The title refers to the name of a Fire Company or station- Ladder 49. Fire companies or brigades are sometimes denoted by the type of equipment they use, a Ladder Company would have hook and ladder...
You answered your own question- the name of the Fire unit- was ladder company #49- so the station was ladder 49 in firehouse parlance. There are usually separate Engine ( pumping) and Ladder ( aerial...
I did not see the film but read it was an accurate description of the many hazards and risks associated with Fire fighters, and these were handled in an accurate way=- as some firemen and fire buffs...