Are carbon monoxide detectors required by law in Scotland?

Yes, carbon monoxide alarms are required in all homes in Scotland from February 2022 if the property has a carbon-fuelled appliance (such as a boiler, gas cooker or open fire) or a flue.

Part 6, rev. 2019: Code of Practice for the Design, Installation, Commissioning and Maintenance of Fire Detection and Fire Alarm Systems in Domestic Premises

This document is intended as a guide to BS 5839 Part 6: 2019 and is not a substitute for reading the Code of Practice itself. Instead, it's designed to help make the implications and recommendations of BS 5839 Part 6 more clearly understood, and to offer advice on how to design, install, commission, and maintain a system that meets the requirements, with reference to the 2019 amendments.

BS 5839-6 is the key standard for fire detection in domestic premises. The standard is used by architects and other building professionals, enforcing authorities, installers, and contractors, and applies to domestic premises accommodating single families, houses in multiple occupation (HMOs) and sheltered housing (housing and common areas). It is written to assist such professionals in compliance and will help make installations easier to audit, but its guidance for simpler systems may be used by non-specialists.

The Document Itself

Each clause of the document is split into 2 parts. Firstly, there is the commentary – in italics – which sets out the reasoning behind the recommendations. The recommendations themselves are written in regular (upright) type, so it is quite possible to simply refer to these alone. The intention of the commentary is to make the document easier to use; whether it succeeds in this aim is a matter of personal perception.

BS 5839 Part 6 – An Introduction

BS 5839 Part 6 is not intended for householders themselves, but to provide guidance and recommendations for architects and other building professionals, enforcing authorities, contractors, and others responsible for implementing fire precautions in buildings. Householders should instead refer to the Government guidelines in Approved Document B Volume 1.

The Code of Practice should not be quoted as if it was a specification and the standard itself warns that particular care should be taken to ensure that claims of compliance are not misleading.

It is also pointed out that compliance with a British Standard cannot automatically confer legal immunity. However, for a landlord or installer, compliance with the latest Code is often the best line of defence in any claim made against them.

The Scope of BS 5839 Part 6

This Code of Practice covers fire alarm systems starting from a simple self-contained battery-powered smoke alarm right through to major systems with central panel(s) in accordance to BS 5839 Part 1.

BS 5839 Part 6 covers the following domestic building types:

  • Bungalows
  • Multi-storey houses
  • Individual flats
  • Individual maisonettes
  • Mobile homes
  • Individual sheltered accommodation as well as their common parts
  • Houses in multiple occupation (HMOs)
  • Certain NHS housing in the community
  • Mansions
  • Shared houses
  • Houses divided into several self-contained single-family dwelling units

Not included are hostels, caravans, boats (other than permanently moored) and communal parts of blocks of flats or maisonettes.

BS 5839 Part 6 is primarily concerned with saving lives and reducing injuries. However, it does contain within it recommendations for helping to reduce property damage too. Good fire safety practice and adherence to the Code can give the best possible early warning of fire and so reduce the financial impact as well as human suffering.

It should also be noted that existing premises with alarm systems installed according to previous versions of the Code, such as those complying with older Building Regulations that reference BS 5839-6: 2004 or 2013, do not automatically need to replace or amend their systems to meet the latest edition.

The Grade System

BS 5839 Part 6 grades fire detection systems from Grade F up to Grade A. Generally speaking, the greater the fire risk and the more demanding the application, the more comprehensive the system needs to be. This relates to system engineering, not level of protection.

  • Grades F1 & F2 – System of one or more battery-powered smoke alarms (and heat alarms if required).
    • Grade F1: the battery must be tamper-proof and last the full life of the alarm
    • Grade F2: the battery is user-replaceable and will not last the full life of the alarm
  • Grade E – System of interlinked mains-powered smoke alarms (and heat alarms if required) with NO stand-by supply. They can be hardwire-interlinked or radio-interlinked. Please note that Safelincs Ltd will not sell Grade E alarms, as we only recommend alarms with backup batteries. Removed from the Standard.
  • Grades D1 & D2 – System incorporating one or more interlinked mains-powered smoke alarms (and heat alarms if required), each with an integral stand-by supply. They can be hardwire-interlinked or radio-interlinked.
    • Grade D1: the stand-by supply must be tamper-proof and last the full life of the alarm
    • Grade D2: the stand-by supply is user-replaceable and will not last the full life of the alarm
  • Grade C – System consisting of fire detectors and alarm sounders (which may be domestic smoke alarms) connected to a common power supply, comprising normal mains and stand-by supply, with central control equipment.
  • Grade B – Fire detection and alarm system comprising fire detectors (other than domestic smoke alarms), fire alarm sounders, and control and indicating equipment to either BS EN 54-2 (and power supply to BS EN 54-4), or to Annex C of BS 5839 Part 6. Removed from the Standard.
  • Grade A – Fire detection system incorporating control and indicating equipment to BS EN 54-2, power supply to BS EN 54-4, and installed to BS 5839 Part 1, with some very minor exceptions.

As the overwhelming number of residential applications in the UK will fall into Grades D or F, this is the area on which this guide will focus.

While it is possible, and acceptable under the Code, to have a mixed-Grade system installed, this is something that should be done based on clear requirements being identified during a risk assessment and in coordination with appropriate Building Regulations and enforcing authorities. An example would be a Grade A Category LD2 system in the communal areas of a HMO supplemented by separate Grade D1 Category LD1 systems in each residential unit.

Battery Operated Smoke Alarms – Grades F1 & F2

BS 5839 Part 6 acknowledges the advantages of the single battery-operated smoke alarm for existing premises, though tamper-proof batteries are preferred. They are simple to install and offer protection at very low cost. Battery-operated smoke alarms conforming to BS EN 14604: 2005, a specification for the manufacturing and performance of smoke alarms, are recommended. Battery operated smoke alarms are typically suitable for owner-occupied buildings (existing buildings) with up to two storeys.

Take care to differentiate between F1 (tamper-proof batteries that last the full life of the alarm) and F2 (user-replaceable batteries that will not last the full life of the alarm) when selecting alarms for your property.

The Code also highlights the fact that user-replaceable battery powered smoke alarms (Grade F2) are only suitable for owner-occupied properties if the likelihood is that batteries will be replaced within five days of a low battery signal, and are only recommended for existing premises – new properties must use Grade D2 (owner-occupied) or Grade D1 (rented).

For additional protection in a property where battery-operated alarms are installed and replacing them with mains-powered units would not be feasible, consider upgrading to alarms that have wireless interlink so that all alarms in the system will sound when one detects a fire.

Mains Powered Smoke Alarms without Backup Battery – Grade E

Grade E was removed in the 2019 revision and is no longer recommended for any new or replaced alarm systems.

The Code does not recommend an application for alarms without backup power sources any longer. Grade E systems have serious drawbacks:

  • Power cuts or the termination of supply for whatever reason disables them totally.
  • They can also be rendered useless by the tripping of a protective device, or even – in some cases – by the fire itself.
  • Householders may also disable them at the mains all too easily if false alarms are a problem.
  • Tenants may have been cut off from power supply which would render the alarms inoperable.

Safelincs is therefore only offering mains-powered smoke alarms WITH a backup battery.

Mains Powered Smoke Alarms with Backup Battery – Grades D1 & D2

The problems outlined above can be overcome by using mains powered alarms that incorporate, within each alarm, a stand-by supply such as a primary or rechargeable battery. The alarms have to be interconnected either through wiring or radio-interlink. The mains power supply can come from a dedicated power supply directly from the fuse box or from the nearest permanently powered light fitting, as long as the smoke alarm heads can be removed without removing the base as well and the light switch does not cut mains power to the alarm.

Grade D2 is required for new, owner-occupied buildings of up to three storeys, while rented properties both new and existing should comply with Grade D1. Existing owner-occupied buildings may use Grade F2 alarms. Premises with very large storeys (>200m2), except single-storey buildings, require a Grade A alarm system.

Take care to differentiate between D1 (tamper-proof backup batteries that last the full life of the alarm) and D2 (user-replaceable backup batteries that will not last the full life of the alarm) when selecting alarms for your property.

Fire Detectors Supplied with Power from a Common Power Supply Unit – Grades A, B, and C

Grade B was removed in the 2019 revision and is no longer recommended for any new or replaced alarm systems.

More expensive high-specification systems can offer connection of all fire detection devices to a common power supply via low voltage transformers, or interlinked fire and security systems. Again, a minimum 72 hour back-up is recommended by the Code. Due to the complexity of A, B and C Grades, we have omitted the descriptions from this short guide.

Levels of Protection – Categories of System

This relates to the level of protection afforded by the system, which is more closely tied to installation locations than the alarms themselves.

Within the A – F Grades defined earlier, the standard identifies three different Categories of protection:

  • LD1 – A system installed throughout the dwelling, incorporating detectors in all circulation spaces that form part of the escape routes from the dwelling, and in all rooms and areas in which fire might start, other than toilets, bathrooms and shower rooms.
  • LD2 – A system incorporating detectors in all circulation spaces that form part of the escape routes from the premises, and in all rooms or areas that present a high risk of fire to occupants.
  • LD3 – A system incorporating detectors in all circulation spaces that form part of the escape routes from the premises.

It is noted that an LD3 type system is intended to protect escape routes for those not directly involved in the fire and may not save the life of anyone in the immediate vicinity of the fire.

Only by quoting Grade and Category can a meaningful and effective alarm system be specified, e.g. Grade D1 Category LD2.

Types of Fire Alarm Sensor

The types of fire alarm identified by the Code are Smoke, Heat, Carbon Monoxide Fire, and Multi-Sensor, and each is discussed in regards to their relevance in different locations and situations.

For smoke alarms, the Code recommends not using them in or near kitchens, bathrooms, or shower rooms. Optical smoke alarms are less sensitive to things like smoke and steam compared to ionisation smoke alarms and so can be used nearer to such rooms, but should still not be used inside them. Smoke alarms are also the recommended type for circulation areas, the rooms that comprise the escape route(s) in your premises such as staircases and hallways, and the Code suggests using optical smoke alarms in such rooms wherever possible. Please note that most manufacturers are in the process of phasing out ionisation alarms due to various environmental and transport issues related to the use of radiation sources; optical sensor technology is now acknowledged as interchangeable where older ionisation models are installed.

For kitchens and garages, dedicated detectors are available called heat alarms. As the name suggests, they operate by detecting abnormally high temperatures in their surroundings. Because of how they work they are immune to the typical causes of nuisance alarms like burned toast, steam from cooking, or dust. However, they cover smaller areas than a smoke alarm and take longer to be triggered by common household fires, so are not usually used in any other rooms.

CO fire sensors are not very common in the domestic market and only react to a specific subset of fires, so the Code only allows them under strict conditions. As with normal CO alarms that are used near boilers, CO fire sensors detect carbon monoxide released during incomplete combustion, but are set to react at a much lower parts-per-million (ppm) threshold. Generally this type of alarm should only be used in systems of Grades A and C according to requirements identified in risk assessment, but can then be used in combination with, or in place of, smoke alarms if the device gives a fault warning in advance of the sensor's end-of-life similar to a low battery warning.

Multi-sensor alarms combine two or more sensor types, most commonly optical and heat, to accomplish: decreased reaction time to a fire event; decreased occurrence of false alarms; or both of these factors. Subject to compliance with either BS EN 54-7 or BS EN 14604: 2005, which are specifications for the manufacturing and performance of smoke detectors, multi-sensor alarms can be used in place of smoke alarms when following the Code.

A more detailed explanation of the types of alarm Safelincs sells can be found in our Smoke Alarm Buying Guide.

Wiring and Commissioning

BS 5839-6 also makes detailed recommendations in regards to wiring and commissioning of fire alarm systems, primarily in relation to Grades A and C but with some relevance to Grades D and F as well.

In terms of wiring, focus is given to correctly labelling isolating equipment attached to circuits powering your alarms. Any such isolator must be clearly labelled as being responsible for isolating alarm power circuits, in the hopes of preventing people from unnecessarily deactivating alarms.

Grade D alarms can be powered from either dedicated circuits or existing lighting circuits, given that the alarms will not be deactivated by the lighting circuit's switches. Wire-interlinked alarms should also ideally be powered by a single, dedicated power circuit, so that power cannot cross over from non-isolated alarms during electrical works. However, it is still common for the alarm system to be powered by the lighting circuit, as this makes it unlikely that residents will disable the alarm system with the help of the fuse box should there be a nuisance alarm or warning signal.

The alarms in a Grade D system can not only be interlinked by cable but also radio-interlink. While each alarm is individually powered, e.g. from the nearest light fitting, the communication between the alarms is done via radio-frequency. Most smoke and heat alarm manufacturers offer RF smoke alarms or bases on which the alarms are fitted to create this wireless communication between alarms.

In HMOs where all residential units are powered by the same key- or card-operated electrical meter then alarms in the common areas can be powered from it. However, if each dwelling unit has its own such meter then the alarm system(s) covering common areas should not be powered from any such residential meter. This is to avoid alarms in common areas deactivating if any occupant fails to pay their electricity bill or if a dwelling is left unoccupied for extended periods of time.

Additionally, the Code recommends that after installations that include wiring, the installer should test cable insulation and earthing to ensure integrity of the system. Further tests should also be carried out to ensure correct and adequate functionality of the system as a whole.

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