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.

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:

• heat alarms, fire alarms, ionisation alarms, smoke alarms,
• domestic alarms,
  
• conventional or analogue alarms,
  
• disabled toilet alarms,
  
• any emergency lighting

and purchase online the preferred or needed alarm system for your home/office.