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Stationary Engines

About Stationary Engines

Stationary engines are internal combustion engines using reciprocating motion to convert heat energy into mechanical work and which is not mobile.

Mobile engines are used to propel a motor vehicle or non-road engine. Engines that are mobile are excluded from permitting and RICE rule requirements.

Portable engines has wheels, skids, carrying handles, dolly, trailer or platform. Note: a portable non-road engine becomes stationary if it stays in one location for more than 12 months (or full annual operating period of a seasonal source)

Combustion turbines, although not reciprocating internal combustion engines, may require an air permit and be subject to other federal air pollution regulations (NSPS KKKK and NESHAP YYYY).

Stationary engines are typically found at manufacturing, agricultural, municipal utilities, hospitals, retail centers, schools, and other types of businesses. This page is a resource for helping the owners and operators of these engines to determine whether they require an air permit for their stationary engine(s) and whether or not they are compliant with the federal rules for reciprocating internal combustion engines (RICE), 40 CFR 63 Subpart ZZZZ. Additional information can be found on the United States Environmental Protection Agency’s (U.S. EPA) Stationary Internal Combustion Engines page.

Regarding the regulated entities that have been assisted, the Indiana Department of Environmental Management (IDEM) is finding most communities are satisfying the federal requirements of the RICE rule due to good maintenance practices. However, we are finding that some of the sources failed to obtain the required State air permits.

Vacatur of Portions of RICE NESHAP and NSPS Provisions for Emergency Engines

Owners of emergency use only engines should be aware of a recent court case (2015) that may affect the emergency use only status if they are participating in an emergency demand response program or operate the engine in order to mitigate voltage/frequency fluctuations effective as of May 2016. Guidance on Vacatur of RICE NESHAP and NSPS Provisions for Emergency Engines [PDF].

New 2016 Federal Reporting Requirements For Owners of Emergency Engines

Owners of emergency engines with a maximum engine power of more than 100 horsepower (HP), which are operated or contractually obligated to be available more than 15 hours/year for emergency demand response, voltage or frequency deviations, or local reliability (as specified in 40 CFR §63.6640(f), §60.4211(f), and §60.4243(d)), must now submit an annual report to U.S. EPA as required by §63.6650(h).

The first report was due on March 31, 2016, and this annual report is to be submitted electronically through the Compliance and Emissions Data Reporting Interface (CEDRI), accessed through U.S. EPA’s Central Data Exchange. It must cover the prior year’s operations and include the information specified in 40 CFR §63.6650(h) (for stationary emergency RICEs), §60.4214(d) (for compression ignition engines), or §60.4245(e) (for spark-ignition engines). More information on the report is available on U.S. EPA’s Stationary Internal Combustion Engines page.

Do I need a permit for my engine?

If you have stationary engines such as generators, pumps, blower motors, or other stationary combustion equipment such as boilers, flares, furnaces, or turbines, you should evaluate these to determine if an air permit is required.

Are my combustion activities combined or separate for permitting purposes?

To determine whether an air permit is necessary, one must identify all the various pieces of stationary air pollutant emitting equipment at that property. Air permits are issued holistically based on the combined emissions of all stationary air pollutant emitting equipment at a single property or source, not on each individual piece of equipment. It is also possible that equipment at multiple property locations may be considered as a single source for permitting purposes if the properties are adjacent (near one another), are dependent on one another, or share staff. Below you will find more information regarding source determinations for equipment on multiple properties.

Do I need an air permit?

The type of air permit that is required is based on the combined equipment’s potential to emit air pollution, not on the actual air pollution emitted from the equipment. The potential to emit (PTE) is essentially a worst-case calculation presuming the equipment will operate at its maximum capacity 24 hours per day, 365 days per year (8,760 hours per year).

If the PTE of a single criteria pollutant, from all your combined equipment, meets or exceeds the permit threshold then a permit is required. The permit threshold varies by pollutant. The thresholds for the most common pollutants of concern are below.

Criteria Air Pollutant Criteria Air Pollutant Symbols Threshold Requiring an Air Permit (tons/year)
Nitrogen Oxides NOx 10
Sulfur Dioxide SO2 10
Volatile Organic Compounds VOC 10
Particulate Matter PM 5
Carbon Monoxide CO 25

To help determine the applicable air permit for your source, the emission thresholds for various levels of permits are discussed within the Threshold Table for Sources based on Potential to Emit [PDF] as well as the E101 Air Manual on the Environmental Education for Regulated Entities (E101) page, specifically the Registration Thresholds Table and the Title V Thresholds for Major Sources.

Do I have a peak shaving/load shedding agreement?

If an engine is committed for a peak shaving or load shedding agreement with the electrical utility, the generator is considered “non-emergency use” for permitting purposes, and the PTE must be calculated based on 8,760 hours per year of operation. Entities should familiarize themselves definition of an emergency engine.

How do I determine my source’s potential to emit?

Emissions are calculated using the power rating or heat input rating of the engine, an emission factor for the pollutant of concern, and the potential hours of operation of the engine. The power rating or heat input rating for a diesel or gasoline-fired engine is measured in horsepower (HP), while a natural gas or digester gas-fired engine is measured in BTU/hour. Regarding the potential hours of operation for a particular engine, “emergency use only” engines may utilize 500 hours per year while every other engine should utilize 8,760 hours per year.

“Non-emergency use” equipment as small as 74 HP diesel-fired engines, 100 HP 4-stroke lean burn gasoline-fired engines, and 0.5 million BTU/hr (fuel input) natural gas-fired engines will require the lowest level of air permit. Please note, a source with three (3) “emergency use only,” diesel-fired, 434 horsepower engines would also require the lowest level of air permit.


A source has three (3) “emergency use only” 450 HP diesel fired engines. The emission factor for NOx for diesel engines less than 600 horsepower is 0.31 lbs NOx/hp – hr. The emissions calculation is:

3 * 450 HP = 1350 HP

1350 HP * 0.031 lbs. (NOx / HP HR) * 500 HR/YR * 1(ton/2000lbs) = 10.5 tons NOx/YR

To help determine your source’s PTE IDEM has developed the Updated Emissions Calculations Guidance [PDF].

How do I find the horsepower or heat input capacity of my equipment?

1 KW = 1.34 HP
1 KW = 9380 BTU (diesel)

Owners of stationary “emergency use only” engines are knowledgeable of the generator power rating measured in kilowatt hours (KW). However, they are typically unaware of the horsepower (HP) for a diesel or gasoline engine, or heat input capacity measured in BTU/hr. for a natural gas engine. If a permit is required, the horsepower or heat input capacity will be needed for the permit application. (They can be obtained from the manufacturer or from the engine plate.) The actual horsepower or heat input capacities are preferred, but for an approximation, one could use a conversion factor.

Do I need to request a source determination for equipment on multiple properties?

If you have equipment located at multiple properties and the combined PTE from the equipment exceeds the permit threshold, you should work with the Office of Air Quality’s (OAQ) permit staff to obtain a source determination for those properties. Please note, for permitting purposes, it must be determined whether the equipment on multiple properties should be treated as a single group or be broken down into smaller groups.

To be considered one source, the equipment located on multiple properties must be under common ownership or common control or have the same two-digit Standard Industrial Classification (SIC) Code. If one of the pieces of equipment serves as a support facility for the other and the source is located on contiguous or adjacent properties then it is also considered one source.

The Source Definition Manual [PDF] explains situations in which connections between properties would cause them to be considered a single source. If your equipment is located on contiguous or adjacent properties, you should complete the Source Determination Form [PDF] and contact the administrative assistant to the OAQ Permits Branch Chief, to schedule a pre-application meeting to discuss the source determination scenario. The Source Determination Form requires information regarding commonalities between ownership and control of the properties, commonalities between material and staff of the properties, and other connections between the properties.

Do my engines comply with federal requirements?

Whether or not your equipment requires an air permit issued by IDEM, there may be federal air pollution regulations that apply to your stationary engines. When federal regulations apply, regardless of whether you have an air permit, compliance must be achieved. Federal regulations that may apply to stationary engines include the:

Exclusions from the RICE rule include non-road engines (e.g., tractors and lawnmowers); portable engines (i.e., positioned on a trailer or having wheels); emergency engines located at residential, institutional, or commercial sources (e.g., hospitals, hotels, or offices); and new engines (installed after June 12, 2006) at area sources for hazardous air pollutants. Please note a portable non-road engine becomes stationary if it stays in the same location for more than 12 months.

Compression ignition (CI) engines burn diesel fuel.

Spark ignition (SI) engines use fuels such as natural gas, landfill gas, digester gas, gasoline, or propane.

The RICE rule applies to stationary engines. The requirements of the rule are defined by categories that define whether an entity is considered an area or a major source for hazardous air pollutants (HAP). The requirements are also dependent on whether a facility has a new or existing engine, a compression ignition or spark ignition engine, or an “emergency use only” or “non-emergency use” engine.

Please note several regulated entities defined as an area source for hazardous air pollutants with “emergency use only” engines have been found to have satisfied the requirements of the RICE rule. If you are unsure what requirements apply to engines at your source, please refer to "What are the RICE rule requirements for my engine(s)?" below, select the appropriate engine from the list, and a summary of applicability for your engines will be defined.

Is my facility considered a major or an area source for hazardous air pollutants?

A major source of HAP is defined as a plant site emitting or having the potential to emit any single HAP at a rate of ten (10) tons or more per year or any combination of HAPs at a rate of 25 tons or more per year. An area source of HAP emissions is any source that is not a major source of HAP emissions.

Is my engine new or existing?

Regarding engines at area sources and engines ≤ 500 HP located at major sources, these engines are defined as “existing” if construction commenced before June 12, 2006, but are defined as “new” if construction commenced on or after June 12, 2006.

Engines located at major sources that are > 500 HP, are defined as “existing” if construction commenced before December 19, 2002, and are defined as “new” if construction commenced on or after that date.

What are the RICE rule requirements for my engine(s)?

What are the New Source Performance Standards for engines?

Engines manufactured after June 12, 2006 are required to comply with New Source Performance Standard (NSPS) 40 CFR Part 60 Subpart IIII or NSPS 40 CFR 60 Subpart JJJJ. These engines are defined as new engines and are exempt from RICE requirements.

CTAP is available to assist Indiana’s businesses engaged in stationary engines.  Contact CTAP using the CTAP Partner Portal to request help.  It will require setting up a free account through Access Indiana.

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