"the fire inside was not fully extinguished"

Having the proper tool often makes the job much easier. In this case, having the proper tool allowed the firefighters to get at the fire without taking down the whole wall.

McCarraher said that when firefighters arrived, they could only see smoke because the fire itself was fragmented and hidden inside the wall. So they used a thermal imaging camera to locate any hot spots. 

Such cameras allow firefighters to see clumps of heat through darkness and smoke by capturing infrared radiation. 

Once the firefighters pinpointed the pockets of heat, they broke through the wall to put the flames out, McCarraher said.

Read more: http://www.milforddailynews.com/news/x1084477878/Franklin-firefighters-put-out-chimney-fire-on-Christmas-Eve#ixzz2GG2WpUEq