LYNN – Heavy rains caused a section of ceiling collapsed in a Chestnut Street apartment and sent a 12-year-old to the hospital Saturday evening.”It was a 6-by-6-foot piece of plaster,” Lynn District Fire Chief Robert Bourgeois said Sunday.”The water got into the insulation and the plaster.”Firefighters responded to 77 Chestnut St. at 5:57 p.m. Saturday on the report of a partial ceiling collapse, Bourgeois said. He said that firefighters went to the third floor of the five-unit building and found that a ceiling in the interior of the building had partially collapsed.The city building inspector also responded to evaluate the scene, Bourgeoise said.The National Weather Service recorded approximately 3.5 inches of rain fell between Friday and Saturday nights at Logan International Airport.Cyrus Moulton can be reached at [email protected].