There are many types of fire alarm systems each suited to different building types and applications. A fire alarm system can vary dramatically in both price and complexity, from a single panel with a detector and sounder in a small commercial property to an addressable fire alarm system in a multi-occupancy building. Systems have to protect both buildings and occupants.

The categories of fire alarm systems are L if they are designed to protect life, P to protect buildings and M if they are manual systems.

M Manual systems, e.g. hand bells, gongs, etc. These may be purely manual or manual electric, the latter may have call points and sounders. They rely on the occupants of the building discovering the fire and acting to warn others by operating the system. Such systems form the basic requirement for places of employment with no sleeping risk.

P1 The system is installed throughout the building - the objective being to call the fire brigade as early as possible to ensure that any damage caused by fire is minimised. Small low risk areas can be excepted, such as toilets and cupboards less than 1m².

P2 Detection should be provided in parts of the building where the risk of ignition in high and/or the contents are particularly valuable. Category 2 systems provide fire detection in specified parts of the building where there is either high risk or where business disruption must be minimised.

L1 A category L1 system is designed for the protection of life and which has automatic detectors installed throughout all areas of the building (including roof spaces and voids)with the aim of providing the earliest possible warning. A category L1 system is likely to be appropriate for the majority of residential care premises. In practice, detectors should be placed in nearly all spaces and voids. With category 1 systems, the whole of a building is covered apart from minor exceptions.

L2 A category L2 system designed for the protection of life and which has automatic detectors installed in escape routes, rooms adjoining escape routes and high hazard rooms. In a medium sized premises (sleeping no more than ten residents), a category L2 system is ideal. These fire alarm systems are identical to an L3 system but with additional detection in an area where there is a high chance of ignition, e.g., kitchen) or where the risk to people is particularly increased (e.g., sleeping risk).

L3 This category is designed to give early warning to everyone. Detectors should be placed in all escape routes and all rooms that open onto escape routes. Category 3 systems provide more extensive cover than category 4. The objective is to warn the occupants of the building early enough to ensure that all are able to exit the building before escape routes become impassable.

L4 Category 4 systems cover escape routes and circulation areas only. Therefore, detectors will be placed in escape routes, although this may not be suitable depending on the risk assessment or if the size and complexity of a building is increased. Detectors might be sited in other areas of the building, but the objective is to protect the escape route.

L5 This is the "all other situations" category, e.g., computer rooms, which may be protected with an extinguishing system triggered by automatic detection. Category 5 systems are the "custom" category and relate to some special requirement that cannot be covered by any other category.

Control Panels.

Fire alarm control panels start with a simple one zone panel for use in smaller premises, such a shop factory unit and surgeries.

Larger, upgradable control panels are available in 2 to 14 zone versions. These control panels would be used typically in shops, schools, factories and houses with multiple occupation. All fire panels are compliant with British standard 5839 part 4, and host a variety of features.

Even larger control panels based on the same specification as its smaller counter parts can be used for systems that require up to 32-zone expansion. These control panels are very versatile and are ideal for up-grades and retro-installations.

Features.

Control panel features include test facility, fault-monitoring, mains and battery power monitoring and evacuation facility. All control panels are easily used and are operated via a keyswitch control. LED lamps identify zone and fault activation.

The larger more complex system control panels have large back lit liquid crystal displays (LCD) with 80-character full english text. These systems also have 999 event memory, which can be printed or downloaded to a computer via onboard RS232 port.

System Features.

Fire alarm systems are designed to be either automatic detection using smoke or heat detectors, or manual systems using breakglass callpoint only.

Systems are then designed to protect property or life, and are divided into categories such as P1 and P2 for property protection. Life protection is divided into categories L1, L2, L3 and M. These categories determine what type of detection equipment is used and where it is placed. Also sounder positions and quantities within the premises are also a consideration within these categories.

Fire Alarm Accessories.

Accessories to the fire alarm control panel would include the following items.

Smoke detectors come in two different types, optical and ionisation. Optical smoke detectors use infrared light to detect the particles within the atmosphere, while ionisation detectors use an electrical current to determine the presence of smoke. Heat detectors, rate of rise, have one sealed thermistor and one exposed thermistor.

Any changes between the two thermistors in temperature will create an alarm condition. Fixed heat detectors are set to a predetermined temperature of 65°C or 75°C and will cause an alarm condition if the temperature rises above this pre-set.

Bells and Sounders.

Fire alarm bells are commonly used, but electronic sounders can be used as an alternative. Bells are normally used where the sound of an electronic sounder may be confused with other sounders within the premises, such as intruder alarm sounders. Sounders and bells cannot be mixed on a system.

Callpoints.

Fire alarm callpoints are fitted within the premises to enable the manual operation of the fire alarm. These callpoints can either be reset with a key or require a replacement glass after activation.

Door Release.

Magnetic door holding devices are used to hold fire doors open during normal use of the building. On activation of the fire alarm the control panel releases the door, containing the fire to that part of the premises.

Remote Signalling.

Fire alarms can be monitored at a central station, which would alert the fire brigade to attend the premises. Remote signalling of the fire alarm can be incorporated into intruder alarm monitoring using the same BT telephone line.