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:
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.
Characterising smoke from modern materials and evaluating smoke detectors was written by Raman Chagger and published by BRE in 2014 states that:
Ionisation detectors use a small radioactive source (americium-241) inside an ionisation chamber that contains charged electrodes. The chamber is arranged to allow a flow of air from outside. As the air enters it becomes ionized, generating an electric current between the charged electrodes. When smoke particles pass into the chamber the ions become attached to them and are carried away, leading to a reduction in the current. More ions are stripped away when there are many small particles, such as those generated during flaming fires. When a material is smouldering it tends to produce fewer but larger particles than it does when in flames. As these cause less current reduction, ionisation detectors are inherently less responsive to the large smoke particles generated during smouldering fires. |
Ref https://files.bregroup.com/research/Test-Fires-Characterisation_2014-November.pdf
[edit] Related articles on Designing Buildings Wiki
- Carbon monoxide.
- Carbon monoxide detector.
- Characterising smoke from modern materials and evaluating smoke detectors.
- Domestic smoke alarms DG525.
- Fire detection and alarm system.
- Fire detector.
- Fire.
- Fire fatalities in Scotland.
- Heat alarm.
- Multi-sensor alarm.
- New requirements for fire detection and alarm network systems IP 12 13.
- Optical smoke alarm.
- Over £1 billion lost every year due to false alarms.
- Smoke detection in high ceiling spaces.
- Smoke detector.
- The causes of false fire alarms in buildings.
Featured articles and news
Investors in People: CIOB achieves gold
Reflecting a commitment to employees and members.
Scratching beneath the surface; a guide to selection.
ECA 2024 Apprentice of the Year Award
Entries open for submission until May 31.
UK gov apprenticeship funding from April 2024
Brief summary the policy paper updated in March.
For the World Autism Awareness Month of April.
70+ experts appointed to public sector fire safety framework
The Fire Safety (FS2) Framework from LHC Procurement.
Project and programme management codes of practice
CIOB publications for built environment professionals.
The ECA Industry Awards 2024 now open !
Recognising the best in the electrotechnical industry.
Sustainable development concepts decade by decade.
The regenerative structural engineer
A call for design that will repair the natural world.
Buildings that mimic the restorative aspects found in nature.
CIAT publishes Principal Designer Competency Framework
For those considering applying for registration as a PD.
BSRIA Building Reg's guidance: The second staircase
An overview focusing on aspects which most affect the building services industry.
Design codes and pattern books
Harmonious proportions and golden sections.
Introducing or next Guest Editor Arun Baybars
Practising architect and design panel review member.
Quick summary by size, shape, test, material, use or bonding..