FR vs FR-LSH
vs LSZH.
Three cable types. Three performance levels. The wrong choice in the wrong building zone fails the fire safety inspection — and fails occupants in a fire. This guide explains exactly what each means, what the standards require, and where each is specified.
The three types — at a glance.
What "FR" and "LSH" and "LSZH" actually mean in measurement.
These are not marketing terms — they are defined test limits in Indian and international standards. Every number below is verified from IS 694:2010 and IS 17048:2018.
| Test Parameter | FR (IS 694:2010) | FR-LSH (IS 694:2010 FR-LS) | LSZH/HFFR (IS 17048:2018) | Standard |
|---|---|---|---|---|
| Oxygen Index (OI) | > 21% (self-extinguishes in air) | > 29% | > 30% | IS 10810 (Part 58):1998 |
| Temperature Index (TI) | > 250°C | > 250°C | Not applicable (HFFR) | IS 10810 (Part 64):2003 |
| Halogen content (HCl) | Not limited (> 20% typical) | < 15% | < 0.5% | IEC 60754-1 |
| Smoke density (transmittance) | Not limited (< 20% typical) | > 60% | > 60% | IEC 61034-2 |
| Flame propagation | IEC 60332-1-2:2004 | IEC 60332-1-2:2004 | IEC 60332-1-2:2004 | IS 10810 (Part 61):1988 |
| Max conductor temperature | 70°C | 70°C | 90°C — HFFR insulation per IS 17048:2018 Clause 10.3 (not XLPE) | IS 694:2010 / IS 17048:2018 |
| BIS standard | IS 694:2010 | IS 694:2010 (FR-LS) | IS 17048:2018 (separate licence) | BIS |
FR-LSH requires HCl < 15%. LSZH/HFFR requires HCl < 0.5%. That is a thirty-fold difference in halogen emission. A BOQ or drawing that specifies IS 17048:2018 HFFR cannot be satisfied by IS 694:2010 FR-LSH. They are separate BIS standards with separate licence requirements. Always check which standard is specified — they are different products, not different names for the same thing.
The National Building Code 2016 mandates specific cable types by building zone.
NBC 2016 Part 4 (Fire and Life Safety) specifies cable selection for different building types and occupancy zones. This is not advisory — it is a compliance requirement that affects building occupancy certification.
| Building / Zone | Required Cable | Why |
|---|---|---|
| Back-of-house, plant rooms, external runs | FR IS 694:2010 | Non-occupied zones — basic flame retardance sufficient |
| Corridors, escape routes, lift lobbies | FR-LSH IS 694:2010 | Evacuation routes — smoke must not impair visibility |
| Occupied floors — offices, residential | FR-LSH IS 694:2010 | People present — low smoke protects evacuation |
| High-rise above G+4 — all areas | FR-LSH IS 694:2010 | NBC 2016 mandatory for tall buildings throughout |
| Hospitals — all wiring | HFFR IS 17048:2018 | Patients cannot self-evacuate — smoke is the primary hazard |
| Hotels — 5-star, all occupied areas | FR-LSH IS 694:2010 | Dense occupancy, public accommodation — NBC mandated |
| Schools, colleges, places of assembly | FR-LSH IS 694:2010 | Public buildings — NBC 2016 fire provisions apply |
| Underground metro stations | HFFR IS 17048:2018 | DMRC specification — underground enclosed, limited exit |
| Airport terminal buildings | HFFR IS 17048:2018 | AAI/DGCA specification — dense passenger occupancy |
| Data centres, server rooms | HFFR IS 17048:2018 | Equipment survival — HCl gas corrodes servers at sub-ignition temperatures |
The fire safety case for FR-LSH and HFFR — in plain numbers.
In most building fires, occupants are incapacitated by smoke before they reach flame. PVC insulation burning in an enclosed corridor can reduce visibility to near zero within 3–4 minutes. Toxic HCl gas impairs coordination and consciousness before it causes direct injury. The rationale for FR-LSH and HFFR is not primarily about the cable burning — it is about what the cable releases when it burns near other burning materials.
Standard FR PVC typically produces smoke with less than 20% light transmittance — meaning less than one-fifth of ambient light passes through the smoke. FR-LSH and HFFR must achieve greater than 60% transmittance. In a corridor, the difference is the ability to see an exit sign at 10 metres versus being unable to see your hand at arm's length.
FR vs FR-LSH vs LSZH — selection questions.
How to decide which insulation family is correct for a specific building zone or application.
Can I substitute FR-LSH (IS 694:2010) for HFFR (IS 17048:2018) in a hospital?
No. Both are flame retardant and both achieve smoke transmittance above 60%, but the HCl emission limits are not interchangeable: FR-LSH permits < 15% HCl per IS 694:2010, while HFFR requires < 0.5% per IS 17048:2018 — a 30-fold difference.
NBC 2016 Part 4 Cl. 4.14 mandates HFFR specifically for Group C institutional buildings (hospitals, nursing homes) because patients cannot self-evacuate, and halogen acid gas at sub-ignition temperatures damages medical equipment and impairs evacuation. Specifying FR-LSH where IS 17048:2018 HFFR is required creates a compliance deficiency at occupancy certification.
Is plain FR sufficient for a residential building?
It depends on building height. NBC 2016 Part 4 Cl. 4.11 permits plain FR (IS 694:2010) for low-rise Group A residential buildings up to G+3.
For G+4 and above (high-rise residential), FR-LSH (IS 694:2010) is mandatory on all floors per Cl. 4.11.3 — escape-route smoke protection is the driver. Specifying plain FR in a high-rise where FR-LSH is required risks rejection at the occupancy-certificate inspection. Always verify the building height classification and the applicable NBC clause before procurement.
Why is LSZH/HFFR specified for data centres and metros if FR-LSH meets the smoke limit?
Data centres and metro stations require HFFR (IS 17048:2018) primarily because of HCl gas damage to equipment, not just occupant safety. Burning PVC insulation — whether FR or FR-LSH — releases hydrogen chloride gas that corrodes electronic circuits, contacts, and metal infrastructure even at sub-ignition temperatures.
HFFR's < 0.5% HCl limit (versus < 15% for FR-LSH) protects equipment survival during a fire elsewhere in the building. For data centres, this can mean the difference between recoverable infrastructure and a total write-off. Underground metro stations carry the additional concern of evacuation in a confined space.
Are LSZH and HFFR the same product, or two different categories?
LSZH (Low Smoke Zero Halogen) and HFFR (Halogen-Free Flame Retardant) describe the same product category — both compliant with IS 17048:2018. "HFFR" is the formal BIS designation; "LSZH" is the colloquial term emphasising the low-smoke and halogen-free properties. The "zero" in LSZH is approximate — IS 17048:2018 permits HCl < 0.5%, not strictly zero.
What matters operationally: ensure the cable carries a valid IS 17048:2018 BIS licence (separate from any IS 694:2010 licence) and meets the limits — Oxygen Index > 30%, smoke transmittance ≥ 70%, HCl < 0.5%.
Specify the correct cable for your project.
Our technical team maps IS 694:2010, IS 17048:2018, and NBC 2016 compliance requirements to the exact project type.