Equivalent Fire Resistance Ratings of Construction Elements Exposed to Realistic Fires
Degree GrantorUniversity of Canterbury
The New Zealand Building Code Approved Documents have recently incorporated reductions in the life safety F-ratings, which determine the fire resistance rating (FRR) requirements of fire barriers in buildings. This reduction has led to concern that in the event of a real fire exposure, where modern synthetic materials increase both the speed of fire growth, peak heat release rates and temperatures within a compartment, fires more severe than the AS1530.4 standard furnace test exposure may result. In such cases construction elements may not provide suitable fire protection for the life safety requirements of the Building Code. These requirements include provision for safe evacuation of occupants and fire service rescue activities. Three full-scale compartment tests were carried out, establishing the actual times to failure of numerous light timber framed (LTF) and light steel framed (LSF) non-loadbearing wall and LTF ceiling/floor assemblies. Each test assembly selected had detailed temperature data available from its respective standard furnace test, which had previously been undertaken to determine the assemblies FRRs. The compartment assemblies, of ISO 9705 room geometry, were exposed to fires of varying severity based on the fuel load energy density within the compartment and the ventilation opening dimensions. Synthetic materials were selected to replicate the initial fast fire growth associated with upholstered furniture. Wooden cribs were used to provide bulk fuel for the remainder of the FLED requirement. A method of predicting assembly failure times when exposed to real fire exposures has been established. The method is based on a correlation of the cumulative radiant heat energy that would impact on an assembly up to the point of its failure during a standard test, and the equivalent time at which a real fire exposure would have produced the same level of cumulative energy. The method provides good agreement and reasonably conservative prediction of a nonloadbearing assembly’s insulation failure. Further validation is required to establish factors of safety to the method for determining assembly integrity failure. The method was found to be non-conservative for use on loadbearing assemblies.