FRLS and LSZH Cable — Fire Performance in Cables

FRLS (Flame Retardant Low Smoke) cable resists flame spread and produces less smoke and acid gas while burning; LSZH cable does the same with zero halogen content. Neither keeps a circuit working in a fire - that is fire-survival cable, a separate product for circuits that must keep operating.

By Dhruv Agarwal · · 1 min read

What it is

A family of cable specifications defined by how the cable behaves in a fire, rather than by its electrical properties.

Three distinct things get confused in Indian specifications:

TypeWhat it does
FRLSResists flame spread, reduces smoke and acid gas while burning
LSZHAs above, with zero halogen content
Fire survivalKeeps the circuit energised during a fire for a stated period

FRLS is not fire resistant. It burns; it just burns less badly.

Why smoke is the specification that saves lives

Most fire deaths are from smoke inhalation, not burns. A standard PVC cable in a burning shaft produces dense black smoke and hydrogen chloride gas, which both obscures escape routes and attacks the lungs. In a stair core or a basement, that is the mechanism that kills.

Reducing smoke and acid gas from the very cables that run through escape routes is therefore a life safety measure, not a specification upgrade.

Mapping cable type to location

Location or dutyTypical requirement
General distribution in open areasFRLS
Escape routes, stairs, lobbiesLSZH preferred
Basements and enclosed shaftsLSZH
Fire pumps, pressurisation fansFire survival
Fire alarm and emergency lightingFire survival
Data centres and critical roomsLSZH

Where projects go wrong

  • FRLS specified for fire pumps. The pump stops when the cable burns through — exactly when it is needed.
  • One grade across the whole project, either overspending everywhere or underspecifying in the places that matter.
  • Fire-survival cable installed with ordinary accessories. The rating belongs to the complete system, including glands, clips and supports; plastic clips melt and drop the cable.
  • Certificates not verified against the delivered drum.

Standards referenced

Fire and life safety provisions for services under NBC 2016, Part 4. Cable construction under IS 7098. Fire performance test methods under IEC 60332.

Standards referenced

  • NBC 2016, Part 4 — Fire and life safety — services (Bureau of Indian Standards)
  • IS 7098 — Cross-linked polyethylene insulated cables (Bureau of Indian Standards)
  • IEC 60332 — Tests on electric cables under fire conditions (IEC)

Frequently asked

No, and this is the most common and most dangerous misunderstanding. FRLS stands for Flame Retardant Low Smoke: it resists spreading flame along its length and produces less smoke and acid gas while burning. It does not continue to carry current in a fire. Circuits that must keep operating — fire pumps, pressurisation fans, fire alarm, emergency lighting — need fire-survival cable, which is a different and more expensive product.

FRLS reduces smoke and acid gas but still contains halogens. LSZH, Low Smoke Zero Halogen, contains none, so in a fire it produces no corrosive halogen acids at all. That matters in enclosed spaces where people escape through smoke and where corrosive gases would destroy electronics and structure. LSZH is the stricter specification and costs more.

NBC 2016 Part 4 drives cable selection by where the cable runs and what it serves. Escape routes, shafts, basements, high-rise buildings and high-occupancy spaces attract stricter requirements, and life safety systems require cables that maintain circuit integrity for a defined period. The specification should map cable type to route and function rather than applying one grade across the whole project.

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