Multi-Layered LSOH Sheath Flame Retardant Optical Cable
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Solution Overview
Problem
Current flame retardant optical cables fail to meet stringent international standards for flame retardancy, smoke release, and mechanical properties, particularly in high-risk areas like underground railways, and increasing material thickness or adding layers does not suffice for certification as low fire hazard cables.
Innovation Solution
A multi-layered sheath is introduced, with an intermediate layer of LSOH flame retardant material having a higher limiting oxygen index (LOI) than the inner and outer layers, which slows flame propagation, reduces heat and smoke release, and maintains mechanical properties without impairing tensile strength or workability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer LSOH sheath is used, then the cable structure is simple and manufacturing is easy, but the flame retardant performance is insufficient to meet stringent international standards
Solution Approach 1:
The single-layer sheath is segmented into three distinct layers with different LSOH material formulations. The intermediate layer has higher LOI (superior flame retardancy) while inner and outer layers have lower LOI (good flexibility and processing). This segmentation allows each layer to perform its specific function, achieving superior overall flame retardant performance while maintaining manageable structural complexity
Solution Approach 2:
Different regions of the sheath are assigned different material properties: the intermediate layer uses LSOH material with high LOI for maximum flame resistance, while the inner and outer layers use LSOH material with lower LOI for better flexibility and ease of installation. This local differentiation of material quality optimizes both flame retardant performance and mechanical properties
2Reliability
If the sheath thickness is increased to improve flame retardancy, then flame spread resistance improves, but mechanical flexibility and workability deteriorate
Solution Approach 1:
The sheath uses different LSOH material formulations in different layers: the intermediate layer has high LOI for flame resistance, while the inner and outer layers have lower LOI for flexibility. This allows the cable to achieve excellent flame spread resistance without sacrificing mechanical flexibility and workability
Solution Approach 2:
The sheath is constructed as a composite of three LSOH material layers with different LOI values. This composite structure combines the flame-retardant properties of high-LOI material with the flexible, workable characteristics of lower-LOI materials, achieving both fire safety and ease of installation
3Reliability
If mica tapes are added to improve fire performance, then flame retardancy improves, but manufacturing cost increases significantly
Solution Approach 1:
Instead of adding expensive mica tapes, the invention changes the chemical composition parameters of the LSOH material itself by adjusting the ratio of inorganic flame retardant fillers (such as magnesium hydroxide, aluminum trihydrate) to polymer base. This allows achieving superior flame retardant performance through material formulation optimization rather than adding expensive auxiliary components
Solution Approach 2:
The invention replaces expensive mica tapes with cost-effective LSOH material formulations that achieve equivalent or superior flame retardant performance through optimized filler content and distribution across the three layers, significantly reducing manufacturing costs while maintaining high fire performance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The multi-layered sheath design enhances flame retardancy, meeting stringent standards for areas with very high fire risks while maintaining mechanical performance, as demonstrated by improved test results in flame spread, heat release, smoke production, and droplet persistence.
Implementation Method 1
a multi-layered sheath wherein an intermediate layer is provided with a LSOH flame retardant material having a limiting oxygen index (LOI) higher than the LSOH flame retardant material of the inner and outer layers
Implementation Method 2
the multi-layered sheath offers improved flame-retardant properties, particularly in terms of slowing flame propagation, heat release
Implementation Method 3
emission of non-harmful smoke while maintaining its optical transmissive properties during and after the fire occurrence
Data Source
Figure 1
AI summary
A flame-retardant optical cable (10) is disclosed which comprises a polymeric central loose tube (3) housing optical fibres (1), a metallic armour (6) surrounding the polymeric central loose tube (3) and a multi- layered sheath (7) surrounding and in direct contact with the metallic armour (6), wherein the multi-layered sheath (7) comprises an inner layer (7a), an intermediate layer (7b) and an outer layer (7c), all made of a LS0H flame-retardant material, the LS0H material of the intermediate layer (7b) having a limiting oxygen index (LOI) higher than the LOI of the LS0H material of the inner layer (7a) and of the outer layer (7c). Such cable has improved flame-retardant properties, particularly in terms of slowing flame propagation, heat release, droplets and emission of smokes, when it is exposed to flames during fire.