EN 45545-2 Explained: How HL1, HL2 and HL3 Are Assigned and How to Check Your Cable Ties

Rail vehicle specifications often include a line like this: "Cable accessories shall comply with EN 45545-2, HL2." Where does HL2 come from? Why can the requirement for cable ties differ between the inside and the outside of the same vehicle? And if the next project says HL3, can the current part numbers still be used? This article explains the EN 45545 grading logic step by step, then uses the KSS cable tie table to show how to check before submission.

1. Why Rail Is So Strict: Evacuation Conditions Drive Everything

The fire risk of a rail vehicle depends less on how much combustible material is on board and more on whether passengers can get out in time. A small fire on a surface section with closely spaced stations allows passengers to leave within minutes. The same fire in the middle of a long tunnel may mean the train has to keep running to the portal before anyone can evacuate. EN 45545 follows this logic: first it looks at where the vehicle operates and how hard evacuation is, then it sets the fire performance thresholds for materials.

2. Where the HL Comes From: Operation Category x Design Category

EN 45545-1 first assigns two categories to the vehicle and then combines them to give the hazard level (HL):

Category	Code	Definition (summary)
Operation category	OC1	Surface or elevated sections with closely spaced stations and side evacuation; short tunnels
Operation category	OC2	Underground sections or tunnels of up to about 5 km, with stations offering access to safety
Operation category	OC3	Tunnels longer than 5 km or sections with limited evacuation points
Operation category	OC4	High-risk cases where vehicles not built to a fire-hardened design could become trapped; rarely applied in practice
Design category	N	Standard vehicles such as passenger coaches, metros and trams
Design category	A	Automatic vehicles with no emergency-trained staff on board
Design category	D	Double-deck vehicles
Design category	S	Sleeping or couchette vehicles

Combining the two categories gives the hazard level (simplified table):

Design category	OC1	OC2	OC3	OC4
N (standard)	HL1	HL2	HL2	HL3
A (automatic)	HL1	HL2	HL3	HL3
D (double-deck)	HL1	HL2	HL3	HL3
S (sleeper)	HL1	HL2	HL3	HL3

The table is a simplified summary of the EN 45545-1 logic. The formal classification follows the standard and the design documents of the vehicle project.

The table shows that a metro running through long tunnels (OC3) with driverless operation (A) moves from HL2 to HL3. The HL is set by the vehicle project, not by the material. The material's job is to reach the level the project requires at the position where it is installed.

3. R22 / R23: Different Thresholds Inside and Outside the Same Vehicle

Once the HL is known, EN 45545-2 divides products into 26 requirement sets, R1 to R26, each with its own tests and thresholds. Small wiring accessories such as cable ties fall under R22 (vehicle interior) or R23 (vehicle exterior), depending on where they are installed. Tests in these requirement sets include oxygen index (EN ISO 4589-2), smoke density (ISO 5659-2) and smoke toxicity (NF X70-100). The higher the HL, the stricter the threshold.

This is why the same part number can be HL2 inside the vehicle and HL3 outside: it is judged against two different sets of criteria.

Exact test conditions and limits for each requirement set are defined in the EN 45545-2 standard.

4. The KSS Cable Tie Table: Check Against the Project Level

KSS cable ties hold EN 45545-2 approval. By material grade, the results are:

Material grade	R22 (interior)	R23 (exterior)	Project levels covered
Nylon 66 (standard)	HL2	HL2	HL1 / HL2 projects, interior and exterior
Nylon 66 (UV resistant)	HL2	HL3	HL1 / HL2 interior; HL3 projects for exterior
Nylon 66 (flame retardant V0)	HL2	HL2	HL1 / HL2 projects, interior and exterior
Nylon 612 (CV-N612 weather resistant)	HL2	HL2	HL1 / HL2 projects, interior and exterior

Two points that are easy to miss:

First, if the project is classified HL3, the UV-resistant grade can be used at exterior (R23) positions. For interior (R22) positions, however, none of the grades in the table reaches HL3. For such projects, please check with our sales team first rather than applying the current part numbers directly.

Second, the V0 grade carries the highest UL94 rating, 94V-0, yet it is still HL2 for exterior use under EN 45545-2, while the UV-resistant grade reaches HL3. UL94 and EN 45545-2 are independent systems, and one cannot be inferred from the other.

Certification coverage varies by specific model and SKU. Please confirm the approved part numbers and certificates for your project with our sales team.

5. EN 45545-2 and Local Standards in Mainland China Are Not Interchangeable

EMU and urban rail projects in mainland China use local standards and product approval schemes in addition to EN 45545, for example TB/T 3237 for EMU interior material flame retardancy and CRCC product certification. Their test methods and pass criteria differ. An EN 45545-2 certificate does not automatically mean compliance with the local standard, and the reverse is also true. Check against whichever system the specification names.

6. Three Checks Before Submission

• Step 1: Get the project HL. Confirm the vehicle's operation category and design category with the vehicle manufacturer or system integrator, or confirm the HL stated in the specification.

• Step 2: Split positions into R22 and R23. Group cable tie positions into interior and exterior, and list exterior positions separately because the threshold may differ.

• Step 3: Check certificates by part number. Approval is granted per model, not per product family. Compare the actual part numbers with the certificate coverage list and confirm the certificate is still valid.

Contact

For EN 45545-2 certification documents, material grade tables or the full part number list for rail projects, please contact:

Jwo Yiih Enterprise CO., LTD.

Contact us at sales@jwoyiih.com or call +886-4-8760280 for the full solution package and part number list.

Note: the operation category, design category and HL matrix are a simplified summary of public technical information on EN 45545-1; the R22 / R23 tests are a summary of public technical information on EN 45545-2, and exact limits are defined in the standard. The KSS cable tie grade x HL table is taken from the approvals page of the KSS rail transit industry presentation and the existing Rail Transit Solutions article. Certification varies by specific model and SKU. For a formal quotation, please confirm current part numbers and valid certificates with our sales team.