What is a closed staircase

According to the explanation in Article 2.0.18 of the Code for Fire Protection Design of Buildings GB50016-2006, an enclosed staircase is a staircase that is separated by building components, preventing smoke and hot air from entering. A closed stairwell is a stairwell that is separated by fire-resistant building components, preventing smoke and hot air from entering. The doors of enclosed stairwells in high-rise residential and high-rise industrial buildings shall be Class B fire-resistant doors that open in the direction of evacuation. 　　Requirements for the installation of enclosed stairwells: (1) The stairwell should be located against an exterior wall, and it must allow for direct natural lighting and ventilation. When direct natural lighting and ventilation are not possible, it shall be installed in accordance with the regulations for smoke-proof stairwells. 　　(2) The doors of the enclosed stairwells in high-rise buildings shall be Class B fire doors and shall open in the direction of evacuation. 　　(3) When the first floor of the stairwell is adjacent to the main exit, the corridors and lobbies can be included within the stairwell to create an enlarged enclosed stairwell; however, fire protection measures such as Class B fire doors should be used to separate it from other corridors and rooms