Labor & Industries (L&I), Washington State

Hearing Loss Prevention (Noise) Chapter 296-817, WAC

Effective Date: 08/01/03

Noise Measurement and Computation WAC 296-817-300

For printing

WAC 296-817-300

Your responsibility:

Conduct noise monitoring or measurement to evaluate employee exposures in your workplace

You must

Make sure that noise-measuring equipment meets recognized standards	WAC 296-817-30005
Measure employee noise exposure	WAC 296-817-30010
Use these equations when estimating full-day noise exposure from sound level measurements	WAC 296-817-30015

 

WAC 296-817-30005

Make sure that noise-measuring equipment meets recognized standards

You must

• Make sure that noise dosimetry equipment meets these specifications:
  • – Dosimeters must be equipment class 2AS-90/80-5 of the American National Rule Specification for Personal Noise Dosimeters, ANSI S1.25-1991, such dosimeters are normally marked "Type 2."

  Note: Make sure any dosimeter you use is Type 2 equipment that: - Uses slow integration and A-weighting of sound levels. - Has the criterion level set to 90 dB, so the dosimeter will report a constant 8-hour exposure at 90 dBA as a 100% dose. - Has the threshold level set at 80 dB, so the dosimeter will register all noise above 80 dB. - Uses a 5 dB exchange rate for averaging of noise levels over the sample period.

You must

• Make sure that sound level meters meet these specifications:
  • – American National Standard Specification for Sound Level Meters, S1.4-1984, Type 2 requirements for sound level meters, such sound level meters are normally marked "Type 2."
  • For continuous noise measurements, the meter must be capable of measuring A-weighted sound levels with slow response
  • For impulse or impact noise measurements, the meter must be capable of indicating maximum C-weighted sound level measurements with fast response.
• Calibrate dosimeters and sound level meters used to monitor employee noise exposure:
  • - Before and after each day's use
    AND
  • - Following the instrument manufacturer's calibration instructions.

Note: - You may conduct dosimetry using an exchange rate less than 5 dB and compare the results directly to the noise evaluation criteria in Table 1 - For measuring impulse and impact noise you may also use a sound level meter set to measure maximum impulse C-weighted sound levels or peak C-weighted sound levels.

WAC 296-817-30010

Measure employee noise exposure

IMPORTANT:

A noise dosimeter is the basis for determining total daily noise exposure for employees. However, where you have constant noise levels, you may estimate employee noise exposure using measurements from a sound level meter. Calculation of the employee noise exposure must be consistent with WAC 296-817-30015.

You must

• Include all:
  • – Workplace noise from equipment and machinery in use
  • – Other noise from sources necessary to perform the work
  • – Noise outside the control of the exposed employees.
• Use a noise dosimeter when necessary to measure employee noise dose
• Use a sound level meter to evaluate continuous and impulse noise levels
• Identify all employees whose exposures equal or exceed the Noise Evaluation Criteria as follows:
  

Noise Evaluation Criteria
Criteria	Description	Requirements
85 dBA TWA8	Full-day employee noise exposure dose. If you have one or more employees whose exposure equals or exceeds this level, you must have a hearing loss prevention program	– Hearing protection – Training – Audiometric testing
90 dBA TWA8	Full-day employee noise exposure dose. If you have one or more employees whose exposure equals or exceeds this level, you must reduce employee noise exposures in the workplace	– Noise controls (in addition to the requirements for 85 dBA TWA8)
115 dBA measured using slow response	Extreme noise level (greater than one second in duration)	– Hearing protection – Signs posted in work areas warning of exposure
140 dBC measured using fast response	Extreme impulse or impact noise (less than one second in duration)	Hearing protection

WAC 296-817-30015

Use these equations when estimating full-day noise exposure from sound level measurements

You must

• Compute employee's full-day noise exposure by using the appropriate equations from Table 3 "Noise Dose Computation" when using a sound level meter to estimate noise dose.

Table 3 Noise Dose Computation
Description	Equation
Compute the noise dose based on several time periods of constant noise during the shift.	The total noise dose over the work day, as a percentage, is given by the following equation where Cn indicates the total time of exposure at a specific noise level, and Tn indicates the reference duration for that level.
The reference duration is equal to the time of exposure to continuous noise at a specific sound level that will result in a 100% dose.	The reference duration, T, for sound level, L, is given in hours by the equation:
Given a noise dose as a percentage, compute the equivalent 8-hour time weighted average noise level	The equivalent 8-hour time weighted average, TWA8, is computed from the dose, D, by the equation: