People in 12 buildings on Broadway Street in Chelsea were evacuated Monday night for about 90 minutes after authorities detected a gas leak, Deputy Chief John Quatieri of the Chelsea Fire Department said. National Grid and firefighters responded to reports of a gas odor outside of 280 Broadway around 7 p.m., said Quatieri. “We detected a near-explosive level gas leak caused by a ruptured 4-inch cast-iron gas main in the rear of a business” said Quatieri. “Approximately 150 people were evacuated around 8 o’clock between Third and Fourth Street on Broadway. Several heated buses were provided for the evacuated people to sit in while the leak was investigated. The leak was repaired and residents returned to the buildings at 9:30 p.m.”Haven Orecchio-Egresitz can be reached at Haven.firstname.lastname@example.org.