WO1994020965A1

WO1994020965A1 - Improved fire proofing method and system for the protection of electrical cables and conduits

Info

Publication number: WO1994020965A1
Application number: PCT/US1994/002633
Authority: WO
Inventors: Adolf R. Hochstim
Original assignee: Adolf R. Hochstim Family Trust
Priority date: 1993-03-12
Filing date: 1994-03-11
Publication date: 1994-09-15
Also published as: AU6364194A

Abstract

Novel methods and systems for fire proofing electrical conductors are disclosed. An inorganic, endothermic, substantially thermally conducting fire proofing material composed of one or more water-binding minerals is applied as a casing around electrical cables and/or conduits to form a fire proof electrical conduit. The electrical cable includes one or more electrical conductors. The fire proof electrical conduit protects the electrical conductors from thermal damage, and does not significantly reduce the current-carrying capacity of the conductors at normal operating temperatures. Several embodiments for the physical structure of the conduit are described, and several methods of fabricating the conduit are set forth.

Description

IMPROVED FIRE PROOFING METHOD AND SYSTEM FOR THE PROTECTION OF ELECTRICAL CABLES AND CONDUITS

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to fire proofing techniques, and more particularly to new methods and systems which use special fire protection materials to protect the physical integrity of electrical power transfer systems outside of fire walls in environments where fires may be present.

2. Description of Related Art

FIGURE 1 illustrates a typical prior art installation for the routing of an electrical power transfer system 102 through a fire wall 104. Electrical power transfer system 102 may include insulated electrical cables, electrical conduits, and/or electrical cable trays. In the present example, the electrical power transfer system 102 is a cylindrical conduit containing a plurality of insulated electrical cables 124, 126. The fire wall 104 separates a first room or compartment 110 from a second room or compartment 112. Fire walls protect a given room or compartment from heat and/or fire damage, as well as from smoke and fumes. The side of the fire wall 104 facing the first compartment 110 is the first side 114 of the fire wall 104, and the side of the fire wall 104 facing the second compartment 112 is the second side 116 of the fire wall 104.

Penetration fire stop material 100 is employed where it is necessary to route the electrical power transfer system 102 through the fire wall 104. To route the electrical power transfer system 102 through the fire wall 104, a clearance hole is formed in the fire wall 104. The radial dimensions a-a' , b-b' of the clearance hole are generally slightly larger than the radial dimensions c-c' , dd' of the electrical power transfer system 102 to facilitate the installation and positioning of the electrical power transfer system 102. However, after the electrical power transfer system 102 has been installed, a space or a void exists between the electrical power transfer system 102 and the fire wall 104. Some or all of the space within the fire wall 104 is filled with fire stop material 100 in order to prevent the spread of flames, smoke, fumes, and/or water through the fire wall.

The purpose of the fire stop material 100 is to protect the portion of the electrical power transfer system

102 situated within the fire wall 104, and to prevent the spread of a fire across the fire wall 104. Fire stop materials 100 may be categorized as caulking, intumescent

(expanding when exposed to heat) , elastomeric heat- absorbing, and/or cementitious heat-absorbing.

The portion of the electrical power transfer system 102 situated within the first compartment 110 is protected using fire damming materials 118. The purpose of the fire damming material 118 around the electrical power transfer system 102 is to prevent the melting and burning of the insulation around the electrical cables 124, 126. Each electrical cable 124, 126 includes one or mare electrical conductors providing one or more independent, electrically- conducting pathways. The electrical conductors may or may not be encased in electrical insulation material, hereinafter referred to as insulation. However, if an electrical cable 124, 126 includes a plurality of electrical conductors intended to form a plurality of independent, electrically conducting pathways, insulation is generally provided around one or more of the conducting pathways to prevent shorting between the pathways, and/or shorting between a conducting pathway and ground.

The temperature of the electrical cables 124, 126 must not exceed a specified value over a specified period of time.

These values and time periods are governed by standards promulgated, for example, by Underwriters Laboratories.

The purpose of these standards is to ensure the electrical and mechanical integrity of the electrical cables under various operational conditions. For example, the performance of insulated electrical cables at high temperatures is often limited by the point at which the insulation starts to melt or burn. The melting or burning of insulation can cause short circuits between the conductors 124, 126, as well as short circuits between a conductor 124 and the inner wall of the conduit.

The performance of uninsulated cables at high temperatures is limited by ohmic heating. The resistance of these cables increases with increasing temperature, until the cable no longer carries the required amount of current, and/or until the cable melts. Since the electrical cables 124, 126 are frequently employed as power supply lines or control signal lines, the shorting of these cables may cause disastrous consequences in critical environments such as nuclear power plants.

When using fire damming materials 118, one important design objective is to ensure that the temperature rise of the electrical cables 124, 126 will remain under a critical value for a given rating time. For example, the U.S. Nuclear Regulatory Commission requires the insulation on cables 124, 126 to withstand a maximum temperature of 325o F (18lo C) without significant degradation. Fire proofing of the electrical power transfer system 102 is complicated by the fact that the material employed for this purpose must perform well under two very different sets of operational conditions. The material must withstand the extreme heat of a fire, and also conduct heat under normal conditions. Unfortunately, a fire damming material 118 which excels in one of these operational environments (i.e., the heat of a fire) will often perform inadequately in the other operational environment (i.e., normal conditions) . This design tradeoff results because the function the material is required to perform is different for each of the operational environments.

In the operational environment of a fire, the material used to protect the electrical power transfer system 102 must minimize the amount of heat transferred from high- temperature surroundings to the electrical cables 124, 126 along line f-f' . The temperature rise of the electrical cables 124, 126 must be kept below a specified value for a specified period of time in order to prevent the physical deterioration of the electrical cables 124, 126 during the fire. If the electrical cables 124, 126 are insulated, excessive cable temperatures may cause the insulation to melt, thereby causing a possible short circuit.

On the other hand, during normal conditions, the material used to protect the electrical power transfer system 102 must function to maximize the heat transfer from the electrical cables 124, 126 to the lower-temperature surroundings on a steady-state basis. During normal conditions, current-carrying electrical cables 124, 126 will generate some heat as a result of the internal resistance of the cables. If this heat is not transferred away from the cable, the current-carrying capacity of the cable will be reduced, and larger-diameter electrical conductors will have to be employed to carry a given amount of current. Under both sets of operational conditions, the major objective of the material used to protect the electrical power transfer system 102 is to keep the temperature of the electrical cables 124, 126 relatively low. However, the temperature of the surroundings at f-f is very different under each of the respective operational conditions. When the surroundings at f-f are relatively hot, as during a fire, the material must prevent heat transfer to the electrical cables 124, 126. However, when the surroundings at f-f are relatively cool, the material must promote heat transfer away from the cables 124, 126.

Present-day, state-of-the-art fire protection systems employ fire damming materials 118 to protect the electrical power transfer system 102 from thermal damage. Fire damming materials 118 are thermal insulators with relatively low thermal conductivities. The materials may or may not have heat-absorbing (endothermic) properties. The low thermal conductivities are advantageous in the operational environment of a fire, because the material reduces the transfer of heat into the electrical cables 124, 126.

Fire damming materials 116 are to be distinguished from the fire stop materials 100 discussed in the paragraphs above. The two categories of materials have been used to serve entirely different purposes. Fire stop materials 100 are used to provide penetration fire stops within fire walls, whereas fire damming materials 118 are used to protect electrical power transfer systems 102 outside of the fire wall. Under normal operating conditions, fire damming materials 118 provide a significant shortcoming. The low thermal conductivities of existing fire damming materials 118 is disadvantageous in applications where the material is used to encase electrical cables. The materials are not capable of sufficiently absorbing and dissipating heat generated by the electrical currents traveling along these cables .

Therefore, these fire damming materials 118 significantly reduce the current-carrying capacity (ampacity) of electrical conductors under normal operating conditions.

To provide a given level of current-carrying capacity, electrical cables having larger-diameter conductors must be used in order to compensate for the ampacity derailing of the fire damming materials 118. In applications where fire damming materials must be added to existing installations, the electrical cables may have to be removed and replaced with cables having larger-diameter conductors. It would be desirable to have a fire proofing material with the lowest possible ampacity derating, to permit use in existing installations without the necessity of replacing electrical cables. A fire proofing material having a thermal conductivity of 0.23 watts per meter-°C or greater would provide a desired low ampacity derating. Existing fire damming materials 118 are available in the form of ceramic fiber blankets, ceramic fiber boards, and thermally insulated fiber wraps or sheets. The E-50 Series of fiber wraps manufactured by the 3M Corporation at 3M Center, St. Paul, N, 55144, have a thermal conductivity of 0.150 Watts per meter-oc at 93<>C (0.143 W/moC @ 38oC) . Thermo-Laq 330 material, manufactured by Thermal Sciences in St. Paul, MN, has a thermal conductivity of 0.175 W/moC. Promat material, manufactured by Promat, P.O. Box 739, Blendon, PA, 19510, also has a thermal conductivity of 0.175 W/moC. These low thermal conductivities result in large ampacity deratings.

Fire damming materials 118 have been rated for the time during which they withstand the heat of a fire. This measurement is termed an F-rating when conducted with reference to a standard heating-time curve. The F-rating is expressed in units of time, such as hours. Fire damming materials have also been rated for the time duration ever which the temperature rise of the electrical power transfer system 102 remains under a critical value, such as 325o F (18lo c) . This time duration is referred to as a T-rating, which may be expressed in units of hours. Fire testing is performed by applying a heat source directed along line f- f in compartment 110 (FIGURE 1) .

In order to obtain approval for a given fire damming material 118 from testing agencies such as Underwriters Laboratories, the material must pass a test where, after being exposed to fire for one hour, a pressurized water stream from a hose is directed at the material. Such a test is set forth in Underwriters Laboratories Subject 1724. The material must not crack, and must not allow gases and smoke to get through. The purpose of the fire damming material 118 is to protect the portion of the electrical power transfer system 102 outside of the firewall 104 and situated within compartment 110. Some prior art fire damming materials are attached by brackets, with the disadvantage that the material may lose its grip on the electrical power transfer system, and is quite susceptible to physical displacement. The performance of existing fire damming materials 118 is strongly dependent upon the care and integrity used in the installation of the material 118 on the electrical power transfer system 102.

Some present day fire damming materials 118 may not adequately protect electrical cabling systems used in nuclear power plants. U.S. Federal regulations require that certain electrical cabling systems in nuclear utility power stations incorporate fire barriers to protect important power and control cables from fire. The use of one presently existing fire damming material 118 to protect these cables has recently been challenged by the U.S. Nuclear Regulatory Commission because of grave doubts that the material meets the required performance criteria.

One commonly utilized fire damming material 118 is known as Thermo-Lag 330, manufactured by Thermal Sciences in St . Louis, MO. In tests performed by the Nuclear Regulatory Commission during the past year, Thermo-Lag 330 often failed to provide the required level of fire protection. In some cases, the material did not protect electrical cables from excessive temperatures. Furthermore, in some cases, Thermo-Lag 330 actually burned, with sufficient loss of weight to be defined as a combustible material. Additionally, the Nuclear Regulatory Commission discovered that, in some cases, the material may not have been installed properly. These improper installations often involve major departures from what is required to ensure proper fire protection.

Other problems with existing fire damming materials 118 relate to the current carrying capacity (ampacity derating) of the protected electrical cables. The Nuclear Regulatory Commission discovered that significant errors have been made in testing the ampacity derating of the Thermo-Lag 330 material. The extent to which this fire damming material impedes the flow of heat from current- carrying cables was often underestimated and/or under calculated, with the unfortunate result that electrical cables in existing installations may overheat when carrying their rated currents.

The recently-discovered problems with fire damming materials, such as Thermo-Lag 330, are of an extremely critical nature. Accordingly, the Nuclear Regulatory Commission has required some of the 80 nuclear power plants using Thermo-Lag 330 to post roving guards and video cameras to monitor Thermo-Lag 330 installations until all questions about the material have been resolved. In December of 1992, the Nuclear Regulatory Commission requested that all utilities using Thermo-Lag 330 justify, in writing, that the performance of their fire barrier systems has been verified through tests. If the utility cannot verify the performance of the fire barrier systems through test procedures, the utility is required to submit a plan of corrective action. The Nuclear Regulatory Commission considers the shortcomings of Thermo-Lag 330 to be a very serious matter.

SUMMARY OF THE INVENTION

The present invention sets forth improved fire proofing methods and systems for electrical power transfer systems. Materials having substantial endothermicity at high temperatures, and substantial heat conductivity at normal operating temperatures, are applied to surround and encase electrical power transfer systems.

According to a preferred embodiment of the present invention, materials having an inorganic, endothermic, substantially thermally conducting fire proofing material composed of one or more water-binding minerals is applied as a casing around electrical cables and/or conduits to form a fire proof electrical conduit. The electrical cable includes one or more electrical conductors. The fire proof electrical conduit protects the electrical conductors from thermal damage, and does not significantly reduce the current-carrying capacity of the conductors.

The invention discloses several embodiments for the physical structure of the fire proof electrical conduit, and several methods for fabricating the fire proof conduit. Fire proofing materials suitable for fabricating the fire proof conduit include materials which are used as fire stop materials within fire walls, and/or water-bound minerals. According to a first method of fabricating the fire proof conduit, a powder containing one or more minerals is mixed with water to create a pourable mixture. The mixture is poured into a form, and cured to create a rigid encasing of water-bound minerals around the electrical conductors. According to a second method of fabricating the fire prod conduit, a powder containing one or more minerals is mixed with water and cured. After curing, the water-bound minerals are powderized and compressed into one or more casings, such as rigid forms or flexible blankets, which surround the electrical conductors. The first method provides a rigid fire proof conduit, whereas the second method provides a fire proof conduit having some mechanical flexibility. The methods and systems of the present invention offer the advantages of longevity, mechanical durability, and superior adhesion of the fire proofing material to the metal of the conduit and/or cable tray encasing the electrical conductors. The methods and systems protect electrical conductors from thermal damage, but do not significantly derate the current-carrying capacity (ampacity) of the conductors, due to the high thermal conductivity of the fire proof conduit material. The use of an endothermic material is advantageous because the material will absorb heat during a fire, thereby keeping the enclosed cables under a specified temperature for a specified time duration.

A preferred embodiment of the present invention provides a fire proof conduit having a central axis and a plurality of electrical cable channels. Each cable channel provides fire protection for a specific time duration. The time duration is dependent upon the overall radial dimensions of the conduit, and upon the position of the cable channel relative to the central axis of the fire proof conduit. In this manner, the fire proof conduits of -li¬ the present invention may be custom tailored to meet the requirements of various system applications.

BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects, features, and advantages of the present invention will become apparent from the following more particular description thereof, presented in conjunction with the following drawings. FIGURE 1 is a side view showing a prior art fire proofing technique which employs fire damming materials between fire walls, and fire steps within fire walls.

FIGURE 2 is a side view showing the operational environment of the fire protection methods and systems of the present invention which are used to provide a fire proof conduit.

FIGURE 3 is a perspective view of a preferred embodiment of the system of the present invention which provides a cylindrical fire proof conduit having one or more electrical cable channels surrounded by special fire proof material, wherein the electrical cables in the cable channels can be either movable or set fixed.

FIGURE 4 is a cross sectional view of a preferred embodiment of the system of the present invention which employs a cylindrical fire proof conduit fabricated of special fire proof material and having a plurality of electrical cable channels disposed at a plurality of distances from the central axis of the conduit to provide a plurality of different levels of fire protection. FIGURE 5 is a perspective view showing a preferred embodiment of the method of the present invention wherein special fire proofing material is poured into a casing surrounding an electrical conduit. FIGURE 6 is a cross sectional view illustrating a preferred embodiment of the method of the present invention wherein conduit claddings are prefabricated using cylindrical half shells made from special fire proofing material.

FIGURE 7 is a perspective view illustrating the technique of encasing one or more electrical conduits with prefabricated panels of special fire proofing material, according to a preferred embodiment of the present invention.

FIGURE 8 illustrates a cross sectional view of an enclosure comprised of fireproof panels fabricated using special fire proofing material, according to a preferred embodiment of the present invention. FIGURE 9 is a graph showing the estimated relationship between ampacity derating and the radial diameter of a cylindrical fire proof conduit fabricated from the Flammadur E 473 material described in TABLE II according to the techniques of the present invention. Flammadur is a registered trademark of AEG ISOLIER UND KUNSTOFF GmbH (AIK) , a division of AEG which is a subsidiary of DAIMLER- BENZ A.G., Federal Republic of Germany.

TABLE I sets forth desired physical properties and characteristics used to select fire proof materials suitable for fabricating the fire proof conduits of the present invention.

TABLE II sets forth the physical properties and characteristics of two exemplary fire proof materials known as Flammadur E 473 and Flammadur E 983, either of which may be used to fabricate the fire proof conduits of the present invention.

TABLE III sets forth measured ampacity derating factors for various fire proof materials, and estimated ampacity derating factors for the Flammadur E 473 material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGURE 2 is a perspective view showing the operational environment of the fire protection methods and systems of the present invention. With reference to FIGURE 2, a fire wall 204 is used to separate a first room or compartment 210 from a second room or compartment 212. The side of the fire wall 204 facing the first compartment 210 is the first side 214 of the fire wall 204, and the side of the fire wall 204 facing the second compartment 212 is the second side 216 of the fire wall 204.

Fire proof conduit 230 encloses insulated electrical conductors 224, 226, electrical conduits, and/or electrical cable trays. Fire proofing material 200 is employed as a fire stop where it is necessary to run the fire proof conduit 230 through the fire wall 204. In order to route the fire proof conduit 230 through the fire wall 204, a clearance hole is formed in the fire wall 204. The radial dimensions a-a' , b-b' of the clearance hole are generally slightly larger than the radial dimensions c-c' , dd' of the fire proof conduit 20 230 to facilitate the installation and positioning of the fire proof conduit 230 in the fire wall 204. However, after the fire proof conduit 230 has been installed, a space or a void exists between the fire proof conduit 230 and the fire wall 204. Some or all of this space within the fire wall 204 is filled with fire proofing material 200 in order to prevent the spread of flames, smoke, fumes, and/or water through the fire wall 204. The fire proofing material 200 is used to protect the portion of the electrical conductors 224, 226 situated within the fire wall 204, and to prevent the spread of a fire across the fire wall 204.

The present invention provides various advantageous physical structures for the fire proof conduit 230, as well as methods for fabricating and installing the fire proof conduit 230. The fire proof conduit 230 is fabricated using special fire proofing materials 200. This technique differs from the prior art methods and systems which protect the portion of the electrical conductors 124, 126 (FIG. 1) traversing the first compartment 110 with fire damming materials 118. These fire damming materials 118 generally include thermally insulated fiber wraps or sheets 120 which are installed by wrapping them around the electrical power transfer system 102. Special fire proofing materials 200 suitable for use in conjunction with the methods and systems of the present invention to fabricate and configure fire proof conduit 230 should possess the physical characteristics and/or properties set forth in TABLE I. Suitable materials consist of one or more water-binding minerals. These minerals are substances having chemical formulae wherein one or more mineral-forming atoms are combined with one or more oxidizing anions to form a water-binding salt. Examples of mineral-forming atoms are those selected from Group IIA of the Periodic Table of the Elements, such as Be, Mg, Ca, and Ba. Some Group IA Elements, including Li, Na, and K, are suitable for use as mineral-forming atoms. Examples of oxidizing anions are borate, aluminate, carbonate, silicate, nitrate, nitrite, phosphate, sulfate, and sulfite. These oxidizing anions contain one or more oxygen atoms combined with one or more atoms of B, Al, C, Si, N, P, and/or S.

The resulting mineral, consisting of one or more water-binding salts, then binds to one or more water molecules to form crystalline structures. The water- binding minerals may be formed by adding water to a powder containing one or more water-binding minerals. The mixture is then allowed to "cure", i.e., reach an equilibrium condition. In addition to water-binding minerals, the fire proof material 200 of the present invention may also contain fill materials. Filler materials include, for example, nylon fibers, organic fibers, mica, and/or binders. The filler material is used to provide enhanced material strength which will more effectively withstand high heat stresses.

When cured, the material should be substantially heat conductive at low temperatures, and substantially heat absorbing at high temperatures. This heat absorption is due to phase changes wherein the bonds that hold water molecules to the minerals are broken in order to absorb therma1 energy.

The material must be non-flammable, non-combustible, and offer low or negligible ampacity derating to electrical conductors. A quick curing time is preferable, such that the material is rigid within 24 hours after being mixed with water. During the curing process, a very slight expansion is desirable to provide enhanced adhesion of the material to metal conduits, although a material that does not change dimensions during the curing process is acceptable.

After the material has cured, it should not conduct electricity, it should be insoluble in water, and it should be capable of bonding to steel and concrete. Preferably, the material should be rigid, strong, and easily drillable.

Various industry standards, such as Underwriters Laboratories subject 1479, require fire proofing materials to withstand water pressure after I hour of exposure to heat. In practice, fire walls may be called upon to wall out a flood. To protect the health and safety of fire fighters and other personnel, the material should not emit halogens (Fl, Cl, Br, I) or toxic vapors in installation or when exposed to fire. The material should be rigid, and should not crack at high temperatures. If the material is to be used in the chemical or petroleum industry, it should be resistant to acids and alkaline substances.

Certain physical properties must be considered in environments where the fire proof conduit may be exposed to nuclear radiation. For example, the material used to fabricate the fire proof conduit should be non-degradable when irradiated by gamma rays over an extended period of time. The material should be comprised of mostly inorganic materials, because inorganic materials will withstand nuclear radiation much more effectively than organic materials.

The purpose of the fire proofing material 200 used in fire proof conduit 230 is to prevent the melting and burning of the insulation around the electrical conductors 224, 226. The melting or burning of the insulation can cause short circuits between the conductors 224, 226, as well as short circuits between a conductor 224 and the inner wall of the conduit 230. Since the electrical conductors 224, 226 are frequently employed as power supply lines or control signal lines, the shorting of these conductors may cause disastrous consequences in critical environments such as nuclear power plants.

When using fire proofing material 200, one important design objective is to ensure that the temperature rise of the electrical conductors 224, 226 will remain under a critical value for a given rating time. The maximum temperature the insulation on the conductors 224, 226 will withstand without significant degradation is often on the order of 325o F (18lo c) . However, fire proofing material 200 possesses the property of heat absorption, adheres the prior art fire damming materials 118 (FIG. 1) are primarily thermal insulators. Although a few of the prior art materials absorb some heat, these materials significantly reduce the current-carrying capacity (ampacity) of electrical conductors, as indicated in TABLE III. Suitable materials which may be employed as fire proofing material 200 according to the methods and systems of the present invention include materials which are utilized as fire stop materials 100 (FIGURE 1) . One exemplary fire proofing material 200 is generally known to those skilled in the art as Flammadur E 473 fire stop material . Another exemplary fire proofing material is known as Flammadur E 983 material. The physical properties and characteristics of these materials are set forth in TABLE II. These materials are available from the Flammadur Corporation of America, P.O. Box 2731, La Jolla, CA 92038- 2731, telephone number (619) 551-1236. Flammadur is a registered trademark of AEG (Allgemeine Elektrizitat Geselschaft, German General Electric Company) . Flammadur E 473 material is marketed throughout the United States and Canada by the Flammadur Corporation of America, under international license with AEG, a German subsidiary of Daimler-Benz GmbH, for technology exchange, distribution, and manufacturing of E 473. Flammadur E 473 is manufactured by AIK/AEG ISOLIER UND KUNSTOFF GmbH, at D 3500 Kassel-Waldau, the Federal Republic of Germany, and is also scheduled to be manufactured in the United States of America under a license granted by AIK/AEG to the Stebbins Engineering and Manufacturing Corporation of Watertown, New York. Flammadur is a registered trademark of AEG.

The physical properties and characteristics of Flammadur E 473 are set forth in TABLE 11. Flammadur E 473 is a non-shrinking, nontoxic, UL and FM listed fire stop material used heretofore only as a penetration fire stop material for fire walls. E 473 material has been successfully used as a fire stop material in fire walls in Europe and Asia for over 20 years. The material has been tested in the United States, as well as in other countries throughout the world, and passes the requirements of ASTM standard E 814-88 and UL Subject 1479. These standards and subjects govern the protection of fire sealant materials, used within penetrations in fire walls on floors, against the penetration of flames, smoke, water, and toxic gases. The material has been tested and listed in Underwriters Laboratories Systems 57, 58, 59, 60, 264, 286, 458, 459, 461, and 462, as set forth in the 1992 Underwriters Laboratories Fire Resistance Directory.

Flammadur E 473 possesses desirable physical properties when used according to the methods and systems of the present invention as fire proofing material 200

(FIGURE 2) . One such property is relatively high thermal conductivity of approximately 0.267 W/moC, which results in a low ampacity derating relative to the prior art materials discussed in conjunction with the Background of the Invention. The desirable properties for fire proofing materials 200 were discussed in greater detail in the above paragraphs, and are set forth in TABLE I .

Referring now to TABLE II, the E 473 material is available in the form of an inorganic, cementitious, granulated powder comprised of minerals. Once water is added to the powder, the mixture forms a homogenous blend that is pumpable and pourable. The mixing ratio by volume is generally 2 parts powder to 0.9 to 1.2 parts water. The pot life of the mixture is 30-45 minutes at 68© F (20° c) . As the mixture cures, it forms a stiff, solid material comprised of water-bound minerals. The curing time is 16 hours at 68° F (20o c) . The material expands in volume during curing by 0.6%. Flammadur E 473 cures to a density of 70-80 pounds per cubic feet at 68° F (1100-1300 kilograms per cubic meter at 18© c) . The bonding strengths of Flammadur E 473 to various materials were tested using two different ratios of Flammadur powder to water. Measurements were made using mixtures of 50% water and 60% water. The 50% mixture provides a bonding strength of 125 psi to aerated concrete, and the 60% mixture yields a bonding strength of 45 psi to aerated concrete. For non-aerated concrete, strengths are 80 psi (50%) and 35 psi

(60%; and for steel pipe, 200 and 650 psi, respectively.

Resistance to water penetration is 45 psi for two hours. The pH value during curing is somewhat alkaline, about 12.

The decadic gamma ray extinction coefficient is 20.5 inches (52.1 cm) for Cobalt-60, and 16.5 inches (41.9 cm) for Cesium-137. Thermal diffusitivity is 0.00074 square meters per hour, specific heat is 310 kcal per cubic meter- °K, heat conductivity of 0.23 kcal per meter-hour-oK (0.267 w/moC) , and short-term loading capacity is 30 psi.

Although Flammadur E 473 is a suitable material for use as fire proofing material 200, materials other than E 473 may be used for fire proofing material 200, according to the method of the present invention. The suitability of a given material for use as fire proofing material 200 is governed by whether or not the material in question possesses a substantial portion of the desirable characteristics discussed in the paragraphs above and set forth in TABLE I. For example, Flammadur E 983 material is also suitable for use as fire proofing material 200.

Flammadur E 963 is especially designed to perform the function of a nuclear radiation shield, and it has no lead content. E 983 has a decading gamma ray coefficient of 14 inches (35.3 cm) for Cobalt-60, and 10 inches (25.4 cm) for Cesium-137, which represent improvements over the Flammadur E 473 material. The physical properties of the E 473 and E 983 materials are set forth in greater detail in TABLE II. Any of the materials described in TABLE II may be used to fabricate the fire proof conduit 230 shown in FIGURE 2. However, fire proof conduit 230 need not be constructed using the materials specifically identified in TABLE 11. Materials other than those described in TABLE II may be employed, so long as these materials possess substantially all of the characteristics and properties set forth in TABLE I.

An important characteristic to be considered in the selection of a suitable fire proof conduit 230 material is the ampacity derating of the material in question. Ideally, a material should offer no ampacity derating whatsoever, as was discussed in greater detail above. The ampacity deratings of several materials are set forth in TABLE III. TABLE III is based upon the assumption that, for each of the specified geometric structures, Flammadur E 473 material is to replace an equal amount of another material such as Thermo-Lag 330, Promat H, or 3M E-50 Series material. In this manner, the figures set forth in TABLE III enable a direct comparison between Flammadur E 473 and each of the remaining materials. For example, with reference to TABLE III, the ampacity derating of the Flammadur E 473 material is estimated to be lower than the ampacity derating of the Thermo-Lag 330 material. An equal amount of Flammadur E 473 was utilized in place of the Thermo-Lag 330 material for the purpose of this comparison.

Although ampacity derating is an important factor to consider in the selection of a fire proofing material, other factors must also be considered. For example, some existing cementitious fire stop materials are unsuitable due to excessive mechanical brittleness. Additionally, some of these materials are water-soluble after being cured, and would deteriorate, for example, after exposure to a water stream from a fire hose.

The selection of a suitable fire proofing material 200 for the fire proof conduit 230 is complicated by the fact that the material must perform well under two very different sets of operational conditions. The material must withstand the extreme heat of a fire, and also perform well under normal conditions. As previously discussed in conjunction with the Background of the Invention, a material which excels in one of these operational environments (i.e., the heat of a fire) will often perform inadequately in the other operational environment (i.e., normal conditions) . This design tradeoff results because the fire proofing material must perform different functions in different operational environments.

In the operational environment of a fire, the fire proofing material 200 must minimize the amount of heat transferred from high-temperature surroundings in compartment 210 to the electrical cables 224, 226. The temperature rise of the electrical cables 224, 226 must be kept below a specified value for a specified period of time in order to prevent the physical deterioration of the electrical cables 224, 226 during the fire. If the electrical cables 224, 226 are insulated, excessive cable temperatures may cause the insulation to melt, thereby causing a possible short.

On the other hand, during normal conditions, the fire proofing material 200 must function to maximize the heat transfer from the electrical cables 224, 226 to the lower- temperature surroundings of compartment 210 on a steady- state basis. During normal, conditions, current-carrying electrical cables 224, 226 will generate some heat as a result of the internal resistance of the cables. If this heat is not transferred away from the cable, the current- carrying capacity of the cable will be reduced, and larger- diameter electrical conductors will have to be employed to carry a given amount of current.

Under both sets of operational conditions, the major objective of the fire proofing material 200 is to keep the temperature of the electrical cables 224, 226 relatively low. However, the temperature of the surroundings in compartment 210 is very different for each of the operational conditions. When the surroundings are relatively hot, as during a fire, the fire proofing material 200 must prevent heat transfer. However, when the surroundings are relatively cool, the fire proofing material 200 must promote heat transfer. Fire proofing materials 200 which possess this desired characteristic are set forth in TABLE II.

As contrasted to fire damming materials 118 which primarily function as thermal insulators, the fire proofing materials chosen as illustrative examples and described in TABLE II are thermal conductors. For example, the E 473 fire proofing material offers a thermal conductivity, which is 50% to 200% greater than the thermal conductivities of existing fire damming materials 118. Accordingly, the materials chosen as illustrative examples in TABLE II perform the function of removing heat from electrical cables 224, 226 (FIGURE 2) much more effectively than fire damming materials 118. In this manner, the current carrying capacity of electrical cables 224, 226 encased in the fire proof material 200 is not appreciably degraded. For example, the ampacity derating of one preferred fire proofing material 200 used in conjunction with the present invention is less than half of the ampacity derating provided the fire damming materials 118 of prior art systems. These prior art systems often offered ampacity deratings as high as 50%. The current state of knowledge in the field of fire proofing techniques would recommend against using the fire stop materials described in TABLE II for the purpose of protecting electrical cables 224, 226 outside of fire walls 204. The typical argument is that the relatively high thermal conductivities of fire stop materials, as, for example, the materials described in TABLE II, would significantly degrade performance during a fire. Hence, the use of fire stop materials for the protection of electrical cables 224, 226 outside of fire walls 204 has not occurred to anyone, or perhaps has been summarily dismissed by these skilled in the art.

The current state of knowledge overlooked the fact that, in actuality, the higher thermal conductivities of certain fire stop materials is not a significant detriment during a fire. Such fire stop materials include those described in TABLES I and II. These types of fire stop materials absorb excess thermal energy in compartment 210 before the energy can reach the electrical cables 224, 226. This result occurs because the materials described in TABLES I and II exhibit excellent heat absorption (endothermicity) at intermediate to high temperatures of 200oc and above. Therefore, the materials of TABLES I and II, employed in conjunction with the methods and systems of the present invention, offer enhanced fire protection performance relative to existing fire proofing techniques. The techniques of the present invention offer improved reliability and longevity, as compared to existing fire proofing techniques. This performance improvement is partially attributable to the greater heat absorption characteristics of the materials utilized by the present invention, and also to the higher thermal conductivities and lower ampacity deratings of these materials at lower temperatures. The present invention sets forth several fabrication methods, and systems of physical structures, for a fire proof conduit 230 (FIGURE 2) comprised of fire proof material 200. Each of the methods and systems provides a fire proof conduit having certain unique and advantageous physical characteristics. For example; FIGURE 3 is a perspective view of a preferred embodiment of the system of the present invention which provides a cylindrical fire proof conduit having one or more electrical cable channels surrounded by special fire proof material 200. The fire proof conduit 230 is fabricated of special fire proof material 200 which substantially conforms to the description set forth in TABLE I. The fire proof material 200 is formed into a solid cylindrical rod 604. The conduit 230 contains a plurality of cable channels 606 for accommodating electrical cables 608, 610. Each electrical cable 608, 610 includes one or more insulated electrical conductors forming one or more electrically conducting paths.

The fire proof conduit 230 of FIGURE 3 is formed using damming and backing materials. For example, Flammadur E 473 or similar material may be backed and/or dammed using a wide variety of materials, selection of a particular damming or backing material is determined by ease of use and availability. The damming material should be capable of supporting the weight of the Flammadur E 473 (or similar) material. Examples of damming materials include cardboard, polyurethane foam, polyurethane low or high density rod or cut stock, expanded polyethylene rod stock, mineral wool batting, fiberglass batting, ceramic fiber, ceramic batting, and/or fabric rags. These damming materials can also be employed in conjunction with fire proofing materials other than Flammadur E 473.

To fabricate the fire proof conduit 230 of FIGURE 3, a hollow plastic cylinder may be employed as a damming material. The fire proofing material is poured into the 1- plastic cylinder. The inner diameter of the plastic cylinder forms the outer surface of the conduit 230 and, hence, determines the outer diameter of the conduit 230. Each of the cable channels 606 are formed by using a hollow or solid cylindrical rod. Each rod has an outer diameter approximately equal to the diameter of the resulting cable channel 606. These rods are introduced into the cardboard cylinder before the fire proofing material is poured into the cylinder. The rods are made of one of the backing materials listed above, such as plastic (polystyrene) . One or more spacers made of backing material may be employed for the purpose of holding the rods at a desired fixed distance from the walls of the cardboard cylinder as measured in a radial direction along the cylinder, and/or for holding each of the rods at a fixed radial distance with respect to any other rods. The rods are removed when the fire proofing material has partially cured. If the fire proofing material is Flammadur E 473, the time for rod removal is approximately one hour after the Flammadur E 473 is poured.

The diameter of the cable channels 606 may be selected to allow for air space around the electrical cables 608, 610. In this manner, the cables 608, 610 are easily installed, removed, and/or replaced. However, the existence of an air space around the cable could permit a fire to travel along the cable.

An alternate embodiment of the system shown in FIGURE 3 prevents fire spread along the cables 608, 610, but the cables are rendered non-removable. This embodiment achieves these objectives without the use of rods to fabricate cable channels 606. The electrical cables 608, 610 are introduced into the cardboard cylinder before the fire proofing material is poured. The cables 608, 610 may be held in place, if desired, using spacers fabricated of backing material. In this manner, the cables 608, 610 form their own cable channels 606, and are rigidly surrounded by fire proofing material.

Rigidly surrounding the cables 608, 610 with fire proofing material offers the advantage that the electrical cables 608, 610 are capable of conducting some current at very high temperatures without short-circuiting. However, to fully exploit this advantage, each electrical cable 608, 610 must include only one electrically conducting path. If one or both of these electrical cables 608, 610 are multi-conductor cables providing a plurality of insulated electrical conductors, the insulation between the conductors on a given cable 608 may melt under high temperature conditions, possibly causing a short circuit. In a further alternate embodiment of the system shown in FIGURE 3, the fire proofing material 200 is not poured into backing and/or damming material. Rather, the fire proofing material, such as Flammadur E 473, is mixed with water and allowed to cure outside of the fire proof conduit 230 system. After curing, the material is powderized and compressed into a hollow cylindrical encasing conforming to surface 602. While the powderized material is being compressed into the encasing, cables 608, 610 are held in place within the encasing by using one or more spacers. The use of powderized and compressed fire proofing material is advantageous in applications where the conduit 230 may be exposed to vibrations and/or earthquakes, because the material will not crack.

According to Underwriters Laboratories Subject 1724, the maximum allowed temperature change for electrical cables in case of a fire is 325o F (181° C) , whereas the allowed average temperature rise is 250 o F (139O C) . If a fire proofing technique keeps the cable temperatures at or below these levels, the insulation on the cable will not burn or disintegrate. If the integrity of the insulation is so damaged, the electrical cables can short out to one another, short out to a metal conduit wall, and/or short out to ground.

Once each of the cables representing independent conducting paths are surrounded by fire proofing material such as Flammadur E 473, or Flammadur-like material, the short circuiting problem described above is eliminated. Flammadur E 473 and Flammadur-like material is not conductive to electricity, even at high temperatures. The flow of electricity will continue under high-temperature conditions, although with increased resistance caused by the excessive heating of the electrical cable.

FIGURE 4 is a perspective view of a preferred embodiment of the system of the present invention which employs a cylindrical fire proof conduit 230 fabricated of special fire proof material and having a plurality of electrical cable channels 812, 814, 816 disposed at a plurality of distances 802, 804, 806, 808, 810 from the central axis of the conduit to provide a plurality of different levels of fire protection.

The fire proof conduit 230 may be fabricated using one or more of the techniques described above in conjunction with FIGURE 3.

There are two embodiments for the fire proof conduit 230 illustrated in FIGURE 4. These embodiments are analogous to the embodiments described with reference to FIGURE 3. For example, in a first embodiment, the conduit 230 of FIGURE 4 is fabricated such that the cable channels 812, 814, 816 allow for the existence of air space around each cable. In a second embodiment, the cables are rigidly surrounded by fire proofing material . The first embodiment allows for the easy installation, removal, and/or replacement of the cables in each cable channel 812, 814, 816, whereas the second embodiment prevents the spread of fire along the cable channels 812, 814, 816.

One advantage of the system set forth in FIGURE 4 is that several different levels of fire protection may be provided within one fire prod conduit 230. Cable channels located near the outer diameter 820 of the conduit 230 offer relatively short-term fire protection (e.g., 1 hour) , whereas cable channels 818 located near the central axis h- h' of the conduit offer relatively long-term fire protection (e.g., greater than 3 hours) . The total distance as measured along line r-r' , and/or the positions of cable channels with respect to the central axis h-h' of the conduit, may be selected to provide virtually any desired combination of fire protection ratings. For example, cable channel 812 may provide one hour of fire protection, cable channel 814 may provide three hours of fire protection, cable channel 816 may provide five hours of fire protection, and cable channel 818 may provide ten to twenty hours of fire protection.

If certain known levels of fire protection are required, the total distance of line r-r' and the radial positions of the cable channels 812, 814, 816, 818 relative to axis h-h' may be empirically determined. The distances necessary to achieve the required levels of fire protection are estimated and a test section of conduit is fabricated. The test section is subjected to fire and the fire protection times for each cable channel are measured. Based upon these measurements, new estimates of distance r- r' and the radial positions of the cable channels are calculated, and the above process repeated until a fire proof conduit 230 having the necessary fire protection times is fabricated.

If the fire proof conduit 230 of FIGURE 4 is fabricated using Flammadur E 473 material, one hour of fire protection, corresponding to a T rating of 1 hour, is obtained using a layer of Flammadur E 473 about one inch thick. Accordingly, if cable channel 812 is required to have a T rating of 1 hour, the cable channel 812 must be positioned no closer than one inch from the outer surface 820 of the fire proof conduit 230. If a T rating of 3 hours is required for cable channel 814, the cable channel 814 must be situated at a distance no closer than about 2.5 inches from the outer surface 820 of the fire proof conduit 230.

Higher T ratings than those discussed in the paragraph above may be provided by expanding the overall diameter of the fire proof conduit 230, and/or by positioning cable channels 818 closer to) the central axis h-h' of the fire proof conduit. Relatively high T ratings may be required in environments such as nuclear power plants or oil refineries. For example, the fire at the Chernobyl nuclear power plant in Russia lasted for approximately 48 hours. The severity of the Chernobyl incident was reported to be partially attributable to fire damage of the electrical cables controlling the positions of the reactor rods.

FIGURE 5 is a perspective view showing a preferred embodiment of the method of the present invention wherein special fire proofing material is poured into a form 301 surrounding a metal electrical conduit 302 to provide a fire proof conduit 230. The metal electrical conduit 302 contains a plurality of electrical cables 310, 312, 314, each having one or more electrical conductors providing one or more current paths. For example, electrical cable 310 is a multi-conductor cable containing a plurality of insulated electrical conductors 316, 318, 320 providing a plurality of conducting paths. Electrical cable 312 consists of one solid insulated copper conductor. However, cable 312 could also be a conductor covered with Flammadur E 473 or similar material. Electrical cable 314 contains a plurality of twisted copper strands 322, 324 which are in direct physical contact to provide but one current path. The twisted copper strands 322, 324 form a cable 314 which is encased in a sheath of insulation.

The fire proof conduit 230 of FIGURE 5 is fabricated by mixing fire proofing material, such as Flammadur E 473, with water. The fire proofing material is introduced into the form 301 by being poured into entrance port 306. For ease of introduction, the fire proofing material may be pressurized using, for example, a compressor. The exit port 304 is blocked until the fire proof material fills the form 301, whereupon the exit port 304 is opened to allow for the release of air and excess fire proofing material. After the fire proofing material is allowed to cure, the form 301 may optionally be removed.

FIGURE 6 is a cross-sectional view illustrating a preferred embodiment of the method of the present invention wherein conduit claddings 404, 406 are prefabricated using cylindrical half shells made from special fire proofing material. The half-shell conduit claddings 404, 406 each may include mating tongue and groove surfaces 408, 410, 412, 416, 418, 420, 422, 424 which are designed to interlock when the claddings are installed around an electrical conduit 402. For example, tongue 408 of cladding 404 mates with groove 418 of cladding 406. Tongue 410 of cladding 404 mates with groove 422 of cladding 406. In an alternate embodiment of the invention, the claddings 404, 406 are fabricated without mating tongue and groove surfaces.

The claddings 402, 404 may be fabricated by mixing fire proofing material such as, for example, Flammadur E 473 with water and pouring the mixture into forms built using damming materials. Suitable forms can be made from removable plastic cylindrical half shells, or from thin non-removable metal sheeting which is left in place an the outer surface 414 of the conduit 402.

One advantage of the fire proof conduit 230 of FIGURE 6 is that the system is readily utilized, for example, in the context of electrical power plants, such as nuclear power plants, and oil refineries. The conduit 230 may be prefabricated (precast) into ready-made forms at the plant site. The cylindrical half shell claddings 404, 406 could alternatively be cast directly onto existing conduits. If the fire proofing material is Flammadur E 473, the current carrying capacity of the electrical cables in conduit 402 will not be significantly degraded. However, the use of other fire proofing materials may degrade the ampacity rating of the electrical cables to such a degree that new, larger-diameter cables may have to be installed. The estimated ampacity deratings of Flammadur E 473 and various other fire proofing materials are set forth in detail in TABLE III. TABLE III is based upon the use of equal geometries and thicknesses for each of the materials.

FIGURE 7 is a perspective view illustrating the technique of encasing one or more electrical conduits 510, 512, 514 with prefabricated panels 502, 504, 506, 508 of special fire proofing material according to a preferred embodiment of the present invention. The prefabricated panels 502, 504, 506, 508 each may include mating tongues 520 and grooves 522, such that four panels may be positioned in a mutually orthogonal relationship and interlocked together to form structure 530 comprising a fire proof conduit 230 having a square or rectangular cross-section. An alternate embodiment of the invention uses prefabricated panels 502, 504, 506, 508 without mating tongue and groove structures.

FIGURE 8 illustrates a cross sectional view of an enclosure 700 comprised of fireproof panels 702, 704, 706, 708 fabricated using special fire proofing material, according to a preferred embodiment of the present invention. The fire proof enclosure 700 is used to enclose an existing electrical junction and/or switch box 724. The junction box 724 is used to join together two or more electrical cables 714, 716, 718, 720, 722 from two or more electrical conduits 710, 712. The fire proof panels are similar to the prefabricated panels 502, 504, 506, 508 discussed in conjunction with FIGURE 7, except that the panels 706, 708 of FIGURE 8 must include openings and/or connectors 730, 740 for accommodating one or more conduits 712, 714.

FIGURE 9 is a graph showing the estimated relationship between ampacity derating and the radial diameter of a cylindrical fire proof conduit fabricated according to the techniques of the present invention from the Flammadur E 473 material described in TABLE II. The ampacity derating is specified as the percentage by which the current- carrying capacity of conductor 1021 is reduced, with reference to the full current-carrying capacity of the conductor 1021 in open air. The outer diameter of the conduit 1023 is specified in inches.

The graph of FIGURE 9 is based upon a fire proof conduit 1023 having a single, solid, uninsulated copper conductor 1021 one inch in diameter. The conductor 1021 is positioned at the central axis j-j' of the conduit, surrounded by Flammadur E 473 material 1025. A 3-inch conduit diameter is required for a T rating of approximately 1 hour, and a diameter of 6 inches for a T rating of approximately three hours.

A number of specific embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications and changes may be made without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiments, but only by the scope of the appended claims. What is claimed is:

TABLE II: Properties of FLAMMADUR^* Materials

TABLE II: Properties of FLAMMADUR^* Materials (Continued)

BONDING 50% 60%

STRENGTH (psi) water water

For

Limestone: 105 60

Aerated Concrete: 125 45 •»

Concrete: 80 35

Plastic Pipe: 30 130

Steel Pipe: 200 650

RESISTANCE 45 psi

TO WATER for 24 hrs. *

PENETRATION

P_H-VALUE c. 12.0 Non-acid*

K-RAY

EXTINCTION

CO-EFFICIENT

(decadic); INCHES

Co 60: 20.3 13.8

Cs 137: 16.5 10.0

CLEANING Water Water SOLVENT

Flammadur^* E 473 Physical Properties

Retrofit and Repairabilitγ Yes

Life Expectancy 50 years plus

Derating of Cables None

Material Shrinkage None

Short-term Loading Capacity 30 psi

Heat Conductivity 0.23 (kcal/m-hr-°K) (1.85 Btu-in/ft²-hr-°R)

Specific Heat 310 (kcal/m³-°K) (19.4 Btu/ft^2oR)

Thermal Diffusitivity 7.4 X 10^'4 (m²/hr) (8.0 X 10^"3 ft²/hr) TABLE III

COMPARISON OF AMPACITY DERATING (%) FOR FLAMMADUR E473 MATERIAL WITH OTHER MATERIALS

THERMOLAG FLAMMADUR PROMAT FLAMMADUR 3M FLAMMADUR 330 E473 H E473 SERIES E50 E473

CONDUIT

1 HOUR 7.47 2.57 15.9 5.46 14-23 6.19-10.2

3 HOURS 9.72 3.35 36.7 12.3 20-27 8.88-12

CABLE TRAY 1 HOUR 8.7 3.00

SOLID BOTTOM 12.5 4.30 28.7 9.72 37-43 1 6.4-19 OPEN TOP

LADDER BACK 27.5 9.33 31 .8 10.7 37-43 16.4-19 OPEN TOP

CABLE TRAY 3 HOURS

SOLID BOTTOM 27.2 9.24 45-52 19.8-22.6 OPEN TOP

LADDER BACK 31 .2 10.5 45.3 14.8 45-52 19.8-22.6 OPEN TOP

THERMAL

CONDUCTIVITY 0.175 0.267 0.175 0.267 0.1 51 0.267

W/m°C

Claims

- 33 -CLAIMS

1. A fire proof conduit for protecting one or more electrical conductors from fire damage and comprising: a conduit having channel means for accommodating and encasing one or more electrical conductors; the conduit being fabricated of fire proof material having the following physical characteristics:

(a) inorganic; (b) endothermic, such that the material undergoes at least one energy-absorbing phase change with heat absorption at temperatures above approximately 200°C; and

(c) thermal conductivity of at least 0.20 watts per meter °C below approximately lOOoC, such that the current carrying capacity of electrical conductors encased within the material is not substantially degraded.

2. A fire proof conduit as set forth in Claim 1, the tire proof material further comprising the following physical characteristics: (a) strong bonding strength to steel of at least 200 psi (1378 Pa) ; (b) strong bonding strength to concrete of at least

80 psi (550 kPa) ; (c) nonflammable;

(d) water-based; and (e) noncombustible.

3. A fire proof conduit as set forth in Claim 2, the fire proof material further comprising the following physical characteristic: (a) non-decomposing when exposed to gamma ray radiation of 200 million rads, such that the material is suitable for use in environments having emissions of nuclear radiation. - 34 -

4. In a system having-one or more electrical conductors, a method for protecting the electrical conductors from fire damage and comprising the step of encasing the electrical conductors in a fire proof material having the following characteristics: (a) inorganic, such that the material is suitable for use, and will have longevity greater than approximately 15 years, in environments having emissions of nuclear radiation; (b) endothermic, such that the material undergoes at least one energy-absorbing phase change with heat absorption at temperatures above approximately 200°C; and (c) thermal conductivity of at least 0.20 watts per meter °C below approximately lOOoc, such that the current carrying capacity of electrical conductors encased within the material is not substantially degraded.

5. In a system having one or more electrical conductors, a method for protecting the electrical conductors from heat damage as set forth in Claim 4 wherein the fire proof material further includes the following characteristics :

(a) strong bonding strength to steel of at least 200 psi (1378 kPa) ;

(b) strong bonding strength to concrete of at least 80 psi (550 kPa) ;

(c) nonflammable; and (d) noncombustible.

6. In a system having one or more electrical conductors, a method for protecting the electrical conductors from heat damage as set forth in Claim 5 wherein the fire proof material further includes the following characteristic: - 35 -

(a) non-decomposing when exposed to gamma ray radiation of 200 million rads, such that the material is suitable for use in environments having emissions of nuclear radiation.

7. A fire proof conduit including: (a) electrical conductor means for conducting an electrical current; (b) thermal energy absorbing means for fire proofing the electrical conductor means and including a water-bound mineral comprised of at least one mineral-forming atom selected from the group of Be, Mg, Ca, Ba, Li, Na, and K, combined with at least one oxidizing anion to form a mineral molecule, the mineral molecule forming a water bond with at least one water molecule, a plurality of water molecules and mineral molecules together forming a crystalline structure which absorbs thermal energy via at least one phase change wherein a plurality of the water bonds are broken.

8. In a system having one or more electrical conductors, a method for protecting the electrical conductors from heat damage as set forth in Claim 4 further comprising the step of fabricating the fire proof material by:

(a) obtaining a mineral-forming substance comprised of at least one mineral-forming atom selected from the group of Be, Mg, Ca, Ba, Li, Na, and K; (b) combining the mineral-forming substance with at least one oxidizing anion to form a mineral molecule; a plurality of the mineral molecules forming a powder-like substance; (c) mixing the powder-like substance with water to form a pourable mixture; -36 -

(d) allowing the pourable mixture to reach an equilibrium state wherein at least one mineral molecule forms a water bond with at least one water molecule, a plurality of water molecules and mineral molecules together forming a crystalline structure which absorbs thermal energy via a phase change wherein a plurality of the water bonds are broken.

9. In a system having one or more electrical conductors, a method for protecting the electrical conductors from fire damage as set forth in Claim 8 wherein step (c) further includes the step of pouring the mixture around the electrical conductors.

10. In a system having one or more electrical conductors, a method for protecting the electrical conductors from fire damage as set forth in Claim 9 wherein step (c) further includes the step of forming the fire proof mixture into a conduit having a central axis and at least one cable channel adapted to accommodate at least one of the electrical conductors.

11. In a system having one or more electrical conductors, method for protecting the electrical conductors from fire damage as set forth in Claim 10 wherein step (c) further includes the step of forming the fire proof mixture into a cylindrical conduit.

12. In a system having one or more electrical conductors, a method for protecting the electrical conductors from fire damage as set forth in Claim 11 wherein step (c) further includes the step of forming a first cable channel disposed at a first radial distance from the central axis, and a second cable channel disposed at a second radial distance from the central axis greater than the first radial - 37 -

distance, such that the first cable channel provides a first level of thermal protection arid the second cable channel provides a second level of thermal protection less than the first level of thermal protection.

13. A fire proof conduit as set forth in Claim 7 wherein the electrical conductor means includes a plurality of electrical conductors, and the thermal energy absorbing means includes a cylindrical conduit having a central axis and at least one cable channel adapted to accommodate at least one of the electrical conductors.

14. A fire proof conduit as set forth in Claim 13 wherein a first cable channel is disposed at a first radial distance from the central axis, and a second cable channel is disposed at a second radial distance from the central axis greater than the first radial distance, such that the first cable channel provides a first level of thermal protection and the second cable channel provides a second level of thermal protection less than the first level of thermal protection.