I think that '7T' refers to 7 Teslas. I think (note that I am an engineer and not really involved in the response to the fires) that the main determining factor to if they can pull the ax off of the magnet is how close the ax got to the magnet. The force of the pull of the magnet is inverse (or inverse squared) to the distance so if the ax gets really close to the magnet then it is basically impossible.