Euroclass Fire Classification for Industrial Insulation: A1 to F, Smoke and Droplet Levels Explained

Insulation fire class is one of the few specifications on a datasheet that carries legal weight. Under the European Construction Products Regulation, a construction product placed on the EU market must declare its reaction-to-fire performance using the Euroclass system defined in EN 13501-1. That declaration is not marketing copy — it is the evidence on which a building control authority accepts or rejects a specification, and increasingly the evidence on which an industrial buyer accepts or rejects a delivery.

Yet the Euroclass code is widely misread. A specifier who asks for "A1" and nothing else has asked for half a fire classification. A buyer who accepts "B" without asking for the smoke and droplet suffixes has accepted a material that may be unlawful in the intended application. This guide explains the whole system — the seven main classes, the smoke and droplet suffixes, the test methods behind them, and how the code maps onto the insulation families used in industrial plant. For the A1-specific detail and the material-by-material comparison, see our A1 non-combustible insulation guide.

Why Insulation Fire Class Has Become a Procurement Question, Not a Marketing Term

Twenty years ago, fire performance was a line on a datasheet that few people read. Today the fire classification is a compliance document, and on many industrial projects it is the first thing an inspector asks to see.

Three pressures produced that shift. First, the Construction Products Regulation made the declaration mandatory: a product covered by a harmonised European standard cannot carry CE marking for the EU market without a declared reaction-to-fire class, and that declaration has to appear on the Declaration of Performance. Second, insurers and lenders have followed the regulators — a plant whose insulation cannot be evidenced to the declared class is a plant that is difficult to insure. Third, the cost of getting it wrong has moved from the material to the schedule: stripping and replacing non-compliant insulation after handover costs multiples of the insulation itself, and it costs them at the worst possible moment.

The practical consequence is that a competent industrial buyer now treats the fire classification as a testable specification rather than a claim. That means naming the class, the suffix, the standard and the evidence in the enquiry document. An enquiry that says "A1" tells a supplier what to.write on a label; an enquiry that says "A1 to EN 13501-1, with a current third-party certificate and a Declaration of Performance naming this product line" tells a supplier what will be checked at goods inward. The second version is the one that survives an audit.

EN 13501-1: The Test Stack Behind the Euroclass Rating

EN 13501-1 is a classification standard, not a test standard. It does not burn anything. It defines how the results of four separate test methods are converted into a class, and understanding those four tests is what turns a class from a label into a piece of evidence.

EN ISO 1182 — non-combustibility. A small specimen is placed in a furnace at about 750 °C. The material passes if the temperature rise stays within 30 °C, the mass loss stays within 50 %, and there is no sustained flaming. This is the test that separates the non-combustible classes from everything below them.

EN ISO 1716 — gross calorific potential. A sample is burned completely in a bomb calorimeter to measure its gross heat of combustion, written as PCS. Class A1 requires a PCS at or below 2.0 MJ/kg; class A2 allows up to 3.0 MJ/kg. This is the test that puts a number on how much energy the material could add to a fire, and it is the reason two materials that both look "non-combustible" can sit in different classes.

EN 13823 — the Single Burning Item (SBI) test. A corner assembly of two vertical panels is exposed to a gas burner, and the test measures how fast the fire grows and how much heat and smoke the assembly releases. The outputs that matter are FIGRA, the fire growth rate index; THR600s, the total heat released in the first 600 seconds; LFS, lateral flame spread along the specimen; plus the smoke integral and any flaming droplets. Almost everything a specifier cares about below class A1 comes out of this one rig.

EN ISO 11925-2 — small flame ignitability. A small flame is applied to the edge or the surface of a specimen for 15 or 30 seconds. It is a screening test, and for the lowest classes it is the only test that matters.

The classes draw on these tests in a fixed pattern. A1 draws on EN ISO 1182 and EN ISO 1716. A2 draws on those two plus the SBI test. B, C and D draw on the SBI test plus the small flame test. E draws on the small flame test alone. F is not a test result at all — it means no performance has been determined.

One route deserves a mention because it saves both time and money. The European Commission publishes classification-without-further-testing decisions for products whose performance is so well established that testing adds nothing. Mineral wool with an organic content at or below 1 % is the classic case: it is classified A1 on the basis of its composition, with no laboratory run. If a supplier quotes a mineral wool product as A1 under that route, that is legitimate — but the Declaration of Performance should still name the decision rather than simply asserting the class.

The Seven Main Classes — A1, A2, B, C, D, E, F

The Euroclass main class describes how much the material contributes to a fire in its early stage, and Euroclass A1 is the only class that carries no combustible contribution at any stage. The table below is the working summary used throughout the rest of this guide.

The thresholds behind the combustible classes are worth knowing, because they are what a test report actually shows. Class B requires a FIGRA at or below 250 W/s, a THR600s at or below 7.5 MJ, lateral flame spread that does not reach the edge of the specimen, and no flaming droplets or particles that persist beyond the limit. Class C relaxes the heat-release limits while keeping the flame-spread and droplet requirements. Class D relaxes them further still.

Where a quotation offers Euroclass F insulation, the honest reading is that no reaction-to-fire performance has been determined at all — not that the material failed a test. F is an absence of evidence, and an absence of evidence is not a specification.

Smoke Classes s1, s2, s3 — What the SBI Smoke Integral Really Says

The smoke class is appended to every class from A2 down to D, and it describes how much smoke the material produces during the SBI test. A1 is normally declared bare, because a material that does not burn produces no smoke worth measuring; where a project wants documented evidence, an A1-s1,d0 declaration can still be produced from an SBI run.

s1 — the smoke integral stays at or below 750 %·min. Smoke production is low, and this is the class specified for escape routes, occupied process buildings and any space where people have to find their way out through smoke.

s2 — smoke production falls between the s1 threshold and the s3 floor. Acceptable in ordinary industrial buildings with straightforward escape and low occupancy.

s3 — no smoke requirement has been met. Smoke production is high enough to affect tenability, and in practice this restricts the material to unoccupied or very low-risk locations.

The reason this matters more than most buyers expect is that in a real fire, smoke incapacitates long before flame reaches people. Two products can both be A2 and behave completely differently in a corridor: A2-s1,d0 keeps an escape route breathable, while A2-s3,d2 fills it. For data halls, hospital plant rooms, chemical control rooms and underground structures, s1 is not a nice-to-have — it is the requirement that makes the rest of the fire strategy work.

Droplet Classes d0, d1, d2 — Why Dripping Disqualifies Vertical Systems

The droplet class records what falls off a burning material, and in vertical applications it is the difference between a contained fire and a spreading one.

d0 — no flaming droplets or particles appear within 600 seconds. This is the class that lets a system be installed without additional fire-stopping measures.

d1 — some flaming droplets appear, but they stop burning within 10 seconds. The risk is lower, although vertical runs may still need a barrier.

d2 — flaming droplets that burn for longer than 10 seconds. Burning droplets fall, carry the fire downward and ignite whatever sits below, which is why a d2 material is difficult to justify on any vertical surface.

This is the mechanism behind what designers call the chimney effect. A C or D class material with a d2 rating installed on a vertical run can propagate fire along a cavity far faster than the material's own class suggests, because the droplets do the travelling rather than the flame front. Specifying d0 removes that path entirely, which is why systems written around A2-s1,d0 or B-s1,d0 frequently avoid the fire barriers a d2 build-up would demand.

Material chemistry drives the result. Phenolic foam and PIR char rather than melt, which is why they commonly reach d0. Polystyrene melts and drips unless it is heavily modified, which is why unmodified EPS and XPS sit at E or F with d2 behaviour.

How to Read a Euroclass Code: A2-s1, d0 and B-s1, d0 Decoded

A Euroclass code has up to three parts: the main class, the smoke class and the droplet class. Reading it correctly is mostly a matter of knowing what is mandatory and what is optional.

Euroclass A1 is declared on its own. No suffix is required, because a material that contributes nothing to a fire has no smoke or droplet performance to declare. Classes A2, B, C and D must carry both suffixes — a bare "A2" is an incomplete classification, and a supplier that quotes one has not finished the sentence. Class E is declared as E, or as E-d2 where droplets occur. Class F carries nothing.

So the codes read like this:

A1 — no contribution to fire, at any stage.

A2-s1, d0 — almost no contribution to fire, low smoke, no flaming droplets. This is the class usually written where A1 is uneconomic but the risk tier still demands near non-combustible behaviour with documented smoke and droplet performance.

B-s1, d0 — combustible, but with a very limited contribution to fire growth, low smoke and no flaming droplets. In a real escape route this material will frequently outperform an A2-s3,d2 product, because the thing that endangers people in the first ten minutes is smoke, not the main class.

Buyers searching the term write it both as Euroclass A1 and as Euro class A1 — the classification is identical and the difference is only typographic, so a specification written either way means the same thing and should be answered with the same evidence.

One further detail catches a lot of specifications out: the fire classification belongs to the tested build-up, not to the raw material. Where a code is written for a product that is installed as a composite — insulation plus facing plus adhesive — the classification applies to the build-up that was tested, not to the core material in isolation. A glass wool core that is A1 on its own can be downgraded by a polymer facing. The declaration has to name the composite.

Insulation Family to Euroclass — A Working Map

The table below maps the insulation families used in industrial plant onto the classes they realistically reach. Treat it as a starting shortlist: the binding number is always the one on the Declaration of Performance for the exact product and build-up quoted.

That last row raises the point that most specifications miss. EN 13501-1 classifies linear pipe insulation separately, with an L suffix appended to the class: A1L, A2L-s1,d0, BL-s1,d0 and so on down to EL and FL. The pipe classification uses a different fire scenario, because a cylindrical section on a small burner behaves nothing like a flat panel in a corner rig. A pipe insulation quoted to a flat-panel class has been quoted to the wrong test, and the insulation fire classification that a pipe specification needs is the one with the L on the end.

Industrial Application Selector by Risk Tier

Most projects do not need the highest Euroclass everywhere. What they need is the right class in the right place, which is a risk decision rather than a materials decision.

Two rules cut across all three tiers. First, the composite must be classified, not the core — a facing, an adhesive or a mechanical fixing can change the result. Second, a multi-layer system is only as good as its weakest declared layer plus its detailing: a penetration that is not sealed to the same performance as the surrounding build-up is where the fire actually goes.

For a material-by-material walk through the five industrial families — temperature band, form factor, fire class and lifetime cost — see the industrial pipe insulation materials selection guide.

Common Procurement Mistakes in Fire-Class Specifications

Specifying the main class only. Asking for "A2" without the suffixes is asking for an incomplete fire classification, because the standard requires A2 to be declared with a smoke and a droplet class. Write the full code.

Assuming the test thickness is the installed thickness. The SBI rig has a practical limit on specimen thickness, and thicker products need a defined mounting method. If the product will be installed at a thickness beyond the tested range, the declaration does not automatically cover it — ask what was tested and how.

Classifying the core instead of the composite. This is the most common failure on site. The core may be A1 while the facing is not, and the finished product carries the lower class. Insist on a declaration that names the build-up being supplied.

Accepting a supplier datasheet in place of a declaration. A datasheet is a marketing document. The documents that carry weight are the Declaration of Performance and the CE marking that accompanies it, backed by a test report from an accredited laboratory. Check that the certificate covers the product line quoted, and check the date.

Forgetting the pipe classification. Flat-panel classes and pipe classes are different tests with different suffixes. Pipe insulation needs the L classification.

Transferring a class between product forms. A board and a blanket made from the same base material can land in different classes, because the binder content, the density and the facing all differ. The class belongs to the product that was tested.

Euroclass, ASTM E84, IMO FTP — How the Standards Cross-Reference

Industrial projects often span more than one regulatory regime, and the three systems that come up most are frequently confused with each other. The most important thing to understand is that they answer different questions.

Euroclass, under EN 13501-1, is a reaction-to-fire classification. It asks how much the material itself contributes to a developing fire. ASTM E84, used in North America, is also a reaction-to-fire test, and reports a flame spread index and a smoke developed index that are grouped into Class A, Class B and Class C. The IMO FTP Code, applied under SOLAS to ships and offshore installations, is different again: codes such as A-60 describe fire resistance — how long a complete assembly holds back a fire, keeps its integrity and limits the temperature rise on the unexposed side.

A reaction-to-fire class and a fire-resistance rating are not interchangeable, and no table can make them equivalent. The approximate comparison below is a translation aid, not a legal substitution.

Several national systems outside Europe use a similar A and B lettering, including the Chinese national classification for building products. The letters look familiar, but the test methods and the thresholds are not the same, and a class in one system does not carry over to another without testing.

For the marine and offshore regime in detail, including what an A-60 rating actually requires and how it is certified, see the marine and offshore fire insulation standards guide, and for the rating itself, A-60 marine insulation explained.

Related Reading

The Euroclass system is not difficult, but it rewards precision: name the main class, name both suffixes for anything below A1, name the standard, and ask for the evidence that matches the build-up being supplied. Do that and the fire classification stops being a line on a datasheet and becomes what it was always meant to be — a checkable statement about how a material behaves in the first ten minutes of a fire.

Three follow-ups cover the ground this guide only summarises:

• A1 non-combustible insulation systems and the material comparison — the A1 class in depth, with the materials that reach it
• Is glass wool fireproof? — the A1 rating of glass wool, and when a facing changes the answer
• Industrial pipe insulation materials — the five families compared by temperature, form and fire class