Not sure about the stamina Gary, I think the adrenalin or something like that just cuts in and off you go. The time really does pass quite quickly.
At the end of the shift you are really glad to get out of the fire ground and breathe some fresh air, we usually drive back to the station with all the appliance windows to get some cool fresh air in your face.
And back at the station a cold beer never tasted so good, believe me.