Refuse Derived Fuel ("RDF" as follows.) system has been promoted as an anti-dioxin measure and one of the refuse disposal system technology to contribute to the formation of the recycling society by the utilization of the biomass energy. However, with an explosion accident in the RDF silo of August, 2003, the promotion was delayed, and the recent fire of a wood pellet storing silo in Sweden, are being reported. Therefore, it is necessary to understand the heat physical properties of RDF when it is stored in large quantity for a long term, and an appropriate management of the fuel is crucial. This paper introduces the safety evaluation technique that can be applied to RDF