WSN-SA is a Wireless Sensor Networks (WSN) framework that is been proposed to support rescue operations in collapsed structures, such as houses and buildings, after natural and human-made disasters. The sensors and actuators are deployed prior to the disaster and ideally such sensor network is a required infrastructure of any building. Such SA systems can help to indicate how to distribute the rescue resources and how to identify imminent risks for rescuers and survivors. So far, few situational awareness (SA) systems based on WSNs have been proposed and no long-term realization of such systems has been reported. The goal of this work is to provide the foundations to change this reality so it would be possible to see a SA system accompanying each existing fire system. To this end, a strong emphasis is given to a) the achievement of low total cost of ownership (TCO), b) reliability, c) and expandability for the adopted SA solution.