This study extends conventional life cycle assessment (LCA), which typically assumes an incident-free service life, to explicitly incorporate fire events and fire protection systems, enabling systematic quantification of their environmental consequences and mitigation effects in timber buildings. A proof-of-concept application was conducted for a timber-based residential compartment under four representative fire scenarios, ranging from minor object ignition to a fully developed enclosure fire, with and without sprinkler protection. Fire-related consequences were decomposed into combustion emissions, emergency response activities, and post-fire material replacement and integrated within a building LCA framework. The results show that fire development is the dominant driver of environmental burdens, with fully developed, non-sprinklered fires increasing impacts by more than 80% compared to small, confined fires. Material replacement emerged as the primary contributor, typically accounting for over 80% of total fire-related impacts, while direct combustion emissions played a comparatively minor role. Automatic sprinkler activation reduced total fire-related impacts by more than 85% across all indicators, while adding only 1–2% to the building's embodied impacts. These findings demonstrate that integrating fire scenarios into LCA enables a more realistic assessment of the environmental performance of timber buildings and supports informed decisions on low-carbon fire safety strategies