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The surrounding or encompassing atmosphere.
Manufactured by pouring molten glass onto a bed of
molten tin which is then cooled, annealed glass is
the product that most people think of as "plate" glass.
This flat glass product has little residual surface
compression and must be handled with care to minimize
thermal stress. It breaks into sharp shards when
shattered.
Colored translucent glass, often called art glass,
opalescent glass, cathedral glass or stained glass,
is also produced by the rolling process, but generally
in small, batch type operations. There are usually
variegated colors within each sheet produced and
no two sheets will match for hue. Thickness will
vary within a sheet as well as from sheet to sheet.
The maximum thickness produced is usually 1/8".
When used as a glazing material, art glass should
be glazed in the same manner as tinted / heat absorbing
glass. Art glass cannot be tempered.
Chemical or mechanical restraint systems that improve
the performance of security window film during blasts,
high winds and smash-and-grab break-ins.
A temporary change in the gas density, pressure and
velocity of the air surrounding an explosion point.
If the initial change is discontinuous, it is referred
to as a shock wave. If the initial change is gradual,
it is known as a pressure wave.
The violent rise in air pressure above normal atmospheric
pressure (14.786 pounds per square inch).
British Thermal Units are the amount of heat required
to raise the temperature of one pound of water one
degree Fahrenheit (1 BTU = 252 Calories).
Clear glass consists of silica sand with added alkaline
salts such as lime potash and soda. It is colorless
and has a visible light transmittance ranging from
75% to 92%, depending upon thickness. It constitutes
the bulk of the flat glass that is used.
The process of applying window film to a piece of glass
from edge to edge. A small untreated area of glass
remains, which is referred to as a “daylight
gap”.
The negative pressure effect felt on the roar face
of a structure as the blast wave moves away from
the building.
The ratio of radiant energy emitted by a surface to
the radiant energy emitted by a black body of the
same temperature.
A sudden release of energy resulting in a blast wave.
Figured / patterned glass is produced domestically
by the continuous pour process in thicknesses of
1/8" to 7/32". A pattern etched on one
or both of the rollers is reproduced on the glass.
Colors are available but are extremely limited. This
type of glass is frequently called "obscure" or "decorative" glass.
The pattern diffuses detail of objects viewed through
the glass, it does not obscure them. The degree of
diffusion achieved is a function of the pattern and
whether the pattern is on one or both sides. Some
patterns cannot be tempered for safety glazing use
because of their depth.
The float glass process accounts for over 90% of the
flat glass presently produced in the United States.
In this process, molten glass is poured continuously
from a furnace onto a large bed of molten tin. The
molten glass literally floats on the tin, spreading
and seeking a controlled level in the same manner
as water poured onto a smooth, flat surface. In the
controlled level seeking process, the molten glass
is allowed to spread to width of 90" to 140",
depending upon the furnace size and glass thickness
being produced. The glass slowly solidifies as it
travels over the molten tin. It is then cooled under
controlled conditions. Afterward, it emerges as a
continuous ribbon of glass at essentially room temperature.
The product is now flat, fire-finished, and with
virtually parallel surfaces.
(1) Glass is made to withstand from between 3000 to
5000 psi (210 to 350 kg/cm) of edge stress. (2) When
edge stress exceeds edge strength, breakage occurs.
(3) Edge strength depends on glass size, thickness,
how it is cut, and treatment of edge by glazier.
(4) A straight clean edge is the strongest. (5) Damaged
edges can reduce edge strength by up to 50%.
The location at which an explosion occurs.
Heat strengthened glass is fabricated by a process
similar to that of tempered glass. Some equipment
can produce both. The glass is heated to approximately
1100° F and the cooling process is slower than
for tempered glass. The strength developed is about
twice that of annealed glass.
Areas particularly affected by solar radiation and
the imbalance of solar energy.
The amount of energy generated in an explosion. It
can be either positive (impact force) or negative
(suction force) energy. Impulse is measured by integration
of the pressure / time curve recorded in an explosion.
Double insulating glass units consist of two panes
of glass that enclose a hermetically sealed air space.
The panes are held apart by a spacer around the entire
perimeter. The spacer contains a moisture absorbent
material called a desiccant that serves to keep the
enclosed air free of visible moisture.
Laminated glass consists of two or more plies of glass
interleaved with clear or tinted polyvinyl butyl
(PF). The application of heat and pressure bonds
the glass and plastic interlayer into one unit. When
laminated glass is fractured, the particles of glass
tend to adhere to the plastic, affording protection
against flying or falling particles. Some combinations
of glass and plastic thicknesses do qualify as safety
glazing materials under the criteria of ANSI Z97.1-1984
and CPSC 16 CFR 1201.
A sheet or pane of glass.
Low-emissivity coatings (Low-E) reflect that part of
the heat spectrum above 3000 millimicrons wavelength
that is called "sensible heat". The heat
from hot water or steam radiators and the heat from
hot air ducts from a furnace are typical examples
of this kind of heat. These coatings have high visible
light transmission. In fact, they are nearly invisible
on the glass. The visible light transmission is typically
about 20 percentage points below that of an equivalent
uncoated glass. The major attribute of Low-E insulating
units is their sensible heat reflecting character
which is apparent from their low U-values. Low-E
coatings are applied to glass by vacuum processes
and by pyrolitic processes.
The rate of visible light transmission and shading
co-efficient (Ke ratio). This is a relationship between
how much heat gain is rejected and the amount of
visible light transmittal.
Most mirrors are manufactured by the wet chemical deposition
method, although a few, for specialized use, are
made by vacuum deposition. Safety mirrors are available
to meet various laws and building codes. A mirror
made from tempered glass will have the inherent distortion
from the tempering process and cannot have the same
quality in reflection as laminated ones made from
mirror quality annealed float glass. Transparent,
or two-way mirrors, are designed to allow vision
through from one direction while presenting a mirror
appearance from the opposite side. Their major application
is to permit undetected observation for study or
surveillance in places such as prisons, gambling
casinos and psychiatric treatment centers. A difference
in lighting level is necessary; in the room to be
studied the lighting level should be at least five
times greater than the lighting level in the observation
room; ten times greater is even more effective. Two
way mirrors are not intended for use in exterior
walls.
The portion of a blast wave, also known as "suction
phase", whose pressure is below ambient.
A glass-filled division of a window, door or wall,
or the glass itself.
Plate glass, manufactured by the grinding and polishing
process, is no longer produced in the United States,
and words referring to it have been eliminated from
the ASTM Specification C103685. It has been replaced
by the float glass process.
The portion of a blast wave whose pressure is above
ambient.
The amount of pressure felt by an object standing directly
in the path of an expanding blast wave.
Reflective glass is a clear or tinted glass coated
with an extremely thin layer of metal or metallic
oxide.
The rolled glass process consists of pouring molten
glass from a furnace, then feeding it through rollers
to produce the desired thickness. The glass ribbon
is then cooled under controlled conditions. There
are three general types of rolled glass: figured
/ patterned, wired and art / opalescent / cathedral
glass.
The ratio of solar heat gain passing through a glazing
system to the solar heat gain that occurs under the
same conditions if the window were made of clear,
unshaded, double strength window glass. The lower
the number, the better the shading qualities of the
glazing system.
The Sheet glass process accounts for a very small portion
of U.S. glass production. Some imported sheet glass
will continue to be used, mainly in thickness of
1/8" and less.
The pressure felt on the sides and top of an object
as the blast pressure wave envelops and passes over
and around it.
The horizontal structure that supports the upright
portion of a window frame.
Spandrel glass panels are heat strengthened or tempered
glasses with a ceramic frit color permanently fused
to one of the surfaces. Glass in spandrel areas is
not subject to corrosion as are some other spandrel
materials. Pleasing aesthetics and economies can
be obtained using a single framing system for an
entire wall. Glass spandrel panels can also save
energy when insulation is placed behind them.
Generally speaking, the further you are from a blast,
the better your opportunity to survive. Each site
should be evaluated to assess its structural strength,
window frame type and attachment, and glass type
to determine which style of film application would
be most appropriate to withstand the blast at a given
distance.
Tempered glass is fabricated by subjecting annealed
glass to a special heat-treating process. The most
commonly used process is to heat the glass uniformly
to approximately 1150° F, and then rapidly cool
it by blowing air uniformly onto both surfaces simultaneously.
The cooling process locks the outer surfaces of the
glass in a state of high compression and the central
portion, or core, in compensating tension. The color,
clarity, chemical composition and light transmission
characteristics remain unchanged. Likewise, compression
strength, hardness, specific gravity, expansion coefficient,
softening point, thermal conductivity, thermal transmittance
and stiffness are unchanged. The only physical property
that changes is tensile or bending strength. Under
uniform loading, tempered glass is about four times
stronger than annealed glass of the same size and
thickness, and is thus more resistant to thermally
induced stresses, cyclic wind loading and hail stone
impacts. When broken, tempered glass breaks into
a multitude of small fragments of more-or-less cubical
shape. Therefore, it qualifies as a safety glazing
material under the criteria of Federal Standard 16
CFR 1201 and the American National Standards Institute
(ANSI) Z97.1-1984, when so labeled and certified.
Spots or blotches may, at times, be visible on tempered
glass, especially when viewed through polarizing
lenses or in certain types of reflected light. The
intensity will vary with lighting conditions and
viewing angle. This is caused by the strain pattern
induced during the cooling stage, and is not inherently
a cause for rejection.
(1) All glass absorbs energy when exposed to solar
radiation. (2) Tinted glass absorbs more energy than
clear glass. (3) Occurs when there is a temperature
differential between center of glass and shaded edges.
(4) The ability of the glass not to break is determined
by its edge strength.
Tinted or heat absorbing glass is made by adding various
colorants to the normal, clear glass batch to create
a desired color. The four colors available by the
float process are bronze, gray, green and blue. Visible
light transmittance will vary from 14% to 83%, depending
upon color and thickness. The color density is a
function of thickness, and increases as the thickness
increases; visible light transmittance will decrease
as thickness increases. Tinting reduces the solar
transmittance of glass, has little effect upon solar
reflectance, and hence increases solar absorption
(heat). This explains why heat strengthening or tempering
is sometimes required for the thicker tinted glasses.
Adding a metallic coating also has the same effect
on thinner glasses.
The quantity (Ib / kg) of an explosive material expressed
in terms of the equivalent mass of TNT required to
generate similar blast values.
The ratio (percentage) of the total amount of solar
energy that is absorbed by glass compared to the
amount of total solar energy that hits the glass.
This solar energy is neither transmitted through
the glass nor reflected back out into the atmosphere.
The ratio (percentage) of total solar energy which
is reflected outward by glass compared to the total
amount of solar energy falling on the glass. (Use
of window film can affect this.)
The ratio (percentage) of the amount of total solar
energy in the entire solar wavelength range that
passes through glass compared to the amount of total
solar energy falling on the glass. (Use of window
film can affect this.)
The amount of radiant energy transmitted from a radiating
object through the atmosphere to a target after reduction
by atmospheric absorption and scattering.
U-value measures the heat transfer that occurs through
the inside and outside surfaces of glass. The U-value
is a function of temperature and is expressed in
BTUs (sec definition) per square foot per hour per
degree Fahrenheit (BTU / sq. ft. / hr. / F°).
Better insulation systems, including window film,
have lower U-values.
The damaging portion of the solar energy spectrum that
causes fading and deterioration to fabrics, furniture
and furnishings. UV rays also age skin and cause
skin cancer.
Chemical and material elements added to products such
as window film and lotions to block and / or filter
out varying amounts of harmful UV rays.
The ratio of the amount of total ultraviolet solar
energy that passes through glass compared to the
amount of total UV solar energy that falls on the
glass. (Use of window film can affect this.)
The percentage of total visible light that is reflected
by glass and that can be seen.
The ratio (percentage) of the total amount of visible
solar energy (usually called light) that passes through
glass compared to the total amount of visible solar
energy that falls on the glass. (Use of window film
can affect this.)
The application of silicone sealant or similar liquid-state
material around the perimeter of the glass, e.g.,
a bead of silicone mastic used to bond the film to
the glass to the window frame.
Wired glass is produced on the same equipment as figured
/ pattered glass. A welded wire netting or parallel
wires are introduced into the molten glass just before
entering the rolls to embed the wire into the glass.
Patterned wired glass has a pattern on one or both
sides, and is sometimes called "rough" wired
glass. Polished wire glass is produced by grinding
and polishing rolled wired glass blanks. Tinted /
heat absorbing wired glass is available only as an
import. The heat absorbing characteristic in conjunction
with the normally poor cut edges and the wire netting
can cause a high rate of breakage from thermal stress,
especially in non-vertical applications. The major
uses of wired glass are in institutional buildings
and fire rated windows and doors. All wires must
be completely embedded in the glass. Some misalignment
of the wires may be noticeable, but this is not considered
cause for rejection. Wired glass cannot be tempered.
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