While office noise rarely threatens workers’ health, it can have a damaging effect on your company’s productivity. The following expert advice can help you successfully handle noise problems in office buildings.
“This office is so noisy that I can’t even think!” A complaint heard, in one form or another, every day in offices around the world. While these complaints are often dismissed as frivolous or a nuisance, you want to satisfy your customers even though office noise is rarely loud enough to damage hearing. Is the noise harmful? Is there a quick fix?
OSHA regulates noise exposures when the sound levels are above 85 decibels (dBA). This is about the level of noise when you have to raise your voice to hold a conversation with someone standing next to you. If people are exposed to noise this loud for an 8-hour day, OSHA requires that a formal hearing conservation program be developed. This program includes noise measurements, engineering controls to reduce noise, hearing examinations for exposed employees, and personal protective equipment.
Although there are no regulations concerning office noise below the 85 dBA level, a series of sound pressure level curves has been recommended to describe acceptable noise levels in various indoor settings. The American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) suggests that an open-plan office have a noise criterion range of 40-50 that corresponds to 49-58 dBA. Noises above this level can interfere with voice communications and, for some people, even thought processes. If productivity is adversely affected, someone will want to know why. Safety officials and building managers need a plan to deal with obtrusive, non-regulated office noise.
The Typical Office
Typical offices are large, open areas with many employees working at individual work stations. The open plan office should be designed to include spaces for noisy devices and conferences. Consideration should be given to barriers of adequate height and sufficient absorption to prevent direct sound paths. All interior surfaces, including walls, ceilings, light fixtures and office furnishings, need treatment to prevent reflections. For private offices or cubicles, on the other hand, high levels of ambient noise are controlled by the transmission loss through partitions.
Common noise sources in the office include copy machines and printers, computers, fax machines, air conditioners, dehumidifiers, humidifiers, piped-in music or personal radios and fans. Most important is people-generated noise such as talking, laughing and walking. Noises from outside the office can also affect office workers. Trucks, airplanes or highway noise may present a problem in office buildings. Noise may originate from one local source or may be diffuse and spread throughout the office.
Characteristics of Noise
Several factors affect how obtrusive or annoying a sound can be. Frequency is a major annoyance factor for typical office noises. While an adult with good hearing can hear frequencies between 20 and 20,000 hertz (Hz), frequencies between 2000 Hz and 8000 Hz are perceived as the most annoying. For noises of the same sound level, those below 500 Hz or above 10,000 Hz are considered less annoying. Frequency is also important when determining what type of noise control is needed, if any.
The loudness or sound level is also a factor, but there is no critical sound level below which nobody will be annoyed and above which everybody will be annoyed. In general, a tone whose sounds level fluctuates is more annoying than one whose level is constant.
Noise duration also affects how obtrusive a noise is perceived; intuitively, long-duration noises are more obtrusive than short-duration noises. However, continuous noise can be ignored. Many complaints of noise involve intermittent, short-duration noises.
Two other factors can also explain why some noises are more bothersome than others: predictability of the noise, and value of the noise. If employees know that at 10 a.m. and 4 p.m. a tractor trailer leaves the loading dock, they may not perceive the noise as being as obtrusive as the dehumidifier that kicks on and off every so often. The value of the noise is also important in determining how obtrusive a noise is perceived. People using the copier feel that the noise they are generating is necessary, while the other employees may be annoyed by the noise coming from that machine again.
Noise Control Plan
Identifying an obtrusive noise is the first step in dealing with noise complaints. Respond to the complaint by visiting the area where the complaint originated. Meet with people and ask for their opinions. Show genuine concern about the “problem” and make sure they know you are interested and willing to help. This appearance is often overlooked but is critical. When people perceive that management is concerned enough about them, the Hawthorne effect creates an attitude of lessened noise interference without any change in work environment.
Employees may sense the noise in two ways. First, employees hear the noise as it travels through the air from the noise generating source. Second, frequently, the employees may “feel” the noise as the noise source vibrates and sends vibrations through the building structure. Sound measurements may be useful to show that harmful sound levels do not exist. Octave band measurements are essential to develop an effective control strategy in complex situations. The obtrusive noise is usually obvious and a quick investigation will often identify the offending noise source.
The next step is to determine why the noise is a problem. Try to identify which specific characteristic of the noise is offensive. This is necessary to determine which noise control measures are warranted. Is the noise too loud, too unpredictable, too high-pitched?
With the objections documented, the safety director or building manager can then develop a noise control strategy. Noise control is an intricate science based on many factors. While we can’t review all those factors here, we can take a look at a simplified strategy based on many of the factors of noise control engineering.
Consider eliminating the noise first. Maintenance for building equipment can often reduce noise from neglected equipment. Typically, this means attention to the HVAC system (low duct velocity, attention to disturbances in the ductwork, isolation of fans and motors from the vibrating surfaces, etc.). Enclosing or isolating noisy office equipment is also helpful. The copier in the center of the office floor may be very disruptive to the people nearby. By moving it to another location, such as a copier room or even the side of the room, you can minimize the number of employees affected by the noise.
Isolating a noise source is done effectively by moving it far away from people. For point sources, sound levels drop off with distance in accordance with the “inverse square law,” which yields a 6 dB sound level reduction for each doubling of the distance from the source. The noise reduction achieved by enclosing a copy machine in a separate room can reduce the noise level by more than 15 dBA. In open plan offices, there are reflections and multiple noise sources to consider, so noises are often isolated by enclosing them. When computer printers became prevalent, a market developed for computer printer noise enclosures.
When noise sources are diffuse, you may consider isolating the people. Room dividers have limited use because they do not extend from the floor to the ceiling, which is necessary to block noise waves from traveling from one side of the room to the other. Dividers should be as large as practical and not less than 5 feet high to optimize sound attenuation. Noise will bend around partitions and even under them if they are not placed as close to the floor as possible.
A separate remote conference room where employees can retire for speech privacy is needed for confidential conversations. Noise will penetrate drop ceilings, traveling long distances above ceilings before reentering the work space through transfer grills or other openings. For this reason, conference rooms should have slab-to-slab walls and appropriate sound absorptive interiors. If speaker phone conferences are common, many conference rooms should be available. Raised voices are common for speaker phone conversations. Open plan office design assumes workers in open plan spaces would learn to speak with lowered speech levels.
In an office, noise generated from a source travels through the air and through the building structure. As the noise travels through the air, it reflects off hard objects and is absorbed by soft objects. Sound-absorbing material should be used on all surfaces near the sound generator that can reflect sound.
Absorbing the noise with “sounds soak” is most effective for higher frequency noise (peaking at or above 1000 Hz). With each frequency of noise having an identifiable wavelength, different sound-absorbing materials will absorb some wavelengths better than others. Sound absorption coefficients have been determined for many building materials.
Office furnishings will affect the sound propagation in an office. Softer materials will absorb more sound. Window treatments and wall coverings can help reduce noise in an office if they are properly selected. Carpet applied directly to walls is not a suitable solution. Generally, about 1 inch of fiberglass under a decorative fabric will provide a suitable sound-absorbing treatment.
Sometimes, maintenance can adversely affect the noise-control properties of some building materials. Repainting an acoustical ceiling can reduce the sound-absorbing properties of some ceilings. Perforated or slotted acoustical ceilings can be repainted often without reducing their sound absorption quality unless a considerable number of perforations are covered over. Fissured acoustical ceilings need more care when repainting to avoid covering over too many large fissures. Acoustical ceilings without openings depend entirely on the porosity of the material for sounds absorption. Repainting this type of ceiling will reduce its ability to absorb noise.
Active Noise Control Systems
Active noise control systems are used for two purposes: to silence an obtrusive noise or to generate a desirable noise. The systems are termed “active” because sound is added to achieve the result. To silence a noise, the system produces a sound that is out-of-phase and cancels the noise. Systems also produce background noise, sometimes called “white noise,” to mask other noises or for privacy.
Active HVAC silencers have been designed into new construction plans of major office buildings. Silencers are comprised of four major components: downstream microphone, loudspeaker, upstream microphone and controller. The downstream microphone picks up the characteristics of the fan noise and transmits that information to the controller. The downstream microphone picks up the characteristics of the fan noise and transmits that information to the controller. The controller determines an opposite phase, equal amplitude and frequency sound for the loudspeaker to play. The upstream microphone completes the feedback loop, picking up any errors for the controller to correct. Active noise control systems can also detect noise that is characteristic of worn fan belts or bearings, a sort of backup to preventive maintenance. Measured noise levels in completed office buildings have met acoustical specifications.
Active HVAC silencers are also available and can be designed into new office construction. Silencers pick up the characteristics of fan noise and transmits that information to a controller, which determines countermeasures to noise amplitude and frequency.
Background noise, a type of active control, is useful as a masking sound in an open office environment. Open plan offices must consider two, often conflicting goals: speech privacy and speech intelligibility. Background noise for speech privacy makes it difficult to hear conversations and noises from other areas. However, the background noise should not interface with the ability to hold a face-to-face or telephone conversation, which is speech intelligibility.
- Music is acceptable, but rarely used because musical tastes are so diverse that an acceptable musical selection, even “elevator music,” is often impossible to achieve.
- Ventilation systems can provide a masking effect, but if they are not constantly on, their unpredictability can be more disruptive than helpful.
- Electronic masking systems are available and have been proven effective in many instances. These systems generate white noise, a tone with equal energy across all band widths from say, 20 Hz to 20,000 Hz. The white noise is then tailored to the environment to achieve noise reductions of 5 dB per band width.
Determining the level of the background noise is often a compromise. The level of noise needed for privacy may be louder than the level needed to hold a normal conversation.
So, what should you do when the noise complaints come in? First, determine if the noise is above 85 dBA and possibly hazardous, or below 85 dBA and just obtrusive, a problem for local management to correct. If it is a hazardous noise situation, OSHA requirements are explicit. If it is obtrusive and affecting the proficiency of employees, corrective action is usually deemed necessary even though no safety and health regulations are broken.
You have a noise control strategy to follow: investigate, identify, characterize and abate. Abetment can involve several options: eliminating noise, absorbing noise, isolating noise and even adding complementary sounds to reduce the overall noise.
By acting on noise complaints and following such a strategy, you have taken the initiative and shown concerns for employees’ well being. You have also taken steps to ensure productivity is not reduced by factors under your control. The corrective action may require some remediation and that is when the management decisions enter the picture. But money wisely spent to improve the work environment is rarely wasted.
To discuss these and other noise management issues, please contact:
John A. Molino, Handbook of Noise Control. 2nd edition, ed. By Cyril M. Harris (New York: McGraw-Hill, 1979), pp. 16-3, 16-5.
Howard K. Pelton, Steven Wise, and William S. Sims, Active HVAC Noise Control Systems Provide Acoustical Comfort. Sound & Vibration, XXVIII (July 1994), 14.
Abstract from “Curing the Noisy Office”:
Hemp, William E., Glowatz, Michael, Jr. Occupational Hazards. 57. no. 8 (1995), 36-39.
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