Ionisation smoke alarm

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

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

It is important that the right type of fire detector is used for different situations, as false alarms can result in occupants disabling fire detection and fire alarm systems.

The most common causes of false alarms are:

• Fumes from cooking.
• Steam from bathrooms, shower rooms and kitchens.
• Tobacco smoke.
• Dust.

Ionisation smoke alarms operate on the principle that the electrical current flowing between electrodes in an ionisation chamber is reduced when smoke particles enter the chamber.

Ionisation smoke alarms are more sensitive to smoke containing small particles such as rapidly burning flaming fires but are less sensitive to steam. As a result of this, they are recommended for use in hallways and stairwells adjacent to bathrooms or shower rooms to reduce the number of unwanted false alarms.

Ionisation smoke alarms should conform to BS EN 14604: 2005 - Smoke Alarm Devices.

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