Evolution of flashover critical mechanisms under partition-wall and skywell retrofitting in Huizhou ancient dwellings

Huizhou vernacular timber dwellings hold immense cultural heritage value but face severe fire risks during adaptive reuse. Utilizing empirical field data, this study develops a full-scale Fire Dynamics Simulator model to systematically evaluate flame spread, heat release rate (HRR), flashover time, and visibility across 14 scenarios spanning three retrofitting strategies: internal partition wall alteration, skywell adjustment, and integrated composite retrofitting. The results indicate that while removing internal partition walls in Strategy 1 facilitates occupant evacuation, it advances the onset of flashover, particularly when large-area partitions are demolished. In Strategy 2, enclosing roof-level skywells improves heritage structural protection, whereas leaving them unenclosed doubles the initial peak HRR to 50.30 MW. Finally, under the combined retrofitting of Strategy 3, pairing enclosed roof-level skywells with extensive partition removal generates a critical peak HRR of 45.40 MW at 211 s. Such fire features greatly threaten the timber heritage’s structural safety and cultural value.