"In my state (AZ), FD's are NFP's and not governmental units."

I would be surprised that this is a Private Charity. All you have to do is google:

arizona fire district accounting

to find answers, such as:

http://www.azfiredistricts.org/wp-content/uploads/2014/03/AFDA-Financial-Procedures-3.pdf

and:

"48-805 - Fire district; powers and duties; definition"

https://www.azleg.gov/ars/48/00805.htm

You seem to be a Special Purpose District.

In any case, your best reference is the Tax form your entity files, such as 990. If you report to a higher authority, such as County or State, you follow their requirements. There is no Generic listing; there is your Requirements.