# Applied Sciences

OSH 4301, Industrial Hygiene 1

Course Learning Outcomes for Unit VI Upon completion of this unit, students should be able to:

2. Apply scientific principles to the practice of industrial hygiene. 2.1 Use time-weighted average (TWA) and permissible exposure limit (PEL) methods to evaluate

noise exposures in the workplace. 2.2 Evaluate characteristics and abilities of sound level meters (SLMs) and noise dosimeters.

4. Evaluate industrial hygiene management practices. 4.1 Summarize the requirements for an effective hearing conservation program. 4.2 Define terms associated with occupational noise.

6. Perform basic calculations related to industrial hygiene.

6.1 Calculate the 8-hour time-weighted average noise (TWA) exposure given several intermediate noise exposures.

Reading Assignment To access the following resources, click the links below: Occupational Safety and Health Administration. (1970). Occupational safety and health standards:

Course/Unit Learning Outcomes

Learning Activity

2.1

Unit VI Lesson Article: “Occupational safety and health standards: Occupational health and environmental control (Standard No. 1910.95)” Unit VI Assessment

2.2 Unit VI Lesson Article: “OSHA technical manual: Noise” Unit VI Assessment

4.1

Unit VI Lesson Article: “Occupational safety and health standards: Occupational health and environmental control (Standard No. 1910.95)” Article: “OSHA technical manual: Noise” Unit VI Assessment

4.2

Unit VI Lesson Article: “Occupational safety and health standards: Occupational health and environmental control (Standard No. 1910.95)” Article: “OSHA technical manual: Noise” Unit VI Assessment

6.1

Unit VI Lesson Article: “Occupational safety and health standards: Occupational health and environmental control (Standard No. 1910.95)” Unit VI Assessment

UNIT VI STUDY GUIDE

Evaluating Exposures to Noise

OSH 4301, Industrial Hygiene 2

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Unit Lesson Noise is one of the most common physical hazards that industrial hygienists must evaluate. Most workplaces have some area where noise is a concern. The Occupational Safety and Health Administration (OSHA, n.d.) estimates that every year, 22 million workers are exposed to noise levels that could result in hearing loss. Workers’ compensation costs for noise-induced hearing loss continue to rise each year with an estimated annual cost today of \$242 million dollars (OSHA, n.d.). Evaluating noise exposures can be more complicated than evaluating exposures to aerosols, vapors, and

gases that occur on a linear scale and can sometimes be visible at higher concentrations. Vapors and gases will produce an odor at some concentrations, though the ability to detect the odor will vary from person to person. Vibrations in the air resulting in waves, called sound waves, produce noise. The OSHA technical manual on noise (required reading in this unit) provides a good explanation of the formation of sound waves and the body’s ability to perceive the noise. The distance between two analogous points on a sound wave is known as the wavelength (OSHA, 2013). Frequency is the number of times each second that a complete sound waves passes. Humans perceive changes in frequency as changes in pitch of the sound. For example, noise with a high frequency (many cycles of the sound wave each second) are perceived as having a high pitch, while noise with

a low frequency (fewer cycles of the sound wave each second) are perceived as having a low pitch. In other words, a soprano will generate higher frequency than a bass. We typically measure frequency in hertz (Hz) and kilohertz (KHz). Many machines in occupational settings generate noise with very high frequencies in the 4 KHz and higher range. The higher frequency exposures in occupational settings result in most noise-induced hearing loss (NIHL) occurring in the high frequency range. The result is typically seen as an inability to understand speech in the higher frequencies. For example, an individual with noise-induced hearing loss in the 4 KHz and 6 KHz frequencies will likely find it harder to understand a female talking than a male, especially if background noise is present. The decibel (dB), the range of sound pressure perceived by humans, is so great that it would be impractical to develop a meter to measure the entire spectrum. Therefore, the dB has become the preferred unit for measuring sound pressure. The dB is a dimensionless measurement on a logarithmic scale. Specifically, the dB is the logarithm of the ratio of the measured sound pressure to a base sound pressure. For occupational noise measurements, the threshold of hearing is almost always used as the base sound pressure level (20 µPa). OSHA has established a definition for standard threshold shift (STS) related to noise-induced hearing loss that is considered an OSHA reportable injury. OSHA defines STS as a change in the hearing threshold (ability to perceive noise) for an audiogram, relative to a baseline audiogram, of an average of 10 dB or more at 2 KHz, 3 KHz, or 4KHz in either ear (OSHA, 2013). OSHA allows some additional adjustments to be made in determining STSs, such as an adjustment for reductions in hearing threshold related to aging (presbycusis) and exposures to noise outside the workplace. However, even with the allowable adjustments, STSs continue to be one of the most reported OSHA injuries. Industrial hygienists commonly use two types of meters to evaluate occupational noise exposures: the sound level meter (SLM) and the noise dosimeter. The SLM is a handheld meter for measuring sound pressure

Factory worker putting in his ear protection (FastCap LLC, 2015)

OSH 4301, Industrial Hygiene 3

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OSH 4301, Industrial Hygiene 4

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used, at 93 dBA only four hours of exposure would be allowed. It is readily apparent that the 3 dB exchange rate is more conservative for worker protection.

https://www.flickr.com/photos/fastcap/28688453401/in/photolist-qc2sCN-qtA7f8-qcb4Jx-pwAQZ5- qc2vJs-qtAbdD-qtwDqu-qtqf7B-qtwCn7-qtAnVX-pwAGmo-qtA7t4-pwAHzf-pwQjyg-qcb9Zx-qc2BpW- pwAG2A-HJbDFr-Ev4V2a-BwqiRK-qMtZbM-yQT9rb-PzQSji-Prnwah-MFFi52-Nnsuhm-MT9q63-MQd

Occupational Safety and Health Administration. (n.d.). Occupational noise exposure: Overview. Retrieved

from https://www.osha.gov/SLTC/noisehearingconservation/index.html Occupational Safety and Health Administration. (1970). Occupational safety and health standards:

https://www.osha.gov/dts/osta/otm/otm_toc.html

Suggested Reading To access the following resources, click the links below: NIOSH recommends exposure limits for hazards, including noise. Originally, NIOSH recommended an exposure limit of 85 dBA with a 5 dB exchange rate. NIOSH continues to recommend an exposure limit of 85 dBA, but now recommends the use of a 3 dB exchange rate. The following document contains a good summary of the physics of noise and why NIOSH recommends the 85 dBA exposure limit and a 3 dB exchange rate. It also contains a summary of evaluation meters. National Institute for Occupational Safety and Health. (1998). Criteria for a recommended standard:

Some sampling methods rely on the orientation of the sample media to ensure that the sample is accurate. The optimal placement of the microphone for noise measurements has been debated for many years. The following article compares the placement of the microphone and the effect on the results of noise dosimetry.

Byrne, D. C., & Reeves, E. R. (2008). Analysis of nonstandard noise dosimeter microphone positions. Journal