By Jim Donovan

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PHILADELPHIA (CBS) — Working smoke detectors can cut the risk of dying in a house fire by half but experts say there’s another simple thing that can be done to increase survival.

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Fires that happen late at night aren’t the most common but they are the most deadly.

“Only 20 percent of fires happen during sleeping hours between 11 and 7, but more than half the fire deaths occur during that time,” said Steve Kerber, director of the UL Firefighter Safety Research Institute.

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Kerber says most people don’t realize how little time they have to escape once a fire starts.

“Our research shows that 40 years ago, you had about 17 minutes to get out once the smoke alarm sounded. Today, that’s three minutes or less, so a huge difference because of the synthetic materials we put in our homes,” said Kerber. “Everything in our homes, from furniture to furnishings and carpet, everything in between, is made of synthetic materials. Those synthetic materials burn faster when ignited giving you much less time.”

This is one reason for UL’s “Close Before You Doze” campaign.

“So Close Before You Doze is a campaign that we kicked off three years ago and we’ve been going ever since to make the public aware of how important a door could be to your survival should you have a fire,” said Kerber.

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A demonstration shows the difference between fire damage in a bedroom where the door was closed, versus a bedroom in which the door was left open. The room in which the door was left open suffered substantial damage in comparison to the room with the door closed.

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Kerber says keeping bedroom doors closed is a simple, lifesaving step.

“It’s so critical because you could have 2,000 degrees on one side of the door and it will only be 100 degrees or less on the other side of the door, giving you time to make a decision to see if you can get out or not, and ultimately allowing you to survive that fire,” said Kerber.