• The two main types of hearing protectors are ear plug and earmuffs.
• Employers should consider what level of noise employees are exposed to, and what the right hearing protection devices are for those conditions.
• Employers must ensure that the sound meters and dosimeters that are used to measure workplace noise levels meet ANSI standards.

There are two types of hearing protectors: ear plugs and earmuffs. Both types reduce the pressure of sound that reaches the eardrum and are the next line of defense when noise levels can’t be reduced to safe levels with engineering or administrative controls.

What are the criteria for hearing protection?

Some factors employers should consider when selecting the right hearing protection devices (HPDs) include:

• Noise hazard—how much noise will workers be dealing with?
• Noise frequency—will it be continuous or intermittent? (Some earplugs or muffs reduce the force of noise better at lower frequencies than at higher frequencies.)
• Fit and comfort—protective devices must fit properly and be comfortable enough to wear for as long as they are needed.
• Noise Reduction Rating (NRR)—All hearing protectors carry a label indicating the NRR; a higher number on the label means more effectiveness.

HPDs filter out loud noise. They do not block out sound completely, but they reduce the amount of sound reaching the delicate parts of the ear. By doing so, HPDs offer some protection so that hearing will not get overloaded by the surrounding noises (glare) that interfere with speech and machinery sounds.

ANSI standards for sound meters

Sound level meters used by the Occupational Health and Safety Administration (OSHA) meet the American National Standards Institute (ANSI) Standard S1.4 “Specifications for Sound Level Meters.” The ANSI standard sets performance and accuracy tolerances according to three levels of precision: Types 0, 1, and 2. Type 0 is used in laboratories, Type 1 is used for precision measurements in the field, and Type 2 is used for general-purpose measurements.

For compliance purposes, readings with an ANSI Type 2 sound level meter and dosimeter are considered to have an accuracy of ±2 dBA, while a Type 1 instrument has an accuracy of ±1 dBA.

A Type 2 meter is the minimum requirement by OSHA for noise measurements and is usually sufficient for general purpose noise surveys.

The Type 1 meter is preferred for the design of cost-effective noise controls.

For unusual measurement situations, employers should refer to the manufacturer’s instructions and appropriate ANSI standards for guidance in interpreting instrument accuracy.

Dosimeter

Like a sound level meter, a noise dosimeter can also measure sound levels. Unlike a sound level meter, the dosimeter is actually worn by the employee in order to determine the personal noise dose during the workshift or sampling period. Dosimeters can be used to:

• Take compliance measurements according to OSHA’s noise standard.
• Measure the employee’s exposure to noise and automatically compute the necessary noise dose calculations.

Factors to consider with the use of a dosimeter include:

• The microphone must be placed in the employee’s hearing zone. OSHA defines the hearing zone as a sphere with a two-foot diameter surrounding the head.
• The user must select specific instrument settings for the dosimeter.
• Special considerations may be involved with the use and care of a dosimeter.

ANSI standards for personal dosimeters

The ANSI standard for personal dosimeters is S1.25-1991, “Specifications for Personal Noise Dosimeters.” Some older dosimeters only meet the 1978 version of this standard. The 1978 version was not intended for measuring noise that is predominantly impulsive. For noise that is impulsive in nature, a dosimeter meeting the 1991 version of the standard is recommended.

Octave-band analyzers

Octave-band analyzers are sound level meters that can be used to:

• Help determine the adequacy of various types of frequency-dependent noise controls.
• Select hearing protectors because they can measure the amount of attenuation (how much a sound is weakened) offered by the protectors in the octave bands responsible for most of the sound energy in a given situation.
• Divide noise into its frequency components.

Some sound level meters may have an octave or one-third octave band filter attached or integrated into the instrument. Usually a Type 1 (precision) sound level meter is used for octave and one-third octave analysis.

The filters are used to analyze the frequency content of noise. They are also valuable for the calibration of audiometers and to determine the adequacy of various types of noise control.

Frequency components may include:

• Most octave-band filter sets provide filters with the following center frequencies: 31.5, 63, 125, 250, 500, 1,000, 2,000, 4,000, 8,000, and 16,000 Hertz (Hz).

For a more detailed analysis, the spectrum is sometimes measured in one-third octave bands.

The special signature of any given noise can be obtained by taking sound level meter readings at each of the center frequency bands. The results may indicate octave bands that contain most of the total sound power being radiated.