دایره المعارف تاسیسات برق (اطلاعات عمومی برق)
Issues to be covered by the Designer should include
The Fire Risk Assessment demands
Systems designed for Protection of Property only, fall into two classifications P1 or P2. The objective of a Category P1 is to provide the earliest possible warning of a fire to minimise the time between ignition and the arrival of the fire fighters. P1 is designed to protect the whole building whilst P2 is installed in defined parts of the building only, which may have an extraordinary high risk or hazard.
Life protection on the other hand will often depend on the number of people accessing a particular building and depending on the variations, the systems can range from simple Type M to L1 categories, these being detailed in the following diagrams.
These diagrams show a typical building with a number of escape routes, side rooms and open plan areas used for escape.
L1 Floor Plan
L2 Floor Plan
L3 Floor Plan
L4 Floor Plan
L5 Floor Plan
M Floor Plan
A Category M system requires manual call points on all exits as well as corridors where persons are not expected to walk more than 30/45m (see design note 3) to operate one.
Generally a building is broken down into smaller compartments to enable the fire fighters to locate the fire as quickly as possible. Even if the system is addressable it is still considered beneficial to have a separate
‘at a glance’ indication of the location of the fire. These compartments of a building are called detection zones, which need to comply with the following criteria.
A detection zone should cover no more than 1 storey, unless total floor area is less than 300m2. Voids in the same fire compartment should be included in the same floor zone. The maximum floor area of a zone should not be greater than 2,000m2, except for some large open plan areas that incorporate manual call points only, which can be extended to 10,000m2. The maximum search distance for the fire fighters to see the seat of the fire within a zone should not exceed 60m assuming the route taken is the worst possible option. Vertical structures like stairwells, liftwells etc should be considered as separate zones.
A manual call point within a staircase should be connected to the zone associated with that floor and ideally be mounted on the accommodation side of the corridor exit. Automatic sensors on the stairwell remain as part of the stairwell detection zone.
An alarm zone is clearly defined within the standard but generally is an area of the building coinciding with the fire compartment boundaries. There must be a clear break between these alarm zones to ensure alert and evacuation messages are not overheard from adjacent areas. The only other criteria is that an alarm zone may consist of a number of detection zones but not visa versa. Alarm zones are only required when phased or staged evacuation is required. It is therefore important that care should be taken to ensure only one message is heard at any one time particularly where two alarm zones are attached.
All manual call points, whatever the system, should comply to BS EN54-11 single action Type
A version only and should be located as follows:
Note In order to comply with the requirements of Building Regulations Approved Document M, which requires electrical switches including manual call points (MCPs) to be mounted at between 1M + or - 200mm on wheel chair access routes, these should be listed as a Variation on the certificate as BS requires MCP’s to be mounted at 1.4M + or - 200mm.
The objective is to select the correct sensor for the appropriate application, to provide the earliest warning of fire without the risk of a false alarm. It is therefore worth trying to visualise the type of fire that is likely to occur in a particular room or area and also to familiarise oneself with the application and the risks that could give rise to a false alarm. For further advice please refer to clauses 21 & 22 of BS 5839-1:2002
It should also be remembered that a Vigilon system can incorporate a whole range of different sensors using S-Quad multi-sensors. These can be set up for different applications and can be switched from ‘state to state’ should particular risks be present for short periods of time. This is achieved by selecting the ‘enable/disable’ software within the standard panel software. At the end of this booklet, a section is attached showing a full application guide for all sensors including the latest S-Quad multi-sensor with a range of selectable ‘states’ for every application and risk. Heat sensors complying to BS EN54-5 Vigilon with the S-Quad heat sensor has a number of pre-programmed ‘states’ that are detailed within BS EN54-5.
Each state has its preferred use as described in the Application guide and incorporates two types of heat sensing element. One can be described as fixed temperature whilst the other is known as a rate rise element. These elements have a broad range of application specific operating states that will respond quickly in the event of fire without risking a false alarm. See guide attached for specific advice on which state is recommended for a particular application.
For example: The default state for the S-Quad heat sensor is Grade A1 (state D) which has a fixed temperature operating point of 59.5o + or - 5.5o C with a ‘normal’ rate of rise element, the current ‘full list’ of states provided by S-Quad and Vigilon are:
Traditionally, ‘point’ type smoke sensors have fallen into two main categories, optical or ionisation. Due to new European Directives for the storage and transport of radioactive sources, ionisation sensors are becoming less favourable and are being replaced by multi-sensors that utilise single or dual optical chambers that are also combined with heat and/or carbon monoxide sensing elements. This creates a whole range of sensors that are suitable for detecting different types of fires and yet ignore signals that previously have led to false alarms such as white dust or steam particles.
The table below shows the various ‘states’ of these smoke sensor options. This should be read in conjunction with the attached application/risk charts to ensure the correct sensor is used for a particular location.
One of the common mistakes is to mount a smoke sensor adjacent to the air conditioning intake or outlet grill. The minimum distance between the two should be at least 1 metre and further if possible. This is due to the fact that smoke may have difficulty penetrating the sensor when the air conditioning is switched on. Also there is a greater risk of the sensor becoming contaminated and giving rise to false alarms.
General rules apply as for point detectors:
Sounders and strobes are generally provided for systems designed to protect life. However, on the rare occasion when only the property is being protected it is still essential to mount a sounder adjacent to the fire control panel as well as immediately outside the main entrance for the fire fighters.
Before deciding on the number and location of sounder/visual alarms, it is important to establish what the ‘Fire Plan’ or cause and effect will be.If the building is not going to have a ‘one out - all out’ arrangement, the evacuation procedures must be established. Once this is known, you can then establish the alarm zone areas where different alarm messages may be given, for example an alert or evacuation tone.
Research* over the last twenty years has proven that a voice enhanced sounder is preferred to a bell or electronic sounder as people pay more attention to a spoken message. The S-Cubed and S-Quad offer sounders that include recorded speech messages delivered in a synchronised manner to create a clear instruction to persons at risk within a building.
* Sources: Brian Piggott (The Fire Research Station) and David Canter (Surrey University)
Audible alarm levels within buildings are generally accepted as 65dB(A) throughout. However, the new standard does not accept that in certain locations this can be as low as 60dB(A). This allows some degree of flexibility, although in general the majority of a site must achieve 65dB(A) or greater to be compliant.
The drawings below illustrates the areas where 60dB(A) is permitted.
It is maintained that to rouse sleeping persons you need to achieve a minimum of 75dB(A) at the bedhead.
For areas with high ambient background noise levels, the Standard recommends a sound level of 5dB(A) above the norm although it now goes on to say the maximum sound levels should not exceed 120dB(A) for health & safety reasons. Finally it is essential that at least one sounder is placed within each fire compartment an the sounder choice should be common throughout the building. You should not mix bells and electronic sounders within the same building although the S-Cubed
& S-Quad, both offer bell and electronic sounders allowing a system upgrade or switch over from a bell tone to an electronic tone when required.
Sound attenuation is affected by numerous physical structures within a room, including the door, furniture, people and materials used for floor, walls etc.
General internal doors will attenuate at least 20dB(A), whilst heavier fire doors may well attenuate by up to 30dB(A). To ensure 75dB(A) is achieved within a bedroom it is accepted that the sounder is mounted within the room rather than the corridor outside. Use of sensor sounders ensures an even spread of sound throughout the building without the need for separate louder sounders. Visual alarms are generally considered as supplementary rather than the only means of providing an alarm, and are included in areas where the dB(A) level exceeds 90dB(A) or where persons within the area have impaired hearing. The exception could be where sound of any description is undesirable, for example operating theatres, TV studios and places of entertainment where a discreet staff alarm system is the best option to avoid panic.
Visual alarms are also included as a requirement of the Disability Discrimination Act and Approved Document M of the Building Regulations and should be included in all sleeping accommodation where people with a hearing disability may be present
Standards & Approvals
For fire systems, the relevant product standard for call points is EN54-11. Using approved devices is important in life safety systems; third-party testing by a reputable test house does far more than simply confirm the physical construction and operation of the device. Extensive tests for environmental factors such as operation at elevated temperatures, corrosion tests, EMC tests and shock and vibration are carried out, so a third-party test certificate gives the installer and user confidence that the device conforms in all respects to the requisite standard. Even if the installation code of practice does not make it mandatory to use approved devices, to use non-approved devices is a false economy that could potentially put life at risk if they do not operate when required.
EN54-11 defines a pictogram of a house that must be used at the top of the body of a call point and two arrows indicating the optimum point on the operating element. In some markets, supplementary wording is often added to the house pictogram to remove any doubt about the function of the call point. For other specialised applications, a legend is normally printed on to the call point to identify the function and the body colour will not be the fire system red. The legend will normally be in the form of wording, for example, “Emergency Door Release”, so the issue of different languages for specific markets immediately arises.
Call Point Siting
In buildings, call points must be installed at locations where they will be immediately obvious. The positioning of call points within premises is defined in the UK by BS5839 part 1:2002, the Code of Practice applicable to the installation of fire systems. All European countries have similar requirements, and although there are minor variations, there are generally few major points of difference. Manual call points should be mounted on all escape routes, and at all exit points from the floors of a building and to clear air, ensuring that occupants can leave the building quickly when necessary and activate the fire system while doing so.
It should not be possible to leave the floor of a building without passing a manual call point, nor should it be necessary to deviate from any escape route in order to operate a manual call point. Call points mounted at the exits from a floor may be mounted within the accommodation or on the stairwell. In multiple storey buildings, where phased evacuation is to be used, call points should be mounted within the accommodation to avoid activation of call points on lower levels by people leaving the building.
In order to provide easy access, call points should be mounted between 1.2 metres and 1.6 metres from the floor, and should be clearly visible and identifiable. The maximum distance anyone should have to travel in order to activate a manual call point is 45 metres, unless the building is occupied by people having limited mobility, or a rapid fire development is likely, in which case the maximum travel distance should be reduced to 20 metres. Call points should also be sited in close proximity to specific potential hazards, for example boiler rooms or paint spray booths, where an environmentally sealed unit will be required.
Choosing a Supplier
When deciding on which call point manufacturer to use, specifiers should consider a number of points:
• Are the products third-party approved to the relevant specification?
• Does the manufacturer produce sufficient variants to cover the requirements of the installation?
• Is the manufacturer set up to produce relatively small quantities of devices in various body colours and with custom legends at an economical cost?
• Is there a learning curve for the installation team because the design varies from type to type, or is the wiring interface constant across all versions?
• How is the manufacturer perceived in terms of product quality, delivery performance, technical support and overall responsiveness?
• Are the conventional products available through reputable channels and can the intelligent ones operate under the main detector protocols: System Sensor, Apollo, Hochiki, Nittan and others?
• How easy or difficult is installation?
• Can the zone or loop wiring be tested for open and short circuits after the first fix installation, or does the actual call point have to be installed?
There will be other criteria based on previous experience, but if the answers to the majority of the above questions are positive, it should be a good indication that the supplier is reputable and its products can be relied on to perform to specification.
To conclude, call points perform a vital role in even the most sophisticated fire system installed in the most modern of premises, enabling anyone to raise the alarm in the event of discovering a fire. In smaller systems, they can be the only method of raising the alarm. Wherever they are installed, they provide a highly visible reassurance for the occupants and visitors to the building that a fire detection system is present.
Resettable versions, in which a plastic element drops down to enable the microswitch to operate when pushed, are a relatively recent development.
Mark Thomson is Head of Marketing at KAC Alarm Company
مدرس دانشگاه و نظام مهندسی.
طراح،مشاور و ناظر برق و BMS.
نویسنده کتب تاسیسات الکتریکی.
مدیر گروه برق خانه عمران و موسسه مهندسان.
قصه های قبیله
معرفی نویسنده و مدیر وبلاگ
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تکنیک های نورپردازی، مهندسی روشنایی
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