It really is amazing the amount of fire fighting equipment a fire fighter has to take with them into the job. I had to research it for a novel once and I don't know how they managed to walk a few steps, let alone run around.
You don't just have the fire pump hoses which are much heavier than you might think (and being able to carry one up some stairs is one of the physical tests before you can become a fire fighter).
You also have the oxygen tanks on your back, and the alarm system attached to those, as well as the heavy layers of fire retardant clothes and jacket and boots and the belt holding more gear, and a helmet and probably an axe as well.
Plus I'm probably forgetting something. If you want to be a firefighter you really have to be fit, and very passionate about your job.