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Review of OGI Wind Tunnel Tests 

and 

Refinery and Chemical Plant 

OGI and Bagging Studies

Jeff Siegell – ERM

EPA – API Meeting

August 18, 2011 - RTP, NC
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Conduct Wind Tunnel Tests

– Controlled wind conditions

– Known species

– Controlled leak rate

Conduct Plant Tests

– Field wind conditions

– Typical plant process streams

– Real-world leaks

Can Optical Imaging Meet/Exceed 

AWP Required Performance?

Photo courtesy Leak Surveys Inc.
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Species

Lowest Detected 

Mass Leak Rates

(g/hr)

Methane 0.3 - 49

Ethane 0.6 – 17.8

Propane 0.4 - 19

Butane 0.4 - 15.9

Pentane 3 - 45.8

Hexane 1.7 - 57.8

Heptane 1.8 - 48

Octane 1.2 - 62.2

Propylene 2.9 - 59.8

Toluene 3.8 - 75.3

Xylene 1.9 - 75.3

Data for FLIR GasFindIR camera, from papers presented at “Smart LDAR Symposium,” AWMA 99th Annual Meeting, 

New Orleans, June 2006.

Wind Tunnel Tests for Instrument 

Detection Limits

Detection Depends on Wind 

Speed & Distance from Leak

– Less sensitive at higher wind 

speeds

– Less sensitive at longer distances 

but can be addressed with 

alternate camera lens

Easier to Find Leaks in Field 

Compared to Wind Tunnel

– Less uniform wind speeds in field

– Less uniform wind direction in 

field 
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Compound Lowest Detected Mass 

Leak Rates - g/hr(a)

1,3 – butadiene 1.3 - 2.7

Acetic acid < 0.02 - < 4.6(b)(c)

Acrylic acid 0.92 - 1.2

Benzene 0.35 - 35(c)

Methylene chloride 4.9 - >70(c)

Ethylene 0.35 - 278(c)

Methanol 0.28 - 22(c)

Pentane < 0.28 - 28(c)

Propane < 0.44 - 13(c)

Styrene 0.35 - 0.70

FLIR GasFindIR MW Camera Method 

Detection Limits from ETV

(a) Detection limits determined at zero mph wind speed unless otherwise noted

(b) Measured at 2.5 mph wind speed

(c) Measured at 5 mph wind speed 

Adapted from Table 1 of ETV Verification Statement, 12/1/10

Test variables 

include wind speed, 

background, and 

distance
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US Gulf Coast

– Project plans reviewed and approved by EPA

– Completed as part of SEP

One Week Test – Spring 2006

73,000 Piping Components Monitored

– 11 different process areas

28 Leaks Found by Optical Imaging

– Method 21 for leaks found by OGI

– 16 leaks bagged to obtain mass emissions rate

Monitoring Rate: 3,600 components/hour

Chemical Plant Test Description
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Chemical Plant Test Results

Methane - 3.7 g/hr

Propane - 4.7 g/hr

Butane - 10.6 g/hr

Propylene - 23.8 g/hr

Toluene - 50.2 g/hr

Xylenes - 17.8 g/hr

Note: These rates are for leaks found during the test program and do not

necessarily reflect the smallest leak that could have been found by the 

instrument.

Data from Environmental Progress, Vol. 26, No. 2, July 2007

These Leak Rates are all 

Within the Range of the 

Wind Tunnel Results

Lowest Emission Rates 

Found by OI During Test 

Monitoring Rate = 3,600 

components / hour
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US Gulf Coast Refinery

– Completed as part of SEP for Consent Decree

– Project plans reviewed and approved by EPA

– EPA participated during data collection

Two Test Periods - Each One Week Long 

– Fall 2006

– Spring 2007

Plant Areas Monitored 

– Alkylation unit

– Cat Cracker light-ends fractionation

– Crude light-ends fractionation

– Hydroforming unit

– Tank farm

> 110,000 Piping Components Monitored

Method 21 for All “Leaks” Found by OGI and Also for “Non-Leaks” 

That Were Bagged

Refinery Test Description
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Refinery Test Results

72 leaks found with optical imaging

− 0.065% of total components 

− Consistent with API SCAQMD study: 0.13% above 10,000 ppmv

Actual mass emissions measured by bagging of 70 components

− 40 leaks found with optical imaging; preferentially bagged the smallest 

leaks found by optical imaging

− 30 leaks found by Method 21 monitoring that optical imaging did not 

show leaking; preferentially bagged the largest leaks not found by 

optical imaging

Smallest leak detected by optical imaging was 0.18 g/hr as 

measured by bagging

“Marginal Detects” 

− Leaks visual by some instrument operators but not others

− Leaks found first by Method 21 after initial miss by instrument, then 

found by instrument operator after closer inspection

All leaks above 11 g/hr were detected by optical imaging
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Detection Sensitivity Well Below 60 g/hr

0.1 1.0 10.0 100.0 1000.0

THC (g/hr)

Detects Marginal Detects Non-Detects Spring Detects Spring Marginal Spring Non-Detects

Largest Non-Detect = 11 g/hr

Smallest Detect = 0.183 g/hr

All Leaks greater than 

11 g/hr detected via 

optical imaging, 

including one marginal 

detect

60 g/hr - US EPA required detection capability

Data from Environmental Progress & Sustainable Energy, Vol. 28, No. 2, July 2009.

Detects

Marginal Detects

Non-Detects

Leak Rate

g/hr

Monitoring Rate = 4,500 components / hour
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Other Refinery Findings

 Monitoring Efficiency

– 24 hours of data collection over 8 days

– 4,500 components / hour 

– Compared to Method 21 monitoring

• Method 21 typically 400-600 components/day

• Method 21 requires “touching” each component

 Method 21 Reading Not Always a Good Indicator of Relative 

Leak Rate

– Some high concentration Method 21 components had lower mass leak 

rates

– Some low concentration Method 21 components had higher mass leak 

rates

 High Method 21 components not detected by Optical Imaging 

confirmed by bagging to have relatively low mass rates (i.e. 

“False Positives”)
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CONCLUSIONS

Chemical Plant and Refinery tests confirm ability of optical 

imaging to find leaks in field at AWP-required emission rates

Chemical Plant tests show sensitivities within ranges of wind 

tunnel tests for individual species - can initially predict field 

performance from wind tunnel tests

Wind tunnel generally provides conservative conditions for 

leak detection – uniform wind speed and direction

Leaks at AWP level are quickly and easily found using optical 

imaging

 No need to focus excessively on each component

 Many components can be monitored in a single view