You have responded to the scene of a structure fire to find…

You have responded to the scene of a structure fire to find several occupants waving you down from the driveway. One of the occupants states they tried to extinguish the fire with a bucket of water with no success. While this occupant is speaking, you notice they are having difficulty finishing their sentences. They begin to complain of a severe headache and dizziness. What concentrations of oxygen do you suspect inside the structure?