In the case of the Eaton Fire, the investigators are likely to use magnets to help them hunt for the tiny, melted pieces of metal that could have been shed by power lines if they slapped together. But the existence of the metal doesn’t necessarily indicate that’s how the fire started, Nordskog said.

Wildfires menacing Los Angeles have killed at least 10 people and devoured nearly 10,000 structures, with five fires burning into a third night, as dry desert winds fanning the flames again gathered strength.