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Fire Precautions - Compartmentation
Fire compartmentation is a vital part of any fire safety design. Compartmentation is a tool that is used in the vast majority of buildings, other than simple low rise developments. Compartmentation is referred to in many different ways: fire walls (and floors); fire separation; protected corridors / stairs etc. All these terms carry the same meaning.
Compartmentation is basically the division of a building into cells, using construction materials that will prevent the passage of fire from one cell to another for a given period of time. The most common feature of compartmentation that we all use and see on a day to day basis is a fire door. However, most building users forget that the surrounding construction will also be fire rated.
This fire precaution is used to achieve a number of goals, although its primary consideration is usually the protection of the means of escape. In some buildings, there will be little / no other fire separation other than the means of escape. For example, a simple office building, served by a single stair. The floor area may be open plan, with no partitions, however, the stair will be enclosed by fire walls (and fire doors) to ensure a fire within any part of the accommodation cannot pass into the stair. As buildings become larger or more complex, the objectives and reliance on fire compartmentation is usually increased. High rise residential buildings are commonplace and are a good example of where great reliance is placed on fire separation, in this example, each flat / unit is generally treated as its own 'cell', therefore fire separation from one flat to another should not occur. Dependant on the size of the flat, additional fire separation may be required within it to protect the occupants means of escape. This example shows how occupancy also has a significant impact on requirements and reliance on fire separation, with the key risk profile being that occupants may be asleep, therefore at greater risk.
Compartmentation falls into the passive category as it doesn't typically react or change in a fire condition and this is one of its many advantages, as a feature, it is effectively a capital cost and can have little maintenance requirements, i.e. once a masonry wall is in place little will change throughout its 'life', it does not need a weekly test or a quarterly service, however, its integrity must be maintained. The most common problem with fire separation is that it frequently needs passing through, whether it is people (passing through fire doors) or building services, these create openings and therefore weaknesses within the separation. Specialist attention needs to be given to these breaches.
Firestopping is the generic term given to various components that are used to seal openings in fire compartmentation. The method adopted will differ greatly, depending on the type and size of the opening as well as the material that is passing through. Other systems, such as fire dampers are used where ductwork passes through fire walls. Technology and industry advances mean that fire separation (if installed properly) can have an enviable success rate, however, it is the weaknesses that must be continually considered, particularly with the constant changing environment in buildings requiring service alterations.
Experience indicates a number of areas that are mismanaged in terms of fire separation. Cavity barriers are a form of fire separation, placed in areas where fire and smoke spread could occur and go undetected, commonly this is not adequately achieved within roof voids, increasing the risk of fire spread within the building. Similarly, deficiencies have been identified within both ceiling and floor voids. The level of deficiencies normally depend on the time of construction, newer buildings, built to current regulations, using modern building systems tend to have less problems, however, where refurbishments have been undertaken in existing buildings, large un-separated areas have been observed.
Fire compartmentation should be included as a significant consideration of your existing fire risk assessment and is an area where competency is critical. This bulletin should have highlighted the importance of this fire precaution and highlighted some of the potential issues affecting it, if these are not adequately considered, this gives rise to a potential failing of the fire risk assessment and far worse than that, could mean that a fire is allowed to spread.
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