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OFNP vs. OFNR vs. CPR vs. LSZH: The Global Guide to Fiber Cable Jackets

Understanding the critical differences between North American (NEC) and European (CPR) fire safety standards for optical fiber infrastructure.

Choosing the right cable jacket is a balance of regional code compliance, material science, and safety priorities. Understanding the difference between NEC and CPR frameworks ensures your network is both resilient and compliant.

Global Classification Guide

Selecting the right jacket is a balance between regional code compliance and specific environmental hazards. North American markets prioritize air-handling safety (NEC), while European and Asian markets focus on human toxicity and emission control (CPR/LSZH).

NEC: OFNP & OFNR

North America

The standard for building codes in the US and Canada. Includes Plenum (OFNP) for HVAC spaces and Riser (OFNR) for vertical shafts.

  • OFNP: NFPA 262 Steiner Tunnel Rated
  • OFNR: UL 1666 Flame Propagation Rated
  • Engineered for specific building zones
  • Primarily Fluoropolymer or PVC based

Euroclass: CPR B2ca/Cca

Europe

Mandatory for permanent installations in the EU and UK. Provides individual ratings for smoke, flaming droplets and acidity.

  • Legally required for all permanent EU installations
  • Superior heat release and fire growth protection
  • Ensures safe smoke levels for public building evacuation
  • Protects hardware from acidic combustion byproducts

LSZH (Low Smoke Zero Halogen)

Asia & Oceania

The preferred standard for Asia and Australia. Rated according to IEC 60754 (and sometimes others).

  • Zero Halogen (IEC 60754)
  • Low Smoke (IEC 61034-2)
  • Non-corrosive to GPU/AI server fabrics
  • Ideal for data centers and buildings in Asia

Regional Safety Benchmarks

Each major global market prioritizes a specific safety metric to define its highest tier of cable infrastructure.

5.0 ft

USA (OFNP) Flame Limit

≤ 20 W/s

EUROPE (B2ca) FIGRA

0.0%

ASIA (LSZH) Halogens

4.3 pH

GLOBAL (Non-Acidic)
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Indoor Cables

ScaleFibre's range of indoor optical fiber cables.

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The Material Science of Protection

1
Thermal Resistance

OFNP jackets use Fluorinated Ethylene Propylene (FEP) with an Oxygen Index >95% to prevent ignition in air.

2
Endothermic Cooling

LSZH jackets contain hydrated minerals that undergo an endothermic reaction, releasing water vapor to cool the cable.

3
Intumescent Char

Flame-retardant polymers can form a thermally stable char or protective layer during combustion that helps slow heat transfer and reduce flame spread, protecting internal cable components.

4
Emission Management

Zero-halogen compounds prevent the formation of corrosive hydrogen chloride (HCl) gas during combustion, reducing toxic and corrosive emissions compared to PVC-based materials.

Primary Hazards in Cable Fires

In enclosed spaces, smoke inhalation and equipment corrosion often cause more damage than the flames themselves.

Jacket Performance Profile

A high level comparison between regional and material standards.

North American NEC (OFNP/OFNR)

  • →
    Application: Standards defined by NFPA 70 for US/Canadian builds.
  • →
    Fire Testing: Focused on the Steiner Tunnel test (NFPA 262).
  • →
    Rating: OFNR (Riser) and OFNP (Plenum) ratings for different spaces.
  • →
    Environmental: Heavy focus on flame travel and smoke density.

European CPR

  • →
    Application: Mandatory Euroclasses under EN 50575 for EU territory.
  • →
    Fire Testing: Focused on FIGRA (Fire Growth Rate) and heat release.
  • →
    Rating: Range from Fca to Aca, with a practical limit of B2ca.
  • →
    Environmental: Stringent ’s, d, a’ ratings for smoke, droplets, and acidity.

Fire Growth Rate Index (FIGRA) by Class

Safety Tiers
CPR B2ca and Cca provide the lowest heat release and are mandatory for modern European high-density builds.

Real-World Applications

Public Buildings
Public Buildings

Using the correctly rated cable jacket for public buildings, which are often a higher level.

Data center and Hyperscale
Data center and Hyperscale

Using the correct class of cable jacket in the right country, ensuring compliance with local regulations.

High-Value GPU Clusters
High-Value GPU Clusters

Using high-tier CPR jackets to prevent acidic gas from corroding multi-million dollar semiconductor fabrics.

Technical FAQ

+ Why is 'Zero Halogen' (LSZH) critical for servers?
Standard PVC jackets contain halogens like Chlorine. When burned, they release Hydrogen Chloride gas. In contact with humidity, this forms Hydrochloric Acid, which corrodes electrical equipment. LSZH helps ensure your expensive compute, storage or GPU fabrics remain functional after a minor fire event.
+ Can I use OFNR in a plenum space?
No. OFNR (Riser) does not meet the smoke suppression or flame retardancy required for plenums. However, you can use OFNP (Plenum) in a Riser space. For high-density North American builds, we recommend TightBEND Plenum cables to maintain compliance across all zones.
+ Can I use OFNP in a riser space?
Yes. In the North American NEC hierarchy, OFNP (Plenum) is the highest rating and is ‘downward compatible’ with Riser (OFNR) and General Purpose (OFNG) environments. While you cannot use a Riser cable in a Plenum space, you can use a Plenum cable in a Riser space. Customers specify a plenum cable like TightBEND Plenum for the entire project to simplify inventory and ensure maximum fire safety throughout the building’s vertical and horizontal runs.
+ What is the difference between IEC and CPR?
IEC 60332/60754 are the testing methodologies for toxicity and smoke. CPR (EN 50575) is the European legal framework that uses those test results to categorize cables into Euroclasses (B2ca, Cca, etc.). While IEC is a standard, CPR is the law in the EU and UK.
+ Why are LSZH cables sometimes stiffer?
To achieve zero-halogen fire retardancy, manufacturers use high concentrations of mineral fillers like Aluminum Trihydrate. This makes the jacket less flexible than standard PVC. To counter this in high-density racks, many customers switch to cables like the range of SlimCORE micro-cables which optimize bend radius despite the stiffer materials.
+ How does the CPR rating impact High-Density AI clusters?
AI clusters generate massive heat. A cable with a low CPR rating (like Dca or Eca) can contribute to a rapid ‘flashover’ fire. Using higher CPR rated MPO Trunks provides the necessary thermal barrier and prevents the fire from traveling through cable trays into the heart of the compute fabric.
+ What are the 's', 'd', and 'a' suffixes in European Euroclass/CPR cable ratings?
These are additional safety criteria under CPR. The ’s’ value reflects smoke acidity/density, with ‘s1’ being the highest performance. The ’d’ value reflects flaming droplets, with ‘d0’ meaning ’no flaming droplets’ (preventing fire from dripping onto equipment below). The ‘a’ value reflects gas acidity, with ‘a1’ indicating the lowest level of acidity.
+ Can LSZH cables be used outdoors?
Standard indoor LSZH jackets are not UV-stabilized or water-blocked. For transitions between buildings, you should use an indoor/outdoor rated cable like SmartRIBBON Indoor/Outdoor that features a water-blocked construction.
+ Is OFNP the same as LSZH?
Not necessarily. OFNP (Plenum) is a North American fire rating that often uses fluoropolymers (which contain halogens but are highly fire-resistant). LSZH is a material specification (Low Smoke Zero Halogen). You can have an LSZH cable that is NOT Plenum rated, and a Plenum cable that is NOT LSZH. For global projects, ScaleFibre provides SmartRIBBON dual-rated cables that are engineered to meet overlapping international safety criteria.
+ How should I handle large cable drums of high-safety rated fiber?
Due to the mineral fillers in high-safety jackets, they are more sensitive to ‘kinking’ or compression during installation. Always follow our Cable Drum Handling Guide and ensure you don’t exceed the minimum bend radius or crush the internal fibers before they are even deployed.

Choose the Right Cables for Fire Safety

Does your next build require North American OFNP or European CPR B2ca? Get in touch today.

Contact Our Team

A range of cable options for OFNP, OFNR, and CPR-rated assemblies.

References & Footnotes

  1. NFPA 262: Standard Method of Test for Flame Travel and Smoke of Wires and Cables (Plenum).
  2. EN 50575: Power, control and communication cables - Construction Products Regulation (CPR).
  3. IEC 60754-2: Determination of acidity and conductivity of gases evolved during combustion.
  4. UL 1666: Standard for Test for Flame Propagation Height of Cables (Riser).
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