to minimize the transmission of heat from one side of the door to the other, as in the stairwell of a high rise building. If the door can limit the transmission of heat for a period of time, it is possible for people in a burning building to safely pass below the floor of fire origin. These doors are built with a specifically designed core and are referred to as temperature rise doors. In addition to the hourly rating, the fire door label will also state the temperature rise rating of the door. Temperature rise ratings are 250°F, 450°F, and 650°F, and indicate the maximum rise in temperature above ambient temperature measured on the unexposed surface (non-fire side) of the door during the first 30 minutes of the standard fire test. The 250°F temperature rise designation is the most stringent rating of the three, since it requires the most limiting rise in temperature. A 250°F temperature rise door meets the requirements of specifications calling for a 450°F or 650°F temperature rise rating.