Introduction
Fiber optic cables come in various types, each designed to meet the specific requirements of different applications. These cables can be customized with different characteristics to suit their intended use, whether it's for armored, aerial, or indoor distribution purposes. Installers must carefully consider the placement of the cables to meet the specific needs of each location.
In building installations, fiber cables often pass through Riser or Plenum areas, each with its own set of requirements for cable selection. It's important to use cables with the appropriate fire ratings to prevent the release of toxic fumes and excessive smoke in the event of a fire. Adhering to safety regulations ensures the well-being of everyone in the building.
Understanding the importance of fire ratings and following the proper protocols is crucial to maintaining an effective and safe fiber optic network. By ensuring the use of cables with the correct fire ratings, the integrity and reliability of the network can be preserved.
Why does the Outer Jacket of the Cable matter?
Fiber optic cables generally consist of fiber cores, coatings, strength members, and outer jackets. The outer jacket serves as a protective layer for the cable, providing fire resistance and moisture resistance.
The performance of the outer jacket is crucial in the event of a fire in a data center. The outer jackets of fiber optic cables come in different material types, each with its inherent characteristics (varying fire resistance) and suitable usage scenarios. Common outer jacket materials include PE, PVC, PVDF, LSZH, Plenum, and Riser. The table below displays the performance and applicable environments for these materials.
| Material | Advantages |
| PE (Polyethylene) |
It has excellent low-temperature resistance, good chemical stability, resistance to most acid and alkali corrosion, abrasion resistance, and high electrical insulation. Therefore, PE is commonly used as the standard outer jacket material for outdoor cables. |
| PVC (Polyvinyl Chloride) |
It has good mechanical properties, high electrical insulation, flexibility, strength, and good flame resistance. However, it has poorer stability to light and heat, making it more suitable as an outer jacket material for indoor fiber optic cables. |
| PVDF (Polyvinylidene Fluoride) |
It possesses multiple excellent properties such as elasticity, low weight, low thermal conductivity, high chemical resistance, and heat resistance. It also has better flame resistance than PE and produces almost no smoke even in the event of a fire. Therefore, PVDF material can be used for the outer jacket of more critical backbone fiber optic cables. |
| LSZH (Low Smoke Zero Halogen) |
It features low smoke, low toxicity, low corrosiveness, and high flame retardancy. LSZH is a safe and environmentally friendly material, making it an ideal choice for both indoor and outdoor installations. However, it should be noted that fiber optic cables with LSZH material are generally more expensive. |
| Plenum | It is one of the main components for producing OFNP-rated fiber optic cables. It has high flame retardancy and does not generate toxic or corrosive gases even at extremely high temperatures. Fiber optic cables with Plenum material are the preferred choice for wiring in ventilation ducts or air handling systems with positive air pressure. |
| Riser |
As one of the main component for producing OFNR-rated fiber optic cables, Riser has relatively weaker flame resistance compared to Plenum material. It is also free from toxic gases and corrosive gases. Therefore, fiber optic cables with Riser material are typically used in vertical risers and horizontal cables within buildings. |
What are the Different Fire Ratings for Fiber Optic Cables?
In the NEC (National Electrical Code) standards, fiber optic cables are commonly classified into OFNP/OFCP, OFNR/OFCR, OFNG/OFCG, and OFN/OFC fire ratings.
OFNP/OFCP is the highest flame-retardant rating in the NEC standards (plenum-grade). If a forced airflow from a fan is directed at a bundle of plenum-grade fiber optic cables, the flames on the cables will self-extinguish within 5 meters and no toxic or corrosive gases will be generated.
OFNR/OFCR is the vertical rating (riser-grade) and ranks second. When a forced airflow from a fan is directed at a bundle of riser-grade fiber optic cables, the flames will self-extinguish within 5 meters, but there are no smoke or toxicity requirements.
OFNG/OFCG and OFN/OFC are commercial-grade and general-purpose-grade, respectively. Fiber optic cables meeting these standards are commonly used in environments with lower fire resistance requirements.
What Fire Ratings can be Achieved with Different Outer Jacket Materials?
Although the fire rating of fiber optic cables is not directly determined by the outer jacket material, in general, if Plenum is used as the outer jacket material, the fiber optic cable can achieve an OFNP fire rating during NEC flame retardant testing. If PVC or Riser is used as the outer jacket material, the fiber optic cable can achieve an OFNR fire rating. If LSZH is used as the outer jacket material, the fiber optic cable can achieve an OFN fire rating.
In summary, fiber optic cables with outer jackets made of Plenum, PVC/Riser, or LSZH materials can meet the fire resistance requirements of data centers.
How should Different Outer Jacket Materials be Selected Based on the Layout Area?
- Plenum material is suitable for horizontal cabling areas and areas withinflatable environments such as conduits and air handling systems. In these environments, where air circulation is present and fire incidents are difficult to control, using OFNP-rated flame-retardant fiber optic cables is the best choice.
- Riser/PVC material is suitable for vertical backbone cabling areas, providing connectivity between entrance equipment or computer rooms and different floor telecommunication closets. The likelihood of large-scale fires is low in these areas, and achieving an OFNR fire rating is sufficient.
- LSZH material is commonly used in general-purpose areas. Even in the event of a fire, LSZH cables release non-toxic smoke, thereby avoiding harm to rescue personnel.
Conclusion
It is worth noting that the outer jacket of fiber optic cables is only one aspect of fire prevention and control. To effectively reduce the risk and losses from fires, careful planning of cabling scenarios and the implementation of fire prevention measures are essential. Only by considering all aspects comprehensively can data center safety be ensured.