Data centers are designed to remain online when normal utility power fails. Batteries can bridge short interruptions, while on-site engines provide longer-duration backup power.
The reliability role
Backup generators support critical computing loads during grid failures and other qualifying emergencies. A large campus may have many generator sets because equipment is distributed across buildings and electrical systems.
EPA identifies stationary compression-ignition engines, spark-ignition engines and combustion turbines among the power sources relevant to data-center air regulation.
When emergency generators run
Emergency and non-emergency operation are not the same regulatory category. Virginia DEQ says emergency units may operate for qualifying disruptions and limited maintenance or testing. Peak shaving or routine generation for extra capacity can be treated differently.
Virginia’s current guidance assumes up to 500 hours per year when calculating the uncontrolled emissions rate of an emergency generator, including testing and maintenance. That assumption is not a claim that each generator actually runs 500 hours.
Which air pollutants are reviewed
Diesel-engine permits can address nitrogen oxides, carbon monoxide, particulate matter, sulfur dioxide and volatile organic compounds. The precise list and limits depend on the engines, fuel, controls, location and governing rules.
Virginia has also updated its data-center generator guidance around Tier 4-equivalent controls for certain new applications received from July 1, 2026. The agency describes controls for nitrogen oxides, carbon monoxide and particulate matter.
Permitted emissions are not measured emissions
A permit often starts with conservative operating assumptions used to calculate potential or maximum permitted emissions. Actual emissions depend on real engine hours and operating conditions. Compliance reports and monitoring provide different evidence than the permit itself.
Common questions
Why do data centers have diesel generators?
They provide backup electricity when the primary power source is interrupted and are also operated for required maintenance and readiness testing.
Do data-center backup generators run all the time?
Normally no. Operating conditions depend on the permit and applicable rules. Virginia distinguishes emergency generation from non-emergency uses such as peak shaving.
What pollutants can diesel generators emit?
Regulatory reviews commonly address nitrogen oxides, carbon monoxide, particulate matter, sulfur dioxide and volatile organic compounds, depending on the source and permit.
Are permitted emissions the same as actual emissions?
No. Permit calculations may use maximum operating assumptions. Actual emissions depend on real operating hours, load, fuel and controls.
Open source-linked Virginia facility records and follow each one to the agency document.
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