Vertical Burning Test Report: A Complete Technical Guide to UL 94 and IEC 60695-11-10 Flammability T

A vertical burning test report documents the flammability performance of plastic and other non-metallic materials when exposed to a standardized 50 W vertical flame, providing internationally recognized classifications such as V-0, V-1, and V-2. Based on standards including UL 94, IEC 60695-11-10, ISO 1210, and GB/T 5169.16, this report is a core requirement for product safety certification of electrical and electronic devices. This article explains the sample requirements, test items, methodology, classification criteria, and typical applications of the vertical burning test report.

Technical Overview

The vertical burning test report is a formal document issued after evaluating the ignition and combustion behavior of polymeric materials in a vertical orientation. It is one of the most widely requested flammability assessments in the electrical, electronics, and appliance industries, because vertical mounting represents the worst-case scenario for flame propagation: heat rises, so a vertically oriented specimen sustains combustion more easily than a horizontally oriented one.

The most common reference standards for this test are the vertical burning methods described in UL 94 (Tests for Flammability of Plastic Materials for Parts in Devices and Appliances), IEC 60695-11-10 (fire hazard testing, 50 W horizontal and vertical flame test methods), ISO 1210, ASTM D3801, and the Chinese national standard GB/T 5169.16. These standards are technically aligned, meaning test data generated under one system is generally accepted by certification schemes referencing the others.

A complete vertical burning test report does more than record burn times. It establishes the material's flammability classification (V-0, V-1, V-2, or unclassified), verifies whether flaming drips occur, and confirms the thickness range for which the rating is valid. Product safety committees, certification bodies, and purchasing engineers rely on this document to demonstrate that enclosures, connectors, insulating parts, and structural components meet minimum fire safety requirements.

Testing Samples

Rigid Plastic Bars for the UL 94 V Test

The standard specimen for the 50 W vertical test is a rigid bar measuring 125 mm in length by 13 mm in width, with the thickness representative of the end-use part. Materials are normally tested at both the minimum and maximum declared thicknesses, because flammability performance is strongly thickness-dependent. A single test set consists of five bars; ten bars may be required when a marginal or borderline result triggers a repeat determination.

Thin and Flexible Materials for VTM Testing

Films, membranes, and flexible substrates thinner than approximately 0.25 mm often distort, shrink, or curl away from the flame in the standard V test. These materials are evaluated using the vertical thin-material (VTM) configuration, in which the specimen is wrapped around a mandrel to form a cylindrical geometry. The resulting classifications VTM-0, VTM-1, and VTM-2 correspond in severity to V-0, V-1, and V-2.

Plaques and Bars for 5VA and 5VB Classification

For applications demanding the highest level of material fire performance, such as fire enclosures in IT and communication equipment, a 500 W flame test is applied to both 125 mm by 13 mm bars and larger plaques. Five successive 5-second flame applications determine whether the material earns the 5VA rating (no burn-through of the plaque) or the slightly less severe 5VB rating (burn-through permitted, flaming drips prohibited).

Sample Identification and Conditioning

Before testing, specimens must be clearly identified with the material name, grade, colorant content, and nominal thickness. Unless otherwise specified, specimens are conditioned at 23 ± 2 °C and 50 ± 10 % relative humidity for a minimum of 48 hours to ensure repeatable and comparable results across laboratories.

Testing Items

The vertical burning test report records a defined set of observations and measurements for every specimen. The principal test items include:

• Afterflame time (t1) after the first flame application, measured in seconds.
• Afterflame time (t2) after the second flame application, measured in seconds.
• Afterglow time (t3), recorded after flaming combustion ceases following the second application.
• Whether combustion or afterglow spreads to the holding clamp.
• Whether flaming drops or particles fall from the specimen.
• Whether falling flaming particles ignite the indicator cotton placed 300 mm below the specimen.
• Total afterflame time summed across all five specimens and both flame applications.
• Final classification: V-0, V-1, V-2, VTM-0, VTM-1, VTM-2, 5VA, 5VB, or unclassified.

The report also documents auxiliary information such as specimen dimensions, density where required, burner gas type, flame height verification, ambient laboratory conditions, and photographic evidence of specimen condition before and after exposure.

Testing Methods

Apparatus and Burner Configuration

The test is conducted inside a fume hood or enclosed combustion chamber with the draft minimized during exposure, since air movement can distort the flame. A methane or natural gas burner produces a 20 mm blue flame, calibrated so the tip of the inner blue cone reaches the designated contact point. The specimen is clamped at its upper end with its long axis vertical, and the lower edge of the specimen is positioned 10 mm above the top of the burner tube. A layer of clean absorbent surgical cotton is spread thinly 300 mm below the specimen to capture any flaming drips.

Flame Application Procedure

The flame is applied to the center of the lower edge of the specimen for 10 ± 0.5 seconds and then withdrawn while the afterflame time t1 is recorded. Once flaming stops, the flame is applied a second time for another 10 ± 0.5 seconds, and the afterflame time t2 and subsequent afterglow time t3 are recorded. Observers note any drips, cotton ignition, or combustion reaching the clamp. This sequence is repeated for all five specimens in the set.

Classification Criteria

To achieve the V-0 classification, the strictest of the three conventional ratings, the following conditions must all be satisfied:

• Afterflame time for any single specimen does not exceed 10 seconds after either flame application.
• Total afterflame time for the complete set of five specimens does not exceed 50 seconds.
• No specimen exhibits combustion or glowing up to the holding clamp.
• No flaming drops or particles ignite the cotton indicator.
• Afterglow does not persist for more than 30 seconds after the second flame application.

For the V-1 classification, the individual afterflame limit is relaxed to 30 seconds, the total for the set to 250 seconds, and the afterglow limit to 60 seconds, while ignition of the cotton by flaming drips remains disallowed. The V-2 classification uses the same timing limits as V-1 but permits flaming drips that ignite the cotton. When a material fails all three sets of criteria, the report states that the material is unclassified at the tested thickness, and evaluation by the horizontal burning method (HB) may be recommended instead.

Content of the Final Report

A professional report issued by an accredited third-party laboratory typically contains the client and sample identification, the applied standard and its edition, specimen preparation and conditioning history, apparatus details, tabulated per-specimen results, calculated totals, the classification conclusion with its valid thickness range, test date and operator, and a statement that the results relate only to the behavior of the tested specimens under the specific laboratory conditions. Many certification programs also require test data obtained at both minimum and maximum wall thickness to support the final rating.

Applications

Vertical burning test reports support design, compliance, and procurement decisions across a broad range of industries:

• Consumer electronics and IT equipment, where fire enclosures are required by product safety standards such as IEC 62368-1 and IEC 60950-1.
• Household appliances and power tools, for enclosures, switch bodies, fan blades, and internal barriers.
• Connectors, sockets, terminal blocks, and other electromechanical components carrying live current.
• Printed circuit board substrates, cable accessories, coil bobbins, and transformer insulation parts.
• Battery packs and energy storage systems, where V-0 rated plastics are frequently mandated for casings and separation barriers.
• Lighting products, medical electrical devices, and industrial control equipment.
• Automotive electronics, where material flammability data complements vehicle-level interior burn requirements.

Because many product safety standards explicitly reference a minimum flammability class, the vertical burning test report often functions as direct evidence of compliance during type testing, factory inspections, and market surveillance.

FAQ

What is the difference between V-0, V-1, and V-2?

V-0 is the most stringent rating: each specimen must self-extinguish within 10 seconds and no flaming drips are allowed. V-1 allows up to 30 seconds of afterflame per specimen while still prohibiting flaming drips. V-2 matches the timing limits of V-1 but tolerates flaming particles that ignite the cotton indicator, which is significant for applications where drips could spread fire to adjacent materials.

Why is the vertical test considered more severe than the horizontal test?

In a vertical orientation, hot combustion gases rise along the specimen and preheat the material above the flame front, promoting sustained burning. Horizontal specimens tend to self-extinguish more readily, which is why the vertical method distinguishes flame-retardant grades more effectively.

Does the flammability rating depend on thickness?

Yes. A classification is only valid for the thickness tested. Thinner sections ignite and burn more readily, so materials intended for parts with varying wall thickness should be evaluated at both the minimum and maximum production thicknesses, and the report should state the applicable range.

Are UL 94, IEC 60695-11-10, ISO 1210, and GB/T 5169.16 results interchangeable?

The vertical 50 W methods in these standards are technically harmonized, covering the same specimen geometry, flame application, and classification limits. Data generated by an accredited third-party laboratory under any of these standards is generally acceptable where the referenced standard permits equivalence, though the specific edition cited by the end-product standard always governs.

How should specimens be prepared for submission?

Specimens should be molded, cut, or otherwise prepared to 125 mm by 13 mm bars at the declared thickness, free from burrs, flash, and surface contamination. The laboratory should also receive the material designation, grade, color, and any flame-retardant formulation details so that the report can fully identify the tested compound.

What happens if a material fails the vertical test?

If the material cannot meet even the V-2 criteria, the report records it as unclassified at that thickness. The client may then pursue the horizontal HB classification, submit an alternative thickness, or select a more flame-retardant grade for the application.