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02 Aug, 2025 17 Views Author: Cherry Shen

UL 94 Flammability Standards: A Comprehensive Analysis of Horizontal and Vertical Flammability Testing for Electrical Equipment and Plastic Components Using LISUN HVR-LS Tester

Abstract
The UL 94 Flammability Standards serve as a cornerstone in evaluating the fire performance of plastic materials and electrical equipment components. This paper delves into the application of these standards in horizontal and vertical flammability testing, with a specific focus on the LISUN HVR-LS Horizontal Vertical Flame Tester. It explores the testing principles, procedures, and significance of UL 94 Flammability Standards, providing detailed insights into how the HVR-LS tester adheres to these standards to assess the combustibility of materials. Additionally, the paper presents relevant data in tabular form to illustrate the key parameters and results of the tests, aiming to offer a comprehensive understanding of the role of UL 94 Flammability Standards in ensuring the safety of electrical products and plastic materials.

1. Introduction
In the realm of electrical equipment and plastic components, fire safety is of paramount importance. The potential for ignition and subsequent flame spread in these materials can lead to catastrophic consequences, including property damage, injury, and even loss of life. To address this critical issue, standardized testing methods have been developed to evaluate the flammability of such materials. Among these, the UL 94 Flammability Standards stand out as one of the most widely recognized and utilized sets of criteria.

The UL 94 Flammability Standards, established by Underwriters Laboratories, provide a systematic framework for assessing the flammability characteristics of plastic materials used in various electrical devices and components. These standards categorize materials into different grades based on their performance in specific fire tests, enabling manufacturers, regulators, and consumers to make informed decisions regarding the safety of products.

The LISUN HVR-LS Horizontal Vertical Flame Tester is a state-of-the-art testing instrument designed to conduct horizontal and vertical flammability tests in accordance with the UL 94 Flammability Standards. This tester plays a crucial role in research, production, and quality inspection processes across multiple industries, ensuring that materials meet the required safety standards. This paper aims to provide a detailed analysis of the application of UL 94 Flammability Standards in horizontal and vertical flammability testing using the LISUN HVR-LS tester.

UL 94 Flammability Standards: A Comprehensive Analysis of Horizontal and Vertical Flammability Testing for Electrical Equipment and Plastic Components Using LISUN HVR-LS Tester

HVR-LS Horizontal Vertical Flame Tester

2. Overview of UL 94 Flammability Standards

2.1 Scope and Objectives

The UL 94 Flammability Standards primarily focus on evaluating the flammability of plastic materials used in parts of devices and appliances. The main objective is to determine the ability of these materials to extinguish after being ignited, as well as their burning characteristics such as burning speed, burning time, anti-drip ability, and whether the dripping material is flammable. By establishing these criteria, the standards help in classifying materials into different grades, which in turn guide the selection of materials for specific applications where fire safety is a concern.

2.2 Classification System

According to the UL 94 Flammability Standards, there are several test methods and corresponding classification grades. These include:
• HB Grade (Horizontal Burning): This grade is determined through the 50W flame horizontal combustion test. Materials are classified as HB40 or HB75 based on their burning speed. HB40 indicates that the burning speed does not exceed 40mm per minute for specimens with a thickness of 3mm or less, while HB75 is for thicker specimens where the burning speed is limited to 75mm per minute.
• V Grade (Vertical Burning): The 50W flame vertical combustion test is used to classify materials into V-0, V-1, and V-2 grades. These grades are determined by the duration of flaming combustion after the removal of the ignition source, the presence of dripping, and whether the dripping material ignites a cotton indicator. V-0 is the highest grade, requiring that the flame extinguishes within 10 seconds after each ignition, with no dripping that ignites the cotton. V-1 allows for a longer flame duration (up to 30 seconds) and no dripping that ignites the cotton, while V-2 permits dripping that ignites the cotton but with a flame duration similar to V-1.
• 5V Grade: This grade is evaluated using the 500W flame combustion test, resulting in classifications of 5VA and 5VB. These grades are more stringent, requiring that the material does not burn through after five 5-second applications of the flame. 5VA additionally mandates that the cotton indicator is not ignited by any dripping material.
• VTM Grade: Designed for flexible thin film materials, the vertical combustion test for VTM grades (VTM-0, VTM-1, VTM-2) follows similar principles to the V grades but is tailored to the specific characteristics of thin and flexible materials.
• HF Grade: For foam materials, the horizontal burning test classifies them into HF-1, HF-2, and HBF grades. HF-1 materials have the lowest flammability, with no burning drips that ignite the cotton, while HF-2 allows for burning drips that ignite the cotton, and HBF is for materials with higher flammability.

3. LISUN HVR-LS Horizontal Vertical Flame Tester: Features and Specifications

The LISUN HVR-LS Horizontal Vertical Flame Tester is a specialized instrument designed to perform flammability tests in accordance with the UL 94 Flammability Standards, as well as other relevant international standards such as IEC 60695 series. Its key features and specifications are as follows:

3.1 Design and Application

The tester is designed to test the horizontal and vertical flammability of electrical equipment and plastic components. It is suitable for a wide range of industries and departments, including research, production, and quality inspection of electrical and electronic products (such as lighting equipment, household appliances, and power tools), as well as insulation materials, engineering plastics, and other solid combustible materials. It is also utilized in the plastic industry, inspection departments, and research institutions.

3.2 Key Specifications

Burning, After-flame, and After-glow Time: All are adjustable within the range of 0~999.9S, allowing for precise timing of the combustion processes.
• Burning Angle: Adjustable to 0°, 20°, and 45°, enabling both horizontal and vertical testing configurations as required by different standards.
• Flame Height: Adjustable from 20mm to 175mm, ensuring compliance with the flame height specifications of various test standards.
• Gas Source: Utilizes 98% pure methane, which is specified in the standards to ensure consistent and reliable test conditions.
• Gas Flow and Pressure: Gas flow is adjustable from 0~1L/Min, and gas pressure from 0~0.25Mpa. An optional digital gas flow meter with higher accuracy is available for enhanced precision, though at an extra cost.
• Bunsen Lamp: The lamp holder has an internal tube diameter of 9.5±0.3mm and a length of 100mm±10mm, conforming to the standard requirements for the flame source.
• Timer: With an accuracy of 0.1S and linear measurement in milliseconds, ensuring precise timing of the flame application and combustion periods.
• Back Pressure: Measuring range of 200mm water column, with slow adjustment in 5mm increments, allowing for control of the test environment.
• Position Adjustment: The sample position can be adjusted exactly according to the standard, ensuring that the specimen is placed in the correct orientation and position relative to the flame.
• User Interface: Equipped with a touch screen and remote control for easy operation and control of the testing process.
• Compact Version: A compact version (HVR-LSS) is available, weighing less than 50kg, which helps reduce delivery costs for overseas markets. However, users need to prepare an additional ventilation system for this version.
• Optional Components: Includes a 50W copper block and thermocouple, with an optional HVR-LSTH500W copper block and thermocouple for 500W tests.

Table 1: Key Specifications of LISUN HVR-LS Horizontal Vertical Flame Tester

Parameter Specification
Burning Time 0~999.9S (Adjustable)
After-flame Time 0~999.9S (Adjustable)
After-glow Time 0~999.9S (Adjustable)
Burning Angle 0°, 20°, 45° (Adjustable)
Flame Height 20mm~175mm (Adjustable)
Gas Flow 0~1L/Min
Gas Pressure 0~0.25Mpa
Bunsen Lamp Internal Diameter 9.5±0.3mm
Bunsen Lamp Length 100mm±10mm
Timer Accuracy 0.1S
Back Pressure Range 200mm water column
Position Adjustment Exact according to standard
Additional Features Touch screen, remote control
Compact Version Weight Less than 50kg

4. Testing Principles and Procedures in Accordance with UL 94 Flammability Standards

testing process using the LISUN HVR-LS tester follows a set of well-defined principles and procedures based on the UL 94 Flammability Standards.

4.1 Test Specimen Preparation

The test specimens are prepared with standard-specified dimensions, which vary depending on the type of test (horizontal or vertical) and the material grade being evaluated. For example, specimens for HB grade testing typically have a length of 125mm, width of 13mm, and thickness as per the material’s intended use. For V grade testing, specimens are usually 125mm in length, 13mm in width, and 3mm or 1.5mm in thickness.

4.2 Test Setup

The tester is configured according to the specific test requirements. The gas source (98% pure methane) is connected, and the flame height is adjusted to the required value (e.g., 20mm for 50W tests). The burning angle is set to the appropriate position (0° for horizontal tests, 90° for vertical tests, etc.). The specimen is mounted in the correct position, ensuring that it is aligned with the flame as specified.

4.3 Test Execution

• Horizontal Burning Test (HB Grade): The specimen is held horizontally, and a 50W flame is applied to one end for a specified duration. The time taken for the flame to spread a certain distance along the specimen is measured to determine the burning speed, which is then used to classify the material into HB40 or HB75.
• Vertical Burning Test (V, 5V, VTM Grades): For V grades, the specimen is held vertically, and a 50W flame is applied for 10 seconds, then removed. The duration of flaming combustion (after-flame time) is recorded. This process is repeated once. The material is classified based on the maximum after-flame time, presence of dripping, and ignition of the cotton indicator. For 5V grades, a 500W flame is applied five times for 5 seconds each, and the material’s performance is evaluated.
• Foam Material Test (HF Grade): The horizontal burning test for foam materials involves applying a flame to the specimen and assessing the burning characteristics, including the spread of the flame and any dripping.

4.4 Evaluation Criteria

The evaluation of the test results is based on the criteria outlined in the UL 94 Flammability Standards. This includes measuring the after-flame time, after-glow time, burning length, presence of dripping, and whether the dripping material ignites the cotton indicator. These parameters are used to assign the material to the appropriate flammability grade.

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5. Significance of UL 94 Flammability Standards and Testing
The UL 94 Flammability Standards and the corresponding testing using instruments like the LISUN HVR-LS tester play a vital role in ensuring the safety of electrical equipment and plastic components. By classifying materials based on their flammability, manufacturers can select appropriate materials for specific applications, reducing the risk of fire hazards. Regulators can use these standards to establish safety requirements and conduct inspections, ensuring that products meet the minimum safety criteria. Consumers can make informed choices by looking for products that use materials with appropriate UL 94 grades, enhancing overall safety.
Moreover, these standards facilitate international trade by providing a common set of criteria for flammability testing, ensuring that products meet consistent safety levels across different markets. They also drive innovation in material science, as manufacturers strive to develop materials with improved fire resistance to meet higher UL 94 grades.

6. Conclusion
The UL 94 Flammability Standards are essential in evaluating the fire performance of plastic materials and electrical equipment components. The LISUN HVR-LS Horizontal Vertical Flame Tester is a reliable and versatile instrument that enables accurate testing in accordance with these standards. Its comprehensive features and adherence to international specifications make it an invaluable tool for research, production, and quality inspection in various industries. By conducting rigorous testing based on UL 94 Flammability Standards, we can ensure that electrical products and plastic materials meet high safety standards, minimizing the risk of fire-related incidents and protecting lives and property.

In future, as technology advances and new materials are developed, the UL 94 Flammability Standards will continue to evolve, and testing instruments like the LISUN HVR-LS will adapt to meet these changing requirements, further enhancing the safety of our built environment.

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