--- title: "How We Design a Fire Alarm System | SPS Technical" url: https://sps-technical.com/services/fire-alarms/system-design description: "Fire alarm categories M, L1 to L5, P1 and P2, detector choice, sounder levels, battery standby and the design paperwork, explained by a BAFE SP203-1 company." lang: en-GB --- Image: Commercial fire alarm system design (https://sps-technical.com/img/opt/a33d2baab_ChatGPTImageJun22202610_32_12PM1.webp) How we design a system # How We Design a Fire Alarm System A fire alarm is only as good as its design. Here's how we decide what your building needs, what goes into the design and the paperwork that proves it was done properly. Book a free fire alarm survey: https://sps-technical.com/contact#type=survey Find your category: https://sps-technical.com/tools/fire-alarm-category-finder Back to the fire alarm hub: https://sps-technical.com/services/fire-alarms Six steps ## From category to certificate Every system we design follows BS 5839-1:2025 and our BAFE SP203-1 procedures. 1. Step 1 ### Agree the category Using your fire risk assessment, we agree whether the system's job is protecting people (L1 to L5), property (P1 or P2) or both, or whether a manual system (M) is enough. 2. Step 2 ### Survey the building Layout, how it's used, who's in it and when, escape routes, fire hazards and any existing systems. 3. Step 3 ### Design the system Detector and call point positions and spacing, sounders and beacons, panel type and location, zones, cable type and routes, and how the alarm links to doors, lifts, ventilation or the monitoring centre (the “cause and effect”). 4. Step 4 ### Prove it on paper Layout drawings, zone chart, device list, cause-and-effect matrix, equipment list and battery calculations, signed off on a design certificate. 5. Step 5 ### Install and test Fire-resistant cabling and fixings, every device labelled, the zone chart fixed by the panel, and cables tested for continuity and insulation before power-up. 6. Step 6 ### Commission and hand over Every detector, call point and sounder is tested against the zone chart and cause and effect is proven. We check battery standby, then hand over drawings, certificates and the logbook, and train your team. System categories ## M, L and P categories explained The category sets how much of the building has automatic detection. Your fire risk assessment decides which one you need. M ### Manual Call points only. People raise the alarm themselves. L1 ### Life, whole building Detection throughout, for the earliest possible warning. L2 ### Life, escape routes plus higher-risk rooms Escape routes plus rooms where a fire is more likely or more dangerous. L3 ### Life, escape routes plus rooms opening onto them Warns people before smoke blocks their way out. L4 ### Life, escape routes only Detection in corridors and stairways. L5 ### Life, a specific risk Designed around one particular risk identified in the fire risk assessment. P1 ### Property, whole building Detection throughout to protect the building and its contents. P2 ### Property, specific areas Detection in defined high-risk or high-value areas. Detector guide ## Choosing the right detector Each room gets the detector that suits how it is used. Choose a type to see where it works best. Our most-fitted detector ### Optical smoke detectors Detects smoke particles with a light sensor inside the chamber. Responds quickly to the slow, smoky fires most likely in offices and escape routes. Best for Offices, corridors, escape routes, bedrooms Watch out for Steam, dust and aerosols can cause false alarms Where smoke would false alarm ### Heat detectors Triggers at a fixed temperature or when the temperature rises quickly. Slower than a smoke detector, so it is used where smoke detection would cause false alarms. Best for Kitchens, plant rooms, dusty or steamy areas Watch out for Not suitable on escape routes where early warning is needed Fewer false alarms ### Multi-sensor detectors Combines smoke and heat sensing and compares the two before raising the alarm. Good where a smoke detector alone suffers occasional false alarms. Best for Mixed-use areas, staff rooms, receptions Watch out for Settings must suit the room; we set them at commissioning High ceilings ### Optical beam detectors Sends an infrared beam across a large space and alarms when smoke blocks it. One beam can cover an area that would need many point detectors. Best for Warehouses, atriums, sports halls Watch out for Needs solid mounting and a clear line of sight Very early warning ### Aspirating smoke detection Draws air through a pipe with small sampling holes to a sensitive detector. Gives very early warning, and the detector can sit somewhere easy to reach. Best for Server rooms, cold stores, high or hard-to-reach areas Watch out for Pipework design is specialist and must be tested Anyone can raise the alarm ### Manual call points The red break-glass or push units that let anyone raise the alarm. Fitted on exit routes and at every storey and final exit, usually about 1.4m from the floor. Best for Every exit route and final exit Watch out for Protective covers help where call points get knocked We install and maintain conventional, addressable and wireless systems from all leading manufacturers. ## Sounder levels and battery standby ### Loud enough to wake you? Sounders must reach at least 65 dB(A) throughout the building, or 5 dB(A) above background noise where that's higher. In sleeping areas the requirement is 75 dB(A) at the bedhead, so people wake up. We plan sounder positions on the drawings and measure the levels at commissioning. ### Still working in a power cut A standard system must run for at least 24 hours on standby batteries and then sound the alarm for 30 minutes. We calculate battery size as part of every design and check it at commissioning and at every service. FAQs ## Design and paperwork questions ### What category of fire alarm do I need? It depends on your fire risk assessment. L categories protect life (L1 is the highest), P categories protect property and M is a manual system with call points only. We agree the category with you at survey before anything is designed. ### What is the difference between conventional and addressable systems? A conventional system tells you which zone an alarm came from. An addressable system tells you the exact device, which makes faults and false alarms quicker to find. Larger or more complex buildings usually suit addressable. ### How long should the batteries last? A standard system should run for at least 24 hours on standby and then sound the alarm for 30 minutes on battery power. We calculate battery size as part of every design. ### What paperwork should I have? Design, installation, commissioning and acceptance certificates, as-fitted drawings with a zone chart, a logbook and a maintenance certificate after each service. If you can't find yours, a takeover audit is the place to start. ## Ready to plan your fire alarm? Book a free survey and we'll agree the right category and design for your building. Book a free site survey: https://sps-technical.com/contact#type=survey 01482 226570: +441482226570 Accreditations ## Why trust SPS Technical Independently certified, working to British Standards. Check every accreditation on the official register. ### SSAIB Registration HUMB018 Intruder alarms to PD 6662, CCTV to SSAIB Code of Practice SS2003, access control to SS2002, and fire alarm systems Verify at ssaib.org (https://www.ssaib.org/) ### BAFE SP203-1 Certificate 104302 · Organisation ID 303286 Fire alarm design, installation, commissioning and maintenance to BS 5839-1 Verify at bafe.org.uk (https://www.bafe.org.uk/) ### ISO 9001 and ISO 14001 1208-QMS-001 · 1208-EMS-001 Quality and environmental management, certified by Alcumus ISOQAR. ISO 9001 held since 1997 ### Safety and procurement CHAS-0004703 · Constructionline 92018 · SafeContractor PE5040 SSIP health and safety approval, procurement registration and Paxton Gold Installer status ### Police-response intruder alarms For intruder alarms, SPS Technical is an approved installer of police-response systems with the following forces, so your intruder alarm can be issued a police Unique Reference Number (URN) under the NPCC Police Requirements for Security Systems. - Humberside Police - Lincolnshire Police - North Yorkshire Police - South Yorkshire Police - West Yorkshire Police - Nottinghamshire Police - Derbyshire Constabulary - Greater Manchester Police Police approval applies to intruder alarms only. Since 1992 Established in Hull 1,750+ Systems maintained 2,850+ Scheduled service visits a year 4 Regional offices: Hull, Grimsby, Lincoln, Sheffield Trusted across universities, NHS and healthcare, local authorities, schools and academy trusts, logistics and industrial sites, transport, and stadiums and venues. 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