Benefits of Low Smoke Zero Halogen Cables

Low smoke zero halogen cables are made with a special thermoplastic jacket. The use of thermoplastic or thermosetting compounds makes this type of insulation exceptionally flame retardant. Low Smoke Zero Halogen materials are most often used when both fire safety and reliability are critical. Low smoke zero halogen Cables are ideal for confined spaces where poor ventilation could be a serious concern.  HFFR or halogen-free flame-retardant cables, are cables with special ethylene copolymer blends for jacketing, which provide similar safety benefits as LSZH.  For the purposes of this article, we will equate LSZH with HFFR materials.

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‘Low smoke’ features

In dense urban areas with tunnels full of cable wiring, fire can pose a significant risk according to Science Direct. It is a well-known fact that the most dangerous component of a fire in its early stages is not the flame but the smoke. In areas with limited ventilation, rapid accumulation of smoke can quickly lead to casualties. Even if ventilating systems are present, heavy smoke greatly diminishes visibility and can conceal exits and escape routes.

Low smoke zero halogen Cable is a low-smoke jacketing material that produces little to no smoke when exposed to fires. It is composed of thermoplastic compounds that give off no or minimal amounts of white smoke when exposed to high temperatures. Cables made with low smoke zero halogen compounds offer excellent physical and electrical insulation, along with superior flame retardant properties.

‘Zero halogen’ features

The burning of common jacketing materials produces high amounts of toxic and/or corrosive gases. Most standard cables have halogens such as chlorine, bromine, and iodine in their jacketing. When this sheathing material burns, it produces toxic chemical gases that are dangerous to your health and can cause suffocation. These noxious gases can also combine with water, such as the extinguishing water used by firefighters or moisture within a person’s airways, to form corrosive acids. Inhaling these toxic fumes can cause permanent damage to the throat and lungs and lead to complex respiratory problems.

On the other hand, Low smoke zero halogen cables do not contain halogens in their jacketing and therefore produce significantly lower amounts of harmful gases and chemicals when burning. While some gases are still released when the sheathing material is exposed to high temperatures, these are not toxic and do not produce corrosive fumes. Another benefit is that LSZH cables are composed of materials that are environmentally safe.

The difference between PVC and LSZH cables

PVC (polyvinylchloride) jacketed cables are modified with plasticizers to add certain features and characteristics.  While PVC generally has very good flame retardancy, it can still emit smoke and toxic gases upon burning.  Because of the lack of standardization, there are variations in the fire retardation properties of PVC cables. Different manufacturers use a range of different additives or a combination of them to lower costs while meeting the installation requirements.

Low smoke zero halogen cables, as the name suggests, produce little to no smoke or toxic gases when exposed to heat or flames. LSZH jacketing materials also go through a robust battery of tests before they are approved for industrial or commercial use. These tests evaluate characteristics including electrical properties, flame propagation, smoke measurement, and halogen content measurement.

Additionally, cables made with low smoke zero halogen compounds are physically quite different from PVC cables. The presence of these compounds in the sheathing makes LSZH cables more rigid, whereas PVC cables are typically softer.

Improved fire safety with LSZH Cables

Low smoke zero halogen Cables are particularly suited for use in confined spaces where people or sensitive electronic equipment are present. The classical examples of such spaces are submarines, aircrafts, tanks, and rail carriages, which is why the military was one of the first groups to take up the widespread use of LSZH cables. In addition to being the standard practice for cabling in the armed services, LSZH cables are also in demand for central offices and other sites with extensive cabling needs.

Low smoke zero halogen Cables do not emit toxic gases and maintain visibility even in restricted spaces. They also ensure smooth functioning of electrical devices that may be susceptible to damage from corrosive gases and fumes. Moreover, LSZH cables are self-extinguishing and inhibit the spread of flames to a larger area.

Specifications

• Better tensile strength (greater than 1.2Kgf / mm2)
• Improved resistance to weathering (~30° C to 105° C)
• Enhanced softness (80-90 hardness)
• Non-shifting (no moving morphic)
• High-volume resistivity (greater than Ω / cm3)
• Responds well to high voltages (up to 15 kV)
• Good elasticity and adhesion

The tests measuring these specifications are conducted under laboratory conditions. The particular values may not be replicated in commercial installations because of external factors.

It is also possible to order custom-made cables that improve on one or more of these properties based on project requirements.

LSZH cable applications

LSZH cabling is routinely used in places with limited ventilation, a high concentration of personnel, or low air density. Mass transit facilities and underground tunnel systems also necessitate the use of LSZH cables. Low smoke zero halogen Cables are routinely used in Europe, but their adoption in the U.S. has been slower due to stringent regulations. Locations that benefit the most from the installation of LSZH cables include:

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• High-rise buildings
• Hospitals
• ‌Server/data centers
• Communication and broadcast facilities
• Public underground settings
• Nuclear power stations
• Oil platforms
• Aerospace, railroad, and maritime applications

LSZH jacketing can be used to fabricate nearly any type of cable or wiring. Cables that use LSZH insulation and sheathing most frequently include:

• Instrumentation cables
• Broadcast audio/video cables
• Power and data cables
• Transportation cables
• Automation cables
• Communication/Ethernet cables
• Security and alarm control cables

Another issue with jacketing materials is the abundance of insulating compounds available. Low-smoke insulation could produce toxic halogens, and zero-halogen insulation could give off heavy smoke on burning. LSZH cabling is, therefore, the most sensible option for applications where both safety and performance are important.

Remee provides standard and custom cables to deliver specialized products that fit your particular needs. We offer LSZH jacketing solutions for a wide range of cables. Being one of the top wire and cable manufacturers in the country, we offer multiple configurations, composite constructions, and a variety of shielding and jacket coloring/striping options for our cables.

Material classification for cable jacketing

Low smoke zero halogen or low smoke free of halogen (LSZH or LSOH or LS0H or LSFH or OHLS or ZHFR) 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.[1]

In the industry, it has many names, summarized in the following table:[2]

LSZH Conduit Industy Abbreviations List Abbreviations Meaning LSZH Low smoke, zero halogen LSF Low smoke, fume LSOH (LS0H) Low smoke, zero (0) halogen LSHF(LSFH) Low smoke, halogen-free(free halogen) LSNH Low smoke, non-halogen NHFR Non-halogen, flame retardant HFFR Halogen-free, flame retardant ZHFR Zero Halogen, Flame Retardant OHLS Zero Halogen, Flame Retardant HFT Halogen Free and Flame Retardant, Temperature Resistant RKHF RK means wall thickness, Halogen Free

Description

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The first commercial thermoplastic LSZH material for cable jacketing was invented by Richard Skipper in and patented by Raychem Corporation.[3] This invention resolved the challenge of incorporating sufficient inorganic filler, aluminium trihydrate (ALTH), into an appropriate thermoplastic matrix to suppress the fire and allow a char to be formed, which reduced emission of poisonous carbon gases and also smoke and carbon particles, whilst maintaining electrical insulation properties and physical properties required by the end application. The preferred inorganic filler to achieve flame retardation continues to be aluminium trihydrate (ALTH). In the event of a fire this material undergoes an endothermic chemical reaction

2Al(OH)3 → Al2O3 + 3H2O (180 °C)

that absorbs heat energy and releases steam when the compound reaches a certain temperature. It is critical that the decomposition of the polymer(s) used to carry the filler happens at approximately the same temperature. The steam disrupts combustion of the evolved gases and helps form a char layer that protects the remaining material and traps particulates. The high level of filler required (≈ 60%) also replaces the base polymer reducing the total amount of fuel available for combustion.

Low smoke zero halogen cable considerably reduces the amount of toxic and corrosive gas emitted during combustion. When burned, a low-smoke zero halogen cable emits a less optically dense smoke that releases at a lower rate. During a fire, a low-smoke cable is desirable because it reduces the amount and density of the smoke, which makes exiting a space easier for occupants as well as increases the safety of firefighting operations. This type of material is typically used in poorly ventilated areas such as aircraft, rail carriages, tanks, subsea and offshore installations, submarines or ships. It is also used extensively in the rail industry, wherever high voltage or track signal wires must be run into and through tunnel systems. The nuclear industry is another area where LSZH cables have been and will be used in the future. Major cable manufacturers have been producing LSZH cables for nuclear facilities since the early s. Construction of new nuclear plants will almost certainly involve extensive use of LSZH cable. This will reduce the chance of toxic gases accumulating in those areas where personnel are working and the lack of corrosive gases where there are computer controlled systems will reduce the possibility of wires being damaged by fire resulting in a short circuit fault.

Since the s, the wire and cable industry has been using low-smoke, low-halogen materials in a number of applications. The introduction of a thermoplastic LSZH extended its use to accessories such as heat shrink tubing, labelling and fixtures. The objective was to create a wire and cable jacketing system that was not only flame retardant but also did not generate dense, obscuring smoke and less toxic or corrosive gases. In the military field its introduction was accelerated after following the dense black smoke emitted from HMS Sheffield after being hit by an Exocet missile in the Falklands War. Several fires, such as the King's Cross fire in London that killed 31 people in London's underground in , increased the awareness of the contribution that wire and cable jacketing makes in a fire. As a result, there has been an increased use of LSZH cables. With an increase in the amount of cable found in residential, commercial and industrial applications in recent years, there is a greater fuel load in the event of a fire and LSZH systems have a major role to play in protecting the public.

Several standards describe the processes used for measuring smoke output during combustion. For military applications Def Stan 02–711 in the UK and ASTM E662 in the US which are both based on an ASTM STP No. 422 pages 166–204, modified by AMTE, Portsmouth in the UK[4] and superseded by E662 in the US. During these tests a specified material sample is standardised and then exposed to a radiant heat source; the optical density of the smoke given off is photometrically measured.[clarification needed] There are various means of measuring optical density: peak smoke release rate, total smoke released, and smoke density at various points and durations during the test. Results must be below a certain value and the material must pass the burn test in order for the material to be labelled as low smoke.

These tests are conducted under laboratory conditions and cannot claim to replicate the range of conditions expected in a real fire scenario. However they do provide a measure by which the potential smoke emission of materials can be assessed and dangerous materials identified before proceeding to further testing of preferred materials, if deemed necessary.

References

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