Posts Tagged fire design

Fire safety and fire design – stages 5, 6 and 7

Posted by admin in fire alarms, technical data on December 2, 2008

In the series of Fire safety design, below there are the last 3 stages: Choice and siting of alarm devices,  The zoning of the building, and selection of control & indication equipment. The previous stages were: Initial design considerations(stage 1), Siting of manual call points(stage 2), Select automatic detectors(stage 3), Siting automatic detectors(stage 4), and the Choice and siting of alarm devices(stage 5), the zoning of the building(stage 6) and the selection of control and indication equipment(stage 7).

Fire Safety Design stage 5 – the choice and siting of alarm devices

For systems protecting property alarms must do no more than alert fire fighters, while those used for life protection it is essential that alarm signals are sufficient to warn all people that the systems is designed to protect, especially if you have to rouse those who are sleeping.

Annex B within the standard shows some typical ambient occupational noise levels, which may help in selection of quantity and siting of alarm devices. It is also generally accepted that a good fire door will attenuate sound by around 30dBA, while a typical office partition door will attenuate by approximately 20 dBA.

Alarm sounders

  • General sound levels should be 65dBA or 5 dBA above ambient noise levels, although 60dBA is acceptable in:
    - specific areas where the rest of the area is 65dBA;
    - in stairwells;
    - in rooms of less than 60 sqm;
    - 75 dBA at the bedhead to wake sleeping persons;
  • dBA levels should not be considered if taken closer than 0.5m of a wall or partition;
  • Maximum sound level provided should not exceed 120 dBA;
  • Frequency of sounder should range between 500 to 1000 Hertz;
  • A common tone throughout a building;
  • A minimum one sounder per fire compartment;
  • For small systems, a minimum of two sounders are required (connected on separate circuits);
  • If ambient sound levels exceed 90 dBA, then Visual Alarms must be provided;
  • In premises used for entertainment, where music is greater than 80 dBA, the music should automatically be silenced.

Visual Alarm Devices

  • Should be readily visible within the total area being protected;
  • Preferably  coloured RED;
  • Flash rate of between 30 to 130 flashes per minute;
  • Should be mounted at minimum height 2.1m or within 150mm of ceiling;
  • Recommended in areas where people have impaired hearing in order to comply with requirements of the Disability Discrimination Act.

Fire Safety design stage 6 – zoning of the building

The purpose of splitting a building into fire zones is to enable the safe and accurate identification of a fire condition within the protected premises. The general rules in determining the number of zones for a particular building is as follows:

  • If the total floor area is greater than 300 sqm, the you must use more than one zone;
  • A detection zone should not extend beyond a particular floor;
  • If you have to walk more than 60m withing a zone before seeing the location of the fire, then you must create another zone;
  • Automatic detectors within a stairwell or another vertical flue-like structure should be considered a separate zone;
  • The total floor area should not exceed 2000 sqm unless using MCP’s only, then the zone can be extended up to 10.000 sqm.

Other points applicable to detection zones:

  • Any call point mounted on the stairwell must be considered as part of the zone for the particular floor, and ideally the MCP should be mounted on the inside of the final exit door to that stairwell;
  • For analogue/addressable systems, the control equipment may give specific text information; however, it is still necessary to provide simple LED indication of a particular zone;
  • Remote indicators for particular detectors can be used to reduce the search distance, however they should be clearly labelled to which detector it is referring to.

Alarm zones

Alarm zones are required when parties have agreed to a “staged” evacuation whereby only parts of the building evacuate immediately. The general rules for alarm zones are as follows:

  • An alarm zone should coincide with the fire compartments of the building;
  • An alarm zone may cover more than one detection zone but not visa-versa;
  • The extent of overlap between alarm zones should not confuse the occupants;
  • An Alert signal must operate at a frequency of 1 second on 1 second off and the sounders should all be synchronized.;

Zone integrity

The integrity of Alarm and Detection zones is important. The decision to install a conventional or addressable system(see the previous diagrams) will determine which of the following points apply:

  • A fault on one circuit albeit alarm or detection should not affect any other circuit;
  • A cross connection between an alarm and detection circuit should not affect any other circuit other than those affected;
  • A short circuit S/C or open circuit O/C on a detection circuit should not disable more than 2000 sqm nor a maximum of 5 devices on floors immediately above and below;
  • Removal of a device should not affect operation of a MCP;
  • In the event of a single O/C or S/C on an alarm circuit it should not prevent at least one sounder, normally mounted adjacent the CIE, from operating.

Design stage 7 – Selection of control and indication equipment

It is now possible to obtain both Conventional and Analogue/addressable control panels(CIE) to suit a wide variety of building sizes. The chart below is designed to help with the selection of a panel best suited to your needs.

Up to
2000 sqm		 Up to
4.000 sqm		 Up to
8.000 sqm		 Up to
16.000 sqm		 32.000 sqm Above
32.000 sqm
Conventional
Zircon EN 2 4 4
Zircon EN 4 4 4
Zircon EN 8 4 4 4
Analogue Addressable
Zirkon +
EN 1		 4 4 4 4 4
Zirkon +
EN 2		 4 4 4 4
Zirkon +
EN 4		 4 4 4

These panels have “in built” power to maintain the system for 24h in the event of mains failure, with additional capacity to operate the alarms for 30 minutes. Should it be necessary to have a longer standby period, an additional remote power supply unit should be added.

Siting of the control and indicating equipment

Ideally, the control and indicating equipment should be sited:

  • In an area of low risk;
  • On the ground floor in the vicinity of the entrance used by the Fire Brigade;
  • In an area common to all building users;
  • Where automatic detectors are in use;
  • Where ambient light levels are sufficient to clearly see the zonal information;
  • Adjacent to an alarm sounder.

Thank you for consulting us in your fire design needs. Was this series of articles useful to you? Let us know. To purchase fire alarms, consult our online offer of:

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Fire Design, further stages – stage 2 and 3; fire safety

Posted by sparksdirect in fire alarms on November 19, 2008

This article is a continuation of the Fire Safety Design stage 1, and continues with Fire Design stage 4. Read more about the second stage(siting of manual call points) and the third stage(select automatic detectors) in Fire Safety Design.

Fire Safety Design stage 2 – Siting of Manual Call Points

All manual call points, whatever the system, should be RED in colour and comply toBS EN 54-11Type A, and should be located as follows:

  • Onall storey existsandall exitsto open air irrespective whether they are designated fire exits;
  • So that nobody has to travel more than45 metresto reach one except if the exit routes are undefined, in which casethe direct line distance should not exceed 30 metres;
  • The above distances need to bereducedto 25 and 16 metres respectively, if there are persons with limited mobility or there is a likelihood of rapid fire development;
  • Onescape routes and exitsto the open air, so that no one has to travel more than 45 metres on a defined route and 30 metres on an undefined route;
  • In all areas withpotential high fire risk, such as kitchens, etc;
  • Wherephased evacuation is planned, call points will need siting on all exits from a particular zone;
  • 1.4 metres + or – 200mm above the floor;
  • Call pointsfitted with protective hinged covers for whatever reason should be listed as a Variation;

Fire Safety Design stage 3 – Select automatic detectors

In is very important to:

  • Havean adequate number ofdetectorsto fully cover the area requiring protection;
  • Selectthe correct type of detectorto match the potential fire type;
  • Tosite the detectorsto give the best chance of detecting the fire quickly;
  • To take into accountthe potential threat of false alarms.

We would strongly recommend that the designer reads Section 2&3 ofBS 5389-1:2002, for further advice on the selection and siting ofautomatic detectors.
Optical detectorsare generally used for detecting slow smouldering fires while ionisation detectors are better suited to free burning high energy fires.

How to avoid false alarms

Within the standard, a strong case is made to avoid false alarms. There are some areas where the placement of automatic smoke detectors should be avoided.

Irrespective of the type of smoke detector, the areas to be avoided are steamy, dusty or smoky enviroments such as kitchens, showers or bathrooms.

Other areas where care should be taken when using optical detectos are: enviroments with large amounts of dust, areas where steam occurs or where there are likely to be infestations of small insects such as grain thrip flies.

Other forms of detectors – some advices

  • Fixed temperature heat detectors
    The fixed temperature heat detectors can be used in areas where smoke detectors are unsuitable; however, they are not advisable for use in corridors or where production of smoke may be a threat to people’s escape;
  • Rate of rise heat detectors
    Rate of rise heat detectors, which have a combined fixed temperature and rate of rise sensing element, may offer improved reaction times. However, they should not be used within kitchens or where there is likely to be a rapid fluctuation in temperature, like the loading bays, boiler rooms, lantern lights, etc.
  • Duct detectors
    This device incorporates anoptical smoke detectorwhich samples the air extracted from the duct via a sampling tube. While this may appear to be an ideal solution for a wide range of applications, it is strongly recommended that before its use, you consult a professional design team for further information. Air velocity and dilution of the air will greatly affect the expected sensitivity of such a device;
  • Beam detectors
    Unlike a point type detector, beam detectors provide detection over a much greater area as well as being suitable for siting at much higher mounting heights. Generally, one beam detector can protect an area of up to 100m in length with a width dependant on the roof construction(flat or apex).
    Ideal for use in shopping malls, warehousing, aircraft hangers or buildings with high atria.

These are the 2nd and 3rd stages ofour recommendation of fire design/fire safety design(seestage 1). To be continued with the next steps.

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Fire Design – fire safety design, stage 4 – Siting automatic detectors

Posted by sparksdirect in fire alarms, technical data on November 19, 2008

In this article, which is a continuation of the Fire Safety Design stages 1, 2, and 3, you can read about: the spacing of detectors in normal applications: for pitched roof, near obstructions or unusual ceilings; siting optical beam detectors, and other considerations.

Spacing of detectors in normal applications

Under flat horizontal ceilings – smoke and heat detectors:

Spacing the smoke detectors(categories P + L) on the centre line in escape routes and corridors
Width of area Radius of detection To wall Between
1.00 7.50 7.50 15.00
2.00 7.50 7.50 15.00
3.00 7.50 7.35 14.70
4.00 7.50 7.23 14.46
5.00 7.50 7.07 14.14
6.00 7.50 6.87 13.75
7.00 7.50 6.63 13.27
7.50 7.50 6.50 12.99
8.00 7.50 6.34 12.69
9.00 7.50 6.00 12.00
10.00 7.50 5.59 11.18
10.60 7.50 5.30 10.60
Spacing heat detectors(Category P) on the centre line in corridors(not escape routes)
Width of area Radius of detection To wall Between
1.00 5.30 5.30 10.60
2.00 5.30 5.30 10.60
3.00 5.30 5.08 10.17
4.00 5.30 4.91 9.82
5.00 5.30 4.67 9.35
6.00 5.30 4.37 8.74
7.00 5.30 3.98 7.96
7.50 5.30 3.75 7.50

Design stage 4.1: Detector spacing for pitched roofs

Generally mount the first row of detectors in apex except where woof rise is less than 150mm for heat or 600mm for smoke, in which case consider as flat ceiling. Coverage increases by 1% for every degree of angle of pitch to a maximum of 25%. If slope differs either side, so will coverage of detectors in apex.

Design stage 4.2: Siting detectors near obstructions or unusual ceilings

Detectors should be sited no nearer than twice the depth of the obstruction.

  • If greater than 250mm, do not site the detector nearer than 500mm.
  • If the obstruction is greater than 10% of floor to ceiling height, treat it as a wall.
  • If the gap between partition or top of racking is less than 300mm, treat as wall.
  • Remember to keep a clear space of greater than 500mm from any detector.
  • Low beams or rafters – refer to table 2 of BS 5839-1:2002, detectors may not be required between each one depending on their construction.
  • For ceiling of floor voids – mount detector in top 10% or 125mm, whichever is the greater.
  • More info – consult section 22.3 of BS 5839-1:2002

Design stage 4.3: siting optical beam detectors

Like “Point Detectors” the furthest distance between the wall and line of detector should be more than 7.5m.

  • If used under a pitched ceiling, you may increase coverage by 1% for every degree of angle of pitch up to 25%. If pitch varies either side, so will the coverage.
  • If used below 600mm of ceiling height in order to provide supplementary detection of a rising smoke plume, for ex. the width of the area protected on each side of the beam should be regarded as 12.5% of the height of the beam, and the nearest likely seat of fire.

Notes:

  • Transmitters and receivers should be mounted on a solid construction, not something that will move with temperature or wind;
  • Avoid mounting beams where high probability of people or equipment may obstruct the beam;
  • Do not hire beam less than 500mm from along side any wall/obstruction;
  • Additional beam detectors can be sited at lower levels if smoke is unlikely to reach the apex due to a natural heat barrier.

Design stage 4.4: further considerations

  • For a type P1 system, every part of the building should be suitably protected. For this purpose each enclosed space should be considered separately.
  • Areas covered by a Type P2 system should be separated from unprotected areas by a fire resisting construction.
  • Voids which are not more than 800mm deep need to be protected unless fire can spread through them from one to the other or it is identified in a Fire Risk Assessment, as a potential High Risk;
  • Where rooms are divided by partitions or storage racks reaching to within 300mm of the ceiling each section should be protected separately.
  • Shafts for elevators, lifts, hoists, escalators and enclosed chutes through floors and stairways should be protected by detectors at the top of the shaft and within 1.5m of openings of each floor.
  • Enclosed staircases should be protected by detectors on each main landing within the staircase.
  • Lantern lights should be protected by a detector unless they are less than 800mm in height above the ceiling and are not used as ventilation.
  • Extra detectors may be needed to cope with structural features within a room.
  • Consideration must be given to possible adverse air flows when air conditioning and ventilation systems are in use.
  • If a detector is concealed, it may be desirable to provide a remote visible indication of its operation.
  • Care should be taken when siting to ensure that adverse conditions such as high levels of shock or vibration are not encountered.

To be continued with the next steps in Fire Safety and Fire Design.

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Fire systems and the first step in fire design

Posted by sparksdirect in fire alarms on November 18, 2008

Comparison between conventional and analogue addressable systems

The conventional system

A conventional system incorporates detectors which are in one of two states: either on or off. The detectors incorporate the criteria for measuring levels of fire phenomenon and, after reaching the levels defined within the standards, will switch from an Off state to an On state. Once the On state is reached, a signal is passed to the CIE(Control and Indicating Equipment) which in turn switches ON the alarm sounders.

The analogue/addressable system

A typical Addressable system is wired with a series of loop circuits, which can either contain: 1. Input devices such as detectors and MCP’s or 2. Input and output devices including sounders and strobes. The detectors are usually Analogue type that are checked at short intervals(up to 10 seconds) on what condition they are in. If the detectors are seeing a fire-like phenomenon and have reached a recognized threshold, the CIE will operate the alarm.

Which system should we choose?

General Conventional systems are used on smaller buildings where the evacuation plan is simple, that is “one out – all out”, or total evacuation. Addressable systems are generally more cost-effective to install in medium to large buildings and also have the additional benefits offered by the Analogue detectors and CIE.

Fire design – the first step

The relevant standard in Britain is BS 5839-1:2002 – the current British Standard for Fire Detection & Alarm Systems in Buildings.

Before setting out to design a fire detection system, it is important to understand the responsibilities and steps involved in the design process. The individual who picks up this role will be expected to signoff the G1 Design certificate and provide all the documentation that will form the foundation of a record that will remain in place for the life of the system. Ideally, the designer should have some recognised competency in fire engineering, having either attended a recognized training course or have proven past experience. The importance of design planning cannot be overstated. The purchaser or nominated designer should consult the following parties before the design is finalized:

  • The building Control Officer;
  • The Local Fire Officer;
  • The Building Insurer;
  • The Health & Safety Executive;
  • The User of Facilities Management Team;
  • The Architect;
  • Consultant Engineers and/or Building Services Engineers;
  • The System Installer.

After speaking with all the interested parties, the responsibilities of the designer will be to complete the following:

  • Ensure all legal requirements are met;
  • Clarify the level of protection that is required, ex: L1, L2, etc;
  • Document the argument and list any “Variations”;
  • If needed, provide a separate Risk Assessment report;
  • Complete the specification & drawings;
  • Prepare a “Fire Plan” or “Cause and effect” matrix;
  • If possible, witness the final test and handover to the client;
  • Sign off the G1 Design certificate shown within BS 5839-1:2002;

Fire detection systems are installed for many reasons and purposes. They may be installed for the protection of life, or for the protection of property, or a mixture of both. The British Standard encourages the building owner to carry out a Risk Assessment of the property to determine the level of protection required, which can be any of the following:

  • Systems for Protecting Property(P)
    The primary objective in protecting property is to ensure the fire is detected at an early stage, in order for the fire fighters to take action and minimise the damage.

    • Category P2
      A lower, but often adequate, standard allowing for automatic detection in specific rooms or areas, which have been highlighted in the Risk Assessment or by the buildings insurer;
    • Category P1
      The highest level of property protection in which all areas of the building will be covered with automatic detection.
  • Systems for Protecting life
    The objective of the fire alarm system is to warn occupants of a fire so that they can safely evacuate. In some instances, automatic detectors are not necessary, all that is required is manual “break glass” system with adequate alarm sounders. However, the majority of life protection categories consider the capability of the occupants to escape, the potential speed of the fire and structural protection afforded by the type of building. These categories are defined as follows:

    • Category M
      A system with no automatic detection for use in a building with no sleeping risk and where the fire can be detected at an early stage before escape routes are affected.
    • Category L5
      A level of automatic detection to high risk rooms or much larger areas or buildings where none of the other life risk categories are adequate.
    • Category L4
      Allows for the provision of automatic detectors within all escape routes, corridors, and stairways and any other area forming the common escape route.
    • Category L3
      In addition to the coverage described in L4, detectors should be provided in all rooms that open onto the main escape route except rooms that open onto a corridor less than 4 metres in length and with fire resistance doors separating the area from other parts of the escape route.
    • Category L2
      Protecting all areas detailed under L3 as well as all areas of high risk such as boiler rooms, etc.
    • Category L1
      L1 provides automatic detection throughout the building.

To be continued, with the next steps in fire design.

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