EN 45545-2 Cable Ties for Rail Vehicles: R22, R23, R24 and HL3 Explained

A cable tie can be honestly described as "EN 45545-2 tested" and still miss the classification your customer actually needs. EN 45545-2 is the European standard for the fire behaviour of materials and components in railway vehicles, and it does not give one verdict — it sorts every small part into a requirement set (R22, R23 or R24) and then into a hazard level (HL1 to HL3). This guide explains how those two axes work, the three numbers that decide the outcome, and how to read a supplier's test report line by line — using our own report, YJ2024120103, with every figure shown.

Why a Cable Tie Is Treated as a Fire Risk Item

A rail vehicle is a sealed, densely packed space with narrow escape routes. In rolling-stock fires, casualties are driven by smoke and toxic gas rather than by the flame front: smoke spreads through a carriage and a tunnel far faster than people can leave it. That is why fire safety rules reach down to the small plastic parts, not just the panels and seats. A tie costs a few cents, but on a cable bundle it is simultaneously a possible ignition path, a smoke source and a toxic gas source.

It also means a generic flame-retardant grade is not sufficient on its own. A tie that passes a small-scale flammability test — a UL 94 V-0 rating, for example — has demonstrated that it self-extinguishes under a small flame. It has not demonstrated how much smoke it makes, or what is in that smoke. EN 45545-2 asks all three questions. If your project mixes those two ideas together, our guide to heat-stabilized vs flame-retardant cable ties covers where the UL 94 line actually falls, and our material specification guide lists the grades themselves.

What EN 45545-2 Is, and What It Replaced

EN 45545 is the European standard series for fire protection on railway vehicles, published by CEN and organised in seven parts. Part 2, Requirements for fire behaviour of materials and components, is the one a component supplier works to. It is a single European framework that replaced a set of national rules — BS 6853 in the UK, DIN 5510-2 in Germany, NF F 16-101 and 16-102 in France, UNI CEI 11170 in Italy — so that one test report can serve a European project instead of four.

The edition in force is EN 45545-2:2020, amended by A1:2023. The amendment reworked toxicity testing so that EN 17084 becomes the normative reference, made complete-seat testing mandatory under EN 16989, and moved the grouping-rule mass thresholds into a flowchart. Conflicting national standards are withdrawn from October 2026, and reports issued under the earlier edition remain valid through the transition. If a customer's specification names a particular edition, follow their document rather than the datasheet's.

The R Sets That Apply to a Cable Tie

The standard sorts products by where they sit and how much of them there is. Large exposed surfaces — panels, ceilings, flooring — fall under the R1 to R21 sets. Cable ties, clips and comparable small parts fall under three:

Two things get misread here. First, R24 is not "the cable tie category" — it is the lightest of the three requirement sets, and a report proving R24 has proved one property, not three. Second, R22 and R23 are not interchangeable: the interior set carries the stricter limits, so an exterior classification does not transfer to a part fitted inside the car. When a tie is described simply as "EN 45545-2 compliant", the first useful question is: R22, R23, R24 — or all three?

HL1, HL2, HL3: The Level Under Each Set

Each requirement set is then judged at one of three hazard levels. The level comes from the vehicle's operating and design category under EN 45545-1, with HL3 covering the highest-risk duty. HL3 is the level worth claiming, and the one to verify when a supplier only writes "HL".

The limits below are the ones printed in the test report we hold, taken from Table 5 of EN 45545-2:2020:

Look at the shape of that table. R22's HL3 smoke limit of 150 is half of R23's 300, and its toxicity limit is half as well. A part can therefore reach HL3 outside the vehicle and stop at HL2 inside it, on exactly the same measured numbers. That is not a marketing distinction — it is the arithmetic of the standard.

The Three Numbers

• Oxygen index (EN ISO 4589-2). The lowest oxygen concentration that will sustain combustion of the material. Air is roughly 21%, so the higher the index, the harder the part is to ignite. Every HL3 classification in the table above requires 32% or more.
• Smoke density Ds max (EN ISO 5659-2, 25 kW/m², with pilot flame). The peak optical density of the smoke a specimen produces in a single-chamber test. Lower is better, and in practice this is the number that decides whether an interior part reaches HL3, because the 150 limit is half the HL2 allowance.
• Toxicity index CITNLP (EN 17084). The yields of eight target gases — CO, CO₂, HCN, HCl, HF, HBr, NOx and SO₂ — are each divided by a reference concentration and summed into one figure. Halogen-free formulations matter here, because HCl and HBr are precisely what halogenated flame retardants add to the smoke.

A useful check when a supplier quotes a figure without a method: an oxygen index or toxicity number means very little on its own, because the same material can be reported differently under different test methods and standard editions.

Reading a Report: Five Checks

1. Which requirement sets were requested? The report should name them. "EN 45545-2" by itself is not a result.
2. Which level was reached, set by set? Read the conclusion section line by line. A report may state HL3 for one set and HL2 for another — that is a normal and correct outcome, and it is not something to round up.
3. Does the sample match what you are buying? Colour, material grade and thickness are part of the tested object. A report on a 2.1 mm black weather-resistant PA66 plate describes that specimen, and a different thickness is a different specimen.
4. Which methods, and which edition? The three methods should be identifiable — EN ISO 4589-2, EN ISO 5659-2 at 25 kW/m², and EN 17084 — and the report should state which edition of EN 45545-2 the judgement was made against.
5. Who issued it, and can it be traced? A report number, an accredited laboratory, a specimen traceability record and a named signatory. Ask for the original rather than a marketing summary.

If the document you have been sent is a North American electrical listing rather than a rail fire report, the checks are different — our guide to verifying a UL certificate for cable ties and our comparison of UL 62275 and IEC 62275 cover that side.

Worked Example: Our Own Report, Line by Line

We had our black weather-resistant PA66 cable ties, trademark HS, tested by Zhejiang CTI Foresight Testing Co., Ltd in Hangzhou against EN 45545-2:2020, requesting R22, R23 and R24 at the same time. Report YJ2024120103, signed 26 December 2024. The classification the report assigns, laid out the way a datasheet presents it (highest level reached in bold):

The conclusion section states it plainly: the submitted sample meets the requirements of R22 for HL1/HL2, and meets the requirements of R23 and R24 for HL1/HL2/HL3. In other words the tie is classified at the highest hazard level for the exterior set and for the oxygen-index set, and at HL2 for the interior set.

The single reason R22 stops at HL2 is smoke density — 296.3 measured against an HL3 limit of 150 — even though the same specimen's oxygen index of 32.3% clears the HL3 bar of 32%, and its toxicity index of 0.54 sits comfortably inside the HL3 limit of 0.75. Under the R22 limits, 296.3 falls inside HL2's 300 ceiling. We publish that number openly because anyone defending this classification to their own customer will be asked why it is not HL3, and smoke density is the answer.

Some detail from the report is worth knowing, because it shows how the numbers were produced. The oxygen index specimen was 125 × 10 × 4.0 mm, tested by top-surface ignition. The smoke test ran three 75 × 75 × 2.1 mm specimens at 25 kW/m² with a pilot flame, returning individual Ds max values of 300.6, 294.9 and 293.3 — an average of 296.3, reached at about 349 seconds. In the toxicity test, CO averaged around 109 mg per gram of specimen and CO₂ around 590 mg/g; HCN was the only other gas found above the detection limit, at roughly 24 mg/g; and HCl, HF, HBr and SO₂ all fell below the method detection limit. That last point is the one that matters for a halogen-free specification.

What This Report Covers, and What It Does Not

Being precise about scope is part of what a test report is for. Report YJ2024120103 covers the black weather-resistant PA66 cable tie as submitted, judged against Table 5 of EN 45545-2:2020. It is a third-party test report, not a certificate, and it does not automatically extend to:

• Other colours, materials or grades in our range — a natural PA66 tie or a V-0 flame-retardant tie is a different specimen.
• Other thicknesses of the same compound.
• Edition A1:2023 specifically. Our report is issued against the 2020 edition. If your specification names EN 45545-2:2020+A1:2023, tell us and we will confirm exactly where we stand instead of assuming it transfers.

There is one more boundary worth stating. Whether a particular tie needs assessing at all depends on its combustible mass and exposed area — under the grouping rules, a very light interior part can fall outside the requirement entirely. Projects differ in how they apply that, and many buyers specify the R22/R23 test regardless because it is easier to defend. We are not going to tell you a test is unnecessary in order to close an order.

Specifying a Rail Tie

If you are sourcing cable management for rolling stock, send us four things and we can answer properly rather than generically:

• The requirement sets your project calls for — R22, R23, R24, or all three.
• The hazard level, and the vehicle category it comes from.
• The environment: interior or exterior mounting, colour, UV exposure, continuous operating temperature, and whether halogen-free is mandatory.
• The format: width and length, bundle range, and whether a mounted fixing is involved — our mounting methods guide covers the screw, adhesive and push-mount options, and the outside-serrated range covers low-profile routing.

For rail enquiries we quote against the report you will actually receive, with the tested specimen identified. The relevant parts of our range — self-locking nylon ties, heat-stabilized grades and the PA46 extra heat-stabilized range — are set out on the cable ties page, and the approvals behind them are listed on our certifications page.

Tell us the requirement set, the hazard level and where the tie is fitted, and we will come back within 48 hours with the closest tested configuration, the report reference, and free samples for your own verification.