Noise Dose Testing Laboratory

Overview

1. Purpose of Noise Dose Testing

The goal is to:

• Evaluate employee exposure to noise.
• Determine compliance with OSHA’s permissible exposure limits (PELs).
• Identify workers who need to be included in a hearing conservation program

2. Key OSHA Standards

The relevant regulation is 29 CFR 1910.95 – Occupational Noise Exposure.

OSHA Permissible Exposure Limit (PEL):

• 90 dBA (A-weighted decibels) for an 8-hour time-weighted average (TWA).
• The exchange rate is 5 dB — meaning that for every 5 dB increase in noise level, the allowable exposure time is cut in half.

Noise Level (dBA)	Maximum Allowable Exposure Time
90 dBA	8 hours
95 dBA	4 hours
100 dBA	2 hours
105 dBA	1 hour
110 dBA	30 minutes
115 dBA	15 minutes

No exposure above 115 dBA is permitted under OSHA’s general industry standard.

3. Action Level (Hearing Conservation Program)

• If an employee’s exposure equals or exceeds an 8-hour TWA of 85 dBA, the employer must:
  • Implement a hearing conservation program.
  • Conduct audiometric testing and training.
  • Provide hearing protection and ensure its proper use.
  • Monitor noise exposure periodically.

4. Noise Dose Measurement

Noise dose testing is typically done using a noise dosimeter worn by the worker during the shift.

a. Equipment Setup:

• Use an integrating sound level meter or personal noise dosimeter.
• Calibrate the instrument before and after each measurement.
• Use A-weighting and slow response settings.
• Place the dosimeter microphone within 1 foot (30 cm) of the worker’s ear.

b. Data Collection:

• Measure over the entire work shift (typically 8 hours).
• Record dose (%) and TWA (dBA) values.

c. Calculation:

OSHA defines noise dose as:

D=100×∑i=1nCiTiD = 100 \times \sum_{i=1}^{n} \frac{C_i}{T_i}D=100×i=1∑n​Ti​Ci​​

Where:

• DDD = noise dose (%)
• CiC_iCi​ = actual time of exposure at a specific noise level
• TiT_iTi​ = permissible time for that noise level (from the OSHA table above)

If D = 100%, the exposure equals the permissible limit (90 dBA TWA).

You can convert noise dose to TWA using:

TWA=16.61×log⁡10(D100)+90TWA = 16.61 \times \log_{10}\left(\frac{D}{100}\right) + 90TWA=16.61×log10​(100D​)+90

5. Reporting and Recordkeeping

• Keep noise exposure measurement records for at least 2 years.
• Keep audiometric test records for the duration of the affected employee’s employment.

6. Engineering & Administrative Controls

If noise levels exceed PELs:

1. Implement engineering controls (e.g., enclosure, damping, isolation).
2. Use administrative controls (e.g., rotating workers).
3. Provide hearing protection devices (earplugs, earmuffs).

7. Summary Table

OSHA Requirement	Exposure Level	Required Action
85 dBA (TWA)	Action Level	Hearing conservation program required
90 dBA (TWA)	PEL	Implement controls to reduce exposure
>115 dBA	Prohibited	Exposure not allowed