Generally speaking, the basic principles behind fireproof safes have remained unchanged since the late 19th century. The body of the safe is designed with a double wall. The gap between each wall is filled with a fire retardant material. When this is heated during a fire, it releases water vapour which helps keep the interior of the safe cool.
Fireproof safes are engineered in such a way as to minimize the amount of heat transferred from the outside to the inside. The type and thickness of steel used, the design and shape of the door, and the structure of the body are all carefully considered.
There are three main types of fireproof safe:
Fireboard safes provide a basic level of fire protection but are very good value. They are also light and so are easy to move from place to place. As the name suggests, they use panels of fire resistant board as their insulation material. These boards are typically inserted into the wall cavities of the safe during the final assembly process. Sometimes several layers of fireboard are used.
Reinforced fireboard safes are similarly constructed, but may have an extra thick outer steel shell to provide higher levels of anti-theft protection. This naturally makes the safe heavier. It may also mean that the safe provides somewhat less fire protection, as thicker steel will more rapidly conduct heat from the exterior to the interior.
Composite safes carry on the tradition of the 19th century’s best fireproof safes. They feature thin steel walls and a special fire resistant cement-like mix – a composite – which is poured into the wall cavity. The exact composition of this material tends to vary from brand to brand, and may include mixes of gypsum, alum or any other fire resisting compound.
Once this material is in place in the safe’s walls, the safe is baked to get rid of excess moisture. This prevents the interior of the safe becoming damp over time without reducing the amount of water vapour released during a fire. Composite safes typically offer the highest levels of fire protection.
High security safes that offer both fire and theft resistance tend to be composite safes; they are sometimes referred to as composite clad. The composite in such safes may have been designed to resist thermal attack from an oxy arc cutter or similar tool as well as the threat of fires. The Duoguard range from Chubb uses a composite called Dualite for just this purpose.
If in doubt about how much protection the insulation in your fireproof safe provides, simply consult the fire rating. Remember that safes with independent certs and ratings are preferable to those without.