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August 5, 2019

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Contact tracing and COVID-19 director’s briefing

LD3 fire alarms

Residential fire alarms: Guidance for new-build dwellings

In England and Wales, Fire Safety: Approved Document B outlines the minimum requirements for fire alarms within new-build dwellings.

It states that Grade D, Category LD3 is the minimum requirement, but what exactly does this mean?

Fire alarms and fire alarm systems are categorised by Grade and Category respectively. The Grade refers to the power supply for the alarm itself ranging from Grade F (one or more battery powered alarms fitted) to Grade A (interlinked fire detection system, including: fire detectors, alarm sounders, fire control panel, with backup power supply).

Grade D, the minimum recommended grade, consists of one or more mains powered, interlinked alarms (smoke and heat), with backup power supply.

The Category relates to the coverage provided by the fire detectors within the dwelling. They range from Category LD3 to Category LD1.

Category LD3, the minimum recommended is a system in a dwelling with detectors in all circulation spaces that act as escape routes (hallways).

Methods of detection

Before looking in a little more detail at how to meet these requirements we are going to take a quick look at the different methods of detection that fire alarms use and where they are best suited for installation.

Optical fire alarms

Optical alarms work by using optical sensors and an infrared beam to detect smoke, they are capable of detecting most types of fire and are not overly sensitive so don’t give rise to false alarms. If used in a kitchen, however, they can be prone to being set off by normal cooking processes so they are best suited for use in hallways, bedrooms, living rooms and the like.

Ionisation smoke alarms

These work by detecting small particles of smoke which enter the ionisation chamber. They can be extremely sensitive and are best suited for detecting fast burning fires such as those caused by burning fabrics. Due to their sensitivity and their ability to detect fast burning fires they are best suited for use in areas like bedrooms where there is a large amounts of fabric present.

Heat alarms

Rather than detecting smoke, heat alarms detect the sudden change in temperature caused by a fire. They are ideal for use in kitchens as they are immune to smoke and can operate without giving false alarms at normal kitchen working temperatures.

Multi sensor alarms

It is possible to buy multi sensor fire alarms that contain two of the above types in one package. However, even if the alarm contains a heat function, it is still best to avoid using them in the kitchen to prevent false alarms.

How to meet the grade requirements

To meet Grade D in your property the alarms will need to be permanently connected to your electricity supply and have a form of backup power. One of the easiest ways to achieve this is to have your fire alarms connected to an existing lighting circuit within your home. This makes the installation much simpler as well as providing the added benefit that if the circuit supplying the power trips, you will notice the first time you try to use your lights. If the fire alarms were installed on their own dedicated circuit, you may not notice that the circuit has tripped until the backup batteries start to run out on the alarms.

A backup form of power is also required, this is easily achievable as most interlinked alarms designed for domestic use will also have a 9V battery acting as a backup as well as a small capacitor acting as further insurance.

The alarms will also need to be interlinked, this can be achieved either through hardwiring, in which case the alarm will be specifically designed for it and will involve a connecting cable between all the alarms in the property, or in the case of manufacturers such as Aico, a radio link. This interlinking will in the event of one alarm going off, set the remainder off ensuring you hear them throughout your property.

How to meet the category requirements

To ensure you meet Category LD3, fire alarms are to be present in all circulation areas which also act as escape routes. In domestic properties this is generally referring to hallways and landings that you would use to leave the house in the event of a fire.

When choosing where to place your fire alarms care should be taken as to their exact location, they should be easily accessible for testing and the replacement of batteries if needed. This means when positioning them on landings, avoid placing them directly above stairs as it makes accessing them difficult and potentially dangerous. Equally if you have a ceiling with beams or some other form of interruption running across it, the alarm would either need to be placed at the lowest point, i.e. the bottom of the beam or alternatively an alarm would need to be fitted either side of the beam as these can act as separate circulation spaces in the event of a fire.

It is worth bearing in mind though that Category LD3 is the MINIMUM requirement. To be on the safe side we would recommend having an alarm in all habitable rooms as well as just your hallways.  The sooner a fire is detected, the sooner it can be stopped and hopefully less damage to life and home will occur.

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Simon Ince
Simon Ince
August 23, 2019 10:01 am

It’s time to change to Grade D LD1 as a minimum. Bedrooms are full of electrical risks, with so much tech and electrical gadgets used in sleeping rooms compared to 20 years ago; the standard isn’t fit for purpose.

michael floyd
michael floyd
November 9, 2019 4:20 pm

Only premises where there is no legal requirement for an alarm should be advised to run to at least LD3. All new premises jumped to LD2 several editions of BS5839-6 ago. Misinformation like this could mean someone else who doesn’t know what they should do.