The door between the garage and the home can be a very important part of fire safety in modern homes. This fact has only been an accepted building technique since the early 80s. If a home was built before that, chances are that the door is not a “fire rated door.”
The garage is a great place for a fire to start. As far as house fires go, the garage is where a vast majority of fires are started. Paint cans, gasoline, natural gas appliances are all things that are usually in garages and are great for burning the house down.
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.