A fire rated door is a very heavy door made of materials like metal or gypsum. Its main purpose is to hold back smoke and to contain fire. The term fire rated means that the door, when installed properly, is not supposed to combust during a certain time period in the average fire. Time ratings vary and some standard ratings include 20-90 minute doors. Depending upon area small companies or government agencies may determine fire ratings..
One thing that renders a fire door ineffective is propping it open. If the door is not shut, it can’t hold back smoke or contain fire. In large buildings there are several ways to deal with this. Doors may have an automatic shut mode if fire is detected. This way people can keep the doors open most of the time. Other doors simply need to be kept shut and many automatically close after they’ve been opened.