Firefighters show difference a closed door can make during fire in Coon Rapids, Minn.

The difference a closed door makes... A photo from the Coon Rapids Fire Department is highlighting why firefighters say you should sleep with your bedroom door shut.

The Facebook post shows the scene of a house fire on Friday. Officials say the fire started with a lightning strike that hit the attic.

While the fire caused damage to the rest of the home, the bedroom appeared to be untouched.

"Take a look at this bedroom and the near-pristine shape it is in," writes the fire department.

Experts say closing your door can slow the spread of a fire but also can reduce the amount of toxic smoke, created by burning synthetic materials, increase oxygen levels, and lower the temperature in the room.

A video from the UL Firefighter Safety Research Institute shows how much smoke a closed door can block. In that demonstration, the open room quickly fills with smoke, eventually going black, while the process takes significantly longer in the closed room.