Cutting through the smoke

by Katie Daniel | November 19, 2014 11:05 am

By Ron Pitts
For decades, the words ‘design flexibility’ and ‘fire-rated glass’ would not have appeared in the same sentence. Traditional polished wired glass was the only glazing material permitted in fire-rated areas. Its network of wires holds together broken glass during a fire to slow the spread of flames and smoke longer than was previously possible with other available glazing products. The tradeoff was its institutional appearance and low impact safety typically limited its use to smaller windows, borrowed lites, and view panes in doors.

In the late 20^th century, the restrictions building teams faced when using traditional wired fire-rated glass led manufacturers to develop better alternatives. As a result, glazing became available with superior fire and impact protection, in larger sizes, and with improved surface quality. These developments paved the way for building professionals to use fire-rated glazing in a range of commercial settings with great design freedom, including:

doors;
openings;
walls;
floors; and
the building envelope.

Today, given the proliferation of fire-rated glazing products and applications, building teams can push the boundaries of fire-rated design like never before. However, increased options also open the door to potential misapplication. To safeguard against incorrect product use—which could put lives and property at risk—this article provides considerations designed to bring greater clarity to fire-rated glazing in commercial building design. It is important to remember they are intended to provide building professionals merely with a starting point; it is crucial to check local building codes since performance criteria vary by occupancy type and location.

Understanding the various fire-rated glazing classifications
To use fire-rated glass correctly and to its full potential, it is essential to understand how its properties affect design and performance outcomes. A critical first step in this process is to distinguish between the two broad types of fire-rated glazing—fire-protective glazing and fire-resistive glazing.

TGP - Image 3 — Fire-resistive glazing can extend wall-to-wall and floor-to-ceiling in applications requiring up to two hours of fire resistance. *Photo courtesy Heidi Gumula, DBVW Architects*

Fire-protective glazing
Fire-protective glazing defends against the spread of flames and smoke. It is tested to CAN4-S104/Underwriters Laboratories (UL) 10b, Fire Tests of Door Assemblies, and 10c/CAN4-S104/UL 9, Fire Tests of Window Assemblies. These tests ensure the glass passes the mandatory fire and hose stream tests without failing for the entirety of its designated fire rating (in minutes). Glass that cracks or separates from the frame during either test may allow flames and smoke to spread through the opening, potentially harming people.

In Canada, building codes require all fire-rated glass to pass both a fire test and a hose stream test before receiving a fire rating. Fire-protective glazing materials able to meet Canada’s building codes include options such as traditional wired glass and glass ceramics. Depending on the product makeup, offerings are available with fire ratings ranging from 20 to 180 minutes, as well as with varying impact safety ratings.

Fire-protective glazing meeting the above criteria is typically suitable where building codes require assemblies to protect against the spread of flames and smoke. However, it is subject to area and size limitations under the applicable building code and/or authority having jurisdiction (AHJ), as discussed in later sections.

Fire-resistive glazing
Fire-resistive glazing adds an extra layer of protection by also limiting the transfer of heat through the glass. This safeguard makes it suitable for use in walls, doors, and other fire-rated assemblies designated to block the passage of excessive heat, hot gases, or flames.

TGP - Image 1 — Since building codes only spell out the required fire rating and general class of protection for a given location, building teams have great freedom to seek out products that also satisfy design and performance goals. *Photo courtesy TGP*

In Canada, fire-resistive glazing satisfies CAN/ULC-S101, Fire Endurance Test of Building Construction Materials—the fire-resistance test standards for walls. It can carry fire ratings up to 120 minutes, pass the fire and hose stream tests, block significant amounts of heat, and protect against human impact. For police stations and other at-risk buildings, it is available with bullet resistance ratings.

Given these performance characteristics, fire-resistive glazing is suitable where building codes require an assembly designated “fire resistant” to enclose a space, including wall applications requiring a 60-minute or greater fire rating that must meet temperature-rise criteria.

While fire-resistant glass technology varies by manufacturer, the systems typically provide the necessary fire resistance in the same way: multiple layers of glass sandwich an inert material that turns opaque and foams up during a fire. The internal reaction allows the glass to remain relatively cool on the non-fire side of the wall, protecting building occupants and valuables from flames, smoke, and high heat for its designated fire rating period.

Remarkably, the multi-laminate makeup of fire-resistive glazing still offers nearly the same level of visual clarity as ordinary float glass. Further, since it is not restricted to 25 per cent of the total wall area, it can bring exceptional clarity and visibility to floor-to-ceiling and wall-to-wall designs requiring a high level of fire protection.

In application
Before moving forward with specification, it is important to recognize which type of fire-rated glazing is suited for use in particular applications, such as doors, windows, or glazed walls.

Doors
Fire-protective and fire-resistive glazing products can be used in doors where glazing is necessary or desired, and where fire and life safety is a concern. Each type of glazing has a different set of fire and life safety performance criteria.

Fire-protective glazing is available with 20 to 180-minute fire ratings for door assemblies. It is subject to area and size limitations depending on whether the application requires meeting temperature-rise criteria. For example, fire-protective glass can typically be used in the maximum size tested (as tested by an independent testing agency) in fire doors requiring a 20- or 45-minute rating. Comparatively, for code applications requiring doors with temperature-rise criteria, such as those in exit enclosures and passageways, fire-protective glass is typically limited to 0.0645-m² (100-si) lites.

Fire-resistive glass is suitable for use in temperature-rise door applications without any size limitations. Its performance is critical in such applications, as the temperature rise on the non-fire side of the door assembly may not exceed 232 C (450 F) above the ambient temperature at the end of the first 30 minutes. This helps ensure occupants may still pass by a door to exit a building if temperatures reach high levels on the non-fire side of the door.

Openings
Similar to fire doors, the location of the opening, required class of fire protection, and size dictate the type of fire-rated glazing suitable for use.

Fire-protective glass is available with up to 90-minute fire ratings for use in openings and windows where protection against heat transfer is not required by code. The limitation on heat transfer makes it important to verify the product satisfies both the application’s required fire rating and type of fire protection. For example, many codes require fire-rated glass in one-hour egress applications to slow the spread of flames, smoke, and heat. While fire-protective glass is available with the necessary 60-minute fire rating, it is unable to protect against the transmission of heat. As such, it is typically unsuitable for such applications.

Walls
Fire-resistive glass and frames can be used in applications where building codes require a fire-resistant wall with no ‘openings’ to enclose a space. Fire-protective glazing does not defend against heat transfer, and is therefore not suitable for such applications as it is considered an ‘opening’ protective. Fire-resistant walls can include, but are not limited to:

stairwell enclosures;
fire-rated curtain walls;
exit access corridors; or
other fire barriers dividing interior construction (so-called ‘building compartmentation’).

Since fire-rated walls allow for great variance in design, the following are some key factors to consider before selecting a product:

generally, only fire-resistive glass and frames may be used in wall applications requiring a 60-minute or greater fire rating;
fire-resistive glazing may exceed 25 per cent of the total wall area;
the entire assembly, including the glass and frames, must be rated equal to (or greater than) the wall; and
like the fire-resistive glazing, the intended frame system must also block radiant heat transfer during a fire.

Assuming these criteria are met, the flexibility to use fire-resistive glazing in various configurations in walls provides building teams with many benefits, from improved daylight transmission to enhanced occupant visibility. For example, project teams can incorporate expansive sequences of fire-rated glass wall panels throughout school corridors, where illumination and views to the outside can help create a quality learning environment. Or, they can install fire-rated curtain walls in stairwells to help create safer walkways and brighten hard-to-light interior cores.

In addition to light transfer, clear fire-rated glass and narrow fire-rated frames make it easier to maintain visual consistency between fire-rated and non-fire-rated materials. This is particularly valuable when using large sequences of fire-rated wall panels or expansive fire-rated curtain walls. Frames can be custom painted or powder coated to match virtually any colour scheme. Framing options also include aluminum and steel. A recent innovation in framing makes it possible for fire-rated applications to be free of front framing members, mirroring the sleek look of structurally silicone glazed (SSG) systems.

Floors
Advanced fire-rated glass floor systems incorporating fire-resistive glazing are available for interior and exterior applications that require a code-approved fire barrier between floors. Common applications include:

lobby floors;
atriums;
corridors near exits; and
other public egress areas at risk for fire progression.

Currently, glass floor systems that pass fire-resistance tests are available with fire ratings up to 120 minutes. Non-egress floor or roof applications typically require 60- to 90-minute fire ratings; public egress areas typically require 120-minute fire ratings.

Beyond fire protection, interior and exterior fire-rated glass floor systems are available approved for loads up to 732.4 kgf/m² (150 psf). This is typically suitable for commercial and high-traffic pedestrian uses, as well as for public gathering areas like airports and railway stations.

To account for a broad range of installation circumstances, manufacturers or suppliers typically offer various surface treatments to improve traction. Embossed glass or cast glass features a slightly uneven surface texture that has good non-slip characteristics and long-term durability. Ceramic frit texturing is another traction-providing option. Its sandpaper-like surface is non-slip, although it is susceptible to wear in high-traffic installations.

The building envelope
Fire-resistive glazing can be used in exterior applications to help prevent a fire from spreading to or from other nearby buildings. This is becoming increasingly relevant in areas with high building density and narrow setbacks from lot lines. Refer to local building codes for horizontal separation distances requiring fire ratings for building exteriors. Generally, the allowable opening area correlates to the distance between the two buildings.

Take responsibility
Since building codes only spell out the required fire rating and general class of protection for a given location—not the material—building teams have great freedom to seek out products that also satisfy design and performance goals. Such latitude makes it crucial to take responsibility and gather all the details to avoid making a costly or dangerous mistake.

TGP - Image 6 — Fire-rated glass ceramic, a type of fire-protective glazing, acts as a safeguard against flames and smoke in a school. *Photo courtesy James Steinkamp*

Whichever type of fire-rated glazing is specified, a best practice is to ensure it has passed all testing requirements, and is listed by a credible third-party agency such as Underwriters Laboratories of Canada (ULC). For example, the National Building Code of Canada (NBC) underscores the importance of third-party testing in article 3.1.7.1., which explains that fire-resistance ratings shall be determined on products tested in compliance with CAN/ULC S101. Be wary of any material that does not pass all required testing or has specific limitations on use. Multiple parties involved in the selection, specification, approval, and installation of products that fail to provide the necessary fire and life safety protection can be held liable.

After examining the building application and the materials, one must review codes and the manufacturer’s or supplier’s product literature in detail. Where any doubts remain, the supplier, manufacturer, or code official should be contacted—many have educational resources and tools available to help guide the design and specification process.

To ensure proper use, the manufacturer or supplier can be consulted when:

it is the design or installation team’s first time using a given fire-rated glass system;
fire-rated curtain wall needs to visually match a neighbouring non-fire-rated curtain wall;
a multi-storey curtain wall is required;
using an exterior fire-rated glazing system (i.e. curtain wall or roof assembly);
impact-resistant, bullet-resistant, or energy-efficient glass is required; or
custom application may require additional testing.

Fire and Wire in the 21^st Century

In the last 30 years, the role of traditional polished wired glass has shifted dramatically. When the Canadian General Standards Board (CGSB) first published its fire safety codes, wired glass was the only glazing material that could offer adequate fire protection for a reasonable length of time. The catch was it could only resist 4.8 kN/m² (100 ft/lb) of impact—equivalent to a five-year-old running into the glass.While building codes typically restrict the use of low-impact safety glazing products in high-traffic areas, the absence of a fire-rated glazing material with the desired impact safety performance led to an exemption. The board deemed wired glass suitable for use in areas requiring fire protection and high-impact safety protection.

Today, although traditional wired glass has a proven track record when it comes to fire safety, there is no reason for building teams to trade fire safety for impact safety in hazardous locations. Over the last two decades, clear and wireless fire-rated products with superior impact safety have emerged. Building teams now have access to wireless fire-rated glass alternatives that can resist approximately 19 kN/m² (400 ft/lb) of impact—similar to withstanding the impact of an adult. Such glass can meet CPSC 16 CFR 1201 (Category II), which is a classification similar to CAN/CGSB 12.1 (Category II).

Despite these developments, CGSB performance guidelines for wired safety glass have remained lenient. However, recently publicized injuries from traditional wired glass are challenging the board’s impact safety stance, and a review of the national standards are in process.

In June 2014, Pierre-Alan Bujold of Public Works and Government Services Canada (PWGSC), was quoted in the article, “Canadian Glass Committee Working to Revise National Wired Glass Standard,” that appeared in the magazine, USGlass.

“The committee determined that in the future, wired glass in Canada should only be used in non-hazardous situations due to the manner in which wired glass fails,” he said.

Ron Pitts is the Canadian sales manager for Technical Glass Products (TGP), a supplier of
fire-rated glass and framing systems, along with other specialty architectural glazing products.
He has served as a glazing-industry professional in Canada for more than a decade. Pitts can be reached at ronp@fireglass.com.

Endnotes:

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