In-Depth Explanation of UL Plastic Flame Retardancy Test: No Wonder Some People Fake It, It's Not Just A Simple Burn

In-Depth Explanation of UL Plastic Flame Retardancy Test: No Wonder Some People Fake It, It's Not Just a Simple Burn

UL, established in 1894 in the United States, is a non-profit organization that evaluates the safety of industrial products from a third-party perspective. With branches worldwide, UL has become a de facto safety standard in the U.S., and products exported to the U.S. must also comply with UL standards.

The "Yellow Card" refers to the data sheet of materials or components that have obtained the above certification and are registered with UL. The collection of these data sheets is known as the "Yellow Book."

Plastic flame retardancy grades increase from HB to V-0:

• HB: The lowest flame retardancy      grade under UL94 standards. It requires samples between 3 to 13 mm thick      to burn at less than 40 mm per minute; samples less than 3 mm thick should      burn at less than 70 mm per minute or extinguish before a 100 mm mark.

• V-2: After two 10-second flame      tests, the flame should extinguish within 60 seconds, with allowed burning      debris.

• V-1: Similar to V-2, but no burning      debris is allowed to fall.

• V-0: After two 10-second flame      tests, the flame should extinguish within 30 seconds, with no burning      debris.

Evaluation criteria for UL94-V specimens

Determine the flammability rating based on the above evaluation results. The evaluation criteria are shown in Table 1. Failure to meet any one of the criteria is unqualified, and the specimen is also unqualified for complete combustion.

UL94 standard test procedures and requirements

(I) UL94HB

Sample: 

5“ x 1/2” x thickness (typical thicknesses are 1/16“, 1/8”, 1/4")

Procedure: 

Three samples of each thickness are to be tested. Prior to testing, the samples are to be placed at 20°C, 50% RH for 48 hours. The samples are placed parallel to the long axis and at an angle of 45 degrees to the short axis. For each sample, draw two lines 1“ and 4” from one end.

A blue flame 1” high is placed on the overhanging end of the sample and burned for 30 seconds and then taken away. If the sample continues to burn after the flame is removed, measure the time the sample burns between the two width marks and the burn rate in inches per minute.

Grade Requirements 94HB

A: For samples between 0.120“ and 0.500” thick, not more than 1.5“ per minute and not more than 3.0” across.

B: For samples with a thickness of 0.120“, the span cannot exceed 3.0”.

C: The sample spontaneously ignites without the flame touching the 4.0” mark.

(II) UL94V-0, V-1, V-2

Sample: 

5“ x 1/2” x thickness (typical thicknesses 1/16“, 1/8”, 1/4")

Procedure: 

A total of 10 samples (2 sets) of each thickness are tested. Five samples of each thickness were left at 23°C, 50% RH for 48 hours before testing. 5 samples of each thickness were left at 70°C for 7 days before testing.

The samples were placed perpendicular to the long axis and mounted. The samples were mounted so that the lower end of the sample was 3/8“ from the top of the burner tube. A blue flame at a height of 3/4” was placed in the center of the lower end of the sample and burned for 10 seconds.

If the sample drips in grains, this liquid drips onto a layer of non-surgically treated cotton placed 12” below the sample.

Grade Requirements:

94V-0

A: There were no samples that still had embers burning for more than 10 seconds after the test flame was taken away.

B: For each set of 5 samples, the total time of burning with embers exceeded 50 seconds after 10 ignitions.

C: There were no samples that burned all the way down to the fixture (both burning with embers and reddened burning).

D: There were no samples in which the droplets of burned and melted liquid dripped down to ignite the cotton that lay 12” below.

E: There was no sample that continued to redden and burn for more than 30 seconds after the second removal of the test flame.

94V-1

A: There were no samples that continued to burn with embers for more than 30 seconds after the test flame was removed. 

B: For each set of 5 samples, the total time of burning with embers was more than 250 seconds after 10 ignitions. 

C: There were no samples that burned all the way down to the fixture (both burning with embers and reddening). 

D: There were no samples in which a droplet of burned melted down and ignited the cotton at the bottom 12“. 

E: There were no samples in which a droplet of burned melted down ignited the cotton at the bottom 12”. 

F: There were no samples that continued to burn for more than 30 seconds after the test flame was removed for a second time. E: There were no samples where the reddening burn persisted for more than 60 seconds after the second removal of the test flame.

94V-2

A: There were no samples that continued to burn with embers for more than 30 seconds after the test flame was taken away. b: For each set of 5 samples, the total time of burning with embers was more than 250 seconds after 10 ignitions. c: There were no samples that burned all the way down to the fixture (both burning with embers and reddened burning). d: Droplets of melted liquid from the burning of the samples were allowed to drip down and ignite the cotton at the bottom 12”, but the cotton burned for a shorter period of time.E: No samples that continued to redden and burn for more than 60 seconds after the second removal of the test flame.

Is the highest UL flame rating V-0?

No! UL94-5VA or UL94-5VB.

Depending on the results of the sample test, the material should be classified as 94-5VA or 94-5VB.

The test procedure is as follows: Samples without burn-through are 94-5VA Samples with burn-through are 94-5VB Samples: 5“ x 1/2” x thickness (bar) 6“ x 8” x thickness (plate) Typical thicknesses are (1/16“,1/8”,1/4")

Procedure for Bar Samples (Method A)

2 sets of 10 total samples to be tested.

Five samples of each thickness are tested after 48 hours at 23°C, 50% RH.

5 samples of each thickness were tested after 7 days at 70°C.

For bar samples, mount perpendicular to the long axis.

Place a 5“ high flame with a 1/2” inner flame on the lower corner of the sample at an angle of 20° to the vertical. Bring the tip of the inner flame into contact with the sample.

The flame burns for 5 seconds and moves for 5 seconds, this action is repeated until the sample has gone through 5 burns.

Level Requirements:

A: No sample continues to burn (including flaming and reddening combustion) for more than 60 seconds after the 5th ignition.

B: No sample burned melted droplets dripping down to ignite the cotton below.

Procedure for Plate Samples (Method B)

Same formulation as for stick samples:

3 pieces of samples (2 sets) are mounted horizontally and the flame is placed in the center of the bottom surface to burn.

Evaluation Criteria for the Plate Test