A tender specification says LSZH throughout. A supplier comes back with a lower number and a reasonable-sounding argument: PVC passes the flame test, the project is not a tunnel, and nobody will ever know.
The last part is usually true, which is exactly why the decision deserves better than a price comparison.
What Actually Stops an Evacuation
Most discussions about cable jackets get the threat wrong. The jacket is not the main thing that burns in a building, and flame spread is not what kills people.
Smoke is. It reduces visibility, obstructs evacuation and makes firefighting harder.
The second threat is chemical and acts long after the fire is out. Halogenated polymers such as PVC release acid gases when they burn. Those gases irritate the respiratory system and, once combined with moisture, corrode metals and electronic assemblies well beyond the fire itself — acidic residues can destroy sensitive electronics far from the source. In confined spaces, those effects can be more dangerous than the fire.
Why PVC Is Flame Retardant, and What It Costs
PVC deserves more respect than it gets here. It is one of the most widely used cable materials in the world, in a huge range of formulations.
The reason it resists flame is also the reason it is a problem. Halogens are used in cable compounds because they improve flame resistance. PVC contains chlorine, and that chlorine does useful work right up until the material burns — at which point the same chemistry produces hydrochloric acid gas and dense black smoke that causes suffocation and loss of consciousness, and impedes escape.
None of that makes PVC wrong for every project. It makes it wrong for certain ones.
What LSZH Changes
LSZH stands for Low Smoke Zero Halogen, and it describes a class of jacket and insulation materials engineered to emit very low smoke density, contain no halogen elements, and avoid producing corrosive or toxic acid gases during combustion.
The halogen list matters, because "zero halogen" is a chemistry claim: chlorine, fluorine, bromine and iodine are the commercial ones.
LSZH compounds are typically halogen-free flame-retardant formulations — cross-linked polyolefin, modified polyolefin blends, and thermoplastic elastomers — selected on flexibility, temperature rating, chemical resistance and applicable standards.
The trade-offs are documented: reduced chemical resistance against some PVC compounds, different mechanical properties, higher material cost, and brittleness under extreme cold.
The Tests Are Separate Questions
There is no single "LSZH test." There are several, they answer different questions, and a good result on one establishes nothing about the others.
Property | IEC reference | What it addresses |
|---|
Smoke density | IEC 61034-1 / 61034-2 | Smoke emission and light transmittance under defined burning conditions |
|---|
Halogen acid gas | IEC 60754-1 | Halogen acid gas evolved from the tested materials |
|---|
Gas acidity and conductivity | IEC 60754-2 | Potential corrosivity of the gases evolved |
|---|
Flame propagation | Applicable part of IEC 60332 | Resistance to flame propagation |
|---|
Circuit integrity | IEC 60331 or BS 6387 | Continued electrical operation during a fire |
|---|
Two numbers show up constantly. Light transmittance of 60 percent is the figure most commonly written into LSZH specs, measured under IEC 61034. And on halogen content, a widely used halogen-free threshold is at or below 5 mg/g of HCl equivalent, against roughly 150 to 350 mg/g for conventional PVC compounds. Corrosivity criteria commonly specified are pH of 4.3 or higher and conductivity of 10 µS/mm or lower.
Read the standards’ wording: they are methods for *determining* values. The thresholds come from the project specification, the local code or the cable specification — not from the acronym.
"LSZH" Is a Material Claim, Not a Classification
This is the single most useful thing to carry into a submittal review.
LSZH describes a cable material. It is not a complete fire-performance classification, and it should not be described as fire-resistant, flame-retardant or circuit-integrity compliant unless separate test evidence for that exact product supports the claim.
Six things the label does not prove on its own:
- It does not mean "no smoke." Low smoke is not the same as no smoke; it is reduced smoke under a defined test.
- It does not automatically prove flame-retardant performance.
- It does not automatically prove circuit integrity during a fire.
- It does not demonstrate compliance with BS 6387 or IEC 60331.
- It does not define conductor size, shielding, voltage rating or installation method.
- It does not make the cable suitable for every hospital, airport, tunnel or data center.
Avoid absolute wording such as "non-toxic," "zero smoke" or "fireproof"; state the exact test evidence and the scope of the claim instead. And a circuit can be both LSZH and fire-resistant, but the two are measured by different methods and must be demonstrated separately.
Sources contradict each other on the mechanical comparison: some call LSZH stiff and rough, others say it feels softer than PVC and is more prone to nicking on sharp edges. Both are describing real products, because material behavior varies by formulation. Installation temperature, bend radius, abrasion resistance and chemical exposure have to be checked in the approved datasheet, not inferred from the sheath type.
Euroclass: The Classification That Is Actually Regulated
If you are supplying into Europe, the acronym is not the requirement. The classification is.
The Construction Products Regulation became mandatory for cables across the EU/EEA from 1 July 2017, with CE marking against a Declaration of Performance. Under the harmonised standard EN 50575, the manufacturer declares the cable’s performance in a Declaration of Performance and marks it accordingly. The reaction-to-fire class itself is assigned using EN 13501-6.
Class | Meaning | Notes |
|---|
Aca | No contribution to fire | Effectively non-combustible; rare for cables |
|---|
B1ca | Very limited contribution to fire | Stricter than B2ca |
|---|
B2ca | Limited contribution to fire | Common high-spec class; tested under EN 50399 |
|---|
Cca | Controlled contribution to fire | Tested under EN 50399 |
|---|
Dca | Acceptable basic performance | Lower than Cca; limited flame spread |
|---|
Eca | Basic flame propagation pass only | Entry level |
|---|
Fca | No performance determined | Fails Eca; do not install |
|---|
Higher up the list is better. The classes carry optional modifiers, and a full designation looks like B2ca-s1a,d1,a1. The suffixes control smoke production (s1a very low, s1b low, s2 moderate, s3 no limit), flaming droplets (d0 none, d1 none persisting beyond 10 seconds, d2 no requirement) and acidity or corrosivity of gases (a1 very low, a2 limited, a3 no requirement).
The modifiers are where an LSZH claim and a Euroclass declaration diverge commercially. On smoke, s1b means light transmittance at or above 60 percent and below 80 percent, while s1a means 80 percent or higher — the 60 percent threshold that LSZH specs quote is only the *bottom* of the s1 band. A cable described as "low smoke" and one declared s1a are not making the same statement.
Reaction to Fire Is Not Circuit Integrity
A Euroclass measures a cable’s contribution to a fire — flame spread, heat release, smoke, droplets, acidity. It does not measure the cable’s ability to keep working *in* a fire. Those are separate properties: reaction to fire sits with the Euroclass system under EN 50575 and EN 13501-6, while resistance to fire and circuit integrity use fire-survival ratings such as BS EN 50200, BS 8434, BS 8519 and BS 7846.
EN 50575 also excludes cables for safety installations such as alarm, way guidance and firefighting installations from its scope. A fire-resistant cable therefore carries a Euroclass and, separately, its fire-survival rating.
Never specify a high Euroclass expecting circuit integrity. They are different purchases.
Europe and North America Are Two Different Systems
In North America the relevant ratings are the flame and smoke classifications behind CM, CMR and CMP, and the plenum rating is a code requirement tied to air-handling spaces. CMP addresses flame spread and smoke, but plenum cable may still contain halogens unless it is explicitly specified as LSZH. A plenum rating plus an LSZH jacket is a distinct combination, not a synonym.
LSZH is not universally mandated by the NEC. It is frequently required by project specifications, OEM standards, transportation authorities and international regulations instead. The working rule: LSZH is a material property, plenum is a US code requirement, and a cable can carry an LSZH material with no plenum rating at all.
How to Decide
Start from the fire strategy, not the acronym. Smoke visibility and gas corrosivity are what LSZH actually improves. If an escape route or dense electronics sit along the cable path, that matters. If the space is ventilated, unoccupied and the code permits PVC, PVC is legitimate and usually cheaper.
In Europe, specify the Euroclass and the modifiers, not "LSZH." A declaration of Cca-s1b,d1,a2 or B2ca-s1a,d1,a1 is verifiable against a Declaration of Performance; "LSZH" alone is not. Confirm the class is printed on the sheath and matches the drum you receive.
Separate the four questions. Low smoke, limited halogen gas, flame propagation and circuit integrity are four different tests. Decide which ones your system needs, and ask for evidence for that exact product rather than the product family.
Then verify the specific SKU. Check the sheath and insulation materials in the current approved catalogue rather than an archived PDF, confirm the IEC 60754-1, 60754-2 and 61034 evidence covers the material being supplied, and resolve every mismatch between website, datasheet, marking and test report.
Our Cat6 premise cable, patch cords and the wider communication cable range can be built to the sheath compound and fire class the project specifies, and every reel is verified through test and inspection with the certifications we hold listed by standard rather than acronym. Sheath compound, printing and export packaging are agreed before production so the marking on the drum matches the documents. How Ethernet cables work explains the construction, and the category comparison covers where each grade is appropriate. If a tender specifies LSZH without naming a class, send us the requirement and we will tell you which classification it needs to resolve to.
Frequently Asked Questions
Is LSZH the same as plenum rated?
No. Plenum ratings address flame spread and smoke as a US code requirement, and plenum cable may still contain halogens unless LSZH is separately specified. A cable can have LSZH material with no plenum rating at all.
Does LSZH cable produce no smoke?
No. Low smoke is not no smoke. Performance is assessed under IEC 61034, where a minimum light transmittance such as 60 percent is typically specified — and that figure is the bottom of the s1b band, not the top.
Is LSZH cable fire resistant?
Not automatically. Circuit integrity needs a separate test such as IEC 60331 or BS 6387. A high Euroclass is a statement about contribution to fire, not about surviving one.
Is LSZH always better than PVC?
No single sheath material is universally better. LSZH may trade reduced chemical resistance, different mechanical behavior and higher cost against its smoke and halogen advantages. Selection depends on the fire strategy and the verified performance of the exact product.
The Short Version
PVC is flame retardant because it contains chlorine, and that same chlorine produces hydrochloric acid gas and dense smoke when the material burns. LSZH removes the halogens, reducing smoke density and eliminating corrosive gas, at the cost of higher material price and formulation-dependent mechanical behavior.
But "LSZH" is a material claim, not a fire classification. It does not prove low smoke, flame retardance or circuit integrity — those are separate IEC tests, each needing its own evidence for the exact product.
In Europe the regulated answer is the Euroclass declared under EN 50575 and assigned by EN 13501-6, with modifiers for smoke, droplets and gas acidity. Specify the full designation, check the sheath marking, and keep reaction to fire separate from resistance to fire. Those are two different products, and the difference only shows up in a fire.
Sources
- Heizka — What Is LSZH Cable and Where Should It Be Used?, covering LSZH as a material rather than a complete fire classification, the IEC 61034-1 apparatus and 61034-2 procedure, the 60 percent minimum light transmittance figure, the IEC 60754-1 threshold of 5 mg/g of HCl equivalent against 150 to 350 mg/g for conventional PVC, the IEC 60754-2 criteria of pH 4.3 or higher and conductivity of 10 µS/mm or lower, the separation between smoke density, halogen gas, flame propagation and circuit integrity results, the six claims an LSZH label does not support, the warning against absolute wording such as non-toxic or fireproof, the environments where LSZH is considered, the variation in compound behavior, the six-step verification workflow, and the confusion between IEC 60754 and IEC 60751 — https://heizka.com/technical-articles/what-is-lszh-cable/
- Galaxy Wire & Cable — What Makes a Cable "Low Smoke Zero Halogen" and When is it Required?, covering the three design objectives of low smoke density, no halogen elements and no corrosive or toxic acid gases, the halogen list of chlorine, fluorine, bromine and iodine, PVC releasing dense smoke and hydrochloric acid gas, halogens improving flame resistance while producing toxic acidic gases and opaque smoke, acid residues destroying electronics far from the fire, the XLPO and TPE material families, the environments where LSZH is commonly required, the standards list including IEC 60754, IEC 61034, EN 50267 and BS 6724, the trade-offs of reduced chemical resistance, stiffer mechanical properties and higher cost, the statement that plenum cable may still contain halogens, and the note that LSZH is not universally mandated by the NEC — https://www.galaxywire.com/connections-blog/what-makes-a-cable-low-smoke-zero-halogen-and-when-is-it-required/
- HELUKABEL — PVC cables vs LSZH cables, covering PVC producing black smoke and hydrochloric acid when burned, PVC being soft and flame-retardant, smoke causing suffocation and loss of consciousness and impeding escape, PVC being suited to ventilated environments without high temperature, the halogen element list including fluorine, chlorine, bromine, iodine, astatine and tennessine, the LS0H and LSHF alternative abbreviations, LSZH often being required with fire-resistant wiring to IEC 60331 for fire alarm systems, and LSZH being suited to buildings with large occupant capacity — https://www.helu.com/vn-en/pvc-cables-vs-lszh-cables.html
- ProjectDesign — CPR Cable Classification Guide, covering CPR becoming mandatory for cables across the EU/EEA from 1 July 2017 with CE marking against a Declaration of Performance, the Declaration of Performance mechanism under BS EN 50575 and class assignment under BS EN 13501-6, the Aca to Fca hierarchy with plain-language meanings and test notes, the s, d and a modifiers with their s1a, s1b, s2, s3, d0, d1, d2, a1, a2 and a3 options, the full designation example, the s1b transmittance band of 60 percent or above and below 80 percent against s1a at 80 percent or above, the statement that Euroclass measures contribution to fire and not the ability to keep working in a fire, the separate fire-survival standards including BS EN 50200, BS 8434, BS 8519 and BS 7846, the exclusion of safety installations such as alarm and firefighting cables from the scope of BS EN 50575, the guidance to avoid specifying a high Euroclass expecting circuit integrity, the requirement to print the CPR class on the sheath, the observation that low-smoke zero-halogen cable can feel softer and is more prone to nicking on sharp edges, the recommendation of Cca or better for public areas and risers, and the treatment of Fca as a failure — https://projectdesign.io/cpr-cable-classification-guide/
- IEC 60754-1:2011+AMD1:2019 — Test on gases evolved during combustion of materials from cables, Part 1: Determination of the halogen acid gas content — https://webstore.iec.ch/en/publication/66144
- IEC 61034-2:2005+AMD1:2013+AMD2:2019 — Measurement of smoke density of cables burning under defined conditions, Part 2: Test procedure and requirements — https://webstore.iec.ch/en/publication/66136
