Fire rated openings are openings in a fire rated wall with the purpose of allowing people a mode of egress while slowing or stopping the spread of fire throughout the building. In almost every commercial building there is at least 1 fire rated opening and are covered by the National Fire Protection Agency (NFPA).
A fire rated opening is rated according to the amount of time it is exposed to direct flames. For metal doors, there are 20 minutes, 45 minutes, 60 minutes, 90 minutes, and 3-hours ratings with the appropriate hardware. For wood doors, there are 20 minutes, 45 minutes, and 90 minute ratings.
The building code in your area dictates the rating of your opening based on the wall assembly rating. See below for a listing of wall assembly ratings and the door openings rating required.
Fire rated door with glass
When using glass in a fire rated opening, the most common is 3/16″ ceramic style glasses. The hourly rating of the opening defines the number of lites and the allowed size of total visible glass in a fire rated opening. The fire rating is preserved iff and only if the glass is used with an approved lite kit. Glass is allowed in all fire rated assemblies aside from 3 hours unless otherwise noted by your local building code. The table below contains a listing of limitations of glass size and number of vision lites for a single opening.
3/16″ Ceramic glass