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:

Occupational health and environmental control (Standard No. 1910.95). Retrieved from https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=9735

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

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Occupational Safety and Health Administration. (2013). OSHA technical manual: Noise, 5-40. Retrieved from https://www.osha.gov/dts/osta/otm/otm_toc.html

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)

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levels in dB. Many SLMs do not have the ability to measure time-weighted average (TWA) noise exposures using data-logging instruments nor are they convenient for an employee to wear during a work shift. Therefore, the most common use of SLMs is to evaluate areas for the need to perform personal noise monitoring and to identify noise sources. OSHA does allow the use of an SLM to evaluate personal exposures for jobs with low mobility, if the data can be shown to be representative of workers’ actual exposures. However, the majority of personal noise evaluations are performed using noise dosimeters. Octave band analyzers are filters that can be added to an SLM to provide additional data about sound pressure levels at different frequencies. Some SLMs already have the octave band analyzers added during manufacturing. A common octave band analyzer will provide sound pressure level readings at 11 different bands ranging from 16 Hz to 16 KHz. See the OSHA technical manual in your Required Reading for photographs and further discussion of octave band analyzers. The results of an octave band analysis will become clearer when we discuss control methods for reducing noise exposure in the next two units. In most occupational settings, it is important to be able to evaluate personal exposures to noise. To get results that represent the worker’s exposure, workers must wear data-logging instruments. These devices, called noise dosimeters, are smaller devices designed to be worn by a worker and use data-logging capabilities to record a time-weighted average (TWA) noise exposure. Noise dosimeters used to consist of a small box with a microphone connected by a wire. The box was placed at the worker’s waist, and the microphone was placed on the collar. The traditional style noise dosimeter is still available, but there are now several models that incorporate the entire dosimeter into a small device that sits entirely on the worker’s shoulder. The placement of the noise dosimeter has been a point of discussion for many years. OSHA states that the device must be placed in the hearing zone of the employee. In OSHA’s technical manual, compliance officers are instructed to place the microphone pointing straight up in the hearing zone, which is defined as a 2-foot- wide sphere surrounding the employee’s ear (OSHA, 2013). Another topic concerning the evaluation of noise exposures that has been discussed over the years is the setting to be used for the evaluation. First, OSHA specifies that readings will be taken using the A scale (dBA) and the slow setting. The responses of an SLM or noise dosimeter can be modified to read based on weighting of different frequencies (OSHA, 2013). The three most common frequency weighting networks are the A scale (dBA), the B scale (dBB), and the C scale (dBC). The human ear does not respond equally to noise at all frequencies, meaning it is more sensitive to noise at some frequencies than others. OSHA uses the A scale because it approximates the way the human ear responds to noise at different frequencies better than the B scale and C scale (OSHA, 2013). The slow response setting is used because the meter fluctuates less and is therefore easier to read. OSHA initially established an 8-hour TWA PEL of 90 dBA for general industry based on ACGIH TLVs in existence at the time. This OSHA PEL remains unchanged to date, even though both NIOSH and ACGIH currently recommend an exposure limit of 85 dBA. OSHA also established an 8-hour TWA action level of 85 dBA for 8-hour work shifts, or an equivalent exposure of 50%. This means that the action level changes with extended shift lengths. The OSHA technical manual (p. 59) shows examples of how to calculate action levels for extended work shifts (83.4 dBA for a 10-hour work shift, 82.1 dBA for a 12-hour work shift) (OSHA, n.d.). Exceeding the action level requires the employer to take specific actions, including implementation of an effective hearing conservation program (OSHA, 1970). Read about the requirements for an effective hearing conservation program in 29 CFR 1910.95. As discussed in OSHA technical manual: Noise, one of the most debated topics in noise evaluation concerns the exchange rate used for noise. The exchange rate represents the change in exposure where the sound pressure doubles or halves, and the allowable exposure time also doubles or halves. OSHA has always maintained a 5 dBA exchange rate. OSHA states that it uses the 5 dBA exchange rate to account for the time when workers are not exposed to noise during the workday (e.g., breaks or time in offices). The ACGIH, NIOSH, and most foreign countries currently use a 3 dBA exchange rate (OSHA, 2013). The 3 dBA exchange rate is believed to be more representative because it has been shown that sound pressure actually doubles every 3 dBA, not every 5 dB. For example, under OSHA, exposure at 90 dBA is allowed for eight hours, but exposure is only allowed for four hours at 95 dBA (an increase of 5 dBA). If a 3 dBA exchange rate were

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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.

References FastCap LLC. (2015, July 22). eyebudz-side [Photograph]. Retrieved from

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:

Occupational health and environmental control (Standard No. 1910.95). Retrieved from https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=9735

Occupational Safety and Health Administration. (2013). OSHA technical manual: Noise. Retrieved from

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:

Occupational noise exposure (DHHS [NIOSH] Publication No. 98-126). Retrieved from http://www.cdc.gov/niosh/docs/98-126/pdfs/98-126.pdf

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

of Occupational and Environmental Hygiene, 5(3), 197-209. Retrieved from https://libraryresources.waldorf.edu/login?auth=CAS&url=http://search.ebscohost.com.libraryresource s.waldorf.edu/login.aspx?direct=true&db=a9h&AN=75127811&site=ehost-live&scope=site

Newer smartphone technology has made it possible to perform noise testing with various applications (apps) that were unavailable a few years ago. The reliability of the data produced by a smartphone is not clear. The following article researches how to improve the accuracy of noise measurements using smartphones. Roberts, B., Kardous, C., & Neitzel, R. (2016). Improving the accuracy of smart devices to measure noise

exposure. Journal of Occupational and Environmental Hygiene, 13(11), 840-846. Retrieved from https://libraryresources.waldorf.edu/login?auth=CAS&url=http://search.ebscohost.com.libraryresource s.waldorf.edu/login.aspx?direct=true&db=a9h&AN=118246347&site=ehost-live&scope=site

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