LSZH Cable | Low Smoke Zero Halogen Cables

The "Low Smoke" element of LSZH cables

According to Part B of The Building Regulations, a leading planning and building regulations resource for England and Wales:

"The primary danger associated with fire in its early stages is not flame but the smoke and noxious gases produced by the fire. They cause most of the casualties and may also obscure the way to escape routes and exits. Measures designed to provide safe means of escape must therefore provide appropriate arrangements to limit the rapid spread of smoke and fumes."

Burning PVC has been found in tests to reduce visibility in the surrounding area by as much as 50% within 10 minutes. After 30 minutes, visibility can be reduced by as 90% making it unnecessarily challenging to escape the area.

By comparison, BS EN specifies a smoke density test, performed inside a chamber 3m x 3m x 3m. The test is often referred to as the 3 metre cube test. By monitoring the transmittance reduction of a white light beam running from one side of the chamber to the other at a set height, the build-up of smoke inside the chamber can be measured. For a cable to be classified as low smoke it will often have a minimum light transmittance of 60%. 

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The "Zero Halogen" element of LSZH cables

Burning PVC and other cable compounds produce a number of chemicals, including hydrogen chloride (HCl), which is highly toxic. Furthermore, when mixed with water, HCl forms hydrochloric acid; a substance which is both toxic and corrosive. In the case of PVC, as much as 30% of the emissions can be HCl.

BS EN stipulates that emissions of HCl by LSZH cables must not exceed 0.5%.

LSZH vs LSF cables

Whilst there is a common misconception that low smoke and fume (LSF) cables and LSZH cables are the same, this is not the case and any confusion between the two could be life-threatening in the event of a fire.

Unlike LSZH cables, LSF cables are manufactured using PVC compounds. If they are labelled as low smoke and fume cables it is due to the manufacturer modifying the compound with various additive in order to reduce (not eliminate) smoke and HCl emissions. However, where low smoke zero halogen cables are subject to strict standards, there are no standards governing LSF cables. As a result, LSF cables have been found to emit HCl levels in excess of 20% when burning.

As a leading rail & metro cable supplier, Eland Cables is well-positioned to understand the implications involved when selecting an LSZH cable for use in any other industry. Please contact our technical team to discuss your specific requirements and our comprehensive range of LSZH cables for all applications, including building & construction, oil & gas, and marine & offshore.

• Family: Thermoplastic
• Use: Sheathing on LSZH cables

General characteristics

The relatively modern development in cables has seen the requirement for fire performance become increasingly important. This has seen requirements for low smoke emission, low corrosivity when burnt, flame retardance and reduced propagation become clearly specified and increasingly specified in many areas of cable installation. This has removed halogenated compounds from many markets to be replaced by LSZH &#; low smoke, zero halogen &#; types. This has dramatically reduced the amounts of PVC and chlorinated rubbers used to be replaced by newly developed LSZH materials.

For more information, please visit lszh compound.

The thermoplastic versions of these compounds are generally based on polyolefins of some sort with relatively high loadings of active fillers, the commonest being hydrated alumina. Compounding technology can be quite complicated, depending on the application. Many compounds use EVA as the base polymer. EVA is a copolymer of ethylene and vinyl acetate, with VA contents being from single-figure percentages to 70% and 80%. The lower percentages are essentially modified polyethylene, and as the VA content increases, so does the softness and the resistance to fluids improves. Other copolymers are often blended with EVA. 

Processing

Thermoplastic LSZH is usually compounded with carefully selected fillers, colouring pigments and processing aids using standard compounding practice. 

Extrusion is usually with single screw extruders, generally with low compression screws.

Good process control is necessary to succeed with these materials.

Uses of material / LSZHCable types

LSZH materials are usually used in applications where PVC would historically have been used, such as armoured cables, and in newer applications such as fire alarm and emergency lighting cables.

Standards

• IEC &#; series
• IEC &#; series
• IEC -1 and IEC -2
• BS EN &#; series
• BS
• BS
• BS
• BS
• BS

List of Polymeric materials for cables used: