So im making heaven in minecraft by changing nether textures.
And it would be stupid that fire generates in nether (now heaven)....
You could remove fire inertly by placing a command block at spawn that is REPEATING, UNCONDITIONAL, and ALWAYS ACTIVE witch has the command
/execute @e ~ ~ ~ fill ~10 ~10 ~10 ~-10 ~-10 ~-10 minecraft:air 0 replace minecraft:fire
You could use the gamerule
/gamerule doFireTick false to stop fire from starting, but this will stop fire from putting itself out. If you have world edit I'd select as much area as possible and do
//replace fire air. But as other people have pointed out, if you are making a texture pack you can't disable fire from there. (Other than making it a completely invisible texture and making it's sound file completely mute. However, if players walk into the block with fire they will take fire damage.)