Fiber Optic Cable: Jacket & Fire Rating - What Are The Differences?

Written by Ben Hamlitsch, trueCABLE Technical and Product Innovation Manager RCDD, FOI

The components of a fiber optic cable include the core, cladding, coating, strengthening member, and the outer cable jacket. Fiber optic cable jackets are necessary to protect the core and cladding within the cable from damage due to the fragility of the bare fiber. The cable jacket protects a fiber optic cable from the elements and other hazards, such as mechanical damage and fire, and depending on the rating, little or no chemicals are released from the cable when it burns.

There are various different types of fiber optic cable. Depending on the application, the correct fiber cable should be utilized. Each variety of fiber optic cable, from armored to aerial, is created with the specific goal of maximizing performance in a given location and with the given set of environmental circumstances in mind. Standard fiber cable types, such as indoor distribution fiber cable, need careful planning by the installer to ensure they are installed in the optimal location to fulfill their intended purpose and meet the customer's requirements.

Fiber optic cables must meet certain standards when passing through riser or plenum spaces throughout the installation within a building. In the event of a fire, a damaged fiber jacket may emit hazardous chemicals and generate heavy smoke. In order to ensure the safety of everyone within the building, it is imperative that the cabling being installed meets all applicable fire ratings.

A well-rounded fiber optic network may be achieved via designing and understanding the correct procedure with regard to fire ratings. These are required to ensure the safety and performance of the fiber cabling system.

Optical fiber cable jackets can have any one of three different degrees of fire resistance. The rankings follow a clear hierarchical structure. When it comes to fire safety, for instance, a higher rating can be substituted for any lower rating, but the inverse is not true. As an additional note, nonconductive materials can be used in place of conductive ones, but not the other way around. Below, in ascending order of specificity, are optical fiber's fire ratings.

Fiber Optic Cable Jacket Material

Below you will find a list of jacket materials and cable jacket benefits!

LZSH: What is it and what makes it different?

The term "low-smoke zero-halogen" (LSZH) refers to a material used in the jacket of cables that is both flame retardant and does not contain any halogen. This particular kind of jacket fabric offers great fire safety properties, including minimal smoke production, low toxicity, and low corrosion rates. Because very little smoke is produced when LSZH fiber optic cables come into contact with a flame, these cables are ideal for applications in which a large number of people are confined in a specific location, such as office buildings, train stations, airports, and other similar locations.

A fire can be extremely dangerous in a building. LSZH fiber optic cables do not contain any halogenated materials such as fluorine (F), chlorine (Cl), bromine (Br), iodine (I), or astatine (At). Halogenated materials, such as these, have the potential to be transformed into toxic and corrosive matter when they are subjected to combustion. Because they produce very little smoke, LSZH fiber optic cables are not only safe but also quite useful. Smoke inhalation is the leading cause of death among victims of fires. In these kinds of settings, the use of LSZH fiber optic cables, which produce little to no smoke and no halogenated byproducts, would be of critical significance to the protection of people.

LSZH Fiber Optic Cables' Various Possible Applications

As the use of data transmission becomes more widespread, there is no question that the number of fiber optic cables that are being installed in buildings is growing at an increasing rate. LSZH fiber optic cables have become increasingly prevalent in the central office areas of telecommunications facilities. Data centers contain large amounts of cables, and are usually enclosed spaces with cooling systems that have the potential to disperse combustion byproducts throughout a large area. LSZH cables can be a good choice in these system critical applications.

In the image below we can see the differences between a standard PVC cable jacket, LSZH, and the highest rating, plenum. Both LSZH and plenum are designed to eliminate the toxicity of the cable in the event of a fire. In the case with plenum there is a self extinguishing feature in which the cable jacket will not generate any toxic fumes.

When there is an enhanced potential for heat and fire hazard, the use of LSZH cables is recommended. There are a lot of positive aspects associated with utilizing LSZH cables such as the benefits for the environment and toxicity levels.

Fiber Optic Cable Jacket Color Code

Different types of fibers have their own unique jacket colors, which are defined by EIA/TIA-598 (SMF or MMF). One common jacket color for single-mode fiber is yellow. However, multimode cables' outer sheathing can be many various colors, including orange (for OM1 and OM2 cables), aqua (for OM3 cables), and either aqua or violet (for OM4 cables). Generally speaking, black is the usual jacket color for cables used in outdoor applications. You can learn more about the meanings of the many colors used in fiber optic cables by checking out the article What do all the colors mean? Fiber Optic Color Coding.

Fiber Optic Cable Fire Rating

The National Electrical Code (NEC) typically specifies eight different degrees of fire resistance for both conductive and non-conductive wires. All fiber optic cables placed indoors, including those in plenum spaces, risers, and multipurpose rooms, must be clearly labeled and installed according to their intended location.

Several different materials can be used to construct the outer sheath of a fiber optic cable. Choose a jacket that is compatible with the connections and environment for your application, with consideration for the space and location where the cable will be installed. Types of fiber cable jacket materials that are often used for both indoor and outdoor cables are listed in the table below.

Note:

(1) A plenum area is a building space used for air flow or air distribution system (drop ceilings and raised floors).

(2) A riser area is a floor opening, shaft, or duct that runs vertically through one or more floors.

(3) A general purpose area is all other areas that are not plenum or riser and are on the same floor.

How do I know if I have a Riser or Plenum Fiber Optic Cable?

On the riser cable, one will often see either OFxR (where "R" stands for "riser") or OFxP (where "P" is for "plenum"). In most cases, the 'x' will be an N for the fiber optic cable that you buy, which indicates that we have the following:

OFNR – Optical Fiber Non-conductive Riser

OFNP – Optical Fiber Non-conductive Plenum

OFNP vs. OFNR

Both OFNP and OFNR are examples of types of fiber optic cables that may be found in residential and commercial structures. OFNP cables contain features that make them resistant to fire and have a low rate of smoke production. This fiber cable has the greatest fire rating of any other cable type, and you cannot use any other cable type in its place. Therefore, plenum cables are put in plenum spaces. The fiber resistance and low smoke of OFNR cables, on the other hand, are not as good as those of OFNP cables. It is fine for OFNP plenum cables to be used in replacement of OFNR cables. When comparing OFNR with OFNP, it is important to note that OFNR fiber optic cable cannot be utilized in plenum spaces in place of OFNP cables. On the other hand, OFNP cables may be utilized in riser areas. In areas designated for general use, either OFNP or OFNR may be utilized.

As a result, plenum-rated cables and riser-rated cables are often utilized for deployment inside structures. If a fire should occur and cables do begin to burn, it is extremely important that the appropriate fire-rated cable was selected. This one detail may significantly cut down on the amount of loss. Always go with plenum-rated cables when your application for cabling demands materials that are fire-resistant or that comply with stringent safety regulations.

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