Fire, flood, earthquake, burglars and computer viruses all pose a critical threat to computer data files, the lifeblood of today's small businesses.

Yet most store vital electronic records on office PCs, with tape or floppy disk backups within a few feet. All are exposed both to natural and man-made disasters.Enter Duke DeForest, whose Data Vault Inc. offers "the first on-line, automatic, off-site and redundant data backup and retrieval service" for IBM-compatible PCs and PC-based LANs, or local area networks.

"Most major corporations equipped with mainframe computers have become very disciplined in off-site data backup," Data Vault's chairman said. "The same cannot be said for the thousands of small businesses using personal computers."

DeForest said such companies go to the trouble of insuring their office equipment, but the data created on their PCs remain at risk to theft, fire or natural disasters like flooding and earthquakes.

Computer industry analysts generally like the idea of remote, off-site data backup but question whether Data Vault will find small- to middle-size businesses willing to pay for it.

"It has a place in the industry," said Perry Harris, of the Boston-based Yankee Group computer consulting firm. "(But) I almost think their market might be better in a more traditional mainframe environment.

"They may find as they attempt to develop the market in small businesses that the market may not be as receptive," he added.

Data Vault has signed 50 customers since opening in Midvale two months ago and is conducting trials at other sites. DeForest wouldn't identify his clients but said they range from banks to law, accounting and consulting firms.

Data Vault, a five-state distributor for Los Angeles-based Secure Data Network Inc., aims to eventually have 1,500 customers in Utah, Idaho, Arizona, Nevada and New Mexico. In coming months, DeForest plans to open Phoenix, Tucson, Albuquerque, Las Vegas and Boise branches, and possibly another Utah office in Provo or Ogden.

DeForest said Data Vault's software, installed on-site, automatically creates backups at customer-specified times, and after scanning for viruses stores them on the client's PC hard disk drive.

The program, using the client's modem, then dials up Data Vault's local substation and transmits the backup file, compressed for speed of transmission and password-encrypted for customer security.

The data also is sent to the network's "master center" in Los Angeles and to another site. Currently, a converted Nike missile silo in the Boston area is used, although DeForest is negotiating for space in a privately owned facility in the Wasatch Mountain caves east of Salt Lake City.

The site is about a mile further up Little Cottonwood Canyon from the LDS Church's genealogical records storage vaults.