You are on the fire ground and you are assigned as part of the RIT Team (rapid intervention team). This means, that as firefighters go into the building, you and your partner (you both are also firefighters) are on standby, just outside the building, incase something goes wrong, and that inside crew needs your assistance.
As you are moving equipment around, you hear "MAYDAY, MAYDAY, MAYDAY. Back room, Engine 1, Joe and Chris, Search Team, 545 psi Air left."
You and your partner spring into action, and run into the building, trying to find the crew, that just called the mayday. You are attempting to reach the crew on the 800 radio, but they are not responding. You two continue to advance into the building, trying to locate the missing crew. As you approach the back room, you see part of an axe coming from the door. You and your partner enter into the room.
You find both men, laying against the wall. As you guys move in, you are screaming their names, but they are not answering.
The very first thing that you do, is check their air supply. The system reading is approximately "50psi." You connect your SCBA from your RIT bag, to the down men, and start giving them air, via the SCBA RIT bag. As that is going on, you are checking for any immediate life threats, that are visible. Nothing is noted. You check on their mental status, and both men are unresponsive, but are breathing.
By this time, the down time of the two firefighters is approximately 10 minutes. Your partner immediately calls for backup, to help get the men out of the building.
Other crews arrive, and the men are pulled to safety. EMS is on scene, and they take over care of the men. They place them on a NRB mask. EMS transports the men priority 1 to the closest emergency department.
After reading this, the reason that the men called "mayday" was because their air supply was low, and they wouldn't have time to get out of the building, in time, before the SCBA ran empty. The two men became unresponsive, because they became hypoxic. This resulted in a decrease in blood flow to the brain, which resulted in no perfusion to the brain, thus the men became unresponsive.
Why do we check the air supply on the SCBA before checking their LOC? The reason is because, the most common reason that firefighters go unresponsive win a fire, is because of hypoxia. Firefighters wear a mask, that covers their entire face, and they are relying strictly on the SCBA air supply to breath. As time goes on, the air supply becomes less and less, until the bottle runs empty. A decrease in this air supply, causes the hypoxia.
The general rule of thumb, is that for every 100psi in the SCBA, that is one minute of breathing. These mens bottle, in particular, hold 2216psi.