A sense of place

Andy Speake of Aico advises on the importance of getting placement right when it comes to alarms.

In the domestic smoke alarm sector there has traditionally been three alarm types: optical, heat and ionisation. These different sensor types react best to certain fire types. As a result, specification and installation requires a good knowledge of BS5839 Part 6 (the British Standard for domestic smoke alarm installation) and Building Regulations, to ensure the best levels of detection for a property.

But, changes are afoot. The new breed of multi sensors, which combine two traditional sensing elements in one alarm, are rising in popularity. What’s more, there’s a further alarm type to hit the market which combines fire detection with another life safety device – carbon monoxide (CO) detection.

What alarm and where?

As the name might suggest, optical alarms essentially ‘look’ for smoke using a pulsed light beam in the sensing chamber. They are most effective at detecting smouldering fires with large particles, such as those produced by burning furniture, and are less likely to react to the type of invisible smoke produced by cooking fumes. They are therefore ideal for circulation spaces such as hallways close to kitchens and landings, as per BS 5839-6.

A heat alarm doesn’t detect smoke at all, but instead reacts to temperatures of 58oC or over, as per BS 5446. A heat alarm should only be used in a kitchen or garage, and only as part of a fire alarm system that also includes smoke alarms. Furthermore, all of the alarms within that system must be interconnected to meet British Standards. A solo heat alarm in a property is not an option.

Ionisation alarms use a small radioactive source to detect the invisible smoke parti- cles given off by fast-flaming, clean burning fires such as bedding and clothing. Ionisation alarms have essentially proven so popular because they have been around the longest (they were the first commercially available smoke alarms), and so are the most familiar and generally are priced lower than other alarm types, making them the default alarm choice. However, with greater understanding of fire alarm types and a wider choice of alarms now available, ionisation alarms are slowly falling out of favour because they can be over-sensitive to cooking fumes and are deemed old technology. Generally, it’s recommend that their use is restricted to bedrooms.

So, to recap: heat alarms go in the kitchen, optical alarms are for circulation spaces, including hallways and landings, and it is now generally believed that ionisa- tion alarms should be avoided as there are more suitable options.

That seems very straightforward, but there are instances when it’s not immedi- ately obvious which alarm type to use. For example, where do you place an alarm, and what type of alarm in an open plan property?

Multiple sensors

Multi-sensor fire alarms are the next step in alarm technology development, and can effectively remove the problem of where to place them. A multi-sensor fire alarm uses both optical and heat sensors within the same alarm unit, and interprets the signals to get a better understanding of what’s really happening in the immediate environ- ment. Because of this, it benefits from a quick response to both slow smouldering and fast flaming fires, yet is more tolerant to kitchen fumes and contamination. Multi- sensor alarms can help take the guess work out of alarm specification and installation.

Introduced to the domestic smoke alarm market in 2014, multi-sensor fire alarms are still relatively new. The alarms have proven themselves most popular in the social housing sector, where their simple specifi- cation (they can be effectively used in all rooms except a kitchen) and exceptionally low rate of false alarms have made for considerable savings, while at the same time provided a superior level of fire protection.

Heat/CO alarm

The multi-sensor is no longer the new kid on the block. That title goes to a brand new alarm type, released this year, in the form of a combined heat/carbon monoxide alarm. Designed specifically for use in the kitchen, the heat/CO alarm is actually two alarms in one unit. The heat alarm aspect works in exactly the same way as that above. The CO alarm detects carbon monoxide (CO), a potentially lethal gas.

Any household appliance that burns fossil fuels (coal, oil, bottled gas, paraffin, wood, petrol, diesel or charcoal) can be a potential source of CO. Requirements to fit CO alarms are somewhat lagging and differ across the nations. Despite this, awareness of the dangers of CO poisoning are driving the installation of alarms, with many fitting them beyond their legal obligations.

The kitchen is an obvious potential source of CO, so combining a heat and CO alarm in one is a cost-effective, convenient option and should help spread the use of this life saving technology. Having only the one alarm on the ceiling also makes for a more pleasing aesthetic.

The introduction of new alarm types has made for more effective fire detection in the home, while at the same time simplify- ing the specification aspect. So, if you haven’t already, consider reviewing your alarm choice, and take a look at the full range that’s on offer.

Andy Speake is national technical manager at Aico