What are Fire Resistant Safes Made of ?

Fire resistant safe door

When you don’t want to worry about your important papers, whether it be bank notes, important contracts, your testament or even that Michael Jackson autograph, you choose a good fireproof safe. But the question arises : are those safes really fireproof ? How long can they resist an important fire ? The only way to find out is to document on how they are made.

What are fire resistant safes made of? Those safes are made of at least two walls of metal to hold the fire resistant material. This material which acts as a thermal insulation usually consist of mineral wool, calcium or sodium silicate, perlite and vermiculite, fire protected concrete. Each brand creates it own patented formula. Furthermore, the door is protected by a fire seal. This seal will expand in case of a fire, protecting valuables from heat and water when the fire is extinguished. A safe can resist from 30 minutes up to 160 minutes. The door itself has an additional layer of insulation to protect the lock in order to have it operational under high heat conditions.

It is very important to differentiate a fireproof safe from a fire-resistant one. Makers and resellers tend to use terms lightly, spreading out the idea that a safe can resist a fire. But it will depend on many conditions and factors. On top of that, a safe should resist burglars, we shouldn’t forget it. Is it really the case?

Structure and Construction of a Fireproof Safe

Most entry-level safes are single walled. This can’t be the case with a fire retardant safe because it has to be made of a double-walled carcass to hold the fire retardant material. That sheet of metal is usually thinner (14 gauge for example, that is to say 0,078 of an inch or 1.98 mm) than an equivalent single doored carcass. But good quality fire resistant safes have thicker steel sheets.

The fire resistant material in itself and the air that acts as an insulator as well takes up space.

The walls of the body are filled with fire insulation material. Some constructors keep their recipe secret and/or patented. In the case of Burg Wachter, for example, that material consists of FCP (Fire Protected Concrete). It can be found inside the body walls as well as the door.

The door itself is further protected by an intumescent seal that swells and seals the door in the event of a fire. This is very important. Because the safe is as protected as its weakest component. The insulation can be good, but if heat can find its way inside by a badly sealed door, it serves no purpose. The intumescent seal has a particularity: it is nonobtrusive in a day to day use and you won’t notice it. But when heat builds up, it expands quickly to take up the space between the door and the walls of the safe, preventing air and heat to come through. This is a very important aspect of heat insulation (and consequently fire resistance). The better the safe, the better the seal. Bad cheap safes don’t even have one.

First layermetal wall0.8 inch
Second layerinsulation1.15 inches
Third layermetal wall0.8 inch
Fourth layerfire expandable seal
Fifth layeradditional insulation (door)0.8 inch
Sixth layeradditional metal wall (door)0.8 inch

To really understand how it works, it is important to study how the National Fire Protection Association and Underwriters Laboratories do their testing.

How fire resistant safes are rated and tested ?

A fire can take less than 30 seconds to spread and, from a small fire, become a major one. Temperature can reach 1200 °F in 5 minutes. Papers inside a safe can be altered or even worse can be subject to spontaneous combustion.

The ratings consist of tests where minutes and temperature are consigned. Temperature and humidity rate are measured inside the safe with each furnace temperature. Underwriters Laboratories give these ratings :

UL30 minutes1550 °F
UL160 minutes1700 °F
UL22 hours1850 °F
UL44 hours2000 °F

In order to simulate fire conditions, laboratories put papers and several types of digital media inside a safe. Humidity rate must be below 65%. Temperature inside the safe must be between 65°F and 75°F. Then the safe is put inside a furnace. The heat then rises at a carefully monitored rate and is evenly distributed around all surfaces of the product.

When a temperature is reached, the furnace is turned off (for example 1700 °F). The safe is then let to cool in the furnace. The temperature is monitored inside the safe. Only products that remain below the temperature and humidity limits are awarded the label.

Then, the safe is opened to check if its content is in usable condition and if walls show structural problems due to heat or humidity.

Such testing doesn’t happen once. A safe has to be retested a year after to check if any sample out of the production line still meets the standard.

UL1 (1 hour at 1700 °F) is usually the way to go as it is compliant with most standard insurance policies.

Is a safe really fireproof ?

Don’t play on words. Many things are said to be and rated waterproof. This can be tested. But fireproof ? No safe is fireproof because it can’t resist indefinitely to a fire. It is only a question of temperature and minutes. So a safe is said to be fire resistant. And that resistance is rated from 30 minutes to 160 minutes usually. So it has to be protected not really from direct fire but heat, as heat can quickly become really extreme in case of a fire. If you consider buying a fire safe, you might be interested in this article I wrote: are fire safes effective?

Cheap Fire Resistant Safes

So, pardon me, every thing is safe and good. Not so fast.
In order not to be too heavy, entry level fire resistant safes use a two walled carcasse consisting of thin metal (1/2 the thickness of a single walled carcasse !). The steel can be up to 18 gauge thick which is merely 1/20 of an inch (1,27 mm).

You can see that the only purpose of that sheet of steel is to hold the fire retardant material in place and not to resist a burglar anymore… No problem: the safe appears to be big and sturdy because of the thickness of the insulation layer; the buyer is happy; but I warn you not to be fooled by the thickness of such a safe…

A cheap fire resistant safe sometimes even lacks a fire expandable seal altogether (intumescent seal) let alone a good one.

Is a fire resistant safe a good protection against burglary ?

At last, cheap fire resistant safes often have a lower quality door lock. The safe is big, it should be sturdy, then, right? Not necessarily!
With a big cheap safe there are often caveats. The most important one is the quality of the lock. It sometimes goes down to a lock from a mailbox!
Those kinds of locks can be opened in a matter of minutes, sometimes seconds with little to no tools. A mailbox in a safe can be opened with a simple drill, can be easily lock-picked, can be sometimes even turned with a screwdriver and a hammer. The last option is to throw the safe to the ground. If you have chosen to buy a cheap safe with light small gauge steel and brought your safe upstairs, chances are a burglar can easily throw it throw the window. You will find an opened safe in your driveway…
The only way a fire resistant safe can provide good security in case of fire AND burglary is once again to forget the cheap route and to chose a medium to good quality safe. Those good safes combine good insulation, good seals, and a good structure with double walls and thick steel and a triple walled door. They are heavy. When properly anchored, they offer as good a security as regular good safes. If thrown from the first floor, they will land closed but you will find a new hole in your garden or driveway. There are drop tests to safes.


I have been passionate about locks and safes for so long; it is a family speciality since 1898. I hope I can share with you all the simple tips that can make the difference for your security. And that you'll buy the right products for your needs.

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