EN 45545-2: Fire Behavior of Materials, R-Sets & Hazard Levels (HL1-3)

EN 45545-2 is the core document of the European railway fire safety series. It specifies the reaction-to-fire performance requirements for materials and components installed on railway vehicles. Simply put, it dictates whether a specific plastic, fabric, or rubber can be used on a train based on its flammability, smoke emission, and toxicity.

The standard replaces older national norms (DIN 5510-2, BS 6853, NF F 16-101) with a unified testing regime centered on the “R-Set” (Requirement Set) system, which links the component type to the vehicle’s Hazard Level (HL).

1. How to Read EN 45545-2: The R-Sets

You cannot simply ask for “Fireproof Material.” The testing requirements change based on the component’s function and location. EN 45545-2 divides components into 26 categories called Requirement Sets (R1 to R26).

2. The “Big Three” Metrics

Passing an EN 45545-2 test requires staying below specific thresholds for three critical physical phenomena:

• MARHE (Maximum Average Rate of Heat Emission): Measured in kW/m² via the Cone Calorimeter (ISO 5660). It predicts if the material will fuel a “Flashover.” For HL3, MARHE must typically be < 60 kW/m².
• Ds(max) (Optical Density of Smoke): Measured via the Smoke Chamber. It ensures that burning materials do not create a smoke screen that blinds passengers finding exits.
• CIT (Conventional Index of Toxicity): A calculated value based on the concentration of 8 lethal gases (like HCN, HF, CO) in the smoke.

3. Impact of Hazard Levels

The strictness of the test depends on the vehicle’s classification (defined in EN 45545-1). A material that passes HL1 (Trams) might fail HL3 (Metro/Sleeper). Engineers must always specify the target HL when sourcing materials.

4. Small Parts & Grouping Rules

Not every single screw needs to be tested. EN 45545-2 defines Grouping Rules for small components (weight < 10g or < 100g). If combustible materials are separated by sufficient distance, or their total mass is insignificant, they may be exempt from full-scale testing under strict calculation rules.