Can carbon monoxide from a floor-heater in a poorly ventilated room eventually be ignited by the fire and explode? I have often wondered about carbon monoxide accidents caused by free-standing heaters burning in a poorly ventilated room causing fatalities. I am aware that CO is explosive between 12 and 75% volume air and wonder why it doesn't eventually ignite from the flames or glow present when the CO level reaches 12%? (This never seems to happen). Or does the decreasing oxygen content in the air due to the combustion cause the fire to die out before the critical level of 12% is reached?
Another possibility:  the "carbon monoxide" formed by combustion is not pure enough CO to get to flammability (12% total CO) in air.  The gas could be mostly carbon dioxide but still enough CO to poison you.