[.:4:.]

So my take on this, yes its not good having such a historical monument see severe damage, but it was a construction site. Im not going to speculate about what the cause was, as an electrician there is a multitude of ways fires can start and ive seen enough small fires caused due to different faults. But being a construction site, even with fire detection systems theres a high chance those systems were isolated due to either hot or dusty works or those systems being worked on and after hours left isolated as they arent in a functional state. Granted australia is a newer country so what we have as old buildings arent as old, but i have done works in a few herritage buildings, earliest being a few from the 1880s, and the amount of well aged dried wooden structual members screams fire hazard. So had the same fault/cause happened in a concrete structure it may just have been a minor thing, but unfortunately in something like the cathedral, things escalate a lot faster.