Why Fire-Rated Glass is Necessary in Schools
by Diana San Diego
The alarm sounds. Teachers swiftly gather the children from the neatly aligned desks in their classrooms; children align themselves quickly, just as they have been taught. As a classroom, they exit the room, exit the building and position themselves outside accordingly.
Today it was just a drill—a fire drill—and it went smoothly. Next time, though, it could be real. Would the exit procedure go as well? Will everyone be safe? These are questions that cannot be answered easily. That’s why building codes exist.
With so many opportunities for glass usage, school designs have seen significant changes over the past few decades. They have evolved from predominantly brick structures to ones that are open and bright. The requirements for fire-rated glass can be found in Chapter 7 of the International Building Code (IBC). In the 2012 version, three tables were updated to clarify where and which type of fire-rated glazing, whether it is fire-protective or fire-resistive (see box on page 59), is allowed in the code. These updated tables were added to make it easier for designers, code officials and installers to clearly categorize and apply fire-protective and fire-resistive glazing.
Here’s a look at common areas where codes affect glazing choices in schools.
1. One-Hour Exit Corridors
An exit corridor is a horizontal means of egress connecting an exit or stairway to a public way that protects people exiting a burning building while preventing the spread of fire. Generally, exit corridors have a fire-resistance rating of one hour. The IBC spells out different ratings for protected openings in a 1-hour exit corridor depending on the glazing application. Highlights include:
• 45-minute fire-protective windows are permitted, but may not constitute more than 25 percent of the total wall area;
• To exceed 25 percent of the total wall, one-hour fire-resistive glazing must be used.
• 20-minute fire doors with 20-minute vision panels (without hose stream) are permitted.
• Sidelites and transoms around a 20-minute fire door in a one-hour exit corridor require a 45-minute fire rating with hose stream.
2. One- and Two-Hour Exit
Stairs are necessary vertical components in an egress path from anywhere other than the ground floor, and the IBC requires that interior exit stairways be enclosed. Vertical exit enclosures/stairwells four stories or more must be two-hour fire-resistance rated; vertical exit enclosures/stairwells less than four stories must be one-hour fire-resistance rated. Restrictions on doors and fire windows in exit stairwell enclosures include:
• Doors must limit temperature rise to 450ºF (unless the building is fully sprinklered).
• Fire-protective glazing in a 60- or 90-minute door may not exceed 100 square inches (even if the building is fully sprinklered).
• Vision panels in 60- or 90-minute doors exceeding 100 square inches must be fire-resistive.
• Fire-protective glazing is not permitted in window, sidelite or transom openings in exit enclosures/stairwells. One- or two-hour fire-resistive glazing rated equal to the wall must be used.
3. Interior Fire Walls,
Barriers and Windows
Fire-rated glazing can also be found in areas that are not necessarily designated as an exit corridor or stairwell/exit enclosure. Table 716.6 shows the different requirements for fire window openings in interior walls:
• Only fire-resistive glazing may be used in fire walls and fire barriers rated one-hour and over, except where 45-minute fire-protective glazing is allowed in one-hour fire barriers used as incidental use areas, mixed occupancy separations, subject to 25 percent area limits.
• Fire-protective glazing may be used in one-hour fire partitions and smoke barriers and limited to 25 percent of the wall area. To exceed the 25 percent area limitation, fire-resistive glazing rated equal to the wall must be used.
• Table 716.5 shows the different requirements for door assemblies in two-hour fire barriers walls versus one-hour fire barriers walls, fire partitions and smoke barriers:
• Fire-protective glazing is limited to 100 square inches in door vision panels in 90 minute temperature rise and non-temperature rise doors. However, fire-resistive glazing can be used in door vision panels larger than 100 square inches.
• Fire-protective glazing is not permitted in sidelites and transoms surrounding the 90 minute door. Two-hour fire-resistive glazing must be used.
• Forty-five-minute fire-protective glazing can be used in doors, sidelites and transoms in some one-hour fire barriers and other fire partitions.
• Twenty-minute fire-protective glazing can be used in door vision panels in one-hour smoke barriers. The sidelites and transoms must use 45-minute fire-protective glazing.
4. The Building Envelope
The IBC works to protect the spread of fire from building to building by defining horizontal separation distances and requiring fire ratings for building exteriors in close proximity. The IBC measures the building face to the closest interior lot line or the centerline of a street, alley or public way. If there is more than one building on the same property, the IBC refers to an “imaginary” property line.
Table 705.8 in the 2012 IBC lays out the percentage of protected and unprotected openings and glazing size limits allowed in exterior walls. Fire-protective glazing, such as glass ceramics, wired glass and specialty tempered glass, is either limited in size or prohibited altogether depending on fire separation distance. In general, as the fire separation distance increases, the allowable opening area and the percentage of allowable fire-protection openings increases. The limitations in Table 705.8 limitations do not apply fire-resistive glazing materials tested as part of a wall assembly.
Protective or Resistive?
What’s the Difference?
Architects commonly ask questions about the differences in fire-protective glass versus fire-resistive. Here’s a close look at the differences and where each product type can be used.
Fire-protective glass is designed to compartmentalize smoke and flames and is subject to application, area and size limitations under the IBC. Fire-protective glass is typically used in doors and openings up to 45 minutes and cannot exceed 25 percent of the total wall area because it does not block radiant heat transmission.
Fire-resistive glass is not limited in size. It functions as a fire-resistance rated wall and is only limited to non structural applications. This type of fire-rated glass compartmentalizes smoke and flames, and blocks the transmission of dangerous levels of radiant heat through the glazing. As a result, it can be used in wall and door applications 60 minutes and above without the size limitations that apply to fire-protective glass.
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