This combination made with undated photos released by the Boston Fire Department via Twitter shows firefighters Michael R. Kennedy, left, and Lt. Edward J.
This combination made with undated photos released by the Boston Fire Department via Twitter shows firefighters Michael R. Kennedy, left, and Lt. Edward J. Walsh, who were killed Wednesday, March 26, 2014, when trapped the basement while fighting a fire in an apartment building in Boston. Kennedy, 33, a Marine Corps combat veteran was assigned to Ladder 15, and had been a firefighter for more than six years. Walsh, 43, and a father of three, was assigned to Engine 33, and had been a firefighter for almost a decade. (AP Photo/Boston Fire Department) (Uncredited)

BOSTON (AP) - Several firefighters remain hospitalized a day after a wind-driven fire in a Boston brownstone that killed two of their colleagues.

Fire Department spokesman Steve MacDonald says he isn't sure exactly how many firefighters remain in the hospital. Thirteen were taken for treatment Wednesday. Some were admitted for burns, heat exhaustion and other injuries.

MacDonald says nothing has been ruled out regarding the cause of the fire, but officials know strong winds made it much more difficult to fight.

Lt. Edward J. Walsh and firefighter Michael R. Kennedy sent out a mayday call from the basement of the brownstone, indicating something extraordinary happened that trapped them there.

The fire union will work with their families on funeral plans.

PHOTOS: Two firefighters killed fighting Boston brownstone fire