Intent 1:
To supersede the requirements of Sentence 3.1.5.15.(1), which would otherwise permit combustible ducts
used in horizontal runs without any other restrictions, and to supersede
the requirements of Article 3.6.5.1., which would otherwise
require noncombustible materials, and permit combustible materials
if certain conditions are met.
This is to limit
the probability that:
- combustible material having inappropriately high flame
spread and smoke development properties will be used in concealed
spaces used as plenums, which could lead to the development of an
inappropriate amount of smoke and the spread of fire across the exposed
surfaces of the material, which could lead to the spread of fire and
smoke from one fire compartment to another fire compartment by means
of the plenum, which could lead to harm to persons in the other fire
compartment, and
- supports for the ceiling membrane will prematurely fail
when exposed to fire conditions, which could lead to the spread of
fire into the floor or roof assembly, and to other parts of the building,
which could lead to harm to persons in the other parts of the building.
Intent 2:
To supersede the requirements of Sentence 9.33.6.2.(1),
which would otherwise require ducts, duct connectors, associated fittings
and plenums used in air duct systems to be constructed of noncombustible
material.