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Sound Remedies For Medical Facilities
How close to the emergency generators can the new microsurgery suite be?
In today’s medical facilities, the only constant is change. It is important to be on the lookout for conflicting needs when siting a new MRI suite or cooling tower. Avoiding the transfer of airborne sound or structure-borne vibration between various adjacencies requires thoughtful planning.
Areas where images are magnified for diagnosis or treatment are potentially susceptible to vibration. The most common areas of concern include microsurgery and lab microscopes. Quantitative criteria for acceptable levels of floor vibration are often provided by system manufacturers or acoustical consultants. This allows for an engineering assessment of what measures are needed to meet the criteria.
On renovation projects, field measurements can be made of existing levels of floor vibration and, if needed, sources of building vibration can be identified through frequency analysis or ON/OFF tests. A major university hospital recently commissioned such tests during planning and expansion to accommodate lab microscopes with 400X magnification. To prevent image blurring, steps were taken to stiffen the building structure and isolate vibration of rotating equipment in a new mechanical penthouse. Ophthalmologic surgery suites and even standard operating rooms all require vibration-free environments to varying degrees.
The proliferation of MRI machines has also caused acoustical problems. The concern here is more “outbound” — that is, sound and vibration generated by the MRI process intruding into nearby waiting and treatment rooms, adjacent horizontally or vertically. With the use of progressively larger magnets, airborne noise and structure-borne sound levels are increasing, requiring better planning and more aggressive measures for control.
Noise and vibration problems can be anticipated. If mitigation measures are planned during the design phase, costly and extraordinary construction techniques can be avoided. Good planning can make it possible to avoid the kinds of steps that are necessary to make building occupants satisfied if, for example, the chiller room is located next to a meeting room. With available expertise, the costs and benefits of various options can be explored while the project is still on paper.
Community Noise Concerns
Many jurisdictions now have regulations covering the sound that may be emitted from building service equipment. The most common noise sources for medical facilities are cooling towers, air-cooled HVAC equipment (usually rooftop units) and emergency generators. While generators may be exempt from community noise regulations during emergencies, there is customarily no exemption for the noise produced during weekly generator tests. So it is wise to test during the day and to meet the daytime noise limit requirements. Nighttime regulatory limits are usually lower. For example, in New Jersey, levels emitted to residential properties are limited to 65 dB(A) during the day and 50 dB(A) at night.
Where lowest first cost is an overriding concern, the trend is to use air-cooled, packaged or custom rooftop air handlers to serve building additions or new facilities. The sound radiated to the community is highest during the summer when cooling demand is highest, and noise is produced by the compressors and condenser fans. Unfortunately, it is difficult to mitigate the noise from such equipment, both during the design stage and after the fact, except by introducing shielding with acoustical barriers. The difficulty of mitigation is all the more reason to ensure good planning occurs.
At one hospital, a new rooftop air-cooled chiller was contributing to noise levels far above allowable nighttime limits. Because the roof could not support the wind load and weight of the needed noise control barrier, the only solution was to use this rooftop unit in the daytime hours and to provide supplemental cooling with additional equipment, selected and located to meet nighttime cooling needs while meeting sound-emission requirements.
Although water-cooled systems relying on cooling towers require greater up-front investment, there are many more options available during equipment selection for controlling sound emissions to the extent required. Options include:
- Equipment style: Centrifugal fan cooling towers and propeller fan towers have different acoustical characteristics and directivity — the way sound emissions differ from position to position around a noise source.
- Fan speed: Because towers are custom-designed for thermal demand, oversizing the tower and slowing the fans can often meet acoustical and thermal needs simultaneously.
- Manufacturer-supplied sound attenuation: Manufacturers of cooling towers can supply sound attenuation sections for centrifugal fan towers, and special fan designs are now available to reduce sound from propeller fan styles.
The opportunity to control sound emissions during the design phase and during equipment selection is one which should not be lost.
Any facility executive who has been present in the engine room while a 2,000 kilowatt diesel generator-set has been fired up will appreciate the task of containing this sound. And that task is complicated by the need to shed considerable heat from the gen-set to the outdoors. The most reliable way to control noise from gen-set installations is to use architectural constructions designed to meet aesthetic and acoustical needs.
Impact of HIPPA
It’s likely that many facility executives can recall overhearing discussions at the reception desk in a medical facility waiting room or maybe even from the room next door when an examination is being conducted. The Healthcare Insurance Portability and Accountability Act, or HIPPA, has provisions that call for security of patient information, both written and verbal. Acoustics comes into play in providing privacy not only for communication between patients and health care providers during consultations, but also during conversations with administrators during patient registration.
Facility executives may be surprised to learn that speech privacy can be measured in existing environments and can be predicted in advance for proposed environments while projects are still on paper. The tools available for increasing the degree of speech privacy available fall into three categories:
- Tool 1: Use sound-absorptive materials on room surfaces to reduce the build-up of speech sound and to avoid reflecting sound to areas where it is not intended to be heard. The ceiling is the first candidate because it is the surface least obstructed and least vulnerable to abrasion. The vulnerability issue is important because common acoustical materials are less durable than normal wall and floor finishes.
- Tool 2: Confine conversations within intended areas by using partial- or full-height (extending above the ceiling) partitions and doors that use well-sealing gaskets.
- Tool 3: Mask speech sound where it is not intended to be audible using electronically-generated masking sound. If the background sound in an area is too low in level, conversations in adjacent areas are more easily overheard.
Over the past 40 years, standards have been developed concerning the rating of speech privacy and the testing of various products used for constructing open and enclosed office environments. The standards development work is overseen by ASTM Committee E-33 on Environmental Acoustics. Acousticians are familiar with the available tools and standards and how to best apply them.
LEED and Acoustics
Some building owners are interested in obtaining certification under the Leadership in Energy and Environmental Design (LEED) green building rating system developed by the U. S. Green Building Council. The design of LEED-certified buildings often influences the type of HVAC systems and equipment used. For example, ground-source heat-pump systems may be employed to reduce reliance on traditional fossil-fuel powered HVAC equipment. The result is the use of different types of equipment, such as very powerful pumping systems for the buried piping loop. The placement and vibration isolation of such equipment requires careful consideration, especially near occupied areas.
The facility executive who appreciates potential sound and vibration issues that may arise in the planning of medical facilities is in the best position to ensure that such issues are satisfactorily addressed during the planning stages, avoiding costly after-the-fact remediation.