Flame retardant optical fiber cable with foamed outer jacket for riser and plenum application

Abstract

Embodiments of a halogenated composition for forming a foamed cable jacket are provided. The halogenated composition includes a polymer component, and a flame retardant package dispersed in the polymer component and a chemical foaming agent that is present in an amount less than 5% by weight of the halogenated composition. Also provided are embodiments of an optical fiber cable having a cable jacket surrounding a cable core. The cable jacket is made from the halogenated composition, which has a first density. The cable jacket has a foamed region with a second density that is 70% to 95% of the first density.

Description

FLAME RETARDANT OPTICAL FIBER CABLE WITH FOAMED OUTER JACKET FOR RISER AND PLENUM APPLICATIONCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of U.S. Provisional Application No.63 / 672,756, filed on July 18, 2024, the content of which is relied upon and incorporated herein by reference in its entirety.BACKGROUND

[0002] Optical fiber cables typically have cable jackets made from a polymeric material. When used in certain applications, it may be desirable to use a flame retardant additives in the polymeric material of the cable jacket. Flame retardant cable jackets may help diminish the effects of a fire or prevent spread when a fire breaks out in a premises. For example, some flame retardants may limit the amount of smoke produced by the fire, and others may limit the ability of the fire to spread along the cable, thereby cutting off one pathway for a fire to spread to multiple rooms of a premises.SUMMARY

[0003] The disclosure relates generally to flame retardant compositions and more particularly to halogenated flame retardant compositions for forming foamed cable jackets and cables including the same.

[0004] According to an aspect, embodiments of the disclosure relate to a halogenated polymer composition for forming a foamed cable jacket. The halogenated polymer composition includes a halogenated polymer component, a chemical foaming agent, and a melt strength enhancer. The chemical foaming agent is present in an amount up to 5% by weight of the halogenated polymer composition. The melt strength enhancer is present in an amount up to 1% by weight of the halogenated polymer composition.

[0005] According to another aspect, embodiments of the disclosure relate to an optical fiber cable. The optical fiber cable includes a cable jacket and a cable core. The cable jacket includes an inner surface and an outer surface. The inner surface defines a central bore along a length of the optical fiber cable. The cable core is disposed within the central bore and includes at least one optical fiber. The cable jacket includes a halogenated polymer composition having a first density and has a foamed region that extends at least a portion of the distance between the inner surface and the outer surface. The foamed region includes a density that is 70% to 95% of the first density.

[0006] According to another aspect, embodiments of the disclosure relate to an optical fiber cable. The optical fiber cable includes a cable jacket and a cable core. The cable jacket includes an inner surface, an outer surface, a first layer extending from the outer surface, and a second layer extending from the inner surface. The inner surface defines a central bore extending along a length of the optical fiber cable. The cable core is disposed within the central bore and includes at least one optical fiber disposed within a buffer tube. The cable jacket includes a halogenated polymer composition having a first density. The second layer includes a foamed region and the foamed region has a second density that is 80% to 90% of the first density.

[0007] Additional features and advantages will be set forth in the detailed description that follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings.

[0008] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.

[0009] The accompanying drawings are included to provide a further understanding and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment s), and together with the description serve to explain principles and the operation of the various embodiments.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a cross-sectional view of an optical fiber cable having a jacket comprised at least partially of a foamed halogenated polymer composition, according to an exemplary embodiment.

[0011] FIG. 2 is a cross-sectional view of an optical fiber cable having a multi-layered jacket comprised at least partially of a foamed halogenated polymer composition, according to an exemplary embodiment.

[0012] FIG. 3 is a cross-sectional view of a chemically foamed cable jacket, according to an exemplary embodiment.

[0013] FIG. 4 is a cross-sectional view of a chemically foamed cable jacket, according to another exemplary embodiment.DETAILED DESCRIPTION

[0014] Referring generally to the figures, various embodiments of a halogenated polymer composition for forming a foamed cable jacket and an optical fiber cable having a foamed halogenated cable jacket are provided. Applicant has found that foaming the cable jacket does not diminish and may even improve the flame retardant performance of the cable jacket while decreasing the cost to produce the optical fiber cable and decreasing the weight of the optical fiber cable. The lack of diminished and / or improved flame retardant performance is unexpected because there is a reduction in the halogenated cable jacket material which itself includes a flame retardant component (e.g., chlorine, fluorine, etc.). As will be generally understood, the reduction in weight of the cable jacket and, therefore, the optical cable itself improves ease of cable deployment and improves sustainability. For example, the cable weight reduction would reduce the carbon footprint of the cable during manufacturing and transportation, therefore, improving the sustainability of the optical cable.

[0015] These and other aspects and embodiments of the disclosed halogenated polymer composition and foamed cable jacket will be described herein and in relation to the figures. Such exemplary embodiments are provided by way of illustration and not by way of limitation. For example, the foamed cable jackets discussed herein can be implemented with non-halogenated cable jackets, including but not limited to low-smoke, zero halogen (LSZH) cable jackets.

[0016] FIG. 1 depicts an exemplary embodiment of an optical fiber cable 10. The optical fiber cable 10 includes a cable jacket 12. The cable jacket 12 includes an inner surface 14 and an outer surface 16. The inner surface defines a central bore 18 of the optical fiber cable 10. In one or more embodiments, the outer surface 16 of the cable jacket 12 is an outermost surface of the optical fiber cable 10. In one or more other embodiments, the cable jacket 12 may be surrounded by an outer layer (not shown), which may be a thin layer extruded around the cable jacket 12, e.g., to reduce the coefficient of friction to promote sliding within a cable duct during blowing or pulling of the optical fiber cable 10.

[0017] Disposed within the central bore 18 is a cable core 20. The cable core 20 includes all of the elements within the cable jacket 12 including at least one optical fiber 22. In the embodiment depicted, each optical fiber 22 is contained in a buffer tube 24. Each buffer tube 24 in the embodiment depicted contains an optical fiber 24 in a tightly buffered configuration. In various embodiments, cable core 20 includes yarn 26. The embodiment of the optical fiber cable 10 is merely illustrative.

[0018] In other embodiments, the cable core 20 can include anywhere from one to several hundred or even thousands of optical fibers 22. Further, the optical fibers 22 may be in a loose tube or ribbon configuration within the buffer tubes 24. In various embodiments, the buffer tubes 24 may be stranded around a central strength member. Additionally, the optical fibers 22 may not be arranged in buffer tubes 24 and may instead be loose within the cable jacket 12 or arranged in ribbons within the cable jacket 12. Still further, the optical fibers 22 may be divided into other subunit structures, such as grouped within binding films or thin membranes. In one or more embodiments, the cable core 20 includes one or more other structures, such as an armor layer; a water-blocking tape, powder, or yarn; a binder wrap or film; and a ripcord, among other possibilities.

[0019] According to embodiments of the present disclosure, the cable jacket 12 comprises a flame retardant composition, in particular a halogenated flame retardant composition, and is at least partially foamed. The cable jacket 12 has a thickness T between the inner surface 14 and the outer surface 16. In one or more embodiments, the cable jacket 12 includes a foamed region that comprises at least a portion of the thickness T.

[0020] FIG. 2 depicts another exemplary embodiment of an optical fiber cable 100. Optical fiber cable 100 is substantially the same as optical fiber cable 10 except for the differences discussed herein. The optical fiber cable 100 includes a cable jacket 112 with one or more layers. In various embodiments, cable jacket 112 includes a first layer 113 and a second layer 115. The cable jacket 112 includes an inner surface 114 and an outer surface 116. The inner surface 114 defines a central bore 118 of the optical fiber cable 100. In one or more embodiments, the outer surface 116 of the cable jacket 112 is an outermost surface of the first layer 113 and of the optical fiber cable 100. In such embodiments, the inner surface 114 is an inner surface of second layer 115. The cable jacket 112 has a thickness T between the inner surface 114 and the outer surface 116.

[0021] In one or more embodiments, a foamed region of cable jacket 112 starts at the inner surface 114 and extends toward the outer surface 116, and in one or more other embodiments, the foamed region starts at the outer surface 116 and extends toward the inner surface 114. In still one or more embodiments, the foamed region is intermediate of the inner surface 114 and the outer surface 116. In one or more embodiments, the positioning of the foamed region can be controlled by extruding foaming and nonfoaming flame retardant composition in different layers.

[0022] In one or more embodiments, cable jacket 112 is an evenly distributed foam. In one or more embodiments, the first layer 113 and the second layer 115 are formed from the same material. In one or more embodiments, the first layer 113 and the second layer 115 are formed from different materials. In one or more embodiments, second layer 115 which directly contacts cable core 120 is a foamed layer and first layer 113 is a non-foamed layer. Applicant believes such embodiments with a foamed inner layer improves the burning performance and reduces cost. The non-foamed outer layer 113 can maintain the cable appearance and reduce surface friction that may impact cable deployment.

[0023] In one or more embodiments, the inner or second layer 115 and first or outer layer 113 are both foamed, but with different void volume. In other words, inner layer 115 has higher void volume (e.g., void volume of more than 10%) and outer layer 113 has a lower void volume (e.g., void volume of less than 10%).

[0024] In one or more embodiment, the foamed portion of jacket 12, 112 has a cell size in the range of 10 pm to 500 pm. In one or more embodiments, the foamed portion of jacket 12, 112 has void volume of less than 50%, preferably less than 40%, more preferably less than 30%. In one or more embodiments, the cable jacket 12, 112 can be formed by physical foaming or chemical foaming. During physical foaming, high pressured gas is injected into the molten halogenated polymer composition as it is being extruded to form the cable jacket 12, 112. In one or more embodiments, the gas used during physical foaming is an inert gas, such as nitrogen or carbon dioxide, or is a hydrocarbon gas, such as butane and pentane. During chemical foaming, a foaming agent is included in the halogenated polymer composition that decomposes during extrusion to produce gas within the molten halogenated polymer composition. In either the physical foaming or the chemical foaming case, the gas is trapped within the halogenated polymer composition, leaving behind gas bubbles within the cable jacket 12, 112. Advantageously, gases trapped in the gas bubbles may be released during combustion of the optical fiber cable 10, 100, which dilutes the oxygen in the vicinity of the optical fiber cable 10, 100, slowing down flame propagation and improving burn performance.

[0025] In one or more embodiments, the jacket 12, 112 material composition is a halogenated polymer composition that includes a halogenated polymer, such as polyvinylchloride (PVC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorinated ethylene polymer (FEP) along with a chemical foaming agent. In some embodiments, the composition used to form the jacket 12, 112 comprises plasticizer(s),processing stabilizer(s), a flame retardant, such as a mineral flame retardant, and / or other synergists.

[0026] In one or more embodiments, the halogenated polymer composition comprises a chemical foaming agent and a melt strength enhancer. In one or more embodiments, the chemical foaming agent is an exothermic chemical foaming agent, and in one or more other embodiments, the chemical foaming agent is an endothermic foaming agent. In one or more embodiments, a combination of exothermic and endothermic foaming agents is used. Examples of exothermic foaming agents include azodi carbonamide, oxy-bis- benzenesulfonylhydrazide, toluenesulfonylhydrazide, benzenesulfonylhydrazide, toluenesulfonylsemicarbazide, 5-phenyltetrazole, dinitrosopentamethylenetetramine, hydrazocarbonamide, azobisisobutyronitrile, barium azodi carb oxy late, and combinations thereof, and examples of endothermic chemical foaming agents include citric acid, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, calcium azide, and combinations thereof. In one or more embodiments, the melt enhancer is active peroxide. In one or more embodiments, the melt strength enhancer is a peroxide masterbatch. Examples of suitable peroxide masterbatches used as a melt strength enhancer include but are not limited to 5% to 20% by weight dicumyl peroxide or di(tert-butylperoxyisopropyl)benzene masterbatches.

[0027] In one or more embodiments, the halogenated polymer composition includes 5% by weight or less of the chemical foaming agent, in particular 3% by weight or less, and most particularly 1% by weight or less. In one or more embodiments, the halogenated polymer composition includes at least 0.1% by weight of the chemical foaming agent. In one or more embodiments, the halogenated polymer composition includes 1% by weight or less of the melt strength enhancer, in particular 0.8% by weight or less, and most particularly 0.5% by weight or less. In one or more embodiments, the halogenated polymer composition includes at least 0.1% by weight of the melt strength enhancer.

[0028] In one or more embodiments, the halogenated polymer composition has density reduction of no more than 50%. That is, the density of the foamed halogenated polymer composition is at least 50% of the unfoamed, fully dense halogenated polymer composition. In one or more embodiments, the halogenated polymer composition has a density reduction of no more than 40%, and in still one or more further embodiments, the halogenated polymer composition has a density reduction of no more than 30%. In various exemplary embodiments, the foamed halogenated polymer composition has density reduction of between 5% and 30%, between 10% and 30%, or between 10% and 20%.

[0029] In one or more embodiments, the gas bubbles have a maximum cross-sectional dimension of up to 100 pm, up to 200 pm, up to 300 pm, up to 400 pm, or up to 500 pm. In one or more embodiments, the gas bubbles have a maximum cross-sectional dimension of at least 10 pm. In one or more embodiments, the gas bubbles are uniformly distributed within the foamed region of the cable jacket 12, 112. In one or more embodiments, the foam has a closed cell morphology.

[0030] Having described an embodiment of the optical fiber cable 10 and a halogenated polymer composition for the cable jacket 12, 112 thereof, an embodiment of a method of extruding the cable jacket 12, 112 around the cable core 20, 120 is now described in relation to the embodiment depicted in FIG. 1. In one or more embodiments, the method involves a first step of preparing the halogenated polymer composition by mixing a polymer component, optionally a flame retardant package and / or a chemical foaming agent, and preferably a melt strength enhancer. Halogenated polymers do not necessarily need a separate flame retardant package, but other flame retardants, such as flame retardant fillers, may be added to enhance the flame retardant effect. The chemical foaming agent is optional depending on whether physical or chemical foaming is used. In one or more embodiments, the melt strength enhancer may be preferable to maintain the mechanical properties of the foamed composition and to reduce the peak heat release rate as will be discussed more fully below.

[0031] After the first step, the halogenated polymer composition is extruded around a cable core 20, 120 in a second step. During the extruding step, the halogenated composition is foamed either by injecting a gas into the halogenated polymer composition to physically foam the composition, or by chemical foaming. If chemical foaming is used, during the extrusion step the halogenated polymer composition is foamed by decomposition of the chemical foaming agent included in the halogenated polymer composition. In particular, the elevated temperature and mixing in the extrusion barrel of the extruder causes the chemical foaming agent to decompose to produce gases that are trapped as bubbles within the halogenated polymer composition upon solidification. Depending on whether the foamed region of the jacket 12, 112 comprises the entire thickness of the cable jacket 12, 112 or only just a portion thereof, the halogenated polymer composition may be extruded in one or more layers to form the cable jacket 12, 112.

[0032] FIG. 3 depicts an exemplary embodiment of a foamed cable jacket 212. Foamed cable jacket 212 includes an inner surface 214 and an outer surface 216. Foamed cable jacket 212 is formed using an endothermic foaming agent (such as Safoam® FPE-50 available fromReedy Chemical Foam & Specialty Additives, Charlotte, NC). In such an embodiment, the endothermic foaming agent has a 0.7% by weight of the halogenated polymer composition and results in a density reduction of cable jacket 212 of 6-8%.

[0033] FIG. 4 depicts an exemplary embodiment of a foamed cable jacket 312. Foamed cable jacket 312 includes an inner surface 314 and an outer surface 316. Foamed cable jacket 312 is formed using an exothermic foaming agent (such as XO-429 from Bergen International, LLC, East Rutherford, NJ). In such an embodiment, the exothermic foaming agent has a 0.6% by weight of the halogenated polymer composition and resulted in a density reduction of cable jacket 312 of 12-18%.

[0034] In another exemplary embodiment, halogenated polymer composition comprises AlphaGary Smokeguard III 1070L (available from Sylvin Technologies, Inc., Denver, Pensylvannia), and the cable jacket is foamed using an exothermic foaming agent (such as Safoam® FPN3-40 available from Reedy Chemical Foam & Specialty Additives, Charlotte, NC) that has a loading of 1% by weight. In such an embodiment, the resulting foamed jacket has an average 20% density reduction with homogeneously distributed gas bubbles (sized 10- 50 pm) with a close cell morphology.

[0035] Table 1, below, provides a comparison of the flame retardant properties of a halogenated polymer composition and the foamed version thereof. The first halogenated polymer composition, Comparative Example 1 (“CE1”), is based on a polymer component of polyvinyl chloride. Example 1 (“El”) was a foamed version of Comparative Example 1. Example 1 contained 1 wt% of an endothermic foaming agent.

[0036] The properties listed in Table 1 include density of the samples, density reduction, total heat release (THR), peak heat release rate (PHRR), and total smoke release (TSR). The density was measured using the buoyancy method and density reduction was calculated as ((1 - density foamed / density unfoamed) x 100). THR, PHRR, and TSR were measured using cone calorimetry. The THR measurement was based on the samples of the same volume.

[0037] Table 1. Properties of Halogenated Polymer Composition and Foam formed therefrom

[0038] From Table 1, it can be seen that Example 1 had a density reduction of about 21.12% relative to Comparative Example 1. Example 1 exhibited a reduction in total heat release (THR) of about 25% and a reduction in total smoke release (TSR).

[0039] In general, the inventors surmise that a decrease in THR relates to the lower mass per volume of the foamed samples. That is, for a cable jacket 12, 112 of a given size (i.e., thickness and length), a foamed cable jacket 12, 112 would have less combustible material than a fully dense cable jacket 12. However, in reducing the material of the cable jacket 12, 112, the amount of the flame retardant element (e.g., the halogen) will also be reduced. As will be discussed in greater detail below, the inventors surmise the improved flame retardant performance is based on the rate of burn.

[0040] Table 2, below, provides a comparison of the flame retardant properties of a halogenated polymer composition and the foamed versions thereof. The first sample group included standard MIC® cables (available from Corning Incorporated, Corning, NY), while Sample Group 2 included the same cables with cables having a jacket density reduction of 6- 8%, and Sample Group 3 included the same cables with cable jackets having a jacket density reduction of 12-18%.

[0041] The properties listed in Table 2 include flame spread, peak smoke, and average smoke. The flame spread and peak smoke were measured according to the 2023 edition of National Fire Protection Association (NFPA) Standard 262 “Method of Test for Flame Travel and Smoke of Wires and Cables for Use in Air-Handling Spaces.”

[0042] Table 2. Plenum Fire Test Results of Standard Cables and Foamed Cables.

[0043] From Table 2, it can be seen that some of the foamed cables showed quicker combustion and showed lower flame spread. As shown by Sample Group 2, the flame spread increases relative to the non-foamed cable, likely due to the decrease in flame retardant cable jacket material. However, as shown by Sample Group 3, with a greater density reduction of the foamed jacket, the flame spread decreases. In particular, when the density reduction of the foamed jacket reached 12-18%, the combustion occurred quickly and completely with no visible flame propagating beyond the first observation window of the test, therefore showing a flame spread of 0 feet. Based on the PHRR and the fire test results, the inventors surmise the foamed jackets discussed herein burn more intensely for a shorter period of time.

[0044] Example 1 of Table 1 and Sample Group 3 of Table 2 demonstrate foamed cable jackets with halogenated compositions can exhibit lower total heat release and quicker combustion and are therefore capable of meeting the flame resistance standard NFPA 262. However, Applicant notes, the tolerable density reduction of cable jackets 12, 112 is limited by the mechanical requirements of the cables 10, 100, such as crush resistance. Thus, in certain embodiments, it may be desirable to have a density reduction of at least 10% to achieve the enhanced flame retardant effect but no more than 50%, in particular no more than 40%, and most particularly no more than 30% to maintain mechanical properties of the cables 10, 100.

[0045] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is in no way intended that any particular order be inferred. In addition, as used herein, the article "a" is intended to include one or more than one component or element, and is not intended to be construed as meaning only one.

[0046] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the disclosed embodiments. Since modifications, combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the embodiments may occur to persons skilled in the art, the disclosed embodiments should be construed to include everything within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1. A polymer composition for forming a foamed cable jacket, the polymer composition comprising: a polymer component; a chemical foaming agent, the chemical foaming agent being present in an amount up to 5% by weight of the polymer composition; and a melt strength enhancer, the melt strength enhancer being present in an amount up to 1% by weight of the polymer composition.

2. The polymer composition of claim 1, wherein the polymer component is polyvinyl chloride.

3. The polymer composition of claim 1, wherein the polymer component is at least one of polyvinylidene fluoride, polytetrafluoroethylene or fluorinated ethylene polymer.

4. The polymer composition of claim 1, further comprising a flame retardant component dispersed in the polymer component, wherein the flame retardant component is a mineral flame retardant.

5. The polymer composition of claim 1, further comprising a plasticizer.

6. The polymer composition of claim 1, wherein the chemical foaming agent comprises an exothermic foaming agent.

7. The polymer composition of claim 6, wherein the exothermic foaming agent comprises at least one of azodi carbonamide, oxy-bis-benzenesulfonylhydrazide, toluenesulfonylhydrazide, benzenesulfonylhydrazide, toluenesulfonylsemicarbazide, 5- phenyltetrazole, dinitrosopentamethylenetetramine, hydrazocarbonamide, azobisisobutyronitrile, or barium azodi carb oxy late.

8. The polymer composition of claim 1, wherein the chemical foaming agent comprises an endothermic foaming agent.

9. The polymer composition of claim 8, wherein the endothermic foaming agent comprises at least one of sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, calcium azide, or citric acid.

10. The polymer composition of claim 1, wherein the melt strength enhancer comprises active peroxide.

11. An optical fiber cable, comprising: a cable jacket comprising an inner surface and an outer surface, the inner surface defining a central bore extending along a length of the optical fiber cable; a cable core disposed within the central bore, the cable core comprising at least one optical fiber; wherein the cable jacket comprises a polymer composition, the polymer composition having a first density; wherein the cable jacket comprises a foamed region that extends at least a portion of a distance between the inner surface and the outer surface; and wherein the foamed region comprises a second density that is 70% to 95% of the first density.

12. The optical fiber cable of claim 11, wherein the foamed region comprises a plurality of gas bubbles having a maximum cross-sectional dimension of 10 pm to 500 pm.

13. The optical fiber cable of claim 12, wherein the gas bubbles are uniformly distributed across the cable jacket.

14. The optical fiber cable of claim 12, wherein the gas bubbles have a maximum cross- sectional dimension of less than 100 pm.

15. The optical fiber cable of claim 11, wherein the foamed region extends an entire distance between the inner surface and the outer surface.

16. The optical fiber cable of claim 11, wherein the second density of the foamed region is 70% to 90% of the first density.

17. The optical fiber cable of claim 11, wherein the cable jacket further comprises an outer, unfoamed layer extending from the outer surface and defining an outermost layer of the cable jacket.

18. An optical fiber cable, comprising: a cable jacket comprising: an inner surface, the inner surface defining a central bore extending along a length of the optical fiber cable; an outer surface; a first layer extending from the outer surface; and a second layer extending from the inner surface; a cable core disposed within the central bore, the cable core comprising at least one optical fiber disposed within a buffer tube; wherein the cable jacket comprises a polymer composition, the polymer composition having a first density; wherein the second layer comprises a foamed region; and wherein the foamed region comprises a second density that is 80% to 90% of the first density.

19. The optical fiber cable of claim 18, wherein the polymer composition comprises polyvinyl chloride.

20. The optical fiber cable of claim 18, wherein the first layer comprises a second foamed region.

21. The optical fiber cable of claim 20, wherein the second foamed region comprises a third density, and wherein the third density is different than the second density.

22. The optical fiber cable of claim 18, wherein the optical fiber cable achieves a flame spread of less than 0.4 feet.

23. The optical fiber cable of claim 22, wherein the optical fiber cable achieves a flame spread of less than 0.1 feet.

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