approx 520 airports in usa have arff

https://www.faa.gov/airports/airport_safety/part139_cert

pretty sure this is correct based on - "Currently, the FAA
certificates approximately 520 US airports. The FAA maintains a list
of US airports certificated under Part 139, which is updated monthly
(see Part 139 Airport Certification Status List below)."

usually every certificated airport has to have at least 1 arff vehicle
- there might be some exceptions in Alaska