The UL Classification on our fire safes is Classification 350 which means that during testing the interior of the safe will maintain a temperature of 350 degrees Fahrenheit or less. At this temperature the interior of the safe is cool enough so that paper does not char or burn. The 1-Hour Fire Safes will maintain this temperature in a fire with heat up to 1700°F for one hour, whereas the 2-Hour Fire Safes will maintain that temperature for 2 hours.