This is a fire warning system that alerts people working on site to make their way to an escape before a fire becomes life threatening. The warning signal should be distinctive and heard above other site noise. Types of alarms used will vary depending on the size of site and the nature of the risk. On small low risk sites the alarm may be raised by shouting but on high risk or larger sites a fixed and interconnected system (wired in or wireless) of call points and sounders will be required to provide an effective warning system.
Further guidance can be found in [BS 5839:1:2002 + A2:2008 Fire detection and fire alarm systems for buildings. Code of Practice for system design, installation, commissioning and maintenance (ISBN 978 0 580 604386) ](http://shop.bsigroup.com/). Fire detectors (smoke or heat) may not be suitable on construction sites during the build phase.