Exposed timber in buildings has proven to have a positive effect on the building’s sustainability, occupant wellness, and increases the aesthetic appeal of the building but is currently limited by most building codes mainly due to fire safety concerns. While compartment fire testing can be carried out to prove a design performance, this approach is costly and time consuming. Models predicting the fire dynamics inside mass timber compartment with exposed surfaces were developed over the last years. The charring rate of the timber elements, in these models, is either the charring rate of timber when exposed to standard fire or the displacement of the 300°C isotherm using finite element analysis involving several parameters to be determined. Furthermore, using the 300°C isotherm does not account for the impact of the oxygen concentration on the charring rate. In this study, a two-zone model has been developed to estimate the heat release rate (HRR), the upper-layer temperature and oxygen concentration, and the char depth of the exposed timber elements during compartment fires. The charring rate is determined as a function of the incident heat flux impinging on the surface and the oxygen concentration. Comparing the model predictions to 20 experimental compartment fires with and without exposed timber surfaces shows that the model captures well the general fire dynamic, i.e., HRR and temperature. The char depth predictions are close to the experimental data, while being mostly conservative. Seven limitations and improvements have been discussed and will be considered in future versions of this model.

事实证明，建筑物中的裸露木材对建筑物的可持续性、居住者的健康具有积极影响，并增加了建筑物的美感，但目前主要由于消防安全问题而受到大多数建筑规范的限制。虽然可以进行隔间防火测试来证明设计性能，但这种方法成本高昂且耗时。过去几年开发了预测具有暴露表面的大量木材隔间内火灾动态的模型。在这些模型中，木材元素的炭化率要么是木材暴露于标准火时的炭化率，要么是使用涉及多个待确定参数的有限元分析的 300°C 等温线的位移。此外，使用 300°C 等温线并没有考虑氧气浓度对炭化速率的影响。在这项研究中，开发了一个两区模型来估计隔室火灾期间的热释放率（HRR）、上层温度和氧气浓度以及暴露的木材元件的炭化深度。炭化率是根据撞击表面的入射热通量和氧浓度来确定的。将模型预测与 20 个有和没有暴露木材表面的实验舱火灾进行比较表明，该模型很好地捕捉了一般火灾动态，即 HRR 和温度。炭深度预测接近实验数据，但大多较为保守。已经讨论了七个限制和改进，并将在该模型的未来版本中考虑。