Vapor Recovery – In-Station Diagnostic System Overpressure Alarms

This page last reviewed December 12, 2017

In late 2008, California Air Resources Board (CARB) staff was informed of an unusually high number of In-Station Diagnostic (ISD) system overpressure alarms at gas stations during winter months. When gas station operators called out service technicians to investigate, in the majority of cases they could not find an underlying vapor recovery system equipment problem that explained the overpressure alarm. This finding was confirmed by CARB staff. To provide temporary relief from the expense and down time associated with overpressure alarm response, CARB staff worked with the California Air Pollution Control Officers Association (CAPCOA) and issued a series of advisories beginning in 2009, the latest is Advisory 405-D.

In cooperation with CAPCOA, CARB staff initiated a series of field studies to determine the root cause and to identify an effective solution. After identifying a possible cause, CARB staff held a series of workshops concerning proposed regulatory solutions. However, further information during the workshop indicated the overpressure problem was more complex than initially expected. As a result, CARB staff, in cooperation with CAPCOA and equipment manufacturers, commenced another series of field studies to identify the possible causes and released Technical Support Documents with the findings.

CARB staff are currently completing overpressure studies and refining data analysis techniques to propose regulatory solutions. Workshops will be scheduled to further discuss and to solicit feedback from CAPCOA and the public. Once regulatory documents are available, they will be posted to this page. 

Relief Provided to Gas Station Operators in Response to ISD Overpressure Alarms

GDF Site

Informational Bulletin - Recommendations to Minimize Winter Time ISD Overpressure Alarms for Assist Phase II Systems
Advisory 405-D
Advisory 405-D Frequently Asked Questions

Public Workshop Presentations


• NEW December 2017 Vapor Recovery Program Presentation
NEW December 2017 Advanced Clean Cars Program Presentation
• November 2015 Overpressure Workshop Presentation
March 2014 Overpressure Workshop Presentation
September 2013 Overpressure Workshop Presentation
November 2012 Overpressure Workshop Presentation

Studies - Technical Support Documents


• DRAFT: VR-OP-G2: 2013/2014 Field Study to Determine the Extent of the Overpressure Issue Occurring at California Gasoline Dispensing Facilities

Assist System Studies 
DRAFT: VR-OP-A1: Results of Vapor Recovery System Performance Testing Conducted at Gasoline Dispensing Facilities Equipped with the Assist Phase II Enhanced Vapor Recovery System which Experience Pressure Increase While Dispensing
DRAFT: VR-OP-A2: Nozzle Replacement Study at Gasoline Dispensing Facility Equipped with Assist Phase II Enhanced Vapor Recovery System Exhibiting Pressure Increase While Dispensing 
VR-OP-A3: Healy Model 900 Assist Vapor Recovery Nozzle ORVR Vehicle Recognition Study
DRAFT: VR-OP-A4: Evaluation of Assist Vapor Recovery Nozzle ORVR Vehicle Recognition Performance Under Controlled Fueling Conditions
VR-OP-A5: Evaluation of Healy Model 900 Assist Vapor Recovery Nozzle with Enhanced ORVR Vehicle Recognition Feature during Winter of 2015/2016
DRAFT: VR-OP-A6: Estimate of Pressure Driven Emissions Occurring at GDF Equipped with the Assist Phase II Enhanced Vapor Recovery Systems
• VR-OP-A7: Evaluation of Healy Model 900 Assist Vapor Recovery Nozzle with Enhanced On-Board Refueling Vapor Recovery (ORVR) Vehicle Recognition Feature during the Winter of 2016/2017 (Coming Soon)

Bagged nozzles

Balance System Studies
DRAFT: VR-OP-B1: Performance of Balance Type Phase II Vapor Recovery Systems Operating at Slightly Positive Underground Storage Tank Ullage Pressure
• VR-OP-B2: Evaluation of Pressure Driven Emissions from GDF Equipped with Balance Phase II Enhanced Vapor Recovery Systems (Coming Soon)


Gas Station Characteristics
• DRAFT: VR-OP-G1: Gasoline Sampling and Analysis to Investigate the Effect of Reid Vapor Pressure on Vapor Recovery System Overpressure 


rules and regulations

    • Coming Soon

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