What is UL94 flame test?

UL94 is the most widely used flame retardant performance evaluation standard for plastic materials, with a total of 12 classifications: HB, V-0, V-1, V-2, 5VA, 5VB, VTM-0, VTM-1, VTM-2, HBF , HF-1, HF-2.

UL94 covers tests for flammability of polymeric materials used for parts in devices and appliances. It is to measure and describe the flammability properties of materials (burning rate, after glow time, after flame time, damage length of the specimen, drip particles, particles ignited the cotton indicator). Many values can be obtained for each tested material based on color or thickness. When selecting the material of a product, its UL rating should meet the thickness requirements of the wall part of the plastic part. The UL rating must be reported with the thickness value.

Commonly UL94 test method

1. Horizontal Burning Test (HB)

HB is the lowest flame retardant grade in the UL94 standard. The test procedure is to clamp the specimen at the end of farthest from the 25mm mark, with its longitudinal axis horizontal and its transverse axis inclined at 45±2 degrees, and then take a wire gauze to be clamped horizontally beneath the specimen, with a distance of 10 mm between the lowest edge of the specimen, adjust the bunsen burner (flame height 20mm) to be tilted 45⁰, and position the burner so that the flame impinges on the free end of the specimen to a depth of 6mm, apply the test flame for 30s without changing its position. Remove the burner after 30s or as soon as the combustion front of the specimen reaches the 25mm mark (if less than 30s). start the timing device when the combustion front reaches the 25mm mark.

2. 50W (20mm) Veritcal Burning test (V-0, V-1 or V-2)

The bunsen burner (flame height 20mm) contact with the center point of specimen for 10±0.5s, immediately withdraw the burner at a rate of approximately 300mm/s, to a distance at least 150mm away from the specimen and simultaneously commence measurement of the afterflame time t_1. As soon as afterflaming of the specimen ceases, even if the burner has no been withdrawn to the full 150mm distance from the specimen, immediately place the burner again under the specimen for an additonal 10s±0.5s, after this application of the flame to the specimen, immediately remove the burner at a rate of approximately 300mm/s to a distance of at least 150mm from the specimen and simultaneously commence measurement of the afterflame time t₂ and afterglow time t_3.

3. 500W (125mm) Vertical burning test (5VA or 5VB)

1). Plate specimen

The bursen burner (flame height 125mm) is applied to the center of the bottom surface of the plate at an angle of 20±5⁰ from the vertical, so that the tip of the blue cone (40mm height) is within 0 to 3mm of the plate surface, apply the flame for 5±0.5s and then remove for 5±0.5s. Repeat the operation for five times, after the fifth application of the test flame, record the afterflame time and afterglow time.

2). Bar specimen

Clamp the specimen, the bursen burner (flame height 125mm) is applied to one of the low corners of the specimen at an angle of 20±5⁰ from the vertical, so that the tip of blue cone is within 0 to 2mm of the specimen edge, apply the flame for 5±0.5s and remove for 5±0.5s, Repeat the operation for five times, after the fifth application of the test flame, record the afterflame time and afterglow time and observe whether or not specimens drip particles and whether the particles ignited the cotton indicator

UL 94 flame retardant rating standard

1. UL94 horizontal burning judgment conditions

2. UL94 50W vertical burning judgment conditions

3. UL94 500W vertical burning judgment conditions

The horizontal and vertical flame test apparatus is the equipment to simulate the 50W vertical flame test includes V-0, V-1, V-2, horizontal flame tester HB, and 500W vertical flame test includes 5VA, 5VB, HF-1, HF-2 and HBF according to UL94.