Code (reference 13p). Secondary structural members (supporting only one
floor) within the distribution zone are not required to be fireproofed.
Lateral and seismic bracing within the distribution zone need not be
fireproofed provided these members do not carry vertical loads (live or dead).
NOTE: A full-scale fire test of the IBS structural assembly was conducted by
NIST (NIST publication NBSIR 85-3158) for the VA in 1985 and again for a
specific DoD project in 1995. Results of the 1985 NIST test determined that
ALL structural steel within the interstitial space (distribution zone) is
adequately protected for 2-hours by the walk-on platform/interstitial space
arrangement without any direct fireproofing to the structural steel within the
Openings. To prevent fire and smoke migration into the
distribution zone, openings through the walk-on platform shall be protected as
a) All penetrations (ducts, pipe, cables, conduit, etc.) shall be
firestopped at the walk-on platform with approved material in accordance with
NBSIR 85-3158 (reference 13m), or with an approved through-penetration
b) Shafts shall be enclosed in properly rated construction and tightly
sealed for the full perimeter of the penetration at the walk-on platform in
accordance with NBSIR 85-3158 (reference 13m), or with an approved through-
penetration protection system.
Ducts and Dampers.
a) Fire dampers are not required where ducts penetrate the 1 hour fire
rated partition between the utility pod and the distribution zone.
b) Fire dampers are required where ducts penetrate 2 hour fire resistive
partitions between the utility pod and the occupied and connection zones.
c) Fire dampers are not required in ducts for openings in the walk-on
platform less than or equal to 150,000 sq. mm (225 sq. in). This includes
supply ducts from the distribution zone to the occupied zone, exhaust ducts,
and return ducts from the occupied zone to the distribution zone.
d) The total cumulative open space created by unprotected duct
penetrations in the walk-on platform above any single smoke compartment or
room in the occupied zone shall not exceed 0.98 percent of the area of the
respective smoke compartment or room.
NOTE: This limit is provided as a design control feature to prevent over-
penetrating a given area of walk-on platform with undampered duct
penetrations. The value of 0.98 percent is based upon the percentage used in
the 1985 NIST test and has been coordinated with the JCAHO Standards group.
e) Flexible duct work (Class 1-UL Standard 181) is permitted in the
distribution zone for connections less than 2.4 m (8 ft.) long and shall be no
larger than 300 mm (12 in.) in diameter.
f) Smoke dampers are required in ducts in the distribution zone where a
duct serves more than one smoke compartment. Where required, the smoke damper
shall be located in the duct at the approximate location where the smoke
barrier is located below in the occupied zone.