Low Smoke Zero Halogen (LSZH) cables, also commonly referred to as ZHLS, 0HLS or halogen-free flame retardant (HFFR) cables, are manufactured for use in applications where the smoke and toxic fumes associated with PE and PVC cables could be harmful to people or sensitive equipment during a fire.
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A shift in safety regulations across Europe has led to LSZH cables becoming increasingly favoured for specific settings. Let's take a closer look at why this is happening, how these cables work and the standards you need to be aware of when selecting an LSZH cable for your project.
In a fire, a cables outer sheathing will begin to combust. When exposed to a flame, cables made of PVC compounds will produce vast amounts of dense black smoke, toxic fumes and acid gases. In poorly ventilated or underground spaces where escape routes might be obstructed by smoke, these fumes can become fatal.
LSZH cables are made of a flame retardant outer covering, meaning that their primary decomposition product will absorb the energy from the flame, diluting the fire gases. This causes a charring which acts as a fire barrier, so less smoke and chemicals are released when the cable is burned.
Prompted by several major fire disasters, developments in LSZH legislation have been in motion for many years. The official investigation into the Kings Cross Station fire of confirmed that the majority of the disasters 31 fatalities were a result of PVC-related toxic fumes. A similar outcome was determined of the Dusseldorf airport fire, in which 27 deaths occurred.
As a result of these incidents, the use of PVC cables has been restricted across several European countries. Ireland, for example, has made the use of LSZH cables mandatory, linking to the Construction Products Regulations (CPR). Meanwhile, countries such as Switzerland, The Netherlands, Germany and Greece have made LSZH a legal requirement in high-risk environments such as evacuation routes and/or high-rise buildings.
Whilst most cable types will now be available with LSZH sheathing, each installation must be considered on its own merits. In order to offer low smoke, zero halogen properties, the jacket of an LSZH cable uses a high percentage of flame retardant additives (fillers). This can impact properties such as flexibility, chemical and water resistance so bear this in mind when weighing up the needs of your project.
For a cable to be verified as LSZH, it must undergo a series of performance and compliance tests to ensure it meets European and international standards. Here are some of the key standards and testing procedures that cable buyers should seek to confirm their cables are in compliance with.
IEC/EN -1/2 specifies a smoke density test performed inside a 3-cubic metre chamber. While burning PVC has been found in testing to reduce light visibility to 10% (i.e, the thickness of the smoke obscures overall vision by 90%), certified low-smoke cables will have a minimum light transmittance of 60%. In the event of a fire in an enclosed space, this ensures that escape routes remain unobstructed and in reasonably clear view.
IEC/EN -1 stipulates that emissions of the highly toxic, acid gas hydrogen chloride (HCI) by LSZH cables must not exceed 0.5%. When PVC is burned, as much as 30% of emissions released can be HCl. To certify a cable as LSZH, a testing process sees 1g+/-0.005g of cable insulation material placed in a tube furnace and heated to 935ºC for 30 minutes. The gases produced are absorbed into a catch solution, which is then made up into a litre of liquid.
Following a similar process, IEC -2 measures the pH of the solution and tests its conductivity values. Low Smoke Zero Halogen materials are defined as having a pH no less than 4.3 and a conductivity not exceeding 10µS/mm.
N2XH cables in both Class 2 and Enhanced Flex Class 5 variants are low voltage 0.6/1kV low-smoke, zero halogen power cables with a flame-retardant, non-corrosive FRNC outer sheath to reduce fire propagation risk and protect sensitive equipment. These cables are available with CPR classifications suitable even for installations designated high-risk. Manufactured to IEC -1. Eland Cables holds the largest stockholding of N2XH cables in Europe, making them available on-demand for projects.
N2XSH & NA2XSH European Medium Voltage LSZH power cables in 6/10kV, 12/20kV and 18/30kV have either copper or aluminium conductors and are also available with additional waterblocking layers. Manufactured to IEC -2 and available direct from stock.
BS & BS AWA single core and SWA multicore LSZH armoured cables (0.6/1kV and 6.35/11kV / 19/33kV respectively) providing additional mechanical protection for buried installations, to British standards. Available from stock for next-day delivery
EN -7 RE-2X(st)H LSZH instrumentation cables to the European standard, available with collective screening or with PimF (pairs in metal foil) individual screening. Available from stock across a large range of sizes.
As a market-leading supplier with a comprehensive range of cables for power, data & control applications, Eland Cables are well-positioned to understand the importance of selecting the correct LSZH cable for your project.
We're committed to assuring product quality and compliance for each and every one of our LSZH cables. Rigorous testing is undertaken in The Cable Lab, our globally recognised facility holding IEC/ISO and IECEE CBTL, including IEC -1 and IEC -2 for halogen gas emissions testing and gas acidity testing, as well as vertical flame testing to IEC -1-2 to assure self-extinguishing properties meet the parameters of the standard.
To discuss your specific requirements, get in touch with one of our experts today.
Low Smoke Zero Halogen or LSZH is a common term youll come across when buying or working with cables.
Its not merely a definition of materials or characteristic of cable, but a highly important distinction, which could ultimately mean the difference between life and death.
LSZH cables are also sometimes referred to as ZHLH or simply halogen-free cables.
This definition of the cable basically helps determine the materials that go into the insulation and sheathing of the cable.
Any materials that are not classified as LSZH do not make the cut.
Countries and industries across the world have strict standards for cable materials, and LSZH is becoming increasingly popular because of the safety these cables offer.
Low Smoke Zero Halogen or LSZH cables are those that dont contain any halogens in their material composition and dont produce smoke in case of fire.
These cables produce a very limited amount of smoke and toxic gases, especially acid gases.
These cables are good for use indoors and in hazardous environments where the threat of fire and harmful gases may be high.
They are essentially fire-retardant cables, too, as they self-extinguish.
However, they are not completely fire-resistant, which means they can burn and bear damage if the fire from the source is continuous.
Low smoke and zero halogen are two separate elements.
So its important to understand them individually.
Low smoke pertains to the cable jacket producing limited smoke.
It doesnt mean that it wont burn or not produce any smoke at all.
It only means that the smoke wouldnt be of dangerously high levels to become toxic, reduce visibility, and hamper rescue efforts.
This is entirely dependent on the jacketing material in the cable, as the sheath is the first layer to come in contact with fire.
In most cases, the flame isnt as dangerous as the smoke and gas it produces.
In indoor settings, most casualties in fire may be caused because of the smoke because it creates respiratory difficulties, reduces the visibility of exit routes, and creates panic.
For instance, tests show that PVC (polyvinyl chloride) can reduce visibility by as much as 50 percent when burning. In half an hour, it can become as high as 90 percent.
This makes PVC high-smoke material; however, there are low-smoke versions of it with appropriate additives.
Many international standardization and certification bodies have specific tests and benchmarks to gauge the smoke emission of materials.
Cables must pass those tests to qualify as low smoke cables.
Zero halogen simply means that no component, primarily insulation and sheathing, should have any halogens in their composition.
Halogens consist of five elements, including Chlorine (Cl), Bromine (Br), Iodine (I), Florine (F), and Astatine (At).
The reason why halogens are emitted from cables is that when the cable is on fire, these can produce toxic gases or liquids, such as highly acidic HCl.
The best example of a material thats not zero halogens is PVC, as it contains Chlorine.
Tests show that PVC can produce as much as 30 percent HCl in case of a fire.
Some cables are labeled as LSF (low smoke and fume), which is different from LSZH.
It only covers part of the equation, as LSF cables might still have halogens in their materials.
For instance, PVC cables that are low smoke are LSF but not LSZH.
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Those cables still pose the threat of halogen gases when burning.
Usually, LSF cables have additives to help make them low smoke and low halogen, but they are not zero halogens.
LSZH cables usually follow even stricter standards than LSF cables.
LSF cables can emit halogen acids far beyond the limits set for LSZH cables.
There are two kinds of LSZH materials essentially: thermoplastic LSZH and thermoset LSZH.
Thermoplastic LSZH materials can be molded by heating many times, whereas thermoset LSZH materials can only be molded once.
Hence, they are not recyclable.
While PVC is the most common thermoplastic, its not an LSZH, as it contains Chlorine.
On the other hand, ethylene-propylene rubber (EPR) and crosslinked propylene (XLPE) are LSZH.
These two materials are very common in cables along with PVC.
Its worth noting that LSZH thermoset materials may not have as high resistance to flames as chlorinated thermosets.
This is one tradeoff when using LSZH cables, as their thermal range may be slightly lower than those with halogens.
That said, crosslinked materials such as XLPE have a much higher thermal range.
The LSZH material you choose comes down to other factors as well, such as voltage rating of the conductor, environmental conditions, and application-specific requirements.
However, the material must meet the set requirements and tests.
LSZH cables are used both indoors and outdoors, but mostly indoors where its usually hard for the smoke to escape.
Just by that requirement, the applications of such cables are many.
Here are some examples:
LSZH cables may be used in any place where the laws and regulations require cables to use LSZH materials.
Many countries and city governments, as well as safety boards, mandate that contractors and construction companies use such cables for all indoor wiring.
This is why LSZH is becoming a standard for indoor cable applications.
There are obvious advantages to using LSZH cables:
There isnt any universal definition or standard when it comes to LSZH cables.
However, most international standardization bodies have tests and standards for cable manufacturers to comply with in order to certify their cables as LSZH.
Manufacturers must test the cables according to the test describes by those standards.
For instance, the standard BS prescribes a test for smoke density.
The test is performed in a 3 x 3 x 3 cubic meter chamber.
A white light is passed through the chamber at a particular height so as to measure how the smoke hinders the transmittance of light.
The test requires the minimum transmittance to be 60 percent.
Similarly, another British cable standard BS EN requires HCl emissions from the cable to be under 0.5 percent for it to quality as zero-halogen.
International Electrotechnical Commission (IEC) has its own set of standards and tests for qualifying cables as LSZH.
Here are the three most frequently used standards in the cabling industry:
The IEC -1 test for flammability is similar to that of BS , which involves a 3 cubic meter chamber and light transmittance.
The IEC -1 test involves burning the cable for 60 minutes and collecting any halogen acid produced.
It should not exceed 5 mg/g.
The second part, IEC -2, measures conductivity and pH.
The pH value should not be less than 4.3 and the conductivity value should not exceed 10 uS/mm.
LSZH cables also comply with the European Union (EU) Restriction of Hazardous Substances (RoHS) directive.
Other standardization bodies around the world may have similar tests for cables to qualify as LSZH.
The cables are not officially LSZH unless they meet the standards set by one of these bodies.
LSZH cable plays a vital role in ensuring the safety of infrastructure and human life.
While they are not immune to fire, they can reduce the danger.
Low smoke and no risk of acidic gases and fluids make these cables a safer option for indoor cabling.
There are strict standards for such cables, especially on marine shipboard, that must be fulfilled for the cable to be labeled LSZH.
The cable manufacturers must comply with those specific standards for the market they are serving.
As for the cable type and materials, that depends on the application they are for.
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