http://www.mediafire.com/file/qxnygywnmqy/Simius_Fires.packagezaroba at MTS made an xml mod that makes fires rapidly burn down your entire house. I altered it slightly so that instead of your house burning down immediately the fire would spread fairly quickly but a few sims should be able to contain it. This makes fighting fires a bit more fun and a bit more dangerous for your sims.
This doesn't seem to affect fires that your firefighter sim responds to while on the job.
The changes from the default fire are:
Smolder Time - 10 to 5
Spread Frequency - 13 to 8
Floor Spread Chance - 150 to 500
Object Spread Chance - 250 to 1000
Chance Fire Goes Out - 15 to 5
Max Fires Per Lot - 10 to 50
Anyway, enjoy.
Credit to zaroba:
http://www.modthesims.info/download.php?t=395290