How Does low smoke zero halogen lszh Work?

Introduction:

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　　• LSZH is the short form of Low Smoke Zero Halogen.

　　• These cables are constructed with jacket material free from halogenic materials such as chlorine and fluorine as these chemical have toxic nature when they are burned.

　　• LSZH cables are used mainly in Europe.

　　• It is used in shipboard applications and computer networking rooms where toxic or acidic smoke and fumes can injure people and/or equipments.

　　• Examples of Halogens include fluorine, chlorine, Bromine and Iodine.

　　• These materials when burned produce acidic smoke that can cause harm.

　　• These cables will self extinguish.

　　•They are used where people are very near to cable assemblies where they do not get adequate amount of ventilation in the event of fire or there is poor ventilated areas.

　　Following are the benefits or advantages of LSZH cable:

　　•They are very cost effective.

　　•They are used in railway systems where high voltage signal wires are used in underground tunnels. This will reduce possibilities of accumulation of toxic gases when cables get fire.

　　•They are constructed using thermoplastic compounds which emit limited smoke with no halogen.

　　•They do not produce dangerous gas when they come in contact with high sources of heat.

　　•LSZH cable jacket helps in protection of people in the event of fire, smoke and dangerous gas due to burning of cables.

　　Following are the drawbacks or disadvantages of LSZH cable:

　　•LSZH cable’s jacket uses high % of filler material in order to offer low smoke and zero halogen. This makes jacket less chemical/water resistant compare to non-LSZH cable counterpart.

　　•Jacket of LSZH cable experiences cracks during installation. Hence special lubricants are needed to prevent it from damage.

　　•It offers limited flexibility and hence it is not suitable for robotics.

　　If protection of equipment or people is a design requirement, consider low-smoke zero-halogen (LSZH) jacketed cables. They emit fewer toxic fumes than standard PVC-based cable jackets. Typically, LSZH cable is used in confined spaces such as mining operations where ventilation is of concern.

　　What is the difference between LSZH cable and common cables?

　　The function and technique parameter of LSZH fiber optic cable is just like common fiber optic cables, and inner structure is also similar, the basic difference is the jackets. LSZH fiber optic jackets is more fire-resistant compared with common PVC jacketed cables, even when they are caught in fire, the burned LSZH cables provide low smoke and no halogen substances, this feature is not only environment protective but the low smoke when it got burned is also important to people and facilities in the fired place.

　　LSZH jacket is made up of some very special materials which are non-halogenated and flame retardant. LSZH cable jacketing is composed of thermoplastic or thermoset compounds that emit limited smoke and no halogen when exposed to high sources of heat. LSZH cable reduces the amount of harmful toxic and corrosive gas emitted during combustion. This type of material is typically used in poorly ventilated areas such as aircraft or rail cars. LSZH jackets are also safer than Plenum-rated cable jackets which have low flammability but still release toxic and caustic fumes when they are burned.

　　Low smoke zero halogen is becoming very popular and, in some cases, a requirement where the protection of people and equipment from toxic and corrosive gas is critical. This type of cable is ever involved in a fire very little smoke is produced making this cable an excellent choice for confined places such as ships, submarines, aircraft, high-end server rooms and network centers.

　　Every coin has two sides. Since LSZH cables have so many benefits listed above, what are the Cons of the cable?

　　1. LSZH is more susceptible to jacket cracking. Special lubricants have been made to minimize damage during installation.

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　　2. LSZH jacket has a high filler content, around 50% to provide the required flame and smoke performance. This results in a lower mechanical, chemical resistance, water absorption and electrical properties then non LSZH compounds.

　　3. The current generation of LSZH cables has not yet established a proven history of long time performance.

　　The LSZH cables are available with 1, 2, 12, 24 fibers, and variable sub-cable dimensions that support specific termination and routing requirements. They are suitable for halogen free and many international installations. LSZH cable contains no flooding gel and is OFNR Riser rated, is perfect for installation in conduits between buildings and run directly thru risers to a convenient network or dome fiber optic splice closure without a separate point of splice at building entrance.

　　There are also LSZH fiber optic patch cords available. Both LSZH fiber optic cables and LSZH fiber optic patch cords are required for the Rosh compliant cable assemblies, but Rosh standard is more strict besides it require the cables to be LSZH type. LSZH fiber optic jumper are used widely used in the places where expensive equipment would be damaged if exposed to corrosive gases, and they are also used in crowded areas like commercial centers and sports centers.

　　The European market is demanding that cables used in LANs, WANs, etc. meet LSZH specification. The IEC -1 governs the Flame Retardant Grade specifications in reference to LSZH cables.Reduction of dangerous/poisonous gases

　　Essentially, the compound used in manufacturing cables meeting the above specification reduces the amount of dangerous/poisonous gases in case of fire. The main difference in specifications between IEC -1 versus UL® , UL and UL 910 is that the cable under the IEC spec can continue to burn while still emitting very low gases. The UL specs demand that the flame be extinguished, but it can still emit dangerous/poisonous gases.IEC specification

　　Today virtually all medium and large installations in Europe must meet the IEC specification. Many public authorities are already demanding that new installations must meet IEC -3 which is a more demanding flammability specification for LSZH.

　　What’s the difference between PVC and LSZH cables

　　Physically, PVC and LSZH are very different. PVC patchcords are very soft; LSZH patchcords are more rigid because they contain the flame retardant compound, and they are aesthetically more pleasing

　　A PVC cable (made of polyvinyl chloride) has a jacket that gives off heavy black smoke, hydrochloric acid, and other toxic gases when it burns. Low Smoke Zero Halogen (LSZH) cable has a flame-resistant jacket that doesn’t emit toxic fumes even if it burns.

　　LSZH cables more expensive and less flexible

　　LSZH cables usually cost more than the equivalent PVC cable, and certain types are less flexible. LSZH cable does have some restrictions. According to CENELEC standards EN, , , screened cables must be halogen free. However, no similar regulation yet applies to unscreened cables.

　　Where do you run the cable?

　　Whether you choose a riser (PVC), plenum or LSZH jacket depends on where you’re going to run the cable.

　　PVC cable is commonly used for horizontal runs from the wiring centre. You can use it for vertical runs between the floors – but only if the building features a contained ventilation system running through the duct work.

　　LSZH cable is used between floors in a building. It has a special flame-retardant coating.

　　A plenum is a space within the building created by building components, designed for the movement of environmental air.

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 Abbreviation 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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