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What does W3-7.5 means for an External Alarm?

Australian Standard AS1670.1 sets out the requirements for the installation of an automatic fire detection and alarm system. The Standard specifies the location and type of device used to indicate the location of the designated building entry point by way of a flashing red strobe mounted on the wall of the facade of the building. The intention is to make it easy for first responders (the fire brigade) to identify a building where an active alarm exists, so they can respond efficiently.

Clause 3.8 of Australian Standard AS1670.1-2008 specifies the location of an external alarm to identify the Designated Building Entry Point ("DBEP").  The Standard specifies the use of a Visual Alarm Device ("VAD") mounted as follows;

  1. wall mounted;
  2. located on the front facade of the building on which the DBEP is present;
  3. shall be not more than 10, from the DBEP;
  4. be active (flashing red) when there is an active (not disabled) fire alarm condition;
  5. be visible from the fire appliance, approaching from at least two directions;
  6. have a minimum rating of W3-7.5;
  7. have a sign with the word "FIRE" in white capital letters on a red background with lettering not less than 50mm in bold sans-serif typeface;
  8. the colour and material of the sign shall be weather resistant (notionally IP65); and
  9. be fade resistant.

From an installation and routine servicing standard, these requirements are quite prescriptive.

What does W3-75 mean?

External Alarm Designated Building Entry Point AS1670 Strobe Bell

In all of these prescriptive requirements and reading through AS1670, it is not clear what does the requirement minimum rating of W3-7.5 mean?

The answer to this is quite simple once you know the code;

  • The letter W means "Wall", the other option is C meaning "Ceiling";
  • The number 3 means the effective height above ground level (ie. 3 meters); and
  • the number 7.5 means the effective radius of the flashing strobe.

The illustration on the Right Hand Side shows the practical application of this requirement.