Factors such as an increase in patient numbers, demands for more hospital beds, and expansion of hospital divisions, all make the original hospital configuration inadequate, and additions or alterations must be added to the building in order to meet both current and future needs. Because hospitals cannot suspend all medical practices or reject patients, the reconstruction of hospital building must coincide with its normal hospital hours. This study focuses on how to carry out the hospitals' reconstruction without interrupting regular hospital operations. The possible effects of a fire ignited in the construction area bridging the new and the original building to its neighboring respiratory care unit's (RCU), and fire safety issues of those areas are analyzed using the FDS + EVAC software. The results show that when without the threat of fire, the fastest evacuation time for RCU was 19.3 minutes. This evacuation time can be further shortened if the door width increases to 2.0 meters or wider. In the event of a fire, human casualties will arise if the patients cannot evacuate within a certain safety time window, even if the temperature is maintained under tolerable condition by the sprinklers. Constructions, which are closely linked to fire accidents, are inevitable when expanding hospitals; therefore, this study centers its attention on how to control fire-related factors and develop effective strategies specifically for evacuating RCU patients.