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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.
48-INCH DROP
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.
18-INCH DROP
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.
12-INCH DROP
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.
THIN
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.
THICK
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.
HIGH ACTIVITY
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.
ABUSE
School hallways and common areas are likely to
be defaced, either intentionally or
unintentionally. The fire-rated glazing chosen
should be durable.
MAINTENANCE
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.
LONGEVITY
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.
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