HomeNews Industry News Check out this super detailed guide on UL flame retardant ratings

Check out this super detailed guide on UL flame retardant ratings

2024-05-29

Check out this super detailed guide on UL flame retardant ratings

CSA fire rating:

FT1: Vertical burning test (no requirement for drops);

FT2: Horizontal burning test;

FT3: Vertical burning incendiary drop test (cannot ignite newsprint);

FT4: Vertical combustion test in a closed combustion chamber (similar to a closed building) heat energy 70,000 btu/h;

FT5: Flame resistance test, usually used in underground work portable CABLE.

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UL fire rating:

A: Horizontal fire test;

B: VW-1: Vertical fire test, drops cannot ignite cotton wool;

VW-1SC: Vertical fire test, insulated core wire is tested separately from finished wire;

C: CL2 (VERTICAL TRAY FLAM TEST): in a closed burning box to do vertical combustion test (similar to the closed building UL1581);

D: CL2R (RISET CABLE);

E: CL2P (PLENUM CABLE);

F: CM (COMMUNICATION CABLE); G: CMR; H: CMP.


UL Plastics 94-V0 (94V0 is the so-called flame-retardant grade, divided into five grades) 94-V0 combustion when the fire is left immediately extinguished will not ignite spontaneously.

94-V1 When burning, the fire will burn for 1 second and then go out immediately without spontaneous combustion.

94-V2 When burning, the fire burns for 2 seconds and then goes out without spontaneous combustion.

94-V5 When the flame is removed, it burns for 5 seconds and then goes out immediately without spontaneous combustion.

94-HB Burns to carbon when flame is removed.


Comparison of UL94 Plastic Flame Retardant Ratings with UL 1581 VW-1 Flame Retardant Ratings

There are 12 types in UL94: HB, V-0, V-1, V-2, 5VA, 5VB, VTM-0, VTM-1, VTM-2, HBF, HF-1, HF-2.

Flammability UL94 rating is the most widely used flammability performance standard for plastic materials. It is used to evaluate the ability of a material to extinguish when ignited. A variety of judgments can be made based on burning speed, burning time, drop resistance, and whether or not the droplets burn. Many values can be obtained for each material tested, depending on color or thickness. When selecting a product


When a material is selected for a product, the UL rating should meet the thickness requirements for the wall portion of the plastic part. the UL rating should be reported along with the thickness value; it is not sufficient to report the UL rating without the thickness.


Flame retardant ratings for plastics increase from HB, V-2, V-1, V-0, 5VB to 5VA:


HB: The lowest flame retardant rating in the UL94 standard. Requires a burning 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 extinguishment before the 100 mm mark.


V-2: After two 10-second burn tests on the sample, the residual flame & afterburning are extinguished within 60 seconds. Dripping particles can ignite cotton.


V-1: After two 10-second burn tests on the sample, the residual flame & afterburning are extinguished within 60 seconds. The dripping particles may not ignite the cotton.


V-0: After two 10-second burn tests on the sample, the residual flame & afterburning are extinguished within 30 seconds. Droplets must not ignite the cotton.


5VB: After five 5-second burn tests, the flame & afterburning are extinguished within 60 seconds. Dripping particles must not ignite the cotton. Burn-through is permitted for lumpy samples.


5VA: After five 5-second burn tests on the sample, the flame & afterburning are extinguished within 30 seconds. Droplets must not ignite the cotton. Lumpy samples are not allowed to burn through.


Burning through.


UL1581: Wire Burning Methods:


1、VW-1:Vertical flammability test (UL Wire Flammability Rating);


2、FT1:Vertical burning test;


3, FT2: horizontal combustion test;


4, FT4: vertical combustion test;


5, FT6: horizontal combustion and smoke test. (FT class of combustion level is the CSA standard wire combustion level)


Of the above classes:


VW-1 and FT1 the same level. FT2 is the easiest to pass, the lowest level. (FT6>FT4>FT1>FT2);


VW-1 is stricter than FT1, both are vertical burning.


Criterion 1. The burn mark (kraft paper) cannot be charred more than 25%;


Criterion 2. five 15-second burns must not exceed 60 seconds.


Criterion 2. Five 15-second burns cannot be continued for more than 60 seconds;


Criterion 3. the combustion droplets must not ignite the cotton;


VW-1 is required to meet criteria 1, 2, and 3; FT1 is required to meet criteria 1 and 2 only.


For the wire industry:


UL 94's V-2, V-1, V-0, 5VA,5VB assesses the materials used in the wires, and the tests are conducted in addition to developing standardized samples with the test materials, which will not be identified on the wires.


VW-1 VW -2 FT-1 FT-2 test is the wire itself, after passing the test, you can mark the corresponding grade on the wire.


Flame retardant wire and UL94 flame retardant are two different things, for example, an insulating material can pass UL94 V-0, but not necessarily pass VW-1;


In addition, UL94 is the flame retardant insulating material, while the flame retardant requirements of electrical wires are generally in UL758 62 1581; the object is different;


Therefore, V-0, V-1 and other UL94 flame retardant is not the flame retardant of the wire at all; there is no “V-0” printed on the AWM wire!


VW-1/FT1 and UL94 V0 combustion test in the equipment there is a big difference:


1, the height and temperature of the flame is different;


2, the methane flow rate used in the test is also different;


3, the back pressure of methane is also different;


4, the volume of the combustion box is also different: VW-1 requires more than 4 cubic meters, while the V0 only requires more than 0.5 cubic meters.


5, the number of combustion is also different;


6, combustion results: V0 requires recording the residual burning time, while VW-1 is not necessary!


But UL94 5V level combustion and VW-1 combustion test conditions and test methods are similar, closer!


Reminder: Whether it is VW-1 or UL94 combustion test equipment, have to refer to ASTM5025 and ASTM5027, UL1581 and UL94 is only the test method, the requirements of the test equipment must be in accordance with ASTM standards!

UL94 and VW-1 test on the difference between the equipment


UL94 combustion test HB, V0, V1, V2, VMT, 5VA, 5VB and other combustion tests, and UL1581 VW-1, FT1, FT2, FT4 and other combustion tests, the two tests in the equipment differences are as follows:

  • VW-1 \ FT1 blowtorch for: 125mm (500W), combustion flame: inner flame height 40 ± 2mm, outer flame 125 ± 10mm

  • UL94 HB, V-class blowtorch for: 20mm (50W), combustion flame: blue flame without cone, height 20 ± 1mm

  • UL94 5V level combustion is used 125mm (500W), combustion flame: inner flame height 40 ± 2mm, outer flame 125 ± 10mm


The flame temperature of the flame is also different:

20mm (50W) test flame: 100±2~700±3℃ for 44±2S.

125mm (500W) test flame: 100±2~700±3℃ is 54±2S.


The test space is also different:

UL94 in the HB, V, VMT its space is only required to be greater than 0.5 cubic meters can be, while 5V requires greater than 0.75 cubic meters; VW-1 requires greater than 4 cubic meters.


The flow requirements for methane are different:

The gas flow rate for HB, V, and VMT classes is 105 ml/min with a back pressure of 10 mm water column or equivalent;


Class 5V gas flow rate is 965 ml/min, 125 ± 25 mm water column or equivalent pressure;

VW-1 is the same as UL94 class 5V back pressure: gas flow rate is 965ml/min, 125±25mm water column or equivalent pressure;

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