Noise Evaluation Versi OSHA

Section I: What is considered “noise” and what are the potential health effects?
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Physics of Sound
Sound is the physical phenomenon that stimulates our sense of hearing. It is an acoustic wave that results when a vibrating source, such as machinery, disturbs an elastic medium, such as air.
• In air, sound is usually described as variations of pressure above and below atmospheric pressure. These fluctuations, commonly called sound pressure, develop when a vibrating surface forms areas of high and low pressure, which transmit from the source as sound.
Additional information (App I:A) on the physics of sound, including basic qualities, sound fields, sound propagation, filtering, loudness, and sound pressure weighting is also available.

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Anatomy and Physiology of the Ear
The ear is the organ that makes hearing possible. It can be divided into three sections:
• External outer ear
• Air-filled middle ear
• Fluid-filled inner ear
The function of the ear is to gather, transmit, and perceive sounds from the environment.

This involves three stages:
1. Modification of the acoustic wave by the outer ear, which receives the wave and directs it to the eardrum.
2. Conversion and amplification of the modified acoustic wave to a vibration of the eardrum (transmitted through the middle ear to the inner ear).
3. Transformation of the mechanical movement of the wave into nerve impulses that will travel to the brain, which then perceives and interprets the impulse as sound.
Additional information (App I:B) on outer ear, middle ear and inner ear is also available.

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Effects of Excessive Exposure
Although noise-induced hearing loss is one of the most common occupational illnesses, it is often ignored because there are no visible effects, it usually develops over a long period of time, and, except in very rare cases, there is no pain. What does occur is a progressive loss of communication, socialization, and responsiveness to the environment. In its early stages (when hearing loss is above 2,000 Hertz (Hz)) it affects the ability to understand or discriminate speech. As it progresses to the lower frequencies, it begins to affect the ability to hear sounds in general.

The three main types of hearing loss are conductive (App I:C-1), sensorineural (App I:C-2), or a combination of the two.

The effects of noise can be simplified into three general categories:
• Primary Effects, which includes noise-induced temporary threshold shift, noise-induced permanent threshold shift, acoustic trauma, and tinnitus.
• Effects on Communication and Performance, which may include isolation, annoyance, difficulty concentrating, absenteeism, and accidents.
• Other Effects, which may include stress, muscle tension, ulcers, increased blood pressure, and hypertension.
In some cases, the effects of hearing loss may be classified by cause.

Additional information (App I:C) about the effects of excessive noise exposure is also available.

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Ultrasonics
Ultrasound is high-frequency sound that is inaudible, or cannot be heard, by the human ear. However, it may still affect hearing and produce other health effects.

Factors to consider regarding ultrasonics include:
• The upper frequency of audibility of the human ear is approximately 15-20 kilo-Hertz (kHz).
o This is not a set limit and some individuals may have higher or lower (usually lower) limits.
o The frequency limit normally declines with age.
• Most of the audible noise associated with ultrasonic sources, such as ultrasonic welders or ultrasonic cleaners, consists of subharmonics of the machine’s major ultrasonic frequencies.
o Example: Many ultrasonic welders have a fundamental operating frequency of 20 kHz, a sound that is at the upper frequency of audibility of the human ear. However, a good deal of noise may be present at 10 kHz, the first subharmonic frequency of the 20 kHz operating frequency, and is therefore audible to most persons.
Additional information (App I:D) on ultrasonics and the applicability of OSHA’s Occupational Noise Exposure standard, 1910.95, health effects and the American Conference of Governmental Industrial Hygienists’ (ACGIH) Threshold Limit Values (TLVs) is also available.

Section III: How do I evaluate noise exposure?
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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 [29 CFR 1910.95, it is necessary to determine exposure levels. The following sections provide information about evaluating noise exposure levels:
• Indications of a Problem
• Walkaround Survey
• Workshift Sampling
• Instruments Used to Conduct a Noise Survey (App III:A)

Checking for noise source
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Indications of a Problem
There are various factors that may indicate 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.
o When noise levels are above 80 decibels (dB), people have to speak very loudly.
o When noise levels are between 85 and 90 dB, people have to shout.
o When noise levels are 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. See more information about effects on communication and performance (App I:C).

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Walkaround Survey
A walkaround survey should be performed to screen for noise exposures and to 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. The following general approach may be followed:
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 (App III:A) to take spot readings of operations that are in question. 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 workers 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 walkaround survey indicate time-weighted average (TWA) exposures of 80 dBA or more, then 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.

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Workshift Sampling
When the results of the walkaround survey indicate that noise levels may exceed those outlined in OSHA's noise standard 29 CFR 1910.95, additional monitoring is necessary.
• Establish a sampling protocol for your workplace. A general protocol (App III:B) is provided as an example.
• In addition to the general information collected during all health inspections, OSHA may collect certain information where it is pertinent to evaluate compliance with OSHA standards (29 CFR 1910.95, 29 CFR 1926.52, or 29 CFR 1926.101). Additional information (App III:C) on inspection data is also available.
• 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 and may be used accordingly. Additional information (App III:A) on dosimeters is also available.
o A dosimeter with a threshold of 80 dBA is used to measure the noise dose of those employees identified during the walkaround 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 [29 CFR 1910.95 Appenix A: Noise Expsoure 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.
o The dosimeter with a threshold of 90 dBA is used to measure the noise dose of those employees identified during the walkaround survey as having potential noise exposures that exceed the sound levels in Table G-16 [29 CFR 1910.95] or Table D-2 [29 CFR 1926.52]. 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, Table G-16a, or Table D-2 (for general industry or construction workplaces, respectively). Instrument accuracy must be taken into account.
• Consider the following with respect to the monitoring results:
o TWA exposures at or above the action level of 85 dBA require a hearing conservation program [29 CFR 1910.95 (c-n)] (results obtained from the 80 dBA threshold).
o TWA exposures exceeding the PEL (Table G-16) require feasible engineering or administrative controls to be implemented [29 CFR 1910.95(b)] (results obtained from the 90 dBA threshold). Refer to the OSHA Field Operations Manual (FOM) for additional information.
• There is also information specific to evaluating noise exposure of employees wearing sound-generating headsets (App III:D).

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