Noise Measurement and Control

Wherever people work, noise will inevitably result. Often the noise is desired, such as intercoms, alarm bells, and conversations. In other cases, noise can be a direct result of work such as hammering, grinding, or running engines. Regardless of whether the noise is desired, noise can be hazardous, either by direct physical damage to human hearing or indirectly by interfering with desired sounds (i.e. being unable to hear an evacuation alarm over loud machinery).

What Is Noise?

Noise is unwanted sound. Sound is acoustical energy generated when a medium such as air or water is vibrated. Sound cannot be transmitted in a vacuum because there is no medium to vibrate. Sound occurs as waves having characteristics of amplitude and frequency. Amplitude determines loudness, while frequency determines tone.

How Is Noise Harmful?

High noise is harmful because it traumatically damages the microscopic hair cells in the inner ear that are responsible for generating nerve impulses perceived by our brain as sound. When these cells are exposed to high noise over time, they deteriorate and do not regenerate. If enough of these hair cells are lost, the ability to perceive loudness and tone will degenerate.

How Are Noise Sources Measured and Analyzed?

Noise is measured in units of decibels (dB) using a sound level meter. Noise levels in a quiet room range from 40 to 60 dB, while noise from a ripsaw can run in excess of 100 dB. Employee or community noise exposures can be evaluated by an industrial hygienist or a safety or acoustical engineer. These individuals can perform an area noise study or a more representative study referred to as a personal noise dosimetry study. Equipment or facility noise commonly is evaluated using an octave band analyzer. A typical equipment or facility noise study involves:

• Obtaining a frequency spectrum
• Turning individual equipment components on and off to isolate the source
• Conducting near-field noise measurements to determine the characteristics of the noise source and the most appropriate abatement option.
• Using temporary controls such as mufflers, insulation, or enclosures to manipulate the sources of noise

What Are The Current ‘Safe’ Limits For Noise?

A number of organizations have published noise exposure limits. The Occupational Safety and Health Administration (OSHA) currently limits employee noise exposures measured as an 8-hour time weighted average (TWA) to 90 dBA (the unit of sound magnitude measured using an A-weighting network similar to the human ear). The American Conference of Governmental Hygienists (ACGIH) and the National Institute for Occupational Safety and Health (NIOSH) recommend limiting employee noise exposures to 85 dBA measured as an 8-hour TWA. Community noise limits are generally lower than occupational limits and are established by local ordinance.

What Are Some Sources Of Workplace And Community Noise?

Noise can be generated by a number of sources. These include:

• Vibrating surfaces (engines, electric motors, fans, ductwork)
• Mechanical impacts (stamping machines, pile driving, nail guns, hammers)
• Pulsating gas flow (air solenoids, pistons, jack hammers)
• Air flowing over a surface (part ejectors, air wipes)
• Compression and rarefaction of a medium (gears meshing, fan blades pushing and pulling air)

How Can Excessive Noise Exposures Be Controlled?

Noise controls generally target three areas:

• The source of noise:
  • Modify/redesign equipment
  • Relocate to a protected location
• The path of the noise:
  • Block transmission using an enclosure or barrier
  • Absorb the noise
• The receiver of the noise (employees, the community):
  • Enclose the receiver
  • Absorb the noise
  • Relocate the receiver
• What Are Some Practical Noise Control Options? .

XL Environmental • Risk Control Division • 520 Eagleview Boulevard, PO Box 636, Exton, PA 19341 • Phone: 800-327-1414 • Fax: 610-458-7285 • xlenvironmental.com

XL Environmental is a division of XL Specialty Insurance Company.