Generator Permit Requirements

The Virginia DEQ Air Division divides generators into two categories: emergency generators and non-emergency generators. Since air permit applicability is based on the generator’s uncontrolled emissions of air pollutants, it is important to understand the difference in the generators and their uncontrolled emission rate.

Emergency Generators:

To qualify as an emergency generator, the unit can only operate when there is an “emergency”.  In Virginia, “emergency” is defined as:

A condition that arises from sudden and reasonably unforeseeable events where the primary energy or power source is disrupted or disconnected due to conditions beyond the control of an owner or operator of a facility including:

  1. A failure of the electrical grid,
  2. On-site disaster or equipment failure,
  3. Public service emergencies such as flood, fire, natural disaster, or severe weather conditions, or
  4. An ISO-declared emergency, where an ISO emergency is:
    1. An abnormal system condition requiring manual or automatic action to maintain system frequency, to prevent loss of firm load, equipment damage, or tripping of system elements that could adversely affect the reliability of an electric system or the safety of persons or property,
    2. Capacity deficiency or capacity excess conditions,
    3. A fuel shortage requiring departure from normal operating procedures in order to minimize the use of such scarce fuel,
    4. Abnormal natural events or man-made threats that would require conservative operations to posture the system in a more reliable state, or
    5. An abnormal event external to the ISO service territory that may require ISO action.

“Emergency” also includes operating during brief maintenance and testing exercises.  The total amount of hours an emergency generator can operate for is not more than 500 hours per year, including testing and maintenance. An emergency generator’s uncontrolled emission rate is assumed to be 500 hours per year under the worst case conditions.

**NOTE:  If the emergency generator operates as stated above and participates in the Emergency Load Response Program (ELRP), then it is still considered an “emergency generator”.

In order for an emergency generator to be exempt from permitting, it must meet one of the following criteria:

  1. Exempt by size: 

    • Diesel engines that have an aggregate brake horsepower of less than 1,675 horsepower (1,125 kilowatts).
    • Gasoline engines that have an aggregate brake horsepower of less than 910 horsepower (611 kilowatts).

      **NOTE: "Aggregate” means the sum or total brake horsepower (or kilowatts) for all generators included in the application. For example, if a facility is installing 4 - 1,000 kW diesel generators, the "exempt by size" comparison would be between the total of 4,000 kW and the 1,125 kW threshold.
  1. If not exempt by size, then by emissions:

    • If uncontrolled emissions of the emergency generator are below exemption levels in 9 VAC 5-80-1105 C (for new sources) and D (for projects) of state regulations (9 VAC 5, Chapter 80, Article 6).

Non-Emergency Generators:

“Non-emergency generators” are those units used for peak shaving, distributed generation, or for generating electricity for any reason other than emergency use previously explained.  A non-emergency generator has an uncontrolled emissions rate based on a maximum 8,760 operating hours per year (24 hours per day x 7 days per week x 52 weeks per year). 

In order for a non-emergency generator to be exempt from permitting, it must meet the following criteria:

  •  If uncontrolled emissions of the emergency generator are below exemption levels in 9 VAC 5-80-1105 C (for new sources) and D (for projects) of state regulations (9 VAC 5, Chapter 80, Article 6).

Any generator used for demand side distribution, or when a utility asks for help producing extra capacity, is NOT emergency generation.

**NOTE:  Per NSPS Subpart IIII, if a facility installs a 2011 (and beyond) model year non-emergency compression ignition (CI) engine, it must be a Tier 4 engine.  Starting January 1, 2013, owners and operators of new non-emergency CI engines greater than or equal to 130 kW (175 hp) will have to install engines that meet the applicable requirements for 2011 model year non-emergency engines (i.e. Tier 4 engines).

Federal Regulations:


Many stationary internal combustion engines are subject to one or more of the following federal regulations, including ones that may be exempt from permitting.  Links to each rule are provided below:

  • NSPS Subpart IIII (Standards of Performance for Stationary Compression Ignition Internal Combustion Engines),
  • NSPS Subpart JJJJ (Standards of Performance for Stationary Spark Ignition Internal Combustion Engines), and/or
  • NESHAP Subpart ZZZZ (National Emissions Standards for Hazardous Air Pollutants for Stationary Reciprocating Internal Combustion Engines). 

    **NOTE:  Currently, Virginia does not have delegation of these federal regulations except for Title V sources.

Because these rules are complex, DEQ staff developed the following flow charts to help navigate the rules.  Please note that these charts do not contain every part of the federal rules and should only be used as guidance.

Per EPA, there are some engines that fall into an “applicability gap” for NESHAP Subpart ZZZZ and NSPS Subpart JJJJ; therefore, they do not have to meet any requirements.

NESHAP Subpart ZZZZ and NSPS Subpart JJJJ Applicability Inconsistencies

EPA Websites:

For all the latest information on the three federal rules, please see the links below.  These links contain information such as:

  • Proposed and Promulgated Rules
  • Regulatory Impact Analysis/Background Information Document (BID)/Response to Comments
  • Fact Sheets
  • Databases
  • Implementation Information, and
  • Outreach and Training Material (including upcoming training events and PowerPoint presentations)

EPA Website: Stationary Internal Combustion Engines

EPA Website: NSPS Subpart IIII

EPA Website: NSPS Subpart JJJJ

EPA Website: NESHAP Subpart ZZZZ and EPA Region 1:  NESHAP Subpart ZZZZ

  • EPA developed an implementation tool for NESHAP Subpart ZZZZ (The Regulation Navigation tool) which is a Turbo Tax-like software program that guides the user through a set of questions.  At the end, a web link provides the specific regulatory text that applies to a particular engine.

 For Virginia air permit applications, please submit a completed Form 7 application to the appropriate regional office.




Guidance on Vacatur of RICE NESHAP and NSPS Provisions for Emergency Engines

  • The D.C. Circuit Court issued a decision vacating provisions in the RICE NESHAP and NSPS indicating that emergency engines may operate for emergency demand response and deviations in voltage or frequency. 
  • Read about the May 4, 2016 mandate and other technical documents.

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Virginia Department of
Environmental Quality
P.O. Box 1105
Richmond, VA 23218
(804) 698-4000

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