Compromising fire resistance performance in the home
Published on 2 April 2009
Fire safety in domestic buildings generally requires that certain walls, floors and ceilings provide fire separation. The construction of fire compartments helps to isolate fire, heat and smoke to limit its spread through the property and also helps to keep escape routes safe. Equally, it is important that the structure resists collapse and provides occupants with valuable time to get out of the building in the event of a fire.
In a typical two-storey house, the floor between ground and first floor has never had anything other than a minor fire separating function, because none of the doors to the rooms off the staircase have to be fire resisting. Indeed, open plan stairs are common.
In fact, in most UK modern domestic premises, it is the load-bearing capacity of the floors that is threatened by the early failure of ceiling linings, not the fire separating function. The upper floor, however, is required to provide 30 minutes load-bearing capacity to prevent complete structural collapse, giving some protection to occupants should they be trapped upstairs, and also to provide protection for firefighters engaged in search and rescue in the property.
With this in mind the Electrical Safety Council has produced a new Best Practice Guide for designers, installers, verifiers and inspectors of electrical installation work in new and existing UK domestic premises, looking at the fire safety aspects. As with all the guides in the series, Electrical Installations and their impact on the fire performance of buildings: Part 1 - domestic premises: Single family units is available to download free of charge from the Council's website: www.esc.org.uk.
Fire hazards from electrical installations and the need to enhance fire protection
Many modern forms of engineered construction, such as lightweight joists, have an inherently lower level of fire resistance when compared to more traditional forms of construction, and are heavily reliant on the plasterboard or similar linings for achieving the requisite level of fire separation. The fire resistance of these elements can be easily compromised by inadequate fire sealing and ‘making good' after any penetration to accommodate electrical equipment and associated wiring.
Installation of these items requires the removal of a part of the ceiling or wall lining, and the replacement with glass, metal or plastic that does not provide the same level of fire protection to the structural members, causing a reduction in the fire resistance performance of the element.
Take, for example, downlighters - generally installed as standard in modern homes and often retro-fitted in older homes. When exposed to a fire from below, downlighters may provide far less protection to a cavity and the structural elements within it than the plasterboard they are replacing, unless suitable precautions are taken.
There are a number of types of downlighter available, and it is important that the type selected for a particular application has test evidence to support its fire performance when incorporated in a ceiling of the type into which it is to be installed. Generally, the tests should have been carried out in accordance with British Standards BS 476: Part 21: 1987 or BS EN 1365-2 (more details can be found in the Electrical Safety Council's guide).
However, not all designs and styles may be available with integral fire protection, especially where higher lighting levels and/or larger coverage is required. In these situations, additional fire protection may be fitted at the time of installation in the form or a ‘fire hood', an insulated fire-protective box, or similar. Such separate forms of protection must be fit for purpose and not be easily dislodged or compromised after installation by subsequent work.
Where flush-mounted accessories penetrate each face of a 30-minute fire separating or load-bearing plasterboard lined wall within the same cavity space, each accessory should be fitted with a back box that incorporates integral fire protection, or be fitted with a proprietary fire protection pad.
Additional hazards influencing fire performance
In addition to items that have a direct influence on the fire performance of floors or walls, other hazards are posed by installations that have an indirect influence on the performance of these elements if the lining provides some or all of their support.
In the event of a fire, the weight of such items may lead to the premature failure of the lining material. Unfortunately plasterboard linings are simply not designed to carry such weights under fire conditions, and unless these items are fixed back to the structural members in the wall or floor, they will pull down the linings if the board is weakened by fire.
This article touches on just a few of the many issues to be considered in order to maintain the fire resistance of walls and ceilings in domestic premises that have been penetrated, or partially penetrated, in the process of installing electrical equipment and wiring. Those interested in finding out more should visit the business and community section of the Electrical Safety Council's website, www.esc.org.uk, where further practical advice and guidance is available.
Mike Clark - Technical Director, Electrical Safety Council (UK)
View all news from
Browse News by