This is the online supplement for a publication entitled "Evaluation of Basic Trainings for Rescue Forces". This research was conducted at the University of Münster, Germany, in cooperation with the State Fire Service Institute North-Rhine-Westphalia, Germany (in German: Institut der Feuerwehr Nordrhein-Westfalen (IdF NRW)). Since members of rescue forces such as firefighters have to deal with sometimes extreme and dangerous situations, high-quality basic trainings are indispensable for their professional success. There is therefore an obvious need for standardized tools assessing the training quality. This research aims to develop and validate such an evaluation instrument. In Study 1, a qualitative analysis (N = 21) was used to identify core characteristics of good firefighter basic trainings and served as theoretical basis for the generation of corresponding items. In Study 2 (N = 257), the item set was piloted and reduced, its structure was assessed in exploratory factor analyses, and first validations were conducted. Study 3 (N = 451) tested the proposed factor structure via confirmatory analyses and validated the questionnaire comprehensively. Factor analyses showed a six-factor structure. The scales of the newly created Feedback Instrument for Rescue forces Education – Basic education (FIRE-B) are to be judged as reliable. Moreover, there are several clear indications of validity. Thus, the present research contributes to the understanding of critical factors and processes of basic trainings. Furthermore, the FIRE-B has a high practical relevance, both in the assessment of training quality and in the identification of opportunities for improvement. Contents of the online supplement: Table A1: Pool of items newly created or adapted on the basis of the results of Study 1, sources as well as reasons for exclusion of individual items in Study 2 Table A2: FIRE-B-items in English and German with indication of the original items which served as basis Table A3: Overview of all validation items of Study 3 their source and response format Table A4: Descriptive statistics and correlations for all measures used in Study 3 Table A5: Optional items depending on the evaluation context Table A6: Descriptive statistics for FIRE-B including kurtosis and skewedness Scoring Instructions (incl. Table A7: Score calculation of FIRE-B scales) Questionnaire templates for FIRE-B in English and German