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Discuss Smoke Alarm - Optical or Ionisation and heat? in the Electrical Forum area at

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  1. jase31

    jase31 Guest

    Plannning a 3 bed detached rewire.

    OSG recommends two smoke alarms, one in the landing (outside bedrooms) and one in the hall.

    Should these be ionisation or optical type?

    Should a heat detector also be fitted into the kitchen area? The OSG states that a Heat detector should be fitted if there is NOT a door between the kitchen and circulation area? I am tempted to add a heat to the system

    Do others usually fit heat detectors, in additon to smokes?
  2. telectrix

    telectrix Scouser and Proud of It Respected Member

    Business Name:
    as kitchens are one of the most common causes of house fires, i would put a heat rise detector in the kitchen.
  3. jase31

    jase31 Guest

    Do you find many false alarms with a heat rise detector? i.e oven door opens and a blast of warm air comes out? I have fitted a fixed heat detector before- but a rise detector would be better (if not affected by false activations)
    Last edited by a moderator: Nov 12, 2011
  4. alarm man

    alarm man Guest

    fixed heat in kitchens and utility rooms for me,rate of rise heat for dusty environments
    • Like Like x 1
  5. MarkieSparkie

    MarkieSparkie Guest

    Hi Jase,
    The Optical Smoke Alarm.
    This type of smoke alarm uses light technology to detect smoke. Inside of these alarms, there is a small light emitting diode or LED. This little light shines a thin beam of infra-red light to a sensor. If any small particles of smoke interrupt this infra-red light the voltage read by the sensor will drop and the alarm will sound. This type of smoke alarm is best where the threat of smoldering, where thicker smoke is present.

    The Ionisation Smoke Alarm.
    This type of smoke alarm employees a completely different technology to detect smoke particles in the air. This type of smoke detector has about one milligram of radioactive metal in it, that has been scientifically proven safe for humans. The sensor part of the smoke alarm is called an ionisation chamber. Inside of this chamber there are a small amount of electrodes with a current running through them.
    If a small particle of smoke enters the chamber it ionises the radioactive element in the alarm and the current flowing between the electrodes is interrupted. This causes the alarm to sound. This type of detector is good at detecting smoke when the fire is more flaming than smoke producing because it can detect such small particles.

    Which Is Better?
    Ionisation smoke detectors can detect smoke quicker than optical smoke alarms due to the difference in technology. However, the ion type of smoke detectors are extremely sensitive and can cause more false alarms than there optical counterparts.
    Many manufacturers are starting to discontinue production of ionisation smoke detectors because of advances in optical smoke detection technology. Those that continue to produce both ion and optical smoke alarms usually house them in the same outer casing.
    The only real way to determine which type of detector you are buying is to read the packaging that comes with your smoke detector. Ion detectors are more sensitive and expensive, while optical smoke detectors are cheaper but less sensitive.
    In order to get the best of both worlds you should employ a mix of both types of detector in your home.

    In practice.
    Optical smoke alarms are the best choice for rooms on the same floor as the kitchen, also for circulation spaces e.g. hallway and landing, because they less effected by low levels of 'invisible' particles contained in kitchen fumes, that cause false alarms.
    Ionisation smoke detectors are the best choice for bedrooms where the speed of detection is paramount.
    Heat detectors or alarms are the best choice for kitchens, garages and any room containing an open fire due to the level of smoke or fumes that would otherwise readily cause false alarms.
    • Like Like x 1
    Last edited by a moderator: Nov 13, 2011

    GLENNSPARK Electrician's Arms

    west yorks.
    My boss fits a mixture of suit the application.....
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