No safe is fireproof, and the people who test them say so. A good fire safe buys time: it keeps the inside cooler than the point at which paper is damaged, for a rated number of minutes. Here’s what that means in a real house fire, and what tends to come out intact.
177°C
(350°F) the inside limit for paper in a UL Class 350 fire safe
52°C
(125°F) the limit for digital media in a Class 125 data safe
Under 5 min
for a room of modern furniture to reach flashover in UL’s tests
30–60 min
the fire rating of most consumer safes, according to UL
Key takeaways
- “Fireproof” has no official definition. UL, which tests most American fire safes, says they should be called fire resistant, and the standards body ASTM calls “fireproof” a misleading term.
- A rated fire safe keeps its inside below a set temperature for a set time in a test furnace: 177°C (350°F) for paper, far less for photographs, film and digital media.
- House fires get very hot very quickly, and a safe in the ruins can stay hot for hours. A 30-minute rating is not a promise for a house that burns to the ground.
- Many cheap boxes and security safes have no fire rating at all, and one of the best-known makers of fire bags says no document bag will survive a significant structure fire.
- After a fire, leave the safe shut until it has cooled, call your insurer, and let a professional open it.
In This Article
The short answer
No. Neither the US Fire Administration nor the National Institute of Standards and Technology defines or regulates the word “fireproof”, and when NBC Bay Area asked seven American safe distributors what it meant, it got five different answers. Underwriters Laboratories (UL), the lab behind the best-known American fire rating, told the station that safes passing its test should be labelled “fire resistant”, and ASTM calls “fireproof” an “inappropriate and misleading term”.1
That doesn’t mean fire safes are useless. A properly rated one does exactly what its label says, for as long as its label says. The trouble starts when a real fire is hotter, longer or messier than the test, or when the box was never rated in the first place.
| Is any safe fireproof? | No. “Fire resistant” for a rated time is the honest description1 |
| What a rating means | The inside stays below a set temperature for a set time in a test furnace2 |
| Limit for paper | 177°C (350°F), UL Class 3502 |
| Limit for film | 66°C (150°F), UL Class 1502 |
| Limit for digital media | 52°C (125°F), UL Class 1252 |
| Typical consumer rating | 30 to 60 minutes, according to UL1 |
| Not covered by a fire rating | Water from firefighting, being buried in hot debris for hours, reuse after a fire |
| After a fire | Do not open it until it has cooled; call your insurer and a professional3 |
This page is built from published standards, statements by test labs, makers and insurers, and news reports. We haven’t tested any safe ourselves; how we research modern safes explains what we check and what we don’t.
What “fire resistant” actually means
A fire rating is a promise about the inside of the box, not the outside. In the American standard, UL 72 (its current edition was published in January 2026), a safe is put in a furnace and the temperature of the compartment is measured. To earn a Class 350 one-hour rating, the inside must stay below 350°F (177°C) for an hour.42 UL told NBC Bay Area its furnace heats up to 2,000°F, about 1,090°C.1
The number after the class is the time, and that’s the part people tend to skip. A safe rated for 30 minutes was tested for 30 minutes. Nothing in the rating says what happens at minute 31.
Ratings come in two kinds: independent ones, where a lab such as UL tests and lists the product, and claims a maker or seller makes from its own testing. Europe has its own standards too. We cover the classes, the test methods and how to read a label in safe fire ratings explained, so this page sticks to what those numbers mean when your house is on fire.
How hot a house fire gets, and for how long
Faster and hotter than most people picture. The US Fire Administration warns that room temperatures in a fire can be around 100°F (38°C) at floor level and 600°F (316°C) at eye level, and that within five minutes a room can get so hot that everything in it ignites at once. That moment is called flashover.5
UL’s Fire Safety Research Institute defines flashover as the point where fire gases above about 600°C (1,100°F) make every fuel surface in the room catch at almost the same time. In its side-by-side burns, a room furnished with modern synthetic furniture reached flashover in between 3 minutes 20 seconds and 4 minutes 50 seconds. An identical room with older, natural materials took 29 and a half minutes in one run and more than 30 in the other three.6
Duration is harder to pin down, because it depends on how quickly the fire service arrives and whether it can save the building. What we do know is that heat doesn’t stop when the flames do. North Carolina’s Department of Insurance warns that a safe involved in a fire “may hold the intense heat for several hours”.3 A safe at the bottom of a collapsed, smouldering house is being cooked long after the test furnace would have been switched off.
Did you know?
George Hayter Chubb, of the Chubb lock and safe firm, wrote in 1875 that no safe kept inside a strong-room had “to my knowledge, ever been destroyed”, but that many light ones in warehouses and offices had had their contents burnt.7 Where the safe stands still matters as much as what it is.
What survives inside, and what doesn’t
Paper is the easy part. The 177°C (350°F) limit in Class 350 was chosen for documents: according to the usual summary of the standard, above it paper is distorted by the heat and what’s written on it can be lost.2 A safe that holds that line protects deeds, certificates and banknotes.
Everything else needs much cooler conditions. Film and photographic media are damaged above 66°C (150°F), and data on hard drives and other magnetic media is lost above 52°C (125°F), which is why UL has separate classes for them.24 A hard drive or a box of old tapes in a paper-rated safe can come out looking fine and still be unreadable. Chubb noticed the same problem with parchment in 1875: a “moderate heat or exposure to steam” could ruin it, and he thought gunpowder easier to protect from fire than parchment.7
| What you store | Damaged above | Rating to look for |
|---|---|---|
| Paper documents, banknotes, certificates | 177°C (350°F) | UL Class 3502 |
| Photographic film, negatives, microfilm, magnetic tape | 66°C (150°F) | UL Class 1502 |
| Hard drives and other digital media | 52°C (125°F) | UL Class 1252 |
| Anything that matters most | n/a | A copy kept somewhere else8 |
That last row comes from a fire captain. After safes failed in Oklahoma’s wildfires, Captain John Chenoweth of the Oklahoma City Fire Department advised making several copies of birth certificates, tax papers, deeds and mortgage documents.8 A scan in the cloud doesn’t care how hot the house got.
Steam and water: damage that isn’t burning
Fire safes keep cool partly by being damp. Chubb described the “evaporating system” used in most British safes of his day: a filling of sawdust and alum between two iron walls, with the alum giving up its water slowly as the fire heated it.7 Turning water into steam soaks up heat, and that’s what holds the inside down. The same steam, he warned, could ruin parchment on its own.7
Moisture is a nuisance even without a fire. SentrySafe says many of its safes are airtight because of their water protection, so moisture from the air gets trapped when the door is shut; it tells owners to open the safe at least once a month and keep a desiccant pack inside.9 Chubb’s old advice still helps too: papers kept in an inner drawer or cupboard of a safe get “a slight extra security”.7
Then there’s the water used to put the fire out. A fire rating says nothing about hoses, and neither does a water-resistance claim unless the maker states the test. SentrySafe’s own fire bag, for example, is “not waterproof” and resists water to the level of a sprinkler system.10 If you want both, look for a separately stated water rating, and expect damp papers anyway.
Why cheap boxes fail
Steel doesn’t burn, but it passes heat straight through. Chubb put it neatly in 1875: “though iron is incombustible, it is itself not fireproof”.7 What protects the contents is the insulation between the walls, and Chubb’s recipe for a safe “proof against an ordinary fire” called for three to four inches of it all round.7 A thin steel cash box, a key cabinet or a lockable document box with no filling is, in a fire, just a small oven.
Three things usually go wrong with cheap or unrated boxes:
- No rating at all. Many safes are built against burglary, not fire. “Fireproof” printed on the box is not regulated, which is how seven distributors managed five definitions.1
- Too little insulation, too short a rating. A light safe heats through faster. Chubb’s warning about light safes losing their contents is 150 years old and still holds.7
- Tests nobody independent watched. Chubb told readers to “put little faith” in fire tests not run by “persons quite disinterested”, because safes could be specially made, carefully packed or the fire built to suit.7 Today the equivalent is a maker’s own claim with no lab listing behind it.
Older fire safes bring one more problem. Some 20th-century fire safes and cabinets were packed or sealed with asbestos, and Ireland’s Health and Safety Authority says any safe or fire cabinet made before 2000 should be checked.11 That matters most after a fire, when a damaged safe may need cutting open. Our guide on whether old safes contain asbestos explains what to look for.
Real fires, real safes
News reports of safes in fires tend to be the failures, because those are the stories people tell. Read them for what they show about conditions, not as a verdict on any brand.
- California, North Bay wildfires. Mike Cobb lost his house and two safes he’d assumed were fireproof: “Both of them just completely disintegrated.” Another victim, Sam Brinkerhoff, said of hers: “It melted.” She’d come to think the label meant “fireproof for a kitchen fire or something”. NBC Bay Area reported their stories in October 2018.1
- Norman, Oklahoma, March 2025. The Davenport family’s safe held birth certificates, passports and college degrees. After the wildfires it crumbled when they tried to lift it from the debris. The Oklahoma City fire captain quoted in the report said ratings on the box typically read 30 minutes or an hour, and that the fire had been “extreme conditions. Houses burned down, completely down.”8
- Missouri, late 2018. A safe in a garage fire hot enough to crack the concrete floor came out with everything inside untouched, according to the safe’s maker, Liberty Safe, which published the owners’ story.12 Makers’ success stories are chosen by the maker, but they show what a rated safe can do when the fire is put out.
- London, 1870s. When the Pantechnicon, a huge London storage warehouse, burned down, Chubb found that “scarcely one of the many safes survived the conflagration without injury”. Cast-iron safes were pulled out of the ruins twisted, or “cracked and broken like glass”.7
The pattern is fairly plain. Safes that survive tend to be rated ones in fires that were fought and put out. Safes that fail are often unrated, or sat in buildings that burned to the ground with nobody coming, which no 30- or 60-minute rating was ever designed for.
Fire-resistant document bags
Fire bags are cheap, light and popular. Most are made of glass-fibre fabric; SentrySafe’s, for example, has a silicone-coated fibreglass outside and an aluminised fibreglass lining.10 The question is what they’ve actually been tested to do.
What they pass
Brief flames
In Bob Vila’s propane-flame test the best bag kept paper undamaged; others shrivelled or split at the seams.13 SentrySafe says its bag is “tested to endure brief fire exposure”.10
What they don’t
A house fire
SentrySafe names no standard, temperature or time for its bag, and states that “no document bag will survive a significant structure fire”.10 We haven’t found a bag listed under UL 72.
How to use one
Inside a rated safe
The maker itself recommends using the bag inside a UL-classified fire safe. On its own it’s a grab bag for leaving in a hurry.10
Be wary of big numbers on the packet. A bag “designed to withstand temperatures up to 2,000 degrees Fahrenheit” tells you about the fabric, not about how hot the papers inside get or for how long.13 A furnace rating for a safe is a measurement of the inside; a temperature on a bag usually isn’t.
After a fire: the safe and what’s inside
- Don’t open it yet. North Carolina’s Department of Insurance warns that if the door is opened before the safe has cooled, “the entering air, combined with the high inside temperature, may cause the contents to burst into flames”.3 Only go back to the site when the fire service says it’s safe.
- Call your insurer before anything is moved. Photograph the safe where it stands and ask how they want the contents recovered.
- Let a professional open it. If the door won’t open normally, a qualified safe engineer or locksmith should deal with it; this isn’t a job for a grinder in the garden. An older safe that has to be cut or drilled may also contain asbestos.11
- Save damaged money. In the US, the Bureau of Engraving and Printing redeems burnt notes free of charge, and pays full value when clearly more than half of a note is present.14 The Bank of England generally refunds a damaged note if you still have at least half of it.15 Handle charred notes as little as possible and keep every fragment.
- Don’t trust the safe again without an inspection. Chubb’s advice in 1875 was that a safe that has been through one fire should not be relied on until “examined and re-proofed by the maker or a thoroughly competent person”.7 Ask the maker what it advises before you use it again.
How we got here: “fireproof” from the Salamander to UL
“Fireproof” is a 19th-century selling word that never went away. In 1833 a double iron chest made by C. J. Gayler of New York came through a fire in Thomaston, Maine, with its contents in good order, and an admiring writer called it a “Salamander”, after the creature said to live in fire.16 Two years later New York’s great fire of December 1835 was a harsher test: about sixty Gayler chests were in use in the burnt district, and only a few saved what was inside.16
Makers went on selling safes on survival stories like these, and on public fire trials, which is why Chubb’s warning about rigged tests reads so pointedly.167 His verdict on the word itself, quoted below, is the same one this page reaches 150 years later. The story of the early fillings, patents and trials is in inventing the fireproof safe.
“In the broadest sense of the term there cannot be such a thing as a burglar-proof or fire-proof safe.”
George Hayter Chubb, 1875
Independent testing is what eventually replaced the bonfire and the newspaper testimonial. UL 72 is the American descendant of that idea; today’s European fire standards play the same role there. Both still measure resistance for a time, never proof.4
Myths and facts
A fireproof safe can’t burn.
“Fireproof” has no official definition. UL says rated safes should be called fire resistant: they protect for a set time, not for ever.
Any heavy steel safe will protect papers in a fire.
Steel passes heat through. Fire protection comes from insulation, and many security safes have no fire rating at all.
If my papers survive, my USB sticks and photos will too.
Paper is protected below 177°C (350°F); digital media need 52°C (125°F) and film 66°C (150°F). A paper-rated safe isn’t enough for them.
A fire bag will save my documents in a house fire.
SentrySafe, which makes one of the best-known bags, says no document bag will survive a significant structure fire.
Once the fire is out, open the safe straight away to check.
A safe can stay hot for hours, and opening it early may let the contents catch fire. Wait, and let a professional open it.
Frequently asked questions
Are fireproof safes really fireproof?
No. The best are fire resistant: they keep the inside below a set temperature for a rated time, which for most consumer safes is 30 to 60 minutes, according to UL. A longer or hotter fire can beat any of them.
Is there a truly fireproof safe?
Not in the sense of “proof against any fire”. Longer ratings and a safe kept in a fire-resisting room give the best odds, as Chubb observed in 1875, but every rating has a time limit.
How long does a fireproof safe last in a fire?
As long as its rating, in test conditions. UL says most consumer safes are rated for 30 to 60 minutes. Real fires can be longer, and a safe in the ruins can stay hot for hours.
Will money burn in a fireproof safe?
Not if the inside stays under its rated limit, 177°C (350°F) for a Class 350 safe. If notes are damaged, the US Treasury and the Bank of England will usually replace them when at least half of each note survives.
Are fireproof safes waterproof?
Not necessarily. Fire and water protection are separate claims, and fire safes can trap moisture. Look for a stated water rating, and air the safe regularly.
Can I use my safe again after a fire?
Not without an inspection. Its insulation has done its job once; ask the maker before trusting it again, as Chubb advised back in 1875.
Sources:
- Chris Chmura and Joe Rojas, “‘Fireproof’ label on some safes may be misleading”, NBC Bay Area, 2 October 2018. Includes UL’s and ASTM’s statements on the word “fireproof”. ↩︎
- Wikipedia, “Fire-resistance rating”, section on UL 72 classes (summary of the standard; temperature limits for Classes 125, 150 and 350). ↩︎
- North Carolina Department of Insurance, “Immediately after the fire”, viewed 27 October 2026. ↩︎
- ANSI Webstore, ANSI/CAN/UL 72:2026, “Tests for Fire Resistance of Record Protection Equipment”, published 27 January 2026. ↩︎
- U.S. Fire Administration (FEMA), “This Is Fire! A factsheet on the nature of fire”, March 1999 (copy hosted by the City of Fort Worth fire department). ↩︎
- UL Fire Safety Research Institute, “New comparison of natural and synthetic home furnishings”, 30 September 2020 (repeat of UL’s 2009 experiment). ↩︎
- George Hayter Chubb, Protection from Fire and Thieves (London, 1875), ch. IV “Safes against fire” and ch. V “Second-hand safes”, via Project Gutenberg. ↩︎
- Mecca Thompson (KFOR), “Family loses valuables as fireproof safe burns in OK wildfires”, NewsNation, 21 March 2025. ↩︎
- SentrySafe store, desiccant pack P50200, product description (advice on moisture in airtight safes), viewed 27 October 2026. ↩︎
- SentrySafe, “Fire Bag, model FBWLZ0”, product page (maker’s description and protection notes), viewed 27 October 2026. ↩︎
- Health and Safety Authority (Ireland), “Asbestos risks in safes and fire resistant cabinets”, information note (updated September 2023). ↩︎
- David Christensen, “Liberty Safe survives a raging garage fire”, Liberty Safe blog, 8 April 2019 (published by the safe’s maker). ↩︎
- Tom Scalisi, “We tested this fireproof document bag to see if it can take the heat”, Bob Vila, updated 12 March 2024. ↩︎
- Bureau of Engraving and Printing (US Treasury), “Mutilated currency redemption”, viewed 27 October 2026. ↩︎
- Bank of England, “Damaged and contaminated banknotes”, viewed 27 October 2026. ↩︎
- One Hundred Years’ Progress of the United States (Hartford, 1870), section on locks and safes, pp. 396–397, via Internet Archive. ↩︎
