FRLS and LSZH Cable — Fire Performance in Cables

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:

Type	What it does
FRLS	Resists flame spread, reduces smoke and acid gas while burning
LSZH	As above, with zero halogen content
Fire survival	Keeps 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 duty	Typical requirement
General distribution in open areas	FRLS
Escape routes, stairs, lobbies	LSZH preferred
Basements and enclosed shafts	LSZH
Fire pumps, pressurisation fans	Fire survival
Fire alarm and emergency lighting	Fire survival
Data centres and critical rooms	LSZH

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.