What testing does fire-rated glass have to pass?
Glass and framing are installed vertically in the test furnace of an independent test laboratory, such as Underwriters Laboratories (UL). The fire is ignited and temperatures are measured on the surface of the glass. Ratings are given based on the length of time the glass remains intact, from 20 minutes to 3 hours.
Ordinary window glass can withstand temperatures of approximately 2500 F. However, after only 5 minutes, a “real world” fire (and the fire test) reaches temperatures of nearly 1,0000 F. Glass that withstands an hour in the fire test is subjected to nearly 1,700′ F.
At the conclusion of the fire test, to achieve a rating greater than 20 minutes, the glass is subjected to the impact pressure and thermal shock of water from a two-man fire hose. This tests the ability of the glass and framing system to stay in place if structural damage takes place. It also proves the glass will stay in its protective position to block passage of flames and the deadly smoke, if subjected to the cooling effect of water from sprinklers or fire extinguishers.
What is the impact safety test for glass?
A 34″ x 76″ piece of glass is mounted in a vertical frame. A punching “speed” bag is filled with 100 pounds of lead shot (similar to BB’s found in shotgun shells). This very heavy bag is hung from a cable and swung, in pendulum fashion, from various heights to impact the glass. The velocity of the bag, at high impact levels (CPSC 16 CFR 1201 Category II), corresponds to the impact of a full grown adult running into the glass. This level of impact resistance is typical for standard tempered or laminated glass. By contrast, wired glass and products meeting only Category I of the CPSC standard could only withstand the running impact of a small child. To qualify for an impact safety rating, glass must either not break, or break in a safe manner.
Are there different levels of impact safety for glazing materials?
Yes. This issue is extremely important in schools and relates to the impact safety test and the level from which the impact bag is dropped. The various impact ratings are very revealing. Let’s start with the most common level of impact safety and work our way to lower levels.
This represents 400 ft./lb. of impact, and is called “Category II” by the Federal CPSC (Consumer Products Safety Commission). It is the highest level of required impact safety. This represents the impact of a full grown adult running into the glass with insignificant or no injury. With few exceptions, all tempered or laminated safety glass in use today falls into this category. More important, there are numerous products available today that meet this impact rating and also offer high levels of fire protection.
This represents 150 ft./lb. of impact, and is called “Category I” by the CPSC. Glass that can only meet this test is limited to a maximum size of 9 square feet per lite (or less). This roughly represents the expected impact from an 85 lb. child running into the glass. As stated above, nearly all tempered or laminated glass has far exceeded this impact level for many years, so Cat. I products are a bit of a “holdover” from earlier times. As you can see, there is a significant difference between the two categories. Cat. II products will withstand the impact of an adult, while Cat. I products may allow injury to many school age kids. If you see fire-rated glazing that only has a Cat. I impact listing, consider the consequences of using this substantially lower impact product.
This represents only 100 ft./lb. of impact and was created as an exception for wired glass. It indicates the glass may only withstand the impact of a very young child. This impact level is now prohibited from use in schools per I BC Section 2406.
When using glass in fire-rated locations, is impact safety glass always required?
No. Building codes clearly define where impact safety glass is required. Common applications for high impact glass are doors, sidelites, glass located near the floor, and other “hazardous locations”, as defined by building codes. In those areas, any fire-rated product would also need to be impact safety-rated.
In areas where human contact is not a concern (transoms, some windows) an impact rating would not be required. For those areas, there are fire rated products that are not impact rated which are generally less expensive than glazing that offers both fire and impact protection.
However, keep in mind that schools are high activity areas that can present abnormal situations. A window in the middle of a school wall that doesn’t technically require impact safety ratings may still fall victim to the energy of students pushing and shoving. Therefore, it may be best to err on the side of caution and use an impact safety-rated product even when codes don’t demand it.
If, due to the IBC, I’m no longer using wired glass, what products are available?
There are two primary categories of alternatives to wired glass that can be labeled as “Thin” and “Thick” glass.
These wireless products are similar in thickness to wired glass (approximately 1/4″). They fit in standard fire-rated frames. Depending on the product, they are available in large sizes and have fire ratings from 20 to 90 minutes (up to 3 hours in small door lites). Products are available with high impact safety (Cat. II) or without impact ratings. School maintenance personnel or local glazing contractors can cut some of these products with standard tools — so availability is nearly immediate. These high impact products are preferable to some thin products that can only meet the lower (Cat. I) impact standards. Again, the energetic nature of students means greater risk of contact with the glass than other occupancies.
These special glass products are commonly called glass walls because they allow virtually unlimited expanses of glass. Tested to the same standards as solid barrier walls, glass walls block heat in addition to flames and smoke. Corridors that contain more than 25% of glass openings should definitely consider these products that, during a fire, block heat transfer through the glass, and allow safe passage. They may not fit in standard window and door frames — although some with lower fire ratings may. Glass walls require special cutting equipment, so shipments usually come from the glass manufacturer/fabricator. A lead time of a few weeks is not unusual, so use as a replacement glass is not always practical. These products typically have a Cat. II impact rating.
What special considerations should be taken into account when choosing fire-rated glazing for schools?
Schools are unique in the construction industry, because they raise several issues that typically do not arise with other occupancies.
Educational facilities are subject to a great deal more activity than a typical office building. The constant movement of students throughout the day means that impact safety must be a high priority.
School hallways and common areas are likely to be defaced, either intentionally or unintentionally. The fire-rated glazing chosen should be durable.
For building and life safety (not to mention legal considerations), damaged products must be able to be replaced or repaired in short order. Be sure the product you choose will be readily available.
Schools are expected to operate for many, many years. Since school construction and maintenance budgets are tight, it is extremely important that building products stand up over time.
Why not just apply a safety film to wired glass?
As we mentioned before, schools are more prone to abuse than other types of facilities. Even the toughest films can be marred, lacerated or peeled by a determined vandal.
When the film is damaged, it not only is unsightly — it potentially can impair the performance ability of the product and render the impact ratings invalid.
It isn’t that we are against the use of film n we even sell a fire-rated product that has a film applied for impact safety. We simply do not recommend its use in high traffic areas such as schools.
Sometimes, choosing the low cost alternative may end up being more expensive in the long run. It’s much better to base your decision on performance rather than price alone.
What specific products do you recommend for schools?
For high traffic, “hazardous” locations, we recommend FireLite Plus©. It meets the CPSC 16 CFR 1201 (Cat. Ii) impact requirements. The high impact laminating materials are sandwiched between two lites of ceramic, so both exposed surfaces are durable. FireLite Plus can be cut with normal glass cutting tools, which means it can be delivered quickly from school maintenance personnel or local glazing contractors.
In non-impact rated areas, we recommend FireLite©. At only 3/16″ thick, it easily fits into new or existing fire-rated frames. Like FireLite Plus, FireLite can be cut in the field for quick delivery. And since it is a ceramic, it has a surface even more durable than regular glass.
When should I use the “thick” glass that is a barrier to heat transfer?
These products are typically used where large expanses of glass are required, i.e., where glazed areas exceed 25% of the wall area. Their ability to block heat transfer can prove invaluable when protecting exit corridors is important. And the benefit of blocking heat is increasingly being considered, even when heat blockage is not required. However, due to the need for special cutting equipment, delivery can take a few weeks. This extended lead time is an important consideration if glass requires immediate replacement. Further, with a typical thickness of at least 3/4″, frames and glazing “stops” may require modification.
Having said that, there are many times when such a product is the best choice. In those instances, we recommend Pilkington Pyrostop™. Pyrostop is available in a broad range of make-ups for interior and exterior use, with ratings from 45-minutes up to 2 hours.