### Question
How does the law define primary fuel?


### Answer
Under *42 U.S.C. § 7511a*, **primary fuel** is defined as:

> the fuel which is used 90 percent or more of the operating time

#### Citation:
  - *42 U.S.C. § 7511a*
  - Heading: **CHAPTER 85-AIR POLLUTION PREVENTION AND CONTROL > SUBCHAPTER I-PROGRAMS AND ACTIVITIES > Part D-Plan Requirements for Nonattainment Areas > subpart 2-additional provisions for ozone nonattainment areas**

