The present study focuses on the monitoring of interior climate parameters of a building, aiming to provide better situational awareness towards heating efficiency and an early warning system in case of critical accidents, such as fire outbreaks. More specifically, in this paper, a digital twin platform of humidity and temperature conditions in a building interior is proposed, which also provides an early detection and warning in case of fire accidents. Furthermore, for the first time Cellular Automata and Digital Twins are combined to predict and simulate the fire spreading inside the building. Finally decision support suggestions are also offered to extinguish the fire as soon as possible. The sensor data of temperature and humidity were acquired by an Arduino platform, which transmits the data to the command and control center. On the other hand, the building interior design, the visualization of the outcome to the operator, the simulation of fire spreading and the decision support were built using the Processing software.