ZHLS cables or halogen-free cables. They are typically flame retardant, making them flame retardant low smoke (FR-LS) cables.
Unlike PVC cables and cables made from other compounds that produce large amounts of dense black smoke, toxic fumes and acidic gases when exposed to fire, LSZH cables produce very low levels of smoke and toxic fumes and do not produce acidic gases. They are essentially halogen-free cables. For this reason, they are often specified indoors, especially in public areas, and in other hazardous environments and poorly ventilated areas. This includes automobiles, aircraft, railroad cars and ships. Low smoke halogen-free sheathed cables are commonly used in tunnels and underground railroad networks.
The "zero halogen" element of low smoke and halogen-free cables
Burning PVC and other cable compounds produces many chemicals, including the highly toxic hydrogen chloride (HCl). In addition, when mixed with water, HCl forms hydrochloric acid; a substance that is both toxic and corrosive. In the case of PVC, up to 30% of the emissions may be HCl.
BS EN 60754 stipulates that HCl emissions from LSZH cables must not exceed 0.5%.
LSZH vs. LSF cables
Although it is commonly believed that low smoke and smoke free (LSF) cables and LSZH cables are the same, this is not the case and any confusion between the two can be life threatening in the event of a fire.
Unlike LSZH cables, LSF cables are manufactured using a PVC compound. If they are labeled as low smoke and low smoke cables, it is because the manufacturer has modified the compound with various additives to reduce (not eliminate) smoke and HCl emissions. However, there are no standards governing LSF cables when low smoke and zero halogen cables are subject to strict standards. As a result, LSF cables were found to emit on combustion HCl
What is low smoke and halogen free cable?
Low smoke and halogen free cables/wires are cables where the cable jacket and insulation are made of materials that produce low/limited smoke and non-toxic halogens when exposed to fire or high temperatures. There are also low smoke cables and zero halogen cables/halogen free cables.
Benefits of low smoke and halogen free cables
Use low smoke zero halogen cables when fire safety is critical, especially in enclosed spaces. Multiple fires at transportation facilities and other locations have led to the development of low smoke zero halogen cables. In these emergency fire situations, low smoke factors help maintain visibility and reduce damage to the respiratory system, while zero-halogen materials reduce the production of toxic halogenated gases.
What is halogen-free cable?
Halogen-free cables/wires, also known as zero-halogen cables, are cables whose sheathing and insulation are made of materials that do not produce toxic halogens when exposed to fire or high temperatures. These halogen-free cables are used in situations where smoke is a minimal consideration. Halogen-free cables also do not use materials that may have an impact on the environment.
What is low smoke cable?
Low smoke cables/wires, also known as smoke limited cables, are cables whose sheathing and insulation are made of materials that produce no or only a small amount of smoke when exposed to fire or high temperatures. These low smoke cables are used when halogen considerations are minimal.
Low smoke and halogen free applications
Because of their low smoke and toxicity benefits, LSZH cables are often selected for a variety of applications. These include.
Rail and subway stations and cars, bus and bus stations, aircraft and airports, other public transportation facilities
Any public underground or poorly ventilated areas
Public recreational and sports facilities
Apartment buildings and hotels
LSZH insulation and jacketing can be used to manufacture virtually any type of cable, including but not limited to
Power and data cables
Video and broadcast cables
In some locations, there are regulations requiring the use of Low Smoke Zero Halogen (LSZH) wire/cable. Local codes should be checked to see if LSZH wire is required.
What are halogens and why are they dangerous?
Halogens are a group of highly reactive elements that include fluorine, chlorine, bromine, iodine and astatine. When products containing halogens burn, they produce very dangerous gases. The public became aware of these dangers after several tragic fires claimed the lives of victims who inhaled deadly halogenated fumes.
Why is zero halogen better?
Two halogens - chlorine and fluorine - are widely used in the compounds that insulate and jacket wire and cable. Many common materials, for example, PVC contains 29% chlorine by weight; CPE 19% chlorine by weight; and Teflon 76% fluorine by weight.
Halogenated compounds are generally very stable. However, when they burn, the halogens separate and become highly reactive, forming highly toxic, extremely dangerous and corrosive gases that can severely damage organic, inorganic and metallic materials. For example, burning PVC produces hydrochlorine gas similar to mustard gas.
As the name implies, an armoured cable has added protective armour that helps protect the cable core. This is important in places where there could be accidental damage to the cable due to mechanical stress or impact.
With the rapid development of optical communication, more and more fiber optic cables are increasingly used in different environments. What if under harsh conditions? Then it's crucial to ensure your cables smooth and reliable operation when transmitting data. This is where armoured cable comes into play.
There is a growing trend toward the use of Low Smoke Zero Halogen (LSZH) cables, which use sheathing materials that are safer when exposed to fire.
As the name implies, unlike conventional materials such as polyvinyl chloride (PVC) and fluorinated ethylene propylene (FEP), they produce a lower density of smoke and produce little of the highly toxic gas known as halogen.
It seems logical that designers should always choose these cables, but the decision is much more complex, so electrical engineers must understand LSZH cables, where they are suitable, and how to select and apply them.
Although cables made with halogenated compounds such as PVC and FEP are considered dangerous in a fire, low smoke and halogen-free cables are not a universal solution to replace them for several reasons.
First, PVC- and FEP-based cables have important advantages that cannot be ignored, and there may be little benefit in replacing them with LSZH cables in open spaces where smoke and gases can dissipate quickly.
In addition, cables are rarely the only source of plastic in the event of a fire, and because PVC- and FEP-based cables are fire-resistant, their contribution to the fire is relatively small.
They are also very flexible, long-lasting, resistant to extreme temperatures and chemicals, and very rugged. In short, low smoke and halogen-free cables are best suited for scenarios where conventional cables can be hazardous.