Look at your post #20, very last word. See the blue box with “Quote” in it right below your last word? Just click on that whenever you want to quote someone else’s post. Delete text as desired.
UPC 510.1 Water heaters generating a glow, spark or flame capable of igniting flammable vapors may be installed in a garage, provided the pilots, burners or heating elements and switches are at least eighteen 18 inches above the floor level.
That sounds pretty definitive to me. 
True, however most manufacturers throw it right back into the lap of the local AHJ. This is from AO Smith’s electric water heater manual:
“The installation must conform to these instructions and the local code authority having juridiction and the requirements of the power company.”
Thanks RR.
G2408.2
Exception: Elevation of the ignition source is not required for appliances labeled flammable vapor resistant and for installation without elevation.
It’s all been discussed before. And seems to have been unresolved.
Electric water heaters are powered by electricity which can have a spark occurrance or possible short that could possibly ignite gas vapors - Just a thought
If a water heater in the garage on a platform that is attached to a firewall, does that platform also need to be fire rated ? Is there a code for a fire rated platform?
No. Unless the platform itself is part of the fire separation.