Safe fire ratings explained: class, temperature, time and who ran the test

"Fire rated" appears on almost every safe sold, from small document chests to 900-pound gun safes. The phrase on its own tells you almost nothing. A real fire rating is four facts: what it protects, for how long, against how much heat, and who measured it. Most labels publish two or three of those. The one most often missing is the one that matters most: the tester.

This guide shows you how to read each part, using real labels from our product registry. We haven't put any safe in a furnace ourselves. The standard details come from UL's published scope for UL 72, and the product examples come from each maker's own page, linked in the table below.

The four parts of a fire rating

1. Class: the interior limit. The most heat the inside of the safe may reach during the test. For paper that is 350°F. Media classes are lower.
2. Time. How long the interior stayed under that limit in the test: 30 minutes, one hour, two hours.
3. Temperature: the furnace, not the contents. The heat outside the safe during the test, such as 1,700°F. This is the number marketing puts in the biggest type, and it is the one most often misread.
4. Tester. UL, Intertek (the ETL mark), or the maker itself. This decides how much weight the other three deserve.

A complete label reads something like "UL Class 350, 1 hour." SentrySafe's SFW123GDC page puts it another way: "UL Classified to protect your valuables in a fire for 1 hour in up to 1700°F." Tester, time and furnace temperature are all there.

The rare label that spells out all four parts is worth studying. Honeywell's manual for its 1103 chest says "Independent testing by Underwriters Laboratories (UL)" verifies the interior stays below 350°F for 30 minutes at up to 1,550°F. Read it back against the list: the interior limit is 350°F (the paper class), the time is 30 minutes, the furnace reached 1,550°F, and the tester was UL. Nothing is left to guess. Most labels you meet will be missing at least one of those four, and the missing one is usually the tester.

UL 72 classes: 350, 150 and 125

The US standard for fire-resistant record storage is UL 72, Tests for Fire Resistance of Record Protection Equipment. It sorts equipment into classes by what it is meant to protect. The class number is the highest interior temperature, in °F, the equipment may reach under test.

The practical reading: a Class 350 safe is built around paper. Photographs, film, tapes, drives and disks need a lower interior limit, which is why the two lower classes also cap relative humidity. If a safe's label doesn't name a class at all, look for the interior temperature in the fine print. Stealth, for example, says the UL28 keeps its interior under 350°F during its fire test, which is the paper threshold.

Time and furnace temperature

The time rating is how long the interior stayed under the class limit in the furnace test. A one-hour Class 350 rating means the inside stayed under 350°F for an hour of furnace exposure.

The furnace temperature is where most comparisons go wrong. It is the heat outside the safe, and it varies with the test. Safe dealers such as Safe and Vault Store explain that UL tests reach 1,700 to 1,850°F, while ETL tests heat safes to 1,200°F and "may vary slightly in ramp-up speed or cooldown." You can see the UL pattern in our registry: SentrySafe's UL-classified 30-minute chests are rated at 1,550°F, its one-hour models at 1,700°F, and Master Lock's two-hour STW123GTCML at 1,850°F. The longer the test runs, the hotter the furnace gets.

That has one important consequence: you can't compare minutes across different temperatures. "60 minutes at 1,200°F" and "1 hour at 1,700°F" are not the same exposure, even before you ask who ran each test. When a label gives no temperature at all, it can't be compared with anything. Cannon's Fortified 73 is an example: Cannon calls its 60-minute rating "certified" but states no test temperature and names no lab.

Gun safes show why this matters. Across the full-size gun safes in our registry, the stated furnace temperatures run from 1,200°F (Stealth, Liberty) through 1,400°F (Kodiak, Winchester, Hollon, Sports Afield) to 1,875°F (Steelwater). Every one of those figures is the maker's own. The only gun-safe fire ratings an outside lab verified, AMSEC's ETL ratings, are all stated at 1,200°F. In other words, the most impressive temperatures on gun-safe spec sheets are the ones nobody else checked. A bigger number on a maker's claim is not stronger evidence than a smaller number a lab measured.

The explosion and impact tests

UL 72 is more than a furnace run. UL's published scope lists three kinds of test:

• Fire endurance, which shows the equipment can keep interior temperature (and, for the media classes, humidity) under the limit.
• Explosion, which shows it can withstand a sudden exposure to high heat without an explosion from steam or gases building up inside.
• Fire and impact, for equipment rated for impact, which shows it protects its contents "before and after an impact due to falling 30 ft (9.1 m)." That is the scenario of a safe dropping through a burning floor.

UL adds a caveat worth knowing: the tests show performance "during exposure to fire, but are not intended to determine acceptability for use after fire exposure." A safe that has been through a fire has done its job. The standard doesn't vouch for it a second time. Our guide to whether any safe is truly "fireproof" covers what that means in a real house fire.

Who ran the test: UL, Intertek (ETL) or the maker

This is the part of the label we weigh most heavily, and the part that most often goes unstated.

• UL classified. UL, or a lab UL recognizes, ran the UL 72 test on that model. You can look up UL certifications in UL's Product iQ database.
• ETL verified (Intertek). An independent lab verified the maker's claim. Intertek says many manufacturers use independent testing "to prove that products meet criteria set by industry associations or independent certification program administrators, like the ETL Verified programs administered by Intertek," and it publishes directories of products that carry its marks. AMSEC's ETL-verified gun safes are the clearest examples on our site.
• Manufacturer claim. The maker ran its own test, or doesn't say who did. Safe and Vault Store notes that factory tests "may follow similar temperatures and durations, but are not verified by a third party." Most gun-safe fire ratings fall here.

Watch the verbs. "Certified" and "verified" mean little without a lab's name. Liberty calls the Franklin's 110-minute rating "certified" and names no lab. AMSEC calls the RF6528's fire rating "independently certified" and doesn't say by whom. Winchester's "UL rated" wording on the Ranger 26 refers to the fireboard inside, not a UL fire classification of the safe. We count a rating as independent only when a named lab stands behind it.

Read the rows in order and you have the whole range of evidence:

• SentrySafe SFW123GDC: UL names the tester, with a time and a furnace temperature. The strongest form of the claim.
• AMSEC NF6036: an independent lab (ETL) at 1,200°F. Independent, but a milder furnace than the UL record-safe tests, so compare it only with other 1,200°F ratings.
• Stealth UL28: time, temperature and an interior limit, all from the maker. Useful, but nobody else checked it.
• Cannon Fortified 73: a time with no temperature and no lab. It can't be compared with anything.
• Honeywell 2605: a two-hour claim where the product page says up to 1,850°F and the manual says up to 1,550°F, with no lab named. When a maker's own documents disagree, treat the lower figure as the claim.

Water ratings and digital media are separate claims

A fire rating says nothing about water, and firefighting uses a lot of it. Water resistance is its own test and its own line on the label. SentrySafe's SFW line, for example, carries an ETL-verified rating for up to 8 in of water for up to 24 hours. Read the manual, too: SentrySafe's manual for that line says the water claim applies only before the bolt-down kit is installed, while Master Lock says its STW123GTCML keeps fire and water protection when bolted down.

Media is similar. A Class 350 rating is about paper. Some makers publish a separate media claim instead of a UL Class 125 rating: SentrySafe's manual for the FPW082HTC lists ETL-verified one-hour protection for CDs, DVDs and USB drives. If you're storing drives, look for a media claim someone other than the maker verified.

Warranty language is a third thing that gets mixed in with ratings. Many fire safes come with an after-fire replacement program: SentrySafe and Honeywell both publish one for the models in our registry. That is a promise to replace the safe after a fire, not evidence about how well it protected what was inside. Weigh it as support, not as a rating.

How much fire rating do you need?

No standard sets a minimum for a home. These are the questions that decide it:

1. What are you storing? Paper needs Class 350. Photos, film and drives need a lower interior limit or a verified media claim.
2. Who measured it? We give more weight to who tested a rating than to how many minutes it claims. A UL-classified hour is better evidence than a maker's two hours.
3. Is the temperature stated? Compare only ratings at the same furnace temperature.
4. Does it need a burglary rating too? Fire and burglary are separate listings. UL's own RSC notice says security containers "are different from fire resistant containers." A document safe with a UL fire rating usually has no burglary rating, and most RSC gun safes carry only a maker's fire claim.

Picks with independently verified fire ratings

These three carry fire ratings a named lab stands behind: a UL-classified fire safe, a UL-classified chest for a small document kit, and an ETL-verified gun safe. For a full ranked list limited to verified ratings, see the best UL fire-rated safes. For larger home fire safes, see our fire safe rankings.

Shopping for a gun safe with fire in mind? Our fire-rated gun safe rankings apply the same rule: who measured the rating comes first.