US Patent 10996413 Fire resistant optical fibre cable with high fibre count

A fire-resistant optical fibre cable includes a core having a central strength member and buffer tubes arranged around the central strength member. Each buffer tube contains optical fibres. A mica layer is arranged around the core. A glass yarn layer surrounds and is in direct contact with the mica layer. Metal armour surrounds the glass yarn layer. A multi-layered sheath surrounds and is in direct contact with the armour. The sheath includes a first layer, a second layer surrounding and in contact with the first layer, and a third layer in a radial inner position with respect to the first layer and in direct contact thereto. The first, second and third layers are made of LS0H flame-retardant material. The LS0H material of the first layer has an LOI higher than the LOI of the LS0H material of the second and third layers. The second layer is the cable outermost layer.