Fire compartmentation: What managing agents need to understand, and why it keeps coming up in fire risk assessments
Compartmentation is one of the most consistently identified areas of concern in fire risk assessments of residential blocks and mixed-use buildings, and one of the least well understood by the people responsible for managing them. This article explains what it is, why the integrity of a building's compartment boundaries tends to degrade over time, and what managing agents should expect when a fire risk assessment flags it as a problem.
When a building is designed with fire safety in mind, one of the core principles at work is that a fire should be contained within the area where it starts for long enough to allow occupants to escape and the fire service to respond. The mechanism by which this is achieved is compartmentation: the division of a building into discrete fire-resisting zones, separated by walls, floors, and doors that are constructed and maintained to resist the passage of fire and smoke for a defined period, typically 30 or 60 minutes depending on the building type and the element in question. In a well-maintained residential block, a fire starting in one flat should, in principle, remain within that flat for long enough that occupants elsewhere in the building can either evacuate or remain safely in place, depending on the evacuation strategy in force.
That principle depends entirely on the integrity of the compartment boundaries, and it is the integrity of those boundaries — rather than the original design intent — that a fire risk assessment is examining when it looks at compartmentation. A building can have been constructed to an entirely appropriate standard and still have compartmentation that is materially compromised by the time it is assessed, because the boundaries between compartments are vulnerable to damage and interference in ways that accumulate gradually and are often not visible without a systematic inspection.
A useful introduction to fire compartmentation and what it means for the UK building stock, from Evolutions Fire Protection.
Why a closed door is doing more work than most people realise
The simplest illustration of compartmentation in practice is also one of the most striking: the difference in fire behaviour between a room with the door open and the same room with the door closed. A closed door cuts off the oxygen supply that a fire needs to grow, removes the draught that accelerates its spread, and buys time — for occupants to escape, for the alarm to reach people further away in the building, and for the fire service to arrive and intervene. The short simulation below makes that point more effectively than any written description can.
A small-scale simulation showing how air flow driven by an open door can accelerate a fire dramatically — and how a closed door limits oxygen and slows spread.
What the simulation illustrates at a small scale is the same principle that underpins the design of compartmented buildings at a large one. Every fire-resisting wall, every properly installed and maintained fire door, and every correctly sealed penetration through a floor or ceiling is performing a version of the same function: limiting the oxygen available to a fire, slowing its spread, and buying time. When those elements are compromised — when a fire door is wedged open, when a penetration through a fire-resisting wall has been left unsealed after a contractor's visit, when a self-closing device has been removed because residents found it inconvenient — that time is reduced, sometimes dramatically.
A fire door propped open is not a minor inconvenience — it is a compartment boundary that no longer exists. The same is true of an unsealed penetration through a fire-resisting wall or a self-closer that has been disconnected. Each of these deficiencies represents a reduction in the time available to occupants and the fire service, and in a building operating a stay-put strategy, that time is the margin on which the strategy depends.
Why compartmentation fails in managed residential buildings
The most common causes of compromised compartmentation in the blocks that managing agents look after are not the result of poor original construction — though that does occur — but of the ordinary life of a building over time. Every time a contractor runs a cable, a pipe, or a duct through a fire-resisting wall or floor, a penetration is created, and that penetration needs to be sealed with an appropriate fire-stopping material to restore the integrity of the compartment boundary. In practice, that sealing is frequently omitted, inadequately specified, or carried out with materials that are not fit for purpose, and because the penetration is often concealed behind a finished surface, it may go undetected for years.
The same applies to services risers and communal service ducts, which in many residential blocks run vertically through multiple floors and represent a significant route for fire and smoke travel if they are not properly sealed at each floor level. Older blocks in particular, where mechanical and electrical services have been upgraded or modified multiple times over decades, often contain a layered history of penetrations, some of which will have been sealed at the time and some of which will not, and where the sealing materials used may have degraded or been disturbed by subsequent works.
Fire doors are the other major area of concern, and the one that tends to generate the most remedial action following a fire risk assessment. A fire door is not simply a door in a fire-resisting wall — it is a tested assembly of door leaf, frame, ironmongery, intumescent seals, and cold smoke seals, all of which need to be present, correctly installed, and in serviceable condition for the door to perform as intended. Any one of those components being absent or defective can materially reduce the door's resistance to fire and smoke, and in a block with a stay-put evacuation strategy, that matters considerably. We carry out fire door inspections as a standalone service precisely because the condition of fire doors in a block often warrants more detailed assessment than a fire risk assessment alone can provide.
The managing agent's position under the Regulatory Reform (Fire Safety) Order 2005
Under the Regulatory Reform (Fire Safety) Order 2005, the responsible person for the common parts of a residential block — which in a managed building will typically be the managing agent acting on behalf of the freeholder or residents' management company — is required to carry out or commission a suitable and sufficient fire risk assessment and to implement the significant findings of that assessment. Where the assessment identifies deficiencies in compartmentation, those deficiencies represent findings that need to be acted upon; the responsible person cannot note them and move on without a programme in place to address them.
The Fire Safety Act 2021 extended the scope of the FSO to make explicit that the structure, external walls, and flat entrance doors of multi-occupied residential buildings fall within the responsible person's duties, which means that compartmentation — including the condition of flat entrance doors and the integrity of floor and wall construction — is squarely within the scope of what a managing agent is responsible for. Enforcement action by fire and rescue services in recent years has increasingly focused on whether responsible persons have acted on the findings of assessments rather than simply commissioned them, and compartmentation deficiencies have featured in a number of prosecution cases. Our managing agents page sets out in more detail how we work with agents to manage ongoing fire safety obligations across their portfolios.
What a fire risk assessment will and will not tell you about compartmentation
It is worth being clear about the scope of a fire risk assessment in relation to compartmentation, because there is sometimes a misunderstanding about what the assessment is examining and what it can reasonably conclude. A fire risk assessment carried out in accordance with the relevant guidance — PAS 79-1 for residential buildings — will identify observable deficiencies: visible penetrations that are unsealed or inadequately sealed, fire doors that are defective or missing components, service risers that are open at floor levels, and so on. What it will not do, and what it is not designed to do, is provide a comprehensive survey of concealed compartmentation within the building fabric, since that requires intrusive investigation beyond the scope of a risk assessment and into specialist compartmentation survey work.
For many buildings, a fire risk assessment will be sufficient to identify the main areas of concern and to form the basis of a remedial programme. For buildings where there is reason to believe that concealed compartmentation may be significantly compromised — older blocks with a long history of services modifications, buildings that have undergone conversion or change of use, or buildings where previous surveys have revealed widespread deficiencies — a more detailed compartmentation survey may be warranted as a follow-on piece of work. The fire risk assessment is the starting point rather than the ceiling of what can be done, and a good assessor will be clear about what has been examined and what has not, so that the managing agent understands what the assessment is and is not covering.
If your fire risk assessment has identified compartmentation deficiencies and you are uncertain about the scope of the remedial works required, or about how to prioritise them, that is a conversation worth having with your assessor before commissioning works. The cost of unnecessary remediation in a large block can be significant, and so can the cost of failing to address the deficiencies that present the greatest risk to occupants.
Common compartmentation deficiencies found in residential blocks
The following are among the most frequently identified compartmentation issues in the blocks we assess across Cheshire, the Wirral, and the wider North West. None of them is unusual, and most are straightforwardly remediable once identified, but all of them represent a reduction in the passive fire protection that a building's occupants are depending on.
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Unsealed service penetrations
Cables, pipes, and conduits passing through fire-resisting walls or floors without appropriate intumescent or fire-stopping materials, most commonly found in plant rooms, meter cupboards, and communal ceiling voids where successive contractors have made modifications without reinstating the compartment boundary.
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Defective flat entrance doors
Missing or damaged intumescent seals, absent cold smoke seals, doors that do not close and latch under their own weight, non-compliant glazing, or ironmongery that has been changed since the door was installed and tested as an assembly. A fire door inspection will assess each of these components systematically across every door in the block.
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Open service risers
Vertical ducts carrying services through multiple floors that are not sealed at each floor level, allowing smoke and fire to travel rapidly through the building via what is effectively a chimney running its full height.
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Compromised ceiling voids
Suspended ceilings that have been disturbed by maintenance works and not reinstated to their original specification, or where the ceiling tiles are not of a fire-resisting type, allowing smoke to accumulate and spread in the void above the finished ceiling line.
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Inadequate firestopping around structural openings
Openings created during the building's life for new services, access panels, or structural modifications that have been closed with non-fire-rated materials or left partially open, often concealed behind decorative finishes that make them difficult to identify without an intrusive inspection.
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Communal door deficiencies
Fire doors to plant rooms, bin stores, stairwells, and other communal areas that are propped open, have had their self-closing devices removed, or have been replaced with non-fire-rated alternatives at some point in the building's history, often without the managing agent's knowledge.
What managing agents should do when compartmentation deficiencies are identified
The first step is to ensure that the fire risk assessment report is clear about the nature and location of each deficiency identified, and that the recommended actions are prioritised in a way that reflects the relative risk each one presents. A flat entrance door with a missing intumescent seal on a floor served by a stay-put evacuation strategy is a different order of concern from an unsealed cable penetration in an external plant room, and the remedial programme should reflect that distinction rather than treating all findings as equivalent items on a list to be worked through in sequence.
The second step is to instruct a competent contractor to carry out the remedial works, which in the case of firestopping and fire door repairs means a contractor who can demonstrate appropriate qualifications and, where the specification of the works requires it, third-party accreditation. The use of unqualified contractors to carry out fire door or firestopping works is a risk in itself, since poorly executed remediation can give a false impression of compliance while leaving the underlying deficiency unaddressed or, in some cases, making the position worse than it was before.
The third step — and one that is frequently overlooked — is to document the works carried out, retain evidence that they have been completed to the required standard, and update the fire risk assessment accordingly. The responsible person's obligation under the FSO is a continuing one, and the ability to demonstrate that identified deficiencies have been addressed, and that the building's fire risk assessment reflects the current condition of the premises, is part of what fire and rescue services will look for in the event of an inspection. Our managing agents clients typically find it useful to maintain a single record of all outstanding fire safety actions across their portfolio, updated as works are completed, so that the position across multiple buildings is visible in one place rather than scattered across individual assessment reports.
Compartmentation concerns in a building you manage?
We carry out fire risk assessments and fire door inspections for managing agents across Chester, Cheshire, the Wirral, and the wider North West. If your current assessment has identified compartmentation deficiencies, if you are not sure whether your assessment is still current, or if you have recently taken on a building and need a fresh assessment, please get in touch.