You might think that a closed door would be no match for a house fire. But the difference between how a room with an open door and a room with a closed door survive a fire is dramatic. Smoke moves up and out and fills a room from the top down. So it reaches the floor last, which means it can't seep beneath the door easily. That's why we're taught to stay low in the case of a fire.
Firefighters have long understood the benefit of compartmentalizing a fire. Fire needs oxygen, fuel and heat to survive. Thus, if a fire can be compartmentalized, its spread will slow because it lacks oxygen. If the oxygen supply is cut off completely, the fire may even go out, Williams says.
"The more control you can have over the oxygen, the more control you can have over the fire," she explains. If you close your bedroom door at night, and a fire starts in the kitchen while you are sleeping, you may have enough time to wake up and figure out what to do. This could give you just enough time to exit the building, or to call 911. But it also might give you a safe place to wait for the fire department while the smoke, heat and toxic fumes are just beyond your door.
Also, in a bedroom with a closed door — even when a fire is raging outside — the temperature can remain below 100 degrees Fahrenheit (37 degrees Celsius) with carbon monoxide levels at 100 PPM (parts per million). Compare that to a room with the door open where temperatures can quickly rise above 1,000 degrees Fahrenheit (377 Celsius) and carbon monoxide levels become extremely toxic at 10,000 PPM.
Williams says you should actually close as many doors as you possibly can at night. One reason it's so important is that home fires spread more quickly today than they used to. Forty years ago, we had about 17 minutes to escape a house fire, but today, that's down to three minutes or less. We can thank contemporary building practices and synthetic materials for the change. Of course, if you can get out, get out.