Fire alarm design category LD3 residential

Fire alarm design category LD3 residential

A Category LD3 fire alarm system is intended only to protect circulation areas that would be used as escape routes, by giving a warning if smoke is detected in these areas, so that occupants can escape before heat or smoke make this impossible. Therefore, the fire detection is positioned on the escape routes.

A Category LD3 fire alarm system cannot be expected, with any degree of reliability, to protect people who might be involved with the fire at ignition or in its early stages. This Category of fire system might not therefore prevent the death or serious injury of occupants in the room where the fire originates; it is intended only to ensure escape for those not immediately involved. If no fire detector is installed in the room in which fire starts, the time available for evacuation of other areas once fire is detected in the circulation area might be quite short. 

In a large family house adapted to provide accommodation for several households in separate self-contained units (a house in multiple occupation), a fire in one dwelling unit can be a hazard to occupants of other units. 

In this case, the fire detection and fire alarm system normally needs to extend across the boundaries between occupancies or be interconnected with systems in other occupancies. In practice, it is often appropriate for there to be a single integrated fire detection and fire alarm system that will alert all occupants before a fire in any dwelling threatens the communal escape routes, and that will provide early warning of any fire that starts in these escape routes. This objective is additional to that of enabling occupants of the dwelling in which fire starts to escape before their escape routes become impassable owing to heat or smoke.

In the case of purpose-built flats or sheltered housing, the degree of compartmentation between occupancies is normally sufficient to ensure that fire is contained in the dwelling of origin for a prolonged period. During this time, other occupants can remain in reasonable safety within their own dwellings. Accordingly, this part of BS 5839 does not provide recommendations for fire detection and fire alarm systems that incorporate detectors in the communal areas or ancillary accommodation (e.g. plant rooms) within purpose-built flats or sheltered housing. If, however, the provision of detection in these areas is considered desirable, it is essential to refer to the guidance contained in BS 5588-1, and it is appropriate that such fire detection and fire alarm systems comply with the recommendations of BS 5839-1.

BS 5839: Pt.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 or flats or maisonettes.

BS 5839: Pt.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.

Mains Powered Smoke Alarms with Back-up Battery - Grade D

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.

Grade D is required for new, owner-occupied buildings of up to three storeys, two storey rented properties and existing, owner-occupied buildings of more than two storeys. Very large storeys (>200m2) might require Grade B alarm system.

A question remains for landlords - can they be sure that their tenants are paying their electricity bills? Given that many tenants may have low incomes (in many local authorities, 70% or more of all tenants are on subsidised incomes), they may well experience periods of disconnection - and yet the landlord could well be liable if the alarm fails to sound because the tenant has not paid his or her bills! Unfair or not, as the law stands, it obviously makes good commercial sense to ensure that a reliable, ideally re-chargeable and sealed-in backup battery is in place.

The minimum back-up duration recommended is 72 hours, and the Code acknowledges that there could well be circumstances where a longer stand-by period is justified e.g. tenants' inability to pay their electricity bill.