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منتدي ممدوح عزت موسي MAMDOUH EZAT MOUSA FORUM

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اليومية اليومية


    Fire Alarm Installations

    شاطر

    ممدوح عزت موسي
    مدير عام المنتدي
    المشرف العام
    مشرف منتدي القصه
    مشرف منتدي العلوم الهندسيه
    مدير عام المنتدي  المشرف العاممشرف منتدي القصهمشرف منتدي العلوم الهندسيه

    عدد المساهمات : 350
    التميز : 9
    تاريخ التسجيل : 13/05/2010

    Fire Alarm Installations

    مُساهمة من طرف ممدوح عزت موسي في الإثنين فبراير 11, 2013 11:47 am

    Fire Alarm Installations
    1. For view

    Fire alarms provide protection to occupants of a building, and its *******s if the system is monitored or has a ‘halon’ gas installation provided.

    A fire alarm system is installed according to the type of use the building may have, for instance, you will have higher protection (ie, smoke detector and bell in every room of a hotel , but may only find two bells in a warehouse used for storage).

    There are generally two types of fire alarm system available today analogue and addressable, though you may find in older installations hand bell systems, and 230 volt break glass systems (without power failure back-up).


    2. Analogue Fire Alarm systems

    Analogue Fire alarm systems consist of a fire alarm panel, which will have a number of ‘zones’ run from it (minimum of two detection and two bell zones).

    Each detection zone is run in a radial from the fire alarm panel to various break glasses, laser, smoke and heat detectors. A zones is generally run to cover a specific area (ie, the first floor is one zone, ground floor is another zone).

    These systems must be wired in fire resistant cables for the bell circuits, and can be wired in a standard cable for the detection circuit, though it is normally good practice within the trade to install the entire system in a fire resistant cable (ie FP200, PYRO), Cable sizes normally used are 1.5mm for detection, 2.5mm for sounders.

    At the end of the radial detection circuit, an ‘end of line’ device is installed ( found inside or beside the last device). This device monitors the circuit to ensure that it has not been damaged or cut between it and the panel, to ‘guarantee’ the circuit will work in the event of an alarm.

    The bell circuits on these systems work in a similar fashion, utilizing two zones, but with one crucial difference: the two bell zones must criss cross each other, ie bell 1 is on zone1, bell 2 is on zone 2, bell3 is on zone1, bell 4 is on zone2 and so on….

    The idea is, that if one of the zones fail for any reason, the next bell away from the failed one is close by (so the alarm can still be heard).

    The bell circuit will also have an end of line device fitted in the last bell on each circuit for monitoring purposes.

    In the event of a fire, one of the devices should be triggered on one of the zones at the fire alarm panel. The fire alarm panel will illuminate that zone, which will then enable cross reference to the chart on the panel to see where in the building the fire may be (ie, 1st floor).

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    3. Addressable Fire Alarm systems

    Addressable fire alarms are available in two main types of system, the most common types are:

    1. Loops for detection, and radials for the sounders

    2. Loops that can both act for detection and sounders together

    These systems must be wired in a fire resistant cable (ie, FP200, and PYRO) , cable size normally used is 2.5mm.

    1. Loops for detection, and radials for the sounders

    This type of system requires two individual circuits to do two separate tasks.

    The loops are run from the panel, through various devices (smoke detectors, break glasses, heat detectors, interfaces) around the selected area of the building, and then back to the panel. The loop also has ‘isolator’ devices installed in the loop at selected points, (normally where the loop cable passes through a wall).

    Loop isolators are installed to protect the continuity of the circuit in the event that the detection loop is damaged for whatever reason. If damage occurs to a stretch of cable, the isolators connected to either end of that piece of the loop will ‘cut it out’ of the circuit – isolating it from the remaining devices, and with the circuit being wired in a loop fashion, none of the remaining devices either side of the isolated cable have been lost from the detection circuit.

    Each device on the loop is either given a number through tagging the base of the detector (Apollo bases use this method), or the device itself is programmed by the commissioning engineer using a laptop type PC. Each devices number is unique to that loop, and once all devices are numbered, the fire alarm panel is then programmed to recognize ie, device 1, to be in the foyer : device 2, to be on stair case 1 landing: device3, to be in bedroom1 etc….

    In the event of a fire, the panel will show the location of the device that has been triggered, providing the fire brigade the best information as to where the fire may be.

    These systems utilizes a minimum of two loops, generally one per floor, with upto a maximum of 128 devices on a loop.

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    Loop isolators are installed to protect the continuity of the circuit in the event that the detection loop is damaged for whatever reason. If damage occurs to a stretch of cable, the isolators connected to either end of that piece of the loop will ‘cut it out’ of the circuit – isolating it from the remaining devices, and with the circuit being wired in a loop fashion, none of the remaining devices either side of the isolated cable have been lost from the detction circuit.

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    2. Loops that can both act for detection and sounders together

    These systems are similar to the systems mentioned above, but do not have a separate circuits for the sounders.

    These loops are capable of changing the polarity of the circuit in the event of a fire to make the sounders ring. (ie red is plus, black is negative during detection mode, and red is negative, black is positive during sounding of an alarm).

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    "لا اله الا الله العليم الحليم،لا اله الا الله رب العرش العظيم،لا اله الا الله رب السموات والأرض ورب العرش الكريم."



     


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