US 3559594 A
Description (OCR text may contain errors)
OR 3 5 5 95 94 SR United States Patent 1,329,511 1,688,849 10/1928 Bellamore etal Walter N. Miller Cannelton, Ind. 841,284
July 14, 1969 Feb. 2, 197 1 Schwab Safe Co., Inc. Lafayette, Ind.
a corporation of Indiana Inventor Appl. No. Filed Patented Assignee FIRE RESISTANT SAFE 8 Claims, 2 Drawing Figs.
us. Cl 109/84,
References Cited UNITED STATES PATENTS 2/1920 Dick et a1. 109/84X Primary Examiner-David .l. Williamowsky Assistant Examiner-Philip C. Kannan Att0rney--Cushman, Darby & Cushman 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 1b., a melting point in the range of 136- -l44 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 F. and the relative humidity of the repository below 85 percent for 4 hours when subjected 109/84 to an external temperature of 2000 F.
PATENTEUFEBZ 9m 3,559 594 sum 2 or 2 FIRE RESISTANT SAFE 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 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 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 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 E, 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 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 12l135 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 F. in the face of an external temperature of 1,850 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 l21-l35 F. Because it melts completely well before the interior temperature approaches the 150 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 1b., a melting point in the range of roughly 135- 144 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. 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 F. and
at a relative humidity below 85 percent while subject to external temperatures of 2,000 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. I shows an exterior view of the novel safe ofthis 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 F. for 4 hours while preventing the temperature of the repository from rising above 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. I 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 l6 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-% 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 fonns the interior of the inner doors 16. While the arrangement shown in FIGS. 1 and 2 employs dual doors l6 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. 1n the embodiment with the 4-%-inch concrete layer, layer 22 was made l-k inches thick.
Finally, interior to the layer 22, an inner layer M, 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-%-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 thennos 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- l44 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 shown in FIGS. 1 and 2 begins to rise the moisture within the concrete layer 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 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.
1. An improved safe for maintaining the temperature of an inner repository within the safe for storing valuables below 150 F. and the relative humidity of the repository below percent for at least 4 hours when the safe is subjected to an external temperature of approximately 2,000 F. comprising:
an outer layer substantially surrounding said inner repositoa 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 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 inches, said foam has a thickness of approximately linches and said inner layer has a thickness of approximately seven-eighths inch.
. 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.