Dive Brief:

• San Francisco fire investigators are nowhere near being able to go through the ruins of a six-story apartment building project, part of a 360-unit complex in the Mission Bay area, but they are trying to puzzle out how the five-alarm blaze got going Wednesday.
• Firefighters who found 40-foot walls of flame when they pulled up to the building on Fourth Street said the fire must have smoldered before erupting and consuming the structure, which had not reached the stage of having its fire-protection system installed.
• Workers had left the site about an hour before the fire was spotted. It burned so hot that windows blew out in nearby apartments and sprinklers went off in those buildings.

Dive Insight:

While the fire investigators try to figure out the building's past, the future of the site is unclear. Developer BRE Properties said it had fire insurance for the project, but it is supposed to merge this year with Essex Properties, and it's unclear if the combined company will choose to build again in that spot.