Flame retardant rating of ordinary optical cables

Optical fiber cables are commonly rated as OFNP (plenum), OFNR (riser), or OFNG (general-purpose) to indicate their flame retardant performance and suitable installation environments.Common Ratings and ApplicationsOFNP (Optical Fiber Nonconductive Plenum): This is the highest fire-resistance rating, suitable for plenum spaces such as air ducts, ceiling voids, and other areas used for air circulation. OFNP cables are tested to stringent standards like NFPA-262 / UL-910, which measure flame spread and smoke density during extended burns, ensuring minimal smoke and toxic gas emission . Plenum-rated cables can also be used in riser or general-purpose areas.OFNR (Optical Fiber Nonconductive Riser): Designed for vertical riser shafts between floors, OFNR cables prevent sustained flame propagation in vertical installations. They are tested under IEC 60332 vertical flame tests but are not suitable for plenum spaces . Riser-rated cables can be substituted for general-purpose use but cannot replace plenum-rated cables.OFNG (Optical Fiber General-purpose): Suitable for areas where less stringent fire resistance is required. These cables are intended for general installations that do not involve plenum or riser spaces .Conductive Versions (OFCP, OFCR): These are similar to OFNP and OFNR but include conductive elements for specific installations requiring electrical conductivity .Material ConsiderationsLSZH (Low Smoke Zero Halogen): Preferred in confined or poorly ventilated spaces, LSZH jackets produce minimal smoke and virtually no halogen-acid gases when burned, reducing toxicity and equipment corrosion . LSZH cables may also meet plenum or riser performance targets if independently tested.PVC (Polyvinyl Chloride): Commonly used for general-purpose or riser-rated cables, PVC is less expensive but produces more smoke and toxic gases compared to LSZH .Testing and CertificationOptical cables must be certified by a Nationally Recognized Testing Laboratory (NRTL), such as UL or Intertek, to ensure compliance with NEC and NFPA standards . Key tests include:NFPA-262 / UL-910: Flame spread and smoke density for plenum cables.IEC 60332: Vertical flame propagation for riser cables.IEC 61034: Smoke density measurement.IEC 60754: Halogen-acid emission for LSZH cables.SummaryWhen selecting optical fiber cables, the installation environment dictates the required flame retardant rating:Plenum spaces → OFNP (highest fire resistance, low smoke)Riser shafts → OFNR (vertical flame protection)General-purpose areas → OFNG (basic fire resistance) Always verify the cable's test certification to ensure compliance with local building codes and safety standards .