What is the difference between needle flame test and glow wire test？

In the field of electrical safety and material fire performance evaluation, the Needle Flame Test and the Glow Wire Test are two commonly used and highly standardized test methods. Both are designed to assess the behavior of materials, components, or complete products when exposed to abnormal high temperatures or ignition sources, particularly in situations where fire hazards may arise due to faults, short circuits, or overload conditions.

Although both tests aim to prevent fire risks, they differ significantly in their testing principles, application scope, procedures, evaluation criteria, and applicable standards. Understanding these differences is essential for product safety design, certification compliance, and performance optimization.

Basic Concepts of the Needle Flame Test and Glow Wire Test

Basic Definition of the Needle Flame Test

The Needle Flame Test is a method that uses a real flame to simulate a small ignition source contacting a material or component. It evaluates whether the material ignites and how flame propagation behaves when exposed to a small flame source. A small-diameter burner (typically producing a flame from a 0.9 mm nozzle) applies the flame to the sample at a specified angle and for a defined duration. Observations are then made regarding ignition, burning duration, flame spread, and related characteristics.

This test is commonly used to simulate small internal flame scenarios in electrical and electronic equipment, such as overheating components, short circuits, or poor electrical contacts. It is specified in IEC 60695-11-5.

Essentially, the Needle Flame Test is a direct open-flame exposure test. It allows observation of the real interaction between flame and material, directly reflecting the ignition characteristics of materials under flame attack.

Basic Definition of the Glow Wire Test

The Glow Wire Test uses a heated resistance wire as the heat source. The wire is electrically heated to a specified high temperature and brought into contact with the sample to simulate the thermal effects caused by overloads or faults inside electrical equipment. Unlike the Needle Flame Test, it does not involve an open flame. Instead, ignition risk is evaluated through thermal radiation and heat conduction from the heated wire.

The Glow Wire Test is primarily used to assess the fire resistance of electrical and electronic product enclosures, insulating materials, and internal components when exposed to high-temperature heat sources. It is typically conducted in accordance with the IEC 60695-2 series standards.

Core Differences in Testing Principles

1. Direct Flame Exposure vs. Heated Wire Contact

The Needle Flame Test uses a real open flame (usually generated by butane or propane gas) applied at a specified angle and duration to the sample surface. This directly simulates ignition by flame contact and allows visible observation of ignition and flame spread behavior.

In contrast, the Glow Wire Test uses an electrically heated wire brought to a specified temperature (such as 775°C or 850°C). The wire itself does not produce a flame but provides a high-temperature heat source to evaluate ignition risk under thermal exposure conditions.

Thus, the Needle Flame Test focuses on flame contact scenarios, while the Glow Wire Test focuses on material response to high-temperature heat sources without open flame.

2. Flame Propagation Simulation vs. Thermal Ignition Risk

From a hazard simulation perspective:

The Needle Flame Test simulates ignition caused by direct flame contact, such as a small flame tip touching material surfaces and causing localized burning. It primarily evaluates flame propagation risk.

The Glow Wire Test simulates overheating conditions inside equipment due to high-temperature components, overloaded heating elements, or accumulated heat. It evaluates whether such thermal stress may lead to ignition or abnormal burning, even without an external flame.

Therefore, the Glow Wire Test is more focused on ignition resistance under high-temperature exposure.

Differences in Application Scope and Test Specimens

Application Scope of the Needle Flame Test

The Needle Flame Test is suitable for various electrical and electronic components, insulating materials, and small parts that may be exposed to small flame faults inside equipment. It is especially appropriate for small components or parts that cannot be tested using glow wire or horizontal/vertical burning methods.

In some cases, if ignition occurs during a Glow Wire Test, a Needle Flame Test may be required to further assess the actual flame propagation risk.

Application Scope of the Glow Wire Test

The Glow Wire Test is mainly used for electrical equipment enclosures, insulating materials, and internal components with standardized or relatively larger sample sizes. The test specimens usually must meet minimum size requirements (e.g., length and width of at least 60 mm).

This test is widely integrated into fire safety requirements for household appliances, industrial equipment, and finished electrical products, and is commonly used in product safety certification processes.

Differences in Test Procedures and Equipment

Procedure of the Needle Flame Test

The typical procedure includes:

Sample preparation: The specimen is mounted in a specified position, often above a tissue or wood board to assess whether flaming droplets ignite underlying materials.

Flame application: A standardized needle flame is generated and applied to the specimen at a defined angle (e.g., 45°).

Burning observation: Observations include whether the specimen ignites, the duration of burning, flame extension length, and the presence of burning droplets.

Evaluation: The specimen passes or fails based on criteria such as self-extinguishing time and absence of flame spread beyond permitted limits.

This method clearly demonstrates material performance under direct flame exposure.

Procedure of the Glow Wire Test

The Glow Wire Test typically involves:

Sample preparation: The specimen is prepared according to standard size requirements and securely mounted.

Heating the wire: The resistance wire is electrically heated to the specified test temperature.

Application of contact: The heated wire is pressed against the specimen surface with a defined force (commonly about 1 N) for a set duration (e.g., 30 seconds).

Observation: After removing the wire, observations are made regarding ignition, self-extinguishing behavior, and whether underlying tissue paper is ignited.

The process records ignition time, burning duration, and any flaming or glowing droplets.

Differences in Evaluation Criteria and Performance Indicators

Evaluation Criteria of the Needle Flame Test

Key evaluation indicators include:

Whether ignition occurs.

Burning duration after flame removal (often required to be ≤ 30 seconds).

Flame spread length on the material surface.

Whether burning or glowing droplets ignite the underlying support material.

Compliance with standard limits determines whether the specimen passes.

Evaluation Criteria of the Glow Wire Test

Key evaluation parameters include:

GWFI (Glow Wire Flammability Index): The highest temperature at which the material self-extinguishes without ignition. A higher GWFI indicates better resistance to high-temperature ignition.

GWIT (Glow Wire Ignition Temperature): The minimum temperature at which ignition occurs. A higher GWIT indicates greater heat resistance.

Post-flame behavior: Whether the specimen self-extinguishes and whether dripping material ignites underlying tissue paper.

These parameters are evaluated in accordance with the IEC 60695-2 series standards to determine the fire resistance classification of materials or products.

Applicable Standards

The Needle Flame Test is primarily conducted according to IEC 60695-11-5. which simulates small flame ignition scenarios. It is also adopted in various national standards.

The Glow Wire Test is conducted according to IEC 60695-2-10 through IEC 60695-2-13 and is incorporated into safety standards such as the IEC 60335 series for household appliances. It is widely used for evaluating material behavior under high-temperature heat source conditions.

Typical Application Scenarios

Typical Applications of the Needle Flame Test

Simulation of internal small flame faults in electrical and electronic products

Evaluation of flame resistance for small components and structural parts

Supplementary flame risk assessment when glow wire testing is not applicable

Typical Applications of the Glow Wire Test

Fire safety evaluation of household appliances

Heat resistance verification of large components or finished enclosures

Safety certification testing by authorized laboratories

Complementarity and Practical Testing Strategies

In practical product safety evaluations, the Needle Flame Test and Glow Wire Test are often used complementarily rather than independently. For example, if ignition occurs during a Glow Wire Test, a Needle Flame Test may be required to more precisely assess flame propagation risk.

Additionally, certain standards specify one or both tests depending on product size, material type, and intended use environment to ensure comprehensive fire risk evaluation.

The Needle Flame Test and the Glow Wire Test are both essential methods for assessing fire risks in electrical products and materials:

The Needle Flame Test uses a real open flame to directly expose the specimen, making it suitable for simulating small flame faults and localized flame propagation. It provides direct and visible evaluation of ignition behavior.

The Glow Wire Test uses a high-temperature heat source without an open flame to assess ignition behavior and heat resistance under thermal stress. It is a highly standardized safety test, particularly suitable for larger components and finished systems.

Together, these two methods provide complementary fire risk assessments. When combined, they offer a comprehensive evaluation of material and product performance under various thermal and ignition conditions, providing a solid scientific basis for product safety design and certification compliance.