A Deeper Look at UL94 and UL1581: A Comparison and Application of Flame Rating Standards

UL94 and UL1581 are two standards developed by Underwriters Laboratories (UL) in the United States for evaluating the flame retardancy of materials and wire and cable. While both are related to flame retardancy, their test methods, applicable targets, and ratings differ. This article will explain the differences in test methods, applicable targets, ratings, and key factors to consider when selecting flame-retardant materials.

UL94 Standard

The UL94 standard focuses on the combustion characteristics of plastic materials and is primarily used to evaluate plastic components in electronic devices. It determines a material's flame retardancy rating through a series of vertical and horizontal burn tests. The UL94 standard defines a variety of flame retardancy grades for plastics, ranging from HB, V-2. V-1. V-0. 5VB, and finally 5VA.

HB: The lowest flame retardancy rating in the UL94 standard. For samples 3-13 mm thick, the burning rate must be less than 40 mm/minute; for samples less than 3 mm thick, the burning rate must be less than 70 mm/minute; or the sample must be extinguished before the 100 mm mark.

V-2: After two 10-second burning tests, the afterflame must be extinguished within 60 seconds. Dropping particles may ignite cotton.

V-1: After two 10-second burning tests, the afterflame must be extinguished within 60 seconds. Dropping particles must not ignite cotton.

V-0: After two 10-second burning tests, the afterflame must be extinguished within 30 seconds. Dropping particles must not ignite cotton.

5VB: After five 5-second burning tests, the afterflame must be extinguished within 60 seconds. Dropping particles must not ignite cotton. Burn-through is permitted for block-shaped samples.

5VA: After five 5-second burning tests, the afterflame must be extinguished within 30 seconds. Dropping particles must not ignite the cotton. Burn-through of bulk samples is not permitted.

UL1581 Standard

The UL1581 standard specifically addresses the flame retardancy of wires and cables. It determines the flame retardancy rating of wires or cables by simulating their combustion behavior in a flame. UL1581 testing includes testing of individual wires or cables as well as bundled wires or cables.

VW-1: Vertical burn test (UL wire flammability rating);

FT1: Vertical burn test;

FT2: Horizontal burn test;

FT4: Vertical burn test;

FT6: Horizontal burn and smoke test (the FT-class flammability rating is the same as the CSA standard for wire flammability rating);

Of the above ratings, VW-1 is the same as FT1. with FT2 being the lowest. The flame retardancy ratings are FT6. FT4. VW-1. FT1. and FT2. respectively.

Although VW-1 and FT1 are the same rating, VW-1 is stricter than FT1.

Criteria

1. The burning marker (kraft paper) must not be charred more than 25%;

2. The afterburn time of five 15-second bursts must not exceed 60 seconds;

3. Flaming drips must not ignite cotton;

VW-1 requires compliance with 1.2.3. while FT1 only requires compliance with 1.2.

Single Wire and Cable Test: Evaluates the combustion performance of a single wire or cable in flame, primarily observing flame spread, duration, and self-extinguishing properties.

Bundled Wire and Cable Test: Evaluates the combustion performance of multiple wires or cables bundled together, which more closely resembles the actual installation conditions of wires and cables in buildings.

For the wire industry

UL94's V-2. V-1. V-0. 5VA, and 5VB ratings assess the materials used in the wires. These ratings require separate testing of the materials and develop standard samples; they are not marked on the wires.

UL1581's VW-1. FT-1. and FT-2 ratings assess the wires themselves. Passing these tests will result in the corresponding rating being marked on the wires.

The flame retardancy of wires and UL94 are completely different things. An insulating material that passes UL94's V-0 rating may not necessarily pass UL1581's VW-1 rating.

Key Differences

1. Different Applications: UL94 primarily targets plastic materials, while UL1581 focuses on wires and cables.

2. Different Testing Methods: UL94 evaluates the flame retardancy of materials through horizontal or vertical burning tests, while UL1581 evaluates the flame retardancy of individual or bundled wires and cables.

3. Different Testing Objectives: UL94 evaluates the general flame retardancy of materials, while UL1581 focuses more on the fire safety performance of wires and cables in practical applications.

4. Safety Requirements: In addition to evaluating flame retardancy, UL1581 may also assess other safety factors such as smoke and toxicity generated during combustion.

Considerations When Selecting a Standard

When choosing an appropriate flame retardancy performance evaluation standard, consider the following factors:

Material Type: Select the appropriate UL standard based on the material type (plastic or wire and cable);

Application Environment: Consider the specific environment in which the material or wire and cable will be used and the potential fire risk;

Safety Regulations: Comply with local building codes and safety standards and select a flame retardancy rating that meets regulatory requirements;

Performance Requirements: In addition to flame retardancy, consider the material's other physical and electrical properties.

UL94 and UL1581 are two different flame retardancy performance evaluation standards, one for plastic materials and one for wire and cable, respectively. When selecting materials or wire and cable, it is important to understand the specific requirements and test methods of these standards to ensure that the product meets the specified safety and performance standards.