This paper describes a basic concept of the method using wireless communication technology for preventing collision accidents of workers with heavy equipment such as a hydraulic excavator and a mobile crane. This method aimed to send worker a warning early to provide sufficient time for a worker to avoid a dangerous situation. Closeness information of workers and heavy equipment on the site was used to identify dangerous situation. The closeness information was estimated using existence area of each object. The area was calculated from detection data of active type RFID (Radio Frequency Identification) device that was attached to workers and equipments. An experiment was performed and shows that the actual distance between two tags became progressively shorter.
