Closing bedroom doors at night could be a lifesaver during a fire

"GMA" demonstrates how something as simple as closing the door could mean the difference between life and death in the case of a fire.
3:23 | 11/23/17

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Transcript for Closing bedroom doors at night could be a lifesaver during a fire
Thank you, Paula. A safety alert for the holiday season. Should a fire break out in the middle of the night ABC's gio Benitez is here with the simple step that could save lives. Gio, good morning. Happy Thanksgiving. Happy Thanksgiving to you. What you're about to see is something so many people have never even heard of. Something as simple as closing a door can mean the difference between life and death. I'll admit I was amazed when ul put this to the test. This is not a Normal house fire. We're with ul which helps that safety standards for a slew of industries and now the company is creating a controlled fire to show the importance of closing a door before you go to sleep. When you can't get out the most important thing you can do is close the door between you and the fire can save your life. Reporter: Alexis king survived the house fire that killed her parents and brother when she was just 10. The smoke alarm wasn't working and she believes closing the door helped save her life. It helped me still have clean air and to really figure out a way to get out. Reporter: Ul relaunching a safety campaign close before you doze. How much of a difference can it make? We're about to find out. Ul built this home to serve as a test facility. You're going to light the house on fire. For safety. For safety. Reporter: It's wired with cameras and sensors to track temperature and gas levels. All the info being fed to this control center so ul can monitor the fire. Two bedrooms will have the doors closed but the other -- We'll leave that one open so we get to see the difference. Reporter: With the Philadelphia fire department standing by, I start a fire with a candle on the living room sofa. Let's get out. We return to the control center. We got our fire in the living room. You can see how -- You can already see the smoke. Reporter: Take a look at the bedroom with the open door. See the smoke beginning to -- Yeah, yeah, yeah. 275 degrees. Absolutely. Not survivable. Reporter: But check out the rooms with the doors closed. The temperatures are much lower. You've got 97 degrees in one. 69 in the other. These are the closed door rooms. Very survivable. So there you go, the top of the window came out. Reporter: After ten minutes ul puts the fire out and we look at the aftermath. Here is the room with the open door. Look at this. We've got the TV melted. Temperatures in that room reached 500 degrees. The carbon monoxide readings 6,000 parts per million. An alarm would go off at 70. But what a difference in the bedrooms with the doors closed. Stuffed animals are just fine. Bed is clear. I mean, what's incredible is that this door sort of acted like a shield. Exactly what it did. Reporter: Temperatures only got up to 100 and carbon monoxide levels were ten times lower than the open room. Every day I wish that my brother would have closed his door and I hope other people know that they really do need to. Reporter: And listen, so many of us like to close doors at night without even realizing it's a life saver. My grandparent has a fire, a big fire years ago but they always slept with their doors closed and that's why they were able to get out and survive that fire. Wow. That's incredible. What else do experts recommend to safeguard the home? This only works if you have a working smoke alarm too. Know that there is a fire in the first place, couple that with an escape plan and you've got something to be thankful for. All right. Like how you tied it into the day there. Coming up on this thankful

This transcript has been automatically generated and may not be 100% accurate.

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