LSZH Compound Testing and Certification: A Complete Guide for Cable Manufacturers

Cable Material Qualification Guide

Qualifying a low-smoke zero-halogen (LSZH) compound for a new cable project usually starts with a stack of test reports that do not align: one shows IEC 60754-1 halogen content, another shows a CPR class, and none covers the rail hazard level the customer quoted. A structured testing and certification checklist closes that gap and shortens the qualification cycle.

What an LSZH Compound Is and What Certification Proves

An LSZH compound is a halogen-free flame-retardant polyolefin formulation that, when burned, releases no halogen acids, keeps smoke density below an agreed limit, and stops flame spread within a defined charred length.

The term LSZH stands for low-smoke zero-halogen, and the definition drives procurement decisions, not just chemistry. A material sold as LSZH must satisfy a measurable composition requirement, a measurable smoke requirement, and a measurable flame-retardancy requirement. Without test reports for all three, the material does not meet the definition.

Low-smoke zero-halogen (LSZH) compounds are cable materials engineered so that their combustion products contain practically no halogen gases (chlorine, bromine, fluorine, iodine), while the smoke evolved during burning stays optically limited enough for people to find an escape route.

Compound producers such as Hangzhou Meilin New Materials Technology Co., Ltd. design their LSZH grades around three validation pillars.

The three validation pillars behind every LSZH certificate

Composition: halogen acid gas content determined by combustion analysis following IEC 60754-1, with a typical limit of 0.5 percent by weight.
Flame retardancy: vertical flame spread tested to IEC 60332-1-2, with a maximum charred length of 425 millimeters.
Smoke and corrosion: smoke density measured to IEC 61034-2 with light transmittance of at least 60 percent, plus acidity and conductivity measured to IEC 60754-2.

In a real enclosure fire, LSZH compounds typically hold light transmittance above 60 percent, while conventional PVC cables often fall below 20 percent within the first minutes of smoke evolution.

Core Test Battery: Parameters, Methods, and Typical Limits

Every LSZH compound should be verified against four quantitative test methods before it enters a cable design: IEC 60754-1 for halogen content, IEC 60754-2 for gas acidity, IEC 61034 for smoke density, and IEC 60332 for flame spread.

The four tests work as a system. Halogen content confirms the halogen-free claim, acidity and conductivity measure corrosion damage, smoke density measures escape visibility, and flame spread determines whether a single cable fire becomes a cable tray fire.

Acceptance limits commonly used for LSZH compound fire-safety testing, with the specific property each method verifies.
Test parameter	Test method	Typical acceptance limit	Property verified
Halogen acid gas content	IEC 60754-1	≤ 0.5% by weight	Halogen-free composition
Acidity of combustion gases	IEC 60754-2	pH ≥ 4.3; ≤ 10 µS/mm	Corrosion potential
Smoke density	IEC 61034-2	≥ 60% light transmittance	Escape visibility
Flame spread	IEC 60332-1-2	≤ 425 mm charred length	Fire propagation resistance

≤ 0.5%

Halogen acid gas limit under IEC 60754-1

≥ 60%

Minimum light transmittance under IEC 61034-2

≥ 4.3

Minimum pH of combustion gases under IEC 60754-2

≤ 425 mm

Maximum charred length under IEC 60332-1-2

LSZH compound versus conventional PVC cable material: typical fire-safety measurements

Smoke density

Light transmittance in %, higher is better

LSZH72%

PVC12%

Halogen acid gas emission

Weight % of combustion gas, lower is better

LSZH0.5%

PVC28%

Acidity of combustion gases

pH scale, higher is better

LSZH5.5

PVC2.3

LSZH compoundConventional PVC

Bar width is proportional to the measured value on each row scale; row scales differ.

The four tests above define the minimum for a basic LSZH claim. Data centers, railway, and marine projects add stricter criteria, including quantitative smoke toxicity and corrosivity assessment, which is why project specifications usually reference a standard family rather than a single test. For a deeper look at how smoke toxicity and corrosivity are quantified, see our analysis of the quantitative hazard assessment of LSZH materials.

Certification Standards by Application Sector

The same LSZH compound can carry different certificates depending on the end market, and the most common error is taking one standard's result and reading it as evidence of compliance with a different standard.

A compound that passes EN 45545-2 for railway applications is not automatically compliant with the European Construction Products Regulation (CPR). Each standard defines its own specimen configuration, aging schedule, and limit values. The table below maps the main certification families that cable buyers reference when specifying LSZH compounds.

Major certification frameworks for LSZH cable compounds, grouped by application sector and the key requirement each one imposes.
Sector	Standard family	Key requirement
European construction	EN 13501-6, CPR	Reaction-to-fire classes B2ca, Cca, Dca with smoke and droplet criteria
Railway	EN 45545-2	Fire safety hazard levels HL1, HL2, HL3
Marine and offshore	IEC 60092-360	Fire retardancy plus smoke and temperature ratings
North America	UL 444, UL 1685	CM, CMR, and plenum smoke limits
China building market	GB 31247, GB/T 19666	Classes B1 and B2 for building wiring

Do not confuse Chinese B1 or B2 classes with European CPR classes. Chinese B1 under GB 31247 evaluates heat release and burning behavior for building cables, while European B2ca under EN 13501-6 is evaluated through EN 50399 and covers fire growth, heat, smoke, and flaming droplets. Both gradings are meaningful, but they are not interchangeable.

Because each sector maps to a different test set, buyers increasingly ask suppliers to document the full chain from raw pellet to test certificate. Our overview of international standard cable compounds explains how these requirements fit together across markets.

For communication cable builds, the thermoplastic LSZH flame-retardant sheath compound MLTH9001 is produced with halogen-free and smoke density data verified on each grade family, with grades oriented to B2ca, Cca, and Dca requirements.

Wholesale ML-TH9001 Thermoplastic LSZH flame- retardant sheath material SupplierWe Are China Wholesale ML-TH9001 Thermoplastic LSZH flame- retardant sheath material Suppliers, Factory, Hangzhou Meilin New Materials Te...View Product →

How to Read a Supplier's LSZH Test Report

A test report is only valid when the specimen preparation, the standard edition, and the laboratory method all match the claim being made.

Certificate numbers on a datasheet only prove that a test was done once, on one sample, in one laboratory. They do not prove that the production lot shipped to your plant has the same composition, which is why experienced project engineers now request the original third-party report, the standard edition, and the batch identity.

Five checks before you accept an LSZH test report

Confirm the standard edition: IEC 60754-1:2011 is not the same as the 1994 edition, and the limit values differ.
Check specimen conditioning and aging: crosslinked LSZH grades must be thermally aged before testing to reflect real service conditions.
Match the grade family: a test performed on a 90 °C sheath grade does not cover a 105 °C insulation grade.
Verify the laboratory: ISO/IEC 17025 accreditation is a meaningful, verifiable signal of competence.
Compare the certificate holder with the manufacturer: certificates issued to trading companies may not represent the actual production site.

Warning signs in test documentation

Results that sit exactly on the acceptance limit across several parameters
Reports without specimen dimensions, conditioning time, or burn apparatus details
One generic certificate applied to ten different compound grades

The solution is not to collect more certificates; it is to audit the process behind them. A manufacturer that runs in-house verification on every lot, and keeps records of raw material and finished batch testing, will always produce a more reliable specification than one that only files an old external certificate.

That is why Hangzhou Meilin New Materials Technology Co., Ltd. maintains an internal testing facility and documents its full verification setup on the in-house laboratory testing equipment page.

For building and power cable projects that need a higher fire class, the B1-grade thermoplastic LSZH sheath material MLH9001B1 is batch-tested for halogen content, smoke density, and flame spread before release.

Wholesale ML-H9001B1 Thermoplastic LSZH flame- retardant B1 grade sheath materiaWe Are China Wholesale ML-H9001B1 Thermoplastic LSZH flame- retardant B1 grade sheath material Suppliers, Factory, Hangzhou Meilin New Ma...View Product →

Production Consistency Is the Other Half of Certification

Certificates certify a tested batch, never a brand, so reproducible production is what turns a one-off test result into a reliable material specification.

A compound that passes certification on a laboratory sample but fails on a production lot creates direct operational and legal exposure for the cable maker. The manufacturing base therefore becomes part of the audit. Suppliers with large, modernized production lines and documented quality management reduce that exposure.

31 automated production lines spread across three production bases in Lin'an, Hangzhou
More than 210 employees, including 5 senior engineers
Over 30 technical management staff with college degrees or higher
New plants commissioned in 2021 and 2024 under a combined registered capital of RMB 85 million
LSZH families organized by grade series (7001, 7002, 9001, 9002) with documented temperature and fire classes

An LSZH certificate is a point-in-time measurement. Production consistency is what makes it a specification.

For marine and offshore projects, the radiation-crosslinked marine LSZH sheath compound MLFH9002 is produced and batch-tested for marine-grade fire, smoke, and temperature requirements.

Wholesale ML-FH9002 90℃ irradiated halogen- free flame-retardant sheath materialWe Are China Wholesale ML-FH9002 90℃ irradiated halogen- free flame-retardant sheath material for marine cables Suppliers, Factory, Hangz...View Product →

Frequently Asked Questions about LSZH Testing and Certification

Does halogen-free mean the compound contains no flame retardants?

No. Halogen-free flame retardancy is achieved mainly with metal hydroxides such as aluminum hydroxide (ATH) and magnesium hydroxide (MDH), which release water vapor above 200 °C and cool the burning zone. Halogen-free refers to the absence of halogen elements in the polymer and additive system, not to the absence of flame-retardant chemistry.

What is the difference between B1/B2 classes and B2ca/Cca classes?

B1 and B2 are reaction-to-fire classes defined by Chinese standard GB 31247 for building cables. B2ca and Cca are European CPR classes defined by EN 13501-6 and evaluated through EN 50399. The test setups, measured parameters, and limit values differ, so the two systems cannot be compared directly.

How often should LSZH compound test data be refreshed?

Halogen content and smoke density should be verified on every production lot, because both are sensitive to raw material changes. Full fire tests, including CPR classification and bundle flame spread, are repeated when the formulation changes, at one-to-three-year intervals, or whenever the customer's certification body requires fresh data.

Can one LSZH compound serve both railway and marine projects?

Sometimes yes, but not automatically. Railway (EN 45545-2) and marine (IEC 60092-360) requirements overlap on flame retardancy and smoke, but differ on thermal aging, oil resistance, and toxicity index values. The compound must be evaluated against each standard's complete requirement table.

Final takeaway: treat LSZH testing and certification as a three-layer system. Verify the compound against the core test battery, map the result to the correct application standard, and audit the manufacturer's production consistency before the material enters your cable design.

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