Fire Alarm Design Guide
Design and verify fire detection and alarm provisions to BS 5839-1:2025 and the wider UK framework. Every claim is referenced to a clause, so you can answer the question "why is this device here" cross referenced to a standard.
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A live summary of your design so far, compiled from what you entered through the stages. It updates every time you return here.
Check a design somebody else proposed, a consultant's or a tenderer's. Pick the item, enter the proposed values in the structured fields, and every verdict comes back cross referenced to the clause that applies. The checks are structured on purpose: the same verified calculations as the design stages, never free text interpretation.
Guidance tool built on a cited rule base. It supports, and never replaces, the judgement of a competent fire alarm designer and the requirements of the project fire strategy. Verify final designs against the current standards.
- 732rules written from the standards, each cited to its clause
- 3,454 + 3,473scenarios in the free and subscriber tests on 0.28.2, no findings
- 66 of 66comparison checks between the live tool and the independent reference calculation
- 732 of 732rules read back word for word against the source
- Last reviewed
- September 2026
- Data basis
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732 rules written from those standards in our own words, each referenced to the clause it came from: 151 from BS 5839-1:2025, 116 from HTM 05-03, 65 from BS 5839-6, 54 from BS 7273-6, 51 from BS 5839-8, 48 from BS 7827, 39 from BS 9991, 30 from BS 8300-2, 28 from Approved Document B, 24 from BS 5839-9, 24 from BS 7273-4, 21 from BS 8519, 18 from BS 8629, 16 from BS 5839-3, 15 from BS 9999, 8 each from BS EN 54-23 and the FIA visual alarm guide, 6 from BS 7346-7, one rule that cites three of the BS 5839 parts together, and 9 from manufacturer guidance, trade correspondence and PD project precedent, each flagged as such where it is used. HTM 05-03 and Approved Document B are Crown copyright, reused under the Open Government Licence v3. The standards themselves are not reproduced here: to read a clause in full you need your own copy.
- Validated against
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15/09/2026 (0.28.1 and 0.28.2): the standards references were read back against the current editions. Where a rule quotes another standard's reference to an earlier edition of BS 5839-1, the reference is kept as that standard prints it and the BS 5839-1:2025 clause is added beside it, for example "BS 5839-1:2017 Clause 45 (now BS 5839-1:2025 Clause 43)", each read from the library copies of the 2013, 2017 and 2025 editions; the HTM 05-03 references state the 2017 edition they cite. On the cables step, emergency lighting fed from a central power supply system is referred to BS 5266-1:2025 8.2.2, "Standard 60" (60 min) or "Enhanced 120" (120 min), where the note had given the fire alarm equivalences of 30 min and 120 min. The wording of the rule texts and the tool was revised in plain UK English, with the meaning unchanged, and four lines that quote a standard word for word now show the quotation in quotation marks, one of them corrected to the clause exactly (BS 8300-2:2018 20.7.4). Two new automated checks read every edition reference and the wording of every program file, in the tool and in the report, and fail on the earlier builds; every release check, the 25 hand-computed cases, the 66 comparison checks and the full set of browser tests in both tiers (3,454 free and 3,473 subscriber scenarios) were re-run on 0.28.2 with no findings; no category, figure or verdict changed; verified live after upload. 10/09/2026 (0.28.0): three profile inputs that only a minority case reads were moved to their case. The number of storeys, read only by a phased evacuation strategy, shows only for one; a property protection category can now be declared alongside a life safety category, so a strategy declaring L2 and P1 is recorded as L2/P1 in the design basis with the P1 coverage lines added and labelled; and a zone left without a search distance prints a request for it instead of a silent default (BS 5839-1:2025 clause 13). The automated tests gained checks for all three, and their links to the fields of the tool were rebuilt to find each field by its label, after the new control was found to shift the earlier position-based links without any warning; every release check, the 25 hand-computed cases, the 66 comparison checks and the full set of browser tests in both tiers (3,454 free and 3,473 subscriber scenarios) were re-run on 0.28.0 with no findings, and the same tests fail on the 0.27.0 build; no rule, limit or verdict changed; verified live after upload. 10/09/2026 (0.27.0): a check across every PD tool for a control asked of every user that only a minority case reads. Five were found and each now shows only for its case: on the zoning step the open plan column only on a call points only zone, and the addressable with location text question only once a search distance exceeds the limit; on the alarm devices step the means of warning only for a bedhead space, a phased evacuation strategy or a venue, opening on voice alarm where it is mandated; on the cables step the two enhanced cable triggers, remote areas that stay occupied and a risk assessment determination, under an exceptions section that is closed until opened, with the standard cable verdict now stating the basis it used; and the networks and radio notes naming their condition so the design basis never reads them as unconditional. The automated tests gained a check that each control is hidden for the case that does not read it and shown for the case that does, that the exceptions section is closed until opened and its trigger works once opened, that the standard basis line prints, and that every networks note states its condition; every release check, the 25 hand-computed cases, the 66 comparison checks and the full set of browser tests in both tiers (3,449 free and 3,465 subscriber scenarios) were re-run on 0.27.0 with no findings, the six controls listed since 0.15 as possibly having no effect were cleared along with the open plan column, and the same tests fail on the 0.26.0 build; no rule, limit or verdict changed; verified live after upload. 10/09/2026 (0.26.0): a check across every PD tool for a figure presented as the designer's that the designer never entered. The design basis was found to work every step the designer had not opened from the tool's default figures and to print the results as the design basis: a detector grid for a default room, a call point verdict for a default route, a visual alarm device pass for a device nobody had declared, a battery capacity from default currents. A step that was not opened is now recorded in the design basis as not entered, with the inputs to enter named, and is never worked from defaults; the cables and containment step is worked from the project profile with its two assumptions stated; steps that take no input are worked from the profile as before. Visual alarm devices are declared on the alarm devices step before a coverage verdict prints. The automated tests gained a check, run first on a fresh page, that every input-taking step shows the not-entered line and no verdict until it is opened, that no cause and effect table exists before the interfaces step is opened, that no visual alarm verdict prints for an undeclared device, and that an opened step is still worked in full; every release check, the 25 hand-computed cases, the 66 comparison checks and the full set of browser tests in both tiers (3,548 free and 3,564 subscriber scenarios) were re-run on 0.26.0 with no findings, and the same tests fail on the 0.25.2 build; no rule, limit or verdict changed; verified live after upload. 04/09/2026 (0.25.2): the same check completed on the two height fields the first pass could not reach. The ceiling height, asked on the detector selection and siting steps, is the height of the ceiling above the floor, which BS 5839-1 Table 3 limits, not the storey height and not the height of the detector below the ceiling (clause 21.2.4); neither field said so and the siting field had no help. The visual alarm device mounting height is the installed height of the device, which BS EN 54-23 clause 4.3.1 rates a device to, not the figure in the category code; the field had no help and the verdict did not print the height it used. All three fields now show that help and the visual alarm verdict prints the mounting height it was assessed at. Every release check, the 25 hand-computed cases, the 66 comparison checks and the full set of browser tests in both tiers (3,554 free and 3,557 subscriber scenarios) were re-run on 0.25.2 with no findings; no rule, limit or verdict changed; verified live after upload. 04/09/2026 (0.25.1): a check of whether every input the standard names by a term of art is defined in the tool, printed back and questioned where a wrong entry can be seen. The total floor area on the project profile had no help, and the BS 5839-1 clause 12 zone limits apply to the building total, not to one storey. The field now says so, and the zone step prints a check where the building total entered is below the zones already entered, which cannot be the whole building. Every release check, the 25 hand-computed cases, the 66 comparison checks and the full set of browser tests in both tiers (3,554 free and 3,557 subscriber scenarios) were re-run on 0.25.1 with no findings; no rule, verdict or clause changed; verified live after upload. 03/09/2026 (0.25.0): a new audit of whether every answer is reached through the input the standard derives it from. Eight defects were found: standby battery capacities were not computed for emergency voice, voice alarm and Grade A systems although the currents were asked for; a Grade A standby was printed as 24 h from an assumed attended premises; a beam or aspirating detector was passed against the Table 3 ceiling limit without asking the height; every point heat detector was treated as Class A1; a residential care home took the HTM complex hospital cable rule; every healthcare space took the HTM 45 dB(A); a design check run could replace the drawing in the design report; and a blank input could produce a figure. All eight are corrected in 0.25.0 with new questions for the missing inputs, the automated tests gained a sweep for this kind of defect, and the full set of browser tests was re-run in both tiers (3,554 free and 3,557 subscriber scenarios, 66 comparison checks) with no findings; verified live after upload. Claims audit 11/08/2026: 192 statements shown to users were extracted from the code and checked one by one against the rule each cites, and every rule reference was verified against the rule base with none missing. Scenario audit 10/08/2026: 7,069 input combinations were driven through the tool and checked against independently written calculations, 3,536 in the subscriber view and 3,533 in the free view, covering every building use, evacuation strategy, risk profile, premises class and declared category, room and corridor geometry from zero to 1,000 m, ceiling heights across the Table 3 limits, all 28 BS 8519 Table 1 systems, the battery load matrix, and cause and effect matrices from 1 to 40 levels. Thirteen defects were found and corrected in that audit, every one of them in how a result was adjudicated, cited or presented rather than in a calculation. Source read-back, completed 11/08/2026: all 732 rules have been read back word for word against the source itself rather than against our own notes, from the clause-cited answers in the tool through every figure, every prose rule, the commentary and guidance, and the PD project precedents; the final two were written directly from their sources the same day to close coverage gaps found in the reading. The read-back found 329 defects. Almost every one was a missing qualifier rather than a wrong number: an exception the standard allows, a condition that limits when a figure applies, a relief written as a prohibition, or a note's example presented as the requirement. All 329 are corrected and included in release 0.22.0. The rule base also increased from 714 to 732 during the reading, as recommendations that had never been turned into rules were written from source and rules that covered several clauses at once were split so each cites exactly its own clauses. Every calculation is compared with an independent reference calculation of the same rule, written in Python: 25 cases computed by hand (battery Annex E sizing, detector spacing and coverage, corridor intervals, zone limits, call point travel, sound levels, visual alarm coverage, cable category) all match, and 66 comparison checks, re-run in the browser on every release, confirm that the live tool returns what the reference calculation returns. Detector spacing reproduces the Apollo pocket guide layout. Two real project fire strategies were used as the reality check on the workflow. The full set of browser tests was re-run on 12/08/2026 at the 0.24 interface releases: 3,533 free and 3,536 subscriber scenarios and all 66 comparison checks, both tiers, with no new findings. They were re-run again on 02/09/2026 after the 0.24.3 wording revision: every release check, the 25 hand-computed cases, the 66 comparison checks and the full set of browser tests in both tiers, with no new findings; no rule, verdict or clause changed.
- Guidance for a competent designer. It does not replace the project fire strategy.
- The system category comes from the fire strategy or the enforcing authority. The guide verifies a category, it does not set one.
- Detector siting covers flat and pitched ceilings, corridors up to 2 m wide and the Table 3 ceiling limits. Beam, aspirating and void detection are advised on, not laid out.
- The cause and effect matrix is a starting point to agree with the fire engineer, not an issued matrix.
- Healthcare, venue and accessibility overlays apply where the project profile calls for them. For hospitals, read HTM 05-03 Part B alongside it.
- A declared BS 5839-1 category and a BS 5839-6 grade are not comparable. Where the two are mixed the guide states the mismatch and gives the requirement for the premises, without a pass or a failure.
- The voice alarm figures cover the alarm signal. Speech intelligibility is assessed separately to BS 5839-8.
- Free to use in the tool with every answer showing its clause: three anonymous sessions, then your email continues free use. The printed and saved design basis, the cause and effect matrix as a landscape PDF and the editable exports are part of the Engineering Toolkit.
What's changed
- Where a rule comes from another document (BS 5839-6, BS 9991, BS 9999, BS 5839-9, BS 7273-4, BS 7273-6, BS 5839-3, HTM 05-03 Part B, FSF 210 or the FIA guide) and that document refers to a withdrawn edition of BS 5839-1, the reference now reads as the document prints it with the BS 5839-1:2025 equivalent beside it, for example "BS 5839-1:2017 Clause 45 (now BS 5839-1:2025 Clause 43)". HTM 05-03 Part B references state the 2017 edition that HTM cites. The bedhead and insulation resistance comparison cites BS 5839-8:2023, BS 5839-9:2021 and BS 5839-1:2025 15.1.1. No design value, category or verdict changed
- Stage 12 BS 8519 cable categories: the note on the parenthesised categories now separates the systems. Fire detection and alarm standard fire resistance is roughly Category 1 (30 min) and enhanced roughly Category 3 (120 min); emergency lighting fed from a central power supply system is "Standard 60" (60 min, roughly Category 2) or "Enhanced 120" (120 min) to BS 5266-1:2025 8.2.2, where the note had given the fire alarm figures for both. The wording of the rule texts and the tool was revised in plain UK English, with the meaning unchanged: the starter fuse shall not clear the locked rotor current before 75% of the hot burn-out time (BS 8519 20.1); three lines that quote a standard word for word now show the quotation in quotation marks, and the BS 8300-2 20.7.4 dimmed cable line now quotes the clause exactly. No category, verdict, figure or clause reference changed
- The Storeys field on the project profile shows only under phased evacuation, the one case that reads it (the cause and effect matrix levels), and the design basis prints it only then. A detector zone with no search distance now prints a request for it, as every other blank input does. A property protection category declared alongside the life safety category, for example L2/P1, can be entered on the profile: the design basis names both, the property coverage is stated with the life safety coverage, and the Category P standby duration applies. No rule, limit or verdict changed
- Five controls that only a minority case reads now show only for that case. On the zoning step the open plan column shows only on a call points only zone, and the addressable with location text question only once a search distance exceeds the limit. On the alarm devices step the means of warning shows for a bedhead space, a phased evacuation strategy or a venue, and opens on voice alarm where it is mandated. On the cables step the two enhanced-cable triggers (remote areas that stay occupied, a risk assessment determination) sit under an exceptions disclosure, and the standard cable verdict states the basis it used. The networks and radio notes name their condition so the design basis never reads them as unconditional. No rule, limit or verdict changed
- A step that was not opened is no longer worked from the tool's default figures when the design basis is built. The report keeps every step, and an unopened step that takes inputs shows one line saying it was not entered and naming the inputs to enter; the cables and containment step is worked from the project profile with its two assumptions stated. Visual alarm devices are declared before a coverage verdict prints: the alarm devices step opens on none declared, and the category, room and mounting height fields appear when Provided is selected. No rule, limit or verdict changed
- The two ceiling height fields now say they take the height of the ceiling above the floor, not the storey height and not the height of the detector below it, and the visual alarm device mounting height field says it takes the installed height of the device, not the figure in the category code. The visual alarm verdict prints the mounting height it was assessed at. No rule, limit or verdict changed
- The total floor area field now says it is the whole building, every storey added together, and the zone step prints a check where the building total is below the zones entered. No category, limit or duration changed
- Every answer now comes from an input the standard names. Standby power sizes the battery for emergency voice communication, Grade A dwellings, voice alarm and Category P systems from the loads and conditions entered, and asks for them when they are blank instead of printing a figure. Detector selection asks the ceiling height, beam sensitivity and aspirating class before it applies the Table 3 limit; siting asks the heat detector class. Enhanced cables for a complex hospital apply only when the profile says it is one; the 45 dB(A) healthcare sound level applies only where patients need assistance to escape. The residential premises class starts unselected. Design Check runs no longer alter the design report
- The wording was revised in plain UK English: standards apply to a system, the design framework and the minimum that applies are named as such, plurals written out. No rule, verdict or clause changed
- On phones and narrow windows the siting and call point drawings now sit directly below their inputs, before the verdict lines, instead of after them. The call point arrangement selector shows its full text
- The manual call point step uses the same side by side layout as detector siting: inputs and verdicts on the left, the route drawing on the right, redrawing as you type. Its drawing title now fits the frame on two lines
- Navigation improvements: each step opens aligned to the module tabs and step list, Back and Next sit in the same place on every step, at the top and again after the results, and the project summary bar stays visible below the site menu. On a wide screen the detector siting drawing sits beside the inputs and redraws as you type. Drawing labels stay inside the frame and have a white background so they read clearly over the coverage circles
- Free use is now measured in sessions: three days of anonymous use, then your email continues free use with no password and no account. The Design Check module asks for your email from the first check. Every answer stays free in the tool with its clause; subscribers are unchanged
- Two rules written from source to close the last coverage gaps the read-back surfaced. BS 9991:2024 clause 46: firefighting shafts with firefighters lifts above 18 m (or basements below 10 m), two shafts where the area served is 900 m2 or more, and the fire main outlet distances that drive shaft placement. HTM 05-03 Part M: voice alarm consideration for atria holding significant numbers of the public, designed to BS 5839-8. The rule base is 732
- The last rule is read: FSF 210, the standby battery guidance, was in the library filed under its title, and every one of its nine values verified against it, including the simplified formula's de-rating factor of 2. The read-back now covers all 730 of 730 rules. The Category P standby condition also states its staffed-premises qualifier in full
- The source read-back is complete: 729 of 730 rules read word for word against their sources, from BS 5839-1 through the HTM 05-03 suite to the PD project precedents. One rule is held back until its reference document is obtained. Across the whole programme 328 defects were found and corrected, nearly all missing qualifiers or dropped exceptions rather than wrong numbers
- The source read-back finished its second band: every rule with a figure a reader can act on, 195 of them, read word for word against the published standard. That found 92 further defects, almost none a wrong number, nearly all a qualifier that had gone missing
- BS 7273-4 Annex B: where a door matches more than one description, the highest recommended category of actuation applies. Now stated on the hold-open, electronically locked and powered sliding door selections
- Two claims split from the clauses that did not state them. Approved Document B paragraph 0.9 is the permission to adopt an alternative standard, and it requires that standard's fire safety recommendations to be followed in their entirety
- Unit correction: the BS 5839-9 minimum for twisted-pair emergency voice communication cables is a cross-sectional area of 0.5 mm², not 0.5 mm (Clause 14)
- The intelligibility note now also cites BS 5839-8:2023 Clause 20.3.4, the recommendation it was already stating
- Risk profiles Ci1 and Ci2 state the requirement as a minimum Category L3 system to BS 5839-1, with automatic fire detection in each individual unit and voice alarm to BS 5839-8
- BS 5839-6 Table 1 splits dwellings into premises with no floor greater than 200 m² and premises above it, and nine of the ten classes differ between them. Only the smaller block was held, so a rented three-storey house over 200 m² came back Grade D1 where the standard gives Grade A. Both blocks are now held, and the premises list states which applies
- The BS 9999 minimum category separates the two requirements in Clause 15.2: Table 7 gives the minimum for the risk profile, and the text after it raises that to Category L3 for phased, staged or zoned evacuation and for primary and special needs schools. Each figure now cites the rule that produced it
- The cause and effect matrix hides the level count where per-level rows cannot apply, and says why, instead of accepting a number that changed nothing
- Sound levels at a bedhead: 75 dB(A) for a sounder and 70 dB(A) for a voice alarm are minimums, so above a 60 dB(A) background the requirement is the greater of that figure and the background plus 5 dB(A). Voice alarms also include the separate intelligibility assessment
- The reference list behind each step now sits with the Engineering Toolkit. Every answer still shows its own clause, free to run, no signup
- Three corrections from a second run of the scenario tests, run in both the free and the subscriber view: changing the building no longer leaves earlier answers in an exported report, and internal references are stripped from any note before it is shown
- Corrections from a scenario audit of 4,470 input combinations. A BS 5839-1 category and a BS 5839-6 category are separate classifications for different premises, so comparing them no longer returns FAIL, and the guide states which standard to declare from
- What is free and what the Engineering Toolkit adds is stated as it is on the other PD tools. All twelve steps stay free to run, no signup, with the clause behind every answer; the Toolkit holds the compiled design basis, the cause and effect matrix, the drawings, the PDF documents, saved projects and the editable exports
- You can add your own causes to the cause and effect matrix, each with its own fire zone, saved with the report and included in the printed matrix and the exports
- The cause and effect matrix downloads as a landscape PDF on A4, A3, A2 or A1 according to its width, produced on the server so the orientation no longer depends on the browser
- The matrix level count follows the building, up to 40, and a saved report reopened from My Projects prints exactly what was saved
- Print or save as PDF sits on the main tool window as well as the Design Summary, and changing the project profile clears the worked steps so a report cannot mix new project details with old answers
- Fix: printing a saved report from My Projects no longer reopens the print dialog over and over
- Reports no longer depend on which steps you happened to open: every step is worked out when the report is built
- The printed report is branded and laid out like the other PD tools, with the drawings included and the cause and effect matrix on its own landscape page, the paper growing to fit it. The drawings also travel into the Word file and onto their own sheet in the workbook
- The exported report includes every step in full and in order, each line with the clause it came from. Two references corrected where a rule had been split in two
- Design Check takes its own figures, starting from the project profile, so a design can be checked as it stands and then varied without altering the design
- Every verdict and note shown in the tool was rewritten in formal UK technical language, with clause references in full, for example BS 5839-1:2025, Clause 15.1.3. Requirements attributed to a PD position are labelled as such and dated
- The rule file the tool downloads holds only the clause reference; page numbers and internal working references are gone
- The design flow is twelve steps: the three stages that only restated the project profile are compiled into the Design Summary and the exported report
- Phone layout: the phase and step rails scroll on one line, and every step fits a 390 px screen with no sideways scrolling
- First release. Design workflow from the project profile through zoning, detector selection, siting and spacing with a scale drawing, call point travel, sound levels, visual alarm coverage, special systems, interfaces, standby batteries, cables and containment, to the documentation checklist. An editable cause and effect matrix, and a Design Check tab for verifying a proposal somebody else has made. Every output line shows the clause it comes from
