The lack of a method to quantify the contribution of exposed timber to a fire was identified as one of the main gaps of knowledge concerning the challenges of building high-rise timber buildings, in a recent gap analysis performed by the NFPA. Recent experimental studies successfully quantified the contribution of large surfaces of exposed timber, in terms of rate of heat release. However, a method to predict these quantities has not been found in the literature.

This report proposes a model that includes the contribution of exposed or protected timber to post-flashover fires in compartments with a floor area up to 100m2. The model consists of a one-zone model and a wood combustion model. Using the one-zone model, the temperatures in the room are estimated from the heat release rate. Using the wood combustion model, the heat release rate coming from exposed or protected timber is estimated. The influence of delamination of lamellas or fall-off of claddings can be estimated with some restrictions regarding accuracy.

Comparative studies showed that predictions of the model correspond well with previous full scale compartment fire tests.

Key words:

Compartment fire, Timber, CLT, natural fire, charring rate, heat release rate, delamination, cladding failure