30 September 2019

Fire-Resistant Fiber Optic Cables


Fire-Resistant Fiber Optic Cables

Fire risks increase as the public living areas increase and thus, life and property safety issues become more important. Therefore, like other fire-resistant products, fire-resistant cables have become an important part of our lives.

As it is known, most of the energy and signal cables used today have fire-resistant types and are widely used in fire systems. As the technological level of fire systems increased, fiber optic cables have become fire-resistant.

Fiber optic cables can be divided into two groups as per usage areas:

  • Armored (metallic) fiber optic cables
  • Unarmored (non-metallic) fiber optic cables

With the increasing security elements in tunnels, subways and industrial facilities where communication systems and display devices are used, the need and demand for fiber optic cables that need to continue to function in the event of fire is increasing day by day.

The most important feature that distinguishes fire-resistant fiber optic cables from other standard fiber optic cables is that they can continue their functions in the event of fire. Another distinguishing feature of these cables is their low emission of smoke during the fire. This minimizes the risk of poisoning or suffocation from smoke and maximizes the safety of life.

Outer sheath material used in fire-resistant fiber optic cables are special materials called LS0H, LSZH (Low Smoke, Zero Halogen), LSHF (Low Smoke, Halogen Free). Smoke emission of this type of materials is so much less than PVC and Polyethylene. In addition to the materials used, the design and performance of the cable during fire are the determining factors for fire resistance criteria.

Fire resistant fiber optic cables are suitable for use in pipes and for direct land burial (armored types).

Cable Structures

1- Armored (Metallic) Fiber Optic Cables






Center element (GRP)

Fiber tubes

Cable core

Water tightness. Water-swellable rope and/or tapes

Flame and heat barrier

Reinforcement elements

Inner sheath


Outer sheath

Figure 1 : Fire-resistant, armored fiber cable cross-section






Figure 2 : Fire-resistant, armored fiber optic cable sample

Dry core: Water-swellable rope or tape is used to ensure water tightness. The reason for using the jelly filling material is to minimize smoke emission in the event of a fire. For this reason, “dry core” is recommended as the core structure of fire-resistant fiber optic cables.

 Flame and heat barrier: Special tapes are used to reduce the effect of flame and heat on the inner layers of the cable and fiber tubes.

 Reinforcement elements: Generally, glass yarn is used. Glass yarns are used to meet the desired tensile force.

 Inner sheath: Special materials with low smoke emission and zero halogen are used.

 Armor: Generally, corrugated steel tape with both sides coated with copolymer material is used. Due to the armor used, the cable core is protected from mechanical impacts and rodents.

 Outer sheath: Special materials with low smoke emission,zero halogen and resistance to environmental conditions are used.

2- Unarmored (Non-Metallic) Fiber Optic Cables






Center element (GRP)

Fiber tubes

Cable core

Water tightness. Water-swellable rope and/or tapes

Flame and heat barrier

Reinforcement elements

Inner sheath

Flame and heat barrier

Reinforcement elements

Outer sheath

Figure 3 : Fire-resistant, armored fiber cable cross-section

Dry core: The intended use and materials used are the same as for armored fiber optic cables.

 Reinforcement elements: Generally, glass yarn is used. Glass yarns are used to meet the desired tensile force. It also provides protection against rodents if used at a certain density.

 Inner sheath: Special materials with low smoke emission and zero halogen are used.

 Outer sheath: Special materials with low smoke emission, zero halogen and resistance to environmental conditions are used.

 Fire-resistant fiber cable tests can be divided into three main groups: Optical tests, mechanical tests and fire tests. Details of these tests, cable standards and specifications may vary according to customer requirements. Basic tests are as follows:

Optical Tests (IEC 60793-1-40):

Cable attenuation measurement

 Mechanical Tests (IEC 60794-1-2):

Cable tensile test (Tensile test – E1)

Crush test (Crush test – E3)

Impact test (Impact test – E4)

Torsion test (Torsion test – E7)

Bending test (Bending test – E11)

Temperature range (Temperature range – F1)

Water penetration (Water penetration – F5B)

Fire Performance Tests:

 IEC 60331-25, Continuation of the functioning under fire:

The duration of the continuation of functioning of the cables under fire is tested. The cable is fixed horizontally to the test mechanism as specified in the standard and the fibers are connected to OTDR or Power Meter so as to make loop. 750°C temperature is applied for minimum of 90 minutes. After this, the 15-minute cooling process starts. Fiber attenuation change is observed during flame application and cooling periods. During these two periods (flame application and cooling), the fiber must not break.







Figure 4 : IEC 60331-25 test mechanism








Figure 5 : Attenuation measurement with OTDR

EN 50200, Continuation of the functioning under fire and impact:

The resistance of the armored fiber optic cables against external factors for falling particles or vibration during fire is tested. The sample to be tested must be a sufficiently long (at least 5m) piece of cable with two ends protruding from the test cell and with approximately 100 mm cover or with the outer sheaths removed at each end. For multiple fiber optic cables; the samples to be connected must be selected from the outermost layer of the cable.

If the length of the sample to be tested is not sufficient, identical fibers are connected to each end of the sample to provide sufficient length for the optical measurement method. The attenuation should be monitored with OTDR or Power Meter during the test.

830°C flame is applied to the cable during the test and the device producing sudden impact is operated. The sudden impact process must impact at intervals of 5 minutes (±10 seconds). The applied impact time can be 30, 60, 90 or 120 minutes. At the end of this process, the fiber must not break. According to this test, the cables are classified as pH30, pH60, pH90 or pH120. The number after the pH expression indicates how long the cable is resistant to impact








Figure 6 : IEC 50200 test mechanism

IEC 60332-3-24, Flame propagation test for inspected cables:

Flame is applied by bringing together the cable samples with the number and length specified in the standards according to the cable diameter. Flame propagation must be ≤ 2.5m.








Figure 7 : IEC 60332-3-24 ( CAT.C) test mechanism

IEC 60754-1/2, Halogen acid gas test, acidic (corrosive) gas test:

It is applied to measure the corrosivity of gases released by cables during fire in terms of pH and conductivity. Values should be: HCl < %0.5 pH ≥ 4.3 c ≤ 10μS/mm.

 IEC 61034-2, Smoke density test:

According to the cable diameter, the light transmission of the cables in the amount specified in the standard is tested by burning with a fuel prepared in a 3x3x3m (27m³) closed cubic test chamber with a mixture of 90% ethanol, 4% methanol and 6% pure water. Measurement result should be at least 60%.

These fire performance tests are the criteria that must be followed in order to minimize the risks of life and property by maintaining the function during fire by applying on the cables on a type basis.

Our purpose for R&D studies as Prysmian Group Türkiye is not only to develop new products or reduce costs, but to combine application-specific products with maximum performance and safety criteria. Our fire-resistant fiber optic cables have all the performance and safety features that are required or necessary for these types of cables. Our fiber optic cables, which complement the entire system with energy and signal cables, have been developed as a part of the overall system security. We continue to develop our products according to all changing demands and needs.















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