What are fire doors and how do they work?

Fire doors are an integral part of a building’s passive fireproofing plan. They’re used for fire compartmentation –  a process that places physical barriers in strategic areas around a building, in order to slow the spread of flames and smoke in the event of a fire. In this post, we explain what they’re made out of, how much protection they offer, and when they’re required by law.

What are fire doors made of?

Fire doors can be made with a combination of timber, steel, gypsum, and aluminium. They can also have windows, which are made from borosilicate or ceramic glass (both of which offer a higher fire resistance than standard glass), and may contain an anti-shattering wire mesh.

To enhance their fire-stopping abilities, fire doors are flush with the frame; any gaps are filled with silicone-based fire-resistant sealant. These are often accompanied by an intumescent strip attached at the base of the door, which expands when exposed to heat to prevent smoke from seeping underneath.

Fire doors are commonly designed to include a closing mechanism. Usually fitted at the top of a door, these spring-loaded or hydraulic mechanisms force the door closed, preventing fire and smoke from passing from one area to another.

It’s worth mentioning that whilst many doors may contain some or all of these features, they may not necessarily be ‘fire doors’. To be called a ‘fire door’, a design must be certified by a manufacturer. Fire door certification is awarded once a door has passed various tests at an approved centre, including a fire and stress simulation. You can tell which doors have been certified by a label attached to their top edge, which states the manufacturer, date of manufacture, and designated fire rating (more on this below).

How long does a fire door protect you for?

There are different grades of fire door, and each one provides a different level of protection. The grades are separated by how long they can withstand fire. The main ones are FD30 (30 minutes), FD60 (60 minutes), FD90 (90 minutes) and FD120 (120 minutes).

The main aspect that differentiates the grades is the ‘certified core thickness’ of the doors. This is the core material of the door over which there can often be aesthetic layer of different material.

FD30 and FD60 are generally used internally for offices and residential buildings. Any grades over FD60 are more common for the protection of highly-valued properties or core infrastructures (for example, archives or server centres)

When are fire doors required?

All regulations pertaining to the use of fire doors are contained in Fire Safety: Approved Document B and following incorporations. According to the legislation, fire doors are required in domestic buildings over 2 storeys high; each door leading to a stairwell (at every level) from a habitable room (not a bathroom, for instance) must be a fire door. For commercial or non-domestic buildings, fire door requirements vary according to whether escape routes are vertical or horizontal (down stairs or through corridors).

If you’re looking to get your building (whether residential or commercial) in line with current fireproofing regulation, get in contact with CLM Fireproofing. As the UK’s leading provider of passive fireproofing services, we ensure full compliance with the latest standards.