Hi Richard:
> When testing plastics, the flame is applied for a specified period of time,
> removed for specified period of time and the process is repeated for a
> specified number of cycles. Is the procedure attempting to correlate with
> observed fire patterns in equipment, or is it designed simply to provide
> repeatable results?
The UL 94 tests are to measure the burning
characteristics of a plastic material AFTER
it has been ignited. For flame-retardant
plastics, four parameters are measured:
1. Duration of flaming.
2. Duration of flaming and glowing.
3. Dripping of flaming drops.
4. Burning to the clamp.
Depending on the data, the plastic material will
be rated V-0, V-1, V-2, or will fail the vertical
burning test.
These flame-retardant parameters are highly
dependent on the temperature, thermal energy,
and duration of the energy transferred to the
material under test. Consequently, the flame
and duration parameters are specified by the
standard:
1. Type of gas.
2. Type of burner.
3. Pre-mixed flame parameters.
4. Duration of flame application to sample.
These flame and duration parameters apply a
standard temperature and a standard amount of
thermal energy to the sample.
The procedure does not correlate to fire patterns
in equipment. It is a measure of the degree of
flame-retardancy (i.e., V-0, V-1, or V-2) to a
standardized flame source.
Yes, the procedure must be repeatable, but it is
not designed simply to provide repeatability.
Rather, it is designed to apply a standard amount
of thermal energy (determined by the preceding 4
flame parameters) to the sample.
The flame-retardancy determined by the UL 94 tests
applies only to flames not exceeding the test flame.
If the applied thermal energy is significantly
higher, i.e., a larger flame or a longer duration,
the sample will ignite and burn continuously until
the sample is fully consumed.
Best regards,
Rich
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