Low Smoke Halogen Free Tape (LSHF/LSZH)

Low Smoke Halogen Free (LSHF), also known as Low Smoke Zero Halogen (LSZH) Tape, is a specialised flame-retardant binding and wrapping tape used inside power, control, instrumentation and fire-resistant cables. It serves as a core-binding layer and oxygen-barrier/flame-retardant layer. When exposed to fire, the tape absorbs heat, forms a stable charred insulating layer, restricts oxygen access to the insulation, suppresses flame propagation and releases only minimal, non-toxic, non-corrosive smoke.

Unlike conventional PVC or halogenated tapes, LSHF/LSZH Tape contains no chlorine, fluorine, bromine or iodine. Combustion gases remain nearly neutral (pH ≥4.3, low conductivity), protecting both people and sensitive electronic equipment. This makes it essential for cables installed in confined or high-occupancy spaces.

Key Technical Advantages for Cable Manufacturers

• Low smoke emission: Maintains high light transmittance (typically >60% per IEC 61034), improving evacuation visibility.
• Zero halogen / halogen-free: Acid gas content ≤0.5% (IEC 60754-1), pH ≥4.3 and conductivity ≤10 µS/mm (IEC 60754-2). No corrosive HCl formation.
• High flame retardancy: Oxygen index (LOI) commonly ≥30% (non-woven grades) up to ≥50% (high-performance coated grades). Temperature index often ≥450°C.
• Superior mechanical performance: Controlled elongation (typically ≥12–15%) enables tight, uniform wrapping without cracking or loose outer diameter. High tensile strength prevents breakage during high-speed cabling. Soft texture ensures smooth sheath appearance and full utilisation of the roll.
• Process-friendly: Non-toxic, odourless, does not affect cable current-carrying capacity or long-term electrical performance. Good dimensional stability at processing temperatures.
• Environmental & regulatory compliance: Asbestos-free, heavy-metal-free, supports RoHS, REACH and modern CPR / EN 50575 requirements when used in complete LSZH cable constructions.

Material Construction and Working Principle

The tape uses alkali-free E-glass fiber cloth as the base substrate. Both surfaces are impregnated and coated with a precisely formulated halogen-free flame-retardant system based on metal hydrates (primarily aluminium trihydrate ATH or magnesium hydroxide MDH) combined with synergistic binders. After coating, the material is baked, cured, and precision-slit to required widths.

When exposed to fire:

• The metal hydrates decompose endothermically, absorbing large amounts of heat and releasing water vapour.
• A stable, insulating carbonized char layer forms that restricts oxygen access to the underlying insulation.
• Smoke density remains low and combustion gases are essentially free of halogen acids.

This dual action (heat absorption + oxygen barrier) helps the finished cable meet the core fire-performance triad of IEC 60332 (flame propagation), IEC 60754-1/2 (halogen acid gas and acidity/conductivity), and IEC 61034-2 (smoke density).

Typical Technical Parameters

Data compiled from leading manufacturers’ specifications :

Comparison with Conventional Binding Tapes

Primary Applications in Cable Construction

• Core binding and filler retention in multi-core power, control and instrumentation cables.
• Oxygen-barrier / flame-retardant layer in fire-resistant cables (often combined with mica tape).
• Bedding or separation layer under LSZH outer sheaths.
• Marine, offshore, nuclear, tunnel, data-centre, hospital and high-rise building cables where low smoke and non-corrosive gases are mandatory.
• Small-section flexible cables and high-flame-retardant constructions requiring thin, soft wrapping without increasing overall diameter excessively.

Performance Contribution to Finished Cable Standards

When correctly applied (typically 20–50 % overlap depending on design), the tape contributes directly to:

• IEC 60754-1: Halogen acid gas ≤5 mg/g
• IEC 60754-2: pH ≥4.3 and conductivity ≤10 µS/mm
• IEC 61034-2: Minimum light transmittance ≥60 % (premium constructions often exceed 80 %)
• IEC 60332-1 / 60332-3 series flame propagation
• Supporting higher CPR Euroclasses (B2ca-s1,d1,a1 or Cca) and regional requirements (EN 45545 for rail, GB 31247 B1 for China, etc.)

Selection and Application Notes for Engineers

1. Thickness selection is driven by required oxygen barrier performance versus finished cable diameter and flexibility targets. 0.15–0.18 mm grades are preferred for flexible or small-section cables; 0.20–0.25 mm for heavier power cables.
2. Ensure the tape has adequate elongation (≥15 %) to avoid cracking or loose wrapping after sheathing, especially in winter production conditions.
3. Compatibility with subsequent extrusion (LSZH or XLPE compounds) must be verified; residual solvents or improper curing can affect adhesion or electrical properties.
4. Storage: keep sealed, dry, 10–30 °C; shelf life typically 12 months.
5. Custom widths, higher oxygen-index formulations, and dual-side coated variants are routinely available for long-term OEM programmes.

Key Technical Takeaways

• LSHF / LSZH tape is not merely a binder; it is an active fire-performance component that absorbs heat, forms a protective char, and keeps smoke and corrosive gases to levels required by modern safety codes.
• Glass-fiber substrate + metal-hydrate coating delivers oxygen indices ≥50–55 % and smoke densities ≤100–150 while maintaining mechanical integrity.
• Correct grade selection and wrapping technique directly influence the ability of the finished cable to pass IEC 60754, IEC 61034 and higher CPR classifications.
• Long-term reliability depends on consistent coating quality, dimensional stability and supplier process control.

For detailed technical data sheets, custom width and thickness options, oxygen-index optimisation, or joint development of fire-resistant cable constructions, Inquiry Now.