Plastic Self-Extinguishing (After-Flame) Performance Testing and Inspection

Plastic self-extinguishing performance testing evaluates whether a plastic material stops burning after the ignition source is removed, using measurable parameters such as after-flame time, after-glow time, and the ignition behavior of flaming drips. This testing is performed in accordance with internationally recognized standards including UL 94, IEC 60695-11-10, ISO 1210, ASTM D635, and GB/T 2408, and it is essential for flame-retardant material selection, product safety certification, and regulatory market access. Accredited third-party laboratories provide these evaluations for manufacturers across the electronics, appliance, automotive, and construction industries.

Technical Overview

Self-extinguishing performance, often referred to as after-flame or flame-retardancy performance, describes the ability of a plastic material to cease combustion once an external ignition source is removed. Because most polymers are organic and inherently combustible, flame retardants, modified polymer structures, or inorganic fillers are frequently incorporated to interrupt the combustion cycle. Verification of the effectiveness of these measures is a fundamental requirement in the safety assessment of plastics used in electrical equipment, appliances, vehicles, and building products.

The core measurable quantities in this evaluation are after-flame time (the period during which the specimen continues to flame after the test flame is withdrawn) and after-glow time (the period of flameless combustion that may follow). Additional observations include whether flaming particles or molten drops fall and ignite a cotton indicator placed beneath the specimen, whether the flame reaches defined reference marks, and the extent of charring or damage. Based on these results, materials are classified into ratings such as V-0, V-1, V-2, 5VA, 5VB, and HB under the UL 94 scheme, which is technically aligned with IEC 60695-11-10, ISO 1210, and the Chinese national standard GB/T 2408.

These small-flame ignition tests simulate the effect of a minor electrical fault, overheated component, or brief external flame contact. Regulatory frameworks such as IEC 62368-1 for audio/video and ICT equipment, IEC 60335-1 for household appliances, and EN 45545-2 for railway applications all reference flame behavior classifications of this type, making self-extinguishing performance one of the most frequently requested plastic safety tests performed by accredited third-party laboratories.

Testing Samples

Molded Bar Specimens

The standard specimen for small-flame testing is a rectangular bar measuring 125 mm in length and 13 mm in width, typically with thicknesses of 3.0 mm and 1.5 mm or the minimum production wall thickness. Specimens are usually injection molded or cut from compression-molded or extruded sheets, and the edges should be smooth and free of burrs, flash, or stress marks that could influence ignition behavior. A complete evaluation normally requires two sets of five bars per thickness.

Specimens Cut from Finished Products

When verifying the compliance of an actual product, specimens may be cut directly from finished parts such as enclosures, connectors, or insulating barriers. In this case, the report records the sampling location, actual thickness, and orientation of the specimen. If the part geometry prevents cutting standard bars, plate specimens of 125 mm × 13 mm are taken from the flattest available region, and any deviation from the standard dimensions is documented.

Films, Thin Sections, and Foamed Materials

Thin films and flexible materials that deform under test may be evaluated using a supported method in accordance with ISO 9773, in which the specimen is wrapped around a mandrel. Cellular and foamed plastics are assessed under ISO 9772, which applies modified specimen and ignition conditions appropriate to low-density materials. These variants allow the after-flame behavior of virtually all plastic product forms to be characterized.

Sample Conditioning Requirements

Prior to testing, specimens are conditioned at 23 ± 2 °C and 50 ± 5 % relative humidity for at least 48 hours. Depending on the applicable standard and end-use specification, a second set of specimens may also receive thermal conditioning, such as 168 hours at 70 °C followed by cooling in a desiccator, to simulate aging. Proper conditioning is critical because moisture content and thermal history can measurably alter ignition and after-flame behavior.

Testing Items

A typical self-extinguishing performance inspection covers the following measured and observed parameters:

• After-flame time after the first application of the test flame (t1)
• After-flame time after the second application of the test flame (t2)
• Total after-flame time summed across all five specimens per set
• After-glow time following the cessation of flaming
• Ignition of the cotton indicator by flaming drops or particles
• Flame spread beyond the 25 mm and 100 mm reference marks (horizontal method)
• Linear burning rate in mm/min (horizontal method)
• Extent of charring or thermal damage on the specimen
• Material classification result, such as V-0, V-1, V-2, 5VA, 5VB, HB, HB40, or HB75

Testing Methods

Vertical Burning Test (50 W / 20 mm Flame)

Specimens are clamped vertically with the long axis downward, and a layer of surgical cotton is placed 300 mm below the lower edge of the bar. A laboratory burner producing a 20 ± 1 mm blue flame is applied to the lower end of the specimen for 10 seconds, then removed while the after-flame time t1 is recorded. After flaming stops, the flame is applied a second time for 10 seconds, and the second after-flame time t2, the after-glow time, and any flaming drips are recorded. For the V-0 classification, each individual after-flame time must not exceed 10 seconds, the total for five specimens must not exceed 50 seconds, and the cotton must not be ignited. V-1 relaxes the timing to 30 seconds per specimen and 250 seconds total, while V-2 permits flaming drips that ignite the cotton. This method is defined in UL 94, IEC 60695-11-10, ISO 1210, and GB/T 2408.

Horizontal Burning Test (HB)

In the horizontal configuration, the bar is supported horizontally with the free end exposed to a 25 mm test flame applied at a defined angle for 30 seconds or until the flame reaches the 25 mm mark. The time at which the flame front passes the 25 mm and 100 mm reference marks is recorded to calculate the burning rate. A material meets the HB classification if flaming does not reach the 100 mm mark, or if the burning rate does not exceed 40 mm/min for thicknesses of 3 to 13 mm and 75 mm/min for thicknesses below 3 mm, with no flaming drips in certain specification versions. This procedure corresponds to UL 94 HB, IEC 60695-11-10, ASTM D635, and GB/T 2408.

500 W Flame Test (5VA and 5VB)

For the most demanding enclosure applications, bar specimens and additional 125 mm × 125 mm plaques are exposed to a 500 W premixed flame applied five times for 5 seconds each. The 5VA rating requires that the plaque not exhibit burn-through, while 5VB allows a hole but requires self-extinguishing within the specified time. These ratings are defined in UL 94 and the corresponding IEC 60695-11-20 method and are frequently specified for enclosures of IT and power equipment.

Complementary Flammability Assessments

Self-extinguishing testing is frequently combined with related fire-hazard evaluations to build a complete flammability profile. The glow-wire tests GWFI and GWIT (IEC 60695-2-12 and IEC 60695-2-13) assess ignition by a heated element, the needle-flame test (IEC 60695-11-5) simulates a small fault arc, and the limiting oxygen index method (ISO 4589-2, ASTM D2863, GB/T 2406.2) quantifies the minimum oxygen concentration required to sustain burning. Together these methods provide complementary insight into how a material behaves under different ignition scenarios.

Applications

Self-extinguishing performance verification supports safety compliance, product development, and supply-chain quality control across a wide range of industries:

• Electrical and electronic products: enclosures, switches, connectors, charging equipment, and printed circuit board substrates requiring V-0 or 5VA ratings
• Household appliances: insulating parts and non-metallic components subject to IEC 60335-1 requirements
• Wire and cable: insulation and sheathing compounds for flame-retardant and low-smoke cable designs
• Automotive engineering: interior trim and functional plastic components evaluated alongside horizontal burn requirements such as ISO 3795
• Railway and mass transit: materials contributing to fire-safety performance under EN 45545-2
• Building products: plastic profiles, panels, and decorative components in regulated construction applications
• Materials R&D and quality control: screening of halogenated and halogen-free flame-retardant formulations, incoming resin inspection, and batch consistency verification

FAQ

What is the difference between after-flame time and after-glow time?

After-flame time is the period during which the specimen continues to burn with a visible flame after the ignition source is removed. After-glow time is the period of flameless glowing combustion that may persist after the flame extinguishes. Both values are recorded in vertical burning tests and both contribute to classification criteria.

Does a V-0 rating mean the plastic cannot burn?

No. A V-0 rating means the material extinguishes rapidly after removal of a small flame, with each after-flame time under 10 seconds, a total after-flame time under 50 seconds for five specimens, and no flaming drips that ignite cotton. The material can still ignite under sustained, larger-scale fire exposure, which is why additional fire-performance tests are specified for higher-risk applications.

Why is the cotton indicator placed below the specimen?

The cotton layer detects flaming droplets or particles released by the specimen, such as molten polymer that continues to burn as it falls. Dripping behavior is a major fire-hazard concern because falling flaming material can spread fire to other parts of a product or to surrounding objects, and it directly distinguishes the V-0, V-1, and V-2 classifications.

Are UL 94, IEC 60695-11-10, ISO 1210, and GB/T 2408 equivalent?

These standards are technically aligned and specify substantially the same 50 W horizontal and vertical flame procedures and classification criteria. GB/T 2408 and IEC 60695-11-10 are recognized as technically consistent with the UL 94 V and HB methods, though the scope, conditioning options, and reporting details may differ slightly, so the applicable standard should be confirmed with the end customer or certification body before testing.

How many specimens are required for a complete test?

A standard vertical or horizontal classification generally requires two sets of five bar specimens per thickness, one tested in the as-received conditioned state and one after additional conditioning where specified. For 5VA or 5VB evaluation, additional bar and plaque specimens are required. Laboratories typically recommend submitting at least 10 to 20 bars per thickness to allow for retests.

Can finished products be tested instead of molded bars?

Yes. Specimens can be cut from finished parts provided that reasonably flat sections of the required dimensions can be obtained. The test report will identify the sampling location and actual thickness, and where a product cannot yield standard specimens, alternative small-flame methods such as the needle-flame test may be applied to verify fire-hazard behavior on the complete component.