Renovations and fires seem to go together. Johnny Cash's old house burned to the ground a few weeks ago.
When I was stationed in Sasebo, Japan the base HQ building (dating from pre-WWII Japanese Navy) was gutted by a fire during renovations. The irony was they were installing a modern sprinkler system.
Back on topic, it will be a real shame if the Cutty Sark is lost.
The plumbing is often shut down for repairs, power tools and temporary wiring (like extension cords) brought in for power tools, temporary lights strung, volatile chemicals brought in to clean and strip paint. Torches brought in for welding and soldering, though I doubt torches were much or an issue on the Cutty Sark.
In the area of more sinister speculation, historic buildings are often on valuable property where someone would like to build something more profitable. Atlanta had a string of fires set in historic buildings by "vagrants setting fires to keep warm" -- I bet if anyone looked hard enough, they'd find that someone had handed a gas can, a gold Zippo and a crisp $50 bill to that vagrant.
This is a shame. One of the Queen’s palaces burned too during renovations. The White House may have also during the Truman era, IIRC.