LSZH Cable | Low Smoke Zero Halogen ...

The "Low Smoke" element of LSZH cables

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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The "Zero Halogen" element of LSZH cables

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%.

LSZH vs LSF cables

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.

Many industries have seen an increasing demand for Low Smoke Zero Halogen (LSZH) cables. Main driver of this increase is the concerns for the safety of people and electronic circuits during fire. Environmental protection and an increase in requirements / specifications from local and international communities has also heightened the demand for LSZH cables.

This increased awareness of negative side effects arising from halogen when exposed to flames has lead to this jacket type being designed.

We answer some of the more frequently asked questions surrounding this cable type.

What is LSZH?

LSZH stands for Low Smoke Zero Halogen. It refers to a group of jacket and insulation compounds that do not contain halogens within their chemical makeup.  The terms LSOH, HFFR (Halogen Free Fire Retardant) and NHFR (Non Halogenated Fire Retardant) are often used interchangeably.

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What are Halogens?

Halogens are a group of elements that are characterized by being 1 electron short of forming a stable molecule, as a result they are highly reactive and will combine with other elements in order to gain this missing electron.

Halogens react with metals to form salts, common table salt is a mixture of the halogen chlorine and the metal sodium. When mixed with water, free hydrogen in water will combine with halogens to make acids. One of the most common acids being Hydrochloric acid which is a mixture of hydrogen and chlorine.

Halogens can also mix with hydrogen (present in water) to create an acid. Hydrochloric acid used to acid etch concrete is a mixture of hydrogen and chlorine.

Why are Halogens used for flame retardancy?

Within some polymers, the introduction of a Halogen atom can produce a flame retardant capability. Poly-Vinyl-Chloride (PVC) is a common example and contains chlorine. When burned the chlorine is released and displaces oxygen from the flame thus helping to smother out the fire.

Some flame retardant polyethylenes have bromine, another halogen, added in order to assist with flame retardancy.

What are the Side effects of Halogen when exposed to flames?

When combined with Hydrogen, Halogens form acids. These acids are toxic to animals and plants. Chlorine is an example where this characteristic is used in a controlled way to sterilize water by killing off microbes and bacteria. In the past solutions based on the halogen iodine where also used for this application.

What about PVC?

When PVC burns, it releases Chlorine which is now free to combine with hydrogen to form an acid. This acid can burn lungs and eyes of people trying to flee the fire. It can also attack equipment that was not destroyed in the fire. Historical experience has shown that equipment located several rooms or floors away from a small fire can fail many months later due to attack by either halogen acids or salts.

What are the benefits of having LSZH cable?

LSZH compounds contain no halogens and instead rely on releasing water or other non-toxic compounds in order to put out a flame. As a result, they are safer for both people and the environment.

Where are LSZH cables predominantly used?

LSZH cables can be used anywhere a normal cable can be used. Typically they are of greater benefit in indoor or restricted spaces where their low toxicity in a fire is a great benefit. This means that they often find use in tunnels, offices, exchanges and datacentres.

Can I still achieve my Green Star credits with LSZH?

Yes, LSZH cables are suitable for Green Star applications.

LSZH cabling is the safest choice for plenum use and any other applications in which smoke is likely to both build up and come into contact with people, since no harmful toxins are actually released. In line with our commitment to sustainability and reducing their impact on the earth, Garland is now pleased to offer Low Smoke Zero Halogen cables as an extension to their environmentally friendly Green Star rated range.