Low smoke zero halogen, or LSZH, refers to using compounds in the cable jacketing manufacturing process that are halogen free. Materials that contain halogens emit potentially harmful gases when burned. Halogen free cable, on the other hand, is made up of a compound called polypropylene, which will not produce a toxic smoke during combustion.
Halogens are found in many common jacketing compounds such as polyvinyl chloride (PVC) and ethylene propylene (FEP). Although both of these compounds contain halogens, they are still widely used in the USA. The main reason these halogen containing cable products are still being installed today is because the use of halogens does allow for superior flame retardancy and they are cost effective.
A low smoke zero halogen cable construction is many times required or preferred. A few examples would be in hospitals, subways, airports and other crowded spaces. They are also preferred in environments with poor ventilation such as a coal mine shaft. They not only reduce smoke, but also acid gas, which reduces toxicity and corrosive effects on both people and equipment.
There is growing debate that halogen containing compounds are hurting the environment and ozone layer. Europe extensively uses LSZH in cable applications due to this believed side effect of halogen containing plastics. However, many argue thermoplastics, such as PVC, are still a better option in many applications. For example, PVC is much more resistant to oils than a halogen free cable making it a better option in those applications. PVC is also more widely manufactured and cost effective.
Various manufactures create LSZH products for virtually any application including power cables, tray cables. thermocouples, fiber and armored versions. As with any application, all factors should be considered when deciding between a low smoke zero halogen product or one that uses halogens. When peoples safety is an issue or critical circuit integrity, the answer the vast majority of time is to install a LSZH product. However, installing PVC or other halogen containing compounds can be the cost effective and prudent decision in many applications where these factors are not an issue.