Fireproof gun safe: What is UL 72?

Fire rating is critical when it comes to how well your gun safe can withstand in during a home fire. However, different gun safe manufacturers have their ratings. Some fire ratings are merely just a made up number or based solely on the fire rating of the fire board that makes up the gun safe. Some other manufacturers put effort into testing their product, but they don’t do it properly on purpose so their gun safes are given higher fire ratings than they should.

UL 72 or Underwriters Laboratories 72 is the test of the real fire safety rating. It’s used to test fire resistance of record protection equipment, one of them being gun safes.

UL 72 classifications

UL fire testing – If the gun safe undergoes UL fire testing, it’s tested by the independent UL (Underwriters Laboratory). A UL listed gun safe is the gun safe that has passed a UL test. You need to keep in mind that when a gun safe is labeled “Tested to UL standards,” it doesn’t mean the gun safe has already passed the UL test, it only means the gun safe has been submitted for UL testing.

UL 72 classifications

Image source:

UL 72 classes

UL 72 Class 350: This testing is necessary if you store documents in your gun safe. The gun safe is subjected at 1,550o in 30 minutes. The gun safe’s interior remains below  177oC.

UL 72 class 150: In which the gun safe’s interior remains below 65oC, and the humidity remains below 85%.

UL 72 Class 125: This testing is necessary if you store media files such as computer disks, photos, and flexible computer disks. The gun safe’s interior remains below 55oC, and the interior humidity remains below 80%.

UL 72 duration

  • 30 minute
  • 1 hour
  • 2 hour
  • 3 hour
  • 4 hour

The duration is not how long the test has taken place. In some cases, UL 72 testing may take as long as 80 hours.

UL 72 ratings

  • Fire endurance test
  • Fire and impact test: Besides being tested with fire, the gun safe is also tested by being dropped from 30 feet which are equal to being dropped from a third story floor into a basement. Keep in mind that in the case of fire, impact resistance is very important for gun safes. Not only there are falling beams, but the gun safe itself can also fall through the floors.
  • Explosion hazard Test: This testing is to make sure the gun safe won’t explode from the build-up of interior pressure due to rapid heating.
  • Explosion and impact combined test.

How is a UL 72 test procedure done?

Fire endurance test procedure

  • The gun safe is loaded with computer media and loosely distributed paper.
  • Include thermocouples in all four side walls, at the top and the bottom of the gun safe.

For UL 72 class 150 and 125 tests, the gun safe also includes 2 electronic humidity sensors. They located each humidity sensor 18 inches away from each other, mid-way between all four side walls. They also condition the gun safes in an office climate at least 12 hours before the test to ensure relative interior humidity below 60% and the interior temperature is between 65o to 75o.

  • Place the gun safe in the oven.
  • Increase the temperature of the oven carefully and a monitored rate to make certain all six sides of the gun safe are heated evenly.
  • Shut off the oven before it reaches the final temperature of the UL test.
  • Continue the test by leaving the gun safe in the oven up to 68 hours without cooling it down until the temperature inside the gun safe falls significantly.

Gun safes that in UL list are those that have internal temperatures, and humidity (UL 72 class 125 and 150) remain below the limits of the test.

Open the gun safe and examine the contents inside to see if they’re in good condition. And if there is any damage caused by humidity and heat on the walls and interior components of the gun safe.

They should retest the sample safe one year later to keep its UL label.

In reality, many gun safes can’t pass the UL 72 procedure when they enter step 7 because, in this step, the gun safes will still absorb heat from the unopened oven which simulates the gun safe still absorbing heat from smoldering remnants of the fire.

Fire endurance test procedure

Image source: Gun Safe Reviews Guy

Fire and impact test procedure

This procedure is conducted after the gun safe has passed the fire endurance test if the manufacturer requests.

  • Preparation is the same as the fire endurance test
  • Throw the safe into the oven and increase the temperature of the oven at a monitored rate.
  • Remove the safe within 2 minutes. Drop it from 30 feet height point to on a pile of broken brick on a concrete base simulating the structure.
  • Examine the gun safe to see if there is an opening of the walls inside. And if there is any cracking of fire insulation.
  • Put the safe gun back into the oven in an upside down position simulating the various orientations of landing.
  • Reheat the oven to a specified temperature.
  • Cool down the gun safe to inspect the overall internal condition, the condition of the contents, lock part, and fire insulation.
  • Retest the gun safe after a year to keep the UL label.
Fire and impact test procedure

Image source: Metro Alarm

Explosion test procedure

  • The gun safe has to pass the explosion test to take the fire endurance test.
  • Preparation is the same as in the fire endurance test, only that the gun safe is in outside of the oven instead of in an office.
  • Preheat the oven to 2,000 degree Celsius.
  • Quickly put the gun safe inside the oven.
  • Remain heating the oven for 30 minutes and allow it to cool down. The gun safe has not to explode.
  • Open and inspect the gun safe.

The safe gun manufacturer can choose to combine the impact test and the explosion test. The Underwriters Laboratory will heat the gun safe for the explosion test, drop it for the impact test, reheat and then cool it.


Above are some basic understandings of the most reliable UL 72 testing procedures conducted by UL. Hopefully, you can find our article helpful. Good luck in choosing the best gun safe to keep your firearms and other valuables in great condition in any situation.