The following is an explanation of the
Underwriter’s Laboratories’ fire resistant container testing
procedures on the Class 350°F, one hour and Class 350°F two hour Fire
Labels.
U.L. Label/Class 350°F-one hour and Class 350°F-two hour. The safe
will maintain an interior temperature less than 350°F when exposed to
fire for a period of one hour at 1700°F or for a period of two hours at
1850°F. Safe must successfully undergo all other requirements for the
Fire Endurance Test, Explosion Hazard Test and the Fire/Impact Test as
stated below.
Fire Endurance Test
After heat sensors and paper are placed inside the safe, the unit is
locked and exposed to a uniformly distributed fire. The furnace is
regulated to reach a maximum temperature of 1700°F for a period of one
hour, or 1850°F for two hours, then allowed to cool without opening the
furnace. The interior temperature is recorded throughout the test and
during the cooling period until a definite drop is shown and must never
exceed 350°F.
Once cooled, the unit is opened and examined for usability. The units
locking mechanisms and parts fastenings are examined for security and the
interior examined for visible evidence of undue heat transmission