The Nuts and Bolts of Low Smoke Zero Halogen Cabling

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IEEE

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Performance Improvements and Growing Applications of LSZH Compounds

Several notorious fires in history have highlighted the extreme dangers posed by burning plastics. For instance, the King's Cross fire in the late 1980s resulted in the tragic death of 32 individuals in a London underground station due to toxic fumes. This incident spurred the U.K. to establish more stringent regulations to prevent halogen-related fatalities, despite the fact that the cable available at the time was less flame-retardant than PVC-jacketed cables.

Figure 1: A modern solution to cabling - the use of low smoke zero halogen wire and cable is documented to produce less smoke, granting individuals more time to evacuate during emergencies. (Source: Adobe Stock)

The vast amount of cabling in residential, commercial, and industrial settings can act as fuel in dangerous fires. As a reaction, fire-resistant materials were developed with minimal performance sacrifices. Low smoke zero halogen (LSZH) compounds not only showcase superior fire protection capabilities but also evolve continually, expanding their applications and yielding decreasing costs.

Before diving into the specifics of LSZH versus PVC-based cables, it is crucial to clarify the myriad of related terminology.

Acronyms, Definitions, and Clarifications

The communication cable industry is familiar with terms like CM, PVC, and LSZH. Yet, a multitude of terms exist that either mean the same, are similar, or differ entirely. Below is a glossary to aid understanding:

• CM

  indicates that the cable complies with National Electrical Code (

  NEC

  or

  NFPA

  70). This designation is for low voltage communications circuits meant for a single floor.

• CMR

  , or riser-rated cable, is specifically designed to prevent fire spread in vertical installations, particularly when cabling traverses through floors.

• CMP

  , known as plenum-rated cable, restricts flame propagation to five feet or less while minimizing smoke production during a fire. It's typically deployed above dropped ceilings to facilitate air movement.

• PVC

  (polyvinyl chloride) commonly appears in

  CM

  and

  CMR

  -rated cables, described extensively throughout this document.

• FEP

  (fluorinated ethylene polymer) is typically paired with

  CMP

  cables, which may feature a low smoke

  PVC

  jacket.

• LSZH

  ,

  LSOH

  , and

  LSNH

  indicate that the materials used in the cable are free from halogens. It’s indicative that low smoke materials are utilized.
• The

  FR

  in

  FRLS

  and similar abbreviations denotes improved fire response materials (low fire). Low-smoke, low-fire, and zero-halogen cables are required to meet

  IEC

  standards.

A common misperception is equating LSF (low smoke and fume) with LSHF (low smoke halogen-free). It should be noted that "low smoke and fume" is not as rigorous a classification as LSHF or LSZH for clarity in this white paper.

Thus, engineers making crucial selections must fully understand their options, ensuring they receive both the necessary requirements and value for their investments.

The Rising Importance of

LSZH

Low smoke zero halogen cable insulation and jackets lack fluorine, chlorine, bromine, iodine, or astatine, leading to minimal toxic and corrosive fume emissions under high heat, while creating minimal smoke. LSZH cables are designed with flame-resistant jackets that do not emit harmful fumes even when burned.

Figure 2: An example of a patch cable. (Source: Quabbin Wire

&

Cable)

Characteristics of LSZH cables include:

• Non-propagation of fire
• Reduced smoke generation
• Compliance with

  IEC

  standards
• Flame-retardant properties

Without PVC, burning LSZH cable releases slightly colored smoke and negligible hydrochloric acid (HCl), significantly aiding escape chances during a fire. The cable’s sheath and conductor insulation can be fabricated from polyethylene, containing minimal chlorine, thus minimizing HCl risk.

A Low Smoke Halogen Free (LSHF) certification from UL indicates compliance with low smoke requirements, verified through IEC testing. Materials must have a halogen content below 0.2% by weight to be classified as zero-halogen. Compliance verification involves testing for halogen content, smoke generation, acid gas equivalence, and pH levels.

Although LSZH typically incurs a premium of about 30%, its flexibility tends to be less than that of PVC, potentially leading to jacket cracking during installation. Special lubricants may be required during setup, particularly in colder conditions. For this reason, LSZH isn’t ideal for robotic or continuous flex applications; however, advancements like ZHTPU, a suitable zero halogen material, are emerging for robotics.

Assessing the Pros and Cons of

PVC

Polyvinyl chloride (PVC) has dominated as the preferred wiring and cable choice for over 60 years. Despite its long lifespan, low manufacturing costs, and gradually improved characteristics, it has notable downsides.

Burning PVC generates harmful chemicals and thick black smoke, quickly reducing visibility. In just 10 minutes, visibility can diminish by 50%, and after 30 minutes, by 90%. This drastic drop greatly hampers escape ability. Moreover, when PVC burns, it emits hydrochloric acid and other noxious gases, with HCl comprising up to 30% of the emissions. Combined with water exposure, this produces hydrochloric acid, which is both corrosive and harmful.

Inhaling HCl can make breathing extremely difficult due to throat swelling, and if it contacts eyes, it can irritate, potentially causing permanent damage. Such physical reactions, combined with poor visibility conditions, pose severe risks in building fires, as exemplified by the King’s Cross Station incident where many lives were lost due to smoke inhalation.

Despite its risks, PVC has several advantages when not located in highly populated areas:

• PVC

  has inherent ignition resistance, which may slow the fire's spread throughout a building. Additionally, PVC compounds often include smoke suppression and additional flame-retardant qualities.

• PVC

  is recyclable, allowing a substantial percentage to be reused in wire and cable production.

• PVC

  requires significantly less energy for production than alternative materials.

Typical wire and cable insulation includes PVC, cross-linked polyethylene (XLPE), and ethylene propylene rubber (EPR), each enhanced with various chemical additives for performance, longevity, flexibility, and robustness.

LSZH

versus

PVC

Both LSZH and PVC cables boast impressive performance. When comparing them directly, their distinctions become apparent.

Halogenated flame retardants are cost-efficient and diminish flammability without impacting the processing features of the polymers. However, when ignited, LSZH exhibits superior performance. In contrast, PVC cables emit harmful gases and acids while burning. LSZH adheres to health and safety regulations.

Producing halogen-free wiring remains more complex and costly, with higher energy and water consumption compared to PVC. PVC is easier to process, requiring less energy for melting and production.

During a fire, visibility can be cut by up to 90%, and HCl emission becomes a critical factor. In environments with safety needs, LSZH justifies its higher price. Otherwise, PVC often serves as a practical solution.

Nevertheless, as LSZH prices approach those of PVC, and the appeal for globally standardized cables increases, LSZH is likely to replace PVC in many applications.

Applications

The applications of LSZH cable often dictate its adoption over PVC.

Halogen-free cables are specifically crafted for settings demanding low toxicity, minimal smoke output, and reduced corrosivity, such as:

• Mass transit systems
• Data centers
• Aerospace
• Industrial settings
• Subway systems
• Buildings
• Nuclear and military facilities
• Shipping
• Any location prioritizing human safety and equipment protection
• Confined spaces with extensive cabling near populated areas or electronics

While the adoption of LSZH exists predominantly in Europe, the United States lags due to cost and performance worries, as well as complicated construction standards. Historically, European cable designs struggled to meet testing standards enforced in the U.S.

Figure 3: Data centers, with their extensive cabling, are especially vulnerable to catastrophic fires. Transitioning to

LSZH

cabling can significantly enhance safety in such environments. (Source: Adobe Stock)

Challenging LSZH cable installations exist in cold settings due to reduced flexibility from high additive quantities, though their low friction allows for jackets that often don’t require lubrication during use.

The drive towards adopting LSZH cable is materializing in modern data centers that host vast cabling networks and cooling systems in enclosed spaces. This trend is expected to grow as LSZH's safety profile and environmentally friendly nature gain recognition.

Insurance providers are also endorsing LSZH cable. A globalized cable design—often termed "dual-rated"—will simplify installation processes, training, and logistics. The ability to serve both European and North American standards will add significant value.

Examining Evolving Global Standards

Across the globe, European safety guidelines primarily focus on LSZH cables and their electrical characteristics, whereas U.S. standards emphasize fire resistance and flame propagation during emergencies. In North America, the emphasis lies in satisfying stringent building codes and electrical requirements, including wet electrical performance.

Given the stark differences between U.S. and European standards, it becomes crucial for wire and cable suppliers and consumers to provide products that meet various specifications while adhering to global guidelines.

Aside from differing standards, considerable confusion often arises regarding LSZH cables and their materials. Misunderstandings stem from various interpretations of LSZH and the challenges posed by self-certification practices. The evolution of standards from earlier editions to contemporary specifications has added to the ambiguity surrounding halogen content, illustrated by:

IEC -1: Test on gases evolved during combustion of materials from cables; Part 1: Determining halogen acid gas content

IEC -2: Test on gases evolved during combustion of materials from cables; Part 2: pH measurement and conductivity

These standards do not consider the halogen content associated with chlorine, bromine, or fluorine and instead utilize titration, pH, and conductivity measures for assessments. IEC -2 focuses on recommended pH performance values rather than enforcing mandatory requirements.

In 2012, the IEC introduced LSHF -1, -2, and -3 standards, addressing Electric Cables; Halogen-Free, Low Smoke thermoplastic-insulated and sheathed cables of rated voltages up to and including 450/750 V.

This standard led UL to design dual certification programs that employ testing methods from IEC -1/-2 and IEC -3. Cables meeting UL's Recognized Component program are listed in their Online Certifications Directory, allowing manufacturers to find compliant halogen-free materials.

UL has developed Halogen-Free (HF) and Low Smoke Halogen-Free (LSHF) certification marks for wires and cables, ensuring adherence to IEC standards across various categories of wiring materials. These designations indicate compliance with general UL certification standards, subject to follow-up assessments through UL's Follow-Up Service (FUS) program.

Numerous additional standards exist that are not as comprehensive as those previously mentioned, with some focusing solely on cable jackets instead of overall cable construction.

Nearly all European installations are required to comply with the latest IEC specifications, with heightened demand for new installations to additionally meet IEC -3, which establishes rigorous LSZH flammability requirements.

Extra tests beyond those applicable to PVC/LSF variants include:

• EN

  -2-1, limiting hydrochloric acid emissions to under 0.5%, and

• EN

  -2, which mandates that visibility not decrease by over 40% during combustion.

BS EN -1 outlines accepted levels of acidity, conductivity, and fluorine from LSZH flexible cables during burn tests.

Behavior in Actual Fire Scenarios

In fire situations, most synthetic materials are flammable. PVC frequently is a contributing factor in fires, with several documented incidents indicating that its presence exacerbates the situation, hastening fire spread or emitting hazardous gases. Four significant elements are responsible for the dangers of PVC combustion: hydrochloric acid in the fumes, dioxins, fire spreading, and cable insulation quality. When PVC burns, fatalities typically arise due to smoke inhalation from hydrochloric acid, compounding dangers in environments rich with synthetic materials.

In Conclusion

Halogens yield toxic and corrosive byproducts during combustion. While they provide flame-retardant properties, burning halogens emit hazardous gases that can damage electronics. PVC will continue serving as a leading wiring solution thanks to its versatility and cost-effectiveness. However, LSZH is rapidly gaining traction in closed environments, offering a significantly safer option for spaces occupied by individuals. Improved formulations and stringent standards are enhancing LSZH compliance with modern testing and chemical regulations.

As LSZH adoption increases, ensuring the authenticity of LSZH claims is paramount. The accessibility of rigorous testing guidelines established by UL facilitates the transition from self-certifying suppliers to standardized, verifiable criteria. However, numerous materials labeled as low-smoke currently fail to meet genuine criteria.

Quabbin Wire & Cable, for instance, presently offers an LSZH product meeting flame and low smoke standards compliant with IEC regulations, though it awaits complete certification. Expectations are high that LSZH adoption will persist as suppliers align with UL's regulations and prices decline.

_______________________________________

Understanding LSZH (Low Smoke Zero Halogen)

Low smoke zero halogen, often abbreviated as LSZH or LSOH, is a classification for materials typically employed in cable jacketing within the wire and cable sector. LSZH jacketing comprises thermoplastic or thermoset compounds that emit limited smoke and absolutely no halogen when exposed to high heat sources.

LSZH cables significantly mitigate the emission of toxic and corrosive gases during combustion. When ignited, they produce less dense smoke at a slower rate. During fire incidents, this reduced smoke generation is critical in facilitating safer evacuations and enhances emergency responders' ability to conduct firefighting operations.

Such materials are especially suited for poorly ventilated environments such as aircraft, rail cars, containers, subsea and offshore installations, submarines, or ships. They are also extensively utilized in rail systems where high voltage or signaling wires enter tunnel infrastructures. The nuclear sector continually employs LSZH cables due to their fire safety features, minimizing toxic gas accumulation in occupied areas and protecting sensitive electronic systems from corrosive damage.

Advantages of LSZH Cables

While PVC is a versatile, economical material, LSZH cables provide distinct advantages, including:

• 1. Reduced Smoke Generation: LSZH cables emit less smoke during a fire, improving visibility and enhancing evacuation safety, vital in confined spaces such as aircraft, trains, and tunnels.

• 2. Low Toxicity: LSZH cables avoid the release of toxic halogen gases, such as chlorine, fluorine, and bromine, during combustion, thus diminishing the risk of inhaling hazardous fumes.

• 3. Low Corrosivity: These cables do not generate corrosive gases when ignited, preserving sensitive electronic devices and instruments from damage.

• 4. Enhanced Safety: LSZH cables boost overall fire safety, supporting efficient emergency evacuations and firefighting efforts.

• 5. Environmentally Sustainable: LSZH cables lack halogenated and other harmful chemicals, making them more eco-friendly.

• 6. Wide Application Scope: LSZH cables are employed in industries with stringent fire safety and environmental requirements, such as aerospace, rail transportation, offshore, and nuclear power sectors.

Contrasts between PVC and LSZH Cables

In terms of physical properties, PVC and LSZH differ notably. PVC cables are flexible, while LSZH cables tend to be more rigid due to the inclusion of flame-retardant compounds, and offer more aesthetic appeal.

A PVC cable produces heavy black smoke, hydrochloric acid, and other poisonous gases upon burning, whereas LSZH cables feature flame-resistant jackets that do not emit toxic gases even when ignited.

Typically, LSZH cables are costlier than their PVC counterparts, and some varieties may be less flexible. Compliance with CENELEC standards EN prohibits halogens in screened cables, though unscreened cables lack similar regulations.

PVC cables are often utilized for horizontal runs from the cabling center and acceptable for vertical runs in buildings with contained ventilation systems. Conversely, LSZH cables are favored for vertical runs, featuring specialized flame-retardant coatings.

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