Fire detector

[edit] Introduction

According to the fire and rescue service, they are called to more than 600,000 fires a year in the UK, which result in more than 800 deaths and 17,000 injuries.

Fire detectors can give early warning of developing fires, allowing occupants to take action to tackle the fire, inform the fire and rescue service, or evacuate the building.

Fire can be detected by; heat detectors, flame detectors, smoke detectors, carbon monoxide detectors and multi sensor detectors, or an alarm can be triggered at manual call points. Detectors may be hard wired, or battery operated, and may be interconnected so that if one detector is triggered, all interconnected alarms sound.

Detectors can also be fitted with an escape light which comes on when the alarm is triggered. For people with hearing difficulties, smoke detectors are available that can, for example, be fitted to pillows, making them vibrate if triggered, or a strobe light effect. They may also be integral to a personal protection system for vulnerable people that discharges a watermist over a bed or chair that is the seat of a fire.

The number of detectors required will depend on the particular building, but, very broadly, the more that are installed, the higher the level of protection.

[edit] False alarms

It is important however that the right type of fire detector is used for different situations, as false alarms can result in occupants disabling, or losing confidence in fire detection and fire alarm systems. In the period 2011-2012 there were 584,500 alarms reported in Britain. 53.4% of these were not fires and therefore considered “False alarms”.

The most common causes of false alarms are:

• Fumes from cooking.
• Steam from bathrooms, shower rooms and kitchens.
• Tobacco smoke.
• Dust.
• Inappropriate detector settings, such as sensitivity.
• Poor maintenance or failures.
• Inappropriate locations or types of detector.

[edit] Types of detector

The Technical Handbook – Domestic, published by Scottish Ministers to provide guidance on the Scottish building standards suggests there are 4 main types of fire detector used in dwellings:

• Optical smoke alarms.
• Ionisation smoke alarms.
• Heat alarms.
• Multi sensor alarms.

[edit] Optical smoke alarms

Optical smoke alarms detect the scattering or absorption of light within the detector chamber. They are more sensitive to slow smouldering fires such as fires involving soft furnishings and bedding.

See Optical smoke alarms for more information

[edit] Ionisation smoke alarms.

Ionisation smoke alarms are more sensitive to smoke containing small particles such as rapidly burning flaming fires but are less sensitive to steam and so are recommended for hallways and stairwells adjacent to bathrooms or shower rooms.

[edit] Heat alarms.

Heat alarms are used where ambient temperatures are likely to fluctuate rapidly over a short period, such as in kitchens, and are less likely to produce false alarms.

[edit] Multi-sensor alarms

Multi-sensor alarms (or multi-criteria alarms) detect more than one fire phenomena, for example optical and heat detection. They may also include other detection capabilities, such as carbon monoxide detection. A multi-sensor alarm provides early warning of fire and can significantly reduce the number of unwanted false alarms in certain circumstances.

[edit] Intelligent detectors

Intelligent detectors are independently addressed and continuously monitored to verify correct operation. They may also have adjustable sensitivity settings and drift compensation to account for environmental conditions. This can help identify when an alarm is genuine, as opposed to resulting from a maintenance issue or incorrect setting, and can significantly reduce the number of false alarms.

See also: Fire detection and alarm system.

[edit] Related articles on Designing Buildings Wiki

• Domestic smoke alarms DG525.
• Fire detection and alarm system.
• Heat alarm.
• Ionisation smoke alarms.
• Making the case for sprinklers and dispelling myths.
• New requirements for fire detection and alarm network systems IP 12 13.
• Optical smoke alarm
• Smoke detector.
• The causes of false fire alarms in buildings.
• The impact of automatic sprinklers on building design.
• The role of codes, standards and approvals in delivering fire safety.
• Visual alarm devices - their effectiveness in warning of fire.
• Automatic fire detection and alarm systems, an introductory guide to components and systems BR 510.
• Personal protection watermist systems in the homes of vulnerable people.