Combustion Performance Analysis of Thermal Insulation Wool: Standards, Testing Methods, and Fire Cla

Ceramic Fiber Wool

Ceramic fiber wool, based on alumina-silica chemistry, is designed for continuous service temperatures of roughly 1,000°C to 1,400°C in furnace linings, kiln cars, and expansion joints. As a refractory inorganic fiber product, it is classified as non-combustible, and testing focuses on verifying mass loss, temperature rise, and the absence of sustained flaming under ISO 1182 or GB/T 5464 conditions, together with shot content and thermal performance verification.

Organic Foam Insulation

Polyurethane, polyisocyanurate, phenolic foam, expanded polystyrene (EPS), extruded polystyrene (XPS), and elastomeric rubber-plastic foam are combustible organic materials. Their combustion analysis emphasizes flame-retardant performance, limited oxygen index, smoke suppression, and dripping behavior. Flame-retardant modified products typically target Grade B1 under GB 8624-2012, corresponding roughly to Euroclass B or C, and testing must include any factory-applied facings or composite structures.

Testing Items

Depending on the material type, product form, and target classification, a combustion performance evaluation typically includes the following items:

• Non-combustibility: furnace temperature rise, mass loss, and duration of sustained flaming
• Gross heat of combustion (PCS) determined by bomb calorimeter
• Ignitability under a single small flame source, including flame spread distance and ignition of filter paper by droplets
• Heat release rate, FIGRA (fire growth rate index), and THR600s (total heat release over the first 600 seconds)
• Lateral flame spread (LFS) on a corner-mounted specimen
• Smoke growth rate (SMOGRA) and smoke production rate (SPR)
• Smoke density rating (SDR) measured in a smoke density chamber
• Occurrence and duration of flaming droplets and particles
• Smoke toxicity, including yields of carbon monoxide, hydrogen cyanide, hydrogen chloride, and other hazardous gases
• Limited oxygen index (LOI) and horizontal or vertical burning characteristics for foam plastics
• After-flame time, after-glow time, and char length for polymeric insulation materials

Testing Methods

Non-Combustibility Furnace Test

Conducted per ISO 1182 or GB/T 5464, a cylindrical specimen is stabilized at 750°C in a tube furnace. The criteria evaluate furnace and specimen thermocouple temperature rise, mass loss percentage, and whether sustained flaming exceeds 20 seconds. Together with ISO 1716 or GB/T 14402 calorific value testing (PCS not exceeding 2.0 MJ/kg for A1 and 3.0 MJ/kg for A2), these tests form the basis of the highest classification grades.

Single Burning Item (SBI) Test

Performed per GB/T 20284 or EN 13823, two specimens are mounted in a corner configuration and exposed to a 30 kW propane burner. The test yields FIGRA0.2MJ, THR600s, SMOGRA, lateral flame spread, and droplet observations. These parameters distinguish Grade A2, B, and C (Euroclass A2, B, C) classifications for products that are not fully non-combustible.

Single Flame Source Ignitability Test

Conducted per ISO 11925-2 or GB/T 8626, a small diffusion flame is applied to the specimen surface or edge for 15 or 30 seconds. Acceptance requires that the flame tip does not reach 150 mm above the ignition point within a specified time and that flaming droplets do not ignite filter paper placed beneath the specimen.

Smoke Density Test

The smoke density chamber method per GB/T 8627 measures the attenuation of a light beam transverse to a flaming or smoldering specimen, producing a smoke density rating (SDR). This item is mandatory for Grade B1 and B2 classifications under GB 8624-2012, with typical limits of SDR not exceeding 75.

Smoke Toxicity Test

Per GB/T 20285, specimens undergo smoldering and flaming decomposition in an airflow chamber, and the generated gases are analyzed quantitatively or qualitatively for hazardous constituents. The result is expressed as a toxicity hazard classification (t0, t1, t2), with t0 representing the lowest acute inhalation hazard.

Cone Calorimeter Test

Per ISO 5660-1 or GB/T 16172, a 100 mm by 100 mm specimen is exposed to a defined radiant heat flux (commonly 50 kW/m²). Key outputs include peak heat release rate, total heat released, and MARHE (maximum average rate of heat emission), which is used as a criterion for Grade A2 classification.

Steiner Tunnel Test

Per ASTM E84, UL 723, or CAN/ULC S102, the specimen is mounted as a tunnel ceiling and exposed to controlled flame and air flow. Results are reported as flame spread index (FSI) and smoke developed index (SDI). Insulation materials with FSI not exceeding 25 and SDI not exceeding 450 are assigned Class A, the category most frequently specified for commercial building applications in North America.

Oxygen Index and Burning Rate Tests

The limited oxygen index is determined per GB/T 2406.2 or ISO 4589-2, reporting the minimum oxygen concentration that sustains candle-like burning; flame-retardant foam insulation typically targets LOI values of 30% or higher. Horizontal and vertical burning tests per GB/T 2408 (equivalent to IEC 60695-11-10) and vertical burning tests for foam plastics per GB/T 8332 and GB/T 8333 measure burning rate, after-flame time, and after-glow characteristics.

Classification Mapping

Under GB 8624-2012, materials are graded A (A1, A2, non-combustible), B1 (B, C, flame-retardant), B2 (D, E, combustible), and B3 (F, highly flammable). EN 13501-1 uses the parallel A1 to F Euroclass system with additional suffixes for smoke production (s1, s2, s3) and flaming droplets (d0, d1, d2). Although the systems are structurally similar, direct equivalence cannot be assumed, and products destined for different markets must be tested against the applicable regional standard.

Applications

Verified combustion performance is a precondition for deploying insulation wool in the following applications:

• External thermal insulation composite systems (ETICS) on residential and public buildings, where codes commonly mandate Grade A or B1 materials
• Fire barriers and compartmentation strips in curtain walls, between floors, and around openings, where A1 rock wool is standard practice
• HVAC duct insulation, fire dampers, and smoke control systems requiring low smoke production and no flaming droplets
• Industrial furnace linings, boiler insulation, and kiln backup layers using ceramic fiber and high-temperature rock wool
• Shipbuilding and offshore platform insulation, where low flame spread and low smoke toxicity are critical for evacuation safety
• Cold storage panels, chilled water piping, and refrigeration equipment insulated with PU or elastomeric foam treated to Grade B1
• High-occupancy venues such as schools, hospitals, tunnels, and transit stations, where specifications typically exclude combustible grades

FAQ

What combustion grade does rock wool achieve?

Standard rock wool with minimal organic content achieves Grade A1 under GB 8624-2012 and Euroclass A1 under EN 13501-1, verified through ISO 1182 / GB/T 5464 non-combustibility testing and ISO 1716 / GB/T 14402 calorific value testing.

Is glass wool non-combustible?

The glass fiber itself is non-combustible, but the resin binder introduces a small quantity of combustible organic matter. Low-binder glass wool typically achieves Grade A2 or A1, while products with higher binder content or organic facings may be limited to lower grades and should be tested in their final configuration.

What does Grade B1 mean under GB 8624-2012?

Grade B1 denotes flame-retardant materials. Classification requires passing GB/T 8626 ignitability testing, GB/T 20284 SBI testing with limited FIGRA and THR600s values, and GB/T 8627 smoke density testing with a smoke density rating not exceeding the specified limit, together with smoke toxicity evaluation.

Which tests are required for Euroclass A1?

Euroclass A1 requires only ISO 1182 non-combustibility and ISO 1716 gross heat of combustion testing. Euroclass A2 additionally requires either EN 13823 (SBI) or ISO 5660-1 cone calorimeter testing to confirm limited heat release behavior.

Can ASTM E84 results be converted to GB 8624 grades?

No formal conversion exists. ASTM E84 reports flame spread and smoke developed indices, whereas GB 8624 and EN 13501-1 integrate multiple fire parameters into a grade. Products for both markets should be tested separately by accredited third-party laboratories against each applicable standard.

How should specimens be conditioned before combustion testing?

Unless otherwise specified by the product standard, specimens are conditioned to constant mass at 23°C ± 2°C and 50% ± 5% relative humidity per GB/T 2918 or ISO 291. For certain protocols, such as EN 13823, additional drying or specific substrate mounting requirements apply and must be followed exactly to ensure valid classification results.