What is fire compartmentation, where is it required and why is it important?

Approved Document B, Volume 2 (2019) defines a fire compartment as; -

“A building or part of a building comprising one or more rooms, spaces or storeys constructed to prevent the spread of fire to or from another part of the same building or an adjoining building.”

This is achieved through the provision of fire resisting walls and floors (commonly offering between 30 minutes and 120 minutes fire resistance). And will include special measures to address any openings in the compartment lines, such as doors, glazing, service penetrations and ductwork.
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The wall or floor must remain functional for the duration of the designed fire resistance period. The compartment wall or floor should not crack or develop holes that allow flames, smoke or hot gases to pass through it, and if appropriate, it should maintain a suitable degree of insulation.
There are two main reasons as to why fire compartmentation is required – for life safety and property protection purposes.

1. It is required for life safety purposes when protecting or sub-dividing escape routes, this may include external or internal means of escape. For example, escape corridors, stair enclosures including those with refuge areas, protected lobbies / firefighting shafts. Fire compartmentation provides occupiers of the building additional time to evacuate before escape routes are potentially compromised by the spread of smoke and fire. It will also decrease the danger which the Fire and Rescue Services may be exposed to. Compartmentation will also be used to limit maximum compartment sizes in premises such as warehouses. Compartmentation is also used to support specific fire evacuation strategies, such as a defend in place strategy in blocks of flats – where each flat is designed as its own fire compartment limiting the need for a full evacuation of a building in the event of a fire in one flat. It may similarly be used to support progressive horizontal evacuation in healthcare buildings – were patients can be moved horizontally away from a fire into adjoining compartments and minimising the need for vertical evacuation of vulnerable patients and/or full evacuation of the entire building.
2. It is required for property protection purposes as it will limit spread and attempt to contain the fire to the location it has originated, this is predominantly for enclosures housing special fire hazards such as plant rooms or other high risk rooms. It may also be used to protect areas of high financial or strategic value, such as IT suites / server rooms or strategic storage spaces. Where a building contains more than one occupier and the nature of their activities significantly different (for example residential premises sited over or alongside retail units) they are likely to require separating by compartment walls and floors to prevent a fire progressing to the other purpose group, this is the same case with wall common to two or more buildings.

Approved Document B Tables B3 and B4 provide detailed information regarding the minimum periods of fire resistance required in buildings for different purpose groups and maximum permitted compartment sizes. In some instances, automatic fire suppression systems such as a sprinkler system may be provided where necessary to reduce the rate and growth of fire which may also impact on permitted maximum compartment sizes.
How do you achieve fire compartmentation?

• Fire resisting construction and cavity barriers, with any fire stopping if necessary.

Approved Document B refers to a cavity as any concealed space and states that cavity barriers should be provided in the following situations.

• To divide cavities at junctions and cavity closures
• To close the edges of cavities at junctions and cavity closures, and
• To protected escape routes
• To cavities affecting alternative escape routes

• Fire doors together with its frame and furniture, it is intended when closed to resist the spread of fire and/or toxic gases and meets the requirements of BS 476-22 and or BS EN 1634-1. Please refer to Approved Document B, Volume 2 (2019), Table C1 and B5 regarding incorporating glazing in the design of the door.

This can include fire shutters or curtains, predominantly found in large open spaces such as atriums, shopping centres and can be installed in roof spaces.

• Fire dampers in air handling ductwork are generally actuated by automatic smoke detection or thermally actuated devices and are sited where ductwork penetrates the fire resisting construction.

All passive fire safety measures should be subject to regular inspection and where necessary testing and maintenance in line with recommendation in standards and manufacturers.

What if my building does not have adequate fire compartmentation?

In the scenarios where fire resisting construction is breached, there are a variety of different methods to use depending on the physical sizes, gaps and type of service penetration or linear gaps between the elements of construction. It is critical that the correct choice is taken to ensure that the required fire resistance of the fire separating wall/floor is maintained, despite the original construction compromised by breaches. Fire stopping will ensure that compartment lines are not breached and help delay the spread of fire, smoke and hot gases. Examples of fire stopping products / methods include proprietary materials such as fire resisting boards or mineral fibre baths cement mortar, Gypsum-based plaster, intumescent mastic, ‘seal bags’ filled with intumescent granules etc. Certain specialist products such as intumescent fire collars may be used to protect certain types of service penetrations.

Any fire stopping should be completed by a competent third-party contractor, preferably accredited by a third-party scheme, for example Warrington Fires FIRAS scheme or Loss Prevention Certification Board (LPCB).

To summarise, fire compartmentation is the sub-division of a building into smaller sections or units in order to withstand and limit damage/growth from a fire situation by preventing the spread of smoke and fire, with the use of fire resisting construction.

Fire compartmentation should be analysed during each Fire Risk Assessment carried out by a competent Fire Risk Assessor. Alternatively, if you are particularly worried about the fire compartmentation within your building, it is recommended that a full compartmentation and fire door survey is carried out by a competent contractor.

​Scenario

A contractor has breached a fire rated ceiling to install fire alarm cables and has replaced the ceiling with non-fire rated suspended false ceiling tiles, is this acceptable? The answer is no, as this now allows the spread of smoke and fire above the fire door through the roof space as there is no adequate compartment. You can resolve this issue by fully extending the wall construction to storey or roof height, using materials which achieve the same period of fire resistance achieved by the fire door.