Designing For Hospital Acoustics

When considering hospital acoustics, a variety of noise and vibration sources can be found in the healthcare environment. Those include HVAC equipment, vertical transportation systems, pneumatic tube systems, and rooftop helipads.

If not handled or addressed properly, these standard healthcare tools and systems can become detrimental to the patient and staff experience and even to medical equipment and testing.

For example, an air handling unit located on a rooftop above an imaging suite can produce structural vibration that may affect imaging equipment and result in blurred and possibly unreadable images. When approaching a new project, planning and designing for such issues early can prevent costly change orders or potential post-construction work.

Noise control

The ambient sound level in a hospital setting fluctuates constantly, influenced by patient monitoring devices, alarms, and general activity in the corridors and at nurses’ stations. Mechanical system noise also can affect the ambient sound level if it’s not designed to be quiet and unobtrusive.

Typically, acoustical consultants assess the specifications of HVAC equipment serving patient spaces and calculate the noise level of the equipment as it would be heard by a patient. If needed, silencers or additional ductwork can be incorporated into the design of the mechanical system to reduce noise as it travels from the unit to the patient, visitor, or staff member. Ultimately, the goal is for general noise levels in patient rooms to be limited to 45 A-weighted decibels (dBA), as this level is considered subjectively comfortable to most.

Another potential source of unwanted noise and vibration is pneumatic tube (P-tube) systems, which offer a quick and safe method for transporting biological samples within healthcare facilities via cylindrical containers (carriers) that are propelled through a complex network of tubes by compressed air or vacuum.

P-tubes often are above the ceiling and in the walls of occupied spaces, hidden with other infrastructure such as electrical conduit and HVAC ductwork. As the carriers pass through the pipe network, they can produce a brief but noticeable noise, including a distinct “whooshing” or “thumping.” While typically no louder than normal speech conversation, the noise’s random and abrupt nature can serve as a distraction or annoyance to those nearby.

Additionally, the head-end “blowers” that are used to pressurize the air within the P-tube systems can produce unexpected and extremely loud levels of noise.

Such issues can be addressed by locating rooms containing these blowers near unoccupied spaces and placing blower equipment on properly specified spring mounts. This works to minimize and dampen noise and vibration by absorbing it through coiled metal springs before it can get to the floor structure.

However, in some cases, substantial wall or floor/ceiling partitions may be needed at the blower rooms, depending on the acoustical sensitivity of nearby spaces. For example, if located near an MRI suite, additional separation is required.

Vibration impacts

In fact, complex imaging equipment, such as MRI and CT machines, is also sensitive to the vibration produced by building systems, lab equipment, and other sources such as carts and beds wheeled down corridors. While locating imaging equipment away from such elements is ideal, designers may have limited layout options, making it critical to ensure building equipment vibration is properly addressed.

This process starts by understanding the specific parts of the HVAC system at hand, whether it consists of many small single fans or a few large packaged air-handling units that have multiple vibration-producing components like compressors.

External isolation of the entire unit is the most common and cost-effective approach, as it involves placing the unit on a steel frame that’s mounted to the structural floor only by spring and/or neoprene mounts to absorb a wide range of vibration frequencies.

Another option is an internal isolation approach, which typically is provided by the unit’s manufacturer. In this case, only the active, rotating components, such as the fan and compressor, are provided with spring and/or neoprene mounts. This type of installation can be effective if the unit isn’t located above sensitive spaces like patient rooms or conference rooms.

While isolation is an effective way to greatly reduce vibration transmission to sensitive equipment, it’s also critically important to ensure that a proper balance is maintained for rotating equipment. Just like an uneven load in your washing machine at home can produce uncomfortable noise and vibration, unbalanced fans and similar equipment can introduce excess noise and vibration into a building structure beyond the capabilities of isolation devices.

Broader solutions

Thorough scrutiny of the acoustical impacts of building systems equipment as well as evaluation of room functions, layouts, compositions, and adjacencies are all a piece of the larger goal of creating a successful healing environment.

One of the major concerns in a healthcare setting is patient privacy. In the acoustic design of spaces, it’s important to make sure conversations stay private. The most prevalent instance of this issue is on patient floors where practitioners have workspaces in close proximity to patient rooms.

While it’s generally understood and accepted that walls are the best way to block sound and maintain privacy, one solution to maintaining acoustical privacy is the use of recessed alcoves. These partially enclosed spaces provide a place where staff can congregate and collaborate but aren’t easily overheard because of the separation between the person speaking and a potential listener.

In addition to alcoves, the orientation of furniture and equipment in areas of acoustic privacy concerns should be examined to make sure they are arranged so that staff face one another or face the patient floor only when needed.

Most hospitals are near outside noise sources, ranging from street or highway traffic to aircraft and helicopters passing overhead. Each facility should look at its unique environment and plan for exterior noise impacts on the building.

The best way to understand these areas of concern is to conduct a site noise survey. If the outdoor environment is noisy, attenuation through the exterior window-wall assembly can include the use of thicker glass panes, increased airspaces in insulating panes, and a reduced number of operable windows that don’t seal to the surrounding frame as well as fixed windows.

Early planning

Addressing acoustical and vibration issues at the earliest point of design helps to alleviate headaches later on for both patients and health systems, allowing for improved patient care. Through a comprehensive understanding of the building program, medical equipment that will be utilized, and building systems, it’s possible to determine noise levels and vibration requirements throughout a facility, as well as key areas to focus on for sound mitigation.

A quiet and comfortable facility can reduce stress for both patients and practitioners alike, making good acoustical and equipment design a prescription for success.

Kristin Salenger is a senior associate in acoustics at Shen Milsom & Wilke (Denver). She can be reached at ksalenger@smwllc.com.

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