Flammability & Fire Safety UL 94
Classification
UL 94 is the standard applied by the American Underwriters
Laboratories for the testing of the flammability and fire safety of
plastic materials used in devices and appliances. The UL 94 HB
(Horizontal Burning) tests the burning of a horizontal plastic
specimen and the most demanding UL 94V (Vertical Burning) tests the
burning of a vertical plastic specimen. Precise details of the
equipment, conditions and test systems to be used can be found in
the UL 94 standard.
UL 94 HB: Horizontal Burning Test
The length of the test specimen is 5" (127 mm) and width 0.5" (12.7
mm). The test sheet cannot be more than 0.5 (12.7 mm) thick. Lines
are marked on the sheet at the 1" and 4" locations. The sheet is
fixed horizontally at one end and tilted 45 degrees in the direction
of the width, as shown in the diagram. The burner used is adjusted
so that it forms a 1" long blue flame. The flame is directed at an
angle of 45 degrees to the front edge of the plastic sheet so that
about 1/4 of the test specimen’s front edge is in the flame. The
flame is applied for 30 seconds, after which it is removed. If the
test specimen burns to the 1" line before 30 seconds have passed the
flame is removed immediately. The test is carried out on three test
sheets.
The material under investigation is classified as UL 94 HB if, after
the removal of the flame either condition below is true:
-
The speed of burning does not exceed 1.5" (38.1 mm) per minute
when the test specimen thickness is .120-.500" (3.05-12.7 mm)
-
The speed of burning does not exceed 3.0" (76.2 mm) per minute
when the thickness of the specimen is less than .120" (3.05 mm)
- Burning finishes before the flame reaches the 4" line
UL 94 V-0, V-1 and V-2 Vertical Burning Test
The test specimen length is 5" (127 mm) and width 0.5" (12.7 mm).
The sheet to be tested can not be more than 0.5" (12.7mm) thick. The
sheet is fixed 1/4" from the upper end in the vertical position. A
metal mesh covered with surgical cotton is positioned 12" (305 mm)
beneath the test sheet. The flame of the burner used is adjusted so
that is forms a 3/4" blue flame. The flame is directed from below at
the lower edge of the plastic sheet at a distance of 3/8" (9.5 mm).
The flame is applied for 10 seconds, after which it is removed. The
burning time of the test specimen is recorded. Immediately the
burning stops the flame is reapplied for 10 seconds. After removal
of the flame the burning time and afterglow time is again noted. The
entire test is carried out on five different test specimens.
The material tested is UL 94 V-O classified if:
-
None of the five test specimen burn for over 10 seconds at any
time when the burner flame is removed.
-
The total burning time of the 10 ignition test does not exceed 50
seconds.
-
No test specimen burns either with a flame or afterglow to the
clamp.
-
No burning drops should fall which would cause the cotton
underneath to ignite from any test specimen.
-
The afterglow burning of no test specimen exceeds 30 seconds.
The material tested is UL 94 V-1 classified if:
-
None of the five test specimen burn for over 30 seconds at any
time when the burner flame is removed.
-
The total burning time of the 10 ignition test does not exceed 250
seconds.
-
No test specimen burns either with a flame or afterglow to the
clamp.
-
No burning drops should fall which would cause the cotton
underneath to ignite from any test specimen.
-
The afterglow burning of no test specimen exceeds 60 seconds.
The material tested is UL 94 V-2 classified if:
-
None of the five test specimen burn for over 30 seconds at any
time when the burner flame is removed.
-
The total burning time of the 10 ignition test does not exceed 250
seconds.
-
No test specimen burns either with a flame or afterglow to the
clamp.
-
Only such burning pieces may fall from the test specimen, which
burn only momentarily, and of which some ignite the cotton
underneath.
-
The afterglow burning of no test specimen exceeds 60 seconds.
UL 94 5V Vertical Burning Test
The length of the test specimen is 5" (127 mm) and the width 0.5
(12.7 mm). The test sheet shall not be more than 0.5" (12.7 mm)
thick. Flammability classification is granted for specific thickness
intervals, for which both the maximum thickness and minimum
thickness sheet must be tested. The test sheet is fixed 1/4" from
the upper end in the vertical position. The flame of the burner used
is adjusted so that it forms a 5" flame whose blue heart is 1,57"
(40mm) long. The flame is directed from below at the corner of the
plastic sheet at a distance of 1". The flame is applied for 5
seconds, after which it is removed for 5 seconds. This is repeated
five times. The entire test is carried out on five test specimen.
The material tested is VI 94-5V classified if:
-
No test specimen burns with a flame or afterglow for more than 60
seconds after the fifth ignition.
-
The total burning time of the 10 ignition test does not exceed 250
seconds.
- No material drops from the test specimen.