Evaluating Noise Exposure

The first step toward solving any noise problem is to define it. To understand what requirements must be implemented according to OSHA's noise standard, it is necessary to determine exposure levels.

Indications of a Problem

There are various factors that indicate when noise is a problem in the workplace. While people react differently to noise, subjective responses should not be ignored because they may provide warnings that noise may be at unacceptable levels.
  • Noisy conditions can make normal conversation difficult. When noise levels are:
    • Above 80 decibels (dB), people have to speak very loudly.
    • Between 85 and 90 dB, people have to shout.
    • Greater than 95 dB, people have to move close together to hear each other at all.
  • High noise levels can cause adverse reactions or behaviors.
Lower levels of noise exposure may actually be riskier than higher levels. Exposures below 95 dBA may be annoying, but don't seem loud enough for hearing protection — though cumulative exposure can lead to hearing loss. Noise levels above 100 dBA, however, are uncomfortable and the discomfort serves as a reminder to wear hearing protection.
Sometimes, overexposure to loud noise can trigger ringing or other sounds in the ears. This is called tinnitus. While tinnitus may be a symptom of damaged hearing, it can also be caused by infections, medications, and impacted ear wax. The only way to know for sure if noise has damaged a person's hearing is to have a hearing examination by a certified audiometric technician, audiologist, otolaryngologist, or physician.
Don't forget that exposure to loud noise doesn't occur in just the workplace. Off the job, employees can be exposed to noise from firearms, motorcycles, snowmobiles, power tools, lawn mowers and snow blowers, and loud music, often from headsets and ipods.

Walk-Around Sound Survey

There's only one way to know if noise has reached a dangerous level — have someone trained to conduct a sound survey. Anyone trained to use a sound-level meter and a dosimeter and evaluate the data should be able to perform the survey.
The walk-around survey will screen for noise exposures and determine if additional monitoring is necessary. When screening for noise exposures, sound level meter measurements and estimates of the duration of exposure are sufficient. The resulting spot readings can be used to determine the need for a more complete evaluation. Survey steps to follow include:
  1. Tour the facility and develop a detailed understanding of facility operations and potential noise sources. Take the tour with someone who is familiar with plant operations. Speak with knowledgeable personnel about operations and maintenance requirements. Make notes on a diagram of the floor plan if possible. Look for indications that noise may be a problem.
  2. Use a sound level meter to take spot readings of operations that are questionable. It may be useful to mark the sound levels on a diagram of the floor plan. Make notes regarding what equipment is on or off.
  3. Estimate exposures by identifying employees and their locations and estimate the length of time they spend in different areas or how long they operate particular equipment or tools.
If the results of the walk-around survey indicate time-weighted average (TWA) exposures of 80 dBA or more, additional noise monitoring should be performed. Remember to take into account the accuracy of the sound level meter when making this estimation. For example, a Type 2 sound level meter has an accuracy of ±2 dBA.

Work Shift Sampling

When the results of the walk-around survey indicate that noise levels may exceed those outlined in OSHA's Occupational Noise Exposure standard at §1910.95, additional monitoring is necessary. Sample the noise exposures of representative employees from each job classification that may be potentially overexposed.
Use a dosimeter with a threshold of 80 dBA (A-weighted sound pressure level) and 90 dBA to measure noise exposures. Most modern dosimeters use simultaneous 80 and 90 dBA thresholds.
  • A dosimeter with a threshold of 80 dBA is used to measure the noise dose of those employees identified during the walk-around survey as having noise exposures that are in compliance with Table G-16 of OSHA's noise standard 1910.95, but whose exposure may exceed the levels specified in Table G-16a [1910.95 Appendix A: Noise Exposure Computation]. In other words, the 80-dBA threshold is used to determine compliance with the 85 dBA time-weighted average (TWA) action level under OSHA's noise standard.
  • The dosimeter with a threshold of 90 dBA is used to measure the noise dose of those employees identified during the walk-around survey as having potential noise exposures that exceed the sound levels in Table G-16. In other words, the 90 dBA threshold is used to determine compliance with the permissible exposure limit (PEL).
As a minimum, sampling should be conducted for a length of time necessary to establish whether exposures are above the limits permitted by Table G-16 or Table G-16a. Instrument accuracy must be taken into account. Consider the following with respect to the monitoring results:
  • TWA exposures at or above the action level of 85 dBA require a hearing conservation program (results obtained from the 80 dBA threshold).
  • TWA exposures exceeding the PEL (Table G-16) require feasible engineering or administrative controls to be implemented (results obtained from the 90 dBA threshold).

Establish a Sampling Protocol

  1. Inform the employee being monitored that the dosimeter should not interfere with his/her normal duties, and emphasize that the employee should continue to work as usual.
  2. Explain the purpose of the dosimeter to each employee being sampled and emphasize that the dosimeter is not a speech recording device.
  3. Instruct the employee being sampled not to remove the dosimeter unless absolutely necessary and not to cover the microphone with a coat or outer garment or move it from its installed position. Inform the employee when and where the dosimeter will be removed.
  4. The microphone should be located in the employee's hearing zone. OSHA defines the hearing zone as a sphere with a two-foot diameter surrounding the head. Clip the microphone to the employee's clothing according to the manufacturer's instructions. Most manufacturers recommend that the microphone be placed on the shoulder area midway between the head and the point of the shoulder. Practicality and safety will dictate the actual microphone placement at each survey location.
  5. Use the microphone windscreen to protect the microphone when the wearer will be outdoors or in dusty or dirty areas. (The windscreen will not protect the microphone from rain or extreme humidity).
  6. When noise levels at an employee's two ears are different, the higher level must be sampled for compliance determinations.
  7. Position and secure any excess microphone cable to avoid snagging or inconvenience to the employee. If practical, the cord should be run under the employee's shirt or coat.
  8. Check the dosimeter periodically to ensure that the microphone is properly oriented.
  9. Obtain and note sound level meter readings during different phases of work the employee performs during the shift. There is no minimum regarding the number of readings to obtain, but it is important to take enough readings to identify work cycles. For statistical reasons, more readings should be taken when noise levels fluctuate widely.
  10. 6/09 Document sampling results.

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