Building standards technical handbook 2022: non-domestic

The aim of compartmentation is to inhibit rapid fire spread within the building by reducing the fuel available in the initial stages of a fire. The intention is to limit the severity of the fire which in turn should help the occupants to evacuate the building and assist fire and rescue service personnel with fire-fighting and rescue operations. This is achieved by dividing the building into a series of fire tight boxes termed compartments which will form a barrier to the products of combustion; smoke, heat and toxic gases.

The use of a building, the height of the topmost storey, the inclusion of automatic fire suppression systems and the fire resistance duration will determine the maximum area of the compartments within a building. Designers may also choose to construct compartments based on client and aesthetic needs. For example, the designer may use compartmentation to classify the building into different uses or to reduce travel distances (see clause 2.9.3).

Common guidance - the guidance in clauses 2.1.14 (Openings and service penetrations), 2.1.15 (Junctions) and 2.1.16 (Fire resisting ceilings) is common, not only to compartmentation and sub-compartmentation, but also to the relevant guidance in Standards 2.2 separation, 2.4 cavities, 2.9 escape and the relevant guidance contained in the annexes. 

Due to the special fire precautions within residential care buildings, hospitals and enclosed shopping centres, additional guidance is grouped in the annexes. The intention is to help designers and verifiers find the information they require quickly when designing or vetting such buildings. However it is important to remember that the guidance in the annexes is in addition and supplementary to the guidance to Standards 2.1 to 2.15. For additional guidance on:

Conversions - in the case of conversions, as specified in regulation 4, the building as converted shall meet the requirement of this standard (regulation 12, schedule 6).

A building, or part of a building, with a total storey area more than the limits given in the tables below should be sub-divided by compartment walls and, where appropriate, compartment floors. The minimum fire resistance duration (see annex 2.D) can be obtained from the tables below (see also clause 2.1.4).

In most cases, a single-storey building poses less of a life risk to the occupants or to fire and rescue service personnel than a multi-storey building, therefore a greater compartment size can be constructed.

Additional information: 

Additional information: 

Where it is intended to install automatic fire suppression systems, guidance can be obtained in the following publications:

Enclosed shopping centres - a smoke and heat exhaust ventilation system (SHEVS) should be installed in the mall of an enclosed shopping centre and in shops with a storey area more than 1,300m2 to prevent cool smoke from entering the mall. Guidance on SHEVS is provided in clause 2.C.1 of annex 2.C.

Similarly, large shops (other than in enclosed shopping centres), with a compartment area more than 5,600m2 should also be provided with SHEVS. Whilst annex 2.C relates to enclosed shopping centres, the guidance in clause 2.C.1 of annex 2.C may also be used for large shops.

Buildings with different uses should be divided by compartment walls and compartment floors. However compartmentation need not be provided if the overall building attains the highest of the performance levels described in the guidance to Standards 2.1, 2.3 and 2.6. The intention is to allow design flexibility without reducing the risk to life safety. This is done by removing the need for compartmentation in a building or parts of a building where the overall building follows the more demanding guidance. For example, a compartment wall between a production area in a factory and part of the building used for storage need not be provided where an assessment of the overall building has been carried out for both uses and:

However certain buildings are considered to present a lower level of risk to life safety and as a result, are given special consideration even where compartmentation between different uses is necessary. The buildings referred to are offices, shops, Factory (Class 2) or storage building (Class 2). Where the affected parts of the building are in the same occupation (see clause 2.2.2), short fire resistance duration is sufficient in lieu of medium fire resistance duration provided an automatic fire suppression system (see clause 2.1.2) is installed on both sides of the compartment wall, or on the storeys above and below the compartment floor where appropriate.

In a residential building, every upper storey and every basement storey should form a separate compartment.

Every floor at a storey height of more than 18m above the ground should be a compartment floor.

Where a building has a basement storey, the floor of the ground storey should be a compartment floor. However where the building comprises one basement storey and not more than 2 other storeys, and no storey has an area more than 280m2, a compartment floor need not be provided.

Where a building has a basement storey at a depth of more than 10m, every basement storey should form a separate compartment.

Paint spraying - a place of special fire risk should be enclosed by compartment walls with a medium fire resistance duration. However this does not apply to a paint spray booth or to a room where cellulose or other flammable liquid spray is used, having a floor area not more than 100m2, constructed of prefabricated factory-made panels and is constructed in accordance with the recommendations in the Health and Safety Executive Guidance Note PM25 ‘Vehicle finishing units fire and explosion hazards’.

Where a place of special fire risk contains any appliance or equipment using hazardous liquid, any opening in a wall or floor dividing it from the remainder of the building should be constructed in such a manner that, in the event of any liquid spillage, the room will contain all the liquid in the appliance or equipment, plus 10%. See section 3, Environment for guidance on catch pits (bunds) for the storage of oil within a building.

A fire-fighting shaft is an enclosure protected from fire in adjoining accommodation and contains an escape stair, a fire-fighting lobby at every storey at which the fire-fighting stair can be entered from the accommodation. The stair may also contain a fire-fighting lift together with its machine room (see clause 2.14.4).

These shafts are used in high buildings, deep buildings and in certain shops or storage buildings to assist fire and rescue service personnel to carry out fire-fighting and rescue operations.

The enclosing structure of a fire-fighting shaft should have a long fire resistance duration. However where the elements of structure in a building have a medium fire resistance duration, then the fire-fighting shaft need only have a medium fire resistance duration. A self-closing fire door in the enclosing structure of a fire-fighting shaft need only attain a medium fire resistance duration (see diagram to clause 2.14.3).

A smoke venting shaft should be enclosed by compartment walls with a medium fire resistance duration, other than at the smoke inlets and smoke outlets to the shaft.

A lift well should be enclosed by compartment walls with at least medium fire resistance duration and, where the lift well is not the full height of the building, a compartment floor with a medium fire resistance duration (see also capping systems in clause 2.1.15). Where a lift is installed, the landing controls and lift car controls should be of a type that do not operate on heat or pressure resulting from a fire.

A platform lift following the guidance in BS 6440: 1999 (see Section 4, Safety), need not be enclosed by compartment walls or compartment floors.

A compartment wall or compartment floor can be constructed of combustible products provided the appropriate fire resistance duration is maintained (see annex 2.D). However compartment walls and compartment floors in hospitals (see annex 2.B), should be constructed from products which achieve European Classification A1 or A2.

Where an element of structure provides support to a compartment wall or compartment floor which attracts a higher fire resistance duration, the supporting element of structure should have at least the same period of fire resistance duration.

General

Compartment walls and compartment floors (including a fire resisting ceiling) are intended to prevent fire passing from one compartment to another. Openings and service penetrations through these walls or floors can compromise their effectiveness and should be kept to a minimum. The solum and roof space should not be forgotten. Openings and service penetrations should be carefully detailed and constructed to resist fire. This can be achieved by following the guidance below.

A self-closing fire door with the same fire resistance duration as the compartment wall should be installed in accordance with the recommendations in the Code of Practice, ‘Hardware for Fire and Escape Doors’, published by the Door and Hardware Federation and the Guild of Architectural Ironmongers.

In some instances a self-closing fire door with a reduced fire resistance duration may be installed. For example, a self-closing fire door with a medium fire resistance duration may be installed in the enclosing structure of a fire-fighting shaft with a long fire resistance duration (see clause 2.1.9).

A lockable door to a cupboard or service duct where the cupboard or the service duct have a floor area not more than 3m2, need not be self-closing.

Hold open devices - Self-closing fire doors can be fitted with hold open devices as specified in BS 5839: Part 3: 1988 provided the door is not an emergency door, a protected door serving the only escape stair in the building (or the only escape stair serving part of the building) or a protected door serving a fire-fighting shaft.

It is important that hold open devices deactivate on operation of the fire alarm therefore some buildings will need automatic fire detection to be installed. Electrically operated hold open devices should therefore deactivate on operation of:

An example of a Category L5 fire alarm system could incorporate only 2 smoke detectors, one installed on each side of the door and positioned at least 500mm and not more than 3m from the door.

As an alternative to the above hold open device, an acoustically activated and/or radio activated door release mechanism and floor plate complying with BS EN 1155: 1997 may be installed on a risk assessment basis (see clause 2.0.8). Additional guidance is contained in BS 7273: Part 4: 2015.

In addition, this type of hold open device is not suitable for use in the following circumstances where:

Additional guidance on the siting and coverage of fire detectors is contained in BS 5839: Part 1: 2017.

Automatically motorised fire shutters - should not be installed in the enclosing structure of a protected zone (see also clauses 2.9.15 and 2.9.27). However they may be used for the protection of service openings and ventilation ducts. Automatic motorised fire shutters should be fitted with audible and visual warning devices that operate on fire detection prior to activation of the fire shutter. However this is only necessary where there is a risk of people moving under the shutter in the event of an outbreak of fire within the building.

The visual warning devices should be fitted on both sides of the opening where the movement of people below the shutter is possible from both directions. Sensors should also be fitted that, when activated, temporarily halt the activation of the shutter. Automatic fire shutters should not be activated by a fire alarm signal from a remote location or out-with the fire alarm zone.

Fire shutter in compartment walls - a fire shutter which is not motorised may be fitted in a compartment wall provided the shutter has the same fire resistance duration as the compartment wall (see table to annex 2.D). Since a shutter activated by a fusible link or other heat sensitive device is not considered to be a threat to the occupants, warning devices need not be fitted.

Fire shutter in compartment floors - where an opening in a compartment floor contains a stair (but not an escape stair) and not more than 2 escalators:

Where an escalator passes through the opening, it should come to a controlled halt before the fire shutter is activated.

A chimney or flue-pipe should be constructed so that, in the event of a fire, the fire resistance duration of the compartment wall or compartment floor is maintained.

A service opening (other than a ventilating duct) which penetrates a compartment wall or compartment floor should be fire stopped providing at least the appropriate fire resistance duration for the wall or floor. This may be provided by:

Fire-stopping of the following services passing through a compartment wall or compartment floor need not be provided for:

Where a pipe connects to another pipe which attracts a more demanding fire resistance duration, and is within 1m from the compartment wall or compartment floor, the pipe should be fire stopped to the more demanding guidance.

Ventilation systems - the potential for ventilation systems to allow the spread of fire and smoke should be considered. A mechanical ventilation system may contribute to the spread of fire and smoke unless it is designed to shut down automatically or operate in a fire-mode if fire is detected. Ventilation ductwork passing through a compartment wall or compartment floor or other fire resisting construction protecting escape routes should be provided with either:

Ventilation ductwork should be designed and installed in accordance with BS 5588: Part 9: 1999. Section 6 of BS 5588: Part 9: 1999 (excluding the third paragraph to clause 6.3.3.2.2) provides guidance on design and construction including fire resisting enclosures, fire resisting ductwork and the use and activation of fire dampers.

Fire-stopping may be necessary to close an imperfection of fit or design tolerance between construction elements and components, service openings and ventilation ducts. Proprietary fire-stopping products including intumescent products, should be tested to demonstrate their ability to maintain the appropriate fire resistance duration under the conditions appropriate to their end use.

Where minimal differential movement is anticipated, either in normal use or during fire exposure proprietary fire-stopping products may be used. The following materials are also considered appropriate: cement mortar; gypsum based plaster; cement or gypsum based vermiculite/perlite mixes; mineral fibre; crushed rock and blast furnace slag or ceramic based products (with or without resin binders).

Where greater differential movement is anticipated, either in normal use or during fire exposure, the use of proprietary fire-stopping products may be used.

To prevent displacement, materials used for fire-stopping should be reinforced with, or supported by, products which achieve European Classification A1 or A2 where the unsupported span is more than 100mm and where non-rigid materials are used. However this is not necessary where it has been shown by test that the materials are satisfactory within their field of application.

General - The basic principle is that junctions between compartment walls and compartment floors (including fire resisting ceilings, see clause 2.1.16) and other parts of the building should be designed and constructed to minimise the risk of a fire in one compartment flanking the wall, floor or ceiling and entering another compartment at the junctions including any solum space or roof space (see annex 2.B for additional guidance on hospitals). Therefore, the building elements, materials or components should not be built into, or carried through or across the ends of, or over the top of a compartment in such a way as to impair the fire resistance duration between the relevant parts of the building.

Technical assessments are often required when designing or verifying the fire performance of junction details.  The ‘Guide to Undertaking Technical Assessments of Fire Performance of Construction Products Based on Fire Test Evidence’ (Passive Fire Protection Forum, 2021) provides advice including the competency of those undertaking technical assessments linked to levels of complexity.  The guidance promotes effective fire safety design to ensure the reliability and quality of passive fire protection materials and systems. The guide also encourages third party certification schemes for the manufacture, installation, inspection and maintenance of products and systems, and relates to the provision of technical assessments that can extend the scope of design and application of a passive product or system by providing a robust and competent approach to technical assessments.

Junctions with walls - Where a separating wall or separating floor forms a junction with an external wall, another separating wall, or a wall or screen used to protect routes of escape (see clause 2.0.6), the junction should maintain the fire resistance duration of the separating wall or separating floor.

Where a separating wall or floor or protected route of escape abuts a structure containing a cavity, a fire barrier or barriers should be installed in the cavity so as to extend the line, and maintain the fire resistance duration, of the wall or floor. This principle also applies where an external wall cladding system is constructed from materials having a European Classification A1 or A2 (other than between two leaves of masonry as described below). For example, in a rendered external thermally insulated cladding system where the insulation achieves European Classification B, C, D, E or F, a fire barrier or barriers should be provided on the line of the separating wall or floor. The barrier should extend from the wall/floor to the inner surface of the render (this may require an intumescent barrier within any drainage cavity that may be present). The guidance in this clause does not apply where the external wall is formed by two leaves of masonry or concrete where both leaves are at least 75 mm thick and the external wall is provided with cavity barriers around all openings and at the top of the wall-head.

There are merits in testing products in a large scale facade fire test to assess how the individual components perform in a complete assembly when exposed to a severe fire emanating from a window or door opening (see annex 2E). 

Junctions with roofs - where a compartment wall forms a junction with a roof, the junction should maintain the fire resistance duration of the compartment wall in accordance with the following:

Junctions with fire resisting ceilings - where a compartment wall does not extend to the full height of the building, the wall should form a junction with a compartment floor.

Non-full height walls - however this may not always be the most practical solution. At the topmost storey of a building for example it is possible for the compartment wall to form a junction with a fire resisting ceiling (see clause 2.1.16), (including a suspended ceiling) or a localised capping system, provided the fire resistance duration is maintained and the junction between the wall and ceiling is fire stopped.

Capping system - to ensure that occupants will be protected during evacuation and to protect fire and rescue service personnel during fire-fighting and rescue operations, a localised capping system could be constructed at the head of a protected zone or a lift shaft. The system should be fire protected on both sides and be sufficiently robust to protect against premature collapse of the roof structure. There is currently no fire test from the top-side of a capping system, the assumption being that if the test satisfies the fire resistance duration from the underside then it will also satisfy the same criteria from the top-side using the same construction.

The junctions between protected routes of escape (see clause 2.0.6) and other parts of the building are particularly vulnerable to fire and smoke. This is because fire and smoke can penetrate weaknesses at junctions, which could compromise the means of escape. The continuity of the fire-stopping should be designed and constructed in order to provide a complete barrier to fire between the relevant parts of the building.

Protected routes of escape - where part of a building is a protected route of escape and forms a junction with any other part of the building including for example, an external wall, a separating wall, another compartment wall or any other wall or screen forming a protected route of escape, the junction should maintain the fire resistance duration of the more demanding guidance.

In order to inhibit the spread of fire and smoke, junctions should be protected in accordance with the above guidance. For additional guidance on fire-stopping materials, see clause 2.1.14.

Where a fire resisting ceiling, including a suspended ceiling, contributes to the fire resistance duration of a compartment floor or is part of a construction as described in clause 2.1.15, the ceiling should be constructed in accordance with the following recommendations:

However the guidance in this clause should not be applied to fire resisting ceilings protecting the load-bearing capacity of a floor only. In such cases, the compartment wall should be taken through the ceiling and floor to form a continuous and complete barrier to fire between the relevant compartments.