If a fire does start in the garage a proper fire rated door and properly constructed fire wall are the best lines of defense to allow you to make your escape before the fire comes into the home.
There are a few ways to tell if your door has been updated. Most solid-core and metal doors are fire rated. There can also be a little metal tag on the hinge side of the door that will give some more information.
The pictures show what a hollow-core door looks like with thermal imaging/Infrared. The strips you can see are actually sections of cardboard.
Jim Allhiser President/Inspector