In confined work sites such as mines and ships, it is important to monitor the worker's current location for safety. When the collapse or sinking accident occurs, quick rescue can be realized based on the location of the workers. However, it is not easy to support a precise real-time monitoring system due to limited infrastructure and constraints of using sensors. In this manuscript, we propose a method of building a precise positioning system in workplace using only WLAN. The method includes a similarity measure to handle highly fluctuating signal strength and a hybrid positioning technique of fingerprinting and proximity. When we test the proposed method by applying it to a limestone mine and a drillship, it demonstrated it can be used practically in the workspace by showing superior positioning accuracy than the conventional methods in a restricted environment.