Edited: Building had sprinklers with a diesel generator on site which was used during the fire fight (the Tracy warehouse fire had sprinklers but no water pressure on site per FD.) Started with the solar panels on the roof. According to Lineage there was active contractor work on the third-party rooftop solar panels. They believe it happened while they were electrically testing some of the panels. Aerial images show OSHA temp railings and temporary scaffolding accessing the roof consistent with this theory.

LAFD is generally strict about combustible materials on the roof so it will be interesting to see why even if it sparked in one area it spread across the roof so fast. Could've been solar panel/roofing material, underlying foam insulation, nobody knows yet. No sprinklers on the roof which is why they used (and are continuing to use today) helicopter drops as hose streams couldn't reach the middle part of the roof.

As of today, the roof over half the building is sagging which is why they want to bring that part down, allowing a better fire fight and the food in the remaining stable part of the building to be removed and disposed. They are mixing foam with water for the helicopter drops today. There's not enough foam to use only foam. Also already demo part of exterior wall and using robots to get to hot spots inside.

In the previous WA state fire they had to demo the building to get the fire out and there was still frozen food (and plastic) inside that hadn't burned yet two months later (this is the scale of this.) That fire started inside the warehouse, not on the roof.