The first explosion knocked J.P. Craven to the ground. The math and science teacher, who had been waiting for his dad to finish running his final Boston Marathon, struggled to his feet, tore off his sweatshirt, which was on fire, and his shirt, which was wet with blood, and ran.

Surgeons at Boston Medical Center operated on Craven’s head, repairing injuries to his ear and nose. They were worried about brain damage. But his parents knew the 25-year-old was going to be all right when his breathing tube was removed and he was able to talk to them.

“The doctors said there’s really no medical explanation why he’s not more injured,” said his father, Joe Craven.

“He was so close” to the bomb, said his mother, Nancy Craven. “All the other victims that close lost legs.”

J.P. Craven had another surgery last Wednesday to reconnect some of the nerves on his forehead. But he knows other survivors of the bombings are in much worse shape. “I’m so blessed to be in the situation I’m in,” he said.

By Saturday — after sleeping through much of the manhunt and lockdown that paralyzed Boston — he was able to come home. He said he thinks his hearing will come back fully once the scar tissue heals on his singed-off ear. He has to have some more metal removed from his leg, but he is already talking about getting back to the classroom.

And he thinks this might not be his dad’s last Boston Marathon, after all.

Joe Craven was half a mile from the finish line when the race was stopped. He didn’t stop, though: He had just gotten word from the hospital that his son was there, and he knew the quickest way to get through the chaos and barricades and the crowds to find his son at Boston Medical, a mile away.

“I did finish,” Joe Craven said. “I ran there.”

Susan Svrluga