LSZH Cables

Low Smoke Zero Halogen (LSZH) cables are designed to minimize the release of toxic and corrosive gasses when exposed to fire. Due to this, they are a crucial component in environments where fire and human safety are of upmost concern. 

Key features and benefits of LSZH:

• Flame Retardancy: LSZH cables possess flame retardant properties, contributing to their ability to resist ignition and slow down the spread of fire.

• Low Smoke Emission: When exposed to fire, LSZH cables produce significantly lower levels of smoke compared to PVC cables. This reduces the risk of smoke inhalation and improves visibility in emergency situations.

• Minimal Toxic Fumes: LSZH cables emit minimal amounts of toxic fumes when subjected to fire, enhancing the safety of occupants in the vicinity.

• Absence of Acid Gases: Unlike PVC cables, which release acid gases when burning, LSZH cables do not emit acid gases.

• Halogen-Free Composition: LSZH cables are essentially halogen-free, meaning they do not contain chlorine, fluorine, bromine, or iodine compounds. This makes them safer for human health and the environment.

1. Suitability: Due to their superior fire performance and low emission characteristics, LSZH cables are commonly specified for use in environments when ensuring fire safety and protecting human well-beings are paramount. This includes public areas, poorly ventilated spaces, cars, aircraft, railway carriages, ships, tunnels, and underground rail networks.

LSZH cables are subject to stringent standards set by organizations like the British Standards Institution (BSI) and the International Electrotechnical Commission (IEC). These standards define the requirements and testing procedures that LSZH cables must meet to ensure their compliance with safety and performance standards.

British Standards

BS 7211

Electric cables. Thermosetting insulated and thermoplastic sheathed cables for voltages up to and including 450/750 V for electric power and lighting and having low emission of smoke and corrosive gases when affected by fire.

The BSI Standard BS 7211 defines the criteria for low smoke zero halogen (LSZH) cables employed across diverse applications such as power distribution, control systems, and communication networks. It covers cables with varying voltage ratings and purposes. This standard outlines the construction, materials, and performance characteristics of LSZH cables to ensure their safety and reliability in the event of a fire. It also stipulates requirements for flame propagation, smoke emission, and the acidity of gases generated during combustion.

BS 6724:2016

Electric cables. Thermosetting insulated, armoured cables of rated voltages of 600/1000 V and 1900/3300 V for fixed installations, having low emission of smoke and corrosive gases when affected by fire. Specification

BS 6724 is a British Standard on low voltage cables that specifies requirements for the construction and performance of thermosetting insulated, armoured cables of rated voltages of 600/1000 V and 1900/3300 V, having low emission of smoke and corrosive gases when affected by the fire. 

BS 6724 is applicable to cables for use in fixed installations in industrial areas, buildings, or similar applications. 

BS 7870 Series 

BS 7870 is a British Standard that is specifically to Low Smoke Zero Halogen (LSZH) cables used in power distribution and control applications. 

BS 7870-3.12

This section of BS 7870 specifies requirements for the construction, dimensions and mechanical and electrical properties of concentric copper wire combined neutral/earth (CNE) service cables having a rated voltage of 0.6/1 (1.2) kV. It is applicable to cables that, when assessed by the specified tests, produce lower levels of smoke and corrosive gases under exposure to fire than cables conforming to BS 7870-3.11.

BS 7870-3.22

This section of BS 7870 specifies requirements for the construction, dimensions and mechanical and electrical properties of split concentric service cables having a rated voltage of 0.6/1(1.2) kV. It is applicable to cables that, when assessed by the specified tests, produce lower levels of smoke and corrosive gases under exposure to fire than cables conforming to BS 7870-3.21.

BS 7870-3.50

This section of BS 7870 specifies requirements for the construction, dimensions, and mechanical and electrical properties of XLPE insulated, concentric copper wire screened waveform or helical cables with solid aluminium conductors having a rated voltage of 0.6/1 (1.2) kV. It is applicable to cables that, when assessed by the specified tests, produce lower levels of smoke and corrosive gases under exposure to fire than cables conforming to BS 7870-3.40.

BS 7870-4.20

6.35/11(12) kV three-core cables. Specifies an over sheath of one of the following compounds: Medium-density polyethylene (MDPE) compound type DMP 5 (Type A cables). Thermoplastic compound type DMZ 4 for cables having low emission of smoke and corrosive gases when affected by fire (Type B cables)

BS 7870-4.10

6.35/11(12) kV to 19/33(36) kV single-core cables. Specifies an over sheath of one of the following compounds: Medium-density polyethylene (MDPE) compound type DMP 5 (Type A cables). Thermoplastic compound type DMZ 4 for cables having low emission of smoke and corrosive gases when affected by fire (Type B cables)

BS 7870-8.5

LV and MV polymeric insulated cables for use by distribution and generation utilities. Specification for multicore and multipair cables for installation above and below ground – Single wire armoured and unarmoured multicore cables with copper conductors and non-halogenated sheath – Section 8.5 Single wire armoured and unarmoured multicore cables with copper conductors and non-halogenated sheath.

BS 7870-8.6

LV and MV polymeric insulated cables for use by distribution and generation utilities. Specification for multicore and multipair cables for installation above and below ground – Single wire or double steel tape armoured and non-halogenated sheathed multipair cable with copper conductors – Section 8.6 Single wire or double steel tape armoured and non-halogenated sheathed multipair cable with copper conductors.

BS 7835

Electric cables. Armoured cables with thermosetting insulation for rated voltages from 3.8/6.6 kV to 19/33 kV having low emission of smoke and corrosive gases when affected by fire. Requirements and test methods

This standard specifies the requirements and test methods for armoured electric cables with thermosetting insulation designed for rated voltages ranging from 3.8/6.6 kV to 19/33 kV. The cables covered by BS 7835:2007 are specifically engineered to emit low levels of smoke and corrosive gases when exposed to fire, thus enhancing safety in case of fire incidents.

BS EN 60332-1

Tests on electric and optical fibre cables under fire conditions – Test for vertical flame propagation for a single insulated wire or cable. Procedure for 1 kW pre-mixed flame

BS EN 60332-1 is a European standard for testing the flame propagation of single insulated wires and cables. It involves subjecting samples to a vertical flame test to assess their flammability. 

BS EN 60332-3

Tests on electric and optical fibre cables under fire conditions – Test for vertical flame spread of vertically mounted bunched wires or cables.

BS EN 60332-3 covers tests methods for the assessment of vertical flame spread of vertically mounted bunched wires or cables, electrical or optical, under defined conditions. 

The standard categorises cables from A to F based on their fire performance, with A being the highest resistance level. Compliance ensures cables are suitable for fire-sensitive applications like buildings and transportation systems, reducing the risk of fire spread and enhancing safety.

BS EN 61034-2

Measurement of smoke density of cables burning under defined conditions – Test procedure and requirements.

BS EN 61034 details a smoke density test conducted within a chamber measuring 3m x 3m x 3m, commonly known as the 3-metre cube test. This procedure involves monitoring the reduction in transmittance of a white light beam traveling from one side of the chamber to the other at a specified height, allowing the accumulation of smoke within the chamber to be measured. To achieve a classification as “low smoke,” cables typically need to maintain a minimum light transmittance of 60%.

BS EN 60754-1

Test on gases evolved during combustion of materials from cables – Determination of the halogen acid gas content.

EC 60754 outlines the procedure for measuring the quantity of halogen gas and acidity released during the combustion of LSZH cables. This standard plays a crucial role in evaluating the toxicity and corrosiveness of the gases emitted when the cable is subjected to fire. IEC 60754 mandates that for a cable to be classified as halogen-free, emissions of hydrogen chloride (HCl) by LSZH cables must not surpass 0.5%. This requirement underscores the commitment to minimizing the release of corrosive and harmful gases during fire incidents, further enhancing the safety and environmental sustainability of LSZH cable applications.

BS EN 60754-2

Test on gases evolved during combustion of materials from cables – Determination of acidity (by pH measurement) and conductivity.

This part of IEC 60754 specifies the apparatus and procedure for the determination of the potential corrosivity of gases evolved during the combustion of materials taken from electric or optical fibre cable constructions by measuring the acidity (pH) and conductivity of an aqueous solution resulting from the gases evolved during the combustion. The heating (combustion) procedure of this part of IEC 60754 is the same as in IEC 60754-3.

Compliance to these standards guarantees that LSZH cables do not emit harmful gases and do not facilitate the propagation of flames in the event of a fire, thereby enhancing their suitability for use in enclosed environments. When sourcing these cables for particular applications, it is important to verify their compliance with the applicable BSI and IEC standards to confirm that they meet essential safety and performance criteria.