Fire Rated Glass in Doors

Today’s building designs are pushing the limits for glass. Green buildings require more natural light to be brought into the building for energy savings and to provide a more inviting environment for building occupants. A challenge faced by specifiers is determining what type of glass to provide in doors to meet the aesthetic needs of architects as well as fire and safety codes of the local market. Many times, commercial door manufacturers are faced with a lack of well defined glass specifications on door orders.   What is the trade off, more glass or better fire protection?   Years ago wire glass was the most commonly used product to provide windows in fire doors. Today, safety requirements require that all wire glass have a protective film in order to pass impact test requirements.   The 2006 International Building Code (IBC) completely removed the wired glass exemption for all buildings; requiring all individual glazed areas in hazardous locations, specifically including doors and sidelights, to pass the test requirements of the stringent CPSC 16 CFR, Part 1201 – Safety Standard for Architectural Glazing Material.

The main questions asked of door manufacturers are:

  1.          What is the maximum size of a window in a fire rated door?
  2.          What type of glass can I use?

Let’s address the first question. If you have a 3 hour fire door, the 2012 version of the IBC only allows flush doors. As far as the other ratings, this is first determined by the door manufacturer and their Underwriters Laboratory (UL) or Warnock Hersey (ITS) fire authorities. The maximum visible area for glass in a fire door can be obtained from the door manufacturer (check their website) Many commercial fire door manufacturers offer a technical chart showing the maximum visible area of glass per each fire rating (20, 45, 60, or 90 minute). They would also point out any door limitations that may limit what is available from the glass manufacturer. Keep in mind that the maximum size listed by the glass manufacturer is not always the same as the door manufacturer. The glass manufacturer does not test with a specific kit, moulding or door construction. The door manufacturer has the final say on the maximum amount of glass that can be fire rated for the door construction. This same rule also applies to hollow metal frame with glass.

It is important to remember what NFPA 80 states about Glazing Material in Fire Rated Doors (section 4.4), “Only labeled fire resistance–rated or fire protection–rated glazing material shall be used in fire door assemblies when permitted by the door listing” (section 4.4.1).

The answer to the second question should be found within the same glass manufacturer’s technical information. This information should show the type of glass required to meet the respective fire authority. Each fire rating may give you a list of options for types of glass (wire glass or ceramic) along with the glass manufacturer and glass model. This list does not limit you to only using the door manufacturers listed glass. If you have a supplier of fire rated glass that works better for you (because of price or specified), you can substitute the other glass as long as you do not exceed the maximum visible glass listing of the door manufacturer. This maximum visible glass area may also include restrictions on minimum dimensions from edge of door to visible glass.

Keep in mind what type of fire openings you are dealing with. The two types are Fire Protective and Fire Resistive. Fire Protective is designed to contain flame and smoke and is limited to 45 minutes. Fire Resistive will need to contain the flame and smoke plus block radiant heat and can be found on walls requiring over 45 minutes of protection.

NFPA 80 – 2013 requires fire rated wood doors to be factory glazed to ensure the correct glass and installation procedures are followed per the door manufacturer’s fire listing. Not all areas of the country have adopted or enforce this version of NFPA 80. If you have questions on what codes are being enforced in your market, I would suggest contacting your local Authority Having Jurisdiction (AHJ) and asking the questions. If your local AHJ is unsure of what size or types of glass he will approve, I suggest providing them with the door and glass manufacturer’s technical information on fire rated door glazing.