Syracuse fire investigators have determined the house explosion earlier this week was caused by a free-flowing natural gas leak in the house's basement.

Also on Friday, five victims from Tuesday's explosion were still hospitalized, all in critical condition – a 33-year-old woman, a 42-year-old man, a 3-year-old, a 2-year-old and 8-month-old, Upstate University Hospital said Friday afternoon. All others had been discharged.

Syracuse Fire Chief Michael Monds said Friday afternoon that the explosion and subsequent house collapse, which injured at least 11 members of two refugee families, came from a leak "into the area of the basement where a dryer hookup should have been located." The investigation, which began a day after the explosion on Carbon Street, revealed the gas meter for the house fed multiple appliances, with two lines coming from the meter. One of those was for the furnace and hot water tank in the basement; the other was for a dryer in basement area and a first-floor stove.

Despite the available line, Monds said, there was no clothes dryer in the basement, and the shut-off valve was "in the fully open position" with no cap on the end of the piping. That allowed gas to freely flow through the pipe.

Investigators have not determined how the valve turned on.

“We have a upper explosive limit where essentially there's too much natural gas to ignite and a lower explosive limit where there's not enough gas to ignite," said Joseph Fenell, captain of the Syracuse Fire Investigation Bureau. "There has to be a perfect fuel air mixture for that to occur, for that explosion to occur. And then it could be as simple as turning a light switch on.”

The home's owner told investigators that there hadn't been a dryer in the "four to five years" he had owned the rental property.

Investigators reported the tenants first smelled a gas odor at 9 a.m. Tuesday, around seven hours before the house exploded. The investigation included the SFD, Syracuse Police, National Grid, and the Bureau of Alcohol, Tobacco and Firearms. 

Seven people who lived in the home at 205 Carbon St., and a visiting family of six, all of whom are from Myanmar and part of the Rohingya ethnic group, were in the residence when it exploded and partially collapsed around 4 p.m. Tuesday, according to firefighters and Syracuse Common Councilor Chol Majok. One child was pinned in the driver's side of a car outside the house, and was freed by firefighters.

"This was a very chaotic scene," Monds said of the explosion and collapse, which occurred around 4 p.m. Tuesday.

Investigators ruled out any involvement of the car in the explosion, Monds said.

More than 60 personnel responded to the scene, the chief said, as well as search dogs brought in from both Albany and Marcy to ensure that no other survivors or casualties were trapped in the house.

“We'll continue to talk to the patients. And if any more information comes forth that makes us open up the investigation and go down a certain pathway our fire investigation team certainly will do that in conjunction with the Syracuse police and our other partners that have been investigating this situation.”

The Onondaga County District Attorney's office has determined that no criminal charges will be pursued at this time, according to Monds, who said it's not believed that there was any "criminal or malicious intent" behind the open gas line.

Syracuse Mayor Ben Walsh said it is "heartwarming" to see the support from the community; Monds said both firefighters and civilians initially helped to rescue people from the house, and was looking forward to all leaving the hospital.

"We're not going to feel good until everybody is discharged," Monds said.