# 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.

## 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**.

## Frequently asked questions

### Does FRLS cable keep working in a fire?

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.

### What is the difference between FRLS and LSZH?

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.

### Where does NBC require these cables?

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.

## Sources

- [NBC 2016, Part 4](https://www.bis.gov.in/standards/national-building-code/?lang=en) — Fire and life safety — services
- [IS 7098](https://standards.bis.gov.in/website/published-standards/department-wise) — Cross-linked polyethylene insulated cables
- [IEC 60332](https://webstore.iec.ch/en/) — Tests on electric cables under fire conditions

---

Source: https://hagerstone.com/materials/frls-cable