Fire safe ratings show how well a safe protects its contents from heat during a fire. A rating covers two key factors: maximum internal temperature and tested protection time.
For example, a Class 350 safe limits its internal temperature to 350°F during its rated test period. Other classes use lower internal temperature limits for more heat-sensitive contents.
Fire resistance ratings can cover periods from 30 minutes to four hours. Understanding both the class and time rating helps you choose suitable protection for documents, cash, media, and other valuables.
How Fire Safe Ratings Work
A fire rating does not simply show how hot a safe can become. It describes the conditions that must be maintained inside the protected storage area during testing.
Two parts of a fire safe rating should always be considered together:
- Class shows the maximum internal temperature allowed during the test.
- Time rating shows how long the tested level of protection must be maintained.
This means a Class 350 one-hour safe and a Class 350 two-hour safe share the same temperature class. However, the two-hour rating covers a longer test period.
INKAS fire rating information includes classifications from one-half hour through four hours.
Fire Safe Rating Classes Compared
The main fire resistance classes covered by INKAS are Class 350, Class 150, and Class 125. Each class sets a different maximum internal temperature.
| Fire Rating | Maximum Internal Temperature | Suitable Contents | Rating Duration |
|---|---|---|---|
| Class 350 | 350°F / 177°C | Paper products, jewelry, guns, and similar valuables | 30 minutes–4 hours |
| Class 150 | 150°F / 66°C | Data tapes, hard drives, compact discs, photographs, and delicate materials | 30 minutes–4 hours |
| Class 125 | 125°F / 52°C | Digital and other highly heat-sensitive media | 30 minutes–4 hours |
Class 350 is the most common of these fire safe ratings. Class 150 and Class 125 maintain lower internal temperatures for more heat-sensitive contents.
Class 350 Fire Rating
A Class 350 safe must keep its internal temperature at or below 350°F during the rated test period.
INKAS identifies Class 350 as the most common fire resistance class. It can be suitable for paper products, jewelry, firearms, and similar valuables.
The fire endurance test also checks the integrity of the test materials and safe mechanisms during heating and cooling.
Class 350 ratings can cover periods from 30 minutes through four hours. The time rating should always be checked together with the temperature class.
Class 150 Fire Rating
A Class 150 safe maintains a much lower internal temperature during its rated fire test.
The internal temperature must remain at or below 150°F. Humidity must also remain at or below 85% during the heating and cooling periods.
This class was originally introduced for computer data tapes and magnetic reel-to-reel tapes. INKAS also lists hard drives, compact discs, photographs, and other delicate materials.
Class 150 can therefore suit contents that require more heat protection than standard paper records.
Class 125 Fire Rating
A Class 125 safe has the lowest internal temperature limit among these three classes.
The internal temperature must remain at or below 125°F during the rated period. Humidity must stay at or below 80% during heating and cooling.
This class was originally developed for floppy disks. It can protect highly heat-sensitive storage media and other delicate materials.
Class 125 should be considered when the stored contents may suffer damage at temperatures far below the limits used for paper protection.
Class 125 vs Class 150 vs Class 350
The main difference between these classes is the maximum temperature allowed inside the safe. It does not describe the temperature of the surrounding fire.
Class 350 allows an internal temperature up to 350°F. It is commonly associated with paper and other standard valuables.
Class 150 lowers the internal limit to 150°F and also sets a humidity limit. It is intended for more sensitive materials.
Class 125 reduces the internal temperature limit to 125°F and uses a lower humidity limit of 80%.
A lower class number does not automatically make a safe the right choice. The correct fire rating depends on the type of contents you need to protect.
The time rating matters as well. A 30-minute rating and a two-hour rating provide different tested protection periods.
How Fire-Resistant Safes Are Tested
INKAS fire rating information covers three major test areas: fire endurance, explosion, and impact testing.
Fire Endurance Test
The fire endurance test checks whether the safe maintains the required internal conditions while exposed to heat.
For Class 350, the internal temperature must remain at or below 350°F during heating and cooling.
Class 150 uses a 150°F limit with maximum humidity of 85%. Class 125 uses a 125°F limit with maximum humidity of 80%.
Test materials and operating mechanisms must also maintain their required integrity.
Explosion Test
The explosion test exposes the unit to very high temperatures. INKAS fire rating data lists exposure at 2,000°F.
Test duration varies according to the classification time. The safe must withstand the required conditions without an explosion occurring.
The test material and safe mechanisms must also maintain their integrity after cooling.
Impact Test
Fire damage can weaken floors and other structural parts around a safe. Impact testing checks protection under these conditions.
The unit is dropped 30 feet after the endurance or explosion test. It is then inverted and exposed to heat again.
The test material and operating mechanisms must maintain their required integrity after the test.
Fire Rating Times and Test Temperatures
Longer fire tests expose the safe to increasingly demanding conditions. The INKAS fire rating guide lists the following heating times and temperatures:
| Test Time | Temperature |
|---|---|
| 5 minutes | 1,000°F |
| 10 minutes | 1,300°F |
| 30 minutes | 1,550°F |
| 1 hour | 1,700°F |
| 2 hours | 1,850°F |
| 3 hours | 1,925°F |
| 4 hours | 2,000°F |
These test temperatures help explain why the time component of a fire rating matters. A longer rating requires the safe to maintain the required internal conditions for a longer test period.
Impact Test Times by Fire Rating
The impact test schedule also changes according to the fire resistance classification.
| Classification Time | Time Before Drop | Exposure Time After Drop |
|---|---|---|
| 30 minutes | 20 minutes | 20 minutes |
| 1 hour | 30 minutes | 30 minutes |
| 2 hours | 45 minutes | 45 minutes |
| 3 or 4 hours | 60 minutes | 60 minutes |
Is a 30-Minute Fire Rating Enough?
A 30-minute fire rating provides a shorter tested protection period than one-hour or two-hour ratings.
Whether that level is suitable depends on the contents you need to protect and the required level of fire resistance.
You should not compare protection time alone. Always check both the fire class and the rated duration.
For example, Class 350 and Class 125 are designed to maintain very different internal temperatures even when both have the same time rating.
INKAS currently offers fireproof safes with one-hour and two-hour fire-rating options for residential and commercial applications.
Fire Ratings vs Burglary Ratings
A fire rating and a burglary rating measure different types of safe protection.
A fire rating focuses on heat exposure, internal temperature, humidity where applicable, and the tested protection period.
A burglary rating measures resistance to forced entry under defined test conditions.
For example, INKAS offers safes with burglary ratings such as TL-15 and TL-30. These ratings relate to resistance against attack rather than fire protection time.
Some safes combine fire resistance with burglary protection. Buyers should check each rating separately when comparing models.
You can learn more about these classifications on the INKAS UL Certifications page.
How to Choose the Right Fire Safe Rating
Start by identifying exactly what you plan to store inside the safe. Different contents can require different internal temperature limits.
Paper records have different needs from digital media, photographs, data storage devices, or other heat-sensitive items.
Next, consider how long you need the tested fire protection to last.
When comparing fire-rated safes, check:
- fire resistance class;
- maximum internal temperature;
- humidity limit, where applicable;
- rated fire protection time;
- type of contents being stored;
- burglary rating, when required;
- safe size and storage capacity.
Do not assume that every fire-resistant safe provides the same burglary protection. These ratings cover different risks and should be reviewed separately.
Find the Right Fire-Rated Safe from INKAS
Understanding fire safe ratings makes it easier to compare safes based on tested protection rather than size or appearance alone.
INKAS provides residential and commercial safes with different security levels and fire resistance options.
Explore our fireproof safes to compare available models. You can also review our UL Certifications information for more details about fire and burglary ratings.