Self Contained Breathing Apparatus...

SCBA gear consists of a high-pressure air tank, a mask, and a PASS (Personal Alert Safety System) device. Unlike underwater SCUBA gear, these tanks are worn with the regulator valve facing down, not up, in order to protect it from being bashed while the wearer is working in a tight area, or crawling
along a floor.

Also unlike SCUBA gear, the firefighter's mask covers the entire face, with no mouthpiece. This mask uses a positive pressure flow, not the on-demand flow that underwater gear uses. This means that air is always being pushed into the mask as the firefighter breaths, keeping the pressure inside the mask slightly higher than the outside air pressure. This ensures that any gaps in the mask won't allow smoke or toxic gasses inside. Although the air tanks provide 45 minutes of air, in reality they supply 15-30 minutes, depending upon how hard the firefighter is working and exercising.