Of course, like all backup plans, once decided upon, it must be tested regularly and fully. Again it comes down to how long you can manage without the system. As Team's Sheridan put it, 'If you can go a week, you're okay. If it's 36 hours, you've got a problem. The steps you can take to guard against disaster go beyond fire protection and the like.
General security is obviously important, as is strict access control to the computer room.
But neither protects against crashing aircraft, for example. Off-site storage of backups has already been mentioned, along with regular and realistic tests of your ability to restore them. Keeping multiple copies of backups in several locations is advisable. Don't forget that if you have a network, it is likely to be the critical part of your DP operation. A variety of companies can recover data from removable-cartridge systems, tape drives, erasable optical drives, and floppy disks.