A fire door assembly can include fire-rated glass in several different locations, namely, the door leaf, a transom above the door and sidelights on one or both sides of the door.

In my last blog, we looked at different codes that can apply to a building throughout its life. Today, I’ll answer the question: Can a fire door also be a fire window?

It’s an important question because a fire door assembly can include fire-rated glass in several different locations, namely, the door leaf, a transom above the door and sidelights on one or both sides of the door. Does the International Building Code (IBC) treat glass differently depending on its location in a fire door assembly? Yes—and that’s why a fire door can also be a fire window!

Thom Zaremba
Thom Zaremba is a shareholder at Roetzel & Andress.

The 2024 IBC defines a “fire door” as “the door component of a fire door assembly.” It defines a “fire door assembly” as “any combination of a fire door, frame, hardware and other accessories that together provide a specific degree of fire protection to the opening.”

If a fire door frame includes a glass fire door and fire-rated glass in a transom or sidelights, they are all part of the “door assembly.” However, while the glass door leaf is treated and tested as a fire door, the glass transom and sidelights are treated and tested as a fire door and a fire window. Why?

Imagine you’re in a storeroom. In the middle of one wall, a glass door opens into a one-hour fire-resistance-rated corridor. There’s a glass transom above the door and two glass sidelights, one on each side of the door. The door, transom and sidelights are all held together in the wall by a single metal frame. Several boxes of files are stacked along the sidelights, but no boxes are in front of the door, allowing people to open and close the door and walk freely into and out of the room.

File boxes stacked near the sidelights expose them to higher fuel loads than the door leaf, where no boxes can be stored without blocking access into and out of the room. Since sidelights may be exposed to higher fuel loads than the door, they require a higher fire rating. The transom above the door can also be exposed to higher fuel loads as heat from a fire rises in the room, requiring it to have a higher fire rating than the door.

Fire doors are tested to NFPA 252, and they can be tested without striking them with water from a fire hose—called a hose stream test. Fire windows are tested to NFPA 257 and are always hose stream tested.

The IBC allows fire doors in one-hour fire-resistance-rated corridor walls to be tested to NFPA 252 for 20 minutes without the hose stream test. However, because they can be subjected to higher fire loads, transoms and sidelights built into the frame of a fire door assembly must be tested for 45 minutes, with the hose stream, to both NFPA 252—the fire door test—and NFPA 257—the fire window test. Had the fire-rated glass in these transoms and sidelights been put into separate frames next to or above the door, they would be considered fire windows and would only need to be tested to NFPA 257 for 45 minutes, including the hose stream test.

Specifiers—please remember to consult your local codes for requirements that may differ from those in the IBC.

With that, I’m already looking forward to my next blog, where we’ll look at the elusive exit access—one component of a means of egress system.

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