Fire Alarm - Categories of Coverage, and What to Expect.
So, the local authority has been around, asked you to have a Fire Risk Assessment performed, and now you need to get a fire alarm installed. They have a suggested a Grade and Category, but what does it all mean?
Let me get one thing straight up top; your Fire Risk Assessor might not be a fire alarm designer (Risk assessors, feel free to come at me, communication links are at the top.) I have faced a number of awkward scenarios in which the risk assessor has briefly described what sort of coverage the property requires, which effectively hamstrings my designs. And then, when I question this on the customers behalf, I’m either totally ignored, or the risk assessor emails the word LEGISLATION at me without any further explanation and their email signature magically has a few more post nominals on it.
I’m not digging out risk assessors by any means, but the layperson might be better off grouping them in with building surveyors; “Foundations look alright but get a builder to check. Electrics look already but get a sparks in. Boiler looks fine but best get a gas safe engineer in to be sure.” The service they provide is useful and essential and I’m not by any means trying to underline it, but they are expected to wear a great deal of hats and in my opinion fine detail is left to specialists. I do a lot of the converted townhouse in flats style systems of varying scales, of which the risk assessor will only have inspected the common ways. So, to recommend that a heat detector needs to be installed behind a door they haven’t opened, isn’t helpful, as there’s a good chance the entire top half of the building would have to be an inferno before that device would trigger.
My spleen suitably vented, lets get into it.
Depending upon the complexity of your building, you will either be recommended a Grade D (domestic style devices, see Aico, Fire Angel, Hispec etc) or a Grade A (commercial style with control panel). That aside, lets look at categories of coverage, and what they mean for your building. We are protecting Life in this blog so expect the letter L, add a D if a domestic system, and a number for coverage amount. You would also do well to consider the fire triangle (oxygen, ignition source and fuel).
Category L1 or LD1
You will have a suitable detector anywhere with the potential for fire. This may exclude very small cupboards unless there’s something that could ignite (electrical stuff probably) and something to burn (stored goods such as linen, chemicals, stationary etc). Whether domestic or non-domestic, we’re smothering the place in detection, as we are after a very quick alert to the presence of fire.
Some buildings get what is called an L1+ or such system in them, due to their nature. Irreplaceable heritage buildings, uninsurable power plants or hyper-continuity minded data centres, to name but a few.
Category L2 or LD2
L2 - Non Domestic
This system is an L3 system (see below) with additional detection in areas of high risk, which should be determined by your risk assessor but hardly ever is (once again, risk assessors you know where to find me). Expect additional devices in high risk areas such as the plant room, boiler house, laundry room, kitchen, staff kitchen, etc. Moderately easy to determine if you consider the fire triangle.
LD2 - Domestic
Owner owned. Tenanted rental.
Circulation areas (your hallway and stairs, escape routes) and in all specified high risk rooms including kitchen and main habitable room, living room usually.
HMO
Circulation areas (your hallway and stairs, escape routes) and in all specified high risk rooms including kitchen and main habitable room(s). In an HMO usually ones bedroom gets used also as a living room and/or a miniature flat of its own, there will often be a load of extension leads in play and moody electrical goods from Amazon. Larger HMO’s actually fall under the non-domestic standard, so keep an eye out for that.
Category L3 or LD3
L3 - Non Domestic
Commercial properties
Designed to let occupants of the building know that a fire has occurred, early enough that they can escape safely before their escape route becomes compromised. We will be considering escape routes (not limited to corridors, literally any route you might take to a point of eventual safety) and rooms that lead onto them. In essence we have detection monitoring the compartmental fire doors that surround the escape routes, so expect a device near the door rather than in the centre of the room. We would always have included lift shafts and lift lobbies here, and BS6839-1:2025 fresh off the presses now includes the low risk little lobbies you get halfway down corridors, and in hotels you can now expect a smoke detector in the room with a sleeping occupant rather than a heat detector by the door; spontaneous human combustion is apparently on the up.
Shared common ways or stairwells within blocks of flats
Hold the phone! Whilst one might assume otherwise, these areas fall under 5839-1 for non-domestic premises, creating an incredibly petty and pedantic bugbear of mine when the recommended categories are LD rather than simply L. Also creates an argument about whether we’re after sound pressure levels of 75db at the bedhead with the door closed as per 5839-1 or 85db at the doorframe as per 5839-6, and whether a sounder in the room is the correct action or having it in the hallway suffices, and the budgetary headaches this creates.
In any event, expect a smoke detector and call point on each floor of the stairs but not the turns unless they’re huge, and heat detectors within the flat monitoring areas that affect the escape route. If the flat is a duplex, one can expect a heat detector on each landing at least, and if the flat goes beneath the ground floor hallway, a heat detector there too. The assumption is that the heat detector would be monitoring the front door, but a heat detector in that specific location might be as useful as an ablutionary orifice at the bend in your arm.
LD3 - Domestic
This is just your circulatory areas / escape routes. Please bare in mind that an escape route is anywhere that leads to a place of eventual safety, so if your kitchen leads into the garden, you’ve got French doors in the lounge or a large window in your bedroom with a metal staircase outside it, you might end up with automatic detection in the vicinity.
Category L4 - Non-domestic
The non-domestic equivalent of LD3 and where we leave the domestic categories. We’re just covering the escape routes on their own, with the 2025 addition of any shaft like structure (lift, dumb waiter, electrical/mechanical riser, etc) included. Whilst important to cover these routes, these systems always feel a bit like value engineering to me. It might genuinely be the most effective and reasonably practicable amount of coverage for the building, but I would personally give the assessment another read over, ensure I were to conduct a thorough survey, and have a word in the Fire Engineers shell-like before adding my signature to the design.
Category L5
These systems are very much an engineered design that form a part of the specific fire strategy of that building and would usually be the remit of a Fire Engineer, rather than something a Fire Alarm Designer would suggest, such as in an Airport or a Train Station.
I will eat some crow here by saying that following the Grenfell tragedy, a Fire Risk Assessor might suggest for a high risk building an L5 system that is an L3 system, but we’re also covering areas that THE SOLID PETROLEUM CLADDING THE ENTIRE BUILDING IS COVERED IN CREATING A FLUE LIKE STRUCTURE SEEN ALSO IN SAMURAI SWORD SMELTING (THEY REALLY DID THAT (JESUS OF NAZARETH AND HIS PARENTS MARY AND JOSEPTH ON A TANDEM PUSH BIKE WE REALLY DO NEED TO TAKE A GOOD LOOK AT OURSELVES)) interacts with or might allow fire ingress, such as via external windows or vents. Big one for wireless systems that.
If you would like a fire alarm designed, the verification of a design and/or the commissioning of your fire alarm, please get in touch.