Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
FIRE ALARM PULL STATION ENCLOSURE
(i) Field of the Invention
The present invention relates to a fire alarm pull station. In particular, the
present
invention relates to a fire alarm pull station enclosure that comprises a
frame having an open
front in which a grooved tempered pane of glass is supported. The invention
further relates
to the use of a tempered glass pane as a front of a fire alarm pull station
enclosure.
(ii) Description of the Related Art
It is well known in the art of fire alarm safety devices to use breakable
glass fronts in
order to gain access to either fire extinguishers, fire hoses or fire alarm
pull levers.
Generally, there are two types of fire alarm pull stations on which all
variations are based.
The first "free lever" pull type employs a small glass rod of minimal diameter
or a small
pane of glass which is shattered upon pull lever activation. The pull lever is
not enclosed by
a pull station "box". Edwards U.S. Pat. No. 2,083,324 issued Jun. 8, 1937
discloses such a
fire alarm pull station in which an exposed pull lever contains a small pane
of glass which is
shattered upon activation of the pull lever in a downward fashion. The pane of
glass only
protects actuation of circuitry and does not prevent tampering with the lever.
The second "box enclosure" type has a pull lever enclosed within a rectangular
or
square box with a breakable glass front. The disadvantages of the free lever
type of pull
station, namely possible tampering with the pull lever due to unimpeded
access, are
substantially overcome by the use of the enclosed pull station. One gains
access to the pull
lever by shattering the glass front. This structure was introduced to
alleviate concerns with
the free lever type pull station through the encasement of the lever. Known
box-type
enclosures use ordinary annealed glass, which is easily broken, to form the
glass front.
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U.S. Pat. No. 5,868,477, issued to Decarie, teaches a fire alarm pull station
enclosure
having a box shaped frame with a front pane of standard annealed glass. This
pane has one
or more vertical score marks formed thereon. These vertical score marks cause
the pane to
controllably break when struck by a striker. The sections of glass formed by
striking are
intended to fall down and out through the bottom of the enclosure, to expose
the fire alarm
lever and permit its actuation. This fire alarm pull station enclosure suffers
from certain
disadvantages. One disadvantage is that the significant size of the sections
of broken glass
and the common occurrence of straight edges (a problem exacerbated by breakage
along the
scoring marks) render them useful as weapons. In short, such an enclosure may
provide an
improvised weapon associated with means for providing a significant
distraction (the alarm
itself). In addition, the sections of glass produced by striking may not fall
cleanly through
the open bottom of the enclosure, but may become jammed within the enclosure,
making
actuation of the lever hazardous to the user. This risk is magnified in that
the user, having
discovered a fire, will invariably be under stress and will try to operate the
device as quickly
as possible. It is a principal object of the present invention to improve upon
these box-type
fire alarm pull station enclosures.
Safety glass and, in particular, tempered glass is known. Tempered glass has a
number of beneficial properties and, in particular, improved strength over
annealed glass and
corresponding improved breakage resistance. Tempered glass is therefore
commonly used in
applications where resistance to breakage is required. Some common
applications, for
example, are glass table tops, computer monitors, oven doors, and the rear
windows of
automobiles.
Heat-treated glass may be classified as fully tempered or heat-strengthened.
Heat
treating of glass creates an initial condition of surface and edge
compression. Generally, this
condition is achieved by heating glass and then cooling the surfaces rapidly.
This leaves the
central glass relatively hot compared to the surfaces. As the central glass
cools, it forces the
surfaces and edges into compression. This compression must be overcome prior
to fracture.
The safety feature of tempered glass comes from its strength and impact
resistance and from
a unique fracture pattern. When tempered glass breaks, the glass fractures
into small,
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relatively harmless fragments generally without sharp edges. Instantaneous
total
fragmentation generally follows full penetration of the compression layer.
Within the context of this application, "tempered glass" includes both fully
tempered
glass and heat-strengthened glass having substantially the same fracture
characteristics of
fully tempered glass.
Due to the high strength and impact resistance of tempered glass, to the
inventor's
knowledge it is not used in applications where easy breakage of a glass
component may be
required.
It is an object of the invention to obviate or mitigate at least one of the
above-
mentioned disadvantages of the prior art.
Summary of the Invention
The disadvantages of the prior art may be overcome by providing an improved
box
type apparatus to allow quick access to the pull lever, in which the user can
actuate the pull
lever without the danger of large glass fragments, either stuck within the
enclosure where
they can present a risk of harm to the user, or otherwise in the vicinity
where they may be
used as an improvised weapon.
The present inventor surprisingly and unexpectedly discovered that a grooved
tempered glass pane could be used as a front for a fire alarm pull station
enclosure.
Surprisingly this arrangement provides acceptable strength for the application
(i.e. the pane
can be broken through the application of reasonable striking force by a user)
while imparting
the beneficial fracture pattern described above.
The fire alarm pull station in its broad aspect comprises: a frame configured
to
enclose a pull lever, the frame having side walls defining an open front; a
tempered glass
pane having a groove formed thereon; the frame having supports adjacent the
open front for
supporting the tempered glass pane between the side walls and over the open
front.
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In another broad aspect the invention comprises the use of a grooved tempered
glass
pane as a front for a fire alarm pull station enclosure.
In a preferred embodiment, the frame is rectangular in shape and is open at
the
bottom end allowing for glass particles to fall through when the device is
employed and the
tempered glass is broken. (Alternatively, means for collecting the glass
fragments may be
provided at the base of the enclosure.) Preferably, in use, the frame is
secured to a mounting
surface (typically, a wall) wherein a pull lever is attached in such a way
that the frame fully
encloses the pull lever. In a preferred embodiment, the frame is made of metal
and, more
preferably, a sheet steel alloy. There may be attached to the outside of one
of the sides of the
frame a tether. At the end of the tether is a striking device which can be
used to break the
tempered glass pane and gain access to the pull lever.
In a preferred embodiment of the present invention, the tempered glass is
provided
with a groove, suitably having an angle of between 30 degrees and 60 degrees
relative to the
surface of the tempered glass pane on which it is formed. More preferably, the
groove has an
angle of between about 40 degrees and 50 degrees relative to the surface of
the tempered
glass pane on which it is formed. Most preferably, the groove has an angle of
about 45
degrees relative to the surface of the tempered glass pane on which it is
formed. In a
preferred embodiment, the groove penetrates about half the thickness of the
tempered glass
pane. This groove permits breakage of the tempered glass upon striking of the
glass by a
user with a reasonable amount of force.
According to another aspect of the present invention, there is provided
supports for
the tempered glass pane. In a preferred embodiment, the frame is rectangular
and has a pair
of spaced-apart parallel side walls, each having supports. Preferably, the
supports include
two detents which support the tempered glass pane at its two lower corners.
The detents act
as support, along with slots on the parallel side walls. Upon striking and
fracturing of the
glass pane, the glass pane collapses and glass fragments are released.
Preferably, the
fragments fall through an open bottom of the frame.
Brief Description of the Drawings
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Drawings which illustrate embodiments of the present invention will now be
described, by way of example only, with reference to the attached Figures,
wherein:
FIG.1 is an exploded perspective view of an embodiment of a fire alarm pull
station
enclosure of the present invention;
FIG. 2 is a horizontal section facing downwardly showing the slot and detent
support
and the grooved tempered pane of the fire alarm pull station enclosure of FIG.
1;
FIG. 2a is an enlarged fragmentary view of the groove of FIG. 2;
FIG. 3 is an enlarged fragmentary perspective view illustrating in detail the
slot and
detent support for the tempered glass pane;
FIG. 4 is a perspective view of the assembled fire alarm pull station in use
showing
the fragmented tempered glass breakage; and
FIG. 5 is a front elevation of the fire alarm pull station shown in FIG. 4
following
tempered glass pane breakage.
Detailed Description of the Invention
FIGS. 1-5 illustrate an embodiment of the pull station enclosure of the
invention
which comprises open-back box enclosure 10 which is screwed to a mounting
surface,
generally a support wall, so as to encase within the box the fire alarm pull
lever 19 (FIG. 5).
The enclosure 10 is preferably of rectangular shape and comprises a frame 11
consisting of a
pair of spaced-apart parallel side walls 12,14 joined at the rear edges
thereof at the top and
bottom by connecting strips 16, 18 respectively, which may be formed integral
therewith.
Enclosure 10 may be secured to a mounting surface by any suitable means. In a
preferred
embodiment, screw holes 20 formed in strips 16,18 permit securement of
enclosure 10 to a
support wall by screws 13 (FIG. 5). Opening 22 defined between side walls
12,14 and strips
16,18 is sufficiently large to receive pull lever 19. Preferably, the front
edges of side walls
12, 14 have inwardly facing flanges 24, 26 for reasons which will become
apparent as the
description proceeds. A front bottom plate 28 secured to flanges 24, 26 such
as by spot
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welding has holes 30 formed therein in alignment with holes 20 in rear bottom
strip 18 to
allow insertion of a screw driver for driving screws through holes 20.
A cap 31 having end flanges 32, 34 and front and rear flanges 36, 38 is
preferably
secured to side walls 12, 14 at the top thereof by screws 40 passing through
end flanges 32,
34. With regard to end flanges 32, 34, it may be necessary to angle the front
edge of one or
both of end flanges 32, 34 (as shown) to accommodate certain glass
thicknesses. Each of
side walls 12, 14 has an upstanding inner rib 42, 44 bent rearwardly at an
angle of about 45
degrees to the plane of front flanges 24, 26 from elongated plates 43, 45
attached thereto
such as by spot welding along their length at a uniform distance from front
flanges 24, 26
respectively to receive the side edges of glass pane 46 in slots 47 defined
between front
flanges 24,26 and inner ribs 42,44. A detent 50, such as a rivet passing
through side walls
12, 14, closes the bottom of slots 47. Flanges 42 and 44 can be crimped at
their bases to
form a detent, not shown, to close the bottoms of slots 47.
In assembly, mounting screws 13 are driven through upper and lower screw holes
20
to secure frame 11 to a supporting wall. Tempered glass pane 46 is inserted
from above in
slots 47 defined between front flanges 24, 26 and ribs 42, 44 and is supported
at its lower
corners by shallow detent 50 projecting from side walls 12,14 into slots 47.
Closure cap 31
is then attached to side walls 12, 14 by screws 40, whereby cap front flange
36, side wall
flanges 24, 26, and bottom plate 28 conceal the edges of tempered glass pane
46.
Tempered glass pane 46 has at least one groove 52 formed thereon. Preferably,
groove 52 is formed vertically on the inner surface of pane 46 (i.e. the
surface that will face
the mounting surface) substantially along the length thereof. Preferably,
groove 52 has an
angle between about 30 degrees and 60 degrees relative to the surface of the
glass on which
it is formed. More preferably, groove 52 has an angle of between about 40
degrees and 50
degrees relative to the surface of the glass on which it is formed. Most
preferably, groove 52
has an angle of about 45 degrees relative to the surface of the glass on which
it is formed.
Preferably, the groove penetrates about half the thickness of the tempered
glass pane. The
depth of the groove must be sufficiently deep to permit easy glass breakage,
but is
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constrained in that if the groove penetrates too deeply the pane may shatter.
A suitable
groove width is between about 1/16 of an inch and about 3/32 of an inch.
While in a preferred embodiment a single vertical groove is shown, other
arrangements are possible. The groove may, for example, be formed horizontally
or at an
angle on glass pane 46. It is also possible to have a plurality of grooves,
and a plurality of
grooves may be necessary where the length of a single groove is constrained by
the
dimensions of the frame, such that the single groove does not provide the
requisite ease of
breakage (i.e. such might be the case where a horizontal groove is formed on a
pane of
limited width.) As will be apparent to a person skilled in the art, however, a
single groove is
preferred because it is less labour intensive and so more cost efficient than
multiple grooves.
In a preferred embodiment, a single vertical groove 52 is formed on pane 46.
On a pane
having dimensions of about 4 inches by about 6'/i inches, which is suitable
for a typical
frame having a width of about 4%z inches by about 7 inches, a single vertical
groove 52 of
about 4'/z inches is suitable. Preferably, groove 52 is centrally located on
pane 46. Suitable
positions and dimensions of the groove may be readily ascertained by a person
skilled in the
art.
To manufacture grooved tempered glass pane 46, a tempered glass pane of
suitable
size can be purchased or manufactured according to methods commonly known in
the art.
Preferably glass pane 46 has a thickness between about 1/8 inches and 3/16
inches. The
depth of groove 52 is preferably between about 1/16 inches and 3/32 inches. A
diamond
blade tool is suitably used for cutting groove 52. Groove 52 is preferably cut
in water, which
the inventor has found reduces chance of fracture during the cutting process.
Groove 52 may
be suitably cut at a temperature of between 70° and 72°
Fahrenheit (between about 21° and
22.5° Celsius). Pane 46 can further be dried at a temperature of
68° to 70° Fahrenheit
(between about 20° and 21° Celsius.).
A striker 60 attached to a side wall by a tether 62, such as a cable or chain,
can be
conveniently used by an operator to strike tempered glass pane 46 which is
rendered
frangible by groove 52 to break it. Preferably, striker 60 and tether 62 are
positioned on the
right hand side of enclosure 10 when installed on a mounting surface due to
the fact that a
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majority of users are likely to be right-handed. The broken pane of glass 46
falls through the
open bottom of enclosure 10 in the form of small fragments 46a, thereby
rendering the pull
lever accessible. In an alternate embodiment, a trap (not shown) may be
provided to receive
fragments 46a.
The present invention provides a number of advantages. The fire alarm pull
station
cover maintains the desired result of protecting the pull lever from easy
access tampering or
accidental actuation, while the groove permits the breakage of the tempered
pane of glass.
It will be understood that modifications can be made in the embodiment of the
invention illustrated and described herein without departing from the scope
and purview of
the invention as defined by the appended claims.
In particular, and without limiting the generality of the foregoing, it will
be
understood that the specific shape and configuration of the frame and the
means of
supporting the tempered glass pane may be changed without departing from the
scope of the
invention. Further, a worker skilled in the art will understand that the
enclosure may be
attached to the mounting surface using any suitable fasteners such as nails,
adhesives, or
may even be integrally formed with the mounting surface and the attachment
means
described herein are merely described for illustrative purposes.
