Guide to UL Classes and Ratings for Fireproof Safes

The leading testing agency for fireproof safes in the United States is Underwriter Laboratories (UL). Under the UL system fireproof safes are given one of three ‘Class’ classifications in combination with five time ratings. The Class classification for fireproof safes is dependent on the internal temperature and internal humidity the fireproof safes can maintain at a pre-determined external furnace temperature. The UL Class classification temperatures for fireproof safes have been determined by the type of product to be protected. Effectively there are three categories of products to be protected by fireproof safes and these give rise to the Class classification.

·         Class 350 - Paper based products including cash that begin to burn at 420 degrees

·         Class 150 - Computer data tapes, magnetic reel-to-reel - tapes

·         Class 125 - Computer diskettes

Class 350 fireproof safes must maintain an internal temperature of 125 degrees F and humidity not exceeding 85%

Class 150 fireproof safes must maintain an internal temperature of 150 degrees F and humidity not exceeding 85%

Class 125 fireproof safes must maintain an internal temperature of 125 degrees F and humidity not exceeding 80%

For each of the above Class classifications the minimum time rating is half an hour. To pass the test, fireproof safes must maintain the internal temperature and humidity required for the Class for half an hour at a furnace temperature of 1700 degree F.

Requirements for other time ratings are one hour at a furnace temperature of 1850 degrees F, two hours at a furnace temperature of 1850 degrees F, three hour at a furnace temperature of 1920 degrees F or four hour at a furnace temperature of 2000 degrees F.

Therefore, Class 350 UL 1 hour rated fireproof safes would maintain an internal temperature of 350 degrees at 85% humidity for one hour in a fire burning at 1850 degrees.

If you were looking for fireproof safes to store data tapes you would be best served purchasing a Class 125 data safe with a UL rating of .5 to 4 hours. For cash and documents you would be looking for Class 350 fireproof safes for home or business.