The study aims at a critical review of the historical research that has supported the declarations of protection of industrial heritage since 1974 in the state of São Paulo (Brazil) by the Council of Defense of Historical, Archaeological, Artistic and Tourist Heritage (CONDEPHAAT), in order to verify the conservation guidelines and the interventions or uses implemented. Our study is linked to broader discussions on the reuse of industrial heritage, as the new possibilities for reuse of the building also depend on the values legally and socially attributed to industrial traces. In recent decades, dozens of studies have been published in Brazil on the subject of railway history and heritage (CORRÊA; OLIVEIRA, 2018, 2019). However, few still specifically try to understand the internal dynamics of protection studies. The researchs closest to a critical reflection on the heritage’s practice have been carried out by scholars of architectural restoration, focused on the theoretical foundations of protection and intervention in protected heritage (KÜHL, 1998, 2009, 2013) and strategies for the preservation of railway assets considering project and political aspects of preservation (RUFINONI, 2019; SOUKEF JUNIOR, 2013). It is already known that, since the creation of the state agency in 1968, architectural or historical values have prevailed in the recognition of railway heritage (OLIVEIRA, 2010). At the same time, there were distinct - if not divergent - positions throughout the studies and judgment of protection, which were defended by the counselors (MORAES; OLIVEIRA, 2016a, 2016b). Some revisions of the protection criteria were made by technicians of the state agency itself in the last decade, besides the elaboration of internal criteria for identification and protection of railway heritage (MARTINS; CARDOSO; ANDRADE, 2012; ZAGATO, 2020). This demonstrates that the patrimonial practice in Brazil begins to reach an important point of inflection and reflection about itself. Our study intends to be one more contribution in this line of reflections on the history of heritage practice. By means of a historical critique methodology, some heritage protection’s processes were analyzed in order to identify which sources were used for the historical foundation and if there was any relation between these sources and the assigned valuation; historical documentation and current specialized bibliography were also consulted. It was possible to identify that the heritage protection’s processes did not bring enough historical information to the architectural nature of the industrial building. At the same time, the national lack of specialized investigations on industrial buildings led to the use of generic works and professional experience, which led to a valuation unrelated to the particularities of the industrial property or, at least simpler than can be attributed today. The study of characterization of the industrial built space was limited even by the primitive idea of factory, original model of concentration of production in a single industrial space (the "factory building"). Even international guidelines on the protection of historic buildings, found in the Paris Charter (1972) and in the debates on the historic center, will not have great repercussions on the protection criteria adopted by local bodies, particularly for state protection of industrial buildings. In questions of preservation and reuse, it is important not to dwell on a particular building that composes an industrial complex, nor even to limit itself to the aesthetic aspect. It is possible to advance even further if based on an industrial archaeology perspective, since multidisciplinary reading allows to expand these thematic inventories: to document and, if possible, preserve the different changes that the good has undergone and that have accumulated over the years, since they witness different moments in the associations between industrial function, constructive material, human work and machinery.