A decade-long study reveals a 900-degree temperature gap depending on whether your bedroom door is open or closed during a fire
Most people never think twice about whether they sleep with their bedroom door cracked open or shut. Some like the airflow, others want to hear movement around the house. But fire researchers say that tiny decision could determine whether you survive a nighttime blaze.
After spending ten years examining how fires move through homes, the UL Fire Safety Research Institute (FSRI) has issued a stark warning: closing your bedroom door at night could dramatically increase your chances of staying alive in a house fire. Their push has evolved into a nationwide reminder known simply as “Close Your Door.”
What the research shows
Using thermal imaging and controlled house-fire tests, FSRI compared two scenarios: one room with the door open, and another sealed by a closed door. The contrast was almost unbelievable.
Rooms exposed to the fire with an open door surged to over 1,000°F, quickly becoming unsurvivable. Meanwhile, the rooms with closed doors stayed under 100°F, despite the fire raging just outside.
FSRI director Stephen Kerber emphasized the importance of this finding:
“The difference is remarkable. A person in a closed room can stay alive far longer.”
Toxic smoke: the silent killer
Temperature isn’t the only threat. The study also measured carbon monoxide levels — the poisonous gas responsible for most fire-related deaths.
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Open-door rooms: around 10,000 PPM of carbon monoxide, an instantly deadly concentration
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Closed-door rooms: roughly 100 PPM, a level that, while dangerous, gives occupants a fighting chance
Firefighters say the numbers speak for themselves.
Why opening windows makes things worse
Many people assume that cracking a window will help the smoke escape. Kerber says this is a dangerous misconception.
Letting smoke out also lets oxygen in — exactly what a fire needs to intensify. That incoming air can accelerate the fire’s growth, cutting off escape routes and flooding the home with even more smoke and heat.
A closed bedroom door, however, slows everything down: less heat, less smoke, less oxygen reaching the fire. It forms a temporary shield, buying rescuers time to get to you.
A simple habit that protects your family
Parents, in particular, should take note. If you close your children’s bedroom doors before going to sleep, Kerber says they immediately gain more survivable time should a fire break out overnight.
He compares the message to another longstanding safety rule:
“If ‘Stop, Drop & Roll’ is for your clothes catching fire, ‘Close Your Door’ is what you do when the house is burning and escape isn’t an option.”
The takeaway couldn’t be clearer: one small nightly habit can be the difference between life and death. Close the door before you turn out the lights.