Prentiss Searles

Sr. Marketing Issues Associate 

1220 L Street, Northwest 

Washington, DC 20005-4070 

Tel 202/682-8227 

Fax 202/682-8051 

E-mail searlesp@api.org

 

April 7, 2004 

Ms. Lisa Rector 

Northeast States for Coordinated Air Use Management 

101 Merrimac Street 

Boston, Massachusetts 02114 

Re: ORVR Compatibility Study 

Dear Ms. Rector: 

The American Petroleum Institute commissioned a study to determine the compatibility between 

ORVR systems and a Stage II vapor recovery system. The study characterized the emissions of a 

vacuum assist system when used with vehicles that have ORVR in place. The study included a 

test of the system at an operating retail gasoline dispensing facility (GDF), a test of refueling 

emissions inside a SHED (Sealed Housing Evaporative Determination), and a test of emissions 

from a UST system during several single refueling events. The research examined in detail the 

performance of a specific vac-assist system in two configurations: an A/L set above 1.0 and an 

A/L set below 1.0 with a mini-boot on the nozzle. We believe that the results of this study provide 

significant new information on ORVR compatibility. 

There are three key conclusions from the research: 

• Emissions during gas cap removal (“puff emissions”) and emissions at the fillpipe during 

refueling are significantly lower for ORVR vehicles than non-ORVR vehicles. 

• For the mini-booted vac-assist system (A/L <1.0), excess UST emissions are essentially 

zero. 

• When refueling a mixed population of non-ORVR and ORVR vehicles at a GDF, the 

installation of mini-boots and a decrease in A/L below 1.0 reduced measured P/V valve 

emissions by 98% and reduced total UST emissions by at least 64% without significantly 

influencing fillpipe emissions. 

Note that the second conclusion is consistent with the results from ARB’s 1999 study, which 

showed that a Wayne system (with A/Ls between 0.9 and 1.1) also had negligible UST emissions. 

An equal opportunity employer 
Ms. Lisa Rector 

April 7, 2004 

Page 2 

In support of the first conclusion above, the emissions measured in the SHED during gas cap 

removal (“puff emissions”) and emissions at the fillpipe during refueling are significantly lower 

for ORVR vehicles than non-ORVR vehicles. These reductions in fillpipe emissions were 

confirmed for a matrix of in-use vehicles (tested as per ARB test procedure TP-201.2) at an actual 

service station in San Bernardino where the A/L was set below 1.0. Specifically, both before and 

after installing mini-boots and reducing the A/L, the average fillpipe emissions from ORVRequipped vehicles were 0.31 lb/1000 gallons lower than those from non-ORVR vehicles. SHED 

tests showed an even greater reduction of 0.46 lb/1000 gallons at the fillpipe. 

The second key conclusion is drawn from the tests done at the UST system during several single 

refueling events. Direct measurements of fugitive emissions from the tank system showed that, for 

the mini-booted vac-assist system (A/L <1.0), UST emissions from ORVR refuelings were 

essentially zero and were less than UST emissions from non-ORVR refuelings. Thus, excess UST 

emissions (ORVR minus non-ORVR) are essentially zero for the mini-booted vac-assist system. 

The results also show that excess UST emissions for the standard (A/L >1.0) vac-assist system 

(0.72 lb/1000gal) are comparable to ARB’s 1999 estimate of 0.86 lb/1000 gal of excess UST 

emissions. However, depending upon temperature conditions, these excess UST emissions may be 

entirely offset by reduction in puff and fillpipe emissions (i.e., see conclusion #1). In addition, the 

study notes that measured fugitive UST emissions were consistently below those calculated using 

ARB’s TP-201.2F methodology by 1-2 orders of magnitude. 

The third key conclusion comes from the San Bernardino test data that show, on average, the 

installation of mini-boots and a decrease in A/L (A/L<1.0) reduced UST emissions (calculating 

fugitives as per TP 201.2F) from 1.38 lb/1000 gal to 0.49 lb/1000 gal (i.e., a reduction of 0.89 

lb/1000 gal, 64%) without significantly influencing fillpipe emissions. Of the 0.89 lb/1000 gal 

reduction, 0.82 lb/1000 gal were reductions measured at the P/V valve, rather than calculated as 

fugitives (see Figure 1 attached). To the extent TP201.2F over predicts fugitive emissions (and the 

study shows TP-201.2F estimates were biased high by 1-2 orders of magnitude), the reduction in 

total UST emissions caused by the use of mini-boot nozzles is likely higher than 64% and possibly 

as high as 98% (if one applies the TP201.2F correction factors derived in this study). 

Consequently, the study’s conclusions are conservative. 

Our data lead us to conclude that ARB has significantly overstated the extent to which there are 

“excess emissions” due to ORVR that were not accounted for in emission inventories prior to the 

EVR program. Specifically, although ORVR vehicles can produce higher UST emissions when 

fueled with a vac-assist VRS with an A/L >1.0, ORVR vehicles produce lower emissions at the 

fillpipe, both when the gas cap is removed and during refueling. Finally, as discussed above, the 

use of the mini-booted vac-assist system eliminates ORVR incompatibility and excess emissions. 
Ms. Lisa Rector 

April 7, 2004 

Page 3 

We look forward to an opportunity to discuss this new information with you. Should you have any 

questions or would like to further discuss this study, please do not hesitate to contact me via the 

information given above. 

Sincerely, 

c: Michael Block 

Attachment 

Enclosure 
Figure 1. UST Emissions Determined Using ARB TP-201.2, While 

Refueling Vehicles at an Operating San Bernardino GDF (RVP 7.0 

gasoline)

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

Standard Gilbarco VRS

(A/L = 1.15)

Mini-booted Gilbarco VRS

(A/L = 0.95)

Emissions (lb/1000 gal)

Measured at P/V Valve

Calculated Fugitives (TP-201.2F)
ORVR COMPATIBILITY STUDY 

FOR THE GILBARCO VAPORVAC VRS

February 2004 

 TECH ENVIRONMENTAL, INC.
ORVR COMPATIBILITY STUDY 

FOR THE GILBARCO VAPORVAC VRS

Prepared for: 

American Petroleum Institute 

1220 L Street N.W. 

Washington, DC 20005 

Prepared by: 

Tech Environmental, Inc. 

1601 Trapelo Road 

Waltham, MA 02451 

(781) 890-2220 

February 5, 2004 
FOREWORD 

The California Air Resources Board (CARB) has recently stated that significant emissions occur 

when currently installed Stage II systems are used to fuel vehicles with onboard refueling vapor 

recovery (ORVR) systems. The purpose of this study was to test the accuracy of CARB's

statement by using a commercially available Stage II system to determine its compatibility with 

onboard vapor recovery systems. The selection of the Gilbarco VaporVac for this research 

project should not be interpreted as an endorsement of this equipment over other commercially 

available equipment. 

2
TABLE OF CONTENTS 

Section Title Page 

1.0 EXECUTIVE SUMMARY............................................................................................ . 1 

 1.1 Overall Study Conclusions..................................................................................2 

 1.2 Results for Phase 1 – Fleetwide Tests..................................................................3 

 1.3 Results for Phase 2 – Laboratory Tests................................................................4 

2.0 INTRODUCTION.......................................................................................................... 6 

 2.1 Overview............................................................................................................ 6 

 2.2 Phase 1 – Fleetwide Tests ..................................................................................7 

 2.3 Phase 2 – Laboratory Tests.................................................................................7 

 2.4 Description of the Refueling Emissions Process................................................ 8 

3.0 SCIENTIFIC PRINCIPLES...........................................................................................11 

 3.1 Factors Affecting Uncontrolled Refueling Emissions.......................................11 

 3.2 Onboard Refueling Vapor Recovery (ORVR) Canisters..................................13 

3.3 Vacuum-Assisted Stage II Vapor Recovery Systems (VRS)..............................16 

 3.4 ORVR / VRS “Incompatibility”....................................................................... 17 

4.0 TESTING METHODOLOGIES.................................................................................. 20 

 4.1 Phase 1 – Fleetwide Tests................................................................................ 20 

 4.1.1 Overview.............................................................................................. 20 

 4.1.2 Testing Details..................................................................................... 22 

. 

 4.2 Phase 2 – Laboratory Tests ..............................................................................23 

 4.2.1 Overview.............................................................................................. 23 

 4.2.2 Testing Details – Outdoor Tests.......................................................... 27 

 4.2.3 Testing Details – Indoor SHED Tests................................................. 30 

 4.3 Ethanol Correction – Phase 1 and 2................................................................. 37 

iii 
TABLE OF CONTENTS (continued) 

Section Title Page 

5.0 PHASE 1 – ANALYSIS AND RESULTS................................................................ 40 

 5.1 Analysis of Factors Affecting “Uncontrolled Emissions”............................... 40 

 5.1.1 Temperatures...................................................................................... 40 

 5.1.2 ORVR................................................................................................. 42 

 5.2 Analysis Of Continuous UST Data................................................................. 45 

6.0 PHASE 2 OUTDOOR TESTS – ANALYSIS AND RESULTS................................ 58 

 6.1 Continuous UST Pressure Data...................................................................... 58 

 6.2 Fugitive Emissions From UST/Piping............................................................ 67 

 6.3 Performance of the CARB Estimation Method for Fugitive Emissions......... 71 

 6.4 Fillpipe Emissions and Return Vapor Line Concentrations............................ 74 

7.0 PHASE 2 INDOOR SHED TESTS – ANALYSIS AND RESULTS......................... 76 

 7.1 Nozzle/Fillpipe Refueling Emission............................................................... 76 

 7.1.1 ORVR................................................................................................. 77 

 7.1.2 RVP..................................................................................................... 82 

 7.1.3 A/L Ratio............................................................................................. 82 

 7.1.4 Temperatures...................................................................................... 83 

 7.2. Fuel Cap “Puff” Emissions and Canister Outlet Emissions............................ 91 

8.0 CONCLUSIONS.........................................................................................................99 

iv 
EXECUTIVE SUMMARY 

The goal of the ORVR Compatibility Study is to investigate refueling emissions and the 

compatibility of a Gilbarco vacuum-assisted vapor recovery system (VRS) with onboard 

refueling vapor recovery (ORVR) canisters installed on motor vehicles. The California Air 

Resources Board (CARB) has stated there is a potential for “excess emissions” of pressurerelated fugitives when the two vapor control systems are used together. To understand this 

report, the reader needs to be introduced to four key terms, defined below. Pressure-related 

fugitives (also referred to as fugitive emissions in this report) are HC emissions from a gasoline 

dispensing facility due to positive gauge pressure in the headspace (ullage) of the Underground

Storage Tank (UST). These occur as leaks in the piping system. These emissions do not include 

transfer emissions at the nozzle/fillpipe interface nor the emissions from the vent pipe P/V valve.

Excess emissions of pressure-related fugitives (also referred to as just excess emissions in this 

report) are the difference between pressure-related fugitives for an ORVR vehicle versus a nonORVR vehicle when refueled with a Stage II VRS. Total incompatibility emissions are the 

difference between all refueling emissions (pressure-related fugitives, P/V valve and fillpipe 

emissions) for an ORVR vehicle versus a non-ORVR vehicle. Uncontrolled emissions are 

emissions from the nozzle/fillpipe interface that would results if neither a Stage II VRS nor an

ORVR system were present. 

There were two phases to the study. In Phase 1, fleetwide tests were done at a California service 

station using CARB test procedures to quantify the differences in refueling emissions for ORVR

vs. non-ORVR vehicles. The service station dispenser was equipped with a Gilbarco VaporVac

Stage II VRS. In Phase 2, laboratory tests were done at a facility in Arizona to study the 

compatibility between the Gilbaraco VRS and ORVR-equipped vehicles. Refueling tests

performed in a Sealed Housing for Evaporative Determinations (SHED) quantified the controlled

nozzle/fillpipe emissions as a function of the type of ORVR equipment, fuel RVP, the 

temperature of dispensed fuel and vehicle tank, and the air-to-liquid (A/L) ratio. In addition,

“excess emissions” of pressure-related fugitives were directly measured during six CARB 

refueling tests at the laboratory. These tests were not designed to measure VRS efficiency under

1
the CP-201 Vapor Recovery Certification Procedure. In the sections below, the overall

conclusions from the study are provided, followed by the results of each Phase. . 

1.1 Overall Study Conclusions

Analysis of the extensive measurements of fillpipe and pressure-related fugitive emissions made 

in this study support the following overall conclusions, which are applicable to statewide HC 

emission inventories: 

• For a standard vapor recovery nozzle (A/L = 1.15) on a Gilbarco VRS, “excess 

emissions” do occur when an ORVR vehicle is refueled. This study documents the vapor 

growth process in the UST for individual refueling events, and measurements reveal 

“excess emissions” of pressure-related fugitives are 0.72 lb/1,000 gallons, slightly less 

than the level CARB assumes (0.86 lb/1,000 gallons). The CARB estimate is less 

reliable as it is not derived from actual measurements of pressure-related fugitives 

associated with refueling ORVR vehicles, the test method used on this study. 

• When a Gilbarco VRS is used, ORVR vehicles produce substantially lower emissions at 

the nozzle/fillpipe than non-ORVR vehicles. This is a significant offset to the excess 

emissions, which CARB does not account for in analyzing ORVR compatibility. Thus, 

CARB in practice assumes that total incompatibility emissions are equal to excess 

emissions (0.86 lb/1,000 gallons). 

• Total incompatibility emissions for the standard nozzle (A/L = 1.15) are only 0.42 

lb/1,000 gallons, about half of what CARB presumes for all ORVR vehicles (0.86 

lb/1,000 gallons). 

• Measured fugitive emissions from ORVR vehicles refueled with a mini-boot nozzle are 

near zero (0.003 lb/1,000 gallons) and are less than measured non-ORVR fugitive 

emissions (0.011 lb/1,000 gallons). Thus, when the mini-boot nozzle (A/L = 0.95) is 

used on a Gilbarco VRS, there is no ORVR incompatibility and measured “excess

emissions” are zero (actually –0.008 lb/1,000 gallons). In addition, with the mini-boot 

nozzle in use the combination of ORVR and Stage II VRS controls produces 0.39 

lb/1,000 gallons less emissions at the fillpipe than if just Stage II controls are used. 

• The CARB estimation method for UST fugitive HC emissions (TP201.2F) over-predicts

actual pressure-related fugitive emissions by factors of 13 to 660. These data support an 

earlier analysis by Tech Environmental that pointed to over-prediction and flaws in the 

analytical form of the equation for pressure-related fugitives. 

• States and EPA should revise the calculation of refueling emissions for ORVR vehicles 

in MOBILE6 to reflect the new variable dependencies found in this study and to ensure 

that future emission inventories are accurate. 

2
• Puff losses were found to be on the same order of magnitude as fillpipe refueling

emissions for both ORVR and non-ORVR vehicles. Puff losses are the losses of 

hydrocarbon vapors that occur when the gas cap is removed and are not captured in 

emission inventories calculated by the EPA MOBILE6 models. 

1.2 Results for Phase 1 – Fleetwide Tests

In this first phase of the test program, testing was done in accordance with test procedures in

CARB method TP201.2 at a Conoco Service Station in San Bernardino, California to provide 

some initial data on ORVR vs. non-ORVR vehicle emissions for an in-use vehicle fleet. Two 

sets of tests were performed: Test 1 with standard nozzles1

 and Test 2 with mini-boot nozzles 

and a reduced air-to-liquid ratio (A/L). The fuel was California summertime reformulated 

federal gasoline (RVP 7.0 with ethanol). UST pressure, headspace concentrations, and emissions 

from the UST P/V valve were monitored continuously. 

 

The results support the following conclusions: 

• CARB’s calculations of total incompatibility emissions are overestimated because they 

ignore the decrease in emissions at the nozzle/fillpipe from ORVR equipment. When a 

Gilbarco Stage II VRS is used, ORVR vehicles had 73% lower emissions from the 

nozzle/fillpipe than non-ORVR vehicles, a difference of 0.31 lb/1,000 gal, when fueled

with RFG (7.0 RVP). This is a significant difference that CARB does not account for

and it partially offsets the 0.86 lb/1,000 gal excess emissions from the UST that CARB

has assigned to ORVR vehicles. Results were the same for standard vacuum assist 

nozzle and mini-boot nozzle refuelings. 

• Use of a mini-boot nozzle with the Gilbarco VRS reduced measured emissions from the

P/V valve by 98%, and reduced total UST/piping system emissions by 64% to 98%. 

This reduction is greater than the 50% reduction CARB claims for the mini-boot. 

• Since the sum of the vapor in the return line plus the fillpipe emissions for ORVR 

vehicles (roughly 1.2 g/gal) is larger than the maximum 0.2 g/gal that is allowed for

emissions from an ORVR car refueling at a non-Stage II service station, it appears that 

the VRS may be preferentially capturing vapors over the ORVR canister. 

Alternatively, the vacuum assisted Stage II equipment may be increasing the 

volatization of liquid fuel in the fillpipe as it is being dispensed. 

 

1

 In this study, the term “standard nozzle” refers to a vapor recovery nozzle with an A/L of 1.15. 

3
1.3 Results for Phase 2 – Laboratory Tests

The second phase of the study was performed at Automotive Testing Laboratories, Inc. in Mesa, 

AZ and directly examined the issue of compatibility between the Gilbarco VRS and ORVRequipped vehicles by measuring pressure-related fugitive emissions. This phase had two 

separate work tasks: outdoor tests using CARB method TP201.2 at a dispenser drawing product 

from a 3,000 gallon UST containing 1,000 gallons of RVP 7.8 summer grade gasoline, and 

indoor SHED tests conducted using a procedure similar to the federal ORVR certification test to 

quantify nozzle/fillpipe emissions and their dependence on independent variables. The effects of 

three processes were documented in the continuous one-second pressure records of the 3,000 

gallon UST: initial positive or negative pressurization (depending on A/L) from the return vapor 

line; vapor growth in the UST headspace from unsaturated return air; and continuous leaks from 

the UST/piping system (simulated with a leak valve on an otherwise tight system). The results 

of the Phase 2 – outdoor tests support the following conclusions: 

• Measured fugitive emissions from ORVR vehicles refueled with a mini-boot nozzle are 

near zero (0.003 lb/1,000 gallons) and are less than measured non-ORVR fugitive 

emissions (0.011 lb/1,000 gallons). Thus, when the mini-boot nozzle (A/L = 0.95) is 

used on a Gilbarco VRS, there is no ORVR incompatibility and measured “excess 

emissions” are zero (actually –0.008 lb/1,000 gallons). In addition, with the mini-boot 

nozzle in use the combination of ORVR and Stage II VRS controls produces 0.39 

lb/1,000 gallons less emissions at the fillpipe than if just Stage II controls are used. 

• “Excess emissions” from the UST/piping system when a standard nozzle (A/L=1.15) is 

used are 0.72 lb/1,000 gallons. Considering the decrease in fillpipe emissions produced

by the ORVR-VRS combination of 0.39 lb/1,000 gallons, total incompatibility 

emissions for the standard nozzle are only 0.33 lb/1,000 gallons, or less than half of the 

figure of 0.86 lb/1,000 gallons that CARB presumes for all ORVR vehicles. 

• In situations where Gilbarco systems are equipped with standard nozzles (A/L = 1.15),

a correction should be applied for the fact that the MOBILE6 model (the tool used to 

create state emission inventories) assumes fillpipe emissions for ORVR cars are lower 

than those for non-ORVR cars controlled with Stage II. That is, some of the fillpipe 

emissions reduction attributable to ORVR (and discussed in the bullet above) are 

already credited in the emissions inventory. Thus, when used in statewide emission 

inventories developed with MOBILE6, a slightly higher figure of 0.42 lb/1,000 gallons 

should be assumed for total incompatibility emissions for the Gilbarco dispenser with a

standard nozzle. 

4
• The CARB estimation method for UST fugitive emissions (TP201.2F) over-predicted 

actual pressure-related fugitive emissions by factors of 13 to 660. These data support 

an earlier analysis by Tech Environmental that pointed to overprediction and flaws in 

the analytical form of the equation for pressure-related fugitives. 

The Phase 2 – indoor SHED tests quantified the dependence of fillpipe emissions on several 

independent variables. The results support the following conclusions: 

• The SHED refueling emissions at the fillpipe for ORVR and non-ORVR vehicles fall 

within the range of values measured in the Phase 1 and Phase 2-outdoor TP201.2 tests. 

• Comparison of ORVR and non-ORVR fillpipe emissions in the SHED tests produced 

results confirming those found in the Phase 1 TP201.2 tests. In Phase 1, fillpipe 

emissions were 73% less for ORVR than for non-ORVR vehicles using a Gilbarco VRS. 

In the controlled refueling tests in the SHED, fillpipe emissions for the ORVR-equipped 

vehicles were 91% lower than those for the non-ORVR vehicles using a Gilbarco VRS. 

• The dependence of fillpipe emissions on RVP, A/L ratio and temperatures is different for 

ORVR and non-ORVR vehicles. 

• For ORVR-equipped vehicles, there is very little to no correlation of fillpipe emissions 

with RVP, no correlation with A/L ratio, no correction with ∆T (vehicle tank temperature 

minus dispensed temperature), and positive correlation with TT (vehicle tank 

temperature). 

• For the non-ORVR vehicle, there is a positive correlation of fillpipe emissions with RVP, 

a negative correlation with A/L, and a negative correlation of emissions with ∆T, as 

assumed in the EPA MOBILE6 model. 

• “Puff” losses of HC vapor that occur when the gas cap is removed on a vehicle are 

comparable to (50% to 100% of) fillpipe emissions from a single refueling event. “Puff”

emissions are positively correlated with TT and RVP. 

• Since fillpipe emissions for ORVR-equipped vehicles do not exhibit the standard 

correlations with RVP and ∆T assumed in the MOBILE6 model, States and EPA should 

revise the calculation of refueling emissions for ORVR vehicles in MOBILE6 to reflect 

the new variable dependencies found in this study and to ensure that future emission 

inventories are accurate.

 

5
INTRODUCTION 

2.1 Overview

This report documents the results from a two-phase study of vapor recovery compatibility 

associated with refueling emissions when a Gilbarco vacuum-assisted vapor recovery system

(VRS) is operated in the presence of a vehicle having onboard refueling vapor recovery (ORVR). 

The test program has two overall goals: 

1. To better quantify refueling emissions for use in emissions inventories under a variety of 

conditions and to address the California Air Resources Board (CARB) claims of ORVR 

excess emissions using scientifically defendable methods; and 

2. To quantitatively address the appropriateness of CARB’s methods for determining 

pressure-related fugitive emissions from the gasoline dispensing facility (GDF) 

underground storage tank (UST) and piping when a VRS is in operation. 

CARB’s methodologies for testing refueling emissions are included in Appendix A and take five 

emissions points into account (see Figure 2-1). These locations are: 1) emitted at the 

nozzle/vehicle interface, 2) returned through the vapor passage of the hose, 3) emitted from the

pressure/vacuum (P/V) valve(s) on the underground storage tank (UST) vent pipe(s), 4) emitted 

from the assist processor, if applicable, and 5) emitted as pressure related fugitives. 

Emissions from points 1 and 2 are on a per-vehicle basis, for vehicles at the dispenser being 

tested, whereas emissions for points 3 and 4 are continuous and influenced by other vehicles 

refueling at the facility since all dispenser vapor return lines are connected together at the UST 

common manifold. Emissions from point 5 are calculated, using the equations in CARB Test 

Procedure TP-201.2F. Location 4 is not applicable in this study. Section 4 discusses these 

methodologies in more detail. A testing program to measure refueling emissions is typically

divided into two components: those from spillage during the fueling process, and those from 

vapor displacement. Uncontrolled spillage emissions are small relative to uncontrolled

displacement emissions, and were not considered in this testing program. 

6
The remainder of this section gives a brief overview of the test program and describes the 

refueling emissions process. Scientific principles are discussed in Section 3, test protocols are 

detailed in Section 4, and the study’s results and conclusions are summarized in Sections 5

through 8. The test reports from VOC Testing, Inc. are included in Appendices B and C of this

report, and the test report from Automotive Testing Laboratories, Inc. is attached as Appendix D. 

2.2 Phase 1 – Fleetwide Tests

In the first phase of the test program, a GDF in San Bernardino, CA equipped with a Gilbarco 

vac-assist VRS was selected for refueling emissions testing of an in-use vehicle fleet in 

accordance with test procedures in CARB method TP201.2. VOC Testing, Inc. of San 

Bernardino, CA is the only known contractor with a depth of experience conducting this type of 

testing, and was subcontracted to perform the testing. Hydrocarbon concentration and pressure 

data were continuously recorded utilizing a strip chart recorder, and one-minute average data 

were stored electronically. The objectives were to quantify differences in refueling emissions 

between ORVR and non-ORVR vehicles, both at the fillpipe and from the UST. (Note that 

TP201.2 measures both vapor displacement losses from refueling and the smaller component of 

UST breathing losses.) These tests were not designed to measure VRS efficiency under the CP201 Vapor Recovery Certification Procedure. 

2.3 Phase 2 – Laboratory Tests

In the second phase of the study, laboratory tests were done at Automotive Testing Laboratories, 

Inc. (ATL) of Mesa, AZ using a dispenser equipped with a Gilbarco vacuum-assist VRS 

(VaporVac). ATL has performed vehicle emissions testing for EPA, CARB, and CRC for many 

years and their Mesa facility is equipped with six SHEDs and two 3,000 gallon USTs. SHEDs 

are used by vehicle manufacturers to certify compliance with EPA refueling emission standards

for ORVR vehicles, and are ideal for studying refueling emissions as a function of different 

variables. In this study, those variables were: type of vehicle ORVR equipment (ORVR with

vapor recirculation to the fill neck, ORVR without recirculation, no ORVR), fuel RVP, 

temperature conditions, and A/L ratio. A matrix of 36 SHED tests was performed to quantify the 

7
dependence of refueling emissions at the nozzle/fillpipe as a function of the above variables and 

to examine the compatibility issue. In addition, six refueling tests using CARB method TP201.2 

were performed by VOC Testing, Inc. outdoors at a dispenser equipped with the same Gilbarco 

VRS and next to the UST. During those tests and for a period of up to two hours after each test, 

ATL collected emissions at the P/V valve and a needle leak valve on the instrumented cap of the 

UST, calibrated to leak at the maximum rate allowed under CARB TP201.3. (The UST and 

piping were first tested to ensure they were airtight.) 

As with the Phase 1 TP201.2 tests, hydrocarbon concentration and pressure data were 

continuously recorded. The objectives were to quantify differences in refueling emissions and 

excess emissions between ORVR and non-ORVR vehicles, and to compare actual measured 

excess emissions to those predicted using the equation in CARB’s method in TP201.2F. These

tests were not designed to measure efficiency under the CP-201 Vapor Recovery Certification 

Procedure. 

2.4 Description of the Refueling Emissions Process

Refueling emissions occur from vapor displacement and from spillage. This testing program 

only examined vapor displacement emissions, which result from the addition of liquid fuel to a 

vehicle’s fuel tank. As the tank is filled, vapor present in the headspace of the tank is displaced

from the tank. For a vehicle without ORVR (“non-ORVR vehicle”), these vapors are pushed out 

the vehicle’s fillpipe. The amount of emissions displaced is known to be dependent upon the 

fuel volatility, the temperature of the vehicle’s fuel tank, the temperature of the fuel being 

dispensed, and the vehicle being refueled (e.g., fillpipe geometry and design).2

 Vehicles 

equipped with ORVR (“ORVR vehicles”) capture vapors from the tank headspace on a carbon

canister within the vehicle; the vapors are later desorbed into the engine while the engine is being 

operated. Some ORVR vehicles are equipped with a recirculation loop that returns a portion of 

the gasoline vapors to the neck of the fill pipe to reduce the intrusion of outside air into the

system. All ORVR systems without a mechanical seal use a “liquid seal” to prevent vapors from 

 

2

 US EPA, “Compilation of Air Pollutant Emission Factors,” AP-42, Chapter 5, Section 5.2.2.3 (rev. 1/95).

8
going out the fill neck. The effectiveness of this nonmechanical seal depends on many factors, 

including the fillpipe and ORVR designs, and the fuel flow rate. 

A VRS—sometimes referred to as “Stage II” equipment3

—is designed to capture vapors from 

the area where the refueling nozzle is inserted into the vehicle fillpipe. Each VRS is designed to 

direct these vapors back to the headspace of the UST. In theory, if the volume of liquid 

dispensed from a UST is equal to the volume of vapor returned and the temperatures and 

concentrations in the vapor return line and UST are identical, there is no change in the UST 

pressure. Some VRS models are vacuum-assisted (“vac-assist”), meaning that a vacuum pump is

utilized to help capture the displaced vapors from the dispenser/fillpipe interface and direct them 

to the UST. When an ORVR vehicle is refueled, however, some of the displaced vapors are not 

being returned to the dispenser/fillpipe interface. Therefore, for most vehicles,4

 if a vac-assist

VRS is utilized on an ORVR vehicle, the VRS may draw in ambient air at the nozzle-fillpipe

interface and return it to the UST. Because this dilutes the concentration of hydrocarbons in the 

UST headspace, there is potential for the gasoline in the UST to evaporate, in order to equilibrate 

the headspace with the liquid. This in turn raises the pressure of the UST, and can cause it to 

vent more often than if no VRS had been present. This concept is commonly referred to as

“ORVR incompatibility” and is discussed further in Section 3.4. 

 

3

 “Stage I” equipment refers to systems that recover vapors during the transfer of gasoline from tanker trucks to the

UST at a GDF. 4

 A small percentage of vehicles—the California Air Resources Board (CARB) estimates 5% or less—are equipped

with “mechanical seals” between the dispenser nozzle and fillpipe, reducing the opportunity for air to be drawn into

the VRS. 

9
FIGURE 2-1 

TP-201.2 TEST POINTS 
3.0 SCIENTIFIC PRINCIPLES 

This section provides a brief summary of relevant existing knowledge on the factors affecting 

uncontrolled refueling emissions, Onboard Refueling Vapor Recovery (ORVR) Canisters, 

vacuum-assisted Stage II Vapor Recovery Systems (VRS), and the issue of ORVR / VRS 

“Incompatibility”. 

3.1 Factors Affecting Uncontrolled Refueling Emissions

Uncontrolled vapor displacement refueling emissions (expressed in units of mass emitted per 

unit volume of gasoline transferred) are known to be a function of the temperature of the 

dispensed fuel (TD), the temperature of the vehicle fuel tank (TT), the fuel volatility (RVP), and 

differences in vehicle design (e.g., fillpipe design) that are not readily quantifiable. EPA’s 

formula for estimating uncontrolled refueling emissions (not including spillage), in EPA’s AP-42 

emissions factor publication,5 involves the use of an equation which takes temperature and 

gasoline volatility (RVP) into account: 

 ER = (-5.909) – 0.0949 (∆T) + 0.0884 (TD) + 0.485 (RVP) (3-1) 

where: 

 ER = emissions factor in grams VOC per gallon transferred (g/gal) 

 ∆T = TT - TD, o F 

 TD = temperature of dispensed fuel, o F 

RVP = Reid vapor pressure, psia 

The dependence upon ∆T results is explained by a hypothesis that “vapor growth” occurs if the 

fuel being added is warmer than the fuel in the tank (i.e., tank temperature increases and 

therefore equilibrium vapor pressure above the liquid increases), while “vapor shrinkage” occurs

if the fuel being added is cooler than the fuel in the tank. Equation (3-1) is applied to all 

gasoline-fueled vehicle types (ranging from motor cycles to vehicles with gross vehicle weights 

of over 60,000 lb) and was developed by EPA in 1985, based upon tests conducted in a Sealed 

 

5

 US EPA, “Compilation of Air Pollutant Emission Factors,” AP-42, Chapter 5, Section 5.2.2.3 (rev. 1/95).

11
Housing for Evaporative Determinations (SHED), on eight vehicles for model years 1979-1984. 

Testing was conducted with gasoline RVP’s of 9.0-12.6 psia, dispensing temperatures of 66-95o 

F, and ∆T values ranging from –12 to +32o F. The equation explains 79% of the variance in the

empirical data.6

 EPA noted that differences between vehicles contribute to emissions factor 

variability (differences of 18% were seen in the results in at least one study) and that other 

factors (fill rate, amount of residual fuel in the tank, total amount of fill, position of the nozzle in

the fill-neck, and ambient temperature) also had an effect but that the magnitude of these effects

was relatively low. 

EPA’s AP-42 formula (3-1) is also incorporated into EPA’s MOBILE7

 models (including 

versions 5ah, 5b, and 6), which calculate ∆T as follows: 

∆T = 0.418*TD – 16.6o F (3-2)

EPA has not provided any documentation for Equation 3-2, and the origin of this equation is 

unclear. There are at least two other issues that are not mentioned in EPA’s documentation of 

the refueling emissions calculations.

7

 First, since TD is not easily measured, the MOBILE model

program code assumes that TD is equal to the ambient temperature TA (an API study by Radian8

found that TD is somewhat higher than TA, and that this offset varies seasonally and regionally). 

The second issue is that the model program code9

 “cuts off” aspects of the formula, as follows: 

 If TD < 20o F, MOBILE sets TD = 20o F. 

 If TD > 95o

 F, MOBILE sets TD = 95o F. 

 If ∆T is calculated to be > 20o F, MOBILE sets ∆T = 20o F. 

 

6

D. Rothman and R. Johnson (US EPA), “Refueling Emissions from Uncontrolled Vehicles,” Report No. EPA-AASDSB-85-6, August 1985. 7

US EPA, “User’s Guide to MOBILE5 (Mobile Source Emission Factor Model),” EPA-AA-AQAB-94-01, May 

1994 and “User’s Guide to MOBILE6 (Mobile Source Emission Factor Model),” EPA420-R-02-001, January 2002. 8

 Radian Corp., “Summary and Analysis of Data From Gasoline Temperature Survey Conducted at Service Stations

by API,” API Publication No. 4278, 1976. 9

See the REFUEL subroutine within the MOBILE models. 

12
If inputs are such that ER is calculated to be less than 1.80 g/gal (= 3.97 lb/1000 gal), ER is set 

equal to 1.80 g/gal. The origin of these cutoffs is unclear;10 the original study only mentions that 

the maximum fuel temperature (TD) studied was 95o F and does not mention the other cutoffs. 

When reformulated gasoline is utilized, MOBILE6 assigns an RVP of 6.7 psia in calendar years 

2001-2002 and an RVP of 6.8 psia in calendar years 2003 and later. 

3.2 Onboard Refueling Vapor Recovery (ORVR) Canisters 

Onboard Refueling Vapor Recovery (ORVR) vehicles incorporate a carbon canister that adsorbs 

gasoline vapors displaced during refueling and desorbs them during vehicle operation, at which 

time they are burned in the engine. ORVR canisters have a finite capacity and are only desorbed 

during engine operation; thus, if a car sits for enough days in the hot sun, emissions will vent off 

the canister through a release line under the car. A potential problem when fueling an ORVRvehicle is that the flow of fuel entering the narrow fillpipe creates a venturi effect resulting in a

suction of outside air through the fuel neck, adversely affecting system performance.11 To

prevent air ingestion at the fill neck and to reduce the vapor load to the canister during refueling,

many ORVR systems are equipped with recirculation line to return vapors in the tank to the top 

of the nozzle/fillpipe area.12 The recirculation line also helps isolate the tank from the outside 

environment and reduce emissions out the fuel neck. All ORVR systems without a mechanical

seal use a “liquid seal” (really a fluid dynamics seal) in which the liquid column of fuel in the 

vehicle’s fuel neck and its downward flow mostly prevents displaced vapors during refueling

from escaping out the fill neck. The effectiveness of this nonmechanical seal depends on many 

factors, including fillpipe and ORVR designs, and the fuel flow rate. 

Section 202(a)(6) of the Clean Air Act requires vehicle manufacturers to equip new vehicles 

nationwide with ORVR systems in accordance with the schedule in Table 3-1. ORVR systems 

 

10Lois Platte (US EPA), in a telephone conversation with Robert Rossi (Tech Environmental), March 12, 2002, 

stated that the cutoffs corresponded to parameter ranges for which data existed, but did not elaborate as to why these 

do not match the parameter ranges in EPA’s 1985 reference document. 11 Belforte G., Carello M., Eula G., Ferraresi C., Ivanov A., “Preliminary study of the liquid seal phenomenon”, 

FLUCOME 2000, Sherbrooke, Canada, 13-17 agosto 2000, ISBN 2-7622-0126-8. 12 Personal communication with Harold Haskew, Harold Haskew & Associates, Inc., Milford, MI, March 18, 2002, 

and Stant Manufacturing, Inc., “Stant ORVR System Theory of Operation,” Connersville, IN, 

http://www.gates.com/index.cfm?location_id=706. 

13
are required by federal law to be 95% effective at reducing refueling emissions from ordinary 

GDFs (not equipped with Stage II VRS) and federal test procedures require that “refueling 

emissions” include both vapor displacement and spillage during refueling. EPA regulations 

require that ORVR canisters keep refueling emissions at or below 0.20 grams per gallon of 

gasoline dispensed throughout the full useful life13 of the vehicles, and when tested most ORVR 

vehicles easily meet the limit, emitting typically 0.10-0.15 g/gal. EPA’s MOBILE6 model

assumes ORVR controls refueling emissions from the fill pipe by 98%, and refueling spillage by

50%. EPA’s refueling emissions test procedures include measurement of both the vapor 

displaced during refueling and the evaporation of any liquid spillage that occurs; testing is

conducted in a SHED. Dispensed fuel temperature (TD) is kept at 67 (+/- 1.5) o

F, and refueling 

is conducted with a standard (non-Stage II VRS) nozzle. 

When EPA promulgated the ORVR standards in 1994, Stage II VRS were no longer required in 

Moderate ozone non-attainment areas (except in the Ozone Transport Region, comprised of the 

States from Virginia to Maine plus the District of Columbia), and section 202(a)(6) also states 

that the EPA Administrator “may...waive the application of the requirements [for GDF vapor

recovery systems in nonattainment areas classified as Serious, Severe, or Extreme]...after such 

time as the Administrator determines that [ORVR] systems...are in widespread use throughout

the motor vehicle fleet.” Although the term “in widespread use” has not yet been formally 

defined, EPA has suggested that it will consider either “the percentage of the automobile fleet 

equipped with ORVR,” or “when ORVR achieves emissions reductions on a one-to-one basis 

when compared to Stage II.”14

 

13EPA defines “full useful life” in 40 CFR 86.1805-01 and 86.1805-04; although the exact definition varies for 

vehicle types, the minimum definition is 10 years or 100,000 miles. 14Letter from Jason Grumet (NESCAUM) to Tom Helms and Gregory Green (EPA), October 11, 2001.

14
TABLE 3-1 

ORVR IMPLEMENTATION SCHEDULE 

Model Years (MY) for Which ORVR Mandate Must Be Met15

ORVR 

Mandate 

(% of 

Vehicles 

Sold) 

Light-Duty 

Vehicles16

Light LightDuty Trucks

17

(0-6,000 lb) 

Heavy LightDuty Trucks

17

(6,001-8,500 lb) 

Medium Duty 

Passenger 

Vehicles18

(8,501-10,000 lb) 

Complete Heavy 

Duty Vehicles19

(8,501-10,000 lb) 

40% 1998 2001 2004 2004 200420

80% 1999 2002 2005 2005 2005

100% 2000+ 2003+ 2006+ 2006+ 2006+

 

15ORVR phase-in schedule is included in 40 CFR 86.1810-01(k) for light-duty vehicles and light-duty trucks;

extended to medium-duty passenger vehicles in §86.1811-04(e)(3)(iii). 16Defined as “a passenger car or passenger car derivative capable of seating 12 passengers or less” (40 CFR

86.1803-01). 17“Light Duty Trucks” (LDT’s) are defined as “any motor vehicle rated at 8,500 pounds GVWR or less which has a 

curb weight of 6,000 pounds or less and which has a basic vehicle frontal area of 45 square feet or less, which is:

(1) designed primarily for purposes of transportation of property or is a derivative of such a vehicle; or (2) Designed

primarily for transportation of persons and has a capacity of more than 12 persons; or (3) Available with special

features enabling off-street or off-highway operation and use.” LDT’s are subdivided into “Light Light-Duty 

Trucks” (up to 6,000 lb GVWR) and “Heavy Light-Duty Trucks” (6,001-8,500 lb GVWR). 18Defined as “any [vehicle rated at more than 8,500 lb GVWR or that has a vehicle curb weight of more than 6,000

lb or that has a basic vehicle frontal area in excess of 45 sq. ft.] with a [GVWR] or less than 10,000 pounds that is 

designed primarily for the transportation of persons.” 19Defined as “any Otto-cycle [vehicle rated more than 8,500 lb GVWR or that has a vehicle curb weight of more 

than 6,000 lb or that has a basic vehicle frontal area in excess of 45 sq. ft.]...that has the primary load carrying 

device or container attached at the time the vehicle leaves the control of the manufacturer of the engine.” 20Manufacturers can choose a compliance option that eliminates the refueling standards for 2004 for this vehicle 

type [§86.1816-05(e)(3)]. 

15
3.3 Vacuum-Assisted Stage II Vapor Recovery Systems (VRS)

Sections 182(b)(3) and (c)-(e) of the Clean Air Act require gasoline dispensing facilities (GDFs) 

in nonattainment areas classified as “Moderate,” “Serious,” “Severe, or “Extreme” to install and

operate vapor recovery systems (VRS) to capture vapor displaced from vehicles’ fuel tanks as 

they are filled. These are commonly referred to as “Stage II” systems and are certified to be 95% 

effective on a fleetwide average at capturing displaced vapors. Historically, the 95% control 

efficiency was determined by only considering emissions at the fillpipe-nozzle interface and at 

the P/V valve on the UST. There was no consideration pressure-related fugitive emissions from 

the UST and piping. Only GDFs with average monthly throughputs of less than or equal to 

10,000 gallons, “independent small business marketers” with average monthly throughputs of 

less than or equal to 50,000 gallons, and marinas/marine vehicles are exempt from these

requirements. 

When fuel is added to a vehicle’s tank, air and gasoline vapor in the tank headspace (which can 

consist of approximately 30-40% gasoline vapor and 60-70% air in the summer) are displaced. 

With a vacuum assist Stage II VRS, a vacuum system pulls the gases in through perforations in 

the nozzle spout to a return hose that connects to the headspace of the underground storage tank 

(UST). For these systems, the GDF’s storage tank is required to be equipped with a 

pressure/vacuum (P/V) valve, which is designed to open only if the pressure inside the tank 

increases to more than 3” water column (w.c.) above atmospheric pressure or decreases to less 

than 8” w.c. below atmospheric pressure. 

The ratio of the volume of air and vapor returned to the UST (A) to the volume of liquid 

dispensed (L) is the A/L ratio, and air flow meters used in CARB method TP201.2 are calibrated 

with nitrogen gas. Stage I gasoline transfers into the UST from a tanker truck can pressurize the 

UST and temporarily affect the A/L. Filter changes at the UST can also affect the A/L through 

the dispensing rate. In theory, if A/L>1, pressurization of the UST will occur. Vacuum assist 

VRS are certified at A/L ratios from 0.85 to 1.20, with the exception that a small percentage of

such systems are equipped with destructive processors (i.e., that thermally oxidize the vapors)

and have higher A/L ratios in the range of 1.35 to 2.4. Some vacuum assist systems use a “mini16
boot” to enable the systems to run at slightly lower A/L ratios (similar to the “vapor balance” 

VRS, which require a boot to make a tight fit during refueling). 

 

3.4 ORVR / VRS “Incompatibility”

The California Air Resources Board (CARB) has stated that there is a potential for “excess 

emissions” of pressure-related fugitives when vacuum assist Stage II VRS are used to refuel 

vehicles equipped with ORVR. Specifically, because the ORVR systems remove much of the 

vapors that vacuum assist Stage II systems are designed to pull back, the vacuum assist systems 

can create negative pressure in the fill pipe. If this occurs, ambient air from the vicinity of the

GDF nozzle/fill pipe interface will be drawn back into the UST. Because this dilutes the 

concentration of gasoline vapor in the headspace of the storage tank, a portion of the liquid 

gasoline in the storage tank will volatize and increase the partial pressures of the gasoline 

constituents towards their equilibrium values. This causes the total pressure in the storage tank

to rise. Increased UST pressure in the headspace (ullage) can increase fugitive emissions

through leaks in the piping system, and if the gauge pressure increases above the positive setting 

of the P/V valve (typically 3” w.c.), the storage tank will vent to the atmosphere. 

To date, the only publicly available test report addressing ORVR compatibility is a 1999 study 

conducted by CARB personnel.21 Two different GDFs were tested, each with a different vacuum

assist VRS: one in Sacramento, CA, which utilized a Dresser Industries WayneVac VRS, and 

one in El Sobrante, CA, which utilized a Gilbarco VaporVac VRS. At the time that testing was 

conducted, few vehicles were equipped with ORVR. To simulate ORVR vehicles, CARB 

modified dispensers at the facility to simply ingest ambient air (0% vapor) to the UST via the

VRS vapor return line. Thus, no ORVR vehicles were actually tested in the CARB study.

CARB calculated (but did not directly measure) fugitive UST emission increases resulting from

ORVR incompatibility from differences in UST pressures. The CARB study did not quantify the 

decrease in emissions at the nozzle/fillpipe interface that resulted from ORVR. 

 

21 California Environmental Protection Agency, Air Resources Board, Preliminary Draft Test Report, “Total

Hydrocarbon Emissions from Two Phase II Vacuum Assist Vapor Recovery Systems During Baseline Operation 

and Simulated Refueling of Onboard Refueling Vapor Recovery (ORVR) Equipped Vehicles,” Project Number ST98-XX, June 1999. 

17
In the CARB ORVR compatibility study, negligible emissions were emitted from the P/V valve, 

i.e., all UST emissions were in the form of pressure-related fugitives from other unknown 

locations. These emissions cannot be measured directly by CARB methods and are difficult to 

quantify. Their existence is assumedly the reason why UST pressure decays slowly with time,

rather than holding steady. Thus, fugitive emissions are estimated by multiplying the 

hydrocarbon vapor concentration in the UST headspace by a fugitive leakage flow rate. The 

volumetric leakage rate is in turn calculated as a function of UST pressure and pressure changes 

with time. CARB’s equation for calculating volumetric leakage rate (TP201.2F) has changed 

significantly over time and has several deficiencies. For example, the assumed dependence of 

volumetric leakage on the square root of tank pressure (see Section 5.2, equation 4-2) is 

inconsistent with data in the 1999 CARB report that show flow rate is a quadratic function of

pressure; this error leads to over-prediction, especially at low tank pressures. In a related study 

by the Bay Area AQMD, testing was done with both standard and mini-boot nozzles, and the 

results showed UST pressures decreased compared to standard nozzle configurations when miniboots were employed. CARB calculated a 50% reduction in fugitive emissions for mini-boot 

nozzles from those test data. 

CARB found higher emissions for the Gilbarco VaporVac system than for the WayneVac 

system, due in part to the lower A/L ratio for the WayneVac compared to the VaporVac. A 

review of CARB’s work by Tech Environmental, Inc. revealed that the calculated Gilbarco 

VaporVac “excess emissions” were biased high because: (1) some A/L values were too high; and 

(2) the A/L values drifted upwards from the time of the baseline testing to the time of the ORVR 

simulations. CARB also acknowledges in their report (p.8) that the incompatibility effect was

overestimated by the introduction of ambient air and no return vapors into the UST headspace. 

Data for the Wayne system support the conclusion that when considering total emissions from 

refueling (from both the fill neck and the UST), there are no “excess emissions” due to ORVR 

incompatibility for the Wayne system that was tested. Other research done by CARB shows that

refueling liquid seal ORVR-equipped vehicles when a Gilbarco VRS is in operation returns a

18
vapor mixture containing an average of 6.6% hydrocarbons in the vapor return line to the UST 

(average of data from 54 tests).22

 

22 California Air Resources Board, “Vapor Return Path Hydrocarbon Concentrations in Vacuum Assist Vapor 

Recovery Systems Dispensing Gasoline to ORVR Equipped Vehicles,” Project C-97-024, March 1998, Tables 6-8

through 6-10. 

19
4.0 TESTING METHODOLOGIES 

4.1 Phase 1 – Fleetwide Tests

4.1.1 Overview

This first phase of the testing program was conducted to investigate vehicle refueling emissions 

from gasoline dispensing facilities (GDFs) and the compatibility of a Gilbarco VaporVac VRS 

with ORVR on motor vehicles. Testing was done in accordance with test procedures in CARB

method TP201.2 at the Conoco Service Station located at 3405 Highland Avenue in San 

Bernardino, California. Mr. Del Powell of VOC Testing, Inc. conducted the testing between 

October 31 and November 7, 2002. 

The test procedures in the most recent adopted version of TP201.2, Efficiency and Emission 

Factor for Phase II Systems, (July 25, 2001) were used, with CARB’s recent 100-vehicle matrix 

(March 18, 2002). This method has a quantifiable minimum value of 0.01 lb/1,000 gallons (see 

Section 4.1 of TP201.2). Two sets of tests were performed: 

1. Test 1 consisted of a 100-car matrix. Standard OPW 11VA1 nozzles were used with the 

Gilbarco system, certified to operate at an air/liquid (A/L) ratio of 1.0 to 1.2, and 

operated in the upper end of the allowable range (1.14-1.19). 

2. Test 2 consisted of a 100-car matrix. OPW 12VW nozzles with “mini-boots,” certified 

to operate at an A/L ratio of 0.9 to 1.1, and operated at the lower end of the allowable 

range (0.92). 

The fuel in the USTs during the entire testing program (through November 7) was California 

summertime reformulated federal gasoline (RFG), oxygenated with ethanol, in grades 87 and 91 

octane, and having a Reid Vapor Pressure (RVP) of 7.0 psi. 

Three CARB test procedures were used: TP201.2 (7/25/01 version) for refueling emissions; 

TP201.3 (3/17/99 version) for pressure decay tests on the UST; and TP201.2F (8/20/02 proposed

revision) for pressure measurements, fugitive emission calculations, and UST headspace vapor 

20
sampling. The CARB test procedures were used to collect research data and not to certify a

GDF, and thus some details for certification were not followed. TP201.2 is a fleetwide average

test and normally a matrix of 200 vehicles is required for the certification test at a GDF. This 

testing program used CARB’s smaller 100-car matrix. A copy of all test procedures is given in 

Appendix A. 

CARB Test Procedure TP-201.2, used in this phase of the test program, was developed to 

quantify the vapor recovery mass efficiency and/or mass emission factor by directly measuring 

the mass of hydrocarbons at the locations shown in Figure 2-1. These locations are: 1) emitted at 

the nozzle/vehicle interface, 2) returned through the vapor passage of the hose, 3) emitted from 

the pressure/vacuum (P/V) valve(s) on the underground storage tank (UST) vent pipe(s), 4) 

emitted from the assist processor, if applicable, and 5) emitted as pressure related fugitives. 

Emissions from points 1 and 2 are on a per-vehicle basis, for vehicles at the dispenser being 

tested, whereas emissions for points 3 and 4 are continuous and influenced by other vehicles 

refueling at the facility since all dispenser vapor return lines are connected together at the UST 

common manifold. Emissions from point 5 are calculated, using the equations in CARB Test 

Procedure TP-201.2F. This first phase of the test program quantified emissions from locations 

1,2, and 3. Location 4 is not applicable. The second phase of this testing program directly 

measured emissions point 5 for ORVR vehicles. 

To quantify the vapor tightness of the VRS system, CARB Test Procedure TP-201.3 was used. In 

this procedure, the VRS is pressurized with nitrogen to 2.0 in. w.c. and then is allowed to decay 

over five minutes. This value is compared with an “allowable value”, which is based on the 

system ullage and pressure decay equations. The test was conducted at the beginning and end of 

Tests 1 and 2, and this information was used to calculate fugitive emissions using the equations

in TP-201.2F. UST headspace vapor concentrations were collected continuously from (and recirculated back to) the UST common header and analyzed with an NDIR. 

21
4.1.2 Testing Details 

The Conoco Service Station at 3405 Highland Avenue in San Bernardino, CA, was selected for 

testing refueling emissions. The station has a fairly low throughput and consists of eight 

dispensers, all Gilbarco VaporVac systems; two of the nozzles are generally equipped with miniboots and six are not. During Test 1 the two nozzles equipped with mini-boots were covered and 

identified as not operational. All TP201.2 tests were done at dispenser #3. Additional minibooted nozzles were installed for Test 2, so that all gas was dispensed from a similarly equipped 

nozzle during each test. To eliminate any variability due to different operators, VOC Testing, 

Inc. performed all fueling at dispenser #3. 

The test procedures in CARB method TP-201.2 were used with CARB’s 100-vehicle matrix 

(March 18, 2002), rather than the 200-vehicle matrix identified in the test procedure. During 

Test 1, 95% of the vehicles identified in the matrix were obtained; during Test 2, 99% were 

obtained. Vehicles tested were identified by make, model, and whether or not the vehicle has 

ORVR. CARB’s methodology for determining whether or not a vehicle has ORVR (by the 

“evaporative family” sticker under the hood) was not always successful, since some vehicles did

not have this sticker. Thus, in some instances the contractor estimated ORVR from the age of 

the vehicle and other factors. 

A factor affecting the nozzle/fillpipe emissions was whether or not a car pre-paid for the 

gasoline. The area where the station is located is economically depressed, which resulted in 

many customers opting to pre-pay for the fuel (generally $5 or $10 worth), rather than filling up 

their vehicle tanks. Since CARB requires a minimum of 6 gallons for refueling tests, customers 

were given an incentive for fueling at least 6 gallons of gas. In a pre-pay refueling, during the 

last 15-30 seconds the liquid and vacuum pumps slow down, executing a slow cutoff; VOC 

Testing noted a spike in emissions towards the end of the refueling. During Test 2, there was 

less of a spike, due to the mini-boot. 

At dispenser #3, less than 20% of the fuel was dispensed to vehicles equipped with ORVR

systems. The ORVR portion of tested vehicles could not be increased because TP201.2 tests at 

22
dispenser #3 were targeting vehicles within a mandated matrix. We also note that this number is

not representative of the percentage of fuel dispensed to ORVR vehicles at the GDF. 

Information regarding all other vehicles refueling at the station was not possible to obtain 

throughout the course of this study, but a short survey one afternoon suggests that approximately 

8% of the fuel normally dispensed by the GDF was dispensed to ORVR-equipped vehicles. The 

station’s location in a low-income area could explain the lower percentage of ORVR vehicles 

than in the general vehicle population. 

This phase of the study was not designed to study differences in refueling emissions linked to

fuel RVP, and over the course of the testing program, the RVP of the fuel was never varied. 

However, given that the RVP of fuel should change from summer-time RVP to winter time RVP 

on November 1, vehicles refueling at the station after November 1 could potentially contain 

higher-RVP fuel, obtained from another station. Drivers were asked when and where they had

most recently refueled and this information was noted, though drivers often did not recall their 

last refueling. From this limited information, it was not possible to definitely determine the

effect of potential change in RVP of the fuel remaining in a vehicle tank before it was refueled

with the RFG RVP 7.0 fuel, and none of the Test 2 vehicle data were excluded. 

During the testing, Underground Storage Tank (UST) temperature data were collected with the 

Veeder-Root system. Meteorological data, including ambient temperature data, were obtained 

from the nearest National Weather Service (NWS) station in Riverside, California (and from the 

Riverside March Air Force Base on one day, November 7, when data were missing from the 

NWS station). 

4.2 Phase 2 – Laboratory Tests

4.2.1 Overview

The second phase of the study was performed at Automotive Testing Laboratories in Mesa, AZ 

under the direction of Mr. Dennis McClement, Vice President of Engineering. Mr. Del Powell 

of VOC Testing, Inc. also conducted refueling tests with CARB methods as part of this phase of 

the program. The second phase directly examined the issue of compatibility between the

23
Gilbarco VRS and ORVR-equipped vehicles and “excess emissions” by measuring the pressurerelated fugitive emissions at the UST (leaks) plus emissions at the P/V valve. The work was 

done between July and October 2003. This phase had two separate work tasks: 

1. Task 1 – Outdoor Tests. Data were taken on three vehicles and two USTs in order to: 

a. Compare fugitive emissions at the UST, 

b. Compare fugitive emissions resulting from ORVR and non-ORVR vehicles, and 

c. Compare fugitive emissions predicted by CARB’s method TP 201.2F. 

To accomplish this work six refueling tests using CARB method TP201.2 were 

performed outdoors at a dispenser equipped with a Gilbarco vacuum-assist VRS 

(VaporVac) drawing product from a 3,000 gallon UST containing 1,000 gallons of RVP 

7.8 psi summer grade gasoline oxygenated with ethanol (91 octane). This method has a 

quantifiable minimum value of 0.01 lb/1,000 gallons. The UST and piping were first 

tested and tightened to ensure they were essentially airtight. During each refueling test

and for up to two hours after, ATL collected emissions at the P/V valve and pressurerelated fugitive emissions at a needle leak valve on the instrumented cap of the UST. The 

needle valve was calibrated to leak at the maximum rate allowed under CARB TP201.3. 

Finally, “excess emissions” related to ORVR incompatibility with the VRS were 

calculated. 

2. Task 2 – Indoor SHED Tests. Thirty-six refueling tests in a SHED were conducted 

following a test procedure similar to the federal ORVR certification test to quantify the

nozzle/fillpipe emissions as a function of four variables: type of ORVR equipment, fuel 

RVP, temperature conditions, and A/L ratio for the VRS. 

Three CARB test procedures were used: TP201.2 (7/25/01 version) for refueling emissions; 

TP201.3 (3/17/99 version) for pressure decay tests on the UST; and TP201.2F (8/20/02 proposed

revision) for pressure measurements, fugitive emission calculations, and UST headspace vapor 

sampling. 

Test Vehicles 

Three vehicles were used in this phase of the program, and all ORVR vehicles used a liquid seal 

typical of such vehicles on the road in the U.S. A baseline certification test was done on each of 

the ORVR vehicles (without the VRS in operation) to verify they complied with the federal 0.2 

24
g/gallon limit as a check on the proper operation of their ORVR systems. The three vehicles

were: 

Vehicle 1 ORVR with vapor re-circulation to the fill neck.

 2003 Toyota Echo 

 (ORVR Certification Test result 0.008 g/gal) 

Vehicle 2 ORVR without vapor recirculation 

 2003 Chevy Blazer 

 (ORVR Certification Test result 0.001 g/gal) 

Vehicle 3 No ORVR 

1995 Nissan Maxima

Fuels and Tanks 

The two fuels used in this phase were RVP 7.8 psi summer gasoline, oxygenated with ethanol 

(5.5% by volume), octane 91 and Certified RFG, RVP 7.0 psi, oxygenated with ethanol (8.3% by 

volume), octane 91. ATL performed RVP testing throughout this phase of the study and a minor 

amount of butane was added as necessary. The RVP had to remain in the range of +0.2 psi to –

0.3 psi of the target RVP (7.0 or 7.8 psi) at the completion of a test for that test to be valid. 

Fuel was stored in a series of ATL’s existing USTs, and where temperature was a constant 83o

 F. 

For Task 1 – Outdoor Tests, 1,000 gallons of the RVP 7.8 fuel were pumped into a 3,000 gallon 

UST, providing 2,000 gallons of ullage (head space) which exceeds the 1,000 gallon minimum 

ullage specified in CARB’s pressure decay test (TP201-3, Section 6.3). ATL continuously 

monitored pressure in the UST during the outdoor tests. For Task 2 – Indoor SHED Tests, 50 

gallons of fuel at a time were pumped into an instrumented fuel delivery cart. 

ATL installed a P/V valve on a riser pipe from the 3,000-gallon UST that opens only at tank 

pressures higher than +3” w.c. and less than –8” w.c. There was a minimum waiting time of one 

hour between the outdoor tests to allow the head space concentration in the UST to reach

equilibrium, and just prior to each such test, the UST was set at 0” w.c. (i.e., depressurized) so 

that each test was done with the same starting tank conditions. 

25
Three temperature conditions were studied using as independent variables: 1) TD, the 

temperature of dispensed fuel; and 2) ∆T = TT - TD , where TT is the vehicle fuel tank 

temperature. TD was controlled by a heating/chiller coil in the fuel line and measured by ATL in 

a coupling between the fuel line and the nozzle. TT was controlled by soaking the vehicle in the

SHED for four hours; this ensured both the vehicle fuel tank and head-space vapor stabilized at 

the specified test temperature. 

A national gasoline temperature survey done for API23 reveals that in the summer months the

highest dispensed fuel temperature for the hottest days (TD) ranges between 75o

 and 90o F and

ranges 0o

 to 15o F above the temperature of the UST, Tg, depending on the region of the country. 

That research also shows that in the summer, vapor shrinkage conditions are 5 times more

prevalent than vapor growth conditions and the average ∆T values are +13o

 F (for vapor 

shrinkage conditions) and –4o

 F (for vapor growth conditions). Using this information in our 

study, reasonable summertime (ozone season) temperatures were selected, making sure to vary 

only one independent variable between test conditions, and to provide significant temperatures 

differences (∆T) so that both vapor shrinkage and vapor growth effects could be studied. Tg is 

assumed invariant at 75o

 F. The three selected summertime conditions are: 

Condition TD ∆T TT

 1 75o

 -5o 70o vapor growth 

 2 75o

 +15o 90o vapor shrinkage 

 3 90o

 +15o 105o vapor shrinkage 

A/L Ratios 

A new Encore 300 dispenser with a Gilbarco VaporVac VRS was purchased by ATL and 

equipped to use either a standard OPW 11VA1 nozzle (certified to operate in the range of 1.0 – 

1.2 A/L) or an OPW 12VW nozzle with a mini-boot (certified to operate in the range of 0.9 – 1.1 

A/L). ATL purchased both nozzles new. The Gilbarco system was set at the following ratios: 

1) A/L = 1.15 with standard nozzle 

 

23 Radian Corp., “Summary and Analysis of Data From Gasoline Temperature Survey Conducted at Service Stations

by API,” API Publication No. 4278, 1976. 

26
2) A/L = 0.95 with mini-boot nozzle 

The A/L ratio was tested first as part of the pre-test integrity verification (see below) and several 

additional times during the test program, especially when the A/L ratio and nozzle were changed. 

All the target values and within the certification ranges. 

The contractor installing the Gilbarco VRS performed the following integrity tests:

CARB TP201.5 Air to Liquid Volume Ratio (2/1/01 version) 

CARB Advisory No. 179 Ring or Bag Test (11/29/00 version) 

4.2.2 Testing Details – Outdoor Tests 

Performing controlled tests outdoors at ATL’s facility in Mesa, AZ during the summer presented 

a timing challenge to the research team. Pressure measurements on the UST over a diurnal 

period showed heating effects of the sun influenced UST system pressures not too long after

sunrise, starting at 8:30 a.m., and did not abate until shortly before sunset. Thus, it was decided 

that all tests would be done at night and end before 8:30 a.m. in the morning. Due to a persistent 

high-pressure ridge over the western U.S. during the month of July, nighttime temperatures in 

Mesa remained high and in general varied no more than 1o

 F per hour. Air temperatures during 

the multi-night tests (as measured at nearby Phoenix Sky Harbor Airport) were in the range of 

87o

 to 99o F. The dry air, lack of rain, lack of solar insulation and fairly constant temperatures 

during the test periods provided fairly consistent weather conditions for the outdoor tests. 

Prior to the tests, the Gilbarco installer (West Star Contracting) did several TP201.3 pressure

decay tests and found the system to be essentially airtight (the measured decay rate was only

0.01-0.02” w.c. from 2.00” w.c. pressurization over five minutes). A second TP201.3 test at the 

conclusion of the outdoor tests by the Gilbarco installer confirmed the same, almost zero leak 

rate (0.02” decay from 2.00” pressurization over five minutes). A TP201.3 test done by ATL 

toward the end of the tests showed a loss of 0.05” w.c. over five minutes. TP201.3 tests done by 

VOC Testing, Inc. showed rates of 0.04” to 0.09” w.c. over five minutes, with the higher decay 

rates measured before minor leaks were found and fixed in their tubing connections to the 

system. 

27
Once the team was confident the UST and piping system was essentially air tight, a needle valve

was installed on the instrumented cap of the UST and calibrated to produce a leak rate equal to

the maximum allowed under TP201.3 (for 2,000 gallons ullage, single dispenser), namely a 

decay from 2.00” w.c. to 1.56” w.c. (a decay of 0.44” w.c.) in five minutes. The orifice of the

leak valve was fit with a coupler for a Tedlar sampling bag. The outlet of the P/V valve was also 

bagged, though pressures in the system never rose high enough to crack the P/V valve, due to the 

engineered leak at the needle valve and the fact that only a single refueling event was being 

studied at a time. 

The six refueling tests used the higher RVP 7.8 fuel and Temperature Condition 1 (vapor growth 

scenario). The three vehicles were tested at each of the two A/L ratios. Prior to the tests, the full

canister certification procedure per 40 CFR 86.151 was performed on each ORVR vehicle once.

At the end of the procedure, the canister was weighed, purged of all hydrocarbons with 300 bed 

volumes, and then reweighed to determine the standard loading for that canister. Prior to each 

test on ORVR-equipped vehicles, the ORVR canisters were conditioned by first purging them 

and then adding an amount of butane equal to the standard loading level. The vehicles were 

soaked in a SHED at 70o

 F prior to each test to ensure the vehicle, its tank and head space vapor 

were at the proper temperature, and then pushed outside to the dispenser above the UST just

before the refueling test. Before the vehicle temperature soak, the fuel tank was drained and

refilled to 10% of capacity. 

To dispense fuel into the vehicle during the test at a temperature close to the target of 75o

 F, an

ice water chiller had to be used on the fuel line from the UST to the dispenser. The actual 

dispensed fuel temperature during the outdoor tests varied from 75.3o

 F to 77.8o F (Mean = 

76.8o

 F, S.D. = 1.0o F). The variability in fuel temperature could have introduced a bias of up to 

+4% in the emissions, a small inaccuracy for the test program.

By conducting a single refueling test under controlled conditions with continuous measurements 

of UST pressure and headspace concentration, and actual bagged samples of fugitive emissions

(leak valve) and P/V emissions, the outdoor tests in this study were able to document as real the 

28
UST vapor growth phenomenon that CARB claims produces ORVR-Gilbarco VRS 

incompatibility (see the discussion in Section 3.4). Under CARB’s incompatibility hypothesis, 

the vapor return line returns unsaturated air back to the UST, and vapor growth occurs over some

period of time until the headspace vapor is again fully saturated. That event would be detectable 

as an S-curve increase in UST pressure (rising rapidly after a period of time for mixing to occur 

and then leveling off as saturation was achieved). Overlaid on the vapor-growth process was the 

constant loss in pressure from the needle valve representing all leaks of fugitive emissions. The 

two effects together produced a pressure trace that rises after a time period for mixing to some

maximum value and then decays back to zero, at which point fugitive emissions cease (see

figures and discussion in Section 6.1). 

A third effect on UST pressure was the A/L for the refueling event. With the standard nozzle 

(A/L = 1.15), a higher return volume produced a short spike upwards in pressure during the 

refueling test, and with the mini-boot nozzle (A/L = 0.95) a lower return volume produced a

short spike downwards in pressure (see Section 6.1 for details). Since the goal of this part of the

study was to fully capture the fugitive emissions associated with the single refueling event, each 

test was allowed to run, with continuous pressure measurement and bag sampling, until the team 

decided the pressure bulge from vapor growth and UST headspace re-saturation had occurred 

and the UST pressure had declined back to essentially zero. In some cases this meant that mass 

sampling continued for up to two hours after the refueling event. In cases where the initial 

pressure was expected to go negative for a period of time (mini-boot nozzle), the sampling bag 

was not connected to the leak valve until pressure returned to zero to allow the system to leak in 

ambient air into the UST, which then contributed to vapor growth, subsequent pressurization of 

the UST, and fugitive emissions leaking out into the sampling bag. The pressure traces from the 

six outdoor tests are presented in Section 6.1. The Tedlar bags of UST leak emissions were 

“washed” repeatedly with ambient air inside a SHED to eliminate “hang up” of HC mass in the 

bags, and the SHED contents were analyzed with an FID to determine the mass. The SHED-FID 

system was calibrated using injection of a known mass of propane and certified to be within the 

+/- 2% limit in federal regulations both before and after the tests. 

29
4.2.3 Testing Details – Indoor SHED Tests 

A Sealed Housing for Evaporative Emissions (SHED) is used by vehicle manufacturers to certify 

compliance with EPA refueling emissions standards for ORVR vehicles, and they were used in 

the 1970’s to determine uncontrolled refueling emissions as a function of RVP, dispensed fuel 

temperature, and vehicle tank temperature for EPA’s AP-42 publication. In this part of the

study, 36 refueling tests were conducted in a SHED following a test procedure similar to the 

federal ORVR certification test in order to quantify the nozzle/fillpipe emissions as a function of 

four variables (described in Section 4.2.1) and to separately quantify any initial “puff” from 

removal of the fuel tank cap: 

1. Type of ORVR equipment (3 different vehicles) 

2. Fuel RVP (2 fuels) 

3. Temperature conditions (3 combinations) 

4. A/L ratio (2 settings corresponding to standard and mini-boot nozzles) 

SHED Procedure 

The detailed test procedure used in the SHED tests is described below within the context of a

federal certification ORVR test, as described in 40 CFR §86.150 – 154.24 This method has a 

minimum quantifiable value of 0.01 g/gallon. Modifications of the CFR procedure applying to 

this program are specified at appropriate points. Figure B98-12 provides an overview of the

CFR test sequence. The ”Integrated Systems” path applies to this program. 

 

24 “Refueling Test Procedures,” 40 CFR Chapter I (7-1-01), Section 86, subpart B “Test Procedures”, paragraphs

86.150-98 through 86.154-98. 

30
31
The steps of a certification test include: 

1. Fuel drain and 40% fill.

2 Soak vehicle 12 – 36 hours 

3. Perform 7.5 mile preconditioning drive 

4. Fuel drain and 40% fill 

5. Canister preconditioning (load to 2 gram breakthrough) 

6. Cold and Hot Start exhaust test (“City” driving cycle) 

7. Additional driving (“running loss” driving cycle). Disconnect canister after completion 

 of driving cycle. 

8. Fuel drain and 10% fill 

9. Vehicle Soak. Reconnect canister immediately before test. 

10. Refueling test. 

Steps 1 – 4 insures that the vehicle fuel system is completely purged of non-test fuel. Step 5 

purges any remaining fuel vapors, and provides a common starting point for the test by loading 

the canister with butane vapors to saturation (2-gram breakthrough). In steps 6 and 7 canister 

loading is normalized by a specific driving cycle under controlled conditions. While running, 

engine vacuum purges the charcoal canister. The canister absorbs vapors when the key is off or 

whenever vapor generation exceeds canister purge. At the end of step 7 the canister is

disconnected from the vehicle load and purge system to “freeze” the loading state. The vehicle 

fuel tank is then drained, and a 10% fuel charge is added. The vehicle is placed in soak at

80±3°F to stabilize the vehicle and fuel tank temperature for the refueling test. 

Experiments were performed to determine a method of reproducing canister loading between 

SHED tests. The canisters of the two ORVR vehicles were weighed as Steps 1 through 10 were 

performed. Later, steps 1 through 7 were performed on all three vehicles. The canisters of the 

latter tests then received a load to 2 gram breakthrough, followed by a 300 bed volume purge. 

The results of this testing demonstrate that the driving in steps 6 and 7 completely purged the 

canister. 

For this program, before each test the canisters received a load to 2 gram breakthrough, followed 

by purge until the following weight reductions (the working capacities of the canisters) are 

achieved:

32
Vehicle 01 – 90 grams less than fully loaded weight 

Vehicle 02 – 184 grams less than fully loaded weight 

Vehicle 03 – 36 grams less than fully loaded weight 

The “canister preconditioning step” in the certification protocol uses the 50/50 butane nitrogen

mix and 40-gram/hour load rate. Purge was performed with a vacuum pump. 

The test vehicles in this program were drained using the onboard fuel rail before each test. The 

vehicle tank then received a 10% fill of fuel for the upcoming test. The vehicle was placed in 

soak at a target temperature ±3° F. Target tank temperatures for this program are 70, 90 and 

105° F. The vehicles remained in soak for 6 to 24 hours. The vehicles passed briefly from a 

controlled temperature soak space through the main soak room at a nominal temperature of 75° F 

to the refueling Sealed Housing for Evaporative Determination (SHED) at the specified

temperature. During the soak period the vehicle canister received the load and purge to target 

weight. The canister was not reconnected to the vehicle until immediately before the refueling 

test. 

For this program, the outlet of the canisters was connected to a leak tight bag to capture all 

canister-venting emissions occurring during the refueling operation. The emissions captured in 

the canister vent bag were measured in a separate SHED by establishing a stable background, 

including ethanol levels, multiple bag fill and purge cycles to rinse the bag and mix the 

emissions in the SHED enclosure, and measurement of a stable final reading, including ethanol 

level. 

The SHED refueling tests were performed as follows: 

1. Transfer the vehicle to the refueling SHED. 

2. Evacuate the canister outlet bag (use shop vac or sample pump). Connect the bag to the 

canister outlet. 

3. Connect the canister to the vehicle purge/load system. 

4. Seal the SHED enclosure door. 

5. Start the data logger and continuously record Flame Ionization Detector (FID) 

calibration and SHED readings. 

33
6. Allow total hydrocarbon (THC) background levels and SHED temperature to stabilize. 

Capture a gas chromatography (GC) sample bag for subsequent ethanol analysis when 

stable background readings are achieved. 

7. Remove the vehicle gas cap. Mark the data logger stream. Allow data collection to 

continue for 2 minutes after fuel cap removal. 

Laboratory equipment designed to perform new vehicle certification ORVR tests has 

been modified to evaluate refueling emissions with the Gilbarco dispenser. The fuel 

delivery cart is instrumented to control the temperature of a fuel reservoir at 67°F (the 

dispensed fuel temperature specified for certification tests) and to dispense fuel at 9.8 

gallons/min through a non-Stage II nozzle. Temperature and flow measurements are 

continuously transmitted to a data logger during an ORVR test. For this program, the 

fuel cart has been modified by the addition of a high-pressure fuel pump (to maintain 

the 9.8 gallon/min flow rate through the Gilbarco dispenser, extended fuel delivery 

lines, and a Stage II nozzle). Fuel is recalculated from the nozzle back to the fuel cart 

with a low volume pump to control variation in dispensed temperature. 

8. During this two-minute period, recirculated fuel through the Gilbarco dispenser and 

stage II nozzle to insure uniform fuel temperature. Pump into the fuel delivery cart 

reservoir. After recirculating, turn off booster delivery pump to avoid unnecessary fuel 

heating and Reid Vapor Pressure (RVP) reduction. 

9. At the end of the two-minute period, insert nozzle into the vehicle, turn on booster 

pump, and start the refueling operation. Operate refueling apparatus to insure dispensed 

temperature is maintained at target temperature ±1.5° F and delivery rate is maintained 

at 9.8±0.3 gal/min. 

10. The final THC and GC sample will be taken 60 seconds after the final nozzle shut off. 

Turn off booster pump after shut off. The change in HC level observed between the 

background reading prior to cap removal and that observed 120 seconds after removal 

of the cap will be used to compute “puff” emissions. The change observed between 120 

seconds after cap removal and 60 seconds after the end of fuel delivery will be used to 

compute refueling emissions. The ethanol speciation data will be used to correct the 

initial and final readings. The middle ethanol reading will be interpolated in proportion 

with the FID readings for the initial, middle, and final readings. 

11. An RVP sample will be collected from the fuel remaining in the ORVR cart following 

completion of the test. This RVP must fall within the target range of +0.2 psi to –0.3 

psi of the target RVP (7.0 or 7.8 psi). The fuel cart reservoir will be refilled with fresh 

fuel as required to maintain final RVP specifications. This is expected to be required 

before each vehicle with the 7.8 psi fuel at the elevated (90° F) dispensed temperature.

12. All equipment and tests must be operated and performed to maintain the specified 

dispensed fuel temperature, dispensed fuel delivery rate, vehicle ambient temperature, 

and fuel RVP levels. 

An ethanol (EtOH) response factor was established for the refueling SHED FID. The response

factor “r” is defined as the ratio of the observed FID response with a known ethanol span gas and 

34
the expected FID response for that concentration. For example, with a 16 ppm Ethanol standard 

(32 ppmvC1), the observed FID response was 22.16 ppmvC1, yielding r = 22.16/32.0 = 0.69. 

FID readings were corrected using the following: 

Non EtOH ppm = FID ppm – “r” x [independently measured EtOH ppm25] 

The Non EtOH ppm was used to compute non-EtOH hydrocarbon mass using the standard (40 

CFR 86) refueling emission hydrocarbon density values. The ethanol ppm was used with the 

density of pure ethanol to compute the ethanol mass result. The ethanol mass was multiplied by

a correction factor to remove the non-HC weight of the oxygen molecule, to be consistent with 

evaporative emission test procedures used by California and EPA. The two masses were then 

summed to compute the total HC mass of the refueling emissions. 

The Canister outlet bags were treated similarly. An initial FID and GC sample were taken to

establish background levels. Following thorough flushing of the bag contents and mixing in the 

SHED, a final FID and GC sample measurement were used to establish canister venting emission 

levels. 

GC samples were collected from a subset of the experimental matrix to permit calculation of 

corrections for ethanol content in the SHED. Samples from one of each of the three vehicles 

tested at each temperature-fuel RVP-A/L combination received speciation analysis, namely 

analysis for 12 of the 36 test conditions. Similarly, the canister outlet bags collected during the

“vapor growth” scenario (70° F Tank/75° F Dispensed) received separate SHED and GC 

analysis. 

The resulting ethanol correction factors were found to be approximately 1.02, i.e., HC 

concentrations from the SHED tests were scaled up by 2% on average to correct for the presence

of ethanol. No significant differences in the ethanol correction factor were found for 

vehicle/ORVR type, RVP, A/L ratio or fuel temperature. Thus, for SHED tests where a GC

sample was not analyzed, a correction factor of 1.02 was uniformly applied. This same factor 

was applied to the outdoor test results for the engineered leak valve, the emissions from which 

35
were collected in Tedlar bags and washed with air inside a SHED to analyze HC mass (see 

Section 4.2.2). 

Ethanol GC Method 

ATL has developed a hydrocarbon speciation method that is functionally equivalent to the dualGC AQIRP26 method. Instrumentation demands are simplified, and overall analysis time is 

shortened, yet high resolution and sensitivity are still achieved. In this single-GC/dual column

method, all components are separated using one column type and temperature program. 

Analysis time for a cycle is 65 minutes. Each exhaust or evaporative gas sample is 

simultaneously injected (using a single sampling from the bag) into two identical columns

present in the GC. Column A contains a 85 μl sample loop (splitless injection) that provides an 

injection volume that is small enough to allow resolution of the C1 through C4 hydrocarbons 

while large enough to retain the highest sensitivity possible. Column B receives a 1000 μl 

splitless injection, providing higher sensitivity for components eluting after isobutene. 

Quantitative comparison of two overlap components (butane and isopentane) provides a quality

control measure. Data from column A is used to detect and quantify the 12 earliest eluting 

hydrocarbons with detection limits of 15-25 ppbvC corresponding to 0.2-0.3 mg/mi hydrocarbon 

for FTP stages 1 and 3, and 0.3-0.5 mg/mi for FTP stage 2. Data from column B gives detection 

limits 0.017-0.04 mg/mi HC for components eluting after isopentane (18th in elution order). The 

components eluting between the 9th and 18th in elution order have detection limits ranging 

between the levels listed above for each column. 

The advantage of this approach is that, even for relatively clean vehicles, essentially all of the 

first 12 species are typically present at levels exceeding the column A detection limit. Those 

speciated components that are below the first column detection limit tend to be in the molecular 

weight range best suited for the 1000 μL injection analysis, which provides the limits 0.017-0.04 

mg/mi HC for components eluting after isopentane. In previous work that applied this analysis 

 

25 “CALIFORNIA NON-METHANE ORGANIC GAS TEST PROCEDURES”, amended August 5, 1999, Part B, 

Section 5.4.1 for “r” factor details. 26 Auto/Oil Air Quality Improvement Research Program.

36
approach, detection limits were determined to be between 0.02 and 0.06 mg/mi for the toxics

1,3-butadiene and benzene. 

ATL’s hydrocarbon method uses Varian 3400 GC's with dual injectors, columns, and flame

ionization detectors, allowing two similar analyses to be run simultaneously, as mentioned 

above. A Varian Star PC-based (using Microsoft Windows) data system is used for data 

acquisition. Custom-made software is used for peak identification and converting data into a 

Microsoft Excel spreadsheet format. A comparison of the total hydrocarbon determined using 

the GC versus the Constant Volume Sampler is used as a quality control measure, and ATL 

routinely achieves hydrocarbon speciation "recoveries" ranging from 93% to 105% for lower 

emitting vehicles. A 23 hydrocarbon standard mixture (Scott Specialty Gases, Troy, MI) is 

analyzed at the start of each day on each GC to provide quantifying coefficients and a quality

control check on daily reproducibility of instrument performance.

For this program, the following modifications to the basic GC method apply. A certified mixture

of ethanol in nitrogen was processed daily in the GC to provide a standard for that species. 

Ethanol elutes at approximately 11.1 minutes. The base column temperature program has been 

modified to accelerate column purge between ethanol-only analysis, reducing the total cycle time 

to approximately 40 minutes. Column B area count readings are normally used for ethanol. 

Column A readings are used as a confirmation/independent measure of the Column B results. 

A/L Adjustments 

A qualified technician performed each A/L adjustment using an OPW VacuSmart Vacuum 

Assist Vapor Recover Analyzer (Model 13000). Multiple readings were recorded prior to each 

adjustment to document any slip from the prior state. Multiple readings were recorded after the

adjustment. A minimum of five readings were recorded in each state. 

4.3 Ethanol Correction – Phase 1 and 2

The type of oxygenate in fuels has been shifting from MTBE to Ethanol for a number of reasons, 

including reports of ground water contamination by MTBE. California banned the use of MTBE 

as a fuel additive as of the end of 2002, and Connecticut and New York have bans set for the end 

37
of 2003. All of the fuels used in this study were oxygenated with ethanol. This study utilized 

both highly prescribed test procedures (CARB TP201.2) as well as nontraditional test procedures

designed to achieve certain research objectives. Both use FID as an analytical method for

measuring total HC in a vapor sample. 

In Phase 2 of this research program at Automotive Testing Laboratories (ATL) in Arizona, 

experiments were done to measure the potential under-estimation of hydrocarbon concentrations 

by a Flame Ionization Detector (FID) when the gasoline vapor contains ethanol as a component. 

The SHED testing chambers use a FID for sample analysis. Air samples from the SHEDs were 

analyzed both by FID and a GC to determine the response factor “r” for the FID. Then, to be 

consistent with evaporative emission test procedures used by California and EPA, a correction 

was made to remove the non-HC weight of oxygen in the ethanol fraction. The resulting ethanol 

correction factor was found to be approximately 1.02, i.e. HC concentrations from the SHED 

tests were scaled up by 2% on average to correct for the presence of ethanol. 

In Phase 1 of this program, testing followed California Air Resources Board’s Test Procedures 

TP201.2 and TP201.2F, used California RFG oxygenated with ethanol with an RVP of 7.0 psi, 

and were performed by VOC Testing, Inc. of San Bernardino, California. ARB has made no 

changes to their Test Procedures to account for the possible effect of ethanol on HC 

measurements, and discussions with ARB staff reveal they are not concerned about the issue and

have no plans to modify their Test Procedures. 27 Both FID and NDIR instruments are used in 

the TP201.2 procedure. To quantify the potential bias in the HC measurements and results for 

Phase 1, known samples of ethanol and gasoline headspace vapors from the UST used in the 

second phase of testing were collected in Tedlar bags, driven from ATL to VOC Testing, Inc. in 

San Bernardino and run through their FID and NDIR analyzers. The FID response factor for 

VOC Testing, Inc. was found to be almost identical to that for the FID at ATL, and the response 

factor for the NDIR as calibrated for the TP201.2 procedure was found to be higher. The 

resulting ethanol correction factors for the instruments used in Phase 1 of the program are 1.02 

for all FID measurements (nozzle/fillpipe emissions) and 1.01 for all NDIR measurements 

(vapor return line of the Stage II Gilbarco system, the P/V valve on the UST and UST headspace 

 

27 Personal communication, Ms. Cindy Castronovo, California ARB, September 12, 2003. 

38
concentrations). These small adjustments of 1-2% have no effect on the conclusions in Section 

5.0, Phase 1 – Analysis and Results. The results for Phase 1 are presented in Section 5.0 with 

ethanol correction and the minor effects of including ethanol correction are discussed in 

footnotes in that section of this report. 

39
5.0 PHASE 1 – ANALYSIS AND RESULTS 

This section details the results of Phase 1 of the ORVR compatibility test program, which was 

conducted using the CARB TP201.2/201.3 test methodology to provide some initial data on ORVR

vs. non-ORVR vehicle emissions for an in-use vehicle fleet. The analysis is broken into two parts. 

Section 5.1 focuses on the factors that affect “uncontrolled emissions”, i.e., emissions that would 

result if the Stage II VRS were not present. Section 5.2 focuses on continuously recorded data 

related to the UST, including calculations of pressure-related fugitive emissions. 

5.1 Analysis Of Factors Affecting “Uncontrolled Emissions”

This first phase of the test program was designed to provide some initial data on ORVR vs. nonORVR emissions for an in-use vehicle fleet and could not fully address all factors affecting 

uncontrolled emissions (particularly RVP, which was not investigated). As stated previously, 

uncontrolled emissions (expressed in units of mass emitted per unit volume of gasoline transferred) 

are known to be a function of the temperature of the dispensed fuel (TD), the temperature of the 

vehicle fuel tank (TT), the fuel volatility (RVP), and differences in vehicle design (e.g., fillpipe 

design) that are not readily quantifiable. The presence or absence of ORVR is an additional variable 

affecting uncontrolled emissions. “Uncontrolled emissions” in this section are defined as the sum of 

mass emissions measured at the nozzle/fillpipe interface (M1) and those measured in the vapor return 

line (M2) and exclude emissions from the UST including fugitive emissions which are discussed in 

Section 5.2. Section 4.1 provides an overview of the five potential emission points. Locations 1 and 

2 in Figure 4-1 correspond to mass emissions M1 and M2 discussed in this section. 

5.1.1 Temperatures 

Uncontrolled emissions are known to be a function of the temperature of the dispensed fuel (TD) and 

the temperature of the vehicle fuel tank (TT). Vehicle fuel tank temperatures were measured directly 

in Phase 1 and are correlated to the ambient temperature (TA), see Figure 5-1. TD, which was not 

directly measured in Phase 1, is assumed to be equal to TA, as in EPA’s MOBILE6 model. 

40
For both ORVR and non-ORVR vehicles, it was noted that M1+M2, the sum of the mass of 

hydrocarbons collected at the nozzle/fillpipe interface (M1) and the mass of hydrocarbons returned 

by the VRS to the UST (M2), shows a slight positive correlation to the ambient temperature TA, see 

Figure 5-2. As discussed in Section 3.1, EPA’s formula for refueling emissions (which is 

incorporated into EPA’s MOBILE6 emissions model) predicts that uncontrolled emissions exhibit a 

positive correlation with the temperature of the dispensed fuel (TD) and a negative correlation with 

the difference between the vehicle tank temperature (TT) and TD, the logic being that if TT > TD, 

refueling with the cooler gasoline will result in vapor shrinkage in the gasoline tank. As mentioned 

previously, TD was not measured directly. In the field, both TT and TD have been found to exhibit 

correlations with TA, although there is some discrepancy in how best to approximate TD. A technical 

report by EPA contends that “vehicle tank temperatures follow ambient temperatures more closely 

[than dispensed temperatures].”28 An API study by Radian investigated temperature trends more 

closely by region, and found that for the region which includes California, TD was actually more 

closely corrected to Tg, the temperature of the underground storage tank (UST).29

Figure 5-3 shows the variation in the temperature of the fuel in the USTs, the temperature of the fuel 

in the vehicle tank, and the ambient temperature over time. It is clear that over the time period 

studied, there are significant differences between these temperature data sets. As expected, the UST 

temperatures are much less variable, and they are also significantly higher than the daily mean 

ambient temperatures. The UST temperatures rose during the course of the study period, possibly 

reflecting warming trends (with respect to daily highs) between Oct. 31-Nov. 3 and Nov. 4-Nov. 6 

(though decreases on Nov. 4 and Nov. 7 are not apparent), but possibly reflecting other variables 

(e.g., if the temperature of the fuel delivered to the USTs before the test program began was 

significantly lower than the temperature of the ground, the temperature rise might be the result of a 

long-term temperature equilibration). Therefore, separating the effects of various temperatures is 

subject to large uncertainties due to their codependency. As anticipated, it was not possible to 

isolate the effects of the various temperatures in this phase of the study, and this issue will be more 

adequately studied in Phase 2. 

 

28 D. Rothman and R. Johnson (US EPA), “Refueling Emissions from Uncontrolled Vehicles,” Report No. EPA-AASDSB-85-6, August 1985. 

29 Radian Corp., “Summary and Analysis of Data From Gasoline Temperature Survey Conducted at Service Stations by 

API,” API Publication No. 4278, 1976. 

41
5.1.2 ORVR 

Uncontrolled emissions are affected by whether the vehicle being refueled is equipped with ORVR 

or not. As described in Section 3.4, CARB has stated that there is a potential for “excess emissions” 

when a vacuum assist Stage II VRS is used to refuel vehicles equipped with ORVR. The results 

obtained in this phase of testing support earlier theoretical work by Tech Environmental that 

suggested CARB’s calculations of total incompatibility emissions are over-estimated because they 

ignore the decrease in nozzle/fillpipe emissions from ORVR equipment.30 The test results 

summarized in Figure 5-4 reveal that, on average, ORVR vehicles emitted 0.05 g/gal (0.0001 to 0.13 

g/gal for individual refueling events) whereas non-ORVR vehicles emitted on average 0.19 g/gal 

(0.003 to 0.71 g/gal for individual refueling events); the difference is 0.14 g/gal or 0.31 lb/1,000 

gallons. There was no discernable difference in average fillpipe emissions for the second set of tests 

(with the mini-boot nozzle) compared to the first set, for either ORVR or non-ORVR vehicles (see 

Figure 5-5). This confirms that the mini-boot, in conjunction with a lower A/L setting, performs just 

as well as the standard nozzle and the higher A/L in capturing vapor. (The effect of the mini-boot on 

UST emissions is described in Section 5.2.) These results show that for the Gilbarco VRS studied 

(with and without the mini-boot), ORVR vehicles when fueled with reformulated gasoline had 0.31 

lb/1,000 gallons fewer emissions. Stated differently, these systems had 73% lower emissions from

the nozzle/fill pipe than non-ORVR vehicles. This is a significant difference that CARB does not 

account for and it partially offsets the 0.86 lb/1,000 gal excess emissions from the UST that CARB 

has assigned to ORVR vehicles fueling with a Gilbarco VRS (assuming RVP 7.8 fuel and high A/L 

settings on the VRS).31

It was confirmed that lowering the A/L increased hydrocarbon concentrations in the vapor returned 

to the UST (M2), and that emissions at the fillpipe did not increase as a result of lowering A/L. 

Figure 5-6 presents the mass emissions, per volume of gas dispensed, at the fillpipe along with those 

 

30 Tech Environmental, “Comments on ARB’s August 20, 2002 Proposed Revision to TP201.2F and Other Issues 

Related to EVR Emission Calculations for Underground Storage Tanks,” comments sent to CARB by API, September, 

2002. 

31 California Air Resources Board, “Revised EVR Emissions Reduction Calculations, Module 3: ORVR Compatibility,” 

in letter from Mr. William Loscutoff, Chief, Monitoring and Laboratory Division, CARB to Mr. Prentiss Searles, API, 

August 5, 2002. 

42
in the vapor return line to the UST. As expected, the vapor concentration in the return line is lower 

(about half) for ORVR vehicles confirming that some ambient air is being pulled in at the 

nozzle/fillpipe interface and being sent to the UST. Since the sum of the vapor in the return line plus

the fillpipe emissions (M1+M2) for ORVR vehicles (roughly 1.2 g/gal) is larger than the maximum

0.2 g/gal that is allowed for emissions from an ORVR car refueling at a non-Stage II GDF, it appears 

that the VRS may be preferentially capturing vapors over the ORVR canister. Alternatively, the 

vacuum assisted Stage II equipment may be increasing the volatilization of liquid fuel in the fillpipe 

as it is being dispensed. 

Figure 5-6 illustrates another interesting point. CARB’s claim of ORVR incompatibility rests on an 

assumption that almost no hydrocarbon vapors are returned to the UST in the VRS return flow, 

causing UST pressurization from subsequent vapor growth. For Test 1, the test data show the 

ORVR return flow emissions to the UST are approximately one-third of the non-ORVR emissions, 

revealing that the return flow is not devoid of hydrocarbon vapor. In fact, the average vapor 

concentration when using the system with the A/L set to 1.15 in the return flow for ORVR vehicles 

was 11.3%32 and ranged from 3 to 20% for individual tests, see Figure 5-7. For Test 2 with a miniboot in place (and A/L set to 0.95), ORVR return flow emissions are even higher, approximately half

of the non-ORVR emissions. With the mini-boot, the average vapor concentration in the return flow 

to the UST for ORVR vehicles was 17.4%33 and ranged from 3 to 25% for individual tests, as shown 

in Figure 5-8. Thus, the return flow is closer to saturation than expected, higher than the 0% used in 

the 1999 CARB ORVR study, and 2 to 2.5 times the average of 6.6% that CARB found in earlier 

tests (see Section 3.4). 

Calculations of the sum of M1+M2 for both ORVR and non-ORVR vehicles were compared to 

uncontrolled emissions calculations using EPA’s AP-42 formula and the formula in MOBILE6 for 

each refueling in the study, as shown in Figure 5-9. As stated previously, TD was not measured 

directly in this study so TD was assumed to be equal to ambient temperature (TA). By comparing the 

sum of M1+M2 to uncontrolled emissions predicted by the EPA formulas, we are assuming that all of 

the hydrocarbons in the vapor return line are emitted directly to the atmosphere and not vented to the 

 

32 With the correction for ethanol (Section 4.3), average HC vapor concentration is 11.4%. 

43
UST. A comparison of the data for the non-ORVR vehicles shows the actual test data (average of 

2.75 g/gal) are close in value and bracketed by the uncontrolled emissions predicted by MOBILE6 

(average of 2.23 g/gal) and AP-42 (average of 2.98 g/gal). The average uncontrolled emissions 

predicted by AP-42 are higher than those predicted by MOBILE6 due to differences in the definition 

of ∆T. Differences between the actual test data and MOBILE6 could be due to many factors, 

including the error in estimating TD using TA and possibly volatilization of fuel in the fillpipe by the 

VRS, which is not considered in the MOBILE6 calculations of uncontrolled emissions. The ORVR 

actual test data are less than half the value of the non-ORVR test data because the ORVR system is 

collecting some level of refueling vapors and less vapor mass is present in the VRS return line flow.

Uncontrolled emissions from non-ORVR vehicles are lower than what has been seen with CARB 

methods in the past: i.e., CARB predicts emissions of 7.6 lb/1000 gal = 3.4 g/gal for vehicles being 

refueled with RFG.34 There are several potential reasons for the discrepancy, namely there are 

differences in test methodology validity (e.g., between CARB’s test method and EPA’s SHED test 

method) and there are differences in test conditions (e.g., the temperature range for the SHED tests is

significantly different from the temperature range used here). 

 33 With the correction for ethanol (Section 4.3), average HC vapor concentration is 17.6%. 34 California ARB, “Staff Report – Enhance Vapor Recovery Technology Review,” October, 2002, p. 6. 

44
5.2 Analysis Of Continuous UST Data

The UST pressure, UST headspace concentrations, and concentrations at the UST P/V valve exhaust 

(diluted with sweep air at a constant flowrate for safety) were monitored continuously. UST 

pressurization and venting (through the P/V valve) were found to depend strongly upon the 

“tightness” of the UST, VRS, and sampling system. At the beginning of the first set of tests, 

pressure decay tests showed pressure decays from 2.00” water column to 1.75” water column in 5 

minutes. This complied with TP201.3, which set an allowable minimum pressure after 5 minutes of

1.68” w.c. (ullage of 3,000 gallons and 8 nozzles). During this time period, continuously recorded 

UST pressures clearly showed the effects of vehicle refuelings, and the decay in pressure after those 

refuelings. The P/V valve rarely opened during these first few days. Then, in the middle of the first 

set of tests, the contractor located and fixed a leak. Immediately afterwards, the character of the 

UST pressures changed dramatically: decays were not seen, the UST pressures were frequently at 

+3” w.c. (the cracking pressure of the P/V valve), and the P/V valve vented frequently. The system

was kept tight for the second set of tests with the mini-booted nozzles. Three leak decay tests done 

after the leak was fixed revealed almost no pressure decay, i.e. decays of only <0.01” to 0.03” w.c. 

in 5 minutes. Unfortunately, interferences from other vehicles simultaneously refueling at the GDF’s 

four other operational dispensers (as well as the tightening of the system) prevented an analysis of 

the effects of ORVR vs. non-ORVR vehicles on UST pressures and UST venting. However, these 

effects were measured in the outdoor portion of Phase 2 of the study (see Section 6). 

Using data for the second half of Test 1 and all of Test 2 when the system was tight (Table 5-1), 

emissions out the P/V valve were measured to be approximately 0.374 g/gal during Test 1 and 0.004 

g/gal during Test 2. Thus, there is approximately a 0.37 g/gal benefit, a 98% reduction in P/V valve 

emissions that resulted from using the mini-boot nozzles. UST fugitive emissions were calculated 

using the CARB TP201.2F method (proposed August 20, 2002 version, but with actual ullage and 

final pressure values used in CARB equation 9.1.1) in conjunction with 1-minute average 

measurements of pressure and headspace vapor concentration. These calculations were made for the 

second half of Test 1 and all of Test 2 when the system was tight. Equation 9.1.1 of TP201.2F 

calculates the pressure-related fugitive flowrate (Q) in cubic feet per hour, as: 

45

( )

( )( ) ⎢

⎣

⎢

⎢

⎢

⎢

⎢

⎡

V P

⎥

⎦

⎥

⎥

⎥

⎥

⎥

⎤

/

2.00 − Pf ( 60 )

5 406.9 ( 7.481) 2

⎢⎣

⎢

⎡ 1 / 2

00

⎟

⎞

2 ⎠

f

.

P .00⎜

⎛

⎝

1

⎥⎦

⎥

⎤ 2 = 1 / 2 Q (4-2)
where: 

Q = Pressure-related fugitive flowrate, cubic feet per hour, ft3

/hr 

V = Total ullage affected by the test, gallons 

 Pf = Final pressure of the leak decay test. 

P = Actual pressure measured in UST containment space, inches H2O 

Once Q is calculated, this is used to calculate the mass emission rate of pressure-related fugitive 

emissions: 

(386.9) * (100) 

⎢

⎣

⎢

⎢

⎢

⎢

⎢

⎡

⎥

⎦

⎥

⎥

⎥

⎥

⎥

⎤

Q * C * MW

Μ= (4-3)

M = Mass rate of fugitive emissions, lb/hour 

C = Hydrocarbon concentration, percent (C3 or C4) 

MW = Molecular weight, lb/lb-mole [44.096 for C3 or 58.123 for C4] 

 

These data are shown along with the measured P/V valve emissions in Table 5-1. The total of actual 

P/V valve and calculated fugitive emissions equal the total UST/piping system emissions. Total 

UST emissions for Test 1 (the standard nozzle) were 0.627 g/gal, and for Test 2 (the mini-boot 

nozzle) were 0.224. Thus, use of a mini-boot nozzle on the Gilbarco VaporVac VRS reduced 

estimated total UST emissions at the UST by 64%.35 To the extent TP201.2F overpredicts fugitive 

emissions (and test data in Section 6.3 show it greatly overpredicts these emissions), the reduction in 

UST emissions attributable to use of the mini-boot nozzle is higher than 64%. If the UST system

had been completely leak tight, the reduction in pressure-related emissions would equal 98%, the 

reduction at the P/V valve. Thus, the true reduction value in total UST emissions is somewhere in 

 

35 With the correction for ethanol (Section 4.3), Test 1 total emissions increase to 0.633 g/gal and Test 2 emissions are 

0.226 g/gal. The reduction in emissions due to the mini-boot nozzle is unchanged at 64%. 

46
the range of 64% to 98%. This reduction is greater than the 50% reduction CARB claims

36 for the 

mini-boot on vacuum-assist systems. 

 

36 The 50% reduction figure is calculated from the reduction in A/L on CARB spreadsheet “tosco em red 120501.” 

47
TABLE 5-1 

DEMONSTRATION OF UST EMISSIONS REDUCTION 

PROVIDED BY THE USE OF A MINI-BOOT NOZZLE 

ON A GILBARCO VAPORVAC VRS 

Date Test 

Measured 

P/V Valve 

Emissions 

(g/gal) 

Calculated 

TP-201.2F 

Fugitive 

Emissions 

(g/gal) 

Total UST/ 

Piping System 

Emissions 

(g/gal) 

11/2/02 1 0.281 0.232 0.513

11/3/02 1 0.560 0.294 0.855 

Test 1 

Standard 

Nozzle

Average 0.374 0.253 0.627

11/5/02 2 0.008 0.146 0.153

11/7/02 2 0.001 0.283 0.284

Test 2 

Mini-boot 

Nozzle

Average 0.004 0.220 0.224

 

 

48
FIGURE 5-1. COMPARISON OF AMBIENT AND FUEL TANK TEMPERATURES

50556065707580859095

100

50 55 60 65 70 75 80 

Ambient Temperature (T

A), Deg. F

Temperature of fuel in tank (TT), Deg. F
FIGURE 5-2. EMISSIONS AS A FUNCTION OF AMBIENT TEMPERATURE

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

50 55 60 65 70 75 80 8

Ambient Temperature, deg. F

Mass Emissions divided by Gas Dispensed (g/gal) 
FIGURE 5-3. TEMPERATURE VARIATIONS DURING THE TEST PROGRAM

30405060708090

100110

10/31 0:00 11/1 0:00 11/2 0:00 11/3 0:00 11/4 0:00 11/5 0:00 11/6 0:00 11/7 0:00 11/8 0:00

Date and Time

Temperature, Deg. F UST 1 

UST 2 AmbieVehicl
FIGURE 5-4. FILLPIPE EMISSIONS AND AMBIENT TEMPERATURE

0

0.10.20.30.40.50.60.70.8

50 55 60 65 70 75 80 85

Ambient Temperature, Deg. F

Mass Emissions divided by Gas Dispensed (g/gal) 
FIGURE 5-5. FILLPIPE EMISSIONS BY TEST

0

0.10.20.30.40.50.60.70.8

10/31/02

0:00

11/1/02 0:00 11/2/02 0:00 11/3/02 0:00 11/4/02 0:00 11/5/02 0:00 11/6/02 0:00 11/7/02 0:00 11/8/02 0:0

Date and Time

Mass Emissions divided by Gas Dispensed (g/gal) 
FIGURE 5-6. EMISSION COMPONENTS M1 AND M2

0

0.5

1

1.5

2

2.5

3

3.5

4

10/31/02

0:00

11/1/02 0:00 11/2/02 0:00 11/3/02 0:00 11/4/02 0:00 11/5/02 0:00 11/6/02 0:00 11/7/02 0:00 11/8/02 0:0

Date and Time

Mass Emissions divided by Gas Dispensed (g/gal) 
FIGURE 5-7. TEST 1, VAPOR RETURN LINE CONCENTRATION

05

1015202530354045

10/31/02 0:00 11/1/02 0:00 11/2/02 0:00 11/3/02 0:00 11/4

Date and Time

VRL conc (% HC) 
FIGURE 5-8. TEST 2, VAPOR RETURN LINE CONCENTRATION 

0

102030405060

11/4/02 0:00 11/5/02 0:00 11/6/02 0:00 11/7/02 0:00 11/

Date and Time

VRL Conc (% HC) 
FIGURE 5-9. COMPARISON OF UNCONTROLLED EMISSIONS

0123456

10/31/02

0:00

11/1/02 0:00 11/2/02 0:00 11/3/02 0:00 11/4/02 0:00 11/5/02 0:00 11/6/02 0:00 11/7/02 0:00 11/8/02 0:0

Date and Time

Uncontrolled Emissions (g/gal) 
6.0 PHASE 2 OUTDOOR TESTS – ANALYSIS AND RESULTS 

This section presents the results of the six outdoor TP201.2 refueling tests, performed to carefully 

measure the UST vapor growth phenomenon and associated “excess emissions” that CARB claims

are caused by ORVR-Gilbarco VRS incompatibility. Section 6.1 presents the continuous UST 

pressure data, while Section 6.2 discusses the measured emissions at the leak valve and P/V valve 

and examines the ORVR compatibility issue. Section 6.3 examines the performance of the CARB 

estimation method for fugitive emissions, and TP201.2 data from the tests are discussed in Section 

6.4. 

6.1 Continuous UST Pressure Data

The pressure in the UST was measured continuously for the duration of each test and for up to two 

hours after to allow the full effects of any vapor growth in the UST to occur (see Section 4.2.2 for 

details). In general, three effects are consistently found in the pressure graphs: 

(1) If the standard nozzle (A/L = 1.15) was used, then a higher return volume of air 

produced a short spike upwards in pressure during refueling, conversely if the mini-boot 

nozzle (A/L = 0.95) was used, a lower volume of return air produced a short spike 

downwards in pressure during refueling; 

(2) The vapor growth process begins after an initial period of time for mixing to occur in the

UST headspace, pressure rises and then levels off as vapor saturation is achieved; 

(3) Overlaid on the other two processes is the constant loss in pressure through the leak 

valve, representing all leaks of fugitive emissions at a gasoline dispensing facility. 

The six tests covered the following conditions: 

Test Vehicle Nozzle A/V

1 01 – ORVR with recirculation Standard 1.15 

2 01 – ORVR with recirculation Mini-boot 0.95 

3 02 – ORVR no recirculation Standard 1.15 

4 02 – ORVR no recirculation Mini-boot 0.95 

 5 03 –ORVR Standard 1.15 

 6 03 –ORVR Mini-boot 0.95 

58
The pressure graphs are shown in Figures 6-1 through 6-6, respectively for Tests 1 through 6. Note 

that the pressures are quite low, none exceeded 0.50” w.c., and for that reason the P/V valve never 

cracked. A description of each test is given below. High frequency variations in the pressure traces

are due to light winds at night in the desert that affected the ambient side of the pressure transducer. 

In Figure 6-1 for Test 1 (ORVR with recirculation / standard nozzle), there is an initial spike 

upwards due to the fact 115% of the fuel volume in the form of air/vapor is being returned to the 

UST. The pressure then begins to drop due to leaks through the engineered orifice. The 12 gallons 

of return air start mixing into the 2,000 gallon headspace of the UST and as the headspace vapor 

concentration declines near the vapor/liquid interface, gasoline vaporizes into the headspace and we 

see the pressure begin to rise in the UST from vapor growth. Since leaks and vapor growth are 

going on simultaneously, vapor growth is first seen by a lessening of the slope in the pressure 

decline and then an increase in tank pressure around 2,500 seconds after the refueling. By 3,000 

seconds, vapor growth seems to have ended and pressure leaks seem to again dominate. Around 

7,200 seconds, the pressure stabilized at 0.06” w.c. and would go no lower. This suggests the 

pressure differential was so small that no further emissions were leaking into the bag through the 

orifice. (Atmospheric pressure is 406.9” w.c., so a positive pressure differential of 0.06” to 

atmospheric represents a differential of only 1/100 of 1%). The dip down at the end of the pressure 

graph represents what happened when ATL disconnected the bag at 7,271 seconds and opened the 

fitting on the top of the UST cap; pressure declined but not fully to zero. 

Test 2 (ORVR with recirculation / mini-boot nozzle) had to be done twice. During the first 

attempt, the sample bag was not disconnected from the leak orifice during the early part of the test 

when the pressure went negative, and it prevented ambient air from leaking into the UST. Figure 6-

2 shows the pressure trace for the second, successful try. There is an initial spike down due to the 

fact only 95% of the fuel volume in the form of air/vapor is being returned to the UST. The 

sampling bag was attached to the leak orifice when the pressure returned to zero at 3,055 seconds. 

Pressure continued to rise and peaked around 5,000 seconds. (The dip around 4,200 seconds is 

unexplained). The bag was disconnected at 7,029 seconds. 

59
In Test 3 (ORVR no recirculation / standard nozzle), there is an initial spike up as expected and a

steady decline toward a stable level of 0.04” w.c. A slight pressure bulge upwards around 1,000 

seconds may reflect vapor growth in the UST. The test was ended at 5,685 seconds when the 

pressure reached zero. 

The pressure trace for Test 4 (ORVR no recirculation / mini-boot nozzle) is shown in Figure 6-4. 

There is an initial spike down as expected and the leak orifice was left open during the early part of

the test when the pressure went negative to allow ambient air to flow into the UST. At 2,387 

seconds when it was judged that the pressure had risen to zero, the sampling bag was attached to the 

orifice. Vapor growth is evident just after 1,000 seconds by a bulge in the curve, and the pressure 

peak is reached around 3,500 seconds before it declined to zero and sampling was ended at 4,272 

seconds. 

Test 5 (no ORVR / standard nozzle) had to be done twice. During the first attempt, the bag was 

left on the leak valve orifice for 2,000 seconds after the pressure level had dropped below zero, 

which means sample mass was sucked back out of the bag. In the second, successful try, two 

sampling bags were used, and the mass in each summed to obtain the leak emissions for the test. 

Figure 6-5 shows there is an initial spike upwards and then pressure declines as air leaks out of the 

orifice. The first bag collected emissions from 0 to 904 seconds, a point in time where the pressure 

was hovering around zero. A second sample bag, connected from 904 to 4,187 seconds, collected 

additional mass. The peak in pressure, possibly due to vapor growth in the UST, occurred around 

1,500 seconds. 

In Figure 6-6 for Test 6 (no ORVR / mini-boot nozzle), there is an initial spike down as expected, 

and then the pressure rises due to air leaking in through the orifice. A possible bulge due to vapor 

growth occurs around 3,500 seconds and then the pressure settles back to zero. The sampling bag 

was connected at 2,500 seconds when the pressure was judged to have risen to zero and sampling 

continued until the end of the test at 3,989 seconds. 

60
FIGURE 6-1. TIME VARIATION OF UST PRESSURE FOR OUTDOOR TEST 1 -

ORVR WITH RECIRCULATION / STANDARD NOZZLE

-0.05

0.000.050.100.150.200.250.300.350.40

0 1000 2000 3000 4000 5000 6000 

Time From Start of TP201.2 Refueling Test, seconds

UST Pressure, inches w.c.

Bag Connected 0 - 7,271 seco
FIGURE 6-2. TIME VARIATION OF UST PRESSURE FOR OUTDOOR TEST 2 -

ORVR WITH RECIRCULATION / MINIBOOT NOZZLE

-0.40-0.30-0.20-0.10

0.000.100.200.30

0 1000 2000 3000 4000 5000 6000 

Time From Start of TP201.2 Refueling Test, seconds

UST Pressure, inches w.c.

Bag Connected 3,055 - 7,029 seconds
FIGURE 6-3. TIME VARIATION OF UST PRESSURE FOR OUTDOOR TEST 3 -

ORVR NO RECIRCULATION / STANDARD NOZZLE

-0.05

0.000.050.100.150.200.250.300.350.400.45

0 1000 2000 3000 4000 500

Time From Start of TP201.2 Refueling Test, seconds

UST Pressure, inches w.c. Bag Connected 0 - 5,686 seconds
FIGURE 6-4. TIME VARIATION OF UST PRESSURE FOR OUTDOOR TEST 4 -

ORVR NO RECIRCULATION / MINIBOOT NOZZLE

-0.50-0.40-0.30-0.20-0.10

0.000.10

0 500 1000 1500 2000 2500 3000 3500 

Time From Start of TP201.2 Refueling Test, seconds

UST Pressure, inches w.c. Bag Connected 2,387 - 4,272 secon
FIGURE 6-5. TIME VARIATION OF UST PRESSURE FOR OUTDOOR TEST 5 -

NO ORVR / STANDARD NOZZLE

-0.30-0.20-0.10

0.000.100.200.30

0 500 1000 1500 2000 2500 3000 3500 

Time From Start of TP201.2 Refueling Test, seconds

UST Pressure, inches w.c.

Bag 1 Connected 0 - 904 seconds

Bag 2 Connected 904 - 4,187 seconds
FIGURE 6-6. TIME VARIATION OF UST PRESSURE FOR OUTDOOR TEST 6 -

NO ORVR / MINIBOOT NOZZLE

-0.60-0.50-0.40-0.30-0.20-0.10

0.000.10

0 500 1000 1500 2000 2500 3000 3500 

Time From Start of TP201.2 Refueling Test, seconds

UST Pressure, inches w.c. Bag Connected 2,500 - 3,989 secon
6.2 Fugitive Emissions From UST/Piping

The six outdoor refueling tests were designed to fully capture the pressure-related fugitive emissions

from vapor growth in the UST associated with ORVR-Gilbarco VRS incompatibility. All fugitive 

emissions were captured in 1-2 Tedlar bags over periods of time up to two hours in length during 

and after a single refueling and then rinsed in a SHED and analyzed for mass. The results are 

conservative for the mini-boot nozzle test since the leak valve orifice was left open during the initial 

negative pressure spike (caused by an A/L of 0.95), allowing ambient air to flow into the UST 

headspace and potentially create more vapor growth. At a gasoline station equipped with mini-boot 

nozzles, the rapid succession of refueling events might tend to keep the UST pressure positive 

(assuming each refueling generates a small amount of vapor growth as shown in Table 6-1 for Tests 

2,4, and 6), and thus inflow of ambient air through system leaks, like that allowed in this study, 

might not occur. As discussed below, fugitive emissions from mini-boot refuelings are near zero. 

The total fugitive HC emissions measured of each test are summarized in Table 6-1. An ethanol 

correction factor of 1.02 has been applied to all measurements (see Section 4.3). As mentioned 

previously, there were no emissions out the P/V valve due to the fact UST pressure never rose above 

0.5” w.c. Table 6-1 shows that the fugitive emissions for all the mini-boot refuelings are near zero 

(about 0.003 lb/1,000 gallons for the ORVR vehicles and 0.011 lb/1,000 gallons for the non-ORVR

vehicle) and below the minimum quantifiable limit of the SHED of 0.01 g/gal. The “excess 

emissions” of pressure-related fugitives from ORVR incompatibility with the Gilbarco VRS are 

defined as the difference between the measured ORVR and non-ORVR emissions for each type of 

nozzle, and these results are summarized in Table 6-2. For a standard nozzle and an A/L of 1.15, the 

measured “excess emissions” from ORVR incompatibility are 0.72 lb/1,000 gallons. For the 

miniboot nozzle and an A/L of 0.95, the measured “excess emissions” are –0.008 lb/1,000 gallons, 

i.e., zero. By comparison, CARB’s presumed figure for “excess emissions” for all ORVR vehicles is 

0.86 lb/1,000 gallons. The CARB estimate is less reliable as it is not derived from actual 

measurements of pressure-related fugitives associated with refueling ORVR vehicles, the test 

method used in this study. Not considered in these figures is the very important decrease in 

emissions at the nozzle/fillpipe from the use of ORVR in addition to the Stage II VRS. The 

fleetwide tests in Phase 1 of this study documented an emissions decrease at the fillpipe of 0.31 

67
lb/1,000 gallons (see Section 5.1.2) while the SHED tests in Phase 2 have established a fillpipe 

emissions decrease of 0.46 lb/1,000 gallons (see Section 7.1.1). The average of these two estimates 

is 0.39 lb/1,000 gallons. From these results, the following conclusions are drawn: 

• Measured fugitive emissions from ORVR vehicles refueled with a mini-boot nozzle are near 

zero (0.003 lb/1,000 gallons) and are less than measured non-ORVR fugitive emissions 

(0.011 lb/1,000 gallons). Thus, when the mini-boot nozzle (A/L = 0.95) is used on a 

Gilbarco VRS, there is no ORVR incompatibility and measured “excess emissions” are zero

(actually –0.008 lb/1,000 gallons). In addition, with the mini-boot nozzle in use the 

combination of ORVR and Stage II VRS controls produces 0.39 lb/1,000 gallons less 

emissions at the fillpipe than if just Stage II controls are used. 

• “Excess emissions” from the UST/piping system, due to ORVR incompatibility with a 

Gilbarco VRS, when a standard nozzle (A/L = 1.15) is used are 0.72 lb/1,000 gallons. 

Considering the decrease in fillpipe emissions produced by the ORVR-VRS combination of

0.39 lb/1,000 gallons, total incompatibility emissions for standard nozzle (A/L = 1.15) 

refueling are only 0.72 – 0.39 = 0.33 lb/1,000 gallons, or less than half of the figure of 0.86 

lb/1,000 gallons that CARB presumes for all ORVR vehicles. 

The application of this information to statewide emission inventories in the case where all Gilbarco 

VRS are equipped with mini-boot nozzles is simple: there are no “excess emissions” and no ORVR

incompatibility. In situations where Gilbarco systems are equipped with standard nozzles 

(A/L=1.15), a correction should be applied for the fact that the EPA MOBILE6 model (the tool used 

to create state emission inventories) assumes fillpipe emissions for ORVR cars are lower than those

for non-ORVR cars controlled with Stage II (98% vs. 95% control). That is, some of the fillpipe 

emissions reduction attributable to ORVR and discussed above is already credited in the emission 

inventories. While uncontrolled emissions will vary, in this study those emissions were found to be 

approximately 3 g/gal for non-ORVR vehicles fueled with RFG 7.0 RVP fuel (see Figure 5-9). 

Assuming MOBILE6 has already credited 3% of 3 g/gal = 0.09 g/gal, that means total 

incompatibility emissions for a standard nozzle refueling is 0.33 lb/1,000 gallons (bullet item above) 

+ 0.09 lb/1,000 gallons (adjustment) = 0.42 lb/1,000 gallons, when assembling an areawide 

emissions inventory with MOBILE6, or about half of what CARB assumes (0.86 lb/1,000 gallons). 

68
TABLE 6-1 

TOTAL UST/PIPING SYSTEM FUGITIVE EMISSIONS 

FOR THE SIX OUTDOOR TESTS 

Test 

No. Vehicle Type Nozzle Type A/L Ratio Fuel (gal) 

HC 

(g) 

Emissions 

(g/gal) 

1 ORVR w/recirc. standard 1.15 10.20 4.25 0.417

2 ORVR w/recirc. miniboot 0.95 10.07 0.02 0.002

3 ORVR no recirc. standard 1.15 15.04 1.57 0.104

4 ORVR no recirc. miniboot 0.95 15.14 0.01 0.001

5 no ORVR standard 1.15 14.14 0.14* 0.010

6 no ORVR miniboot 0.95 14.08 0.07 0.005

* Bag 1 contained 0.06 grams. Bag 2 contained 0.08 grams. 

69
TABLE 6-2 

“EXCESS EMISSIONS” OF PRESSURE-RELATED 

FUGITIVE HC EMISSIONS FOR ORVR VEHICLES 

REFUELED USING A GILBARCO VAPORVAC VRS 

“Excess Emissions” of Fugitives Type of Vehicle Nozzle Type

(A/L Ratio) (g/gal) (lb/1,000 gal) 

ORVR with 

recirculation 

Standard 

(1.15) 0.407 0.90

ORVR no 

recirculation 

Standard 

(1.15) 0.094 0.21

Weighted Average* Standard 

(1.15) 0.329 0.72

ORVR with 

recirculation 

Miniboot 

(0.95) -0.003 -0.007

ORVR no 

recirculation 

Miniboot 

(0.95) -0.004 -0.009

Weighted Average* Miniboot 

(0.95) -0.003 -0.008

* Assumes 75% of ORVR-equipped vehicles in the population are equipped with a recirculation 

line to the top of the fillpipe. See footnote 37 in Section 7.1.1. 

70
6.3 Performance of the CARB Estimation Method for Fugitive Emissions

UST fugitive emissions were calculated for the Phase 2 outdoor tests in the same way calculations 

were made for Phase 1 (see Section 5.2), using the TP201.2F method with actual ullage (2,000 

gallons) and final pressure for the leak decay test (1.56” w.c.). Table 6-3 compares actual, measured 

fugitive emissions to those predicted by the CARB method for the six outdoor tests and the data are 

plotted in Figure 6-7. The results reveal that the CARB method consistently and substantially 

overpredicts pressure-related fugitive emissions, by factors of 13 to 660, namely one to two orders of

magnitude. Tech Environmental has previously pointed out overprediction problems with the TP201.2F equation to CARB in comments on proposed changes to the EVR Test and Certification 

Procedures. That earlier analysis showed that the estimation method could overpredict the leak rate 

(and therefore fugitive emissions) by more than a factor of 10 for low positive pressures in the UST 

due to an incorrect analytical form of the equation, with the greatest overprediction occurring for 

very low UST pressures (very low fugitive emissions), and the data in Figure 6-7 confirm this very 

same behavior: for the actual fugitives associated with the standard nozzle the overprediction is in 

the range of 13 to 36 (roughly a factor of 20) with the greatest overprediction occurring for the 

lowest actual fugitive emissions. While there appears to be a statistically significant correlation 

between measured and calculated fugitives for the standard nozzle, such is not the case for the 

miniboot nozzle data where there is no correlation. Whereas actual fugitive emissions are much 

lower for the miniboot nozzle, again we see that the CARB estimation method produces larger 

overpredictions in the range of 31 to 660 (roughly a factor of 300). 

While the objective here was not to develop a better method for calculating fugitive emissions, the 

consistent overprediction of fugitives by the CARB TP-201.2F estimation method could be roughly 

corrected by dividing predictions for standard nozzles (A/L>1) by 20 and dividing predictions for 

miniboot nozzles (A/L<1) by 300. 

71
TABLE 6-3 

PERFORMANCE OF CARB TP201.2F METHOD IN 

PREDICTING ACTUAL PRESSURE-RELATED 

FUGITIVE EMISSIONS 

Phase 2 Outdoor Test Nozzle Type

Total Measured 

Fugitive HC 

(grams) 

Calculated TP201.2F 

Fugitive HC 

(grams) 

1 Standard 4.25 55.0

2 Miniboot 0.02 13.2

3 Standard 1.57 34.3

4 Miniboot 0.01 1.65

5 Standard 0.14 5.08

6 Miniboot 0.07 2.20

72
FIGURE 6-7. PERFORMANCE OF CARB TP201.2F METHOD IN PREDICTING ACT

PRESSURE-RELATED FUGITIVE EMISSIONS

05

1015202530354045505560

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Measured Pressure-Related Fugitives (g)

TP201.2F Calculated Pressure-Related Fugitives (g) 
6.4 Fillpipe Emissions and Return Vapor Line Concentrations

The CARB TP201.2 test procedure was followed for the Phase 2 outdoor tests to provide a rigorous 

protocol for the refueling tests, the focus of which were UST pressurization and fugitive emissions. 

The measurements of nozzle/fillpipe emissions and return vapor line HC concentrations from the 

TP201-2 tests are summarized in Table 6-4. (These data have been corrected for ethanol, see 

Section 4.3). Excluding one data point invalidated by an apparent splash-back at nozzle cut-off, the 

ORVR vehicles emitted 0.001 to 0.012 g/gal, which is in the same range as TP201.2 measurements 

made in Phase 1. The non-ORVR vehicle emitted 0.697 to 0.959 g/gal, levels somewhat higher than 

the TP201.2 measurements made in Phase 1, which ranged up to 0.710 g/gal. 

Vapor return line concentrations for the non-ORVR vehicle were close to saturation at 33% to 39% 

HC. The return line concentrations for the ORVR vehicles, which ranged from 0.6% to 7.6%, are 

lower than the levels measured in the Phase 1 TP201.2 tests (3% to 25%). This means that the 

Gilbarco returned lower than expected HC concentrations to the UST during the outdoor tests on the 

ORVR vehicles, producing possibly higher than normal levels of vapor growth and pressure-related 

fugitive emissions. Thus, the measurements of fugitive emissions presented in the previous sections 

are conservative, and actual fugitives at a service station will likely be less. Also, since the P/V 

valve at a station cracks occasionally from the effects of multiple refuelings and releases headspace 

air, some of which is below-saturation vapor return line air, the full potential for vapor growth as 

measured in this study is not realized at a service station. (The Phase 2 measurements of pressurerelated fugitives considered the full potential for vapor growth over a 1 to 2 hour period following a 

refueling event.) Thus, the results of this study likely overpredict actual fugitive emissions as they 

occur at a service station. 

74
TABLE 6-4 

FILLPIPE EMISSIONS AND RETURN VAPOR LINE 

HC CONCENTRATIONS FOR THE TP201.2 

PHASE 2 OUTDOOR TESTS 

Test 

No. 

ORVR 

? 

Nozzle/Fillpipe 

Emissions 

(g/gal) 

Return Vapor Line 

HC Concentration 

(%) 

1 

2 

3 

4 

5 

6 

Yes 

Yes 

No 

Yes 

Yes 

No 

0.011 

0.001 

0.697 

0.267* 

0.012 

0.959 

3.0 

5.4 

33.2 

7.6 

0.6 

38.8 

* Splash back of fuel into the sampling sleeve (placed over the nozzle) likely occurred as evidenced

by a single concentration spike at the end of the refueling test, invalidating this data point.

75
7.0 PHASE 2 INDOOR SHED TESTS – ANALYSIS AND RESULTS

This section presents the results of the indoor SHED tests to quantify the dependence of refueling 

emissions on the following independent variables: type of vehicle ORVR equipment, A/L ratio, fuel 

RVP, and temperature conditions. Section 7.1 discusses refueling emissions at the nozzle/fillpipe as 

a function of these variables and examines the ORVR compatibility issue. Section 7.2 discusses the 

separate and initial “puff” emissions from removal of the fuel cap before refueling begins. 

7.1 Nozzle/Fillpipe Refueling Emissions

The results from the 36 refueling tests in the SHED are summarized in Tables 7-1 through 7-3 for 

vehicles 01 through 03, and are graphed in Figure 7-1. It can be readily seen that nozzle/fillpipe 

emissions are substantially less for the two ORVR-equipped vehicles (01,02) compared to the nonORVR vehicle (03), generally confirming results found in the Phase 1 fleetwide tests that emissions 

are 73% less for ORVR than non-ORVR vehicles (see Figure 5-5). The measured refueling 

emissions of 0.001 to 0.041 g/gal for ORVR vehicles, and 0.031 to 0.693 g/gal for the non-ORVR 

vehicle, fall within the range of values measured in the Phase 1 fleetwide tests. 

The differences in Phase 1 test results attributable to individual vehicle and fuel system designs are 

represented by the scatter of data points in Figures 5-4 and 5.5. Similarly, there is a difference 

between average refueling emissions for the two ORVR vehicles used in the Phase 2 SHED tests. 

Vehicle 01 (the 2003 Toyota Echo, ORVR with vapor recirculation) had average refueling emissions 

of 0.026 g/gal, a value that is quite low. By comparison, vehicle 02 (the 2003 Chevy Blazer, ORVR

without recirculation) had emissions of only 0.003 g/gal. Considering the fact that uncontrolled 

emissions are in the range of 3 to 5 g/gal (see Figure 5-9) and that 95% control by either ORVR or 

Stage II controls brings those emissions down to no more than 0.2 g/gal, the measured emissions for 

vehicle 02 of 0.003 g/gal are essentially zero and represent 99.93% control. Given the fact all test 

results for vehicle 02 were essentially zero and scatter in the data may just represent measurement 

imprecision, no data analysis was performed for vehicle 02. While the Phase 2 tests cannot identify 

exactly why vehicle 02 had such low emissions, the possibilities include: 1) the Chevy Blazer has a

larger carbon canister than the Honda Echo in its ORVR system with double the “working capacity,” 

76
while its fuel tank is only 50% larger (18 gallons for the Blazer versus 12 gallons for the Echo); and 

2) the Blazer’s fuel tank, fillpipe and ORVR system design, including the absence of a recirculation

loop, is superior to that of the Echo’s in terms of vapor capture during refueling. 

7.1.1 ORVR 

As described in Section 3.4, CARB has stated that there is a potential for “excess emissions” when a 

vacuum assist Stage II VRS is used to refuel vehicles equipped with ORVR. The results from Phase 

2 confirm findings from Phase 1 (Section 5.1.2) that CARB’s calculations of total incompatibility 

emissions are over-estimated because they ignore the decrease in nozzle/fillpipe emissions from

ORVR equipment. The test results in Tables 7-1 through 7-3 reveal that, on average, the two ORVR 

vehicles emitted 0.015 g/gal (0.001 to 0.041 g/gal for individual refueling tests), whereas the nonORVR vehicle emitted on average 0.23 g/gal (0.031 to 0.693 g/gal for individual refueling test). 

Since approximately 75% of new car ORVR systems are equipped with recirculation,37 for the 

purposes of this comparison a weighted average is used, namely 0.020 g/gal (see Table 7-1). Thus, 

the difference in fillpipe emissions between ORVR and non-ORVR vehicles when a Gilbarco VRS 

is operating is 0.21 g/gal or 0.46 lb/1,000 gal. This is a significant difference that CARB does not 

account for and it partially offsets the 0.86 lb/1,000 gal excess emissions from the UST that CARB 

has assigned to ORVR vehicles refueling with a Gilbarco VRS (assuming RVP 7.8 fuel and high 

A/L settings on the VRS).38 The ORVR vehicles had 91% lower HC emissions from the 

nozzle/fillpipe than the non-ORVR vehicle. 

 

37 Auto industry consultant, Mr. Harold Haskew (Milford, MI) estimates 75% of all new passenger vehicles have a 

recirculation loop in their ORVR system. Personal communication, November 7, 2003. 38 California Air Resources Board, “Revised EVR Emissions Reduction Calculations, Module 3: ORVR Compatibility,” 

in letter from Mr. William Loscutoff, Chief, Monitoring and Laboratory Division, CARB to Mr. Prentiss Searles, API, 

August 5, 2002. 

77
TABLE 7-1 

SUMMARY OF INDOOR SHED REFUELING TEST RESULTS 

FOR VEHICLE 01-ORVR WITH RECIRCULATION (FORD ECHO) 

RVP (psi) A/L 

Target Actual 

Dispensed 

Temp. o F 

∆T 

o

 F 

Nozzle/Fillpipe

Emissions 

(g/gal) 

1.15 

1.15 

1.15 

1.15 

1.15 

1.15 

7.8 

7.8 

7.8 

7.0 

7.0 

7.0 

7.79 

7.78 

7.67 

7.12 

6.97 

7.04 

75 

75 

90 

75 

75 

90 

-5 

15 

15 

-5 

15 

15 

0.033 

0.028 

0.024 

0.015 

0.018 

0.028 

Average For A/L 1.15 0.024 

0.95 

0.95 

0.95 

0.95 

0.95 

0.95 

7.8 

7.8 

7.8 

7.0 

7.0 

7.0 

7.84 

7.93 

7.68 

7.03 

7.16 

7.16 

75 

75 

90 

75 

75 

90 

-5 

15 

15 

-5 

15 

15 

0.020 

0.041 

0.039 

0.012 

0.022 

0.028 

Average for A/L 0.95 0.027 

Average for Vehicle 01 0.026 

78
TABLE 7-2 

SUMMARY OF INDOOR SHED REFUELING TEST RESULTS 

FOR VEHICLE 02-ORVR NO RECIRCULATION (CHEVROLET BLAZER) 

RVP (psi) A/L 

Target Actual 

Dispensed 

Temp. o F 

∆T 

o

 F 

Nozzle/Fillpipe

Emissions 

(g/gal) 

1.15 

1.15 

1.15 

1.15 

1.15 

1.15 

7.8 

7.8 

7.8 

7.0 

7.0 

7.0 

7.76 

7.73 

7.63 

7.03 

6.91 

6.96 

75 

75 

90 

75 

75 

90 

-5 

15 

15 

-5 

15 

15 

0.002 

0.001 

0.002 

0.003 

0.005 

0.005 

Average For A/L 1.15 0.003 

0.95 

0.95 

0.95 

0.95 

0.95 

0.95 

7.8 

7.8 

7.8 

7.0 

7.0 

7.0 

7.88 

7.94 

7.66 

7.07 

7.15 

7.10 

75 

75 

90 

75 

75 

90 

-5 

15 

15 

-5 

15 

15 

0.002 

0.002 

0.003 

0.004 

0.003 

0.003 

Average for A/L 0.95 0.003 

Average for Vehicle 02 0.003 

79
TABLE 7-3 

SUMMARY OF INDOOR SHED REFUELING TEST RESULTS 

FOR VEHICLE 03 - NO ORVR (NISSAN MAXIMA) 

RVP (psi) A/L 

Target Actual 

Dispensed 

Temp. o F 

∆T 

o

 F 

Nozzle/Fillpipe

Emissions 

(g/gal) 

1.15 

1.15 

1.15 

1.15 

1.15 

1.15 

7.8 

7.8 

7.8 

7.0 

7.0 

7.0 

7.77 

7.83 

7.56 

7.03 

7.20 

7.03 

75 

75 

90 

75 

75 

90 

-5 

15 

15 

-5 

15 

15 

0.311 

0.093 

0.117 

0.224 

0.031 

0.099 

Average For A/L 1.15 0.146 

0.95 

0.95 

0.95 

0.95 

0.95 

0.95 

7.8 

7.8 

7.8 

7.0 

7.0 

7.0 

7.88 

7.85 

7.62 

7.14 

7.17 

7.23 

75 

75 

90 

75 

75 

90 

-5 

15 

15 

-5 

15 

15 

0.693 

0.261 

0.157 

0.430 

0.170 

0.170 

Average for A/L 0.95 0.314 

Average for Vehicle 03 0.230 

80
FIGURE 7-1. FILLPIPE EMISSIONS AND FUEL RVP

0.0000.1000.2000.3000.4000.5000.6000.700

6.80 7.00 7.20 7.40 7.60 7.80 8.00

Reid Vapor Pressure (RVP), psi

Mass Emissions divided by Gas Dispensed (Q), g/gal 
7.1.2 RVP 

The dependence of refueling emissions on fuel RVP is summarized in Figure 7-1 and reveals that 

emissions are: 

• Positively correlated with fuel RVP, as assumed in the EPA MOBILE6 model, for the nonORVR vehicle (vehicle 03) with a slope of 0.2 g/gal per psi. 

• Very slightly positively correlated with fuel RVP for the ORVR vehicle with recirculation 

(vehicle 01) with a slope of 0.02 g/gal per psi. 

• Uncorrelated with RVP for the ORVR vehicle without recirculation (vehicle 02) as all 

values are essentially zero. 

The empirical formula for fillpipe emissions in EPA’s Publication AP-42 and MOBILE6 model 

assumes a positive correlation with fuel RVP with a slope of 0.5 g/gal per psi (see Section 3.1). That 

equation was developed using SHED tests for conditions quite different from those in the present 

study: all vehicles (1979-1985) were non-ORVR and did not have tank/fuel systems designed to 

minimize evaporative emissions, the fuel used had a much higher RVP and RVP range (9.0 to 12.6 

psi), and no Stage II VRS was in operation during EPA’s “uncontrolled emissions” tests. 

The results from Phase 2 of the present study suggest that as more refueling emission controls are 

implemented (just Stage II control for vehicle 03, and both ORVR and Stage II controls for vehicles 

01and 02), the dependence of fillpipe emissions on fuel RVP declines. 

7.1.3 A/L Ratio 

Looking at the data grouped by A/L ratio in Tables 7-1 through 7-3, refueling emissions at the 

fillpipe for the ORVR vehicle (01) are the same whether the standard nozzle with a high A/L of 1.15 

is used or a mini-boot nozzle with a low A/L of 0.95 is employed. (A t-test on the six-sample 

subsets shows no statistically significant difference at the 95% confidence level.) Thus, the 12 data 

points for vehicle 01 can be analyzed as a complete set to determine the dependence of emissions on 

temperature conditions. 

82
For the non-ORVR vehicle (03), there is a negative correlation of fillpipe refueling emissions with 

A/L ratio, showing the miniboot in combination with a low A/L setting did not perform as well as 

the standard nozzle and a high A/L setting for this particular vehicle (a 1995 Nissan Maxima). The 

fleetwide test results in Phase 1, however, demonstrate that for a broad population of non-ORVR 

vehicles there is no discernable difference in refueling emissions for the two combinations of nozzle 

and A/L ratios (see Figure 5-5). 

7.1.4 Temperatures 

As discussed in Section 3.1, EPA’s formula for refueling emissions (which is incorporated into 

EPA’s MOBILE6 emissions model) predicts that uncontrolled emissions exhibit a positive 

correlation with the temperature of the dispensed fuel (TD) and a negative correlation with ∆T the 

vehicle tank temperature (TT) minus TD, the logic being that if TT > TD, refueling with cooler 

gasoline will cause vapor shrinkage in the gasoline tank. Conversely if TD > TT, then vapor growth 

in the vehicle tank is assumed to produce higher refueling emissions. These hypothesized effects are 

for uncontrolled emissions from an automobile without evaporative emission controls or ORVR and 

assume no Stage II controls on the dispenser. The Phase 2 SHED test was designed to test whether 

these relationships still apply for today’s vehicles, fuels and refueling conditions. 

Two temperature variables were treated as independent variables: 1) TD; and 2) ∆T. As shown in 

Section 4.2.1, the three summertime temperature conditions included in the test matrix were: 

Condition TD ∆T TT 

 1 75o

 -5o 70o vapor growth 

 2 75o

 +15o 90o vapor shrinkage 

 3 90o

 +15o 105o vapor shrinkage 

Figure 7-2 presents refueling emissions for the ORVR vehicle with recirculation (vehicle 01) vs. 

RVP, with data partitioned by temperature conditions. By comparing temperature conditions 1 and 

2, TD is held constant and only ∆T is varied. The results are the opposite from that assumed in the 

83
EPA formula, namely emissions for the vapor growth case (condition 1) are lower than those for the 

vapor shrinkage case (condition 2). Since that is implausible, the difference in emissions must be 

related to the tank temperature (TT), which is lowest for temperature condition 1, and not to ∆T. 

By comparing temperature conditions 2 and 3 in Figure 7-2, ∆T is held constant and TD is varied, 

but it turns out TT is also varied and since the first comparison suggests TT is an important 

independent variable (a situation not anticipated in the experiment design) the increase in emissions 

between condition 2 to condition 3 can only be said to be due to some combination of the variables 

TD and TT. The average of TD and TT is graphed vs. refueling emissions in Figure 7-3. The graph 

reveals that (TD+TT)/2 is positively correlated with emissions, with the relationship being stronger 

for the lower RVP fuel. 

For the ORVR vehicle with recirculation (vehicle 01), the following conclusions are drawn 

regarding refueling emissions and temperature conditions: 

• Emissions are not correlated with ∆T as in the EPA formula for refueling emissions, and the 

vapor growth and shrinkage scenarios which affect refueling emissions in non-ORVR 

vehicles do not appear to influence emissions in ORVR vehicles. This is likely due to the 

rapid and continuous removal of headspace vapors from the tank by the ORVR canister. 

• Emissions are positively correlated with the tank temperature (TT), although the rate of 

change is fairly low: 0.003 g/gal per 10o

 F. Emissions may also be positively correlated 

with dispensed temperature (TD), but any separate effect could not be quantified. 

Figure 7-4 presents refueling emissions for the non-ORVR vehicle (vehicle 03) vs. RVP, with data 

partitioned by temperature conditions. A comparison of temperature conditions 1 and 2 reveals that 

emissions are negatively correlated to ∆T and that the vapor growth/shrinkage hypothesis in the 

EPA formula for refueling emissions applies to the non-ORVR vehicle. A comparison of 

temperature conditions 2 and 3 in Figure 7-4 shows no relationship between emissions and 

dispensed temperature (TD) or tank temperature (TT). The correlation between emissions and ∆T is 

shown clearly in Figures 7-5 and 7-6, with the relationship being stronger for the higher RVP fuel 

and the lower A/L ratio. 

84
For the non-ORVR vehicle (03), the following conclusions are drawn regarding refueling emissions 

and temperature conditions: 

• Emissions are negatively correlated with ∆T as in the EPA formula for refueling emissions. 

 The rate of change is an increase of 0.125 g/gal per –10o

 F ∆T. 

• Emissions are not correlated with dispensed temperature (TD) or tank temperature (TT). 

85
FIGURE 7-2. FILLPIPE EMISSIONS, RVP AND TEMPERATURE

FOR VEHICLE 01 - ORVR WITH RECIRCULATION

0.0100.0150.0200.0250.0300.0350.0400.045

6.80 7.00 7.20 7.40 7.60 7.80 8.00

Reid Vapor Pressure (RVP), psi

Mass Emissions divided by Gas Dispensed (Q), g/gal T

TTLLL
FIGURE 7-3. FILLPIPE EMISSIONS AND AVERAGE FUEL/TANK TEMPERATUR

FOR VEHICLE 01 - ORVR WITH RECIRCULATION

0.0100.0150.0200.0250.0300.0350.0400.045

70 75 80 85 90 95 

Average of Dispensed Temperature (TD) and Vehicle Tank Temperature (TT), o

F

Mass Emissions divided by Gas Dispensed (Q), g/gal 
FIGURE 7-4. FILLPIPE EMISSIONS, RVP AND TEMPERATURE

FOR VEHICLE 03 - NO ORVR

0.0000.1000.2000.3000.4000.5000.6000.700

6.90 7.00 7.10 7.20 7.30 7.40 7.50 7.60 7.70 7.80 7.90 8.00

Reid Vapor Pressure (RVP), psi

Mass Emissions divided by Gas Dispensed (Q), g/gal T

TTLLL
FIGURE 7-5. FILLPIPE EMISSIONS AND T (TANK-FUEL) TEMPERATURE

FOR VEHICLE 03 - NO ORVR

0.0000.1000.2000.3000.4000.5000.6000.700

-10 -5 0 5 10 15 

T = Vehicle Tank Temperature (TT) - Fuel Temperature (TD), oF

Mass Emissions divided by Gas Dispensed (Q), g/gal 
FIGURE 7-6. FILLPIPE EMISSIONS AND T (TANK-FUEL) TEMPERATURE

FOR VEHICLE 03 - NO ORVR

0.0000.1000.2000.3000.4000.5000.6000.700

-10 -5 0 5 10 15 

T = Vehicle Tank Temperature (TT) - Fuel Temperature (TD), oF

Mass Emissions divided by Gas Dispensed (Q), g/gal 
7.2 Fuel Cap “Puff” Emissions and Canister Outlet Emissions

“Puff” losses of HC vapor that occur when the gas cap is removed on a vehicle are not counted as 

refueling emissions in the EPA ORVR certification test (see 40 CFR 86.154-98). One of the goals 

of Phase 2 of this study was to quantify these emissions and the SHED test protocol was designed to 

separately measure “puff” emissions, defined as those occurring in a two-minute period after the gas 

cap is removed and before the nozzle is inserted into the fillpipe. The measured levels are 

summarized in Tables 7-4 through 7-6 and in Figures 7-7 through 7-9. These emissions are 

presented as grams of HC per refueling event since the amount in the “puff” is unrelated to the 

gallons of fuel dispensed. Average fuel cap “puff” emissions for the two ORVR-equipped vehicles 

(01, 02) of 0.05 to 0.14 grams are one to two orders of magnitude less than comparable emissions for 

the non-ORVR vehicle of 2.26 grams. 

Using data on the average amount of fuel dispensed in each of the 36 SHED tests and the average 

refueling emissions, Table 7-7 compares the “puff” emissions to the total refueling emissions 

averaged over the 12 tests on each vehicle. The results show that the fuel cap “puff” emissions are 

correlated with refueling emissions. The total HC “puff” mass is about half that of the refueling 

emissions mass for vehicles 01 and 03, and equal to the refueling emissions mass for vehicle 02. 

Carbon canister outlet emissions during refueling (bagged during each SHED test) are also shown in 

Table 7-7 and the levels are very low as one would expect. The fact that “puff” emissions are almost 

equal to and correlated with refueling emissions raises an interesting point regarding EPA’s 

MOBILE models that only count vapor displacement and spillage from refueling activities, one 

component of motor vehicle HC emissions. The data in Table 7-7 suggest that by not counting fuel 

cap puff emissions, the MOBILE models may underestimate the effect of reductions in refueling 

emissions on total motor vehicle HC emissions in coming years as the vehicle population shifts from

being predominantly non-ORVR to ORVR-equipped. Figures 7-7 through 7-9 reveal that “puff” 

emissions are positively correlated with tank temperature for vehicles 01 and 03, and only slightly 

for vehicle 02. The vehicle 02 results in Figure 7-8 are difficult to interpret since the emissions are 

near zero. A positive correlation between “puff” emissions and fuel RVP exists. 

91
TABLE 7-4 

SUMMARY OF INDOOR SHED PUFF EMISSIONS 

FOR VEHICLE 01 – ORVR WITH RECIRCULATION 

Fuel RVP 

(psi) 

Vehicle Tank Temperature 

(

o

 F) 

Puff Emissions 

(g/refueling event) 

7.8 

7.8 

7.8 

7.0 

7.0 

7.0 

70 

90 

105 

70 

90 

105 

0.133 , 0.119 

0.143 , 0.125 

0.178 , 0.167 

0.102 , 0.099 

0.162 , 0.156 

0.146 , 0.136 

Average for Vehicle 01 0.139 

Note: Two refueling tests were done for each RVP/TT combination. 

92
TABLE 7-5 

SUMMARY OF INDOOR SHED PUFF EMISSIONS 

FOR VEHICLE 02– ORVR NO RECIRCULATION 

Fuel RVP 

(psi) 

Vehicle Tank Temperature 

(

o

 F) 

Puff Emissions 

(g/refueling event) 

7.8 

7.8 

7.8 

7.0 

7.0 

7.0 

70 

90 

105 

70 

90 

105 

0.059 , 0.042 

0.053 , 0.056 

0.053 , 0.052 

0.051 , 0.035 

0.046 , 0.041 

0.071 , 0.045 

Average for Vehicle 02 0.050 

 Note: Two refueling tests were done for each RVP/TT combination. 

93
TABLE 7-6 

SUMMARY OF INDOOR SHED PUFF EMISSIONS 

FOR VEHICLE 03 – NO ORVR 

Fuel RVP 

(psi) 

Vehicle Tank Temperature 

(

o

 F) 

Puff Emissions 

(g/refueling event) 

7.8 

7.8 

7.8 

7.0 

7.0 

7.0 

70 

90 

105 

70 

90 

105 

0.571 , 0.031 

2.771 , 3.351 

4.340 , 5.147 

0.092 , 0.031 

0.080 , 3.219 

4.334 , 3.127 

Average for Vehicle 03 2.258 

Note: Two refueling tests were done for each RVP/TT combination. 

94
TABLE 7-7 

COMPARISON OF FUEL CAP “PUFF” EMISSIONS 

AND CANISTER OUTLET EMISSIONS 

TO SINGLE REFUELING EVENT EMISSIONS 

Vehicle 

Fuel Cap Puff 

Emissions 

(g/gal) 

Canister Outlet 

Emissions 

(g/gal) 

Refueling 

Emissions 

(g/gal) 

Puff/Refueling 

Ratio 

 01 – ORVR with 

 recirculation 

 02 – ORVR without 

 recirculation 

 03 – no ORVR 

0.014 

0.003 

0.146 

0.001 

0.002 

0.001 

0.026 

0.003 

0.230 

0.5 

1.0 

0.6 

95
FIGURE 7-7. FUEL CAP "PUFF" EMISSIONS, VEHICLE TANK TEMPERATURE AND 

FOR VEHICLE 01 - ORVR WITH RECIRCULATION

0.0900.1000.1100.1200.1300.1400.1500.1600.1700.180

65 70 75 80 85 90 95 100 105 

Tank Temperature (TT), o

F

Mass Emissions from Releases of Fuel Cap, g 
FIGURE 7-8. FUEL CAP "PUFF" EMISSIONS, VEHICLE TANK TEMPERATURE AND 

FOR VEHICLE 02 - ORVR NO RECIRCULATION

0.0350.0400.0450.0500.0550.0600.0650.0700.075

65 70 75 80 85 90 95 100 105 

Tank Temperature (TT), o

F

Mass Emissions from Releases of Fuel Cap, g 
FIGURE 7-9. FUEL CAP "PUFF" EMISSIONS, VEHICLE TANK TEMPERATURE AND 

FOR VEHICLE 03 - NO ORVR

0.0001.0002.0003.0004.0005.0006.0007.0008.000

65 70 75 80 85 90 95 100 105 

Tank Temperature (TT), o

F

Mass Emissions from Releases of Fuel Cap, g 
8.0 CONCLUSIONS 

From the first phase of the test program, Phase 1 – fleetwide tests using CARB method TP201.2 at a 

Conoco Service Station in San Bernardino, California, the following conclusions can be drawn: 

• CARB’s calculations of total incompatibility emissions are overestimated because they 

ignore the decrease in emissions at the nozzle/fillpipe from ORVR equipment. When a 

Gilbarco Stage II VRS is used, ORVR vehicles had 73% lower emissions from the 

nozzle/fillpipe than non-ORVR vehicles, a difference of 0.31 lb/1,000 gal, when fueled 

with RFG (7.0 RVP). This is a significant difference that CARB does not account for and 

it partially offsets the 0.86 lb/1,000 gal excess emissions from the UST that CARB has 

assigned to ORVR vehicles. Results were the same for standard vacuum assist nozzle and 

mini-boot nozzle refuelings. 

• Use of a mini-boot nozzle with the Gilbarco VRS reduced measured emissions from the 

P/V valve by 98%, and reduced total UST/piping system pressure-related emissions by 

64% to 98%. This reduction is greater than the 50% reduction CARB claims for the miniboot. 

• Since the sum of the vapor in the return line plus the fillpipe emissions for ORVR vehicles 

(roughly 1.2 g/gal) is larger than the maximum 0.2 g/gal that is allowed for emissions from

an ORVR car refueling at a non-Stage II service station, it appears that the VRS may be 

preferentially capturing vapors over the ORVR canister. Alternatively, the vacuum

assisted Stage II equipment may be increasing the volatilization of liquid fuel in the 

fillpipe as it is being dispensed. 

The Phase 2 – outdoor tests done at Automotive Testing Laboratories (ATL) in Mesa, Arizona 

provided direct measurements of the fugitive emissions from the UST/piping system and the changes

in pressure in the UST caused by the simultaneous use of ORVR and Gilbarco VRS vapor control 

systems. The effects of three processes were documented in the continuous one-second pressure 

records of the 3,000 gallon UST: initial positive or negative pressurization (depending on A/L) from

the return vapor line; vapor growth in the UST headspace from unsaturated return air; and 

continuous leaks from the UST/piping system (simulated with a leak valve on an otherwise tight 

system). 

The following conclusions were made: 

99
• Measured fugitive emissions from ORVR vehicles refueled with a mini-boot nozzle are 

near zero (0.003 lb/1,000 gallons) and are less than measured non-ORVR fugitive 

emissions (0.011 lb/1,000 gallons). Thus, when the mini-boot nozzle (A/L = 0.95) is used 

on a Gilbarco VRS, there is no ORVR incompatibility and measured “excess emissions” 

are zero (actually –0.008 lb/1,000 gallons). In addition, with the mini-boot nozzle in use 

the combination of ORVR and Stage II VRS controls produces 0.39 lb/1,000 gallons less 

emissions at the fillpipe than if just Stage II controls are used. 

• “Excess emissions” from the UST/piping system when a standard nozzle (A/L=1.15) is 

used are 0.72 lb/1,000 gallons. Considering the decrease in fillpipe emissions produced by 

the ORVR-VRS combination of 0.39 lb/1,000 gallons, total incompatibility emissions for 

the standard nozzle (A/L = 1.15) are only 0.33 lb/1,000 gallons, or less than half of the 

figure of 0.86 lb/1,000 gallons that CARB presumes for all ORVR vehicles 

• In situations where Gilbarco systems are equipped with standard nozzles (A/L = 1.15), a 

correction should be applied for the fact that the MOBILE6 model (the tool used to create 

state emission inventories) assumes fillpipe emissions for ORVR cars are lower than those 

for non-ORVR cars controlled with Stage II. That is, some of the fillpipe emissions 

reduction attributable to ORVR (and discussed in the bullet above) are already credited in 

the emissions inventory. Thus, when used in statewide emission inventories developed 

with MOBILE6, a slightly higher figure of 0.42 lb/1,000 gallons should be assumed for 

total incompatibility emissions for the Gilbarco dispenser with a standard nozzle. 

• The CARB estimation method for UST fugitive emissions (TP201.2F) overpredicted actual 

pressure-related fugitive emissions by factors of 13 to 660. These data support an earlier 

analysis by Tech Environmental that pointed to overprediction and flaws in the analytical 

form of the equation for pressure-related fugitives. 

The Phase 2 – Indoor SHED tests done at ATL quantified the dependence of refueling emissions on 

several independent variables. The following conclusions were reached: 

• The SHED refueling emissions at the fillpipe for ORVR and non-ORVR vehicles fall within

the range of values measured in the Phase 1 and Phase 2-outdoor TP201.2 tests. 

• Comparison of ORVR and non-ORVR fillpipe emissions in the SHED tests produced 

results confirming those found in the Phase 1 TP201.2 tests. In Phase 1, fillpipe emissions 

were 73% less for ORVR than for non-ORVR vehicles using a Gilbarco VRS. In the 

controlled refueling tests in the SHED, fillpipe emissions for the ORVR-equipped vehicles

were 91% lower than those for the non-ORVR vehicles using a Gilbarco VRS. 

• The dependence of fillpipe emissions on RVP, A/L ratio and temperatures is different for 

ORVR and non-ORVR vehicles. 

• For ORVR-equipped vehicles, there is very little to no correlation of fillpipe emissions with 

RVP, no correlation with A/L ratio, no correction with ∆T (vehicle tank temperature minus

dispensed temperature), and positive correlation with TT (vehicle tank temperature). 

100
• For the non-ORVR vehicle, there is a positive correlation of fillpipe emissions with RVP, a 

negative correlation with A/L, and a negative correlation of emissions with ∆T, as assumed 

in the EPA MOBILE6 model. 

• “Puff” losses of HC vapor that occur when the gas cap is removed on a vehicle are 

comparable to (50% to 100% of) fillpipe emissions from a single refueling event. “Puff” 

emissions are positively correlated with TT and RVP. 

• Since fillpipe emissions for ORVR-equipped vehicles do not exhibit the standard 

correlations with RVP and ∆T assumed in the MOBILE6 model, States and EPA should 

revise the calculation of refueling emissions for ORVR vehicles in MOBILE6 to reflect the 

new variable dependencies found in this study and to ensure that future emission inventories 

are accurate. 

Analysis of the extensive measurements of fillpipe and pressure-related fugitive emissions made in 

this study support the following overall conclusions, which are applicable to statewide HC emission 

inventories: 

• For a standard vapor recovery nozzle (A/L = 1.15) on a Gilbarco VRS, “excess emissions” 

do occur when an ORVR vehicle is refueled. This study documents the vapor growth 

process in the UST for individual refueling events, and measurements reveal “excess 

emissions” of pressure-related fugitives are 0.72 lb/1,000 gallons, slightly less than the level 

CARB assumes (0.86 lb/1,000 gallons). The CARB estimate is less reliable as it is not 

derived from actual measurements of pressure-related fugitives associated with refueling 

ORVR vehicles, the test method used on this study. 

• Since the P/V valve at a station cracks occasionally from the effects of multiple refuelings 

and releases headspace air, some of which is below-saturation vapor return line air, the full 

potential for vapor growth as measured in this study is not realized at a service station. (This 

study’s Phase 2 measurements of pressure-related fugitives considered the full potential for 

vapor growth over a 1 to 2 hour period following a refueling event.) Thus, the results given 

in this report likely overpredict actual fugitive emissions as they occur at a service station. 

• When a Gilbarco VRS is used, ORVR vehicles produce substantially lower emissions at the 

nozzle/fillpipe than non-ORVR vehicles. This is a significant offset to the excess emissions,

which CARB does not account for in analyzing ORVR compatibility. Thus, CARB in 

practice assumes that total incompatibility emissions are equal to excess emissions (0.86 

lb/1,000 gallons). 

• Total incompatibility emissions for the standard nozzle (A/L = 1.15) are only 0.42 lb/1,000 

gallons, about half of what CARB presumes for all ORVR vehicles (0.86 lb/1,000 gallons). 

• Measured fugitive emissions from ORVR vehicles refueled with a mini-boot nozzle are near 

zero (0.003 lb/1,000 gallons) and are less than measured non-ORVR fugitive emissions 

101
(0.011 lb/1,000 gallons). Thus, when the mini-boot nozzle (A/L = 0.95) is used on a 

Gilbarco VRS, there is no ORVR incompatibility and measured “excess emissions” are zero

(actually –0.008 lb/1,000 gallons). In addition, with the mini-boot nozzle in use the 

combination of ORVR and Stage II VRS controls produces 0.39 lb/1,000 gallons less 

emissions at the fillpipe than if just Stage II controls are used. 

• The CARB estimation method for UST fugitive HC emissions (TP201.2F) over-predicts 

actual pressure-related fugitive emissions by factors of 13 to 660. These data support an 

earlier analysis by Tech Environmental that pointed to over-prediction and flaws in the 

analytical form of the equation for pressure-related fugitives. 

• States and EPA should revise the calculation of refueling emissions for ORVR vehicles in 

MOBILE6 to reflect the new variable dependencies found in this study and to ensure that 

future emission inventories are accurate. 

• Puff losses were found to be on the same order of magnitude as fillpipe refueling emissions 

for both ORVR and non-ORVR vehicles. Puff losses are the losses of hydrocarbon vapors 

that occur when the gas cap is removed and are not captured in emission inventories 

calculated by the EPA MOBILE6 models. 

102
APPENDIX A 

CARB TEST PROCEDURES 
APPENDIX B 

PHASE 1 

TEST REPORT FROM 

VOC TESTING, INC. 
APPENDIX C 

PHASE 2 

TEST REPORT FROM 

VOC TESTING, INC. 
APPENDIX D 

PHASE 2 

TEST REPORT FROM 

AUTOMOTIVE TESTING 

LABORATORIES, INC.