We supply a comprehensive range of Low Smoke Zero Halogen (LSZH) cables for use in applications where smoke emission and toxic fumes could pose a risk to human health and essential equipment in the event of a fire.
The cables are also commonly referred to as ZHLS cables or halogen free cables. They often have flame retardant properties, making them flame retardant low smoke (FR-LS) cables.
Unlike PVC cables and those made of other compounds which produce vast amounts of dense black smoke, toxic fumes and acid gas when exposed to fire, LSZH cables produce very low levels of smoke and toxic fume and no acid gases. They are essentially halogen free cables. They are therefore often specified indoors, especially in public areas, and in other hazardous environments and poorly ventilated areas. This includes cars, aircraft, railway carriages and ships. LSZH sheathed cables are commonly used across tunnels and underground rail networks.
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 61034 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%.
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 60754 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.
LSZH cable selection
There have been many developments in relation to LSZH cable standards and legislation since the Kings Cross Station fire of November 1987 which resulted in 31 fatalities. Findings from the official investigation outlined that the majority of these deaths were as a result of toxic fumes, pointing to the vast quantities of PVC present in the building, much of which was in PVC cables. PVC cables were subsequently banned by London Underground.
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.
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