Police and federal agents found guns, weapon parts, live ammunition and a chemical cocktail that went horribly wrong at the scene of a powerful explosion in East Boston yesterday, but were “comfortable” saying there’s no link to terrorism.

A 28-year-old man authorities described as a “person of interest” was in critical condition under guard at Massachusetts General Hospital. Boston police Commissioner William B. Evans said the suspect suffered second-degree burns to his arms and legs when an experiment he was working on in his second-floor apartment on Webster Street blew up shortly after 12:30 a.m. yesterday. Two dogs were also in the home and survived, the landlord told police. He declined to speak to a reporter.

Evans wasn’t immediately sure what the resident was attempting to create. He declined to release his name, explaining he is likely facing illegal weapon charges.

Working in partnership with the FBI and Bureau of Alcohol, Tobacco, Firearms and Explosives, Evans said, “We moved in along with our bomb squad, along with arson squad. We’ve been sifting through the evidence. We don’t believe there’s any nexus to terrorism at all. He was experimenting with chemicals and powder and from that it blew up in his face. … We don’t believe it was a bomb.”

Investigators cleared residents and onlookers from the area prior to entering the property yesterday with a search warrant shortly after 3 p.m. Among law enforcement on scene was the Boston police Special Operations Hazardous Materials Response Team.

“We know there was live ammunition in there, there were live weapons and air rifles. That’s all going to be processed,” he said. “The good thing is we don’t believe there’s anything to do with terrorism here. Based on what we found in there, we don’t believe there was any sort of sinister plot.”

After consulting with Harold “Hank” Shaw, special-agent-in-charge of the FBI’s Boston offices, Evans said, “We’re very comfortable saying we don’t think there was any link to terrorism. It doesn’t raise the alarm bell.”

The blast blew out three windows, showering parked cars and the sidewalk on the opposite side of the road with broken glass, shredded insulation and mangled screens. One window frame was left impaled on a tree outside the ornate gold triple-decker.

FBI Boston spokeswoman Kristen Setera said the agency responds to explosions “as standard protocol … to support our local law enforcement partners at the scene.”

Neighbors, including Rafael Fernandez, said the resident told police his computer exploded when he turned it on. Fernandez was brushing his teeth, getting ready for bed, when the explosion rocked the quiet street of families and young couples.

“Smoke came out the windows and the building was on fire,” Fernandez said. He saw the burned man walking on broken glass with bare feet. “He was speaking to the police, saying he’d turned on his computer and it exploded.”

Pedro Morales said his 7-year-old son slept soundly through the event that sent others running into the street in a panic.

“It sounded like a very loud thud,” Morales said. “At first I thought to myself it was a large air-conditioner that fell out a window, but there was a powerful smell of gunpowder. It was unsettling, for sure.”

Nicolaus Czarnecki contributed to this report.