Stairs with smoke-proof filter

Ministerial Decree 30 November 1983 “Fire Prevention Terms, Definitions, General Definitions and Graphic Symbols"(downloadable here in pdf format) reports, within the section dedicated to crowding and escape, the types of stairs in the context of the design of the escape route system.

Fire Prevention Terms, General Definitions and Graphic Symbols
The legislation concerning fire prevention uses specific terminology which, therefore, has a different meaning from that commonly used.
It is advisable, especially for those who are dealing with this subject for the first time, to read the Ministerial Decree of 30 November 1983 – Fire Prevention Terms, General Definitions and Graphic Symbols – in order to understand the meanings of the terms used since almost all specific legislation refers to this decree for these aspects.
It is appropriate to pay some attention to these aspects also when drafting reports since an incorrect use of the terms could achieve a different result than expected.

Smoke-proof staircase.
Staircase in a room constituting a fire compartment with access to each floor – via doors of at least predetermined REI fire resistance and equipped with a self-closing device – from an open space or from an open hallway on at least one side onto an open space equipped with an open parapet.

Internal smoke-proof staircase.
Staircase in a fire compartment with access to each floor via a smoke-proof filter.

Protected staircase.
Staircase in a fire compartment with direct access from each floor, with doors of predetermined REI fire resistance and equipped with a self-closing device.

See also the Technical Standards for Fire Prevention (pdf)
Consolidated text of Annex I of the Ministerial Decree of 3 August 2015 Fire prevention code