NICU Sound Control
The first step in NICU noise control is
to evaluate the sound levels that exist within the NICU
with a sound level meter so that acoustical solutions
can be determined. While the best solution is to
implement noise control in the design process of the
NICU, that is not an option for many existing NICUs. In
these cases the acoustical solutions involve adding
sound absorption materials and sound transmission
Unger Technologies has experience in NICU noise level
monitoring, sound reduction analysis, and NICU
acoustical solutions. Please call or email with your
NICU noise control questions.
NICU Standard 23: Acoustic Environment
Infant rooms (including airborne infection isolation
rooms), staff work areas, family areas, and staff lounge
and sleeping areas and the spaces opening onto them
shall be designed to produce minimal background noise
and to contain and absorb much of the transient noise
that arises within them.
• In infant rooms and adult sleep areas, the combination
of continuous background sound and operational sound
shall not exceed an hourly Leq of 45 dB and an hourly
L10 of 50 dB, both A-weighted slow response. Transient
sounds or Lmax shall not exceed 65 dB, A-weighted, slow
response in these rooms/areas.
• In staff work areas, family areas, and staff lounge
areas, the combination of continuous background sound
and operational sound shall not exceed an hourly Leq of
50 dB and an hourly L10 of 55 dB, both A-weighted slow
response. Transient sounds or Lmax shall not exceed 70
dB, A-weighted, slow response in these areas.
To achieve the required noise levels in infant rooms and
adult sleep rooms, building mechanical systems and
permanent equipment in those areas shall conform to
Noise Criteria (NC) -25 based on manufacturers’ noise
ratings with allowance for other sound sources and
adjustment for room loss if less than 10 dB. Areas in
open communication with infant rooms and adult sleep
rooms shall conform to NC-30. Building mechanical
systems and permanent equipment in other areas specified
in the Standard shall conform to a maximum of NC-35.
Building mechanical systems include heating,
ventilation, and air conditioning systems (HVAC) and
other mechanical systems (e.g., plumbing, electrical,
vacuum tube systems, and door mechanisms). Permanent
equipment includes refrigerators, freezers, ice
machines, storage/supply units, and other large
non-medical equipment that is rarely replaced.
Where personal address speakers are located in sensitive
areas, announcing systems shall have adjustable volume
controls for the speakers in each room and for each
microphone that sends signal through the system.
Speech privacy and freedom from intrusive sounds shall
be provided by acoustic seals for doors and building to
meet STC criteria (below) for demising partitions in
infant rooms, on-call and sleep rooms, family transition
rooms, and conference rooms or offices in which
sensitive staff and family information is discussed. All
other penetrations for conduits, inset boxes, pipes,
ducts, and other elements in sound demising partitions
shall be sealed airtight to prevent noise flanking
(leakage) through gaps and openings.
The acoustic environment is a function of both the
facility (e.g. building mechanical systems and permanent
equipment, the intrusion of exterior sounds, the sound
containment afforded by doors and walls, and the sound
absorption afforded by surface finishes) and operations
(e.g. the activities of people and function of medical
equipment and furnishings).
The acoustic conditions of the NICU should favor speech
intelligibility, normal or relaxed vocal effort, speech
privacy for staff and parents, and physiologic
stability, uninterrupted sleep, and freedom from
acoustic distraction for infants and adults(24). Such
favorable conditions encompass more than the absence of
noise and require specific planning for their
achievement. Speech Intelligibility ratings in infant
areas, parent areas, and staff work areas should be
"good" to "excellent" as defined by the International
Organization for Standardization ISO 9921:2003. Speech
intelligibility for non-native but fluent speakers and
listeners of a second language requires a 4 to 5 dBA
improvement in signal-to-noise ratio for similar
intelligibility with native speakers. The Leq, L10 and
Lmax limits will safeguard this intelligibility and also
protect infant sleep(25).
The permissible noise criteria of an hourly Leq of 45
dB, A-weighted, slow response in infant rooms and adult
sleep areas is more likely to be met in the fully
operational NICU if building mechanical systems and
permanent equipment in those areas and the areas in open
communication with them conform to NC-25 or less. NC-25
translates to approximately 35 dBA of facility noise. A
realistic addition of 10 dBA of operational noise above
this background will result in an Leq of about 45 dBA.
Limiting operational noise to only 10 dBA above the
background will require conscientious effort.
Acoustically absorptive surfaces reduce reverberation
and, therefore, sound levels at a distance from the
sound source. When possible, two perpendicular walls
should be covered with sound absorptive surface
materials with an NRC of at least 0.65. Where this is
not possible the upper portions of all four walls (above
areas likely to be damaged by the movement of equipment)
should be covered with such material. Glass should be
limited to the area actually required for visualization
in order to leave wall surface available for absorptive
surface treatment. While a variety of flooring will
limit impact noise somewhat, specialized carpeting
offers the most protection.
Fire alarms in the infant area should be restricted to
flashing lights without an audible signal. The audible
alarm level in other occupied areas must be adjustable.
Telephones audible from the infant area should have
adjustable announcing signals.
The type of water supply and faucets in infant areas
should be selected so as to minimize noise, and should
provide instant warm water in order to minimize time
Noise-generating activities (e.g., linen and supply
carts, conference areas, clerk’s areas, multiple-person
work stations, and travel paths not essential to infant
care), permanent equipment and office equipment should
be acoustically isolated from the infant area. Vibration
isolation pads are recommended under leveling feet of
permanent equipment and appliances in noise-sensitive
areas or areas in open or frequent communication with
Post-construction validation of specifications for the
building mechanical systems and permanent equipment
should include noise and vibration measurement,
reporting, and remediation. Measurement of NC levels
should be made at the location of the infant or adult
bed or at the anticipated level of the adult head in
other areas. Each bed space must conform to the
With space at a premium, many incompatible adjacencies
are possible in NICU designs (e.g., break area, meeting
room, or mechanical room sharing a wall with an infant
room or adult sleep room). Specialized wall and
floor/ceiling treatments will help to meet criteria in
these non-optimal conditions.
The criteria below are for sound transmission loss (TL)
or attenuation through horizontal barriers (e.g., walls,
doors, windows) and vertical barriers (e.g., between
floors). The Sound Transmission Class (STC) rating spans
speech frequencies and is relevant for separation of
spaces with conversational and other occupant-generated
noise. The Noise Reduction (NR) rating, which covers a
wider frequency span, is more relevant for mechanical
noise dominated by low frequencies. The recommended
criteria for TL below apply to barriers between adjacent
spaces and infant areas or adult rest or sleep rooms.
Pedestrian-only corridor STC 45
Equipment corridor STC 55
Infant area STC 40
Reception STC 55
Meeting room with amplified sound STC 55
Staff work area STC 55
Administrative office, conference STC 45
Non-related area STC 50
Mechanical area NR 60-65
Electrical area NR 50-55
(adapted from Evans JB, Philbin
MK. Facility and operations planning for quiet hospital
nurseries. J Perinatol 2000; 20(8):S105-12. Revised and
reprinted with permission of Jack B. Evans, PE, M.
Kathleen Philbin, RN, PhD, The Journal of Perinatology,
and Nature Publishing Company).
Sound transmission from the exterior of the building
should meet the NC criteria inside all spaces identified
in the Standard.
It is advisable to enlist the services of an acoustical
engineer from the onset of the project through
post-construction validation. This specialty service is
usually not covered by architectural fees and can assist
in program and design development, design of mechanical
systems, specification of equipment and building
construction, and test and balance validation.
Enlistment of acoustical services late in the design
process often results in fewer and more costly options
for meeting performance standards.