LYNN – National Grid technicians ruled out a natural gas leak as the odor source that prompted 1,600 students and 200 Classical High School employees to evacuate the O’Callaghan Way school Thursday morning.Students and employees spent an hour outside the school before returning at 9 a.m. as Lynn firefighters and utility workers tried to find the cause of the odor centered in one of the school’s classrooms.”We’re still trying to figure it out. There doesn’t appear to be a gas leak,” said Classical Principal Gene Constantino.District Fire Chief Robert Bourgeois responded to the school at 8:17 a.m. with Ladder 2 and Engine 9 firefighters to find the evacuation completed.”They did a great job,” he said.”C” wing where the classroom is located remained closed through the morning with students temporarily relocated to other classrooms while firefighters and investigators tried to pinpoint the gas odor.”Our technician found no unusual gas readings. We determined that there was not a gas leak or emergency,” said National Grid senior media specialist Danielle Williamson.