Closing your bedroom door at night could save your life in a fire “Every day I wish my brother had closed the door," a house fire survivor said.

 -- Fire safety experts are urging people to close their bedroom doors before they go to sleep, saying the simple task can potentially save lives in the event of a fire.

“When you can’t get out, the most important thing you can do, close that door between you and the fire," Stephen Kerber, the director of the UL's Firefighter Safety Research Institute (UL FSRI), told ABC News, adding that the simple act "could save your life.”

Alexis King told ABC News that she survived a house fire in Corpus Christi, Texas, that killed her parents and brother when she was only 10 years old. Her family home's smoke alarm battery was not working, and King said she credits closing her bedroom door with saving her life.

"The door helped me to still have clean air ... and to really figure out a way to get out," King said.

Following devastating wildfires in northern California earlier this month that left 42 people dead, the UL FSRI is re-launching its safety campaign, "Close Before You Doze," calling on people to always remember to shutter their doors before they go to sleep.

Approximately half of home fire deaths result from fires reported between 11 p.m. and 7 a.m., according to a 2017 joint report from the U.S. Fire Administration and the Federal Emergency Management Agency. Researchers with the UL FSRI found that during a fire's spread, closed-door rooms had average temperatures of less than 100 degrees Fahrenheit, while open-door rooms had average temperatures of over 1,000 degrees Fahrenheit.

The UL FSRI used a model home to serve as a test facility in order to demonstrate how crucial it can be to close the door. The model home was outfitted with cameras and sensors to track temperature and gas levels, and all of the information was fed into a control center where the UL FSRI monitored the data.

During the demonstration, which was overseen by the Philadelphia Fire Department, a fire was started in the living room and two bedroom doors were closed, while one bedroom door was left open.

When fire experts opened the model home's front door to feed more oxygen to the fire and increase its strength, part of the window in the room with the open door flew off.

After 10 minutes, the UL FSRI and the Philadelphia Fire Department put the fire out and examined its aftermath.

The bedroom with the open door reached temperatures of 500 degrees Fahrenheit, enough to melt the TV that was inside. Carbon monoxide levels soared to 6,000 parts per million. An industry standard carbon monoxide machine would go off at approximately 70 parts per million.

Meanwhile, the bedrooms with the closed doors reached temperatures of up to 100 degrees Fahrenheit, and carbon monoxide levels were 10 times lower than what was recorded in the room with the open door.

The UL FSRI called a closed bedroom door versus an open bedroom door the difference between "life or death" in a fact sheet on its website.

King told ABC News that she wishes her brother had known this information.

“Every day I wish my brother had closed the door,” she said.