Low smoke zero halogen or low smoke free of halogen (LSZH or LSOH or LS0H or LSFH or OHLS) 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.


With the increased demand for safety in public areas and buildings, contractors are now being advised to install materials that are non-hazardous to members of the public in case of fire. Halogen-free cables are applicable in delicate areas as, for example, public buildings and institutions or railway vehicles and in areas where the general safety requirements for cables are very high.


What are halogens?

Halogens are non-metallic elements found in the periodic table. The five halogens are fluorine, chlorine, bromine, iodine, & astatine. A common material that contains halogens in the chemical structure is PVC. Halogens make cable jackets and insulation highly flame retardant. Some naturally non-halogenated materials have halogen added because of the flame retardant properties. When burned, halogens emit a thick toxic smoke and become corrosive. These characteristics can cause damage to equipment and pose a safety concern.

Why consider halogen-free cable?

Over the last few years, halogen-free wire and cabling products have seen an increase in popularity. Halogen-free cables are used in consideration of issues including fire safety, fire damage prevention, and the environment. Halogen-free cables help eliminate the use of environmentally sensitive materials

What does LSZH mean?

LSZH stands for low smoke zero halogen. The compounds in the cable insulation and jacket have no fluorine, chlorine, bromine, iodine, or astatine. This means that the cable emits little to no toxic halogens and minimal smoke when in contact with fire. These are important safety precautions and they often appear together in wire and cable specifications. LSZH wire and cable is also called: low smoke non halogen (LSNH), low smoke halogen free (LSHF), and low smoke zero (0) halogen (LS0H).

In what applications can halogen-free cable be used?

Halogen-free cable is intended for use in applications in which insulation with low toxicity, low smoke generation, and low corrosiveness is needed. Examples include rapid transit, industrial, shipboard, and commercial fields where human safety and protection of equipment is a concern.

Is there a difference between low smoke and zero halogen?

Low smoke and zero halogen are not equivalent. Low smoke cable emits a thinner and clearer smoke when burning. This feature makes evacuation and firefighting efforts much easier and safer. A cable may be low smoke and still contain toxic halogens. Zero halogen means that the cable does not contain fluorine, chlorine, bromine, iodine or astatine. Zero halogen cable may still emit a thick smoke when burned. Both properties are not always needed for all cables. Check specifications to be sure that the cable meets both requirements if necessary for your application.

Are there any disadvantages to using low smoke zero halogen cables?

Low smoke zero halogen cables provide a lot of great safety advantages, but there is a bit of an electrical and mechanical trade-off. In order to be low smoke zero halogen, the cable jacket must incorporate a high percentage of filler material. This increase in filler material could make the jacket less chemical and water resistant and could provide poorer mechanical and electrical properties than a non-LSZH counterpart. LSZH jackets are also more likely to experience jacket cracking during installation, so special lubricants may be necessary to avoid damage. This is especially true in cold environments. Because of the limited flexibility of LSZH, it is not recommended in robotic or continuous flex applications. As a result, LSZH cable is commonly chosen for applications where fire safety is more of a concern than the cable’s specific electrical and mechanical properties. Advances in compound materials and processing have decreased some of these issues.

Can LSZH pass a flame test?

Yes. LSZH may pass a standard flame test. To determine how an LSZH cable will react in a fire, the following five criteria are considered:

  • How easily the cable will catch fire
  • How quickly the fire will spread along the cable
  • How much smoke is produced upon combustion
  • How toxic are the byproducts
  • How corrosive are the byproducts

What should be considered when choosing LSZH?

When choosing LSZH products, factors such as the environment and price should be considered. An environmental factor such as the temperature of the installation could reduce the flexibility of the cable. Will the application be in an open area or confined? Will other flammable material be present? Low smoke zero halogen cable also tends to be higher in cost. Consult an expert from Allied Wire and Cable to find the best fit for your application.