hi,
Martina, as I already said: it depends on schematic you have there. We do not know how does your "fire sensor" is connected? Does it produce [not]debounced high/low level at active state? Is it just a switch for test purposes or is it complex unit?
At least you may comment switch control instructions just to see if rest of code works. Remember my "fix post about 0x1A which must has slash (\x1A).

Good luck,
Oleg