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Does gas water heater need to be installed on 18" stand?

" FVIR certified gas water heaters can be installed on a residential garage floor without use of 18-inch stand in accordance with the National Fuel Gas Code, NFPA 54, ANSI Z223.1, unless otherwise directed by State and Local code requirements."

I don't know. In 2019, I cannot find a listing on each manufacturer's website that shows or mentions certification for any of the different models.
Nor have I seen a spec sheet that shows certification.
True, most 30-40,000 BTU residential heaters have a FVIR system as specified on applicable spec sheets and manuals ... and some have the FV sensor located on bottom front of heater ... but that is no guarantee heater is certified in my mind.
And note that the FVIR mandate does not apply to heaters with larger burners (75,000 BTU etc), used in homes with higher consumption. The mention of FVIR protection does NOT show in spec sheets and manuals for these heaters in 2019
So you would need to call manufacturer of your heater and give them the serial number (available on label located on side of tank) ... PLUS consult local plumber or local plumbing inspector to find relevant codes that apply to your installation.

Because flammable vapors can still be sucked into heater where ignition can cause internal damage depending on how much vapor and how the FVIR reacts. Damage can include part replacement or full replacement of heater. Warranty does not cover damage from an FV event.
Moreover, there is no guarantee that a conflagration (fire or explosion) inside the combustion chamber won't accelerate back out into the room, causing personal and property damage that will raise insurance premiums.

Why? because gasoline is the most common cause of water heater related fires .... and gasoline vapors are heavy and will hug the floor.

Buy:
Water heater stand
Water heater drip pans
Resource
18" regulation .pdf