Cause, origin and evidence, UK wide
Fire Investigation
After a serious fire the physical evidence starts disappearing within hours, usually to people acting in good faith who are trying to make the building safe or get the business running again. Whoever clears the scene first decides what the rest of you get to prove. AL23 Safety scopes, manages and reports fire investigations for building owners, employers, insurers and their solicitors UK wide.
What is a fire investigation?
Working out where it started, what started it and what that means for you
A fire investigation determines the origin of a fire, then its cause, then the circumstances that brought the ignition source and the first material ignited together. Origin comes first. A hypothesis about cause formed before the area of origin has been established is a guess with a report cover on it.
There is more than one investigation and they are not doing the same job. Knowing which one you are in and which ones you are not part of, decides what you should be doing in the first 48 hours.
The three kinds of investigation
Same fire, three different purposes
Fire and rescue service investigation
Section 45 of the Fire and Rescue Services Act 2004 gives an authorised officer power to enter premises to obtain information needed for the authority's functions or to investigate the cause of a fire or how it spread. There is no entry by force and no demand for admission to a private dwelling without 24 hours' written notice, though a justice of the peace can issue a warrant. The purpose is the authority's statutory functions, community risk reduction, national incident statistics and identifying failures that feed enforcement under the Fire Safety Order. It is not primarily an evidential exercise for a civil court and you should not assume its report will answer your questions.
Police investigation
Engaged where arson, other criminality or a death is suspected. Arson is criminal damage by fire under the Criminal Damage Act 1971, with arson endangering life as the aggravated offence. Where there is a death the coroner has jurisdiction under the Coroners and Justice Act 2009 and may direct a post-mortem and an inquest. Forensic work is subject to the statutory Forensic Science Regulator Code of Practice issued under the Forensic Science Regulator Act 2021. Version 1 came into force in October 2023 and version 2 was published on 20 March 2025. Expert evidence in criminal proceedings is governed by Part 19 of the Criminal Procedure Rules.
Private, insurer led or civil investigation
Instructed by an insurer, a loss adjuster, a forensic firm or a party's solicitors. The purposes are policy liability and indemnity, subrogated recovery against a third party, product liability and the defence of a claim. A private investigator has no statutory power of entry. Access rests on the occupier's consent or on a court order and a scene under police control needs police agreement. Expert evidence is governed by CPR Part 35 and Practice Direction 35, with the overriding duty to the court taking precedence over any duty to the party paying the fee.
Where several parties have an interest, a joint scene examination protocol is normal. Agreed sampling, agreed photography and agreed preservation so that nobody can later argue that evidence was destroyed unilaterally.
Who needs one
Anyone whose position depends on why the fire happened
- Building owners and employers facing an HSE or fire and rescue authority investigation after a fire.
- Insurers and loss adjusters deciding indemnity or considering a subrogated recovery.
- Policyholders where an insurer is relying on a breach of warranty, for example a hot work warranty or an alarm set condition.
- Manufacturers, distributors and installers named as the likely source of ignition.
- Solicitors instructing on a civil claim in negligence, breach of contract, nuisance or under the Defective Premises Act 1972.
- Duty holders who need to know what actually failed before they rebuild it the same way.
- Responsible persons whose fire risk assessment is about to be examined by someone hostile.
The standards position, stated honestly
There is less British Standard here than people assume
If you have been told that BS 8593 is the fire investigation standard, that is wrong and it is worth correcting early. BS 8593:2017 is the code of practice for the deployment and use of body worn video. It was published on 30 June 2017 and withdrawn on 12 December 2025. It has nothing to do with fire investigation.
We could not identify any current British Standard specific to fire investigation and we will not assert that one exists. The accepted reference is American and international: NFPA 921, "Guide for Fire and Explosion Investigations", which is routinely relied on by UK forensic investigators and in UK courts. It sets out the systematic application of the scientific method. Recognise the need, define the problem, collect data, analyse it, develop a hypothesis, test the hypothesis, then select a final hypothesis. It defines the cause classifications of accidental, natural, incendiary and undetermined and it warns explicitly about expectation bias and confirmation bias. Its companion, NFPA 1033, covers professional qualifications for fire investigators. We name the edition of each in the report rather than on this page because editions are revised and quoting a stale one is the sort of detail that gets picked apart in cross-examination.
On competence, the UK Association of Fire Investigators is the UK chapter of the International Association of Arson Investigators and references the IAAI Certified Fire Investigator, FIT and ECT programmes. It maintains a code of practice for investigators of fires and explosions for the justice systems in the UK, with version 3 out for comment as at January 2026. Confirm which version has been published before anyone cites it in a report.
Cause and origin and how it is actually done
Origin first, then cause, then testing
The evidence set is physical before it is anything else. V-patterns, U-patterns and truncated cone patterns. Depth of char and calcination of plasterboard. Arc mapping to locate the earliest electrical faulting. Heat and smoke horizons. Direction of collapse. Melting temperatures of materials used as a rough thermometer. Then the documentary and electronic material: witness accounts, CCTV, alarm and sprinkler activation data and building management system logs.
Hypothesis testing is not optional. A hypothesis that has not been tested against the physical evidence and against the alternatives, is an opinion rather than a finding. "Undetermined" is a legitimate and often correct conclusion. The investigator who reaches a definite cause on inadequate evidence is the one who is dismantled in the witness box. Concluding an incendiary cause purely by eliminating accidental ones, sometimes called negative corpus reasoning, is discouraged by NFPA 921 and should be treated with suspicion wherever it appears in someone else's report.
Evidence preservation and continuity
The part that is lost in the first 24 hours and cannot be recovered
Scene control
Cordon the scene, restrict entry to those with a role, log every entry and exit and do not disturb the seat area during salvage or overhaul beyond what safety requires.
Continuity of evidence
Every exhibit needs a unique reference, the identity of the person who recovered it, the date, time and precise location of recovery and an unbroken record of every subsequent transfer, storage location and examination. A break in continuity is the standard route by which fire evidence is discounted.
Sampling for ignitable liquid residues
Nylon bags or clean metal cans, control samples from an unaffected area and disciplined avoidance of cross-contamination from equipment, clothing and vehicles. Analysis is normally by GC-MS in an accredited laboratory.
Documentation
Comprehensive photography and video before anything is moved, scale plans, contemporaneous notes and a record of the condition and position of every item removed.
Preservation of the failed component
Where the cause points at a product or an installation, the item itself is the case. It should be recovered, packaged and stored, not skipped with the rest of the debris.
Spoliation
Destroying evidence or allowing it to be destroyed, before other interested parties have had the chance to inspect will be held against the party responsible. The practical rule is simple. Do not clear a fire scene until every party on notice has inspected it or has declined in writing.
Forensic providers working to the criminal justice system are expected to hold accreditation under the Forensic Science Regulator's Code, ISO/IEC 17025 for laboratory testing and ISO/IEC 17020 for inspection. The exact requirement and commencement for fire scene examination specifically is something we confirm for your matter rather than assert here.
What the investigation feeds
Insurance, prosecution or a civil claim and they want different things
The insurance claim
Cause determines whether the peril is insured, whether an exclusion applies and whether a warranty has been breached. It also drives quantum, through the extent of fire, smoke and water damage. A cause finding of "electrical fault, precise mechanism undetermined" and a finding of "failure of a specific appliance" produce very different claims.
Subrogated recovery
Where cause points at a defective product, a negligent contractor or a failed maintenance regime, the insurer stands in the insured's shoes and pursues the third party. This is the commercial engine behind most private fire investigation and preservation of the failed component decides whether it is possible.
Prosecution
Two separate routes. Criminal prosecution for arson or manslaughter, brought by the Crown Prosecution Service. Regulatory prosecution under the Regulatory Reform (Fire Safety) Order 2005, brought by the fire and rescue authority or by the HSE on a construction site or under the Health and Safety at Work etc. Act 1974. Penalties for certain Fire Safety Order offences rose from level 3 to level 5, an unlimited fine, with effect from 1 October 2023. Our HSE enforcement support work picks up from there.
The civil claim
Negligence, breach of contract, breach of statutory duty, nuisance or a claim under the Defective Premises Act 1972, for which the limitation period was extended by section 135 of the Building Safety Act 2022 to 30 years retrospectively and 15 years prospectively. Expert evidence runs under CPR Part 35, which we also handle through expert witness services.
Our process
From the first call to a defensible report
- 01
Immediate advice
A call on the day, covering scene preservation, who to notify, what not to move and what to photograph before anyone else arrives.
- 02
Scoping and appointment
We define the question to be answered, agree the instruction and appoint the right specialist for the scene, whether that is a certificated fire investigator, a forensic electrical engineer or a materials laboratory.
- 03
Scene examination
Systematic origin and cause work, joint examination protocol where other parties are involved, full documentation and exhibit recovery.
- 04
Analysis and hypothesis testing
Laboratory results, alarm and BMS data, maintenance and inspection records and testing of each competing hypothesis.
- 05
Report
A written report suitable for its purpose, whether that is a claim file, an internal review or CPR Part 35 compliant expert evidence.
We scope the work, appoint the right specialist, interpret the results and turn them into an action plan you can actually deliver. Where the finding shows a management failure rather than a product failure, the fix belongs in your fire risk assessment and your maintenance regime and we take it there rather than leaving it in the report.
What you get
Evidence, hypotheses and an honest conclusion
- A cause and origin report setting out the evidence, the hypotheses considered and the reasons for accepting or rejecting each one.
- An exhibit schedule with continuity records for every item recovered.
- A photographic and plan record of the scene as found.
- A findings note separating what is established, what is probable and what remains undetermined.
- Where instructed, a CPR Part 35 compliant expert report with the statement of truth and declaration.
- A remedial action plan where the investigation exposes a live risk in a building still in use.
What we need from you
Early notice and access to the scene
- Early notification. Hours matter here in a way they do not on most instructions.
- Access to the scene or the contact details of whoever controls it.
- The fire risk assessment, maintenance records, permits, alarm logs and any recent inspection reports.
- Names of every other party with an interest, including insurers, contractors and manufacturers.
- Any statement, note or photograph already taken by your own people however rough.
Why AL23 Safety
Undetermined when the evidence says so
Accountable
If the evidence does not support a cause, we record it as undetermined. We will not sign an opinion that we cannot defend under cross-examination.
Expert and chartered
Qualified, chartered professionals, with the fire engineering and fire risk assessment knowledge to read a building as well as a fire scene.
Practical, not just compliant
An investigation that does not change what happens in the building afterwards has failed, whatever the claim outcome. Our incident investigation work is built on the same principle.
UK wide
We respond to incidents across the UK and work alongside your insurer, loss adjuster and solicitors.
Call us before the scene is cleared
The first day decides what can be proved
If there has been a fire, phone us before anyone starts clearing. Even a short conversation about preservation and notification protects your position at no cost.
Common questions
Answers, up front
Cannot see your question? Get in touch and we will answer it directly.
Contact usSometimes and not always in the detail you need. A fire and rescue service investigation exists for the authority's own statutory functions, national statistics and fire safety enforcement. It is not conducted to answer your insurer's questions. If indemnity, recovery or liability is in issue, commission your own investigation and do it early.
Not until every party with an interest has inspected the scene or declined in writing. Clearing early is the fastest way to lose a subrogated recovery or a defence and the destruction will be held against whoever authorised it. Make the building safe by all means and log everything you have to move.
We could not identify a current British Standard specific to fire investigation so we will not tell you there is one. NFPA 921 is the accepted international reference and is relied on in UK courts. If someone quotes BS 8593 at you, that standard is about body worn video and was withdrawn in December 2025.
Not automatically. A report written for a claim file and a CPR Part 35 expert report have different requirements, including the expert's declaration and the overriding duty to the court. Tell us at instruction which one you need. Writing to the higher standard from the start is cheaper than converting later.
Cost is driven by the size and condition of the scene, the number of parties involved, whether laboratory analysis is needed and whether the report has to be Part 35 compliant. A single unit with a clear origin is a very different job from a multi-occupied building with three interested insurers. Attendance can usually be arranged quickly. Call us with the location and the date of the fire and we will tell you what is realistic.
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