There is no 14 CFR 91 or 14 CFR 135 requirement for any fire coverage at all at the airports these operators use, but some companies have instituted such requirements. Even if you don’t have such a requirement, knowing your aircraft’s Airport Rescue and Fire Fighting (ARFF) code may help you decide between two airports of otherwise equal attractiveness. A G450, for example has a US code of A and an ICAO code of 5. A G550 raises these to a US code of B and an ICAO code of 6.
What follows comes from the references shown below.
[ICAO Annex 14, Table 9-1]
Portions of this page can be found in the book International Flight Operations, Part VIII, Chapter 2.
14 CFR 139, Title 14: Aeronautics and Space, Certification of Airports
ICAO Annex 14 - Aerodromes - Vol I - Aerodrome Construction and Design, International Standards and Recommended Practices, Annex 14 to the Convention on International Civil Aviation, Vol I, July 2009