Caniford, 36, said a co-worker drove him to Washington County Hospital, where he was treated and released. He said Wednesday night that his right hand was still numb.
Caniford said the white piece of metal turned black after it hit the wire. He was wearing work gloves and said a fire official told him that his sneakers probably saved his life.
Preliminary estimates placed damage to the 24 Broadway building at between $35,000 and $40,000, said Hagerstown Fire Department Capt. Brian Pile.
Battalion Chief Ronald Horn said it took about 45 minutes to bring the blaze under control. Firefighters acted quickly to cut away the walls of the third-story apartment, stopping the fire from spreading to the rest of the building.
"It was a quick stop," he said. "Luckily, it isn't windy like it was yesterday."
Horn said power was shut off for about an hour as a precaution.
City Light Department Manager Terry Weaver said about 50 to 60 customers were affected between North Mulberry and North Potomac streets and from Wayside Avenue to East Avenue.
Weaver estimated that 8,000 to 13,000 volts of electricity raced through the metal slab. The manner in which the current passed through was the most important factor, he said.
"Electricity is a funny thing. Sometimes it doesn't affect you that much; other times it does," he said. "The pass is the big thing."
Brian Miller, one of two roofers working with Caniford, said he saw a bright flash and a loud boom.
"It hit the wire and a big ball of fire came up," he said. "It actually sounded like a 12-gauge shotgun...I'm just glad it didn't knock him off the roof."
Residents who were home were caught off guard by the fire. Joe Longnecker said he moved swiftly to make sure his neighbors got out. He helped an older woman out of her apartment but left his pet in his first-floor apartment.
"I got a cat in there still," he said. "I forgot to bring him out."
Laura Wilson, who was with her great-granddaughter when the fire broke out, said she had trouble moving.
"It's very hard for me to get out," she said. "I opened up the door and saw a flash. I was screaming."
Caniford said he was glad he was able to go home to his wife and 4-month-old son.
"It really makes you think," he said.