For the purposes of this test procedure the following definition
oxidation not accompanied by flaming which is self-propagating, i.e.,
independent of the ignition source. It may or may not be accompanied
In practice it has been found
that there is usually a clear distinction between materials which
may char under the influence of the ignition source but which do not
propagate further (non-progressive) and those where smouldering develops
in extent and spreads (progressive).