Stationary Internal Combustion Engines 

Many businesses and industries use stationary reciprocating internal combustion engines (RICE) to run or augment their processes. Engines may be either compression or spark ignition, and emit various key pollutants regulated under the National Emission Standards for Hazardous Air Pollutants (NESHAP) 40 CFR 63 Subpart ZZZZ, often called the 4Z rule. Other engine air quality rules include two New Source Performance Standards (NSPS). The 4I NSPS applies to compression ignition engines and the 4J NSPS applies to spark ignition engines. Compression ignition engines are typically diesel-fired while spark ignition engines are gasoline- or natural gas-fired.  Resources below provide links and information to determine rule applicability and compliance.  

On 8/4/22, EPA finalized amendments to the RICE NESHAP and NSPS in response to a 2015 court decision. Emergency engines are not allowed to operate for emergency demand response or during periods where there is a deviation of voltage or frequency. Since 2016, engines used for emergency demand response must be in compliance with the emissions standards and other applicable requires for non-emergency engines. EPA resources 

Regulatory navigation tool for the 4J and 4I rules 

State-specific resources  

Vendor and other resources  

  • Combustion portal provides basic engine compliance and pollution prevention information. This resource is supported by the National Compliance Assistance Centers.  


  • NESHAP: National Emission Standards for Hazardous Air Pollutants 
  • NSPS: New Source Performance Standards 
  • RICE: reciprocating internal combustion engine