As AI training clusters continue to grow, increasing rack power density is driving greater demand for fiber optic cabling. In high-density, enclosed, and increasingly liquid-cooled data centers, smoke, corrosive gases, and flame spread during a fire can significantly impact equipment and network reliability. As a result, cable jacket materials and fire ratings have become key considerations in data center infrastructure design.
A fiber optic cable typically consists of the fiber core, strength members, and outer jacket. As the cable’s outermost protective layer, the jacket provides mechanical protection while helping resist moisture, environmental damage, and fire. It is expected to offer adequate mechanical strength, moisture resistance, chemical resistance, thermal stability, and flame-retardant performance to ensure safe transportation, installation, and long-term operation.
Fiber optic cable jackets are available in different materials, each offering distinct performance characteristics, fire resistance, and recommended application environments. The most common jacket materials include PVC, PE, HDPE, LSZH.
PVC（Polyvinyl Chloride）
PVC is one of the most widely used jacket materials for fiber optic cables. It offers low cost, good flexibility, excellent chemical resistance, and inherent self-extinguishing properties, making it suitable for general indoor applications. However, when exposed to fire, PVC produces dense smoke and corrosive gases. As a result, its use in high-performance data centers is gradually declining.
PE（Polyethylene）
PE is one of the most commonly used jacket materials for outdoor fiber optic cables. It offers excellent low-temperature performance, outstanding chemical stability, and good resistance to most acids and alkalis. PE also provides excellent electrical insulation and UV resistance, making it well suited for outdoor applications.
Depending on its density, PE is classified into Medium-Density Polyethylene (MDPE) and High-Density Polyethylene (HDPE). With a more tightly packed molecular structure, HDPE delivers superior abrasion resistance, impact resistance, and environmental stress crack resistance, making it the preferred choice for outdoor cable jackets.
LSZH（Low Smoke Zero Halogen）
LSZH is a widely used flame-retardant jacket material. In the event of a fire, it produces minimal smoke and does not release halogen gases, significantly reducing corrosive emissions compared with conventional PVC materials. These characteristics make LSZH well suited for enclosed or densely occupied environments, such as data centers, metro systems, and high-rise buildings.
Compared with traditional PVC, LSZH provides a higher level of fire safety. As data centers continue to evolve toward higher-density and more enclosed architectures, LSZH has become the preferred jacket material for minimizing smoke generation and reducing corrosion risks during fire incidents.
Fire Ratings for Fiber Optic Cables
Fiber optic cables are classified according to their fire performance, including flame propagation, smoke generation, and other fire-related characteristics. Different regions adopt different standards and classification systems. The most widely recognized include IEC 60332 flame propagation tests, the UL/NEC fire rating system in the United States, and the Construction Products Regulation (CPR) classification in Europe.
Under the UL/NEC system, fiber optic cables are commonly classified as OFNP/OFCP, OFNR/OFCR, OFNG/OFCG, and OFN/OFC. In Europe, the CPR classification includes Aca, B1ca, B2ca, Cca, Dca, Eca, and Fca.
According to the National Electrical Code (NEC) and UL 1651, fiber optic cables are classified based on their intended installation environment into Plenum, Riser, and General-Purpose applications. Each installation environment has specific requirements for flame propagation, smoke generation, and overall fire performance.
Each fire rating is further designated as either Conductive (C) or Non-conductive (N). Non-conductive fiber optic cables contain only non-metallic components and do not include conductive materials.
The UL/NEC abbreviations can be interpreted as follows: “OF – Optical Fiber”, “N/C – Non-conductive / Conductive”, “R/P – Riser / Plenum”.
OFNP（Optical Fiber Non-conductive Plenum） & OFCP（Optical Fiber Conductive Plenum）
They represent the highest fire rating under the UL/NEC classification for fiber optic cables. They are specifically designed for installation in plenum spaces, such as air-handling ducts and return-air plenums, without requiring installation in metal conduit. Because these spaces are directly connected to a building’s air circulation system, smoke can spread rapidly in the event of a fire. Therefore, OFNP and OFCP cables must provide superior flame resistance and minimal smoke generation.
In general, OFNP/OFCP cables may be used in applications requiring lower fire ratings, whereas lower-rated cables cannot be used in plenum installations.
OFNR（Optical Fiber Non-conductive Riser） and OFCR（Optical Fiber Conductive Riser）
These are designed for installation in vertical riser shafts between floors. They provide the next highest level of fire performance after OFNP/OFCP and are tested to prevent flame propagation from one floor to another.
The general hierarchy of fire rating is OFNP / OFCP ＞ OFNR / OFCR. In general, cables with higher fire ratings can be used in applications requiring lower fire ratings. However, lower-rated cables cannot be used in environments that require higher-rated cables, such as plenum spaces.
CPR（Construction Products Regulation）
In Europe, the CPR classifies fiber optic cables according their fire performance. Unlike traditional classifications that focus primarily on flame resistance, CPR evaluates a cable’s overall behavior in the event of a fire, including flame spread, heat release, smoke production, flaming droplets, and acidity of combustion gases.
The most common CPR classes for fiber optic cables are B2ca, Cca, Dca, and Eca. These classifications are often accompanied by additional performance indicators for smoke production (s), flaming droplets (d), and acidity (a), such as Cca-s1, d1, a1.
B2ca: One of the highest fire performance classes under the CPR system. Cables rated B2ca exhibit extremely limited flame spread and very low heat release, helping to significantly reduce fire propagation in the event of a fire. They are commonly used in critical applications such as hospitals, metro systems, high-rise buildings, airports, and other public facilities where stringent fire safety requirements apply.
Cca: Provides moderate fire performance and is suitable for most commercial buildings, including office buildings, shopping malls, and structured cabling systems in data centers.
Dca: Provides basic fire performance with limited flame spread and heat release. It is commonly used for horizontal and vertical cabling in residential buildings and small to medium-sized commercial facilities.
Eca: Represents the basic level of fire performance under the CPR system. It is suitable for low-risk environments and general indoor or outdoor cabling applications, but is typically not recommended for densely occupied buildings.
Under the CPR classification, the fire performance hierarchy is: B2ca ＞ Cca ＞ Dca ＞ Eca.
A cable jacket is more than just an outer protective layer - it plays a critical role in fire safety, environmental protection, and long-term reliability of data center infrastructure. As AI drives the adoption of higher-density optical interconnects, the importance of jacket materials and fire ratings continues to grow. Selecting the appropriate combination for the intended installation environment has become an essential part of modern data center cabling design.
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