OK

Flammability UL94

Preliminary Screening of Plastics for Fire Performance


Screening of Plastics for Fire PerformanceUL 94 (Underwriters Laboratories test standard UL 94) is one of the most widely used flammability tests for determining relative flammability for plastic materials. It measures the ability of plastic part to extinguish the flame after ignition and its dripping behavior in response to a small open flame or radiant heat source under controlled laboratory conditions.

The tests results are intended to serve as a preliminary indication of the material’s suitability with respect to flammability for a particular application, such as plastic materials used for parts in electronic devices and appliances.

The flammability is influenced by several factors such as:

  • Ease of ignition – how rapidly a material ignites
  • Flame spread – how rapidly fire spreads across a polymer surface
  • Fire endurance – how rapidly fire penetrates a wall or barrier
  • Rate of heat release – how much heat is released and how quickly
  • Ease of extinction – how rapidly the flame chemistry leads to extinction
  • Smoke evolution
  • Toxic gas generation

Hence, the study of how plastics burn has been, and continues to be, a major area of research to examine:

  • The nature of the burning phenomenon in plastics
  • Various methods to reduce plastics flammability, and
  • Methods to test flammability

Also read about Limiting Oxygen Index Test


Check out more on Flammability UL 94 Test:

» Main types of Testing & Flammability Ratings
» Vertical Burning Test for Classifying Materials
» Horizontal Burning Test for Classifying Material


Main Types of Testing & Flammability Ratings to Classify Plastics


The UL standard classifies plastics according to the minimum thickness at which it stops burning when tested in a horizontal or vertical orientation.

Types of testing/flammability ratings covered in the UL 94 standard for flammability of plastic materials include:

  • Vertical burning tests (V-0, V-1, V-2, 5V, 5VA, 5VB, VTM-0, VTM-1, VTM-2)
  • Horizontal burning tests (HB, HBF, HF-1, HF-2)

Class
Orientation of Test Sample
Definition
Time of Burn Allowed
Particle Drop Allowed
plaque Holes
Flaming Non-Flaming
UL 94 HB Horizontal Slow Burning Burning rate of less than 76mm/min for a specimen less than 3mm thick and burning stops before 100mm
UL 94 V-2 Vertical Burning Stops 30 seconds Yes Yes
UL 94 V-1 Vertical Burning Stops 30 seconds No Yes
UL 94 V-0 Vertical Burning Stops 10 seconds No Yes
UL 94 5VB Vertical Burning Stops 60 seconds No No Yes
UL 94 5VA Vertical Burning Stops 60 seconds No No No
UL Classifications Majorly Used for Plastics
(Source: W. L. Gore & Associates, Inc.)


The UL test methods are aligned with IEC 60707, IEC 60695-11- 10, IEC 60695-11-20, ISO 9772 and ISO 9773 standards used to determine fire properties.


Vertical Burning Test for Classifying Materials


UL 94 V Rating: V-0, V-1, V-2


This test measures the self-extinguishing time of the vertically oriented polymer specimen. The top of the test specimen is clamped to a stand and the burner is placed directly below the specimen. The test evaluates both the burning and afterglow times and dripping of the burning test specimen.

The material will be rated:

  • V-0: if flame extinguishes within 10 seconds with no dripping
  • V1: if flame extinguishes within 30 seconds with no dripping
  • V2: if flame extinguishes within 10 seconds with dripping

Flammability rating UL 94 V
Test Criteria V-0 V-1 V-2
Burning time of each individual test specimen (s)
(after first and second flame applications)
≤10 ≤30 ≤30
Total burning time (s)
(10 flame applications)
≤50 ≤250 ≤250
Burning and afterglow times after second flame application (s) ≤30 ≤60 ≤60
Dripping of burning specimens
(ignition of cotton batting)
no no yes
Combustion up to holding clamp
(specimens completely burned)
no no no
(Source : UL LLC)



UL 94 VTM Rating: VTM-0, VTM-1 and VTM-2 - Thin Material Vertical Burning Testing


This test method is used for thin specimen or materials that are too flexible or may distort, shrink or flex during the traditional vertical testing (failure to pass the UL 94 V test is a precondition of all VTM ratings). This test is similar to the vertical burning test except that the material is wrapped around a mandrel before clamping to the stand and the flame application is reduced. In this test, the flame is applied only for 3 seconds.

Flammability rating UL 94 VTM
Test Criteria VTM-0 VTM-1 VTM-2
Burning time of each individual test specimen (s)
(after first and second flame applications)
≤10 ≤30 ≤30
Total burning time (s)
(10 flame applications)
≤50 ≤250 ≤250
Burning and afterglow times after second flame application (s) ≤30 ≤60 ≤60
Dripping of burning specimens
(ignition of cotton batting)
no no yes
Combustion up to holding clamp
(specimens completely burned)
no no no
(Source : UL LLC)



UL 94 5V Rating: 5V, 5VA, 5VB - Vertical Testing is done on both bar and plaque specimens


For any material to achieve 5V classification, the test specimens must not burn with flaming and/or glowing combustion for more than 60 sec after the fifth flame. Also, the test specimens must not drip.

Flammability rating UL 94
Test Criteria 5VA 5VB
Burning and afterglow times of specimens after fifth flame application (s) ≤60 ≤60
Dripping of burning specimens no no
Hole formation no yes
(Source : UL LLC)


Horizontal Burning Test for Classifying Material


Specimens molded from the plastic material are oriented in either a horizontal depending on the specifications of the relevant test method, and they are subjected to a defined flame ignition source for a specified period of time.


UL 94 HB Rating


A material having a thickness between 3 and 13mm will be classified as a HB material if it does not have a burning rate exceeding 40mm per minute. For material with thickness less than 3mm the burning rate should not exceed 75mm per minute. The material will also be rated as HB if it ceases to burn before the 100mm mark independent of thickness.

Test criteria Burning rate in V Flammability rating
Test specimen thickness 3-13mm ≤40 mm/min HB
Test specimen thickness < 3 ≤75 mm/min HB
Flame is extinguished before first mark ≡ 0 mm/min HB
(Source: UL LLC)


UL 94 HBF: HBF, HF-1 and HF-2 - Horizontal Burning Foamed Material


This test grants three different types of ratings depending on burning rates and or afterflame times. A material will be classified as a HBF material if it does not have a burning rate exceeding 40mm per minute over a 100 mm span or if ceases to burn before flaming or glowing reach the 125mm mark.

Flammability rating UL 94 HBF
Test criteria (test specimens) HF-1 HF-2
Burning time (s)
4/5 ≤ 2
1/5 ≤ 10
4/5 ≤ 2
1/5 ≤ 10
Burning and afterglow time of each individual specimen (s) ≤ 30 ≤ 30
Dripping of burning specimen
(ignition of cotton batting)
no yes
Damaged length of individual specimen (mm) < 60 < 60
(Source: UL LLC)


Check out an interesting video about UL 94 Horizontal & Vertical Flammability Tester, Flammability Test Chamber


(Source: TESTEX Testing Equipment)


Find commercial grades matching your thermal properties target using "Property Search - Flame Rating" filter in Omnexus Plastics Database:

Omnexus Plastics Database - Property Search


Commercially Available Flame Retarded Polymer Grades




Also read about Limiting Oxygen Index Test  


Disclaimer: all data and information obtained via the Polymer Selector including but not limited to material suitability, material properties, performances, characteristics and cost are given for information purpose only. Although the data and information contained in the Polymer Selector are believed to be accurate and correspond to the best of our knowledge, they are provided without implied warranty of any kind. Data and information contained in the Polymer Selector are intended for guidance in a polymer selection process and should not be considered as binding specifications. The determination of the suitability of this information for any particular use is solely the responsibility of the user. Before working with any material, users should contact material suppliers in order to receive specific, complete and detailed information about the material they are considering. Part of the data and information contained in the Polymer Selector are genericised based on commercial literature provided by polymer suppliers and other parts are coming from assessments of our experts.

Copyright SpecialChem SA
Back to Top