Fire doors perform a vital safety function, to contain fire and prevent its spread and to provide protected escape and firefighter access routes. Additionally, the combination of glass and finely finished timber doors can have a dramatic aesthetic affect on design and style such that more and more designers are looking to glass fire resistant assemblies.

Where fire-resistant glass is concerned, however, there seems to be a bewildering choice. However, specification of the correct product is crucial in order to attain the performance and protection required.

Whichever glass is specified, it must only be used as part of an approved fire door assembly tested to the relevant British Standard (BS 476: Part 22, and the new European tests BS EN 1363-1 and BS EN 1634-1). Some glazings may not perform as effectively as others in the same framing systems and the mixing of individual components between different systems may cause the whole to fail in a fire. Small differences between fire resistant glass types can have a major influence on behaviour in a fire. For example, some fire resistant glazing (such as special toughened) requires special glazing conditions, regarding edge cover and glazing sealant, to function safely and reliably.

The cutting and glazing of fire door apertures to take a fire resistant glass pane is a critical element of fire resistance performance. Apertures should always be formed as part of the door manufacturing process. They should not be produced as a secondary operation on a finished door except under controlled conditions and in accordance with manufacturer’s instructions. It must not be done on site as it could prejudice fire performance. Glazing itself can range from a small vision panel to a full size glass door but, whatever the size, apertures and screens must contain glass that is appropriately rated as fire resistant.

Classification of fire resistant performance is based on two criteria – integrity, and integrity and insulation. Integrity is the ability of a glazing system to perform as a barrier to fire, keeping back flame and smoke with no sustained flaming on the non-fire side for the duration of the test period. With integrity glazings that remain clear in a fire, the traditional advice is to use only sloped, rather than square topped, timber glazing beads to minimise the risk of ignition of the bead on the non-fire side. The risk is lower for those integrity glasses based on a foaming interlayer, where the radiant heat transfer through the glass is effectively reduced to the point where the risk of timber bead ignition is much lower. Pilkington Pyrodur is such an integrity glass, comprising glass laminated with special layers which foam and turn opaque when exposed to heat, forming an effective partially insulating, smoke and flame proof barrier.

The latest advances in glass technology mean that being safe does not automatically mean compromising appearance. The tradition of large, bulky fire doors with thick, weighty glass is giving way to a much slimmer version with glass that complements the surroundings while still providing the required fire resistance. Pilkington has recently launched Pilkington Pyrodur Plus, a 7mm intumescent laminate fire resistant glass developed specifically for fire doors and other internal applications. For the first time in the integrity class it is possible to benefit from a glass that brings a combination of fire and impact performance features normally associated with thicker product. In tests, integrity was achieved in excess of 40 minutes, with full insulation performance achieved for more than 20 minutes. Measured radiant heat values stayed below 3Kw/m2. This innovation provides a great deal of design flexibility with an enhanced performance that would normally come only from thicker glass.

Insulation performance is the ability of the glazing system to restrict the temperature rise on the non-fire side to below specified levels for the duration of the test. Fire resistant glazing with an integrity and insulation performance is a high performance product. With such glazings the total heat transfer from the fire is reduced to very low levels. The Pilkington Pyrostop range is an example of such a fire resistant glass, providing integrity and insulation performance from 30-180 minutes in suitable glazing systems. This glass is based on a sandwich of glass and an interlayer that forms an insulating, resilient shield when subject to fire. It is ideal for use in screens, doors, and fire walls, such as those found in lobbies and atria.

The bottom line is that all components forming a fire door or screen assembly must be compatible. Fire resistant glass works within an approved fire resistant system. That means the glass together with the frame, the beads, glazing material and fixings. There are a number of different fire resistant glass systems with their own particular features, which means that it isn’t straightforward to compare one with another, certainly not to make unauthorised substitution of key components. Use only approved systems and have them installed exactly as approved, ideally by certified installers.