A fire rating is minutes at a temperature
No safe is fireproof. Every fire label states how long the inside stayed below a limit while the outside burned in a laboratory furnace — and the labels differ in the furnace, in the limit, and in what happens once the burners are switched off.
Three things every fire label states
| The label states | What that means |
|---|---|
| How long the safe was in the furnace | Thirty minutes to four hours, depending on the standard and the model. The figure is the length of the fire, not a promise about your house. |
| How hot the furnace was | Not one fixed heat but a standard curve that keeps climbing. The European curve reaches about 842 °C at thirty minutes and 945 °C at an hour; UL's one-hour test rises to 1700°F (927 °C). |
| How warm the inside was allowed to get | This depends on what the safe is for. Paper tolerates far more heat than a hard drive, so the same fire produces different limits for different contents. |
The labels side by side
| Label | Standard | Furnace time | Inside may rise by, or stay below | After the fire |
|---|---|---|---|---|
| S 60 P · S 120 P | EN 1047-1 | 60 / 120 min | 150 K above 21 °C — about 171 °C; for paper | Keeps measuring as the safe cools; separate fire shock and impact test |
| S 60 D · S 120 D | EN 1047-1 | 60 / 120 min | 50 K — about 71 °C, at most 85% humidity; for data media | As above |
| S 60 DIS · S 120 DIS | EN 1047-1 | 60 / 120 min | 30 K — about 51 °C, at most 85% humidity; for highly sensitive data media | As above |
| LFS 30 · LFS 60 | EN 15659 | 30 / 60 min | 150 K above 21 °C; for paper only | Test stops; the safe is cooled artificially |
| 60 · 90 · 120 Paper, Data | NT Fire 017 (Nordic) | 60 to 120 min | 150 K for paper, 50 K for data | Test stops; no natural cooling phase |
| Class 350 | UL 72 | ½ to 4 hours | 350°F (177 °C); for paper | Cools inside the closed furnace, still measured |
| Class 150 | UL 72 | ½ to 4 hours | 150°F (66 °C); film and magnetic media | As above |
| Class 125 | UL 72 | ½ to 4 hours | 125°F (52 °C); digital media | As above |
| “60 minutes at 1200°F” | ETL (Intertek) | As stated | 350°F (177 °C) | Depends on the test — ask |
The European standards write their limits as a rise above the starting temperature, measured in kelvin; a laboratory starting at 21 °C gives the absolute figures shown. Class 150 and Class 125 also cap humidity. Until 2019 the EN 15659 levels were called LFS 30 P and LFS 60 P — older safes and certificates still carry those names.
Why the cooling phase matters
A safe keeps heating up on the inside after the fire has gone out: its walls have soaked up heat and go on passing it inward. EN 1047-1 and UL 72 keep measuring through that phase, so a pass means the contents survived the whole event. EN 15659 and NT Fire 017 stop the test at the set time and cool the safe artificially, which is why they are the lighter labels. EN 15659 says so itself: protection after the fire exposure is not ensured by that standard, but by EN 1047-1.
EN 1047-1 adds a second test, a fire shock and impact test, in which the hot safe is dropped. In UL 72, an impact test is the manufacturer's option, while an explosion test — the locked safe placed in a furnace already at 2000°F (1093 °C) — is part of the rating.
What goes in which safe
| Contents | Look for |
|---|---|
| Passports, deeds, cash, paper records | S 60 P or S 120 P · UL Class 350 · LFS 30 or LFS 60 as a lighter option |
| Photographic film, magnetic tape | S 60 D or S 120 D · UL Class 150 |
| USB sticks, hard drives, memory cards | S 60 DIS or S 120 DIS · UL Class 125 |
A paper-rated safe can pass its test with the inside just below 177 °C. That is fine for documents and far beyond the 52 °C a Class 125 safe must hold for digital media — so a USB stick in a paper safe is not protected by the paper rating.
After a fire: leave the door shut
FEMA's advice is direct: if you have a safe or strong box, do not try to open it. A safe can hold intense heat for several hours, and if the door is opened before it has cooled, the contents can burst into flames. Let it cool completely; if the lock or the door has suffered, call a technician rather than forcing it. Find a technician ›
Short answers
- Is any safe fireproof? No. A fire rating says the inside stayed below a set temperature for a set time in a laboratory furnace. Longer or hotter fires, or a safe opened too early afterwards, can still destroy the contents.
- What does UL Class 350, 1 hour mean? The safe spent an hour in a furnace rising to 1700°F (927 °C), cooled inside it, and the interior never passed 350°F (177 °C), the limit for paper. The rating also includes an explosion test.
- What is the difference between S 60 P and LFS 60? Both mean sixty minutes of fire with paper inside. S 60 P comes from EN 1047-1, which keeps measuring while the safe cools and adds a fire shock and impact test. LFS 60 comes from EN 15659, which stops at sixty minutes and cools the safe artificially.
- Can I keep USB drives or hard drives in a fire safe? Only in one rated for them: S 60 DIS or S 120 DIS under EN 1047-1, or UL Class 125. A paper rating allows the inside to reach about 170 to 177 °C, far too hot for digital media.
- When can I open my safe after a fire? Not until it has cooled completely. FEMA warns that a safe can hold intense heat for several hours and that opening it early can make the contents burst into flames.
Where this comes from
- EN 1047-1:2019 — scope and Table 1 (protection classes, temperature rise, humidity), CEN preview
- EN 15659:2019 — scope and foreword (LFS 30 and LFS 60, 150 K, the 2019 renaming), CEN preview
- Estonian Centre for Standardisation — EN 15659:2019 scope
- Nordtest — NT Fire 017, filing, data and diskette cabinets
- Atelier Boonen — Fire resistance classes and test methods
- American Security — Fire ratings explained
- Liberty Safe — Understanding UL and ETL ratings for your home safe
- FEMA — What to do after a fire (archived copy)
Every source above was read on 18 Oct 2026. If one of them changes or disappears, the line that rests on it is corrected or removed — see method.