In data center and building cabling, safety is critical. Many users ask: What are OFNP, OFNR, LSZH? What do these flame‑retardant grades mean? Which one should I use for plenum, riser, or indoor areas?  The flame retardant grades of optical cables can be divided into three types, OFN, OFNR and OFNP. This article explains definitions, standards, performance, and applications to help you choose safely and correctly.

I. What Is LSZH (Low Smoke Zero Halogen)?

As early as the mid-1980s, halogen (especially brominated) flame retardant polymer systems were widely used because of their outstanding flame retardant effect. In the wire and cable industry, polyvinyl chloride (PVC) is a good example, but PVC has a disadvantage that it will release a lot of smoke when it is burned, and it will produce serious corrosive and toxic gases. Therefore, cables are now made of low-smoke halogen-free materials. 

LSZH (low smoke and halogen free) material has some obvious advantages: low smoke, low toxicity, low corrosion, and high flame retardancy. LSZH is a jacket material property, not a UL flame rating. It means the cable produces little smoke and no toxic halogen gas when burned, making it ideal for closed, crowded, or safety‑critical areas.

II. What Is OFNP (Plenum Grade)?

OFNP is the highest grade optical cable. When a fan is used on the optical cable to force the flame to blow, the cable will extinguish itself within 5 meters of the flame spread. At the same time, the cable will not emit toxic smoke or steam. It is usually installed in a ventilation duct in communication wiring applications. or in the air return booster system used in air handling equipment.

OFNP = Optical Fiber Non‑conductive Plenum
Highest flame‑retardant rating (UL 1651, NFPA 262)
For plenum/air‑handling spaces (HVAC ducts, ceiling voids)
Self‑extinguishing, low smoke, non‑toxic
Can replace OFNR, but not vice versa

III. What Is OFNR (Riser Grade)?

OFNR is the second-ranked optical cable. Under the condition of forced air blowing by the fan, the optical cable must extinguish itself within 5 meters of the flame spread, which is usually encountered in trunk fires, so this kind of fire rated optical cable is usually used. in floor trunks and horizontal cables.

OFNR = Optical Fiber Non‑conductive Riser
Second‑highest flame rating (UL 1651, UL 1666)
For vertical shafts, risers, floor‑to‑floor cabling
Prevents fire from spreading upward
Cannot be used in plenum areas

UL 1651 Full Classification of Optical Fiber Cables

The types of optical fibers are divided into the following four categories according to the UL1651 standard:

1. OFNP, OFCP: P-class non-conductive and conductive;

2. OFNR, OFCR: R-class non-conductive and conductive;

3. OFN, OFNG: non-conductive optical fibers for general purposes;

1. OFC, OFCG: conductive optical fibers for general purposes;

OFNP vs OFNR vs LSZH Full Comparison Table

The selection of system cables has become an element that cannot be ignored. Here, ETU-LINK reminds everyone that in addition to considering performance when choosing integrated wiring cables, fire protection and environmental protection should also be considered to improve the building safety index.

ETU-LINK provides full series optical patch cords with OFNP, OFNR, LSZH jackets, suitable for data centers, buildings, industrial, and public safety applications.

Last updated: May 27, 2026