UL94

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Back of a printed circuit board marked “94V-0” at the bottom left

The regulation UL94 " Tests for Flammability of Plastic Materials for Parts in Devices and Appliances " ("Tests for the flammability of plastics for parts in devices and applications") of the Underwriters Laboratories (UL) describes a method for assessing and classifying the flammability of plastics. It was adopted with the same content in the standards IEC / DIN EN 60695-11-10 and -20 and the Canadian CAN / CSA C 22.2 No.017.

General approach

For the classification, test specimens measuring 125 × 13 × S (mm) ³ are produced. The thickness S must correspond to the smallest wall thickness in the intended application and may not exceed 13 mm. Often one or more of the grid levels 0.40 mm, 0.75 mm, 1.5 mm and 3.0 mm are checked.

The samples are then tested at the expense of the respective material supplier at Underwriters Laboratories or in an accredited test laboratory. The classification achieved is entered in publicly accessible so-called yellow cards . Users can use these to find out whether a certain material corresponds to the required fire protection classification.

Test procedure

The tests are carried out with an open flame ( Bunsen burner ). The ignition source has an output of 50 watts (20 mm high flame) or 500 watts, depending on the desired classification. In the HB test, it acts on the test specimen for 30 s or until the start mark is reached, in the V test twice for 10 s and in the 5V test five times for 5 s and is then removed again. The burning time and, in the case of the V tests, the falling off of burning parts are evaluated with the aid of a cotton swab located under the test specimen.

Classification

The classification is carried out for the tested specimen thickness in the steps HB ( H orizontal b race-test), as well as V-0, V-1, V-2, 5VA and 5VB ( V ertikalbrennprüfung). These stand - sorted according to the level of the requirement - in detail for:

  • HB : slow burning of a horizontally clamped specimen (self-extinguishing or with thickness <3 mm; rate <75 mm / min (HB75); with thickness 3 ... 13 mm; rate <40 mm / min (HB40)).
  • V-2: Extinguishing a vertically clamped sample within 30 seconds. Burning droplets of plastic melt permitted.
  • V-1: like V-2, but no burning droplets of plastic melt permitted. Afterglow for a maximum of 60 seconds.
  • V-0: like V-1, but the flame is extinguished within 10 seconds. Afterglow for a maximum of 30 seconds.

Plastics that meet at least classification V-2 can also be tested with the 500 watt flame (125 mm flame height):

  • 5VB: extinguishing of a vertically clamped specimen after being exposed to flame five times for five seconds each time; no dripping allowed.
  • 5VA: like 5VB, additional test on a horizontally clamped plate; neither dripping nor the formation of burn holes with a diameter> 1 mm are permitted.

There are similar classifications for foams (HF-1, HF-2, HBF) and thin films (VTM-0, VTM-1, VTM-2).

Web links

Individual evidence

  1. ↑  ( page no longer available , search in web archives )@1@ 2Template: Dead Link / www.pultex.de
  2. ↑ Yellow Card with linked pages for the individual properties
  3. ↑ a b c Fire behavior according to UL94