by Benjamin Davenny
Noise levels in hospitals have become an increasing concern as more noise sources have been added to the hospital environment. These sources range from noisy medical instruments to the layout of patient rooms as they relate to the nurses’ station. Numerous studies have evaluated the impact of noise levels on the hospital environment, but few have considered the type of noise source. The sound of a fan is different from an alarm, even if they measure at the same sound levels. Without clear objectives on the type of noises studied, there is a false impression that a quieter environment is always a better one.
Some of these noise sources are necessary in a modern working hospital. The trick is to take a different look at their sources and develop more efficient methods to reduce disturbance to patients. The often-cited World Health Organization (WHO) and Environmental Protection Agency (EPA) guidelines for hospitals require low noise levels in patient rooms, precluding conversation in corridors with patient doors open. This requirement conflicts with nurses’ needs to see patients and discuss patient care. The WHO and EPA guidelines are also based mainly on transportation noise, whose character is quite distinctive and bothersome to building occupants.
Introducing a constant noise source as background sound helps to reduce the impact of impulsive tonal noises such as speech. The typical background noise level can be considered a constant noise with full frequency content. These noise sources include air movement from the building’s HVAC system and cooling fans, as well as electronic sound masking systems. Tonal and impulsive noise sources typical of healthcare activity include conversation, alarms, paging systems, pneumatic tubes, phones, and cart movement.
Most studies indicate that impulsive noise events should be limited as much as possible and that excessive constant background noise levels will cause sleep disturbances. What may be counterintuitive is that the quieter the background noise level, the more intrusive the impulsive noise source. The difference in levels between the background noise and the impulsive noise is key. Subjectively, the higher this difference, the more our ears distinguish the impulsive noise.
Since increasing the background noise will reduce the impact of impulsive environments, increasing the background noise level in a controlled manner with sound masking will reduce the impact to occupants during sleep as well. Keep in mind that too high of a background noise level, either broadband or tonal, will still reduce sleep quality. To determine the appropriate average noise levels in a hospital, facilities can consider the following methods for evaluation:
- Measure background noise levels in a large sample set of patient rooms. Evaluate the Hospital Consumer Assessment of Healthcare Providers and Systems (HCAHPS) survey question: “How often was the area around your room quiet at night?” The hospital’s rating on this question is based on the average noise level in the patient room as well as the peak noise sources’ amplitudes and frequency.
- Once it is determined that sound masking can help the HCAHPS rating, increase background noise levels electronically. Implement a patient-controlled sound masking system in a number of single-bed patient rooms for an extended period of time.
- Once the sound masking system is added, reassess the HCAHPS quietness scores along with patient outcome metrics for the rooms in which sound masking was deployed.
In addition to increasing the background sound level with the addition of sound masking, acoustically absorptive materials should be included in the hospital design to reduce the amount of sound energy ‘bouncing’ around the occupied areas. Television speakers are now kept at the bed of the patients rather than far away on a wall, and hospitals should limit overhead pages, turn pagers to vibrate, and inform staff to be cognizant of their conversational level. Careful design of the nurses’ stations will also help mitigate conversations and noise sources to patient rooms.
Benjamin Davenny is a senior consultant in acoustics at Acentech, Inc. in Cambridge, Mass.