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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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%.
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.
Low smoke zero halogen or low smoke-free of halogen (LSZH or LSOH or LS0H or LSFH or OHLS or ZHFR) is a material classification typically used for cable jacketing in the wire and cable industry. LSZH cable jacketing is composed of thermoplastic or thermoset compounds that emit limited smoke and no halogen when exposed to high sources of heat.
Low-smoke zero-halogen cable considerably reduces the amount of toxic and corrosive gas emitted during combustion. When burned, a low-smoke zero-halogen cable emits a less optically dense smoke that releases at a lower rate. During a fire, a low-smoke cable is desirable because it reduces the amount and density of the smoke, which makes exiting a space easier for occupants as well as increases the safety of firefighting operations.
This type of material is typically used in poorly ventilated areas such as aircraft, rail carriages, tanks, subsea and offshore installations, submarines or ships. It is also used extensively in the rail industry, wherever high voltage or track signal wires must be run into and through tunnel systems. The nuclear industry is another area where LSZH cables have been and will be used in the future. Major cable manufacturers have been producing LSZH cables for nuclear facilities since the early s. Construction of new nuclear plants will almost certainly involve extensive use of LSZH cable. This will reduce the chance of toxic gases accumulating in those areas where personnel are working and the lack of corrosive gases where there are computer-controlled systems will reduce the possibility of wires being damaged by fire resulting in a short circuit fault.
PVC is a very versatile and cost-effective material. Its main properties and benefits include:
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1. Low Smoke Generation: LSZH cables produce less smoke when burning in a fire, which improves visibility and enhances evacuation safety. This is particularly important in confined spaces like aircraft, trains, and tunnels.
2. Low Toxicity: LSZH cables do not release toxic halogen gases, such as chlorine, fluorine, and bromine, during combustion, significantly reducing the risk of personnel inhaling toxic fumes.
3. Low Corrosivity: LSZH cables do not produce corrosive gases when burned, which helps to protect sensitive electronic equipment and instruments from corrosion.
4. Improved Safety: The safety features of LSZH cables enhance overall fire safety, facilitating emergency evacuation and firefighting operations.
5. Environmentally Friendly: LSZH cables are free of halogenated and other harmful chemicals, making them more environmentally sustainable.
6. Broad Application: LSZH cables are widely used in industries with strict fire and environmental safety requirements, such as aerospace, rail transportation, subsea and offshore facilities, and nuclear power plants.
Physically, PVC and LSZH are very different. PVC cables are very soft; LSZH cables are more rigid because they contain the flame-retardant compound, and they are aesthetically more pleasing.
A PVC cable (made of polyvinyl chloride) has a jacket that gives off heavy black smoke, hydrochloric acid, and other toxic gases when it burns. Low Smoke Zero Halogen (LSZH) cable has a flame-resistant jacket that doesn't emit toxic fumes even if it burns.
LSZH cables usually cost more than the equivalent PVC cable, and certain types are less flexible. LSZH cable does have some restrictions. According to CENELEC standards EN, , , screened cables must be halogen-free. However, no similar regulation yet applies to unscreened cables.
PVC cable is commonly used for horizontal runs from the cabling center. You can use it for vertical runs between the floors - but only if the building features a contained ventilation system running through the ductwork. LSZH cable is used between floors in a building. It has a special flame-retardant coating.