Contents lists available at ScienceDirect Fire Safety Journal journal homepage: www.elsevier.com/locate/ firesaf Transparency vs magic numbers: The development of stair design requirements in the Italian Fire Safety Code Emanuele Gissi a , Enrico Ronchi b, ⁎ , David A. Purser c a Corpo nazionale dei Vigili del Fuoco, Comando provinciale di Genova, via Albertazzi, 2, Genova, Italy b Department of Fire Safety Engineering, Lund University, P.O. Box 118, SE-221 00 Lund, Sweden c Hartford Environmental Research, Hatfield, Hertfordshire, UK ARTICLE INFO Keywords: Egress Magic numbers Transparency Fire code Stair design ABSTRACT Practitioners may face difficulties in the interpretation of fire codes since they often present so called “magic numbers”, i.e. numbers available in the codes which are listed for providing the design of building fire safety, for which the derivation and justification are not explained. The present paper discusses the need for a transparent regulatory approach, in which legislators publicly justify each of the choices made during the development of the fire codes. This approach has been used for the first time during the development of the Italian Fire Safety Code DM03/08/15, where the process adopted for the development of the code requirements has been publicly released in parallel with the code itself. This is deemed to facilitate the interpretation of the fire code, avoiding mis-use and preventing criticism on lack of transparency. To address this issue, the Italian legislators have conducted a process of reconstructing the assumptions adopted for the definition of magic numbers in other International codes (i.e., British Standard 9999) in order to identify suitable specifications for the national context under consideration. This includes the performance of a series of calculations rather than a mere historical examination of their basis. As a first attempt towards an increased transparency in fire code development at an International level, this paper publicly summarizes the process adopted by the Italian legislators for the development of the new Italian fire code, focusing on the exemplary case of the calculations performed for the definition of the requirements concerning stair design (i.e. vertical evacuation). This is presented by comparing the deemed-to-satisfy provisions of the Italian code with the ones given in the British Standard 9999. The process of developing fire codes is discussed together with the benefits associated with transparency in the assumptions adopted for their definition. 1. Introduction Regardless of the approach used in a Fire Safety Code (i.e., prescriptive, performance-based or hybrid [1,2]), interpretation and understanding of the origin of the so called “magic numbers” addres- sing fire safety design is a common issue for practitioners and code users. “Magic numbers” are here intended as those numbers available in the codes which are listed for providing the design of building fire safety, for which the derivation and justification are not explained. Numbers such as these, for example tables of exit and stair widths serving different populations and building sizes, have often been developed and modified over many years. Examination of the history of such numbers [3,4] reveals that they were developed according to the best information available at the time, sometimes informed by experimental studies, often involving some degree of experience or engineering judgment, or in some cases simply to standardize products (such as door sizes). Although the basis for development may be stated in early docu- ments, this is often dropped from later standards and codes, usually for simplification [4]. These numbers may be available in both pure prescriptive codes (e.g. generally as fixed prescriptive values for design) as well as in performance-based or hybrid codes (e.g. values for input into calculation methods). While the basis for the numbers may be somewhat less important for application of prescriptive codes, this becomes particularly important for the application of semi perfor- mance-based (hybrid) codes or full performance-based codes. If the basis and derivation is explained then it can be interpreted and modified in the light of more recent knowledge, objectives, demo- graphic changes and modern developments in design. The scope of this paper is a discussion on the need for transparency on the basis and assumptions used for the development of fire codes. Transparency would enhance users’ understanding of the codes with a subsequent improved application and increased safety in building design. This issue is exemplified in this paper through the presentation http://dx.doi.org/10.1016/j.firesaf.2017.03.037 Received 31 January 2017; Accepted 15 March 2017 ⁎ Corresponding author. Fire Safety Journal xxx (xxxx) xxx–xxx 0379-7112/ © 2017 Elsevier Ltd. All rights reserved. Please cite this article as: Gissi, E., Fire Safety Journal (2017), http://dx.doi.org/10.1016/j.firesaf.2017.03.037