuts, and
          (3)  injection of lubricant into the packing or seal.
 These valve  components are illustrated in  Figure  2-2.   But  simple on-line
 techniques are not always applicable or effective  in reducing emissions.   For
 example, operational or safety requirements may prohibit repair of some valves
 such as  control  valves by  simple means.    Other  valves simply  cannot be
 repaired effectively  on-line  and cannot be removed  from service.  In  some
 instances, repair of valves can  be effected through more sophisticated repair
 techniques.  An example would  be the injection of a sealing  fluid  into the
 equipment.  Though  relatively  expensive,  sealant  injection has  been  proven
 effective in petroleum refining  applications  in California where virtually
 complete elimination of leaks has been mandated.3  In cases where maintenance
 or repair of valves is not possible,  valve replacement may be required.
     There are some valve types  and  designs that have  little  or no  potential
 for  leakage  of  process  fluids:   valves  with  "leakless"  or "seal!ess"
 technology.  Two examples  are bellows sealed  valves  and diaphragm valves.
 Bellows seals are the most effective sealing mechanism for valves.  Since  the
 service life of the bellows can be quite variable,  bellows seals are typically
 backed up with  conventional  packing glands.   Bellows  seals  have been  used
primarily in the nuclear power industry where the  relatively  high cost  can be
justified by stringent safety requirements.   Diaphragm valves, the other major
type of "leakless11  valve,  use a diaphragm  of some appropriate  material to seal
the process fluid from the stem of the valve.  In  some designs, the diaphragm
acts as the  flow control  element  as well  as  the  sealing  mechanism.    Two
                                      2-4

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 PACKING
 GLAND

 PACKING
  VALVE
  STEM
 POSSIBLE
LEAK AREAS
  70-1769-1
FIGURE  2-2.  DIAGRAM OF A GATE VALVE
                   2-5

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typical  designs  of diaphragm  valves  are shown  in Figure 2-3.   Diaphragm
valves,  however, are a source of fugitive emissions if the diaphragm fails.

2.2  PUMPS

     Pumps  are  integral  pieces  of  equipment in  most  chemical  processes,
providing the motive force  for transporting  fluids throughout a  plant.  The
centrifugal pump is the chief design used in  the  SOCMI,  but  other pump types
are also used.  Leakage of process fluid to  the atmosphere can occur where the
moving pump shaft meets the stationary casing.  To minimize  such  leakage,  two
sealing techniques are commonly applied:  packed seals  and mechanical seals.
     Leak detection and repair programs,  described earlier  for  valves,  are
also applicable to pumps with the potential  to  leak at the seal.   Pumps with
maintained mechanical  seals generally  leak  less  than do pumps with packed
seals.  Failure of a mechanical  seal, however,  can result in large emissions
from the pump.  Routine monitoring  can  effectively identify pump seal  leaks
and maintenance repair can reduce emissions.
     Packed seals consist of a  "stuffing box"  in  the pump casing.  Specially
selected packing materials (chosen on the basis of the process materials and
environment) are  compressed  into the  stuffing  box with  a packing  gland,
resulting in a tight seal  around the shaft.   Since the  shaft must move, either
rotationally or laterally, lubrication  must  be supplied  to  the  packing and
shaft to prevent excessive heat generation from the friction between the shaft
and packing which could shorten  the life of the equipment.  Leaks may result
from the degradation of the packing.
     Leaks from packed seals can often  be reduced by tightening  the packing
gland.  But at some point, the packing  will  have  deteriorated to the  extent
that it must be replaced.  Often, pump  packing  can only  be replaced when the
pump is out of service.
     Mechanical  seals,  single and dual, are used  to seal  pumps with rotating
shafts.  Both have  the common  attribute of  a lapped seal  face  between a
stationary element and a  rotating seal  ring.   Although  mechanical seals are
not leakless sealing devices,  the leakage of  process fluid from  the seal can
be minimized by a properly installed and operating mechanical seal.
                                      2-6

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DIAPHRAGM
     DISK
                                                         STEM
                                                          DIAPHRAGM
                                                             70-1771-1
      FIGURE  2-3.  DIAGRAMS OF VALVES WITH DIAPHRAGM SEALS
                                 2-7

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      Since  a mechanical  seal  will leak  (unless routinely  replaced),  the
 ultimate  potential  for leakage can be reduced  through  redundancy of sealing
 mechanisms.   For instance, a  single  seal  may  employ  a packed seal  as an
 auxiliary sealing mechanism to reduce fugitive  emissions.  Or  the same  purpose
 might be just  as  easily accomplished with  some  dual mechanical  seal
 arrangements  (either back-to-back or tandem.)   As  shown  in  Figure 2-4, the
 dual  mechanical  seals  in  both  arrangements form a cavity.
      In the  back-to-back  arrangement,  a  barrier fluid circulates between  the
 two  seals.   With the  barrier  fluid  pressure  maintained  above  the  pump
 operating pressure,  any leakage  is across  the  inboard seal  face into  the
 process fluid and across the outboard seal face  to the  atmosphere.  The  tandem
 arrangement basically has  a single seal backed  up by another single seal;  both
 seals are mounted facing the same direction.  The seal  fluid (also referred to
 as the buffer or barrier  fluid) is circulated through  the space  between the
 seals.  Any  process  fluids that may leak into  the  barrier fluid  across the
 inboard seal interface may be  removed with the  barrier  fluid or degassed in  a
 reservoir.  The degassed materials could then be treated in a control system.
      In general,  mechanical  seals have the  advantage  of  improved sealing
 characteristics and  auxiliary  control for VOC  that  may  leak  into the barrier
 fluid system.  However, repair of mechanical  seals can be both costly and time
 consuming.  To eliminate a leak from a pump equipped  with  a  mechanical  seal,
 the pump must be taken off-line and dismantled to permit repair or replacement
 of the  seal.   Additionally,  care  must  be exercised to minimize  emissions
 resulting from dismantling the pump.
      In addition to these pump types and seal  designs, there are  several types
 of sealless  technology  available.  Three designs have  been  applied  in  the
 chemical  industry where leakage cannot be tolerated.  The canned-motor pump is
 a shaftless design in which the  pump bearings  run in  the  process  fluid.  The
motor rotor  housing  and pump  casing  are interconnected.  Diaphragm pumps
eliminate all seals  and packing  exposed to the  process  fluid through the use
of a flexible diaphragm (constructed of metal,  rubber,  or plastic material) as
the driver for moving the  fluid.   Magnetic-drive pumps  also  have  no seals  in
contact with the process fluid; the impeller in  the pump casing  is driven  by
                                      2-8

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                                        SEAL LIQUID
POSSIBLE LEAK
INTO SEALING
    FLUID
       FLUID END
                                                                  GLAND
                                                                  PLATE
                        PRIMARY
                         SEAL
                                              V
  SECONDARY
     SEAL
              FIGURE 2-4a. DIAGRAM OF A DOUBLE MECHANICAL SEAL
                         (BACK-TO-BACK ARRANGEMENT)
                FLUID
                END
                   PRIMARY
                    SEAL
                                      BUFFER LIQUID

                                      OUT    IN
                                      (TOP) (BOTTOM)
SECONDARY
   SEAL
                                                              GLAND
                                                              PLATE
                                                             70-1767-1
             FIGURE  2-4b.  DIAGRAM OF A DOUBLE MECHANICAL SEAL
                          (TANDEM ARRANGEMENT)
                                  2-9

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an  externally-mounted magnet coupled  to the motor.   Examples  of uses  of
seal less  technology for pumps  include the  handling  of organic  solvents,
organic  heat  transfer liquids,  toxic  or  hazardous  materials,  and expensive
materials.

2.3  COMPRESSORS

     Compressors  provide  motive force for  transporting gases throughout  a
process unit  in much the same manner that pumps are used to transport liquids.
Compressors are  driven with rotating  or reciprocating  shafts.   Thus,  the
sealing mechanisms  for  compressors  are similar  to those for pumps; that  is,
packed and mechanical seals are the designs  primarily  used.  Again, it  is  the
sealing mechanism that is the potential source of fugitive VOC emissions.
     The mechanical  seals  used  on compressors  reduce  but  do not  eliminate
leakage of the process fluid.  The types of seals commonly used on compressors
include:

          -  Labyrinth, comprised of interlocking teeth to restrict flow;
          -  Restrictive carbon  rings,  comprised of multiple stationary
             carbon rings;
          -  Mechanical contact, which  is similar to the mechanical seal for
             pumps; and
          -  Liquid film,  which  employs an oil film between the rotating
             shaft and stationary gland.

These mechanical  seals can be vented in  various manners to a control device
for elimination of  VOC  which may  leak  from the process.   The use of  packed
seals is generally  restricted to  reciprocating  compressors where  mechanical
seal designs cannot be used.
     Leakage of VOC to the atmosphere from compressor seals can be detected by
instrument monitoring  at  the seal.   Repair of  mechanical  seals  requires
removing the compressor from service.  Since  compressors in  the  SOCMI do not
typically have spares,  immediate  repair may not be practical or possible
                                      2-10

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without  a  process unit shutdown.  There are optional control techniques  that
are  considered  effective  means  of controlling  emissions  from mechanical seals
on compressors.   One  example is venting the barrier fluid system or the  seal
to a control  system  (for  example,  a closed  vent system connected to a control
device).
      Leakage  from packed  seals  may  be reduced  by tightening  the  packing gland.
Figure  2-5  shows  a  typical  arrangement  of a  single  stage  reciprocating
compressor.   On  some  reciprocating designs  (particularly newer  compressors),
the  distance  piece between the  compressor cylinder  and the drive crankcase can
be vented  to  a  control device to treat any leakage  through  the  packing.   On
the  older  designs,  however,  this  practice may not be  possible  without
replacing  (or possibly recasting)  the  distance piece to  accommodate the  vent
line or completely  replacing  the  older  compressor with  a  newer  design
incorporating a  vent  line connection.

2.4   RELIEF DEVICES

      Relief devices  are safety  devices commonly  used  to prevent  operating
pressures from  exceeding  the maximum allowable working pressures of  process
equipment.   The  most  common  pressure relief device  is a spring-loaded  valve
(as  shown in  Figure 2-6) designed to open when  the  operating pressure  exceeds
a set pressure.   The  pressure  relief valve (PRV) is constructed so that it
will   reseat after  the operating pressure  has  decreased  to a  level  below  the
set pressure.
      Leaks  of VOC from relief devices occur through the valve seat.  Basically
two mechanisms are cited for relief device  leaks:   (1) leakage resulting  from
improper reseating of the valve after a release and (2)  leakage resulting from
process operation at or near the valve set  pressure.  The latter condition is
often referred to as "simmering" or "popping."
     Rupture disks (RDs)  are pressure  relief  devices that  allow no fugitive
emissions,  if the integrity of the disk is maintained.   Upon  pressure relief,
however, the  disk  bursts  and the process vents  directly  to the atmosphere
                                      2-11

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                                                                           Distance Piece
ro
i
                            Figure 2-5.  Simple Single-stage Reciprocating Compressor

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                               —Ttmion-idjustmtm
                                      thimble
                                ......Spring
                                                    CONNECTION FOR
                                                    PRESSURE GAUGE
                                                    4 8UEEO VALVE
                         RUPTURE DISK
                           FROM SYSTEM
Figure 2-6.  Pressure Relief Valve in a  Basic RD/PRV  Combination
                                 2-13

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until the process pressure has normalized with the atmosphere.  Replacement of
the rupture disk restores the process to a condition of no fugitive emissions.
     Rupture disks  should be  used  in conjunction  with relief  valves  to
eliminate potential  fugitive emissions  from  relief valves.   When  mounted
upstream of  a  relief valve,  fugitive  emissions are blocked  prior to  the
potential leak source, the valve seat.   (Leakage may occur if the integrity of
the disk is not maintained.)  A  typical  arrangement of an RD/PRV combination
is shown in Figure 2-6;  such  systems have  been  specified  by ASME Codes  which
establish the  design constraints and  criteria to  avoid  potential safety
hazards from the practice.  For instance, to meet ASME requirements, the space
between the RD and the  PRV  must  be  equipped with a bleed valve  and pressure
gauge that  would  indicate any pressure  build-up resulting from a leaking
disk.4
     To ensure no fugitive emissions to the atmosphere, the rupture disk  must
be replaced after an  overpressure relief.   One option  that accommodates this
procedure consists of block valves  mounted upstream of the relief devices.
This option is only  possible where  safety rules permit the use of a block
valve in relief line  service.  (Even where permitted,  this  practice generally
includes provisions for  locking  the  block  valve in the open  position during
normal operation.)  The  other options  are  dual  relief  valve systems equipped
with 3-way valves.  By using a 3-way valve, a relief system will always remain
in  service,  even when  replacing a  rupture  disk  on  the  other relief
combination.  A  number of  possible  configurations are possible for this
option.   For instance, the "primary"  side (which would be used normally) could
employ the RD/PRV combination, while the "secondary" side (which would  be  for
back-up service only) could consist  of  a  rupture disk,  a  pressure relief
valve, or another RD/PRV combination.
     Soft-seat technology for relief valves consists of using an elastomeric
0-ring to provide an improved seal  when the  valve reseats after  an  over-
pressure release.  The  applicability  of soft-seat  technology  is limited  by
materials compatibility  and operating  conditions.   Furthermore,  soft-seat
technology has no impact on emissions from "simmering."
     Fugitive emissions  from all mechanisms can  be  stringently controlled by
routing the discharge of the pressure relief device to  an appropriate control
                                      2-14

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device via a closed vent system.  The most prevalent example of this procedure
is the use of a flare header.

2.5  OPEN-ENDED VALVES AND LINES

     Open-ended valves  and  lines are found throughout chemical plants;  they
are generally drain valves, purge valves, and vent valves.  Process fluids may
be emitted to  the atmosphere through the valve  seat  as a result  of  faulty
seats or  incompletely  closed valves.  To prevent  any  atmospheric emissions
from valve seat leakage, a pipe plug, cap, or blind flange can be  installed on
the open end.  Another option is the use of a second valve,  in  something like
a "block-and-bleed" arrangement. Using this arrangement, after the valves have
been opened to allow flow of  process  fluid,  it  is  best to close the upstream
valve first.  In  this manner, no process fluid can be  trapped  between  the two
valves.

2.6  SAMPLING SYSTEMS

     Routine periodic  checks of process  unit  operation are often made  by
sampling process  streams to evaluate the performance of reactors, distillation
units  and  other  operations,  and  to verify  purity and  composition  of
feedstocks, intermediates, and products.  Process  fluids  contained in sample
lines must be purged prior to sampling to obtain a representative sample for
analysis.  The purged fluid  is  often  merely  drained onto the ground or  into
the sewer drains, where VOC may be released to the atmosphere.
     Sampling emissions  can  be  reduced  by  using  a  closed purge  sampling
system,  designed to return the purged VOC to  the process or to send the VOC to
a closed disposal system  (e.g.,  a  closed  vent  system connected to a control
device).   Examples of closed purge sampling  systems are shown schematically in
Figure 2-7.  In one case, the sample  is  collected  as  a side-cut stream  from
the purge  stream,  which flows around  a  flow-restricting device  (e.g.,  an
orifice or valve)  in the main process line.   In the second example, the  purge
is directed through the sample container.  These  two  examples are  not the only
                                     2-15

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       PROCESS. LI
                                                      PROCESS  LI WE.
                                                     —c-
ro
i
en
LJ
T
  o
                                                    SAUPL.E.
                                                    COK1TA.IMER
                     SAMPLE.
                     COMTAUUE.R
                Figure 2-7. Schematics of Closed Purge Sampling Systems

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closed purge  sampling  systems  possible.   For instance,  closed purge sampling
may also be done with partially-evacuated sample containers.

2.7  FLANGES AND OTHER CONNECTORS

     Flanges  and  other  connectors  comprise the  single largest  class  of
fugitive emission  sources in  a  process  unit,  in  terms of total  numbers.
Flanges are gasket-sealed junctions used to mate pipe and other equipment such
as valves,  vessels,  and pumps.   Flanges  may be used  in  pipe sizes 50 mm
(2 inches) or greater in diameter.  Other connectors, such as threaded connec-
tions and nut-and-ferrule connections, perform the same function as flanges,
but they are used primarily on line sizes less than 50 mm in diameter.
     Flanges and other connectors may leak VOC as a result of:

          -  improperly selected gaskets;
          -  poorly assembled flanges;
          -  poorly assembled nut-and-ferrule combinations; or
          -  cross-threaded pipe connections.

The major  cause of  VOC  leakage from flanges  and  other  connectors is
deformation of sealing surfaces as a result of thermal stress.  VOC leaks from
flanges and other  connectors  can be determined using  instrument monitoring
techniques; potential  leaks  may be evidenced  through other  means  such  as
visual, auditory,  or  olfactory means.  Tightening  bolts  on  flanges is one
method of  effectively sealing  VOC  leaks  from  some  flanges.   Generally,
however,  flange gasket  replacement or  correction  of  a leaking  connector
requires  partial or complete process  unit  shutdown.   And emissions from  the
shutdown  or repair procedure could  even  exceed  the long-term emissions from
the leak  itself.
                                      2-17

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                            3.0  EMISSION FACTORS

     In evaluating  standards  of performance or even  the effectiveness of
individual programs of emissions reduction, the estimation of emissions from
a  given  source is  a  key element.  Source  testing  for  process  emission
sources,  such  as reactor  vents,  etc.,  is  a relatively  straightforward
procedure.   Estimating  emissions  from widely dispersed  fugitive emission
sources can  be somewhat more difficult.
     One of  the first published studies  of  fugitive emissions was  conducted
in  several  petroleum  refineries in the  Los Angeles  County Air  Pollution
Control District.   The  estimates  of this  1950's  joint  study showed  that
potentially  a large quantity of hydrocarbons could be lost to the atmosphere
from various sources  such as valves,  pump  and  compressor seals,  cooling
towers, flanges, and pressure relief valves.
     It was  the  middle  1970's before  another comprehensive  assessment of
emissions  from petroleum  refineries  was made.    In  this newer study,
emissions  measurements  were  made  at 13  refineries located  throughout the
United States.  Emission  factors, screening relationships, and  correlations
were generated from  data collected  on valves,  flanges, pump  seals,
compressor seals, drains,  and pressure  relief  valves.  The  focus of  this
study was  the  assessment  of  atmospheric emissions in  petroleum refineries,
and it was surprising to many people to  find that fugitive emissions  were  a
major contributor to the total air emissions from a refinery.
     The  Refining Assessment Study was subsequently used  as  a  primary
reference  in standards  development  activities  by  EPA. The   Refining
Assessment Study was then augmented with other  information available  in the
literature  and  additional studies  of  fugitive emissions conducted  in
chemical  process units.

3.1  STUDIES CONSIDERED IN SOCMI EMISSION FACTOR DEVELOPMENT

     Since the initial fugitive emissions work done in the 1950's  LA  County
studies,  numerous research efforts  have focused on understanding  fugitive
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emissions of  VOC.   Studies have  considered leak  frequency,  leak rate,
emission factors, methods of leak prevention, and the effectiveness of leak
prevention techniques on  reducing  the  number of leaks and  mass  emissions
associated with them.  The studies listed in Table  3-1  are briefly described
below.  Each study is summarized with respect to method and results.   Actual
numerical results  have  been  summarized in  the Additional  Information
Document (AID) for Fugitive Emission Sources of Organic Compounds.7

3.1.1  Petroleum Refining Assessment Study

     The Refining Assessment  Study was designed to  provide comprehensive
emissions data from a representative number of fugitive emission  sources  in
each refinery tested.   In each of the 13 refineries tested,  equipment in
several process units were sampled.  A total of 500 to 600  emission sources
in each refinery were screened or sampled.   To eliminate potential bias from
source selection, all  individual  sources were preselected from piping and
instrumentation drawings before entering the refinery.
     Unlike previous studies,  data  were  gathered on  screening value (i.e.,
portable organic vapor detector instrument  reading)  and mass emissions.
These  data  permitted the development of average emission  factors and the
correlation  of the  maximum  observed screening  value  and  the measured
non-methane leak rate  of VOC.  The leak frequencies determined from  field
measurements  and the  average emission  factors  computed  are shown  in
Table  3-2.  These results  served  as the  principal  data against which other
fugitive emissions work by EPA would be compared.
     The Refining Assessment  Study  also  provided some  other very  important
results.  The only  equipment or process variable  found  to correlate with
fugitive emission rates  was  the  volatility  of the  stream components.   This
result led  to the  separation of equipment component emissions by service:
gas/vapor,  hydrogen, light liquid  and  heavy liquid.   These classifications
have been used  in  most fugitive- emissions standards to direct effectively
the major effort toward equipment most likely to leak.
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               Table 3-1.  FUGITIVE EMISSIONS STUDIES IN THE AID
Reference
   No.
    6       Petroleum Refining Assessment Study
    8       Four Unit EPA Study
    9       EPA 6-Unit Study
   10       Du Pont Study
   11       Exxon Cyclohexane Study
   12       EPA 24-Unit Study
   13       Evaluation of Maintenance for Fugitive VOC Emissions Control
   14       Analysis of Fugitive Emissions Data
   15       Revision of Emission Factors/SOCMI Processes
   16       German Studies
   17       Union Carbide Study
   18       Evaluation of Allied HOPE Study
 19,20      Coke Oven By-Product Recovery and Gas Plants Studies
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            TABLE 3-2.   LEAK FREQUENCIES AND EMISSION FACTORS:
                         REFINING ASSESSMENT STUDY

Equipment
Valves


Pump Seals

Compressor Seals
Pressure Relief Valves
Flanges
Open-Ended Lines
Service
Gas
LLb
HLC
LL
HL
Gas
Gas
All
All
Emission Factor3
kg/hr/source
0.0268
0.0109
0.00023
0.114
0.021
0.636
0.16
0.00025
0.0023
Percent of
Sources
>10,000 ppma
10
11
0.2
24
2
36
7
0.5
7.7
 From Appendix B of the Refining Assessment report
 (EPA-600/2-80-075c).   Reference 21.
 LL - light liquid service; i.e., compounds with vapor pressure greater than
 kerosene.
CHL - heavy liquid service; i.e., compounds with vapor pressure of kerosene
 and lower.
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3.1.2  Four Unit EPA Study8

     Although designed  along  the same  lines  as the  Refining  Assessment
Study, this study conducted by  EPA-IERL (RTP)  was  too limited in scope  to
yield results with  reasonable confidence  intervals for most source types.
The most important  result  of the  Four Unit Study was that of  illustrating
the need for more intensive sampling and screening.

3.1.3  EPA 6-Unit Study9

     The 6-Unit Study was  the next  level  in testing of fugitive emissions
conducted by EPA.   For  this study,  leak frequencies  (as  determined  using a
portable organic analyzer  and  considering a 10,000  ppmv  leak  definition)
were evaluated for  all  potential  sources  on  an individual  component basis.
Plant personnel  identified those equipment believed to handle organics.  And
no attempt was made to  segregate  equipment by service (e.g.,  in gas/vapor
service, in light liquid service,  etc.).  No emission rate measurements were
made, so no emission factors were determined.

3.1.4  Du Pont Study10

     E. I. duPont de Nemours conducted an independent survey of two of their
process units to evaluate  the leak  frequencies of  pumps  and valves  and the
leak rates of valves. A portable organic analyzer  (calibrated to hexane) was
used to identify leaks  of  10 ppm or greater.   Du Pont evaluated actual  leak
rates on only 6-8 valves.  The  study  had  a  limited data  base for pumps and
valves  and  was  restricted to two  older process units.   Du Pont's leak
definition was  inconsistent  with EPA work.   And  finally,  there was  no
determination of an average emission factor.

3.1.5  -Exxon Cvclohexane Study

     Exxon Chemical  Company conducted a study  of fugitive emissions sources
at its Baytown cyclohexane unit.  Valves were screened using a soap  solution
(soaping); pump seals,  compressor seals and safety valves were instrument
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screened using an undefined leak definition.  Valve leaks were classified as
small,  medium,  or large for selection  for mass emissions sampling.   The
percentage of leaks and emission factors determined from the study could not
be  related  to  EPA's work due  to  the  inconsistencies in leak  definitions
between the two studies.

3.1.6   EPA 24-Unit Study12

     In 1980,  EPA coordinated  a study  of  24 individual chemical process
units.  The process units were selected to represent a  cross-section of the
population across  SOCMI.   Among the  chemical  compounds included in  the
survey  were   acrylonitrile,   ethylene   dichloride,    formaldehyde,
perch!oroethylene,  and  vinyl   chloride.  Selections  of  equipment  to  be
screened were made prior to screening activities; screening was conducted by
two-person teams  using  portable  organic analyzers.  Calibration was  done
daily at a minimum.  A large number of the following types of equipment were
screened in the  24 units for  determination  of  leak frequency:  flanges,
process drains, open-ended  lines,  agitator seals, relief  valves,  valves,
pump seals,  and compressor seals.   These sources were further grouped by the
chemical phase of the material  being handled: in gas/vapor service,  in light
liquid service, and in heavy liquid service.

3.1.7  Maintenance Study13

     A  study  of the effects of  maintenance on  emissions  was performed
concurrently at six of the  units  screened  in the 24-Unit Study.   This work
yielded quantitative estimates of  leak  occurrence  and  recurrence rates and
of the effects of maintenance  on fugitive emissions.  Coincident with  these
estimates, correlations of screening values and leak rates were made.
     The Maintenance Study  focused on gas  valves,  light liquid valves, and
light liquid pumps  in three types  of  process units:   ethylene, cumene, and
vinyl acetate.  The units selected were considered to  be representative of
the level  of control existing in the chemical industry.
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3.1.8  Analysis Report14 and Revision of SOCMI  Emission Factors1

     Data gathered during the 24-Unit Study  and  the  Maintenance  Study were
subjected to a more in-depth analysis.  The data analysis tasks  included  in
the report were  generation  of average emission  factors,  analysis  of leak
frequency as a function of process parameters and equipment design, analysis
of the impact of instrument response factors on leak frequency, and analysis
of the impact  on mass emissions of leak occurrence  and  recurrence rates.
Leak frequencies for  the  various  source types  varied among the  15  process
units  and  among  source types.  Higher  leak  frequencies  were found to  be
associated with  higher line pressures,  while line temperature appeared  to
have no consistent effect.
     Average emission  factors  were developed for gas valves,  light liquid
valves, and light  liquid  pumps  in the three process unit types examined  in
the Maintenance  Study.  In  this case, emission factors were generated only
for  these processes  since the  leak rate/screening  value correlations
developed  depend on process type.  These emission factors were later  revised
to  account for  data   biasing due to off-scale  instrument  readings  and
maintenance effects.   The values  determined  were generally  found to be  lower
than  the  average emission factors determined for petroleum  refineries.

 3.1.9  German  Studies on  Fugitive Emissions

      Four studies conducted  by  industry  and  government groups in  West
 Germany investigated  fugitive emissions  and  methods  of  prevention in
 chemical  and petrochemical plants.   The  sources studied included  flanges,
 threaded  connections,  compressor seals,   pump  seals,  agitator  seals and
 valves.    Four different  methods  of leak  rate determination  or  estimation
 were employed.
      The studies were inconclusive in giving the quantitative dependence of
 leakages  on chemical,  physical,  and  design .parameters of sealing  elements.
 Insufficient  data were cited  as  the reason.    Leak  rates  found  for the
 sources  investigated  were  in general about 1/10 of the values previously
 published in  the  literature.5   It is important  to  note that the low values
 represent leakage rates  for well-maintained facilities.  In addition,

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the studies noted that prior to any directed maintenance activity, the leak
rate for valves  was  200 percent of the  published value.  Most of  these
emissions were reduced by repair of a single large leak prior to additional
measurements.

3.1.10  Union Carbide Study17

     Union Carbide conducted a study of a single process unit to 1)  find all
leaking points in the unit, 2) quantify the leak rates for these points, and
3) develop a  statistical  fugitive  emission  sampling  plan for future work.
Leaks were determined  using a portable  organic  analyzer calibrated with
hexane for a  1,000 ppmv  leak  definition.  An overall  leak frequency of 6.7
percent was found for the  1,569 points screened.  Pump  seals and open-ended
lines demonstrated the highest leak frequencies at over 30 percent.
     Point leak  rates  were determined by  various means  for  all  sources
determined to  be leaking (i.e.,  screening at  or  above 1,000 ppmv).   The
method of determining the leak rate depended upon the rate of leakage (high;
medium; low) and temperatures.  The leak rates were not classified by source
type  (eg.,  pump  seal,  valve, etc.).   Rather,  they were  reported by the
degree or extent of  leakage:  (1) small leak  (0.001 -  0.02 Ib/day);  (2) wet
surface (0.1  - 0.5 Ib/day);  (3) dripping or  strong unbearable  odor  (1  - 20
Ib/day); and  (4) continuous flow  (50  -  150  Ib/day).   No leak rates were
established for  sources  screening  less than 1,000 ppmv.  The leak rates were
not used  in  developing EPA's factors since they  could  not be compared to
data gathered  by EPA.
      In  its  recommendations, Union Carbide  cited development  of  a leak
rate/screening value correlation as an improvement in estimating  emissions.
In  addition,  the work done by Union Carbide recognized that,  in  order to
establish leak rates for 13  equipment  types, some 23,000 sources  would have
to  be  screened and 1,000 leak measurements made to obtain  data within  the 90
percent levels of confidence  desi.red.
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3.1.11  Analysis of Allied HDPE Unit Data18

     Kemron Environmental Corporation, in conjunction with Allied  Chemical,
conducted a  10-month  study of flanges and  valves  in a  new  high density
polyethylene (HDPE) unit.   Basically  focusing on maintenance effects,  six
screening and  emissions measurement tests  were  performed on valves and
flanges over the course  of  the study.  Screening was done using a portable
organic analyzer calibrated to 1,000 ppmv hexane.  (Unlike the  EPA studies,
a high concentration calibration standard was not used,  nor  was  calibration
verified at  the completion of daily  screening.   While  leak rates  were
determined for sources screening at 10,000 ppmv or greater,  these  rates are
not comparable  to  average  emission  factors.   (Average  emission factors
consider emissions  from  all  valves  across  an entire  distribution  of
screening values, not just  values  higher  than 10,000 ppmv.)   Further, some
of the  valves  sampled  for  leak  rate had  been  subjected to  a  directed
maintenance program  prior to sampling.   This action  resulted  in  lower
emissions than would be expected in the absence of any maintenance efforts.

3.1.12  SCAQMD Study22

     To evaluate the effectiveness of fugitive emission control  regulations,
EPA conducted a  survey  of two refineries in  the South Coast Air  Quality
Management District  (SCAQMD)  in  California.   Accessible valves,  pumps,
agitators,  open-ended lines, drains,  and  relief  valves in 8 process  units
were screened  using  EPA Reference Method  21.  No  flanges were surveyed
during this study.  Since  this  was a maintenance-oriented study,  no mass
emission rate measurements were made.
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3.1.13  Coke Oven By-Product Recovery19 and Gas Plant Studies20

     Three coke  oven  by-product  recovery plants were tested  for  fugitive
benzene emissions.  Source  screening was done  with two different types  of
portable  organic analyzers.   Emissions  data  gathered  were  categorized
according to source type and stream benzene  content,  but  no distinction of
service was made.  Non-methane hydrocarbon emission  factors were  generated
for valves, pump seals, and exhausters (i.e., compressors mainly in hydrogen
service).
     A total of six natural gas processing plants were tested by EPA and the
American Petroleum Institute (API).23  Screening  was done by both  soaping
and portable  organic   analyzers.   Leak rate data  collected  during  the
combined study were used to estimate leak rates for emitting sources.  These
results were then applied to the population to estimate the average emission
factors for  connections and flanges,  open-ended  lines,  pressure  relief
devices, valves, pump seals, and compressor seals.

3.2  EPA'S CHOICE OF DATA FOR SOCMI EMISSION  FACTORS

     EPA used three major  criteria in  evaluating data to  use to  estimate
fugitive VOC emissions:  1) relevance to fugitive emissions,  2) validity of
the testing and analytical  procedures,  and 3) comparability to other studies
to allow validation of results.
     The studies of fugitive emissions  summarized  above were evaluated  in
the AID with  respect  to their relevance  to  estimating fugitive emission
factors.  For example,  the emission factors  generated in  the Maintenance
Study were not considered  the  highest  quality,  best  available data on mass
emissions; estimation  of emission  factors was  not  the principal  purpose of
the Maintenance  Study.   The factors were used,  however,  to  evaluate  the
results of the emission factor estimates made.
     The second criterion was used to eliminate from consideration data that
were not collected by clear,  consistent, acceptable test  procedures.   For
example, the result of studies under scrutiny would  need  to  be evaluated
with respect to  1) how the samples were  collected,  2) how the measurements
were made  (field or  laboratory), and  3)  what  type of  equipment  was
                                    3-10

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represented by the reported data (only leaking equipment,  complete distribu-
tion of  equipment,  etc.).   This same  sort of evaluation  was needed to
consider differences  in leak  definition, method  of determining  leaks
(soaping, instrument screening), and monitoring instruments.
     The final criterion was comparability of the studies. Data from both
the Refining Assessment Study  and  the  combined SOCMI  studies were gathered
in  the  same manner using  comparable instrumentation and  leak detection
criteria.  Statistically,  the data  were  handled in a  similar manner in
studying  emissions and  the various  effects  of  various  parameters  on
emissions.  It was  only  because the data  from the Refining Assessment Study
and the  combined SOCMI  studies  were  comparable that the two studies could be
evaluated  against one  another. Mass  emissions  data from  the Refining
Assessment  Study  and leak  frequency data from the SOCMI  work were  then
combined to form  a single  set  of emission factors.
      As  detailed  in the AID, EPA determined that  the best  data available  for
estimating emission factors for fugitive VOC emissions from  SOCMI was  from
the Petroleum Refining Assessment  Study  and  from the  SOCMI 24-Unit Study.
These studies satisfied the  three major  criteria  for  emissions estimate
 data.   EPA compared the  two  data sets  and acknowledged  there were
 differences that  could not  be explained  conclusively.    The Petroleum
 Refining Assessment data  were considered the best data on mass  emissions
 from fugitive emissions sources.   The Refining Assessment  Study was  planned
 with estimation of VOC fugitive  emissions as one  of  its  objectives.  VOC
 emissions  data were gathered  according to equipment type  and service (i.e.,
 gas/vapor,  light  liquid,  heavy   liquid).   These  data  are  considered
 applicable to VOC fugitive emissions,  regardless of industry. The  24-Unit
 Study best represented the leak  frequencies  that might be expected  across
 SOCMI.  Therefore, fugitive source  emission  factors for SOCMI were  based  on
 the Refining Assessment and SOCMI emissions  data, adjusted using the results
 of the  24-Unit Study.  This procedure is detailed  in Section  3.4.
      Several approaches to estimating the emission factors were  considered.
 The  estimation procedure  presented in the AID maintained  consistency  with
 the  mathematical  procedure followed  in developing the  emission factors
 presented  in  the Refining Assessment Study  and SOCMI Maintenance  Study.
 Before  detailing  the estimation procedure presented  in the AID,  the methods
                                      3-11

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followed  in  the Refining Assessment  and  SOCMI Maintainance  Studies  are
presented.

3.3  EMISSION FACTOR DEVELOPMENT

3.3.1  Detailed Procedural Method

     The  development  of average emission factors  for  individual  fugitive
emission  sources was laid out in the  Petroleum Refining Assessment Study.21
Since then, embellishments have been  added to this procedure  to account  for
censoring of data (i.e., sources screened at the maximum instrument reading)
and other sampling effects (eg., pre-maintenance screening, post-maintenance
screening, etc.). The average emission factor  is  not merely the average of
the mass  emissions measurements made  on  anv given type of  equipment.   The
process is somewhat more involved than a simple average.
     Two  types of fugitive emissions  data were gathered for the development
and  analysis  of  emission  factors.    First,  screening  data  (i.e.,
concentration measurements)  were  collected for a  set  of sources.  Using
these raw screening data,  empirical cumulative distribution functions were
generated. The  empirical  distribution function would be a  key element in
estimating an average  emission  factor.   It was found  that the cumulative
distribution  functions  were  adequately  described   by  a  log-normal
distribution.  This led to the generation of modeled cumulative distribution
functions for source screening.   These functions relate the screening  value
of a  source  to a  leak frequency.  An example of a modeled  cumulative
distribution function  is found  in  Figure 3-1.   From such  a  figure,  the
percentage of sources "leaking"  (based upon a selected leak definition)  can
be established.
     The  second  type  of  fugitive emissions  data  gathered for  average
emission  factor development  was mass  emissions data.   Individual  sources
were "bagged" and measured for mass emission rate  (leak rate)  and  screening
value.  The mass  emissions  rate data pairs were  regressed to yield  leak
rate/screening value correlations for the various source types.  As with any
experimental  program,  there will be some degree of variability in the data
gathered, especially  as it  is  applied  to  estimate other  emissions  from
sources not tested.  Confidence  intervals  give an indication of the  range
                                    3-12

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CO

I—"
CO
                  p

                  R  100
                  c
                  E
                  N
                  T   80
S
C
R
E
E
N
I
N
G

G
R
E
A
T
E
R
                       60
                        40
                         0
                                                         	  Eat luted Percent of Source*
                                                              Screening Greater Then the Selected Source

                                                         	9SS CooUdeoce Llalu
                                                    345
                                             LOGI0COVA SCREENING  VALUE!)
6
                     Figure  3-1.  Cumulative Distribution:  Cumene  Gas Valves

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and the  degree  over  which the results are applicable.  The number of  data
pairs  necessary to develop this  correlation  depends  upon the  confidence
intervals  desired  in the  final  value.   For example,  for  the 95 percent
confidence level currently used  in fugitive emissions work,   76 data pairs
distributed over the range of screening values found  are needed to generate
the screening value/mass emissions rate correlation for valves.24
     By  combining  these  two  data  sets,  cumulative  mass  emissions
distributions were established.   The  leak  rate/screening  value correlation
(from  mass  emissions data) was  applied to  the  cumulative distribution
function (from  screening  data)  to result  in  a  cumulative mass emissions
distribution function for each source type.  Figure 3-2 shows an example of
this distribution  for  cumene  gas valves.  The  cumulative  mass emissions
distribution yields  the  percentage of mass emissions  (of  a  source type)
associated with  a  selected leak definition.  This  value  is  important  in
generating the leaking and non-leaking emission  factors discussed in  Section
3.3.3.
     The generation of the average emission factor made use of the empirical
screening distribution data and the leak rate/screening value correlation.
Using the correlation (developed from mass emissions data), leak rates  were
estimated for all sources that had been screened.   The sum of the individual
leak rates represented the total mass emissions leak  rate  for the class of
sources  being  considered.   The average  emission  factor was  derived  by
averaging the sum over the total number of sources that were  screened.  The
resultant  average  emission  factor,  therefore,   considered   the  entire
distribution of  sources  (and  screening values).   It  was   not  merely  the
average  of measured  leak rates determined  for  some  sources  out  of the
population.  Because the  result  of the procedure  is  an average emission
factor,  it should only be  applied  to  populations  of sources,  and  not  to an
individual  component.

3.3.2  Statistical  Considerations

     Of  course,  in  generating emission factors  and in evaluating  their
quality, statistical  considerations must be made.   For  example,  there  is  a
                                    3-14

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CO
 I
E
R
C
E
N
T

T
0
T
A
L

E
M
I
S
S
I
0
N
                                  20
                                   0
                                     0
 — Estimated Percent of Total
  Maaa Ealaaiona Attributable
  to Sources With Screening
  Valuea Greater Than the
  Selected Value

— 95Z Confidence Llalta
            2345
        LOG10COVA  SCREENING  VALUE)
                             Figure  3-2.  Cumulative Mass  Emissions  Distribution:  Cumene Gas  Valves,

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 minimum number  of data  pairs  (screening value and mass emission measurement)
 required to generate  a  statistically  valid screening  value/leak rate
 correlation.  And the  number of data collected in the screening  survey  of
 any  population  of sources  will  have a direct  impact on the  confidence
 intervals  associated with the modeled results.
     From  the  previous  discussion on  the emission  factor development
 procedure  used  in the Refining Assessment and the SOCMI Maintenance Studies,
 three  models  are necessary  to  generate average  emission factors.   The
 screening  value distribution  is  first modeled to  a  log-normal  distribution
 for sources screening  at more than 10 ppmv.  The confidence intervals for
 the cumulative  function are evaluated using the published  values for the
 Binominal  Distribution.  At the  95 percent  confidence level,  the estimated
 cumulative percent leaking (p) is given as:

                    P  ±  1-96 [p  (1 - p)/n]1/2

where n  is the  number  of screening values  for  the particular  source  type
 under consideration.   From  this equation,   it is  evident that, since the
width of the confidence  interval varies with the inverse  square root  of  the
 number of  sources screened,  a larger population of screened sources yields a
 smaller confidence interval.
     Next, the  screening value/leak rate correlations should be considered,
 again with respect to the confidence interval.  Leak  rates are modeled in  a
 log-log relationship assuming a binomial distribution, according to:

     Log (leak  rate)  -  a+p (log(screening value)) + Z (standard error)

where:  a  , p   «   model parameters;
           Z    -   standard normal  random number;  and standard error is
                   associated with  the individual  predictor equation.

Again, published Binomial Confidence  Interval tables are used to generate
the confidence  intervals around  the average  of the  log  (leak  rate)
estimates, (y).   For example,  the value at  the lower  confidence interval  is:
                                     3-16

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          GI   -  y  -  2.24 [s2/(n-r)]1/2

where:    s2   -  variance of the estimate;  and
        (n-r)  =  number of leaking sources.

The equation shows the effect of the number of data points in the survey on
the size of the  confidence  interval.   During  studies  of fugitive emissions
in On-Shore Gas  Production units, a minimum of 76 data  pairs were necessary
to develop  the  screening  value/leak  rate correlation  within  the 95 percent
confidence  interval required of the final emission factor.
      The  final  confidence  interval  values  for the  emission factor  are
actually  the product  of  the value  for the  (bias-corrected)  leak rate
estimate  (shown  above) and the value  for the percent of sources leaking.
The  confidence  intervals for percent  of  sources  leaking are  obtained  by
iterative  solution of summation series equations.  For example,  the  lower
confidence limit,  PL,  should be  determined from:

           "     ,.   ]           n-i      a
         jfk  (")>L  U-\>      "I

 where:  (1-a) represents the confidence level, n  is  the number of sources
 screened, and k is the number of leaking sources.  As the number of  sources
 screened  increases,  the  confidence level  increases and  the confidence
 interval narrows.  This  is vividly  illustrated in Figure 3-3  which  shows
 95 percent  confidence intervals for  a cumulative  distribution function,
 assuming 100 and 1,000 components.

 3.3.3  Leak/No-Leak Approach

      The leak/no-leak approach to estimating  emission  factors,  as  presented
 in the AID, is  an extension of the complicated process described above.  The
 expanded   process  considers  a  leak  rate/screening  value  correlation
 integrated  over  a  continuous  distribution  function;   the  leak/no-leak
 approach  instead  assumes  only  two  emission  rates  and two  populations:
 sources  that "leak"  (with screening  values greater  than  or equal  to

                                       3-17

-------
CO

I—1
oo

100


 90


 80


 70






 50


 40


 30


 20


 10


   0
                                            • Estimated Ptrctnt of
                                             Total Mass Emissions
                                   — — — -90S Confidence Interval
                                             for Ptrctnt of Emissions
                                             from Total  Population of
                                             Valves  (n - •)
                                          — 90S Confidence Interval
                                             for Percent of Emissions
                                             In a Random Sample of
                                             1000 Valves
                                    	90S Confidence Interval  for
                                             Percent of Emissions In  a
                                             Random Sample of 100 Valves
                                   2345  10      50100       1000      10.000     100.000    1.000.000

                                                   Screening Value  (ppmv) (Log1Q Scale)
                  Figure  3-3.   Cumulative Distribution of Total  Emissions by Screening Values
                                  Comparison of Confidence  Intervals.

-------
10,000 ppmv) and sources  that  do  not  leak (with screening values less than
10,000 ppmv).
     The basis  of  this extension is as follows:  when  a group of sources
"leak" (i.e., have a screening value >  10,000  ppmv),  they leak at a  certain
mass emission rate on  the  average.  Similarly,  as a  group,  sources  screened
at less than 10,000 ppmv  (i.e.,  non-leaking sources)  have on the average a
certain mass emission  rate  associated with  them.  Thus,  the overall  average
emission  factor for a population of emission sources  consists  of two
components:  leaking source emissions and non-leaking source emissions.
     It  is important  to  remember  that  fugitive  emissions  are  found
distributed over a wide range of screening values. Mass  emissions associated
with fugitive emission sources are similarly distributed.  Therefore,  only
emission factors generated using distribution data can be used in estimating
emissions  from  equipment  leaks.  Finally,  only those  emission   factors
generated  in such  a manner can be used  in the extended  procedure discussed
below.
     3.3.3.1  Generation   of  Leaking  and  Nonleaking  Emission Factors.
Leaking and non-leaking  emission factors are  generated  using  three data:
(1) the average emission factor,  (2) the leak  frequency  associated with  the
average emission factor,  and  (3)  the  percent of mass emissions  associated
with leaking sources.  As  an  example,  consider the  data for light liquid
valves in the Refining Assessment Study:

          Average Emission Factor                 0.0109 kg/hr/source
          Leak Frequency                          11%
          Percent of Mass Emissions, Leakers      86%

Assuming 1,000 valves, the total  mass  emissions would be  10.9 kg/hr;  and
110 valves of the  total  1,000 would account for 86 percent of  the  mass
emissions, or 9.37 kg/hr.  Since  this amount of emissions would be shared,
on the  average,  by all leaking  valves, the  individual  leaking  emission
factor would be (9.37 kg/hr)/(110  valves)  or 0.0852  kg/hr/source.   The
non-leaking emission factor is  similarly  computed.   For this  example, 890
valves that are  "non-leaking"  account  for  only 14  percent  of the  total
                                    3-19

-------
emissions, or 1.53 kg/hr.  This yields an average nonleaking emission factor
of (1.53 kg/hr)/(890 valves) or 0.00171 kg/hr/source.
     Put in  more  general  terms,  the emission  factors  for leaking sources
(LEF) and the emission  factors for  nonleaking  sources  (NLEF)  were computed
according to the following equations:

          LEF  .  OEF * PCM  and  NLEF  -  OEF * HOO-PCMl
                     PCL                      (100 - PCL)

where:  LEF  -  emission factor for leaking sources
       NLEF  -  emission factor for nonleaking sources
        OEF  =  overall average emission factor
        PCM  =  percent of mass emissions due to leaking sources
        PCL  -  percent of sources found leaking

The leaking and nonleaking emission factors generated by  this procedure  and
presented in the AID are shown in Table 3-3.
     3.3.3.2  Computation  of Average  Emission  Factors.   Having  computed
leaking and  nonleaking emission  factors  in the  above manner,  average
emission factors  can  be determined by merely  applying a  leak  frequency
determined from field studies.  Continuing with the example from  above,  the
leak frequency for light liquid valves in SOCMI was found to be 6.5 percent
on Ihe average  (based  on the 24-Unit  Study).   For  1,000  valves  in light
liquid service,  an estimated  65  would  leak at  a rate, on the  average,  of
0.0852 kg/hr/valve, or  5.5 kg/hr.   The 935  valves  predicted to  be not
leaking would account for an estimated 0.0017 kg/hr/valve, or 1.6 kg/hr.   So
all  1,000 valves  in light  liquid service  would have a predicted  composite
leak  rate  of  7.1 kg/hr,  for  an  average  emission  factor  of
0.0071 kg/hr/source.   This procedure,  restated  below in a more general  form,
can be applied to a population of sources to determine the average emission
factor (AEF),  provided the  leak frequency of  the  population  has  been
established.
          AEF  -  LEF * PCL -t- NLEF  *  HOP -
                               100
                                     3-20

-------
          TABLE 3-3.  LEAKING AND NON-LEAKING EMISSION EACTORS FOR
                      FUGITIVE EMISSIONS (kg/hr/source)'

Equipment
Valves


Pump Seals

Compressor Seals6
Pressure Relief Valves
Flanges
Open-Ended Lines
Service
Gas
LLb
HLC
LL
HL
Gas
Gas
All
All
Leaking
(>10,000 ppm)
Emission Factor
0.26263
0.0852
0.00023d
0.437
0.3885
1.608
1.691
0.0375
0.01195
Non-leaking
(<10,000 ppm)
Emission Factor
0.0063
0.00171
0.00023
0.0120
0.0135
0.0894
0.0447
0.00006
0.00150
 The leaking and non-leaking 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 15 and 13.


 LL - light liquid service.


 HL - 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.
                                  3-21

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3.4  EMISSION FACTORS PRESENTED IN THE AID

     Table 3-4 presents the results of this estimation process for the leak
frequencies determined in the  SOCMI 24-Unit  Study.   As the AID discussed,
these leak frequencies were  considered to be representative values  for  a
cross-section of the  large,  diverse  industry that is  SOCMI.   The  average
emission factors computed  based on these  leak  frequencies were used  to
estimate emissions  for the entire industry.   As applied  to  the entire
population of sources  in the  industry, these  "typical"  average emission
factors were deemed appropriate for standards-setting activities.  This was
particularly true  because  they were  applied consistently  to  different
regulatory alternatives to  arrive  at  comparisons.
     EPA considered the  variability of leak frequency in  the  industry in
developing its fugitive emission standards.  The extension of the procedure
for generating emission  factors considers the  "typical"  average  emission
factor  to  be a  function of leak  frequency  considered typical  of  the
industry. Also,  in evaluating valve standards for low leak frequency plants,
the technical analysis included emission  factors  that varied with  leak
frequency for valves.  Results  of this  analysis  provided  support for  the
provision in  the  SOCMI standards allowing annual  monitoring  for process
units with 2 percent or less valves leaking.
     The average emission  factors given  in  Table  3-4 were derived  in a
straightforward manner using the  leaking  and non-leaking emission factors
from the Refining  Assessment Study  (derived  in  the manner just discussed)
and the leak frequencies from  the  SOCMI  24-Unit Study.   There are two
instances where  this  approach  was not used, however.   These  two cases
deserve specific mention.
     First, the emission factor for  sampling connections  is based  on  the
amount  of  sample  purge and not on a  field-measured  emission  factor like
other source types.  In  essence, a sampling connection is  considered either
"uncontrolled"  (that  is, the  sample  purge was  assumed  drained to  the
environment) or "controlled" with the sample purge collected and returned to
the process line or disposed  of properly.  The  actual value used  for  the
emission factor  is based on the quantity  of  sampling purge reported  for
                                     3-22

-------
    TABLE 3-4.  AVERAGE  EMISSION  FACTORS  FOR FUGITIVE EMISSIONS  IN SOCMI
 Equipment Component
"Average"  SOCMI  Factors
      kg/hr/source
Pump Seals
     Light Liquid
     Heavy Liquid
Valves
     Gas
     Light Liquid
     Heavy Liquid
Compressor Seals
Safety  Relief Valves  - Gas
Flanges
Open-Ended Lines
Sampling  Connections
          0.0494
          0.0214
          0.0056
          0.0071
          0.00023
          0.228
          0.104
          0.00083
          0.0017
          0.0150
                                       3-23

-------
                                     25
1,000 barrels  of refining throughput   and the average  count  of sampling
connections  reported  for  every  1,000  barrels of  refining throughput
capacity.    The  ratio  of these two values yields  an emission factor of
0.0150 kg/hr/source.  It  is important  to  emphasize that  emissions  from
sampling connections do not include  emissions  through the seal or stem  of
the sampling valve.  These  emissions are  considered part of the emissions
from the valve and open-ended line categories.
     The second case worthy of specific mention is  the emission factor for
valves in gas  service.  After computing average emission factors  using the
Refining Assessment leaking and non-leaking emission  factors,  a comparison
was made  with  the  values  determined for  the  three equipment  types  in
ethylene, cumene,  and vinyl  acetate  process units  presented in the  SOCMI
Maintenance Study.  From this comparison,  the emission factor for gas valves
calculated from  the Refining  Assessment data appeared different  from the
SOCMI values.   The four emission  factors  for  gas  valves  determined  for
petroleum refining, ethylene  units,  cumene units,  and vinyl acetate  units
were then compared  visually as in  Figure 3-4.  The  confidence  intervals  for
the SOCMI gas  valve emission  factors are  much  narrower than those for the
refining emission  factor.   Furthermore, there  is  almost  no overlap between
the SOCMI  confidence  intervals and  those  for petroleum  refining.   This
comparative  analysis  indicates  that  (1) the SOCMI  gas valve  factors  are
different from the  factor for petroleum refining and (2) the SOCMI gas valve
factors are better estimators of SOCMI gas valve emissions.
     As a result  of this  comparative analysis,  new  leaking and non-leaking
emission factors for SOCMI gas valves were computed, based  on  data from  the
SOCMI Maintenance  Program.   The  final  values used  in  forming  the average
emission factor for SOCMI gas valves were:

     -  0.0451 kg/hr/1eaking source and
     -  0.00048 kg/hr/nonleaking source.

The factors  for  valves  and  pumps  in  light  liquid  service,  shown in Figure
3-5, were  not  found to  be different.  Therefore,  the emission factors
developed during  the  Refining Assessment Study (being  based  upon a  more
substantial data  base) were used  as  the basis  for leaking  and  non-leaking
source emission factors.
                                     3-24

-------
     0.050
     0.040
o
O
CO
     0.030
O O
tO O
CO
CO
     °'020
     0.010
                         Vinyl
                         Acetate
                                            Petroleum
                                             Refining
Cumene
                                                          Ethylene
                                                         15
                             Leak  Frequency (10,000 ppm), %
        Figure  3-4.   Comparison  of Emission Factors:  Gas Valves.
                               3-25

-------
                                                Emission Factor, kg/hr/source
                                                      (95% confidence)
                                         o
                                         o
                                         o
                                                                                p
                                                                                b
                  JPS
                  is =
                  sri
                                                                                    .0
                                                                                    C

                                                                                    O."
o
a
o
•o
1
                                              Emission  Factor,  kg/hr/source
                                                     (95%  confidence)
                               p
                               o
                                      o

                                      o
~o
i
      •o
      1
                                                               = 3
                                                               38
                                                                                              It
                                                                                              s
                                                                                              It

-------
     These "typical" average emission factors presented  in Table  3-4 would
also be appropriate for use in estimating emissions for process units where
no additional data are available.  Taken on an individual basis,  the factors
themselves represent a hypothetical "average", not necessarily any  specific
unit or process.   Given data  on  a specific process unit, average emission
factors could  be  generated using the procedure  illustrated  above for the
average SOCMI factors.  For example, assume a process unit has been surveyed
for leaks  (sources with  screening values > 10,000 ppmv)  and 4 percent of
light liquid valves were determined to be leaking.  Then an average emission
factor for that unit could be computed as follows:

          AEF  =   0.0852   *   (0.04)  +  0.0017  *  (1 - 004)
               =   0.0051 kg/hr/source

     The  concept  of an emission factor that varies with  leak frequency is
 also  consistent with  the  data  gathered during  the  SOCMI studies.  Close
 examination  of Figure 3-14 shows  some  relationship  of leak  frequency  and
 average  emission  factor  for gas  valves  in  the three  process  units studied  in
 the Maintenance Study. Furthermore, there  is  wide variation  in process unit
 types  across SOCMI,  as  evidenced in Table 3-5  by the variation in  leak
 frequencies  for the process units  in the 24-Unit  Study.  The  causes of such
 variation are many, but include chemicals  processed,  process parameters such
 as operating  temperatures and  pressures,  and the safety and maintenance
 practices at a given site.

 3.5  EXAMPLE HYPOTHETICAL CASE

      In  this  section, an  example  of estimating  emissions  for a  hypothetical
 chemical  process unit will  be  considered.   This case assumes  that  the
 process  unit  has been surveyed in accordance with Reference Method 21 and
 that the leak frequencies have  been established.
      Table  3-6 shows this hypothetical process unit and a  procedure for
 estimating  emissions using data in this report.  The  first  column presents
                                      3-27

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TABLE 3-5.  LEAK FREQUENCIES BY PROCESS FOR EQUIPMENT IN 24 SOCMI UNITS12
Percent of Sources
Process
Vinyl Acetate
Ethyl ene
Cumene
Acetone/Phenol
Ethylene Dichloride
Vinyl Chloride
Formaldehyde
Methyl Ethyl Ketone
Acetaldehyde
Methyl Methacrylate
Adipic Acid
Chlorinated Ethanes
Acrylonitrile
1,1,1-Trichloro-
_ j. i 	 	
Valves,
Gas
3.7
14.8
14.1
0
1.0
7.3
2.4
9.2
4.5
0
0
0
2.3
-
Valves,
Light Liquid
0.4
23.2
10.5
0.3
1.1
1.0
0
5.1
0.5
0.1
0
0.6
0.9
1.1
Pumps,
Light Liquid
4.5
26.3
16.0
2.3
5.2
10.8
0
3.2
9.4
4.4
-
8.3
8.2
10.0
Leaking
Flanges
1.0
5.7
2.9
0
1.1
3.2
10.0
0
0
0
0
0
0.4
0

Open-Ended
Lines
3.7
12.8
9.1
1.3
2.8
5.1
0
9.9
5.7
0.3
0
1.4
2.7
1.8
                                  3-28

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               TABLE 3-6.   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 Valves
Gas/Vapor
Open-Ended Lines
Compressor Seals
Sampling Connections
Flanges
Number
Screened

47
3

625
1180
64

31
278
4
70
2880
Computed
Number Percent Emission Factor
Leaking Leaking kg/hr/source

3 6.4
1 33.3

19 3.0<:
13 1.1C
0 0

1 3.2
9 3.2
0 0
-
20 0.7

0.0256
0.1385

0.0018
0.0026
0.00023

0.0978
0.0018
0.0894
0.0150
0.00032
Annual
Emissions
Mg/yr

10.5
3.6

9.9
26.9
0.1

28.2
4.1
3.1
9.2
8.1
aBased on values from Table 3-3,  using  AEF  -  (LEF *  PCL + NLEF  *  (100-PCL))/100.

bAssumes 8,760 hours of operation annually.

Composite percent leaking for valves  is 1.8%.   NOTE -  In this  case,  valves would  only
 need monitoring annually to ensure less than 2  percent leaking.
                                         3-29

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the number of sources  identified  in  the  process  unit  for each 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 resulting
percentage of sources  leaking  is  shown in the third  column.   The average
emission factors for  this  hypothetical  process unit  can  then be computed
using the leaking and  non-leaking emission factors found  in Table 3-3.   For
example, 6.4 percent of pump seals in light liquid service were  found to  be
leaking.  Using the leak/no-leak approach, the unit-specific emission factor
is estimated as:

        (0.437 kg/hr/source)(0.064)  + (0.012 kg/hr/source)(l - 0.064),

or 0.0256 kg/hr/source.  The total estimated  emissions for pumps in light
liquid service would  then be  computed  by multiplying  the  unit-specific
emission factor by the equipment count.  The last column  in Table 3-6 shows
the results of this process for the  hypothetical  unit.
     A further extension of this procedure would  be to examine the procedure
to estimate the  emission  factor for a certain  specie in the  line.   For
example, consider this same hypothetical  case, where the light liquid pumped
contained 20 percent  of compound  A.   The compound  A  emission factor for
light liquid pumps  is  easily  computed  by applying the  weight percent  (20
percent in this case)  to the emission factor generated above:

          (0.20)(0.0256 kg/hr/source) = 0.0051 kg/hr/source.

Emission factors calculated in this  manner could then  be applied to the
equipment counts  (where the material  in the process  line contained 20
percent of compound A) to estimate emissions of compound A.
                                     3-30

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                           4.0 EMISSION REDUCTION

     No single emission reduction technique can be used for all fugitive
emission sources. The techniques applicable to fugitive emission sources
range from equipment to work practices. The various control techniques
considered were described briefly in the earlier section on fugitive
emission sources. They are covered in this section in the context of their
emissions reduction potential.

4.1 OVERVIEW OF TECHNIQUES

     The techniques used to control emissions from equipment leaks can be
classified into two categories: equipment and work practices. An equipment
control  technique means that some piece of equipment is used to reduce or
eliminate emissions. A common example is an add-on control device such as an
incinerator that is used to reduce organic emissions from a process vent.
For fugitive emission sources, equipment controls include:  (1) leakless
technology for valves and pumps; (2) plugs, caps, blinds, etc. for
open-ended lines; (3) rupture disks and soft-seats (0-rings) for PRVs; (4)
dual mechanical seals with non-VOC barrier fluid/degassing vent systems for
rotary equipment; (5) closed loop sampling systems; and (6) enclosure of
seal area/vent to a combustion control device for dynamic seals. These
equipment control techniques can generally attain up to 100 percent
reduction of emissions, depending upon the control efficiency of the control
device. Mechanical seals and those techniques that rely upon a combustion
control technique have been assigned an overall control efficiency of 95
percent, which is consistent with the efficiency assigned to some typically
applied recovery techniques.
     The control techniques used for the largest number of fugitive emission
sources are work practices. The primary work practice applied to PRVs,
valves, pumps, and other sources is leak detection and repair of sources.
                                     4-1

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4.2 LEAK DETECTION AND REPAIR (LDAR)

     The emissions reduction potential for LDAR as a control technique is
highly variable depending upon several factors. The principal element
impacting emissions reduction is the frequency of monitoring (surveying)
sources for leak detection. For example, a monthly monitoring plan would
typically be more effective in reducing emissions than a quarterly
monitoring plan since leaks would be found and corrected more quickly. Some
characteristics of individual sources also affect emissions reduction:
leaking emission factor (as compared to the nonleaking emission factor),
leak occurrence rate, leak recurrence rate, and repair effectiveness.
Gathering of these data for valves and pumps through extensive field testing
was the focus of the SOCMI Maintenance Study.
     Using specific source characteristics, an evaluation of control
effectiveness can be made for different monitoring plans using the LDAR
Model.    The model is a set of recursive equations that operates on an
overall population of sources that can be segregated into the following
subgroups for any given monitoring interval: (1) sources that leak due to
the leak occurrence rate; (2) sources that leak and cannot be repaired below
the 10,000 ppmv leak definition; (3) sources that leaked, were repaired
successfully, but leaked again soon after the repair (i.e., leak
recurrence); and (4) sources that do not leak (i.e., those screening below
the 10,000 ppmv leak definition). The relative numbers of sources in each
subgroup change with each monitoring interval step, based on the
characteristics for the sources. Figure 4-1 shows these subgroups and how
they may interact according to the individual source characteristics.
     The LDAR Model also has the capability to examine complex monitoring
plans such as the plan permitted by EPA under its fugitive emissions
standard for valves in SOCMI. This plan allows quarterly monitoring of all
valves, supplemented with monthly monitoring of those valves that leaked and
were repaired.
                                     4-2

-------
CO
                           <€•• !•«
                                         •«|*I«««M:« ••• ••• a«cc*«*f«l.
                                               Figure  4-1.   Schematic  Diagram of the LDAR Model.

-------
     Perhaps the best way to illustrate the LDAR Model  is to present an
example. The particular example considered here is the  "typical"  SOCMI unit
presented in the AID. Table 4-1 shows the inputs used in examining a LDAR
program for valves and pumps based on monthly monitoring. The input values
were derived primarily from the SOCMI Maintenance Study. The selection of
each input value is detailed in the AID. The LDAR Model  used to estimate
emissions reductions gives incremental results as well  as results for a
program that has been established.  For the example,  once a monthly
monitoring plan is in place, emissions reductions of 73  percent and 59
percent can be expected for valves in gas and light liquid services;
likewise a 61 percent reduction in emissions can be achieved for pumps in
light liquid service under a monthly LDAR plan.
     Table 4-2 presents the results of LDAR modeling published in the AID
for valves and pumps in SOCMI.  The table presents results for simple
monthly, quarterly, semiannual, and annual monitoring of valves and pumps.
Additionally, the monthly/quarterly hybrid program allowed by EPA for valves
is shown.  These results show that, as monitoring frequency is increased,
the anticipated emissions reduction increases.  Further, the results
indicate some instances where there is no positive effect in reducing
emissions due to monitoring and repair on too infrequent a schedule.  Such
results, however, are subject to interpretation for specific cases since
they are based on "average" input values for an entire  industry.
     The ability to model the results of LDAR programs  provided the means to
examine alternative standards for valves. The LDAR Model was used to
consider monthly LDAR programs for process units exhibiting low leak
frequencies. With decreasing leak frequency, there is an associated decline
in the average emission factor and emissions reduction.  Coupling this
information with the costs of the LDAR program, an analysis of the resultant
cost effectiveness values led to the selection of 2 percent leaking as the
performance limit. Thus, process units with low leak rates (and low leak
frequencies) were given a special provision in the NSPS  for SOCMI fugitive
VOC emissions.
                                     4-4

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      TABLE 4-1.  LDAR INPUTS AND COMPUTED REDUCTIONS FOR SOCMI/MONTHLY MONITORING

Input
Emission factor,
kg/hr/source
Occurrence rate


Initial leak
frequency
Fractional emission
Description
Initial average emission
factor for all sources
Fraction of nonleakers that
became leakers over the
interval
Fraction of sources leaking
at initiation of LDAR program
Reduction from sources not
Valves,
Gas/Vapor
0.0056
0.013


0.114
0.63
Valves,
Light
Liquid
0.0071
0.013


0.065
0.63
Pumps,
Light
Liquid
0.0494
0.034


0.088
0
reduction from
unsuccessful repair

Fractional emission
reduction from
successful repair

Fraction of un-
successful repairs
Fraction of early
failures
Turnaround frequency,
months
repaired below 10,000 ppmv
Reduction from sources           0.98
repaired below 10,000 ppmv
Sources that leaked but          0.10
attempted repair below
10,000 ppmv failed

Sources repaired below           0.14
10,000 ppmv but leaked
within the next interval

Period between plant               24
shutdowns
0.98
0.10
0.14
  24
0.972
  24
          EMISSION REDUCTION COMPUTED:
                                 0.73
0.59
0.608
                                          4-5

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           TABLE 4-2.   LDAR MODEL RESULTS FOR SOCMI  VALVES  AND PUMPS
Monitoring Interval
Monthly
Monthly/Quarterly3
Quarterly
Semi-annual
Annual

Valves, Gas
0.73
0.65
0.64
0.50
0.24
Source Tvoe
Valves,
Light Liquid
0.59
0.46
0.44
0.22
(0.19)

Pumps,
Light Liquid
0.61
-
0.33
(0.076)
(0.80)
aMonthly monitoring with quarterly monitoring of "low leak" components.

NOTE:  Numbers in parentheses indicate a negative control  efficiency.   Negative
numbers are generated when the occurrence rate for the monitoring interval
exceeds the initial leak frequency.  Negative results are  subject to inter-
pretation and may not be meaningful.
                                     4-6

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4.3 -SUMMARY OF EMISSION REDUCTIONS

     Emissions reductions for fugitive emissions control techniques can be
extremely variable, particularly for work practices like leak detection and
repair programs. In terms of standard-setting activities, criteria for
selection of a given control technique or a particular level of control
(eg., monitoring interval of a leak detection and repair program) can be
quite different. For example, the criterion used in establishing the best
demonstrated technology (BDT) for NSPS may not necessarily be equivalent to
the choice in setting the reasonably available control technology (RACT)
presented in control techniques guidelines (CTG) documents used by States.
These two levels of control  are compared in Table 4-3 for VOC equipment
leaks (fugitive emissions) from SOCMI; the associated control effectiveness
values are also presented.
                                    4-7

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                                TABLE 4-3.  CONTROL LEVELS FOR SOCMI FUGITIVE EMISSIONS:  NSPS AND CTG
CO

Source
Pumps* Light Liquid
Valves, Gas
Light Liquid
Pressure Relief
Valves, Gas
Open-Ended Lines
Compressors
Sampling Connections
CTG NSPS

Percent Percent
Control Technique Control Control Technique Control
Quarterly leak detection and repair 33 Monthly leak detection and repair
Dual mechanical seal/heavy liquid
barrier fluid
Quarterly leak detection and repair 64 Monthly leak detection and repair
44
Quarterly leak detection and repair 44 Rupture disk, soft seats (0-rlngs),
vent to control device
Plugs, caps, blinds, etc. 100 Plugs, caps, blinds, etc.
Quarterly leak detection and repair 33 Seal enclosed/vented to control device
Closed purge sampling
61
100
73
59
100
100
100
100

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                           5.0   LISTS  OF  REFERENCES

 1.   U.S.  Environmental  Protection  Agency.  VOC  Emissions  in  Synthetic Organic
     Chemicals  Manufacturing  Industry  - Background  Information  for Promulgated
     Standards.    Research  Triangle   Park,   N.C.    Publication   No.
     EPA-450/3-80-033b.   June 1982.

 2.   Memo  from  Stelling,  J.H.E.,  Radian Corporation,  to  SOCMI Docket.
     November 1,  1982.   10 p. Estimate of VOC  Emissions  from  SOCMI.

 3.   Honerkamp,  R.  L.  and  M.  L.  Schwendemen.    (Radian  Corporation.)
     Evaluation of Maintenance  Effect  on  Fugitive Emissions for Refineries in
     the  South  Coast Air  Quality Management district.  (Prepared  for U.S.
     Environmental   Protection   Agency.)   Research   Triangle  Park,   N.C.
     Publication  No. EPA-600/7-82-049.  June 1982.

 4.   American Petroleum  Institute.   Guide for  Pressure Relief and  Depressuring
     Systems.  API  RP  521,  First  Edition.  September  1969.

 5.   Palmer,  R.  K.  Hydrocarbon  Losses  from  Valves  and  Flanges.   Joint
     District,  Federal and  State Project of  the  Evaluation of  Refinery
     Emissions.   Report No. 2.   March  1957.

     Steigerwald,  B.  J.    Hydrocarbon  Leakage  from Pressure  Relief Valves.
     Joint District, Federal  and State Project of the Evaluation of Refinery
     Emissions.   Report No. 3.   May  1957.

     Steigerwald,  B. J.    Emissions  of Hydrocarbons  to the Atmosphere from
     Seals on  Pumps and  Compressors.   Joint  District,  Federal and  State
     Project of the Evaluation  of Refinery Emissions.  Report  No.  6.   April
     1958.         .

 6.   Wetherold, R.G.,  L.P. Provost, and  C.D.  Smith.   (Radian  Corporation.)
     Assessment of Atmospheric  Emissions  from  Petroleum Refining,
     (Prepared for  U.S.  Environmental  Protection Agency.)   Research Triangle
     Park, N.C.  Publication No.  EPA-600/2-80-075a-d.  April  1980.

 7.   U.S.  Environmental  Protection  Agency.   Fugitive Emission  Sources of
    Organic Compounds -  Additional  Information  on  Emissions,  Emission
    Reductions, and Costs.   Research  Triangle  Park,  N.C.   Publication No.
     EPA-450/3-82-010.   April 1982.

8.  Memo from Hustvedt,  K.C.,  EPArCPB, to Durham, J.F.,  EPA:CPB.
    December 2, 1980.   170 p. MRC SOCMI Fugitive Testing.

9.  U.S. Environmental Protection Agency.  Air Pollution Emission Test at
    Dow Chemical  Company.  Research Triangle Park,  N. C.  EMB Report
    No. 78-OCM-12C.

    U.S. Environmental  Protection  Agency.  Air Pollution  Emission Test  at
    Union Carbide Corporation.   Research Triangle Park,  N.C.   EMB Report
    No. 78-OCM-12A.


                                    5-1

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     U.S. Environmental  Protection  Agency.   Air Pollution  Emission  Test at
     Stauffer Chemical Co.  Research Triangle Park, N.C.  EMB Report
     No. 78-OCM-12D.

     U.S. Environmental  Protection  Agency.   Air Pollution  Emission  Test at
     Phillips Petroleum Co.  Research Triangle Park, N.C.  EMB Report
     No. 78-OCM-12E.

     U.S. Environmental  Protection  Agency.   Air Pollution  Emission  Test at
     Refinery E.  Research Triangle Park, N.C.  EMB Report No. 78-OCM-12F.

10.  Meeting Report.  Honerkamp. R., Radian Corporation, to Hustvedt, K.C.,
     EPA:CPB, and distribution list.  June 12, 1979.  14 p.  Minutes of
     meeting between EPA and DuPont representatives about fugitive emission
     sampling.

11.  Letter and attachment from Cox, J.B., Exxon Chemical Company, to
     Weber,  B., EPArCPB.  February 21. 1978.  4 p.   Copy of letter about
     cyclohexane unit fugitive loss data sent to Hydroscience.

     Letter and attachment from Cox,  J.B.,  Exxon Chemical  Company,  to Walsh,
     R.T.,  EPA:CPB.   March  21,  1979.  4  p.   Information about  cyclohexane
     unit.

12.  Blacksmith, J.  R.,  et  al.   (Radian  Corporation.)   Problem-Oriented
     Report:  Frequency of Leak Occurrence  for  Fittings in Synthetic Organic
     Chemical  Plant  Process  Units.   (Prepared  for  U.S.  Environmental
     Protection Agency.)   Research  Triangle  Park, N.C.   Publication  No.
     EPA-600/2-81-003.  September 1980.

13.  Langley, G. J. and R. G. Wetherold.  (Radian Corporation.)  Evaluation of
     Maintenance for  Fugitive VOC  Emissions  Control.   (Prepared  for U.S.
     Environmental   Protection  Agency.)   Research  Triangle  Park,   N.C.
     Publication No. EPA-600/52-81-080.  May 1981.

14.  Langley, G. J.  et al.   (Radian Corporation.)  Analysis  of SOCMI VOC
     Fugitive Emissions  Data.   (Prepared for U.S.  Environmental Protection
     Agency.)  Research Triangle Park, N.C.   Publication No. EPA-600/2-81-111
     June 1981.

15.  Langley, G.J.,  and L.P. Provost.   (Radian  Corporation.)   Revision  of
     Emission Factors for Nonmethane  Hydrocarbons  from  Valves and Pump Seals
     in SOCMI Processes.   Technical  Note.   (Prepared  for U.S.  Environmental
     Protection Agency.)  Research Triangle Park,  N.C.  November 1981.

16.  Schwanecke, R.  "Air Pollution  Resulting from Leakage from Chemical
     Facilities."  Luftverun-reinicmna.  1970, pp.  9-15.  Translated for  the
     U.S. Environmental  Protection  Agency  by   SCITRAN.   Santa Barbara,
     California.
                                     5-2

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     Kremer,  H.   "Leakages from  Static  and Dynamic  Seals  in Chemical  and
     Petrochemical Plants."  4th  Meeting OG  EW/DGMK.  Salzburg.   October 1976
     Translated for the U.S. Environmental Protection Agency  by  SCITRAN,  Santa
     Barbara, California.

     Bierl, Alois, et al.   "Leakage Rates of  Sealing  Elements."  Chem. Ina.
     Tech.  49 (No. 2) 1977, pp.  89-85.  Translated for the U.S.  Environmental
     Protection Agency by SCITRAN.  Santa Barbara, California.

     Schwanecke, R.   "Air  Pollution Through Small Leakages for  Equipment of
     the Chemical Industry and Ways for Their  Prevention."  Translated  for the
     U.S.  Environmental  Protection  Agency  by  SCITRAN.    Santa  Barbara,
     California.

17.  Lee, Kun - Chich, et al.   (Union  Carbide  Corporation.  South Charleston,
     West  Virginia.)    "A   Fugitive  Emission   Study   in   a  Petrochemical
     Manufacturing Unit."   Presented  at  the 73rd Annual  Meeting of the  Air
     Pollution Control Association in Montreal, Quebec.  June 22-27, 1980.

18.  Harvey, Cynthia  M. and A.  Carl  Nelson.   (PEDCo Environmental Inc.)  VOC
     Fugitive  Emission  Data  -  High  Density  Polyethylene  Process  Unit.
     (Prepared for U.S. Environmental  Protection  Agency.)  Research Triangle
     Park, N.C.  Publication No.  EPA-600/2-81-109.  June 1981.

19.  DuBose, D.A., et al.   (Radian Corporation.)   Emission Factors  and Leak
     Frequencies for  Fittings in  Gas Plants.   (Prepared for U.S.  Environmental
     Protection Agency.) EMB  Report No.  80-FOL-l.  Research  Triangle  Park,
     N.C.  July 1982.

20.  Wiesenborn, D.P.,  et  al.   (Radian  Corporation.)  Leak  Frequency  and
     Emission Factors for Fittings  in  Coke Oven By-Product  Plants.   (Prepared
     for U.S.  Environmental  Protection Agency.)  EMB  Report  No. 81-BYC-12.
     Research Triangle Park, N.C.  January 1982.

21.  Wetherold, R. G., L. P. Provost,  and C. D. Smith.   (Radian  Corporation.)
     Assessment of Atmospheric Emissions from  Petroleum Refining,  Appendix  B:
     Detailed Results.  (Prepared for  U.S.  Environmental  Protection Agency.)
     Research Triangle Park, N.C.  Publication No.  EPA-600/2-80-075c.   April
     1980.

22.  Reference 3.

23.  Eaton, W.S., et  al.   Fugitive Hydrocarbon Emissions from Petroleum
     Production Operations.  American Petroleum Institute Publication
     No. 4322.  1980.

24.  Harris, G. E.   (Radian  Corporation.)    Emission  Test  Report:  Fugitive
     Test Report at the Gulf Venice Gas Plant,  Volume I.   (Prepared for U.S.
     Environmental  Protection Agency.)  Research Triangle  Park, N.C.   EMB
     Report No.  81-OSP-8.   July 1981.
                                    5-3

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     Harris, G. E.  (Radian Corporation.)  Emission Test Report:  Fugitive VOC
     Testing at the Texas Paradis Gas Plant, Volume  I.   (Prepared for U.S.
     Environmental Protection  Agency.)  Research  Triangle  Park, N.C.   EMB
     Report No. 80-OSP-7.  July 1981.

25.  U.S. Environmental Protection Agency.  Compilation of Air Pollutant
     Emission Factors.  Research Triangle Park, N.C.  AP-42.  February 1980.

26.  Powell, D., et al.   (PES, Inc.)  Development of Petroleum Refinery Plot
     Plans.  (Prepared  for  U.S.  Environmental Protection Agency.)   Research
     Triangle Park, N.C.  Publication No. EPA-450/3-78-025.   June 1978.

27.  Williamson, H. J.,  et  al.   (Radian  Corporation.)  Model for  Evaluating
     the Effects of Leak  Detection and Repair Programs on Fugitive  Emissions.
     Technical  Note DCN 81-290-403-06-05-03.   September 1981.
                                    5-4

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                                    TECHNICAL REPORT DATA
                             (Please read Instructions on the reverse before completing)
 1. REPORT NO.
  EPA-450/3-86-002
                                                             3. RECIPIENT'S ACCESSION NO.
 4. TITLE AND SUBTITLE
  Emission  Factors for Equipment Leaks of VOC and  HAP
                                                             5. REPORT DATE
                                                               February 10. IQflfi
              6. PERFORMING ORGANIZATION CODE
 7. AUTHOR(S)

  John H. E.  Stelling III
              8. PERFORMING ORGANIZATION REPORT NO
               DCN  86-203-024-63-06
9. PERFORMING ORGANIZATION NAME AND ADDRESS

  Radian Corporation
  3200 E. Chapel  Hill  Road/Nelson  Highway
  Research Triangle Park, M.C.   27709
              10. PROGRAM ELEMENT NO.
              11. CONTRACT/GRANT NO.

               68-02-3889, WA 63
 12. SPONSORING AGENCY NAME AND ADDRESS
  U.S. Environmental  Protection Agency
  Office of Air  Quality Planning  and  Standards
  Emission Standards  and Engineering  Division
  Research Triangle Park, M.C.  27711	
                                                             13. TYPE OF REPORT AND PERIOD COVERED
              14. SPONSORING AGENCY CODE
 15. SUPPLEMENTARY NOTES
  Project Officer  is  Robert E. Rosensteel, Mail Drop  13,  (919) 541-5605.
16. ABSTRACT
        The report  summarizes the development of emission factors for  volatile organic
  compound (VOC) equipment leaks.  The  background information used in  emission factor
  development is reviewed.  The estimation techniques  for generation of VOC emission
  factors are described and illustrated with an example.   The application of the
  estimation techniques is demonstrated for both VOC and  hazardous air pollutants
  (HAPs).
 7.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                               b.lDENTIFIERS/OPEN ENDED TERMS  C.  COSATI Field/Group
                                                Fugitive Emissions
                                                Volatile Organic
                                                   Compounds
                                                Hazardous Air  Pollutants
 8. DISTRIBUTION STATEMENT

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