After a yearlong investigation, hospital officials are blaming a faulty warming device for sparking a fire that burned a newborn baby at Mercy Hospital in Coon Rapids last January.

The baby, Maverick Werth, narrowly survived the fire, which erupted in his bassinet when he was just 12 hours old. He still has scars on his scalp and upper body, and wears special gloves to protect his right hand, according to his father, Justin Werth, of Elk River.

Investigators hired by the hospital's owner, Allina Hospitals and Clinics, concluded the fire was "most likely caused by a hot particle falling from the bassinet's warmer assembly into the oxygen-enriched environment near the infant's head," according to a summary released by Allina Thursday.

Allina said the investigators, including national safety experts, also concluded that the hospital staff was not at fault because the defects in the device "are not visible to the naked eye," and did not result from improper maintenance.

Dr. Penny Wheeler, Allina's chief clinical officer, said she was satisfied they had found the cause of the fire. In the end, she said, "we cannot see any action that we could have taken to avoid this." Mercy and other Allina hospitals stopped using the device after the fire.

Investigators recommended that the device involved in the fire, a Hill-Rom 1250, and similar models should be "removed from service," but Draeger Medical Systems, which acquired the Hill-Rom business in 2004, disputed the findings. Spokesman Bill Keegan said that the investigators relied on speculation. "There were no conclusive results," he said, adding that the warmers "are safe and effective when used as directed." He said about 4,000 units of the same or similar design were sold before being discontinued in the late 1990s.

Chris Messerly, the Werth family's lawyer, called the investigation "exceedingly thorough." He said that his own experts will review the report. "We would just like to hold the responsible party accountable for this little boy," he said.

Maverick suffered second- and third-degree burns in the fire on Jan. 22, 2008. Witnesses said flames erupted inside a plastic oxygen dome placed over the baby's head to help him breathe. His bassinet had been placed beneath the warming device in the nursery.

Two nurses standing beside him put out the fire immediately, hospital officials said. Maverick was soon transferred to Hennepin County Medical Center, where burn specialists said he was the youngest person treated for such injuries.

Maverick, who was born three weeks premature, spent a week in critical condition with burns over nearly 18 percent of his body, primarily on his scalp, cheeks, shoulders and hands. Doctors told his parents, Melissa and Justin Werth, that he would have died if he had inhaled the smoke. He was hospitalized for nearly three weeks.

Today, Maverick and his family are still coping with the lingering effects. "He has a good disposition," his father, Justin, said in an e-mail to the Star Tribune. But scarring has made it difficult for him to crawl and grasp objects.

"The strains of this ordeal injured our family, but we are putting the pieces back together," Justin Werth said.

So far, no lawsuits have been filed in the case. Messerly said the boy's medical bills have largely been covered by insurance. But, he said, "that doesn't include his future [skin] grafting on his hand, or pain and suffering, or how his future will be having to live with burns." Maura Lerner • 612-673-7384