Smoke Alarm Buying Guide

Which smoke alarms does this guide cover?

This guide is a short introduction to smoke and heat alarms classified in the British Standard BS5839 part 6 as Grade D and F. These alarms are typically found in housing and small businesses/ organisations. The guide does not address areas where a fire alarm system with a central fire alarm panel is required. We have purposefully excluded Grade E smoke alarms (mains smoke alarms without backup batteries), as we regard them as unsafe.

What determines the fire detection system requirements?

In new built properties and substantial extensions of existing properties Building Regulations will determine the standard applicable. In new built and existing rented properties, assembly areas and businesses, a fire risk assessment will have to be carried out to determine the type of protection required. There are official fire risk assessment guides available for different industries and applications which must be adhered to. The process of a fire risk assessment offers quite a bit of room for common sense judgement and is placing responsibility on the ‘Responsible Person’ of an organisation (usually the owner, although the responsibility can be delegated). In some industries/ areas there are additional, generally accepted, guidance documents available to clarify best practice (see links at bottom of guide).

You will typically find the following smoke alarm requirements:

• Domestic, owner-occupied housing: BS5839 part 6 Grade F
• Extensions of domestic, owner-occupied housing: BS5839 part 6 Grade D
• Small businesses, church halls, many let properties: BS5839 part 6 Grade D with additional Manual Break Points in circulation spaces and sometimes additional Grade F smoke or heat alarms within let flats.

What do the different Grades mean?

Grade D

Mains-powered, interlinked smoke and heat alarms. These are usually powered with a cable from the nearest light fitting. To create an interlink (all alarms go off at the same time in the case of a fire) they either require cable connection between the units or a radio-interlink connection. In businesses and larger let properties, these are often combined with manual break points.

With the appearance of ten year sealed smoke alarm units with radio-interlink, these are becoming more acceptable as an alternative to mains-powered, interlinked smoke alarms. Radio-interlinked manual break points are also available. However, we still recommend you check with your Building Inspector (in case of extensions), Local Council (rented accommodation), Fire Service (business) to ensure these alternative alarms are acceptable.

Grade F

Battery operated, free standing smoke and heat alarms. On their own they are mainly designed for domestic, owner-occupied housing. However, F Grade alarms with radio-interlink (especially when provided with 10 year sealed lithium batteries) can sometimes be applied as if they were Grade D. Again we recommend that you check first with the relevant authority.

Which smoke alarms for which room?

Once it has been established what grade of system is required, the correct smoke alarm sensor types have to be selected. In the type of properties mentioned in this guide there are typically three types of sensors installed:

Ionisation smoke alarm:

The traditional smoke alarm containing a small amount of radioactive material. This alarm is best used for the detection of fast flaming fires. However, it can be quite sensitive and give false alarms near kitchens. Best installed on landings and in offices

Optical smoke alarm (also called photo-electric smoke alarm):

A type of smoke alarm that ‘sees’ the smoke and is less prone to false alarms. It is also fast at detecting smouldering fires (cables, soft furnishings etc). Best near (not in) kitchens, hallways, bedrooms, living rooms.

Heat alarms:

A sensor type that detects the rapid change of temperature in case of a fire. This alarm avoids false alarms altogether and can be installed in kitchens and garages. There are also combination alarms available (eg optical and heat), sometimes called multi-sensors. These combine the advantages of the other sensor technologies, achieving high sensitivity while avoiding false alarms.

When selecting smoke alarms make sure that the alarms are certified to the relevant British Standard (BS EN 14604:2005 for ionisation and optical smoke alarms, BS5446-1:2000 for battery operated heat alarms and BS5446-2:2003 for mains heat alarms)

A word about mains operated smoke alarms

Mains powered smoke alarms to BS5839 part 6 grade D contain a backup battery. This can be an alkaline backup battery which needs to be replaced every year or so. The alternative is a sealed-in ten year rechargeable lithium battery, which makes a battery change unnecessary over the life of the alarm. Of course, regular testing is still required. The choice of battery is entirely up to the customer, although we recommend rechargeable batteries if the alarms are not tested and maintained by the customer themselves (eg in rented premises) to avoid batteries being removed or batteries becoming flat without being replaced.

Mains smoke alarms can be fed with power either from the nearest light fitting or directly from the fuse box. We recommend power supply from the light fitting. This is more cost-effective, especially when retro-fitting, and it is less likely that the lighting circuit is disabled to stop the ‘nuisance’ of bleeping alarms should the backup battery run low etc.

Whilst mains smoke alarms give you peace of mind for many years without false alarms or defects, it is dangerous to assume that they work forever. Smoke and heat alarms should be replaced after ten years, as they then start to become unreliable.

Recommended reading

1. LACoRS guide: Housing: Fire Safety Guidance on fire safety provisions for certain types of existing housing
2. Local Government Group: Guidance for Fire safety in purpose-built blocks of flats
3. Fire Risk Assessment Guides
4. A guide to BS5839