Used in October 17, 2017 Webinar by Melanie King and Sara Ayres, EPA, for the NSC technical subcommittee.

Comparison of requirements for stationary non-emergency engine at area source in remote area:

Older engine (installed before June 2006) / New engine
Not reconstructed / Reconstructed (50%)
If CI <300 HP, or SI:
  • Maintenance requirements
  • Operate/maintain per manufacturer’s instructions
  • Keep records of maintenance
If CI >300 HP:
  • CO limit (likely requiring retrofit of engine with catalyst)
  • ULSD and crankcase controls
  • Performance test (ongoing if >500 HP)
  • Continuous parameter monitoring
  • Semiannual compliance reports
  • Notifications and recordkeeping
/ NESHAP requirement is to meet NSPS
If CI:
  • If cost is 50-75%, Tier 1 emission standards for NMHC+NOx, CO, PM
  • If cost is >75%, Tier standards for NMHC, NOx, CO, PM for model year in which reconstruction occurred (likely requiring SCR and DPF)
  • ULSD
  • Initial performance test
  • If >175 HP, initial notification and records of maintenance
If SI:
  • NOx, CO, VOC emission standards (likely require catalyst for rich burn engines)
  • Initial performance test
  • If >500 HP, initial notification
  • Records of maintenance
/ NESHAP requirement is to meet NSPS
If CI:
  • Purchase engine certified to applicable standards for model year, engine power, application (see attached slide)
  • Emission controls, if necessary, will be included with engine
  • Install, configure, operate, maintain engine per manufacturer’s instructions
If SI:
  • If <25 HP, gasoline, or rich burn LPG, purchase engine certified to applicable standards for model year, engine power, application (emission controls, if necessary, will be included with engine)
  • Install, configure, operate, maintain engine per manufacturer’s instructions and keep records of maintenance
  • If >25 HP and not gasoline or rich burn LPG, meet NOx, CO, VOC emission standards (likely require catalyst for rich burn engines)
  • Performance test if >25 HP (ongoing if >500 HP)
  • Maintenance plan and records of maintenance

Other topics:

  • Costs of emission controls:
  • See memos
  • Stationary vs. mobile
  • Engines used in a piece of equipment that is self-propelled (such as a bulldozer) or intended to be propelled while performing its function (such as a weed-eater) are always mobile engines.
  • Engines used in a piece of equipment that is portable or transportable, meaning designed to be and capable of being carried or moved from one location to another, are mobile unless the engine remains or will remain at a location for >12 months (or the operating period of a seasonal source). A location is defined as “any single site at a building, structure, facility, or installation.”
  • We have issued a few determinations on this issue, which can be found at or
  • Residential/institutional/commercial exemption – only exists in the NESHAP and is only for existing emergency engines at area sources of HAP that do not operate in a financial arrangement to mitigate local transmission and distribution limitations.
  • Limited use engines in the NESHAP
  • For engines >500 HP at major sources of HAP, limited use engines have no requirements other than an initial notification for new engines.
  • For engines ≤500 HP at major sources of HAP, and any size at area sources, certain limited use engines have less frequent testing and reporting requirements. They can test every 5 years instead of every 3 years. What happens if the engine exceeds 100 hours within the 5 years?
  • “Gap” or “doughnut hole”
  • Subpart ZZZZ specifies that new engines ≤500 HP at major sources and new engines of any size at area sources comply with the NESHAP by complying with the NSPS. New is defined in the NESHAP as construction commencing after June 12, 2006. Commencing construction is defined as entering into a contractual obligation for the on-site installation of the engine.
  • CI Engine NSPS applies to engines ordered after July 11, 2005, and manufactured after April 1, 2006. SI Engine NSPS applies to engines ordered after June 12, 2006 and manufactured after dates ranging from July 1, 2007, to January 1, 2009, depending on type of engine.
  • Situations have arisen where the engine is new under the NESHAP any is only required by the NESHAP to comply with the NSPS, but the engine was ordered and/or manufactured prior to the applicability dates specified in the NSPS. This is addressed in Q&A # 40 here:
  • Guidance for when reports are past due? Should the small business just send them in? Paper or electronic?
  • Waivers for stack testing
  • We have granted them for testing of identical engines at the same facility. Examples can be found here: or Also see p. 8-10 in the CAA National Stack Testing Guidance, which can be found here:
  • Useful life for certified engines:
  • Response to comments from original CI Engine NSPS rulemaking: “The useful life period is designed to represent the time during which the engine manufacturer is responsible for the engine meeting the emission standards as long as the owner operates the engine according to the manufacturer’s specifications. After the useful life of the engine, it is the owner or operator’s sole responsibility to ensure that the engine continues to meet the emission standards. EPA expects that owners and operators will continue to operate regulated engines in a manner that provides for continued emissions control. Throughout the life of the engine, the owners and operators must operate and maintain the stationary CI engine and control device according to the manufacturer’s written instructions (or procedures developed in cooperation with the engine manufacturer). The engine must also be installed and configured according to the manufacturer’s specifications.”
  • Funding for engine replacement
  • Guidance for engines at area sources:
  • Here is a link to a document we prepared a few years ago. We could consider updating it to reflect the vacatur and also to include information about the NSPS, if that would be useful.