The guy appaears to be wearing what is known as a rebreather, possibly the same type that was manufactured by Draeger starting in 1907.
Basically the air that the rescue worker breathes out is recycled, with the carbon dioxide being chemically absorbed (usually by a proprietary formula) and the 75% or so of oxygen that the body doesn't use in each breath is then supplemented from the tanks on the worker's back. Draeger still makes devices based on the same principle although with a far more modern design. I do know that in the mines of Nova Scotia the rescue teams are known as "Draegermen."
The "leather knee contraptions" are needed since a lot of time these guys would be crawling over jagged rock. Rather incongruous with what appear to be street shoes but may be boots that lace up.
