LSZH Cables — The “Safety Revolution” in Modern Wiring

Low Smoke Zero Halogen (LSZH) cables are specialty cables featuring insulation and sheathing made from halogen-free, environmentally friendly materials. During combustion, they do not release halogen gases (such as chlorine or bromine) and produce significantly lower smoke concentrations than traditional cables.
In modern society, the importance of LSZH cables stems primarily from the “safety shortcomings” of traditional cables: When traditional PVC cables burn, they release high concentrations of hydrogen chloride gas (exceeding 3000ppm). Upon contact with water, this forms highly corrosive hydrochloric acid, which can burn human respiratory tracts and corrode precision instruments. Simultaneously, the black smoke emitted blocks over 70% of light, reducing visibility to less than 5 meters during fires and hindering escape and rescue efforts. In contrast, LSZH cables utilize halogen-free polyolefin substrates and flame-retardant systems. During combustion, their smoke light transmittance exceeds 80% (providing visibility over 20 meters), with toxic gas concentrations below 50ppm, effectively mitigating “secondary fire hazards.”
Today, with the mandatory implementation of regulations like GB 50217 “Code for Design of Power Engineering Cables” and EN 50575, LSZH cables have evolved from an “optional upgrade” to a “mandatory requirement” in public buildings, transportation systems, data centers, and similar applications.

Core Attributes of Low-Smoke Zero-Halogen (LSZH) Cables

Definition and Key Metrics
LSZH cables must simultaneously meet three core criteria: halogen-free, low-smoke, and low-toxicity, while obtaining international standard certification: Regarding halogen-free properties, per IEC 60754, total halogen content in materials must ≤500ppm, with post-combustion halogenated hydrogen gas release ≤5mg/g; For low smoke emission, compliance with IEC 61034 requires smoke light transmittance ≥60% during combustion (premium products achieve ≥80%), preventing dense smoke from obstructing visibility; For low toxicity, it must pass the EN 50267-2-1 toxicity test, with concentrations of toxic gases released during combustion—such as carbon monoxide (CO) and hydrogen fluoride (HF)—far below thresholds harmful to human health.
Additionally, LSZH cables offer aging resistance (service life exceeding 20 years), oil resistance (withstands mineral and vegetable oils), and extreme temperature tolerance (-40°C to 125°C), making them suitable for diverse applications.
Material Composition: The “Core Formula” Determining Performance
The insulation and sheath materials are pivotal to LSZH cable performance. Mainstream formulations comprise three key components:
- Base materials: High-density polyethylene (HDPE), polypropylene (PP), and polyolefin elastomer (POE) form the foundation, ensuring halogen-free properties while providing fundamental insulation. Flame retardants utilize inorganic halogen-free compounds (magnesium hydroxide, aluminum hydroxide), forming flame-retardant coatings through “heat absorption and dehydration” to eliminate toxicity issues associated with traditional halogenated flame retardants; Modifying additives include toughening agents (enhancing low-temperature flexibility), antioxidants (delaying aging), and UV stabilizers (enabling outdoor use), compensating for inherent performance limitations of halogen-free materials.
Advantages of LSZH over Traditional Cables
Compared to PVC and standard PE cables, LSZH cables excel in safety and environmental aspects. Regarding combustion toxicity: LSZH cables emit no halogen gases and are low-toxicity (CO ≤ 50 ppm), while traditional PVC cables release highly toxic hydrogen chloride (HCl ≥ 3000 ppm). Standard PE cables are halogen-free but emit moderately toxic CO. In smoke density: LSZH cables are low-smoke (light transmittance ≥ 60%), while traditional PVC cables produce high smoke (light transmittance ≤30%). Ordinary PE cables are low-smoke (light transmittance ≥70%) but have poor flame retardancy. For environmental friendliness, LSZH cables are halogen-free, heavy-metal-free, and recyclable. Traditional PVC cables contain halogens, are difficult to degrade, and pollute soil and water sources. Ordinary PE cables are recyclable but require additional additives for flame retardancy. For equipment protection, LSZH cables produce non-corrosive combustion byproducts that safeguard precision equipment. Traditional PVC cables release hydrochloric acid during combustion, corroding circuit boards and increasing equipment failure rates. Standard PE cables are non-corrosive but prone to dripping, potentially causing secondary fires.

Why Must LSZH Cables Be Selected?

Choosing LSZH cables fundamentally builds a “safety net” for the environment, with value summarized across four dimensions:
Ensuring Personnel Safety: Securing the “Golden Time” for Fire Escape
Fire statistics reveal that 80% of fire fatalities result from inhaling toxic gases or suffocating in dense smoke. LSZH cables safeguard personnel through two key properties: First, low smoke and high light transmission—their combustion produces sparse smoke with high visibility, enabling rapid identification of evacuation routes and reducing risks of stampedes or disorientation. Second, low toxicity and halogen-free composition—they prevent chlorine gas from burning respiratory tracts, minimizing long-term health impacts even after brief smoke exposure (particularly critical in settings like hospitals and schools where vulnerable populations congregate).
Reducing Economic Losses: Protecting High-Value Equipment
In data centers, industrial control rooms, and similar environments, individual servers or semiconductor equipment can be worth hundreds of thousands of yuan. Hydrochloric acid produced by burning traditional PVC cables can corrode core components within 10 minutes, causing irreversible damage. In contrast, LSZH cables emit non-corrosive combustion products. After fire suppression, most equipment can be cleaned and restored to functionality, significantly reducing corporate property losses.
 Meeting Compliance Requirements: Avoiding Project Acceptance Bottlenecks
Global mainstream regulations mandate “low-smoke, zero-halogen” (LSZH) cable properties. Failure to use LSZH cables directly prevents project acceptance:
- China's GB 50217 explicitly requires LSZH cables in subways, hospitals, data centers, and underground utility tunnels; European EN 50575 mandates LSZH cables for public buildings and rail transit systems; North American UL 1685 standards set limits on cable smoke and toxicity, making LSZH cables the preferred choice for large shopping malls and airports.
 Aligns with Environmental Trends: Supporting “Dual Carbon” Goals
With the advancement of “carbon neutrality” policies, eco-friendly cables have become an industry trend: LSZH cables contain no harmful substances like halogens, lead, or cadmium, ensuring no environmental pollution during production or disposal. Some high-end LSZH cables utilize recycled polyolefin materials, complying with EU RoHS and China GB/T 26572 standards to help enterprises achieve green production goals.
Where Must LSZH Cables Be Used?
Based on “occupant density, enclosure integrity, equipment value, and regulatory requirements,” the following six scenarios mandate LSZH cables:
Public Buildings: The “Safety Bottom Line” for High-Occupancy Areas
Public buildings experience high foot traffic and pose significant evacuation challenges, making fire consequences severe. LSZH cables are mandatory in: - Hospital wards, ICUs, operating rooms, etc., where both patient respiratory safety (especially for critically ill patients unable to evacuate independently) and protection of medical equipment like MRI and CT scanners from corrosion must be ensured; In schools/kindergartens, children and students have limited self-rescue capabilities. The low-smoke, zero-halogen properties reduce escape risks and prevent mass casualties. Airports/train stations/shopping malls feature enclosed spaces and complex passageways where dense smoke easily blocks evacuation routes. The low-smoke characteristics of LSZH cables are critical for rescue operations.
Transportation Systems: A Critical Safety Requirement in Enclosed Environments
Cables in transportation systems are often laid in confined spaces where toxic gases cannot disperse easily, making LSZH cables the only viable option: Subway/light rail tunnels and carriages are enclosed spaces. Hydrogen chloride gas from burning PVC cables can fill a tunnel within 5 minutes, causing suffocation. All subway lines in China (e.g., Beijing Metro, Guangzhou Metro) mandate LSZH cables. High-speed rail/bullet train cabins feature dense internal wiring. LSZH cables not only ensure safety but also prevent secondary fires caused by burning drips. Ship/aircraft cabins and compartments are confined spaces requiring compliance with International Maritime Organization (IMO) and aviation (FAA) standards. The low-smoke, zero-halogen properties of LSZH cables safeguard passengers and crew.
Data Centers & IT Facilities: The “Safety Barrier” of the Digital Economy
Data centers serve as the “heart of the digital economy.” Servers and switches are highly sensitive to smoke and corrosion: Cable trays are often concealed in ceilings or under floors. During fires, dense smoke and corrosive gases from traditional cables can rapidly spread, causing network-wide equipment failure. Major cloud providers like Alibaba Cloud, Tencent Cloud, and Huawei Cloud mandate that data center LSZH cables pass both the IEC 61034-2 smoke density test and the EN 50267-2-1 toxicity test.
Industrial Facilities: Essential Protection for High-Risk Environments
Certain industrial settings involve high temperatures, flammable/explosive hazards, and precision equipment. LSZH cables provide dual benefits of “fire resistance” and “equipment protection”:
- Chemical/oil & gas plants may contain combustible gases. LSZH cables' flame-retardant properties reduce ignition risks, while halogen-free design prevents corrosion of production equipment. Semiconductor/electronics factories demand zero tolerance for dust and corrosive gases during chip production. LSZH cables release no impurities when burned, meeting cleanroom requirements. Automotive manufacturing welding and painting processes involve high-temperature fire sources. LSZH cables prevent chain reactions caused by cable fires.
Residential & Commercial Buildings: The “Quality Standard” for Premium Projects
While not yet mandatory for standard residences, mid-to-high-end projects have adopted LSZH cables as a “safety upgrade”: Owners of luxury apartments/villas demand high safety and environmental standards. LSZH cables eliminate post-renovation “cable odors” while reducing fire risks. Grade A office buildings primarily house finance and tech firms with dense office equipment. LSZH cables enhance building safety ratings, attracting premium tenants.
Underground Projects: “Safety Assurance” for Enclosed Spaces
Poor ventilation in underground projects makes toxic gas dispersion difficult after fires, necessitating mandatory LSZH cable use:
- Underground utility tunnels house power, communication, and gas pipelines; cable fires can trigger chain reactions, with LSZH cables mitigating risks. Fuel leaks from vehicles in underground parking garages can easily ignite fires. The low-smoke, zero-halogen properties of LSZH cables ensure safe evacuation and vehicle protection.

Global LSZH Cable Compliance Requirements Breakdown

Regulatory standards for LSZH cables vary by region. Selection must align with local project regulations to avoid compliance risks:
 International Core Standards Overview
Within the International Electrotechnical Commission (IEC) framework, core standards include IEC 60754-1/2, IEC 61034-1/2, and IEC 60332-3-24. Specifically: - IEC 60754-1/2 mandates halogen content ≤500ppm, and halogenated hydrogen release ≤5mg/g, serving as the globally recognized baseline halogen-free testing standard; IEC 61034-1/2 requires smoke light transmission ≥60%, acting as the globally accepted smoke characteristic testing standard; IEC 60332-3-24 addresses flame retardancy for single-cable vertical burning, applicable to construction and transportation sectors.
Within the European standard (EN) system: EN 50575 mandates halogen-free + low toxicity + flame retardancy for European public buildings and transportation systems; EN 50267-2-1 focuses on combustion toxicity testing (low toxicity), primarily applied in European high-occupancy areas.
Within the North American standard (UL) system, UL 1685 sets limits for smoke density and toxicity while requiring flame spread ≤1.5 meters, applicable to North American buildings and data centers.
In the Chinese standard (GB) system:
GB/T 19666 specifies general technical requirements for low-smoke, halogen-free cables, applicable to all scenarios in China; while GB 50217 mandates compulsory application scenarios covering Chinese buildings, transportation, and industrial projects.
Key Regional Differences
Europe imposes the strictest “corrosivity” requirements, mandating EN 50305 testing (combustion product pH ≥4.3) to prevent equipment corrosion. China emphasizes combining “flame retardancy rating” with “halogen-free” properties. GB/T 19666 classifies LSZH cables into three categories (A, B, C, with A being the highest flame retardancy), requiring matching grades for different scenarios; North America focuses more on “flame spread rate,” with UL 1685 standard requiring flame spread length not exceeding 1.5 meters during vertical burning.
 Key Certification Markings
When selecting cables, verify corresponding certifications to ensure compliance:
- China market requires CCC certification (mandatory for listed products)
- European market requires CE certification (compliant with EN 50575) and VDE certification
- North American market requires UL certification and CSA certification
- Globally recognized certifications include IECEx certification (hazardous environments) and TÜV certification.
Limitations of LSZH Cables and Mitigation Strategies
LSZH cables are not “universal solutions”; their limitations must be addressed proactively:
Slightly Inferior Flexibility Compared to PVC
The base material of LSZH cables (polyolefin) inherently offers less flexibility than PVC. It tends to stiffen at low temperatures (below -20°C), making bending more difficult. Solutions include selecting “high-flex LSZH cables” (enhanced with POE toughening agents) or preheating cables before installation in cold conditions (maintaining temperatures between 5°C and 25°C) to prevent insulation damage from sharp bends.
Higher cost requires budget balancing
LSZH cable material costs are 30%-50% higher than PVC, potentially straining budgets for small projects. The solution is “layered selection”—use LSZH cables in core areas (bedrooms, equipment rooms) and PE cables in non-core areas (balconies, storage rooms) to balance safety and cost.
Enhanced mechanical protection required during installation
While LSZH cable jackets offer superior abrasion resistance compared to PVC, their impact resistance is slightly lower. When installed in impact-prone areas like underground conduits or workshop floors, additional CPVC protective tubing must be used to prevent jacket damage.
Conclusion
From safeguarding occupants in public buildings to protecting equipment value in data centers, and securing enclosed spaces in transportation systems, low-smoke zero-halogen (LSZH) cables are no longer merely an optional upgrade. They have become the core cabling solution mandated by regulations, essential for specific scenarios, and providing fundamental safety assurance.