In this part of the test, the unit is left in the oven with the heat turned off and allowed to cool. The next part of the UL test comes in the form of a mandatory explosion hazard test . In this procedure, the unit is inserted into a preheated 2000 degree oven. If not constructed properly, the rapid heating of the insulation would likely cause an explosion. All UL fire-rated safes must pass this intensive test.
Further testing is done with the drop test .
In this test, the unit is subjected to a 1550 oven for 30 minutes and then hoisted 30 feet in the air and dropped on a pile of rubble. As if that's not enough, the unit is then inverted and resubmitted to the oven for another half hour at 1550 to assure that no structural damage allowing heat penetration occurred in the drop. Just as important as the fire and burglary testing is the UL follow-up service . Taking many forms, this service allows a UL inspector to drop in unannounced and at any time to see that all units are being built under the same construction methods used on previously tested units. In addition, UL required that manufacturers keep accurate logs of all products produced and even requires that a sample of insulation is kept on hand for spot testing by the UL inspector.