The fire's temperature probably reached 550 degrees - so intense that it began to melt furniture and dishes.
As smoke poured out of the one-story home late Friday, neighbours in Spokane, Washington, called 911, dragged a garden hose across the street and tried to douse the flames.
Awakened by the fire, the man and woman who lived inside the rental house had dashed out with three children.
But a fourth child, a 3-year-old, was still inside.
Neighbours and police officers who arrived shortly after the call weren't able to get into the home because of the intense heat and flames, Brian Schaeffer, Spokane's assistant fire chief, told The Washington Post.
Firefighters arrived a little later and went through the front door in their protective suits. They found the boy's body in the back bedroom. Next to him was a teddy bear and the family's dog, a terrier mix. The dog was huddled over the boy, trying to protect him.
"The injuries were so extreme, his injuries were just incompatible with life," Schaeffer said. "There was no way to survive that. It leaves a permanent scar in someone's memory. You can't unsee that."
Fire officials haven't said what caused the fire, which remains under investigation. The Spokane police department's major crimes unit was investigating the child's death, which is typical when a fire kills someone.
Between the fire and the investigation, Schaeffer estimated that he'd been up for 24 hours straight. When he woke upon Sunday morning, he told The Post, he was still fuming over what investigators found in the home's charred wreckage: A smoke detector with no battery inside.
"With it being 2016, there's no reason a person should not have a smoke detector in their home," Schaeffer said. His department hands out smoke detectors free. "People are so busy and oftentimes the smoke detector falls way behind paying the rent or getting a job or putting food on the table."
"This is kind of what I'm struggling with," Schaeffer said. "This is our third fire fatality in a couple months. It's not only emotional, it's preventable. We would love our business to be proactive versus responsive. We wouldn't have to go through what we went through a few days ago with a grieving family."
According to the US Fire Administration, three out of five deadly fires happen in homes without working smoke alarms.
Having a working smoke detector cuts the chances of dying in a house fire in half, the administration says.
Schaeffer's fire department had been spreading a fire-prevention message for National Fire Prevention Week, which was earlier this month.
The campaign, Schaeffer said, is more likely to save a child's life.
"You know children are at risk," he said. "They don't have the experience to get low and close the door, which is huge. (A smoke detector) will give you minutes in a residential fire."
Investigators haven't said what actually alerted the family to the smoke and flames on Friday night, or how they were able to save three children but not four. All that remains under investigation.