Protection
Glass can be a dangerous material.
When standard annealed glass breaks,
it forms potentially lethal shards and
splinters. The reputation for dangerous
fragility is however fast disappearing.
Glass manufacturers have developed a
range of safety glasses adding strength
and integrity to this beautiful building
material and allowing glass to be used
in areas where safety is critical and in
unprecedented situations.
Security is now also possible with
glass. A range of high performance
glasses allows light and vision into
areas formerly excluded from natural
light. Situations where customer
interface and high security must
coexist, need no longer seem threatening
and unfriendly. There is a glass in the
SAINT-GOBAIN GLASS range to meet
virtually any safety and security needs.
New technology has granted architecture
a range of high-performance glasses,
which not only meet the need for fire
protection, but also offer impact safety
andenvironmentalcontrol.SAINT-GOBAIN
GLASS offers the widest range of fire
protection glasses, developed by its
specialist division, VETROTECH
SAINT-GOBAIN.
Safety glass
Safety glass is defined as glass which
must have passed an impact test
(currently BS 6206: 1981 -Specification
for impact performance requirements
for flat safety glass and safety plastics
for use in buildings) and either must
not break or must break safely.
There are three levels of impact: C, B and
A, ‘A’ being the highest. Each involves
the glass being impacted by a leather
bag containing 45kg of lead shot. (The
test roughly simulates the impact of a
373 • Protection
Technical questions
child weighing 100lbs [45kg] hitting
the glass with varying degrees of force.)
glazing material
Drop heights
Class A – 1219 mm
Class B – 457 mm
Class C – 305 mm
Three generic types of glass meet the
requirement of this British Standard:
• Laminated Glass
• Toughened Glass
• Wired Safety Glass
(only to a limited extent -
see Wired glass)
All Security Glasses (see following
section) automatically qualify as
Class A safety glasses.
Note
At the time of writing BS 6206 is still
in use, however in the near future
BS EN 12600 will supercede it and
relevant guidance documentation will
be published.
Please contact SAINT-GOBAIN GLASS for
more information.
Laminated glass
There are two types of laminated glass:
PVB laminated and cast resin laminated
glass. PVB laminated is the more
commonly used variety.
PVB laminated safety glass
Two or more sheets of glass are bonded
together with one or more layers of
polyvinyl butyral (PVB), a plastic
interlayer in sheet form. The principal
benefit of laminated glasses is their
performance under impact.
The glass may fracture but any broken
fragments will remain firmly bonded
to the interlayer.
The interlayer also absorbs impact
energy, reducing the risk of penetrating
the panel. When properly glazed, even
safety grade laminates will resist
attack, acting as a deterrent to burglars
and normally remaining in place until
replacement is convenient.
Depending on the arrangement, number
and thickness of glass sheets and
interlayers in the construction of the
laminated glass, different levels of
protection are possible including
against firearms and explosions.
Security glazing is discussed in more
detail in Section 24.
The interlayer in laminated glass
provides two additional benefits:
• sound transmittance is reduced,
particularly at the higher frequencies
• Ultra-violet radiation (between 320
and 380 nanometres) is reduced by
up to 99%.
For more information on the PVB
laminated glass range from
SAINT-GOBAIN GLASS see SGG STADIP /
SGG STADIP PROTECT page 203.
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Protection
Resin laminated safety glass
Resin laminated glass is manufactured
by pouring liquid resin into the cavity
between two sheets of glass which are
held together until the resin cures.
Also sometimes referred to as cast-in-place
laminated glass, this method is ideal for
laminating glass having a heavily
textured or patterned surface.
It is also possible to add a wide variety
of colours to the resin for decorative
effect. Not all resin laminates have
safety performance. They are principally
used for decorative and acoustic
purposes, where safety performance is
normally of secondary importance.
To u g h e n e d g l a s s
Toughened glass, also sometimes referred
to as tempered glass, is four to five
times stronger than ordinary annealed
float glass and, if broken, disintegrates
into small fragments with dulled edges
that are unlikely to cause serious injury.
Prepared sheets of glass, which have been
cut to size, processed and edgeworked
as necessary, are heated to about
700°C in a furnace, which is just above
the softening temperature of glass.
They are then chilled rapidly by cold air
blown onto both surfaces.
This results in the two outer surfaces
contracting and solidifying before the
interior, which induces permanent
compressive stresses into the surfaces
of the glass, effectively increasing the
strength of the glass. The interior of the
glass naturally balances the compressive
stress surface layers by being under
tensile stress. It is these properties
which result in the increased strength
and safe breakage characteristics of
thermally toughened glass.
Protection • 374
32
Protection
When the central tensile section of the
glass is ruptured, the stress is explosively
released, producing the fracture
characteristics of small, relatively
harmless fragments sometimes
referred to as dice.
Technical questions
This means that in all cases the glass is
supplied to size and all processing of
the glass such as edgeworking, holes
and notches must be carried out
before toughening.
Compression
Tension
Compression
Cross-section: Toughened glass (see SGGSECURIT)
In addition to being a Class A safety glass
to BS 6206, the increased resistance of
toughened glass to mechanical stress
and to large temperature variations,
render it ideally suited for use in structural
glazing systems, where the glass is to
be bolt or clamp fixed, and also in areas
subject to high levels of thermal stress.
For more information on the range of
toughened glass products available
from SAINT-GOBAIN GLASS, please see
SGGSECURIT on page 193.
Note
A new British Standard for the
manufacture of thermally toughened
safety glass has now been adopted. The
new standard is BS EN 12150 and will
cover tolerances, flatness, edge-work,
fragmentation and physical and
mechanical characteristics of flat
thermally toughened safety glass.
Please contact us for more information.
Wired glass
A steel wire mesh is embedded within
the glass and is intended to hold it in
place if cracked. Under impact, the
375 • Protection
glass breaks in almost the same way as
ordinary annealed glass into sharp
dagger-like pieces.
Marking of
safety glazing
materials
BS 6206 requires that ALL safety
glazing materials are permanently
marked in a position that will be visible
after glazing with the following:
1.The British Standard number BS 6206.
2. A code to identify the material
e.g. L for laminated, T for toughened
(tempered), P for plastic, W for wired,
SFB for safety film backed.
3. Its classification – C, B, or A. (An ‘o’
suffix designates front impact only).
4. A name, trademark or identifiable
mark of the manufacturer or the
company who last cut the material
if the original mark is lost in cutting.
(The marking requirement applies to
all panes, even in a multi-pane
door and to both panes of a
double-glazed unit.)
The use of
safety glasses
The architectural use of safety glazing is
primarily governed by British Standard
BS 6262: Part 4: 1994 - Glazing for
buildings-Safetyrelatedtohumanimpact.
BS 6262 is a national standard applying to
all glazing work, including replacement
glazing and its essential requirements
are detailed on the following pages.
BS 6262 identifies critical locations in
general terms only and sets the
minimum standards of glazing
materials acceptable for use in these
areas. It is the responsibility of the
designer or the specifier to assess the
risk in ANY area, taking account of the
use of the building and the likely
activity of the users.
Bathing areas, swimming pool, showers
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Protection
Glass in doors and side panels to Glass
indoors(1,2,3,4,5)mustbeatleast:
• a Class B safety glazing material if the
smaller dimension of the glass is
more than 900mm
• a Class C safety glazing material if
the smaller dimension of the glass is
less than 900mm
• annealed (non-safety) glass in small
panes may be permitted under
certain controlled circumstances if it
meets the criteria given below.
See “Glazing in small panes.”
Glass in low level glazing (6, 7, 8) must
be at least Class C, or in small panes.
Annealed (non-safety) glass may be
used in the unshaded areas (9, 10, 11, 12).
Robust annealed glass may be used in
commercial frontages, details of which
are given later in this section.
and other wet areas and gymnasia are
all examples of areas of special risk.
Additional guidance is also provided by
Building Regulations appropriate to the
country - ie. Approved Document N for
England and Wales, Part V for Northern
Ireland and Part P of the Building
Standards in Scotland.
Compliance with BS 6262 Part 4 will also
satisfy the requirements of Regulation 14
of the Health and Safety at Work Act.
Diagram 1
CriticalLocationsinInternalandExternalWalls(shadedinblue)asspecifiedinBS6262:Part4.
800
mm
300
mm
300
mm
1500 mm
800
mm
Floor/Groundlevel
Protection • 376
32
Technical questions
Protection
Permanent screen protection
PLAN VIEW ELEVATION
Screen
Glazing
Screen
75 mm
800 mm from
floor level
The use of annealed (non-safety) glass
is permitted in a critical location if
protected by a permanent, robust screen.
The screen must prevent the passage of
a 75mm diameter sphere and must not
beclimbable.BS6262:Part4detailsspecific
requirements for such screens and the
full document s
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