The NEK 606 standard qualifies two types of outer sheath: SHF1 and SHF2. SHF1: a thermoplastic outer sheath which is halogen-free and causes minimal smoke in case of fire. The resistance to these. The first ITU-T Handbook related to optical fibres, Optical Fibres for Telecommunications, was published in 1984, and several others have been produced over the years. It is an honour to present you with the latest version, which is another example of how ITU-T is bridging the standardization gap. The Fiber Optic Association, Inc. Different types of. Corning Optical Communications manufactures quality flame retardant optical fiber cables for indoor applications, which comply with the requirements of the National Electric Code® (NEC® 2023) published by the National Fire Protection Agency (NFPA).