MIL-HDBK-1191
plenum, and then into neighboring spaces through the ceiling again. These
ratings are often further degraded by return air slots, registers, and
grilles, and recessed light fixtures with openings to a return air plenum.
The medical facility designer shall evaluate the following elements with
respect to providing required sound isolation:
a.
Ceiling/wall joint: A continuous, suspended ceiling system should
not extend over adjacent acoustically sensitive spaces that
require confidential speech privacy, such as examination rooms.
The ceiling system should be cut or interrupted at the line of the
intervening partition.
b,
Plenum barrier: To minimize sound transmission between
acoustically sensitive spaces, a sound isolation barrier should be
provided in the plenum space between the suspended ceiling and the
underside of the structure above, following the line of the
partition below and extending along perpendicular walls as well.
The plenum barrier must consist of a dense, impervious material
such as gypsum board, but need comprise only one layer of gypsum
board. Superior to this construction is a full-height slab-to-slab
partition system wherever possible. See construction type #1 in
Figure 23.3.
c.
Insulation on top of the partition: When a construction, slab to
slab barrier is not provided, the medical facility designer shall
consider insulation on top of the partition. In order to improve
the sound isolation through the acoustic tile ceiling (that is, to
achieve a higher CAC rating), 75mm (3-inch) thick, foil-backed
noncombustible blanket of insulation material such a glass fiber
or mineral wool may be installed, foil side down, on top of the
suspended ceiling system. This blanket should extend 1200mm (4
feet) from each side of the partition below. This acoustical
insulation works best when the plenum depth is less than 400mm (16
inches) high. Care must be taken so that moisture is not trapped
in the ceiling space and heat dissipation of light fixtures in not
impaired. See construction type #2 in Figure 23.3. Disadvantages
to this system are that when maintenance operations occur at the
ceiling in the future, the insulation is often removed or damaged
and not put back in place or repaired properly.
d.
Special acoustical tile ceilings: Where plenum barriers and
insulation are impractical, the medical facility designer shall
consider utilizing special acoustical tile with a higher CAC than
standard (35-39). See construction type #3 in Figure 23.43.
e.
Solid ceilings: When required to provide the required degree of
sound isolation between spaces, and when permitted by Appendix A,
a suspended sound barrier ceiling, consisting of a dense,
impervious, noncombustible material such as gypsum board or
plaster, should be considered.
23.2.2.3
Floors. The type of floor construction used between spaces shall
be selected and detailed to achieve the required degree of airborne and impact
sound isolation. Airborne and impact isolation provided by a floor system are
different characteristics of construction, and each shall be considered
separately.
a.
Flanking transmission. Typical flanking paths of airborne noise,
which shall be evaluated in medical facility design include
mechanical and elevator shafts, piping, conveyor, and pneumatic
tube penetrations.
23-3
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