Unprotected Floor Assemblies and Tenability Conditions in a Test House Under Two Basement Fire Scenarios

A full-scale experimental program was undertaken to study the impact of two basement fire scenarios on the structural integrity of unprotected floor assemblies above a basement and the tenability conditions in a test facility representing a typical two-storey detached single-family house with a basement. The experiments utilized relatively severe, fast-growing fires set in the basement, which had an unprotected (unfinished) ceiling, to challenge the structural integrity of the floor system above the basement, which provides the normal egress route on the first storey for occupants. A range of floor assemblies constructed with various types of engineered floor joists and trusses (including wood I-joists, steel C-joists, metal plate wood trusses and metal web wood trusses) and with solid-wood joists, were used in the experiments with the basement side unprotected (unsheathed). Potential exposure to toxic gases, heat and smoke obscuration under the test conditions was analyzed to estimate the time available for escape. The results help establish the sequence of fire events such as fire initiation, smoke alarm activation, onset of untenable conditions, and structural failure of the floor assembly above the basement to understand how these factors affect the ability of occupants on the upper storeys to escape in the event of a basement fire.