For most buildings, the time when they are most exposed to fire risk is when they are having building work done on them. Fire detection and alarm / fire suppression systems isolated; compartmentation temporarily breached; means of escape altered; temporary and altered wiring; uncontrolled build-up of combustibles; hot works... the list goes on. If this does prove to be a fire started by construction works, then in our own part of the world the Windsor Castle fire; Glasgow school of art etc, etc. are all precursors.
The risk is to life can be substantial if they remain partially occupied during the works, & in many cases the FRAs aren't reviewed to take this into account. I've just done a FRA for a part-occupied construction site and found fire exits chained shut, 100m+ dead ends formed in an occupied space, to name but a few issues. The client and the contractors both have to take responsibility for managing these risks (the client can't really just leave it all up to the contractor and view it as their risk).
When I'm reviewing these types of premises, I always keep in mind that these are construction works. Whilst the construction industry is getting better, I keep in the back of my mind what I once heard from a surveyor colleague (a long time ago, but there's still an element of truth in it): "...what you've got to remember about the construction industry is that it's full of the guys who p***ed about at school, managed by guys who also p***ed about at school, wearing ties.... Things have changed now of course.
They don't tend to wear ties any more.