BS EN 1991-1-2 and BS 7974, UK wide
Structural Fire Engineering
A tabulated fire resistance period tells you how long an isolated element survived a furnace test, not how your frame behaves in a real fire in a real building. AL23 Safety provides structural fire engineering, from checking a prescriptive specification to a full performance based analysis under BS 7974, on projects UK wide.
What is structural fire engineering?
Whether the frame stands up, not whether a sample passed a furnace test
Structural fire engineering is the analysis of how a structure carries load while it is heated and while it cools again afterwards. It asks three questions in order. What fire could occur in this compartment. What temperatures does that fire impose on these members. Does the structure retain enough capacity, stability and continuity to meet the objective set for it.
That objective is not always the same. On many buildings it is the tabulated period in Approved Document B. On complex buildings it can be survival of complete burnout of the movable fire load, which is a more demanding target than any nominal test period. The work sits alongside the wider fire engineering strategy rather than replacing it because a structure that stands up in a building nobody can escape from has solved the wrong problem.
Who needs one
Where the tabulated answer runs out
Large or irregular compartments
where the uniform burning assumption behind the standard fire curve does not hold, such as open plan offices, atria and transfer level plant rooms.
Long span and transfer structures
where the failure of a single member has consequences well beyond its own bay.
Car parks
, particularly open sided and undercroft parking, where the fire load and the fire behaviour have both changed.
Buildings seeking a reduction or a rearrangement
of prescriptive fire protection, for example exposed steel for architectural reasons.
Higher-risk buildings
going through Gateway 2, where the Building Safety Regulator applies multidisciplinary scrutiny to the structural fire case.
Refurbishment of existing frames
where the original protection is unknown, damaged or no longer matches the intended use.
Existing buildings after a fire
, where the residual capacity of heated members has to be assessed before reoccupation.
Timber and mass timber structures
, where charring rate, encapsulation and self-extinguishment all have to be argued rather than assumed.
The regulations that apply
Your legal framework, in plain terms
The Building Regulations 2010 set two separate requirements that meet in this work. Requirement B3 of Schedule 1 deals with internal fire spread and the stability of the building for a reasonable period. Requirement A3 deals with disproportionate collapse. Approved Document B and Approved Document A are the statutory guidance to those requirements, which means they carry evidential weight without being law. The Building Regulations etc. (Amendment) (England) Regulations 2023 inserted Part 2A, regulations 11A to 11Q, into the Building Regulations 2010 with effect from 1 October 2023 and those competence duties apply to all building work rather than only to higher-risk buildings.
Requirement B3
The building must be designed and constructed so that its stability is maintained for a reasonable period in the event of fire.
Requirement A3
The building shall be constructed so that in the event of an accident it will not suffer collapse to an extent disproportionate to the cause.
Regulations 11F to 11I
Competence means skills, knowledge, experience and behaviours for an individual and organisational capability for an organisation. It must be verified before appointment. A person must not accept an appointment beyond their competence.
BS EN 1991-1-2 with its UK National Annex
The Eurocode part covering actions on structures exposed to fire, which supplies the thermal actions used in analysis.
BS 7974:2019
The code of practice for applying fire safety engineering principles to the design of buildings, which frames the qualitative design review, the quantitative analysis and the assessment against acceptance criteria.
Two things we will not tell you. We do not publish an edition date for Approved Document A because the current amendment status of that document and the outcome of recent work on A3 could not be confirmed against a primary source. We also do not publish a transition date for the second generation structural Eurocodes. CEN has published EN 1991-1-2:2024 but the UK adoption date, the National Annex date and the withdrawal date for the 2002 text are not something we are prepared to state as fact. Design to the version your approving body will accept, confirmed in writing at the outset.
Prescriptive periods or a performance based analysis
Two legitimate routes, with very different burdens of proof
The prescriptive route uses the tabulated minimum periods of fire resistance in Approved Document B, set by building use and height. Research published by the Building Safety Regulator describes that range as 15 to 120 minutes, running from 15 minutes for open sided car parks up to 30 metres to 120 minutes for residential buildings of 8 to 50 storeys. Performance is expressed against three criteria under the BS EN 13501-2 classification, R for loadbearing capacity, E for integrity and I for insulation. The route is quick, it is well understood and building control is comfortable with it.
The performance based route replaces the nominal period with a calculated demonstration. The standard time temperature curve used in furnace testing to BS EN 1363-1:2020 does not represent real fire behaviour and has no decay phase once the fuel is consumed. Parametric fire curves in Annex A of BS EN 1991-1-2 vary with compartment geometry, opening factor, fuel load and the thermal properties of the boundaries. They also include a cooling phase. They suit relatively small, well ventilated compartments. Travelling fire models are used where a compartment is too large for uniform burning to be credible, with a near field of intense burning moving across the floor plate while a far field of hot gases affects the rest.
Be clear about the status of that last method. Travelling fire methodologies are research derived. They are not codified in BS EN 1991-1-2 and they are not in Approved Document B. No UK standard prescribes them. Their use is an engineering judgment that has to be justified in writing and, in practice, independently reviewed.
The honest constraint
A performance based structural approach is not something you adopt and then present. It has to be agreed with the approving body at the qualitative design review stage of BS 7974, before the analysis is run. The QDR is where the fire scenarios, the acceptance criteria and the modelling assumptions are set. If building control or the Building Safety Regulator does not accept them there, the calculation that follows is worthless however good it is. We get that agreement recorded before we start modelling and we tell you plainly when we think the prescriptive route is the better commercial decision.
What the service covers
The full route, from thermal action to residual capacity
- Qualitative design review under BS 7974:2019, run as a minuted workshop with the design team and the approving body, fixing objectives, fire scenarios and acceptance criteria.
- Quantitative structural response analysis under PD 7974-3:2019, the structural sub-system of the BS 7974 framework.
- Thermal action modelling using the standard curve, parametric curves from Annex A of BS EN 1991-1-2 or travelling fire models where the compartment justifies it.
- Heat transfer analysis to member temperatures, then mechanical response, using the fire parts of the structural Eurocodes for concrete, steel, composite, timber, masonry and aluminium.
- Fire protection specification for steelwork by section factor and limiting temperature, covering reactive thin film intumescent coatings, non-reactive boards and sprays, flexible blanket systems, concrete encasement and blockwork infill between flanges.
- Review of applied protection against the BS EN 13381 series of assessment standards, together with the assessment report behind the manufacturer's thickness tables.
- Concrete design by the tabulated data, simplified methods or advanced methods of BS EN 1992-1-2, with explicit attention to spalling risk in high strength and high moisture content mixes and to polypropylene monofilament fibre mitigation.
- Disproportionate collapse review against Requirement A3, using the consequence class system derived from BS EN 1991-1-7, from horizontal ties at Class 1 through to systematic risk assessment at Class 3.
- Assessment of fire damaged structure, including residual capacity and the reinstatement specification that follows.
- Coordination with the fire strategy, the compartmentation design and the external wall build up so the structural case and the escape case rest on the same fire scenarios.
Our process
Agree the rules, then do the arithmetic
- 01
Scoping
We establish what the structure has to achieve, what the client and the insurer expect and whether the prescriptive route already answers it. Sometimes the honest advice is that it does.
- 02
Qualitative design review
We convene the QDR, record the fire scenarios, the trial designs and the acceptance criteria, then obtain the approving body's position in writing.
- 03
Analysis
We run thermal and mechanical analysis to the agreed scenarios, with a sensitivity study on the assumptions that drive the answer.
- 04
Specification
We convert the result into a protection specification, section by section, that a contractor can price and an inspector can check.
- 05
Support through approval
We answer building control and regulator questions and we support independent peer review where the complexity of the approach makes it sensible.
What you get
Documents that survive scrutiny two years later
- A qualitative design review report with the agreed fire scenarios, acceptance criteria and the record of who agreed them.
- A structural fire analysis report setting out the thermal actions, the heat transfer method, the mechanical model, the results and the sensitivity study.
- A fire protection schedule by member, giving section factor, limiting temperature and required protection thickness or specification.
- A disproportionate collapse note stating the consequence class, the measures adopted and how the fire case and the accidental action case have been reconciled.
- A departures and assumptions register, written so that a reviewer can see exactly what the answer depends on.
- Where relevant, a residual capacity assessment and reinstatement specification for fire damaged structure.
What we need from you
The structure as designed and the fire load as it will really be
- Structural drawings, member schedules and design loading, plus the structural designer's calculations where a check is required.
- Architectural plans and sections with compartment lines, opening sizes and ventilation.
- The intended use of each space and any known fire load, including racking heights and stored commodity where the building is industrial.
- The fire strategy at its current revision or an instruction for us to develop it.
- The identity of the approving body and any pre-application correspondence already exchanged.
Why AL23 Safety
Analysis you can defend, not analysis that flatters the design
Accountable
If the modelling does not support the reduction you were hoping for, we say so and set out what would. We do not tune assumptions until the answer arrives.
Expert and chartered
Led by a Chartered Building Engineer and Health and Safety Professional working to current standards and legislation. There is no statutory register of structural fire engineers so we set out our competence evidence and let you verify it, as regulations 11F to 11I expect.
One team, three disciplines
Fire engineering, fire safety and health and safety in-house, which means the structural case and the evacuation case are built on one set of fire scenarios.
UK wide
We support structural fire engineering on projects across the UK from our Manchester base.
Before you commit to exposed steel
A short conversation now is cheaper than a rejected submission
Tell us the frame, the compartment sizes and what the architect wants to leave visible. We will tell you whether the analysis is likely to support it.
Common questions
Answers, up front
Cannot see your question? Get in touch and we will answer it directly.
Contact usSometimes it does. Sometimes it increases the protection you need. A calculated approach can show that a structure survives burnout of the movable fire load, which may justify less applied protection than the tabulated period implies. It can equally show that a long span transfer structure needs more. The analysis has to be agreed at the qualitative design review stage before anyone relies on the outcome.
For most buildings, yes. Approved Document B is statutory guidance and following it is normally accepted as demonstrating compliance. It is worth knowing that BS 9991:2024 and BS 9999:2017 are not statutory guidance and have no deemed to satisfy status so choosing a British Standard route is a design decision that has to be justified rather than a default.
Research published on 22 December 2025, "Fire safety: structural fire resistance and fire separating elements", found that standard testing exposes isolated elements to a defined curve and does not account for whole system behaviour or the cooling phase. It also found that smouldering combustion cannot be evaluated by standard tests alone. It states that the underpinning basis for 15 minutes fire resistance for open sided car parks up to 30 metres is no longer valid and recommends the provision be revisited. It is research rather than guidance so nothing has changed in law. Read alongside the joint review of Approved Document B consulted on between 25 March and 1 July 2026, with a target implementation date of 2 September 2029, it tells you where the direction of travel points.
Not directly. A3 is an accidental action provision. Fire induced disproportionate collapse is not covered by the A3 guidance and Approved Document B's tabulated periods are aimed at the fire scenario. The two regimes have to be reconciled by the designer rather than assumed to align. That reconciliation is one of the reasons performance based structural work gets commissioned.
The variables are the number of compartments to be analysed, whether the frame is steel, concrete, composite or timber, whether travelling fire modelling is needed and how much iteration the design team expects. A single compartment parametric study is a very different piece of work from a whole building travelling fire analysis with a peer review attached. Send us the drawings and the fire strategy and we will scope it properly before quoting.
The approving body, meaning building control or the Building Safety Regulator where the building is higher-risk. Their position should be recorded at the qualitative design review rather than sought at the end. On complex or novel approaches expect them to want independent review as well, which is normal and which we plan for rather than resist.
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