Classification of Flame Spread Tests. Flame spread tests can
be classified in terms of the angle between the exposed surface
of the specimen and the horizontal. This angle may vary between
0° (a horizontal material burning on its upper surface),
through 180° (a horizontal material burning on its lower surface),
240° (a material burning on its lower surface but rotated
a further 60° from the horizontal), up to 270° (for a material
burning vertically downwards).19 This surface angle is closely
related both to the extent to which the gaseous products of combustion
heat the surface before the flame front reaches it and
to the extent to which the hot gases penetrate into the tested
material. Sample sizes range widely, from the size of a candle
to quite large—24 ft × 22 in. (7.3 m × 0.56 m) in NFPA 255,
Standard Method of Test of Surface Burning Characteristics of
Building Materials/ASTM E84, Test Method for Surface Burning
Characteristics of Building Materials, otherwise known as
the Steiner tunnel test.