(NECN: Katelyn Tivnan, Boston) - The investigation into the cause of a deadly brownstone fire in Boston's Back Bay continued Thursday, as a Boston Fire official said something "extraordinary" must have happened to prompt firefighters to issue a mayday call minutes before two sustained deadly injuries while battling the flames.
"The one thing we do know is the wind contributed to how fast this fire turned from bad to worse," said Boston Fire spokesperson Steve MacDonald Thursday morning.
Two Boston firefighters, Lt. Edward Walsh and firefighter Michael Kennedy, died fighting a brownstone blaze on Beacon Street Wednesday afternoon.
"There was some kind of extraordinary event that happened in the basement," MacDonald said.
MacDonald explained that mayday calls are procedural for those in danger.
"When you hear 'mayday,' it's basically to get everyone to shut up on the radio, everyone keep quiet. They assign a separate radio channel," he said.
Officials say Walsh and Kennedy went into the basement and they called a mayday two or three minutes after entering, but couldn't be saved.
The fire appears to have started in the basement of the four-story apartment building. Several residents of the building were rescued, but none were injured. Thirteen firefighters were hurt in the blaze along with several police officers. By Thursday afternoon, three firefighters remained in the hospital recovering from non-life threatening injuries.
MacDonald says he is not sure how many firefighters remain in the hospital at this time.
The U.S. flag outside the station has been placed at half-staff in honor of the fallen firefighters.