What is noise?
When air molecules surrounding our ears vibrate, parts inside the ear can sense the changes in pressure. These parts amplify the vibrations and ultimately cause tiny hairs in the inner ear to bend. Bending those hairs creates nerve impulses that the brain perceives as sound. The hairs can easily deform and return to their original position. However, if the vibrations are too strong, or they last for an extended period, the hairs can be permanently damaged causing hearing loss. In general, noise is an unwanted sound. When it comes to the workplace, noise is sound that is intense enough to cause hearing damage.
How do I know if noise levels in my workplace are safe?
The hazard noise poses is dose-related. The higher the dose of noise a worker receives the greater the risk to the workers hearing.
A workers noise dose is dependent on the following 3 factors:
- Intensity/Loudness: This factor is measured by a noise level meter and the units are described in decibels (dB)
- Frequency: Frequencies between 3000-4000 Hz are most likely to damage human hearing. Sound level meters account for this by using an “A” weighted filter
- Duration: The length of time you have been exposed to noise
There are strict limits for the intensity of sound permissible in the workplace.
- 85 dBA daily noise exposure level (A-weighted filter, averaged over an 8 hour period)
- 140 dBC peak sound level (maximum intensity on a C-weighted filter)
The Hierarchy of Control
Occupational safety and health professionals use the hierarchy of control (shown in the figure below) to determine how to implement feasible and effective controls. This approach groups actions by their likely effectiveness in reducing or removing the noise hazard.
In most cases, the preferred approach is to eliminate the source of hazardous noise. When elimination is not possible, substitution of the loud equipment for quieter equipment may be the next best alternative to protect workers from hazardous noise. If the hazardous noise cannot be controlled through elimination of the source or substitution of quieter equipment, engineering controls may be installed to reduce noise to safer levels or remove noise at the source.
Engineering controls require physical changes to the workplace such as redesigning equipment to eliminate noise sources and constructing barriers that prevent noise from reaching a worker. If it is not possible to remove the hazard through elimination, substitution or engineering controls, the next step is to reduce noise exposure through the use of administrative controls. For example, an employer may change an employee’s work schedule to avoid too much noise.
Personal protective equipment (PPE), such as ear plugs or other hearing protection devices, is the last option in the hierarchy of control. PPE is generally less effective than elimination, substitution, and engineering controls because they rely on human actions to reduce noise. Used in combination with other levels of control, such as administrative controls, PPE may provide worker protection when engineering controls do not adequately remove the noise hazard.
NIOSH encourages occupational safety and health professionals, employers, and workers to learn more about controls for hazardous noise exposure. Consult a workplace safety and health professional to determine solutions for your work setting and employees. TO provide some perspective, 85 dBA sounds like a kitchen blender operating on high. 140 dBC sounds like a military aircraft with afterburners on.
Solutions for Reducing Noise in the Workplace
Occupational safety and health professionals and employers can take the following actions to reduce noise in the workplace. Consider these solutions when creating your hearing loss prevention program:
- Buy Quiet – select and purchase low-noise tools and machinery
- Maintain tools and equipment routinely (such as lubricate gears)
- Reduce vibration where possible
- Isolate the noise source in an insulated room or enclosure
- Place a barrier between the noise source and the employee
- Isolate the employee from the source in a room or booth (such as sound wall or windows)
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