Optical FiberCable used in vertical shafts, or in runs between floors, must have fire-resistant characteristics capable of preventing the spread of fire from floor-to-floor. OFNR refers to the fiber rating of the cable jacketing.
Riser cables can be used in vertical passages connecting one floor to another. These cables are termed OFNR (optical fiber nonconductive riser). Plenum cables can be installed in plenums without the use of conduit. Meeting specific requirements for flammability and smoke generation, these cables are termed OFNP (optical fiber nonconductive plenum). General-use cables cannot be used in riser or plenum applications without fireproof conduits. These cables are rated OFN (optical fiber nonconductive). OFN cables can be used in offices space – to connect from a wall jack to a computer, for example.
OFNR cables has fire-resistance characteristics tested to UL-1666 "Standard Test for Flame Propagation Height of Electrical and Optical Fiber Cable Installed Vertically in Shafts." OFNP-type cable can be used as a substitute for this cable.