INTERNAL FIRE HYDRANTS IN RESIDENTIAL AND PUBLIC BUILDINGS AS A FIRE-RISK MITIGATION MEASURE

Abstract

Internal fire hydrants (IFHs) are an active measure for initial fire suppression and for supporting firefighting operations by providing immediately accessible water within the building. This paper integrates a regulatory analysis, processing of statistics for 43,127 registered fires in public and residential buildings during 2015-2025, an analysis of 66 registered fires in 2015-2024 in which an IFH was used, data from thematic inspections of 2,203 high-rise residential buildings, and a parameterized event tree for evaluating the weighted contribution of IFHs to fire-risk reduction. The analysis shows that the current regulatory framework in Bulgaria imposes measurable requirements for coverage, flow rate, pressure, minimum water-supply duration, and maintenance. Of the 66 incidents analyzed, 63 (95.5%) involved an IFH reported as operational, yet inspections of the building stock reveal a widespread presence of latent deficiencies - missing equipment, lack of maintenance, and missing signage. This confirms that the actual risk-reduction effect of IFHs depends simultaneously on their regulatory provision, technical readiness, and the human factor. Primary numerical results from the questionnaire surveys and experiments are not available in the uploaded files; therefore, the paper shows how these data enter the model without introducing unsupported values.