Have you ever heard the saying “close before you doze” when it comes to fire safety? Well now you won’t be able to get the phrase out of your head, thanks to a jarring image from a viral TikTok shared by a retired fire investigator.

The video, posted last year, shows a home completely ravaged by a fire. Every single part of the home we can see has been destroyed and burned—except for what appears to be a little girl’s bedroom. It’s a haunting visual, but it’s also an incredibly important reminder to add “closing doors for fire safety” to our nightly routines.

@medic_cole Remember to close bedroom doors before sleeping for the night, it could make a big difference. #closebeforeyoudoze ♬ original sound – EC

How does closing doors for fire safety prevent the fire from spreading?

Daniel Madrzykowski, a director of research for the Underwriters Laboratories’ Fire Safety Research Institute, tells the New York Times that fires feed on oxygen. And when a door is left open, it provides a source of air that “essentially acts as a pump” to fuel the flames.

When we close our doors, the source of air is cut off. This starves the fire of oxygen and provides an effective barrier to temporarily inhibit the spread of the flames and the smoke. This allows firefighters enough time to respond to the fire.

“Closing the door limits smoke spread and limits the oxygen that is available for combustion,” Dr. Madrzykowski said.

Related: Watch this brave woman save a family from a house fire

It doesn’t matter what type of door it is: hollow or solid. Having a closed door will still buy you precious time to wake up and get out of the house or wait for rescue. This can also serve as a reminder to test your smoke detectors.

Commenters shared their own experiences.

“Married to a firefighter. Yep, this is why we close our doors.”

“Having my bedroom door closed saved my life. My whole apartment was engulfed in flames.”

“We started doing this a few years ago after a friend showed me a safety video. All doors get shut now!”

Related: How to tell when your baby should sleep in their own room, according to a sleep expert

If your children, like mine, are freaked out by sleeping with the door closed—and plenty of mamas in the comments shared their concern for not being able to hear their kids if their doors were closed—you can gradually get them used to the idea by reinforcing it and making it part of your bedtime routine, and assuring them they’re safe and OK.

Slumber and Bloom has a helpful YouTube video for parents full of suggestions for this very thing:

A version of this story was originally published on Nov. 4, 2022. It has been updated.