Authorities in Stamford, Conn., say a deadly Christmas Day fire that killed three young children and their two grandparents was an accident.

Investigators said the blaze started when someone put coals from a fireplace into a trash bin.

The children's mother and her friend were able to escape from the house. The grandfather reportedly died trying to save one of his grandchildren.

"It appears the grandfather had one of the children with him, tried to exit the structure, but was overcome and passed away, and the little one passed away just inside the window," said Antonio Conte, Stamford's acting fire chief.

The fire was so intense that officials say several rescue attempts proved impossible for firefighters. Stamford officials are offering counseling to any fireman who needs it.

"After 37 and a half years, 38 years, on the job, you're never prepared for anything like this," Conte said.

"It's heart-breaking. I had to recall 70 firefighters today for debriefing, and most of them broke down," he explained.

Fire officials also said there were no working smoke detectors in the home.