October 2011

Intelligent Hearing Protection: A Primer

Bottom line, it is best to find a solution that strikes the appropriate balance between hearing protection and situational awareness.

In many industrial environments, Hearing Conservation Program managers seek to strike a balance between worker hearing protection and their ability to communicate, especially in extreme noise environments and remote work sites.

The hearing capabilities of a worker are very important for communication, gaining situational awareness, and reducing the risk of other hazards or injury. However, understanding communications in extreme noise and at work sites is always challenging while wearing hearing protection. Too much protection, and a worker cannot hear and is vulnerable to other safety hazards. Too little protection, and the worker is inadequately protected and at a higher risk for noise-induced hearing loss.

For those who seek to bridge the gap between traditional hearing protection and communication, the technology now exists to intelligently protect and connect workers in extreme environments. In this article, we will examine the growing segment of intelligent hearing protection technologies that offer a variety of passive and active technologies, and better understand their applications in industrial workplaces.

Safety in Situational Awareness
Situational awareness is the ability to identify, process, and comprehend the critical elements of information about what is happening in your environment. More simply, it's understanding what is going on around you, assessing the situation, and making appropriate decisions. The term is used extensively in military and aviation environments but is certainly applicable in industrial settings.

On a job site, it is important and necessary for workers to remain aware of their surroundings. Imagine the danger created by not hearing an alarm or the sound of nearby machinery that puts both a worker and his or her team at risk of accident. For example, a worker who may be overprotected or distracted by other sounds may not hear that forklift behind him.

In addition to hazardous noise, general environmental/background sounds at safe levels could distract a worker who is focused on a task. This distraction may either cause a disruption in that worker's task or mask other important verbal communication or alarms.

There are a few technologies that enable situational awareness in intelligent hearing protectors.

Sound Amplification: Simply put, sound amplification raises ambient sound levels above normal thresholds. Some systems amplify ambient sound up to five times normal -- but to safe levels. Some systems allow the user to adjust amplification levels as needed.

  • Pro -- Can enhance listening and basic situational awareness, especially for workers with an existing hearing impairment.
  • Con -- Systems that do not allow the user to adjust amplification levels may not be appropriate for some job tasks.

Active Noise Reduction (ANR): Through both analog and digital processing technologies, exterior microphones monitor ambient sound, and ANR reduces the levels of noise across the spectrum of frequencies to acceptable levels, often to 85 dB, in real time. This allows the user to hear all of the sounds but manages listening to safe levels at all frequencies. ANR can also remove certain frequencies.

  • Pro -- User still can hear all ambient sounds at safer levels, enhancing situational awareness.
  • Con -- Analog ANR processing may delay the transmission of sound to the user's ear.

Active Noise Cancellation (ANC): Commonly used in personal and aviation headsets, ANC technologies eliminate sound in specific frequencies. Through digital processing, noise in specific frequency is sampled and its sine wave is inverted, providing an "anti-noise." This cancels out that specific sound frequency completely. Most ANC headsets are set to mitigate low-frequency sounds often associated with engines and other commuter noise.

  • Pro -- Ideal for eliminating continuous levels of noise.
  • Con -- Depending on setting, ANC can eliminate some ambient sounds that the user should be able to hear.

Personal Hearing Protection
In addition to basic passive attenuation, some intelligent hearing protectors offer special technologies to ensure more effective protection when turned both on and off.

Fit Check: While most intelligent or active hearing protectors deliver a moderate level of passive attenuation and adapt to changing noise environments, there are some protectors that feature in-ear voice pick-up that can identify a minimum amount of attenuation in each ear upon start-up. This is done not only to verify adequate attenuation, but also to ensure clear voice pick-up from the ear canal.

  • Pro -- Ensures proper fit upon start-up.
  • Con -- Requires user to properly fit eartip within ear canal. If not, user will be required to refit until he or she achieves adequate fit and protection.

Two-Way Communication
Most important to any job is the ability to clearly communicate with co-workers and hear important signals, alarms, and other communications. Work sites with mobile workers, such as construction sites, airports, and petrochemical processing plants, often require supervisors and other employees to use two-way communication radios as they travel through different areas.

Integrated Communication Headsets: There are a wide variety of communication radios and headsets with either integrated communication radios that use specific radio frequencies or that connect to two-way com radios.

  • Pro -- Simple to use.
  • Con -- May not be sophisticated enough to manage noise in extreme noise environments.

Bluetooth Headsets: Bluetooth is a wireless communication technology that transmits voice or data between electronic devices, essentially allowing two devices to talk to each other. In-ear Bluetooth headsets are commonly used with mobile phones and with personal computers.

  • Pro -- Enable immediate transmission of data and are comfortable to wear.
  • Con -- Devices must be synced together in order to transmit data.

Boom Microphones: External microphone captures voice for transmission through intelligent hearing protector and communication radio. These are often attached to ear muff-style communication headsets.

  • Pro -- Easy to use and maintain.
  • Con -- May pick up external noise and compromise speech intelligibility.

In-Ear Voice Pick-Up: Microphones within well-fit eartips capture and transmit voice communication. Some systems capture voice through bone conduction, which require the eartip to have contact on the ear canal itself. Others capture voice through air conduction, which picks up sound through the vibration in the air within the ear canal (between the end of the eartip and ear drum). Since it is quieter in the well-protected ear canal (as confirmed through ear plug fit testing) than in the environment, the signal to noise ratio is stronger with in-ear voice pick-up vs. boom microphones.

  • Pro -- Isolated sound pick-up enables more clear voice communication, eliminating environmental or background sounds.
  • Con -- Requires deeply inserted eartips, which may take time to get used to fit and wear over a full work day.

Conclusion
The spectrum of intelligent hearing protection devices continues to grow, as does their application in industry. Some devices have very advanced technologies intended for specific noise hazards or job applications and may not be suitable for situations where basic hearing protection or communication is required. Bottom line, it is best to find a solution that strikes the appropriate balance between hearing protection and situational awareness.

This article originally appeared in the October 2011 issue of Occupational Health & Safety.

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