GRP Standards: 2026 GRP Fire Ratings
The Most Important Change in a Generation
If you buy, specify, or install GRP products for UK construction projects, this article is essential reading. The way fire performance is assessed for construction products in the United Kingdom has fundamentally changed, and the implications for every participant in the GRP supply chain are significant.
On 2nd March 2025, the UK government withdrew BS 476 Part 7 from Approved Document B of the Building Regulations, following a direct recommendation from the Grenfell Tower Inquiry. In its place, EN 13501-1 is now the mandatory standard for reaction to fire classification of all construction products in England and Wales.
This is not a cosmetic change. It is not a simple renaming exercise. EN 13501-1 is a fundamentally more comprehensive, more rigorous, and more revealing standard than BS 476-7 ever was. Products that carried comfortable classifications under the old system may perform very differently when tested under the new one. And critically, old BS 476-7 results cannot be carried over — products must be retested.
For the GRP industry, this creates both a challenge and an opportunity. The challenge is that testing must be arranged, paid for, and completed. The opportunity is that quality manufacturers who invest in compliance can clearly differentiate themselves from those who cannot — or will not — provide the evidence.
1. Why the Standard Changed: The Grenfell Legacy
On 14th June 2017, a fire broke out in a fourth-floor flat at Grenfell Tower in North Kensington, London. Within minutes, the fire spread rapidly across the external cladding of the building. Seventy-two people lost their lives.
The subsequent public inquiry exposed fundamental weaknesses in the UK’s fire testing and classification regime. Among its findings, the Inquiry identified that BS 476 — a standard dating from the 1970s — tested only one parameter: surface spread of flame. It did not assess how much a material contributed to fire growth. It did not measure smoke production. It did not evaluate whether a burning material produced flaming droplets that could spread fire to other levels of a building or injure people below.
The Inquiry recommended that the UK adopt the more comprehensive European classification system, EN 13501-1, which had been in use across European Union member states for years. The UK government accepted this recommendation and confirmed in September 2024 that BS 476 would be withdrawn in two tranches:
Tranche 1 — Reaction to fire (including BS 476-7): Withdrawn from Approved Document B on 2nd March 2025. This is now in effect.
Tranche 2 — Fire resistance: To be withdrawn by 2nd September 2029.
THE POSITION TODAY
Any GRP product specified for a UK construction project that relies solely on a BS 476-7 classification is referencing a withdrawn standard. This does not automatically make the product non-compliant, but it means the fire classification data is no longer recognised under current Building Regulations. New projects require EN 13501-1 classification.
2. What BS 476-7 Tested — And What It Did Not
Understanding what the old standard measured is essential to understanding why it was replaced.
How BS 476-7 worked:
A specimen was mounted vertically next to a radiant heat panel inside a combustion chamber. A pilot flame was applied for one minute, then extinguished. The test measured how far the flame spread across the surface of the material over ten minutes.
Products were classified into four classes:
| Class | Flame Spread Limit | Performance |
| Class 1 | Not exceeding 165mm in 10 minutes | Best — minimal spread |
| Class 2 | Not exceeding 215mm in 1.5 min; 455mm in 10 min | Moderate |
| Class 3 | Not exceeding 265mm in 1.5 min; 710mm in 10 min | Poor |
| Class 4 | Exceeding Class 3 limits | Worst — rapid spread |
What BS 476-7 did NOT measure:
- Heat release: How much heat energy the burning material contributed to the fire. A material could achieve Class 1 for surface spread yet release enormous amounts of heat.
- Smoke production: The rate and total quantity of smoke generated. In building fires, smoke is the primary cause of death, not flame.
- Flaming droplets: Whether the burning material produced drops of flaming material that could fall onto people, ignite materials below, or spread fire vertically through a building.
- Ignitability: How easily the material caught fire in the first place.
- Fire growth rate: How quickly the fire developed once ignition occurred.
In short, BS 476-7 answered one question: how far does the flame spread across the surface? It said nothing about how dangerous the material was in a real fire scenario.
3. What EN 13501-1 Tests — The Complete Picture
EN 13501-1 is the European harmonised standard for the reaction to fire classification of construction products. It was developed by the European Committee for Standardisation (CEN) and has been mandatory for CE marking across EU member states for over a decade.
Where BS 476-7 used a single test method measuring a single parameter, EN 13501-1 uses multiple test methods to assess multiple parameters. The result is a classification that tells you far more about how a material will behave in a real fire.
3.1 The Three-Part Classification
Every EN 13501-1 classification has three components. All three are mandatory. An incomplete classification — one that states only the main class without smoke and droplet ratings — is not compliant and cannot be used for Building Regulations purposes.| Component | What It Assesses | Possible Ratings |
| Main Class | Contribution to fire — ignitability, flame spread, heat release, fire growth rate | A1, A2, B, C, D, E, F |
| Smoke (s) | Rate and total quantity of smoke produced during combustion | s1, s2, s3 |
| Droplets (d) | Whether burning material produces flaming droplets or particles | d0, d1, d2 |
A complete classification reads: B-s1, d0 — this tells you the main fire class, the smoke performance, and the droplet behaviour. All three parts must be present.
3.2 The Main Fire Classes Explained
| Class | Description | Real-World Meaning | Typical Materials |
| A1 | Non-combustible | No contribution to fire whatsoever | Steel, concrete, stone, ceramic |
| A2 | Very limited combustibility | Negligible contribution to fire; essentially non-combustible in practice | Mineral fibre insulation, plasterboard, some cement boards |
| B | Very limited contribution to fire | Self-extinguishing; limited flame spread, low heat release | HIGH-PERFORMANCE GRP (ECL products) |
| C | Limited contribution to fire | Fire-retardant materials with some flame spread | Standard fire-retardant GRP, some timber products |
| D | Acceptable contribution | Burns but at an acceptable rate; the typical level where old BS 476 Class 2 products sit | Timber, some plastics, economy GRP |
| E | Acceptable reaction | Ignitable, burns readily, passes only basic ignitability test | Some untreated plastics |
| F | No performance determined | Either failed testing or has not been tested at all | Untested products |
WHERE DOES OLD BS 476-7 CLASS 2 SIT IN THE NEW SYSTEM?
There is no direct conversion. However, industry experience indicates that a product achieving BS 476-7 Class 2 under the old standard would typically achieve Class D or Class E under EN 13501-1. That is a substantial difference from Class B. Anyone assuming their old Class 1 or Class 2 rating translates to a high Euroclass is making a dangerous assumption. The only way to know is to test.
3.3 Smoke Production Classes
In building fires, smoke kills more people than flame. The smoke classification is not a secondary consideration — it is a life-safety parameter.
| Class | Criteria | Practical Meaning | Visibility Impact |
| s1 | SMOGRA ≤30 m²/s² AND total smoke ≤50 m² in 600s | Little or no smoke | Escape routes remain visible |
| s2 | SMOGRA ≤180 m²/s² AND total smoke ≤200 m² in 600s | Moderate smoke production | Reduced visibility; evacuation impacted |
| s3 | Exceeds s2 limits | Substantial smoke | Serious visibility loss; life risk |
For GRP products used in enclosed or semi-enclosed environments — tunnels, underpasses, covered platforms, plant rooms — the smoke classification is arguably more important than the main fire class. An s1 rating means that in a fire event, smoke production is minimal and escape routes are far more likely to remain navigable.
3.4 Flaming Droplet Classes
When GRP products are installed overhead or at height — as grating on elevated platforms, as handrails on walkways, as cladding panels — the question of flaming droplets becomes critical. Burning droplets can fall onto personnel below, ignite materials at lower levels, and spread fire vertically through a building.
| Class | Criteria | Practical Meaning |
| d0 | No flaming droplets or particles produced within 600 seconds | Safe for overhead and elevated installations; no risk of fire spread downward |
| d1 | Flaming droplets produced but none persisting longer than 10 seconds | Limited risk; droplets self-extinguish rapidly |
| d2 | Flaming droplets persisting longer than 10 seconds, or does not meet d0/d1 | Significant risk of secondary ignition and personnel injury from falling burning material |
For GRP grating and profiles installed at height, d0 should be the minimum specification. A d2 classification on elevated grating means that in a fire, burning material will drip onto whatever — and whoever — is below.
4. The Test Methods Behind EN 13501-1
EN 13501-1 is a classification standard, not a test standard. The actual testing is carried out to a suite of European test methods, each designed to measure a specific aspect of fire behaviour. Different classes require different combinations of tests.
| Test Standard | What It Measures | Required For |
| EN ISO 1182 | Non-combustibility — whether the material burns at all | Classes A1 and A2 |
| EN ISO 1716 | Gross heat of combustion — total energy content (calorific value) | Classes A1 and A2 |
| EN 13823 (SBI) | Single Burning Item test — heat release rate (FIGRA), total heat release (THR600s), lateral flame spread (LFS), smoke production (SMOGRA), flaming droplets | Classes A2, B, C, D |
| EN ISO 11925-2 | Single-flame source ignitability — small flame applied to surface and edge | Classes B, C, D, E |
| EN ISO 9239-1 | Radiant panel test for floorings — critical heat flux at extinguishment | Flooring products only (Bfl, Cfl, etc.) |
4.1 The SBI Test: The Heart of the New System
The Single Burning Item (SBI) test to EN 13823 is the most important test in the EN 13501-1 suite for classes B, C, and D. It is this test that most buyers need to understand, because it is where the real differentiation between GRP products happens.
The test configuration simulates a real-world fire scenario: a single burning item (a gas burner producing 30kW) is placed in the corner of a room formed by two specimen panels arranged in an L-shape. The test runs for 20 minutes and measures:
- FIGRA (Fire Growth Rate Index): How quickly the fire develops. Measured in watts per second. Class B requires FIGRA ≤120 W/s; Class D allows up to 750 W/s. The lower the number, the slower the fire growth.
- THR600s (Total Heat Release): The total heat energy released in the first 600 seconds. Class B requires THR600s ≤7.5 MJ. This measures total fire contribution, not just surface behaviour.
- LFS (Lateral Flame Spread): Whether the flame reaches the edge of the specimen. For Class B, the flame must not reach the edge.
- SMOGRA (Smoke Growth Rate): How quickly smoke production increases. Used to determine s1/s2/s3 classification.
- TSP600s (Total Smoke Production): Total smoke produced in 600 seconds.
- Flaming droplets: Observed and recorded throughout the 20-minute test. Determines d0/d1/d2 classification.
WHY THE SBI TEST MATTERS FOR GRP
The SBI test exposes the full fire behaviour of a material in a way that BS 476-7 never could. A GRP product that achieved Class 1 under BS 476-7 based on limited surface spread might reveal high heat release, rapid fire growth, heavy smoke, or flaming droplets under SBI testing. The SBI test tells you the truth about how the material will behave in a corner fire scenario — which is how the majority of real building fires develop.
5. Profiles vs Grating: Different Product Categories, Different Classification Routes
5.1 GRP Pultruded Profiles (Structural Sections, Tubes, Channels, Angles)
These are classified under the main construction product category. Their classification takes the format:
B-s1, d0
Testing requires EN 13823 (SBI test) and EN ISO 11925-2 (ignitability) as a minimum for classes B through D. The product is tested in its as-supplied form.
5.2 GRP Grating (Moulded and Pultruded, Used as Flooring)
When GRP grating is used as a flooring product, it falls under the flooring category. Its classification uses the ‘fl’ suffix:
Bfl-s1
Flooring products are tested to EN ISO 9239-1 (radiant panel test) and EN ISO 11925-2 (ignitability). The radiant panel test simulates a developing fire in a corridor and measures the critical heat flux at which the flame front is extinguished.
Note that the flooring classification uses only two components (main class and smoke), not three. The droplet classification is not applied to flooring products under the standard test methodology because grating is the walking surface, not overhead.
5.3 GRP Grating Used as Non-Flooring (Elevated Platforms, Overhead Panels)
Here is the critical distinction that many specifiers miss: when GRP grating is installed overhead or as an elevated platform where personnel or equipment may be below, it is no longer functioning solely as a flooring product. In these applications, the droplet classification becomes directly relevant to safety.
Best practice: For elevated grating applications, specify a full three-part classification (e.g., B-s1, d0) tested to the construction product route (EN 13823 + EN ISO 11925-2), not just the flooring route. This gives you the droplet data you need for elevated installations.
6. The UK Testing Challenge: Where Do You Actually Get Tested?
This section describes a situation that I believe reflects a fundamental failure of joined-up thinking between UK government policy and UK industry capacity.
The government withdrew BS 476-7 and mandated EN 13501-1 testing. At broadly the same time, Warringtonfire — which had been the primary UK testing facility for composites fire testing — closed its composites fire test unit. The very facility that the GRP industry relied upon for fire testing ceased to offer the service precisely when the industry needed it most.
There was no consultation with the composites industry. No transition plan. No alternative provision. Just a regulatory requirement and a closed door.
The current UK testing landscape for EN 13501-1:
- BRE Global (Watford): UKAS-accredited, large facility, but long lead times and primarily focused on mainstream construction products.
- Warringtonfire (Warrington): Opened a new Birchwood Park facility in early 2025 with expanded fire resistance capacity, but their composites-specific fire testing capability remains limited.
- System Laboratories (Leighton Buzzard): UKAS-accredited, advertise fast turnaround for EN 13501-1.
- Attain RTC: UKAS-accredited, offers SBI testing.
- Efectis UK/Ireland: Small and large-scale testing with EN 13501-1 classification capability.
Our approach:
At Engineered Composites, we recognised early that the UK testing bottleneck would delay compliance for many companies. We took the decision to use SGS — the largest testing, inspection, and certification company in the world, US-owned, with testing facilities near our manufacturing plant in China. This gave us a globally recognised test report from a laboratory whose accreditation is accepted worldwide.
Our classification: B-s1, d0
That is: very limited contribution to fire (B), little or no smoke (s1), and no flaming droplets (d0). This is among the highest fire classifications achievable for any GRP product and places our materials at the top of the market.
A NOTE TO BUYERS
If a UK GRP supplier tells you they have not yet been able to arrange EN 13501-1 testing because of UK laboratory availability, ask them what alternative arrangements they have made. SGS, TUV, Bureau Veritas, and Intertek all operate accredited fire testing facilities internationally. Testing capacity exists. The question is whether the supplier has the commitment to pursue it.
7. What Every Buyer Must Demand: The Fire Documentation Checklist
When you are purchasing GRP profiles or grating for any UK construction project, you should request the following fire-related documentation before placing an order. If the supplier cannot provide these items, the product cannot be verified as compliant.
| # | Document / Information | Acceptable | Not Acceptable |
| 1 | Complete EN 13501-1 classification with all three components (main class, smoke, droplets) | B-s1, d0 (three-part) | ‘Class B’ alone or ‘BS 476 Class 1’ |
| 2 | Fire test report from an accredited laboratory | UKAS, IAS, or equivalent accredited lab | ‘In-house testing’ or no report |
| 3 | Test report identifies the specific product tested | Named product, resin, construction detail | Generic ‘GRP’ with no product identification |
| 4 | Test standard references (EN 13823, EN ISO 11925-2, etc.) | Specific EN test numbers stated | ‘Tested to European standards’ |
| 5 | For flooring grating: Bfl classification with smoke rating | Bfl-s1 (tested to EN ISO 9239-1) | ‘Fire retardant’ with no classification |
| 6 | For elevated grating: droplet classification | d0 or d1 with evidence | ‘No droplets’ without test data |
| 7 | Confirmation that the classification applies to the product being supplied, not a similar product | Direct product match confirmed | ‘Tested on a comparable product’ |
| 8 | Fire-retardant resin system confirmed | FR isophthalic polyester or specified system | ‘Standard polyester’ |
8. Common Pitfalls and Misleading Claims
In our experience working with buyers, specifiers, and clients across the rail, water, utilities, and construction sectors, we encounter the same misunderstandings and misleading claims repeatedly. Here are the most common:
8.1 ‘Our product is fire retardant’
‘Fire retardant’ is not a classification. It describes a resin formulation, not a tested performance level. A product containing fire-retardant additives could achieve anything from Class B to Class E depending on the formulation, the glass content, the profile thickness, and the manufacturing quality. Without an EN 13501-1 test report, ‘fire retardant’ means nothing.
8.2 ‘We have Class 1 fire rating’
Class 1 under BS 476-7 is a withdrawn classification. It cannot be used for current Building Regulations compliance. More importantly, a product that achieved Class 1 under BS 476-7 would not necessarily achieve the equivalent high classification under EN 13501-1, because the new standard tests parameters that BS 476-7 did not measure.
8.3 ‘Euro Class 1’
There is no such classification as ‘Euro Class 1’. This is a confusion between BS 476-7 Class 1 and the Euroclass system. The Euroclass system uses letter designations (A1 through F), not numbers. If a specification asks for ‘Euro Class 1’, it needs correcting before the product can be properly specified.
8.4 ‘Bfl’ with no smoke or droplet rating
An incomplete classification. The flooring classification must include the smoke rating (e.g., Bfl-s1). For elevated applications, a droplet assessment is also essential. If the supplier provides ‘Bfl’ alone, the classification is incomplete and non-compliant for Building Regulations purposes.
8.5 ‘Tested to ISO 11925-2’
EN ISO 11925-2 is the single-flame source ignitability test. It is one component of EN 13501-1 classification, not the entire classification. For classes B, C, and D, products must also pass the SBI test (EN 13823). A supplier who claims EN 13501-1 compliance based solely on EN ISO 11925-2 has not completed the required testing programme.
8.6 ‘Tested on a comparable product’
Fire test results apply to the specific product tested. A test certificate for a 6mm flat panel does not cover a 50mm box section profile. A test on one resin formulation does not cover a different formulation. Extended application rules (EXAP) exist under EN standards, but they have strict boundaries. If the supplier cannot confirm that the test report covers the specific product you are buying, the certification is insufficient.
9. Resin Systems and Fire Performance: The Material Behind the Classification
The fire performance of a GRP product is primarily determined by its resin system. The glass fibre reinforcement is inherently non-combustible — it is the polymer matrix that burns. Understanding the resin options is essential for specifying the right fire performance.
| Resin System | Fire Performance | Typical EN 13501-1 Class | Applications |
| Standard polyester (orthophthalic) | Poor — no inherent fire retardancy | D to E | Non-regulated applications only |
| FR isophthalic polyester | Good — fire-retardant additives in a chemically resistant base | B to C | Standard UK construction, rail, water |
| FR vinyl ester | Good to very good — fire retardancy with superior chemical resistance | B to C | Chemical plants, marine, offshore |
| Phenolic | Excellent — inherently low flame spread, very low smoke and toxicity | A2 to B, s1, d0 | Rail tunnels, enclosed spaces, high fire-risk |
Key point: A product described only as ‘polyester resin’ without specifying whether it is fire-retardant, isophthalic, or orthophthalic is an unknown fire risk. Always confirm the specific resin system and demand the fire test certificate that proves the classification.
10. What Engineered Composites Has Achieved
We invested in full EN 13501-1 testing before the UK market required it. Our products have been tested by SGS, the largest testing, inspection, and certification company in the world, and our classification is: B-s1, d0
This classification applies to our pultruded structural profiles manufactured using fire-retardant isophthalic polyester resin with E-glass fibre reinforcement. It means our products are suitable for the most demanding fire-safety specifications across rail, construction, water, utilities, and marine sectors.
We are also actively working with advanced resin systems through our partnership with BYD, giving us access to specialist GRP composite formulations that outperform standard fire-retardant grades significantly. These developments are pushing the boundaries of what GRP can achieve in fire performance, and we look forward to sharing more details as these products enter the market.
11. The Bottom Line
The transition from BS 476-7 to EN 13501-1 is the most significant change in UK fire testing standards in a generation. It happened because the old standard was not comprehensive enough to protect people in buildings. People died because the old system had gaps.
For GRP products, the message is clear:
1. BS 476-7 classifications are no longer valid for current Building Regulations compliance. Products must be retested.
2. EN 13501-1 classifications must include all three components: main fire class, smoke, and droplets. Incomplete classifications are not compliant.
3. The SBI test (EN 13823) is the critical test for classes B, C, and D. Ignitability testing alone (EN ISO 11925-2) is insufficient.
4. For elevated GRP grating, always specify the droplet classification. A d2 rating on overhead grating puts people at risk.
5. ‘Fire retardant’ is a resin description, not a fire classification. Demand the test certificate.
6. If a supplier cannot provide a complete EN 13501-1 classification from an accredited laboratory, the product is an unknown fire risk.
