Depending on the specifications of the test method, specimens
molded from plastic material are oriented in the horizontal or
vertical position. They are subjected to a flame ignition source
for a specified period of time. Some test specifications require
the flame applied only once while others require multiple exposures.
Materials with an HB rating
were tested in the horizontal
position and found
to burn at a rate less than
the specified maximum.
HB classified materials are
generally not permitted
where flammability is a
major concern.
The “V” ratings indicate
the material was tested in
a vertical position. V-0,
V-1, and V-2 indicate that
the material self-extinguished within a specified time period after
the flame was removed and whether the test specimen
dripped flaming particles that ignited a cotton indicator below
the sample. VTM ratings are derived from tests designed for
very thin materials. 5V ratings are the result of the most severe
tests where the flame was applied 5 times.