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, stitched by @disastroushistory, begins with an original video that 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.

“Former fire investigator here,” the stitch begins. “I have done about 40 fatality fires, and a little over half of them would be alive if they: 1. Slept with their doors closed, and 2. Had working smoke detectors in the proper places in their house. Both of those things will literally save yours, and your children, and your pets’ lives.”

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 “esssentially 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

“I don’t care what kind of door it is,” @disastroushistory says in his video. “It can be those thin, cheap, hollow core doors. It will still give you time to wake up, get out, or, if you have to, wait for the fire department to rescue you.”

He says that, tragically, people don’t wake up from the smoke or the smell of it, and reminds viewers once again to get working smoke detectors and to please sleep with the doors closed.

“I promise you that a vast majority of people who die in fires die in their sleep. They never woke up.”

Commenters shared their gratitude for his video, and some even shared their own experiences.

“I was picked out of my bed to wake up in a smoke filled room by a fire fighter. I did not wake up because of the smoke, he’s telling truth.”

“When my house burned down, my daughters room was the only door closed. Everything was destroyed, except her room. Untouched.”

“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: