A member performing maintenance at the Seventh Day Adventist Church in Braintree survived an 18-to-20-foot fall down an air shaft Thursday and was trapped in the ventilation duct for approximately 45 minutes while firefighters maneuvered to rescue him, Lieutenant Joe McLaughlin said. Firefighters climbed more than 8 feet, then crawled more than 25 feet through the duct, which was less than 4 feet by 4 feet, to reach the victim, McLaughlin said. Once they located the victim, McLaughlin said responders slid him out on a board. According to McLaughlin, the victim, who was taken to South Shore Hospital, appeared to have suffered no injuries worse than a possible broken bone. Firefighters train for confined space rescues, but rarely perform them, McLaughlin said.