UL 94, the Standard for Safety of Flammability of Plastic Materials

UL certification

UL is the abbreviation of the English Underwriter Laboratories (Underwriter Laboratories Inc.). The UL Safety Laboratory is the most authoritative in the United States and the largest private institution engaged in safety testing and identification in the world. It is an independent, not-for-profit, professional organization that conducts experiments for public safety. Use scientific testing methods to study and determine whether various materials, devices, products, equipment, buildings, etc. are harmful to life and property and the degree of harm; determine, write, and issue corresponding standards and help reduce and prevent damage to life and property. Lost data while conducting fact-finding research operations. It is mainly engaged in product safety certification and operating safety certification business, and its ultimate purpose is to obtain products with a relatively safe level for the market, and to contribute to the guarantee of personal health and property safety.

 UL (Underwriters Laboratories) is an independent product safety certification body. It establishes and maintains industry-wide safety standards for mechanical, electrical and chemical products. Since its inception, UL's safety standards have included design recommendations and testing/construction requirements for a variety of products, in addition to electrical requirements for cables. UL is also a globally recognized testing laboratory and one of the most widely accepted certification marks. In the United States, the logo appears on 22 billion products each year. UL regularly conducts product testing in accordance with applicable standards. Further audits follow to monitor compliance and product consistency.

 UL was founded in 1894. In the initial stage, UL mainly relied on the funds provided by the fire insurance department to maintain its operations. It was not until 1916 that UL was completely independent. After nearly a hundred years of development, UL has become a world-renowned certification body, with its own set of strict organizational management system, standard development and product certification procedures. The UL organization is managed by a council composed of representatives of safety experts, government officials, consumers, education, utilities, insurance and standards departments. Currently, UL has five laboratories in the United States and is headquartered in North Chicago. Northbrook Town.

Types of UL product certifications 

• 1) LISTED: Generally speaking, listing is only applicable to complete products and qualified personnel in other electrical components, etc. Products listed by UL can usually be marked with the UL listing mark on each product. Usage of column name flags.

• 2) Recognized: Recognized service is a project in UL service, and the products recognized by it can only be used as components and raw materials on UL listed, graded or other recognized products. Approved products are not structurally complete, or have certain limitations in use to ensure the expected safety performance. Tracking services for approved products fall under the R category in most cases. Approved products belonging to category L are electronic wire (AVLV2), processing wire (ZKLU2), wire harness (ZPFW2), aluminum wire (DVVR2), and metal flexible tube (DXUZ2). Approved products are required to carry the approval mark.

• 3) Classification: The classification service only evaluates the specific hazards of products, or evaluates products that implement other standards than UL standards (including internationally recognized standards, such as IEC and ISO standards, etc.). In general most graded products are not for consumer use, but for industrial or commercial use. The grading mark in the UL mark indicates that the product has certain restrictions and regulations when it is identified by UL. For example, chemicals such as industrial solvents are evaluated only in the range where fire may occur when the temperature reaches the ignition temperature.

• 4) Multiple listing, multiple accreditation or multiple grading services: When a UL applicant obtains the above-mentioned listing, accreditation or grading services, and its products are produced in the name of another company to meet the needs of sales, it can apply for Multiple Listing, Multiple Approval or Multiple Rating Services, in which case the manufacturer listed, approved or graded is permitted to use the name of another company in the product list, but the product is subject to a company code, product code or Except for other characteristics that UL considers acceptable, it must be consistent with the original listed, approved or graded product.

• 5) "AL" listing, accreditation or grading services: If the UL applicant does not want to obtain listing, accreditation or grading services in the name of his own company, he can apply for the name of another firm (usually a retailer or wholesaler) Application for listing, accreditation or grading is called "AL" listing, accreditation or grading service. It differs from multiple listing, multiple recognition or multiple classification services in that the applicant is not a listed person.

• 6) System certification services: As one of the members of the International Accreditation Committee, UL is widely involved in ISO9000 quality system certification, ISO14000 environmental protection certification, QS9000 automotive industry quality system certification and AS9000 aircraft industry quality system certification services. So far, a total of 116 factories in China have obtained UL system certification; 21 of them are ISO9001 certified, 85 are ISO9002 certified, 1 is ISO14001 certified, and 9 are QS9000 certified.

• 7) UL's other services: such as certification services, inspection services, factual judgment services, research services, etc.

UL 94 Plastic Flammability Standard /Plastic fire protection standard/Fire rating definition

UL 94 is a plastic flammability standard issued by Underwriters Laboratories in the United States. This standard classifies plastics according to how they burn with different thicknesses. Most of the plastics that come into contact with are flammable, but many electrical appliances and electronic equipment inevitably have plastic materials inside. So in the case of fire safety considerations, how to choose plastic materials? So people have developed a set of standards and tests, the purpose is to test the ability of materials to be extinguished after being ignited. The results of different plastic flammability tests will be classified into different fire and flame retardant grades, which are used as safety references. in accordance with.

UL 94 Flame Classification Overview / Plastic Fire Rating Instructions

UL 94, Safety Standard Testing for the Flammability of Plastic Materials for Parts of Equipment and Appliances conducts two types of preselected test procedures on plastic materials to measure flammability. First determine the tendency of the material to extinguish or spread the flame once the sample is ignited. The first procedure was described in UL 94 and is now aligned with IEC 60707, 60695-11-10 and 60695-11-20 and ISO 9772 and 9773. The second test procedure measures the flame resistance of plastics to electrical ignition sources. The fire resistance and surface tracking properties of this material are described in UL 746A, similar to the test procedures described in IEC 60112, 60695 and 60950.

UL 94 Test Method

The UL 94 flammability test includes the following four test methods:

• 1. The material is classified as UL 94HB horizontal burning test method.

• 2. The material is classified as UL 94V0, UL 94V1, UL 94V2 vertical burning test method.

• 3. The material is classified as UL 94-5VA, 94-5VB vertical burning test method.

• 4. The material is classified as UL 94VT M0, 94VT M1, 94VT M2 vertical burning test method.

UL 94 Test Result Rating

According to the ability of the tested object to extinguish the flame after being ignited, including: burning speed, burning time, anti-dropping ability, and whether the dripping object is burning, etc., various grade standards are formulated.

Sample size

5" x 1/2" x thickness (typical thickness is 1/16", 1/8", 1/4")

Condition 1, test the burning rate of HB:

Three samples of each thickness are to be tested. Before testing, the samples are placed at 20°C, 50%RH for 48 hours. The sample is to be placed parallel to the long axis and at a 45° angle to the short axis. For each sample, draw two lines 1" and 4" from one end. Place a 1" high blue flame on the end of the sample where the sample is suspended and burn for 30 seconds before removing it. If the sample continues to burn after the flame is removed, measure the time the sample burns between the two width marks, and Burn rate is calculated in inches per minute.

Condition 2, test combustion standard:

A total of 10 samples (2 sets) were tested for each thickness. Five samples of each thickness were placed for 48 hours at 23°C and 50%RH before testing. Five samples of each thickness were placed at 70°C for 7 days before testing.

The sample is placed perpendicular to the long axis and mounted. Install with the lower end of the sample 3/8 inch from the top of the burner tube. Place a blue flame 3/4 of the height in the center of the lower end of the sample and burn for 10 seconds.

If the sample drips off grain by grain, the liquid drips onto a layer of unsurgically treated cotton below the sample, which is placed 12 inches below the sample.

The classifications from the lowest (minimum flame retardancy: HB) to the highest (maximum flame retardancy: 5VA) are:

• HB: Slow burning on horizontally placed samples, less than 75 mm/min for materials less than 3mm thick

• V2: After two 10-second burning tests on the sample, stop burning within 30 seconds on the vertically placed sample, allowing the cotton wool below 30cm to be dropped and ignited

• V1: After two 10-second burning tests on the sample, stop burning within 30 seconds on the vertically placed sample, allowing dripping but not igniting the cotton wool below 30cm

• V0: After two 10-second burning tests on the sample, stop burning within 10 seconds on the vertically placed sample, allowing dripping but not igniting the cotton wool below 30cm

• 5VB: Stop burning within 60 seconds on a vertically placed sample, no dripping allowed, holes allowed on the sample

• 5VA: Stop burning within 60 seconds on a vertically placed sample, no dripping is allowed, and no holes are allowed on the sample

The test generally uses a 5" by 0.5" sample. Strip and sheet samples are tested for both 5VA and 5VB ratings, and the flame is approximately five times more intense than those used to test other materials. There are other classifications available for low density foams (HF-1, HF-2, HBF) and films (VTM-0, VTM-1, VTM-2).

Basically, the burning difficulty of the material is 5VA > 5VB > V0 > V1 > V2 > HB

UL94 flame resistance test methods and standards

In relation to the plastic materials offered by Professional Plastics, there are 6 flame classifications specified in UL 94 which are used to grade the material based on the results of these small flame tests. These classifications, listed in descending order in each of the following three groups, are used to differentiate the combustion characteristics of the material after exposing the specimen to the specified test flame under controlled laboratory conditions. These classifications relate to materials commonly used in the manufacture of housings, structural components and insulators in consumer electronics (UL 94 5VA, 5VB, V-0, V-1, V-2, HB).

Horizontal and vertical positioning

Specimens made of plastic material are oriented in a horizontal or vertical position according to the specifications of the relevant test method and are subjected to a specified flame ignition source for a specified period of time. In some tests, as with the horizontal burn (HB) test, the test flame is applied only once, while in others, the flame is applied at least twice.

HB

The HB flame rating indicates that the material was tested in a horizontal position (horizontal burn) and found to burn at a rate less than the specified maximum. It is required to burn at a rate of less than 40 mm per minute for samples 3 to 13 mm thick; less than 70 mm per minute for samples less than 3 mm thick; or to extinguish before the 100 mm mark.

V2, V1, V0

Vertical ratings V2, V1 and V0 indicate that the material was tested in a vertical position and self-extinguished within a specified time after removal of the ignition source. The vertical rating also indicates whether the test sample dripped burning particles that ignited the cotton indicator located below the sample. UL 94 also describes a method in which a test flame can be used in up to five applications when testing for 5VA or 5VB classification. These small-scale tests measure a material's likelihood of extinguishing or spreading the flame when ignited.

Differences in test methods and standards

When looking at the flammability rating of plastics typically used to make housings, structural components and insulators in consumer electronics (5VA, 5VB, V-0, V-1, V-2 and HB), they are classified as 5VA or The 5VB withstands flame ignition sources approximately five times more intense than those used in the V-0, V-1, V-2 and HB tests. In addition, the sample must not drip any flame particles.

There are 3 main levels of flame burn testing:

20mm flame, judgment result: HB, V-0, V-1 or V-2

125mm flame, judgment result: 5V-A or 5V-B

20mm flame for thin, film materials, judgment result: VTM-0, VTM-1 or VTM-2

The starting point for the possibility of any material being rated V-0, V-1 or V-2 is the test starting with the 20mm flame. All three grades are based on this single test. Ratings are based on test results; there are no separate tests for each of these ratings.

5 samples are required for the V grade and only 3 for the HB. The remaining 3rd sample can be used to convert the test to HB when starting with V but if the material shows poor characteristics in the first 2 samples.

When the material test becomes V-0, the material can then be tested with a 125mm flame to see the possibility of a 5V-A or 5V-B rating. However, this VTM test can only be performed if the material passes a V-0 rating.

If the material is so thin that it cannot be tested against any V rating because the material will "fly" in the heat of the flame due to thermal turbulence, the material should be tested as a thin material by the VTM test procedure. Likewise, the VTM test should only be performed if the material fails or cannot be properly tested in accordance with the V test procedure.