NSPS OOOO and OOOOa and Storage Tank Requirements
December 8, 2016

For storage tanks, NSPS OOOO and OOOOa have similar requirements in regards to applicability, emission limitations, recordkeeping and reporting requirements. Some exceptions for storage tanks are different applicability dates for the two rules and NSPS OOOOa added requirements for closed vent systems (piping) used to control NSPS OOOOa affected facility storage tanks.

Below is a summary of key parts of the rules. Unless specified, the requirements apply to NSPS OOOO and OOOOa. Consult the written rules for details.



  • NSPS OOOO affects storage tanks constructed, modified or reconstructed after August 23, 2011, and on or before September 18, 2015.
  • NSPS OOOOa affects storage tanks constructed, modified or reconstructed after September 18, 2015. 
  • These rules do not apply to a storage tank that was constructed on or prior to August 23, 2011, and not reconstructed or modified after August 23, 2011.
  • A storage vessel (tank) that is in crude oil, intermediate hydrocarbon liquids, condensate or produced water service and has the potential for VOC emissions equal to or greater than 6 tons per year (tpy) is considered an “affected facility” if constructed, reconstructed or modified after the rule dates.
  • If a storage tank is an affected facility, then must comply with rule requirements.
  • A storage tank affected facility that subsequently has its potential for VOC emissions decrease to less than 6 tpy remains an affected facility. It may be able to remove controls if uncontrolled VOC emissions are less than 4 tpy , but is still an affected facility.
    • The rule exempts process vessels (such as vapor recovery towers), surge control vessels, knockout vessels. Also exempt are temporary tanks onsite for less than 180 days and pressure vessels designed to operate at more than 15 psig with no emissions.
    • Storage vessels with a capacity greater than 100,000 gallons used to recycle water that has been passed through two stage separation are exempt.

 Emission Limitations

  • NSPS OOOO/OOOOa affected facility storage tanks that have emissions greater than or equal to 6 tpy VOCs must reduce VOC emissions by 95% or greater.
  • There are no emission limitations on methane (CH4) for storage tanks.

Emission Control Options

Typical emission controls include:

  • Vapor recovery units (VRUs)
  • Enclosed combustors (VCUs)
  • Open-tipped (candle stick) flares.

The most desirable control method is a VRU since this recovers the natural gas product and sends the gas to the sales line or back to the process for facility use. Gas recovery lowers emissions and increases profits to the facility.

Guidance on controlling emissions from storage tanks at oil and gas production facilities can be found in the September 2015 EPA Compliance Alert: https://goo.gl/F12VdS

Emission Estimation

  • Storage tanks VOC emissions result from flashing, breathing (standing) and working emissions. See Texas Commission on Environmental Quality document link: https://goo.gl/J3MehD
  • Flash emissions can be determined by direct measurement of vent gas, pressurized gas-oil-ratio (GOR) sampling/analysis, processor simulation models and E&P TANKS Software.
  • Breathing and working emissions can use methods given in EPA’s AP-42, Compilation of Air Pollutant Emission Factors, Chapter 7: Liquid Storage Tanks. The AP-42 equations do not calculate flash emissions.
    • Many State permitting agencies accept the EPA’s TANKS4 software calculations for breathing and working emission estimates. This software does not calculate flash losses. Note that EPA does not currently support this software. See link: https://goo.gl/djNL2W

Storage Tank Emission Allocation

  • For NSPS OOOO and OOOOa, VOC emissions are determined on a per storage tank basis. Flash, breathing (standing) and working VOC losses are to be allocated to each storage tank based on actual operation and production to the storage tanks.
  • If the flash occurs in one storage tank only and the other storage tanks receive only de-pressured (dead oil), then flash emissions should be allocated to only those storage tanks with flash emissions.

Pollutants Covered

Storage vessels included in NSPS OOOO and OOOOa only have VOC limitations.

Ways to Avoid NSPS OOOO and OOOOa

  • Install a vapor recovery unit (VRU) and capture the vent gas. VRUs are considered process equipment by EPA and the gas recovered by the VRU does not count toward the VOC potential to emit (PTE) emissions for the storage tanks. VRUs should meet the EPA minimum definition of a VRU (proper compressor selection, etc), and should be specifically designed for high BTU, “wet” gas streams.
  • Obtain an air permit for the facility that is “practically enforceable” from the air permitting agency such that the permit limits VOCs to less than 6 tons per year per storage tank. Such tanks are exempt from NSPS OOOO and OOOOa. The air permit will require that each storage tanks emit less than 6 tpy VOC. The storage tank emissions used to determine applicability would be based on after control emissions..
  • Use centralized batteries to process the crude oil/condensate which allow more efficient VRU systems. Centralized batteries receiving oil from several to many wells flowing can have a more constant flow of oil to storage tank which improves efficiency of a VRU system. VR Towers can also be used to effectively eliminate oxygen ingress.
  • Ensure storage tank hatches and piping to the control device (flare/combustor) or VRU operate in a leak-free manner.

NSPS OOOOa only - Closed Vent Systems (Piping) Design Certification

The rule requires certification by a qualified professional engineer that the closed vent system is properly designed to ensure that all emissions from the unit being controlled are sent to the control device and allow for proper control.

This applies only to NSPS OOOOa required closed vent systems for emission control devices used to control vent gas from affected storage tanks, centrifugal compressor wet seal fluid degassing systems, reciprocating compressors rod packing and pneumatic pumps.

Initial Notification

No initial notification to EPA or State regulatory agency for storage tanks with applicable requirements under NSPS OOOO and OOOOa.


Consult the rules for the recordkeeping requirements for affected source storage tanks.


An annual report is due for storage tanks (and other regulated emission sources)

  • The NSPS OOOO Annual Report is due within 90 days after the end of the annual compliance period. The initial compliance period began on October 15, 2012. Annual reports are due each January 15 (estimated) of the following year for the previous annual reporting period.
  • The NSPS OOOOa Annual Report is due within 90 days after the end of the initial annual compliance period. The initial compliance period began on August 2, 2016.

Estimated due date is October 31, 2017.

  • Consult the EPA or your State regulatory agency for exact dates.

Review the rule for details on reporting requirements. Report data required includes constructed, modified or reconstructed location, VOC emission rate, records of deviations from standards, affected tanks removed or put back into service, and statement that have met requirement of the rule.

Stay in Compliance

HY-BON/EDI can assist your company comply with the NSPS OOOO and OOOOa requirements.

Our IQR (Identify, Quantify and Rectify) services obtains data on storage tank VOC emissions.  Using our IQR services and our ongoing Vent Gas Management (VGM) system we can support VOC emission reductions and stay in compliance with NSPS OOOO and state air permits. This can make your company money. HY-BON/EDI’s vent gas management (VGM) system is a cost effective way to take this issue off of your plate. We use “best in class” vapor recovery units (VRU), Vapor Recovery Towers (VRT) and enclosed combustors (ECU) to comply with storage tank emission control requirements.