U.S. patent number 3,559,594 [Application Number 04/841,284] was granted by the patent office on 1971-02-02 for fire resistant safe.
This patent grant is currently assigned to Schwab Safe Co., Inc.. Invention is credited to Walter N. Miller.
United States Patent |
3,559,594 |
Miller |
February 2, 1971 |
FIRE RESISTANT SAFE
Abstract
A fire resistant safe, particularly for the storage of EDP
records such as magnetic tapes, discs, microfilm and the like,
wherein an inner storage area or repository is surrounded by at
least three layers of heat resistant material, an outer layer of
concrete, a middle layer of insulation such as urethane foam
separated from the concrete by a polyethylene moisture shield and
an inner layer comprised, at least in part, of Sodium Acetate
Trihydrate which is a material with a heat fusion of 100 Btu per
lb., a melting point in the range of 136--144.degree. F. and a
density of approximately 90 lbs. per cubic foot. Such a safe has
been shown to maintain the temperature of its inner repository
below 150.degree. F. and the relative humidity of the repository
below 85 percent for 4 hours when subjected to an external
temperature of 2000.degree. F.
Inventors: |
Miller; Walter N. (Cannelton,
IN) |
Assignee: |
Schwab Safe Co., Inc.
(Lafayette, IN)
|
Family
ID: |
25284490 |
Appl.
No.: |
04/841,284 |
Filed: |
July 14, 1969 |
Current U.S.
Class: |
109/84;
220/592.26; 220/560.01 |
Current CPC
Class: |
E05G
1/024 (20130101) |
Current International
Class: |
E05G
1/00 (20060101); E05G 1/024 (20060101); E04b
002/02 () |
Field of
Search: |
;109/29,49.5,80,82,83,84
;52/249,405 ;220/9 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Williamowsky;David J.
Assistant Examiner: Kannan; Philip C.
Claims
I claim:
1. An improved safe for maintaining the temperature of an inner
repository within the safe for storing valuables below 150.degree.
F. and the relative humidity of the repository below 85 percent for
at least 4 hours when the safe is subjected to an external
temperature of approximately 2,000.degree. F. comprising:
an outer layer substantially surrounding said inner repository;
a middle layer of insulation within said outer layer and
substantially surrounding said inner repository; and
an inner layer comprising, at least in part, Sodium Acetate
Trihydrate, within said middle layer and substantially surrounding
said inner repository, for undergoing a solid to liquid phase
transformation to absorb heat when said inner layer is subjected to
a temperature above 150.degree. F.
2. A safe as in claim 1 wherein said insulation is urethane foam
and said outer layer is concrete, and further including a moisture
shield comprised of polyethylene disposed between said concrete and
said urethane foam.
3. A safe as in claim 2 wherein said concrete has a thickness of
approximately 4-3/4 inches, said foam has a thickness of
approximately 1-1/2 inches and said inner layer has a thickness of
approximately seven-eighths inch.
4. A safe as in claim 1 wherein said safe has a first set of outer
doors and a second set of inner doors for access to said repository
and wherein said outer doors are filled with concrete and said
inner doors are filled with urethane foam.
5. A safe as in claim 1 wherein said safe is for storing EDP
records and including means to store said EDP records.
6. A safe as in claim 1 wherein said inner layer is comprised
solely of Sodium Acetate Trihydrate and including a container for
holding said Sodium Acetate Trihydrate.
7. A safe as in claim 1 wherein said outer, middle, and inner
layers surround said safe on the top, bottom and three sides.
8. A safe as in claim 1 wherein said outer layer is comprised of
concrete.
Description
BRIEF DESCRIPTION OF THE PRIOR ART AND SUMMARY OF THE INVENTION
The invention relates to a fire resistant safe capable of
maintaining for at least 4 hours temperatures below 150.degree. F.
within its inner storage area or repository and a relative humidity
below 85 percent in the repository when subjected to an external
temperature of 2,000.degree. F.
The necessity to protect valuable records and other data from
destruction by fire or other disasters, as well as from loss by
theft, has been an important consideration in safe development and
construction for many years. The increased use by modern society of
electronic digital-processing equipment and the resultant storage
of priceless business and other information on magnetic tapes,
discs, microfilm and the like, which can be easily erased or
destroyed if subjected to certain conditions of heat and/or
humidity, has intensified this problem.
Underwriters Laboratories has established a temperature of
150.degree. F. and a relative humidity of 85 percent as defining
the safe limits for EDP records. Although most high quality tapes
and the like can withstand substantially higher temperatures, the
possibility of some information loss, especially from low quality
records, exists at temperatures above this level. Consequently,
safes are rated accordingly to how long they maintain their
repository below this standard at a given external temperature,
usually around 2,000.degree. F., which is greater than the melting
point of copper.
In the past, safes were protected from fire simply by surrounding
the storage area with walls of insulation. However, keeping the
interior temperature below 150.degree. F., which is not far above
normal room temperature, for a number of hours requires far too
much insulation to be practical. One solution to this problem is to
employ a material in the safe which will not only act as an
insulator but will also actively absorb heat leaking into the
repository, for example, by changing phase at some temperature
below the danger temperature.
One particular safe employing such heat absorbing material was
constructed with an outer layer of concrete, a middle layer of
urethane foam or similar insulation within the concrete and
separated from it by a moisture shield, and finally an inner layer
of semirefined or other paraffin which absorbs considerable heat in
a solid-liquid phase transformation when the temperature of the
paraffin rises to its melting point between roughly
121--135.degree. F. because of an external fire or similar
disaster. This particular construction in tests has been shown
capable of maintaining the repository temperature below 150.degree.
F. in the face of an external temperature of 1,850.degree. F. for
at most 2 hours, and a 2-hour rating has been given to this
safe.
An ideal heat absorbing material in such a safe which was to absorb
heat in a solid to liquid transformation would have a melting point
just below the rated level and a very high heat of fusion. Paraffin
has a high heat of fusion less than that of water and a melting
point of 121--135.degree. F. Because it melts completely well
before the interior temperature approaches the 150.degree. F. mark,
it retards temperature increase far too soon and is of little
effect after completely melted when temperature approaches the
critical level.
The present invention relates to an improved safe construction
which is comprised of an outer layer of concrete, gypsum or other
material having high water crystallization, a middle layer of
urethane foam or other insulation, and an inner layer comprised, at
least in part, of Sodium Acetate Trihydrate, which is a material
having a heat of fusion of approximately 100 Btu per lb., a melting
point in the range of roughly 135--144.degree. F. and a density of
90 lbs. per square feet. Because its heat of fusion is much higher
than paraffin and its melting point closer to 150.degree. F., it
has been found to be much more effective in such a safe. In fact,
this improved arrangement maintains its repository at a temperature
less than 150.degree. F. and at a relative humidity below 85
percent while subject to external temperatures of 2,000.degree. F.,
for at least 4 hours, approximately double the 2-hour rating of the
comparable safe using paraffin.
Many other purposes and objects of the invention will become clear
from reading the following detailed description of the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an exterior view of the novel safe of this application
with the doors open and the repository in view.
FIG. 2 shows a cutaway top plan view of the safe of FIG. 1.
DETAILED DESCRIPTION OF THE DRAWINGS
Reference is now made to FIGS. 1 and 2 which show in detail the
improved safe construction of this invention which results in the
unique capability to withstand temperatures of up to 2,000.degree.
F. for 4 hours while preventing the temperature of the repository
from rising above 150.degree. F. In the embodiment shown in FIG. 1,
the safe 10 has an inner storage area or repository 12 which is
filled with various racks, shelves and drawers for holding diverse
tapes, canisters, discs, microfilm cartridges, punched and other
cards, etc.
These holders are preferably removable to permit the safe to store
any kind and number of records or other valuables. Moreover, the
repository 12 in FIG. 1 is sealed by a double door arrangement with
a few discs even being stored on the inner side of the inner door
as shown. A suitable outer cabinet 14, which may be metallic and
decorated as desired, encloses the three layers which protect the
repository, and the two sets of doors 16 and 18 complete the
enclosure. Of course, a single door can be used if desired and many
double door arrangements other than as illustrated in FIG. 1 can be
usefully employed. A conventional lock which may be equipped with a
spyproof dial preferably protects the repository against theft.
FIG. 2 shows a cutaway top view of the unique three-layer safe of
FIG. 1 with an outer concrete wall or layer 20, a middle urethane
foam wall or layer 22 and an inner wall 24 comprising, at least in
part, Sodium Acetate Trihydrate surrounding the top, bottom, and
three sides of the repository with the fourth side sealed by doors
16 and 18. As illustrated in FIG. 2, the outer doors 18 are filled
also with concrete and may be considered part of layer 20. In one
embodiment of the invention, this concrete wall is made
approximately 4-3/4 inches thick.
Within this outer concrete wall or layer 20 is a second middle wall
or layer 22 which is comprised of a suitable insulating material,
such as urethane foam. The foam layer 22 also encircles the
repository 12 on the top, bottom and three sides and forms the
interior of the inner doors 16. While the arrangement shown in
FIGS. 1 and 2 employs dual doors 16 and 18, a single door
embodiment in which the layer of foam insulation is incorporated
into the doors or otherwise formed thereon or associated therewith
could be alternately employed. This middle wall or layer 22 of
insulation is preferably isolated from the concrete wall 20 by a
thin sheet 21 of a moisture shield such as reinforced polyethylene.
In the embodiment with the 4-3/4-inch concrete layer, layer 22 was
made 1-1/2 inches thick.
Finally, interior to the layer 22, an inner layer 24, which is
comprised at least in part of Sodium Acetate Trihydrate, is
disposed so as to surround the repository 12, again on the top,
bottom and three sides. A layer can likewise be disposed in or on
the inner doors 16 if desired. A hollow container 28 of any
suitable material such as 18 guage steel holds the layer 24 in
place and also provides support for the shelves which can be
installed as shown in FIG. 1. This container preferably is open on
the one side where the doors are placed and is otherwise closed to
hold the Sodium Acetate Trihydrate in place. In the embodiment with
the 4-3/4-inch concrete layer, the layer 24 was made to be
seven-eighths inch thick.
The safe shown in FIGS. 1 and 2 can be constructed in any suitable
manner. However, one simple way is to first pour the concrete into
the hollow space inside cabinet 14 provided for it. Next, the
polyethylene shield and urethane foam are mounted interior to the
concrete. The Sodium Acetate Trihydrate is then melted and poured
as a liquid into container 28 where it solidifies. The container 28
is then fitted in place and the doors and other structures
added.
As mentioned briefly above, the unique arrangement shown in FIGS. 1
and 2, when constructed with appropriate thicknesses such as given,
doubles the heat resisting capability of the safe in comparison to
a similar arrangement which employs paraffin instead of Sodium
Acetate Trihydrate. Sodium Acetate Trihydrate has been used before
with other products and some of its previous uses are described
briefly on page 600 of Kirk and Othmer, ENCYCLOPEDIA OF CHEMICAL
TECHNOLOGY, Vol. 12 (1954). Since it has a heat of fusion which is
approximately 4 times as large as an equal volume of water,
according to the above Encyclopedia it is or has been in the past
used in foot warmers and thermos bottles, in addition to being used
as a mordant for dyeing, and in food preserving, photography,
medicine and analytical chemistry. Also, as mentioned briefly
above, Sodium Acetate Trihydrate has a heat of fusion of
approximately 100 Btu per lb., a melting point between roughly
136--144.degree. F., and a density of roughly 90 lbs. per cubic
foot. It is readily available commercially at a price which makes
it practical material for use in a safe such as illustrated.
It may be desirable to mix other materials such as paraffin with
the Sodium Acetate Trihydrate to change somewhat the temperatures
at which heat is absorbed. However, it is believed that relatively
pure Sodium Acetate Trihydrate alone is most effective in absorbing
heat.
As the temperature surrounding the three-layer safe 10 shown in
FIGS. 1 and 2 begins to rise the moisture within the concrete layer
20 begins to turn to steam and absorb much of the heat penetrating
into the safe. When sufficient heat has penetrated the concrete
layer 20 and the insulation layer 22, the temperature of the Sodium
Acetate Trihydrate in layer 24 reaches its melting point, which is
less than 150.degree. F., at which time the Sodium Acetate
Trihydrate begins to change from solid to liquid, while absorbing a
great deal of heat from the surrounding layers of concrete and
insulation and thus keeping the repository 12 at a relatively cool
temperature for at least 4 hours, during which heat is supplied by
a furnace and 40 to 80 hours thereafter while cooling of the safe
takes place.
Accordingly, the above invention results in a safe which has a
superior capability of withstanding temperatures far beyond the
present art and which approximately doubles the capability of
similar fire-resistant safes now in use. The above example of the
invention is intended to illustrate the operation and structure of
the invention and the scope of the invention is limited only by the
following claims.
* * * * *