In most fire fatalities, smoke and toxic gases kill before the flames do. Standard PVC cable insulation is part of that problem. When PVC burns, it releases hydrogen chloride gas—a colorless acid gas that corrodes lungs and equipment alike, turning any enclosed space into a hazard well beyond the immediate fire. LSZH power cable was developed to eliminate that combustion profile. Understanding what that means in practice and what it does not cover starts with the material itself.
What Makes a Cable LSZH
LSZH stands for Low Smoke Zero Halogen, describing two material properties that together define how a cable behaves when it burns.
- Low Smoke: A compliant LSZH cable produces minimal, translucent smoke when burned, rather than the dense black output of burning PVC, directly affecting whether evacuation routes stay visible and whether firefighters can locate the fire source.
- Zero Halogen: The material contains no chlorine, fluorine, or bromine. Combustion produces no hydrogen chloride or other acid gases; the gases released are virtually pH-neutral, eliminating corrosive secondary damage to electronics, switchgear, and structural metalwork.
Both properties come from the same material: a halogen-free polyolefin compound loaded with metal hydroxide additives, typically aluminium hydroxide or magnesium hydroxide. Under heat, these additives absorb energy through an endothermic reaction, releasing water vapor that dilutes flammable gases. The metal oxides left behind form a dense char layer on the cable surface, physically blocking oxygen access and slowing further combustion.
When LSZH Alone Is Not Enough
What LSZH does not cover is whether the cable keeps working during a fire. An LSZH cable with no fire-resistance rating loses electrical continuity when direct flame reaches its conductors. For most circuits, such as general power distribution, lighting, and HVAC, that is an acceptable failure mode.
But some circuits cannot fail. Emergency lighting must keep corridors illuminated during evacuation. Fire suppression systems must stay active. Firefighter communication lines must remain live. These circuits require fire-resistant LSZH cable—a construction that maintains electrical continuity under direct flame for a defined duration, as specified by the applicable project standard.
The fire-resistance performance comes from a mica-based tape layer applied to the conductors, beneath the halogen-free insulation. Mica tape—mica flakes bonded to a glass fiber cloth backing—retains its insulating properties at temperatures exceeding 1,000°C. The glass fiber backing reinforces the structure against the thermal stress and mechanical shock that real fire conditions impose. When the outer insulation is gone, the mica layer holds the circuit intact.
| Property | LSZH Cable | Fire Resistant LSZH Cable |
| Halogen-free material | Yes | Yes |
| Low smoke output | Yes | Yes |
| Circuit integrity under direct flame | Not guaranteed | Yes (duration and conditions per project standard) |
| Typical application | General wiring in enclosed or public spaces | Emergency, life-safety, and critical circuits |
Where These Cables Are Required
LSZH and fire-resistant LSZH cables are standard in enclosed or high-occupancy spaces where smoke toxicity or loss of power during a fire extends harm beyond the fire itself.
- Underground transit and tunnels: Metro stations, rail tunnels, and underground concourses have limited ventilation and few exits, making visibility during evacuation critical. The circuits supplying emergency ventilation, platform lighting, and traction power must remain live through an evacuation, which is why fire-resistant LSZH is the specification for these installations, not LSZH alone.
- Hospitals, airports, and high-occupancy public buildings: Loss of power to critical hospital circuits during a fire is not a tolerable failure. In airports and shopping centers, toxic gases in enclosed spaces create secondary casualties independent of where the fire is located. LSZH cable throughout these buildings keeps the cable infrastructure from worsening the event; fire-resistant LSZH on life-safety circuits keeps those circuits running through it.
- Data centers: In data centers, the primary concern is not evacuation but equipment damage. Hydrogen chloride from burning PVC forms hydrochloric acid on metal and moisture, corroding server components, copper busbars, and circuit boards across a facility, including areas well away from the fire source. LSZH removes that damage pathway; on critical power and communication circuits, fire-resistant LSZH keeps those circuits live until the fire is controlled.
- Industrial environments: Oil and gas facilities, chemical plants, and enclosed processing areas combine fire risk with process instrumentation and pressurized systems. Halogen-free cable is frequently a defined project requirement in these environments, driven by both fire safety codes and the sensitivity of on-site process equipment.
What to Verify Before You Order
Fire performance standards are not interchangeable across regions. A cable compliant with one framework does not automatically satisfy another, and submitting test reports against the wrong standard is a compliance failure on any regulated project.
| Region | Framework | Key Standards |
| International / Asia / Middle East / Africa | IEC | IEC 60332 (flame), IEC 60754 (halogen/acid gas), IEC 61034 (smoke), IEC 60331 (circuit integrity) |
| European Union | CPR / EN | EN 50575; Euro classes Aca–Fca (single classification covering flame, heat, smoke, and acidity) |
| United Kingdom | BS / EN | BS 7211 (LSZH building wire), BS 6724 (armored variants); CPR-derived classes apply to many product categories |
| United States | UL / NFPA | UL 1685 (flame and smoke), NFPA 262 (plenum/tunnel); IEC test reports are not accepted as substitutes for UL listing |
| Australia / New Zealand | AS/NZS | AS/NZS IEC 60332; national overlays apply, particularly on government infrastructure |
Once the applicable framework is confirmed, verify that your supplier can provide documentation against it. A complete submission typically includes:
- Smoke density test report with measured transmittance values
- Acid gas and halogen content test report
- Flame propagation test report (single cable or bundled installation, as applicable)
- Circuit integrity test report confirming test duration and conditions (FR-LSZH only)
- Material certificates traceable to production batch
- Declaration of conformity for the applicable standard framework
For projects under UL jurisdiction, confirm UL listing status in addition to test documentation.
GENGU CABLE: FR & LSZH Power Cables for International Projects
At GENGU CABLE, we manufacture both LSZH and fire-resistant LSZH power cables—the WDZ and WDZN series—across a full range of conductor types and cross-sections, with installations across international markets including the Asian Games. All cables use halogen-free polyolefin insulation and sheathing throughout; the WDZN series adds a fire-resistant layer to the halogen-free construction for use in life-safety and emergency circuits.
Send us your project specification and we will confirm availability, lead time, and the compliance documentation your project requires.
