What are UL-94 flammability ratings?

UL-94 flammability ratings are testing standards developed by Underwriters Laboratories to measure the flammability characteristics of plastic. There are six UL 94 specified flame classifications that apply to plastic enclosures used to house electronics (5VA, 5VB, V-0, V-1, V-2, HB).

These ratings are used to distinguish a material’s burning characteristics after test pieces have been exposed to a test flame under controlled laboratory conditions, as summarized below:

  • 5VA: Surface burning stops within 60 seconds. The test piece does not ignite under flame and does not have a burn-through hole.
  • 5VB: Surface burning within 60 seconds. The test piece does not ignite under flame but may have a burn-through hole.
  • V-0: Vertical burning stops within 10 seconds with no flaming drips off the test piece.
  • V-1: Vertical burning stops within 60 seconds with no flaming drips off the test piece.
  • V-2: Vertical burning stops within 60 seconds, but flaming drips may occur.
  • HB: Slow horizontal burn with a rate of less than 3 inches per minute or self-extinguishes before 5 inches.

Plastics meeting UL 94-5VA or UL 94-5VB have been tested with a flame source five times more severe than what is used in the remaining four tests, plus they are not allowed to have any flaming drips. These are considered to be the most flame-retardant plastics. Polycase offers several enclosure series meeting the UL 94-5VA flame rating, like the XR Series or DC Series.

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