Authorities and fire investigators released their preliminary findings on Tuesday of the cause of the fatal Lowell fire that killed four adults and three children last week.
State Fire Marshal Stephen Coan said the fire was started by an electrical failure in an empty space between the second and third floors of the Branch Street building and that it burned for some time. It eventually broke through the space, became visible and fed off of a sudden rush of oxygen.
"It quickly became an inferno with intense heat and thick, black, choking smoke," said Coan.
Media outlets reported that fireworks were present in the building, but Coan said that while they did detonate during the blaze, they did not play a role in the fire.
Coan also said that when the eletrical fire took hold of the building, it disabled the fire alarm system.
The fire hurt other residents and a firefighter and displaced dozens who lived in the building. A fund was set up to help those impacted by the fire.