Standard 29: Acoustic Environment
Infant rooms (including airborne infection isolation rooms) and adult sleep rooms, as well as the hallways or other areas in open communication with them, shall be designed to mitigate a combination of continuous background sound and operational sound of at least L50 of 45 dB A-weighted, slow response and an L10 of 65 dB A-weighted, slow response, as measured three feet from any infant bed or other relevant listener position.
Staff work, lounge, and meeting rooms and family lounge and gathering areas, as well as the hallways or other areas in open communication with them shall be designed to mitigate the combination of continuous background sound and operational sound of at least an L50 of 50 dB A-weighted, slow response, and an L10 of 70 dB A-weighted, slow response, as measured 3 feet from any relevant listener position.
To achieve the required sound levels in infant and adult sleep rooms, building mechanical systems and permanent equipment in the room shall conform to Noise Criteria (NC) -25 based on manufacturer's noise ratings with allowance for other sound sources and adjustment for room loss of less than 10dB18. Areas in open communication with infant rooms and adult sleep rooms shall conform to NC-30. Building mechanical systems and permanent equipment in other spaces specified in the Standard shall conform to NC-35. Building mechanical systems include heating, ventilation, and air conditioning systems as well as plumbing, electrical and vacuum tube systems and door mechanisms. The room or area shall meet design criteria when permanent equipment usually in the area is in operation. Permanent equipment includes refrigerators, freezers, ice machines, storage/supply units, and other large non-medical equipment that is rarely replaced.
If a refrigerator or freezer is located in the infant room or a hallway in open communication with it, the condenser and fan noise shall not exceed 40 dBA.
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.
Traffic unrelated to a particular patient’s care, adult sleep rooms, and rooms for activities that require close attention to detail shall be routed outside these areas.
Speech privacy and freedom from intrusive sounds shall be provided by acoustic seals for doors, room-room and hallway-room windows and by selecting materials and room components that meet design sound transmission class (STC) criteria and noise reduction criteria (NRC) given below for demising partitions in infant rooms, adult 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 demising partitions shall be sealed airtight to prevent noise flanking (leakage) through gaps and openings.
Fire alarms and occupant notification appliances shall be in accordance with NFPA 101 Life Safety Code and the building code as required. At a minimum, fire alarm occupant notification systems in the NICU shall be designed using the private operating mode as permitted and described in NFPA 72, National Fire Alarm and Signaling Code. Only the attendants and other personnel required to evacuate occupants from the NICU shall be required to be notified. Only visible alarm-indicating appliances shall be permitted to be used in all infant critical care areas.
Interpretation: These criteria are more likely to be achieved with active participation of an acoustical engineer throughout the programming, design, construction, and validation phases of the project.
The acoustic environment is a function of both the facility (e.g., building mechanical systems and permanent equipment, intrusion of exterior sounds, sound containment afforded by doors, windows, and walls, and sound absorbing surface finishes) and its operations (e.g., human activity and the function of medical equipment and furnishings). Control of intrusive noise and a lower noise baseline (a.k.a. noise floor) can support autonomic, motor, and behavioral state stability for infants19. These measures can also help protect staff from the deleterious effects of workplace noise and support attention and precision in communication and task performance by lessening the noise-related risks of masking, distraction, and error20.
The acoustic conditions of the NICU should favor speech intelligibility, normal or relaxed vocal effort, speech privacy for staff and parents, and freedom from acoustic distraction for infants and adults. 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, staff work areas, and areas of sensitive staff and family communication 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 4-5 dBA improvement in signal-to-noise ratio (the difference between speech and background levels) for similar intelligibility with native speakers.
Air handling and mechanical equipment noise typically determines background noise levels. The use of flexible ducts listed and labeled to the UL 181 Standard for Factory-Made Air Ducts and Air Connectors and Class 0 or Class 1 can help lower the noise at the supply air outlets. Duct lining should conform to ASHRAE 170 Ventilation of Health Care Facilities.
Acoustically absorptive surface materials on multiple surfaces can help provide effective noise control. The ceiling has the largest surface area available for sound absorbing materials. Flooring materials absorb only a small amount of high frequency sound but can limit sound production from striking—e.g., footfall, dragging equipment.
Vibration isolation pads or specialty spring assemblies are recommended under leveling feet of permanent equipment and appliances in noise-sensitive areas or areas in open or frequent communication with them.
Telephones audible from the infant area should have adjustable announcing signals.
Water supply materials and faucets in infant areas and adult sleep rooms be selected to minimize on/off noise, and should provide instant warm water in order to minimize time “on”.
Many incompatible adjacencies are possible in the NICU—for example, break area, meeting room, or mechanical room sharing a wall with an infant room or adult sleep room. The transmission loss or attenuation criteria below apply to horizontal barriers (for example, walls, doors, windows) and vertical barriers (for example, between floors). The sound transmission coefficient (STC) rating spans speech frequencies and is relevant for separation of spaces with conversational and other occupant-generated noise.
Recommended STC and NRC ratings
Infant and adult sleep rooms STC-50
Procedure rooms STC-50
Consultation rooms STC-55
Conference rooms STC-50
Pedestrian-only corridor STC-45
Equipment corridor STC-55
Meeting room with amplified sound STC-60
Staff work area STC-50
Administrative office STC-45
Mechanical area NRC 60-65
Electrical area NRC 50-55
Post-occupancy validation 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 Standard.