FIELD OF THE INVENTION
The present invention relates to firestops, more particularly to firestops for cables, even
more particularly to firestops in the form of barriers for cables.
BACKGROUND OF THE INVENTION
Firestops are designed to restore the fire-resistance ratings of wall and/or floor
assemblies by impeding the spread of fire. This is done by sealing openings with fireresistant
materials and covering cables and joints with fire resistant coatings or
materials. There are some basic material types of thermal insulation and fireproofing
materials like fiberglass, glass wool, polymeric materials, cellulose fibers, and ceramics
or refractories. Each of these materials has a particular range of temperatures over
which it is effective and its associated cost. Thus, one has to choose the fireproofing
material and then modify it as per the structural requirement. For instance, a single
cable may be provided with a cylindrical jacket of fireproofing material by virtue of the
cylindrical symmetry.
In large buildings, it is common to place several wires/cables together in trays
commonly called cable trays. The term "cable" as used herein, refers to "A conductor
for transmitting electrical or optical signals or electric power". Cable trays are used as
an alternative to open wiring or electrical conduit systems, and are commonly used for
cable management in commercial and industrial construction. This placement of cables
may be disadvantageous in some cases because during peak hours, cables are at very
high loads, so there is a good chance of sparking leading to fire in one or more cables.
Since numerous cables are placed together in trays, the fire can spread to other wires
which can prove to be very dangerous. Such a fire hazard is unacceptable and thus
firestops are necessary for such cables. In other cases, fire started due to other reasons
can spread through the cables and wires. This is because in building construction,
electrical cable jacket material is a potential source of fuel for fires.
One method to solve the above mentioned problem is to provide fireproof material over
the cable trays. This however is a costly proposition considering that large buildings
2
have cable trays and cables having a length of hundreds and thousands of meters.
Similarly, replacing all the existing cables with special fire-proof cables also involves
huge capital investment.
The present invention provides a system for ensuring that fire can be isolated and
extinguished easily by providing firestop barriers which segregate the cable tray into
multiple sections. Fire emanating at one section can only damage the cables in that
section and is extinguished while traversing the firestop barriers due to the lack of air.
Thus, fire isn't allowed to spread to adjacent sections, without investing heavily in fireproofing
materials or replacing the cables in the building.
The present method relates to a system for passively increasing the fire safety of
buildings by providing firestops for cables in cable trays at several locations. Further,
the cables are provided with fireproof coating when they are not grouped together in the
cable trays. The dimensions of the firestop barriers are such that fire cannot propagate
through their length and is quenched before it can spread to other sections of the cables.
Thus, fire can be isolated easily since it is unable to spread out from the location where
it started.
SUMMARY OF THE INVENTION
In accordance with an embodiment of the invention, is provided a Firestop Barrier for
cable trays, comprising: a Sheath made from insulating material packed in a wire mesh,
the sheath enclosing a section of the cable tray; and, a cladding enclosing the sheath.
In accordance with another embodiment of the invention, is provided a Firestop Barrier
for cable trays, wherein the insulating material used in the sheath is glass wool and the
cladding (160) is made from aluminum. In accordance with yet another embodiment of
the invention, the glass wool has a density of 10-48 Kg/m3 and the Aluminum cladding
has a thickness of about 0.55 mm/24 SWG (Standard Wire Gauge).
In accordance with an embodiment of the invention, is provided a method of passive
fire protection in a building by intermittently providing firestops for the cables and/or
cable trays.
3
In accordance with another embodiment of the invention, is provided a method of
passive fire protection in a building, wherein the firestops are spaced according to the
location of the cables; the firestops being placed close to each other in crucial areas of a
building and spaced at larger distances in other less crucial areas.
In accordance with yet another embodiment of the invention, is provided a method of
passive fire protection in a building, wherein firestops in the form of firestop barriers in
accordance with any of the aforementioned embodiments are provided intermittently
for cable trays.
In accordance with yet another embodiment of the invention, is provided a method of
passive fire protection in a building, wherein the firestop barriers are provided after
every 10 meters in crucial areas of the building, and every 15 meters in the less crucial
areas of the building.
In accordance with yet another embodiment of the invention, is provided a method of
passive fire protection in a building, wherein firestop barriers in the form of fire
resistant coatings are provided intermittently for cables.
In accordance with yet another embodiment of the invention, is provided a method of
passive fire protection in a building, wherein the fire resistant coatings are provided
after every 5 meters in crucial areas of the building, and every 10 meters in the less
crucial areas of the building; each coating covering at least 1 meter length ofthe cable.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of a conventional cable tray used for securing a plurality of
cables in a building.
Fig. 2 is a perspective view showing a section of the cable tray of Fig. 1 enclosed by a
glass wool sheath.
Fig. 3 is a perspective view showing a section of the cable tray of Fig. 1 enclosed by a
firestop barrier in accordance with an embodiment of the invention.
4
It is to be noted that the above mentioned figures are with reference to a particular
configuration of cable trays. However, the teachings of the invention can be readily
applied to other configurations of cable trays also, with or without some minor
modifications.
DESCRIPTION
Discussed below are some representative embodiments of the present invention. The
invention in its broader aspects is not limited to the specific details, representative
devices and methods, and illustrative examples shown and described in this section in
connection with the embodiments and methods. The invention according to its various
aspects is particularly pointed out and distinctly claimed in the appended claims read in
view of this specification, and appropriate equivalents.
It is to be noted that, as used in the specification and the appended claims, the singular
forms "a," "an," and "the" include plural referents unless the context clearly dictates
otherwise.
Fig. 1 is a perspective view of a conventional cable tray used for securing a plurality of
cables in a building. The cable tray (11 0) has a long U-shaped channel for holding
several cables (120) together. The tray is usually open from the top to avoid
overheating of the cables. The bottom portion of the tray, where the cables rest may be
solid or can have several holes punched in it for ventilation. The cables may be grouped
together as shown in the figure or can be spaced apart in case of large power cables
where there is a risk of overheating. The cable tray and cables are supported by a
support structure (130) which transfers their weight to a roof or wall in the building. In
the present figure, a number of angle supports are provided at several locations along
the length of the tray to provide support to the cable tray.
Fig. 2 is a perspective view showing a section of the cable tray of Fig. 1 enclosed by a
glass wool sheath. The glass wool sheath comprises layers of glass wool packed inside
a wire mesh (150). The glass wool is typically compressed into sheets prior to packing
into the wire mesh. The wire mesh prevents any loose glass wool from falling down.
The glass wool sheath ( 140) is then tightly wrapped around a section of the cable tray
5
(11 0) as shown in the figure. The tight packing of the glass wool and completely
wrapping a section of the tray with the same restricts the amount of air available in the
enclosed space. Thus, a fire on reaching this section is automatically extinguished due
to lack of oxygen and cannot propagate further.
Fig. 3 shows a complete firestop barrier (1 00) comprising a glass wool sheath (140) and
a cladding (160). The cladding is preferably made from a material like aluminum to
provide thermal insulation without making the firestop barrier too heavy. The cladding
also provides structural support, corrosion resistance and protects the fire wool from
moisture and other contaminants. In the given figure, the cladding comprises an
aluminum sheet rolled into the shape of a hollow cuboid open from two sides. It is to be
noted that the thickness of the glass wool sheath and the width of the barrier depend
upon the number of cables and the amount of current flowing through them. The shape
of the aluminum cladding is in accordance with the shape of the glass wool sheath so as
to avoid open spaces within the firestop barrier.
It should be apparent to a skilled person that the shape of the firestop barrier will vary
depending upon the arrangement of cables in a circular array or rectangular array etc.
For instance, if cables are grouped in a circular array, the firestop barrier would be
substantially cylindrical in shape.
The present invention provides a method of passive fire protection in a building by
intermittently providing firestop barriers for the cable trays. The firestop barriers are
spaced according to the location of the cables such that the barriers are placed close to
each other in crucial areas like the main power supply and spaced at larger distances in
other less crucial areas like basements. In many cases, it is practicable to only provide
the firestops where the cable trays are traversing substantially horizontally with
reference to the ground.
Further, wherever firestop barriers cannot be provided over cables or cable trays
running horizontally, firestops in the form of multiple layers of fire-resistant coating are
provided intermittently on the cables. The fire-resistant coating is not provided
throughout the length of the cables, but spaced depending upon the fire hazard at a
particular location. The coating is done at smaller intervals around the crucial areas like
6
the main power supply, and at larger areas in less crucial areas like the basement. The
coating thickness and length is such that a fire cannot propagate from one end of the
coating to the other and is quenched in between.
Further, a fire-resistant coating is provided throughout the length of the cables running
in the vertical direction. Electrical cable jacket material is a potential source of fuel for
fires. Thus, to limit the spread of fire along cable jacketing, one may use cable coating
materials in existing constructions or may use cables with fire retardant jacketing in
new constructions. The spread of fire would be faster in vertical cables because the
flame will naturally rise upwards in the direction of the cables. This necessitates the
provision of the coating throughout the length of the cable instead of intermittently, as
in the case ofhorizontal cables.
In accordance with an optional embodiment of the invention, a fire-resistant coating is
provided at both the end points of a cable emanating from the main power supply and
going to subsidiary power supply locations. The thickness and width of the coating is
chosen as explained in the preceding two paragraphs.
In accordance with another optional embodiment of the invention, firestop mortar is
provided wherever holes or opening are provided in the walls for passage of the cable
trays. This does not allow fire to propagate within the building through unsealed
openings. Common materials like Plaster of Paris (POP) and cement can be used as
mortar.
Thus, the present invention provides relatively cheap firestops and methods of using the
same for passively enhancing the fire resistance of the building. Existing installations
which do not have fire resistant cables can be protected by firestops in the form of
barriers or coatings. Since the firestops are provided intermittently, the capital
investment is relatively small. Moreover, the firestop barriers can be easily installed,
replaced and uninstalled as and when required, unlike other barriers known from prior
arts which permanently bind themselves with the cable trays.
Several variations are possible within the scope of the invention. For instance, the glass
wool can be replaced by other similar fire resistant/insulating materials. Likewise, the
7
wire mesh of different shapes and sizes can be used, depending upon the nature of
insulating material to be packed. One may also cover the glass wool by a cloth or
plastic sheet to prevent it from disintegrating and falling down. The teachings of the
invention are not limited to cables and cable trays, and can be easily applied to other
articles that need fire protection.
The invention is not limited to the embodiments which have been described and
illustrated by way of example and numerous modifications and variations would be
apparent to a person skilled in the art, without departing from the scope of the appended
claims.
8

We Claim:
1. A Firestop Barrier for cable trays, compnsmg: a Sheath (140) made from
insulating material packed in a wire mesh (150), the sheath ( 140) enclosing a
section ofthe cable tray; and, a cladding (160) enclosing the sheath (140).
2. The firestop barrier as claimed in claim 1, wherein the insulating material used
in the sheath ( 140) is glass wool and the cladding ( 160) is made from
aluminum.
3. The firestop barrier as claimed in claim 2, wherein the glass wool has a density
of 10-48 Kg/m3 and the Aluminum cladding has a thickness of about 0.55
mrn/24 SWG (Standard Wire Gauge).
4. A method of passive fire protection in a building by intermittently providing
firestops for the cables and/or cable trays.
5. The method as claimed in claim 4, wherein the firestops are spaced according to
the location of the cables; the firestops being placed close to each other in
crucial areas of a building and spaced at larger distances in other less crucial
areas.
6. The method of passive fire protection as claimed in any of the claims 4 or 5,
wherein firestops in the form of firestop barriers in accordance with any of the
claims 1 to 3 are provided intermittently for cable trays.
7. The method of passive fire protection as claimed in claim 6, wherein the
firestop barriers are provided after every 1 0 meters in crucial areas of the
building, and every 15 meters in the less crucial areas of the building.
8. The method of passive fire protection as claimed in any of the claims 4 or 5,
wherein firestop barriers in the form of fire resistant coatings are provided
intermittently for cables.
9
9. The method of passive fire protection as claimed in claitr' 8, wherein the fire
resistant coatings are provided after every 5 meters in crucial areas of the
building, and every 10 meters in the less crucial areas of the building; each
coating covering at least 1 meter length of the cable.
10. The method of passive fire protection as claimed in any of the claims 8 or 9,
optionally wherein a fire-resistant coating is provided at both the end points of a
cable emanating from the main power supply and going to subsidiary power
supply locations.