OCCUSAFE UPDATE
Monthly Round Up of Important Ideas and Standards in
Industrial Hygiene and Safety
April 2014
IN THIS ISSUE: Better Standards for Protecting Workers’ Hearing
What is the right noise standard to protect workers against hearing loss? This vitally important question is also a difficult one to answer. It requires reviewing some basics about sound and noise:
- Noise is often referred to as sound pressure. A common logarithmic unit of measurement for noise is the decibel (dB).
- Humans are more sensitive to sound pressures in the frequency range of 1 kHz to 4 kHz than to low or high frequencies. Therefore, industrial hygienists use instruments that weights frequencies at those levels. This weighting scale is referred to as dBA.
- An alternative C scale (dBC) weights frequencies differently and attempts to measure the ear’s sensitivity to tones at high noise levels. However, research has found that, due to the ear’s ability to filter out certain frequencies, the dBA scale better measures actual damage to hearing.
- Most rule making organizations will use the dBA scale in measuring noise. For impact noise, most organizations have a limit of 140 dBA. The American Conference of Governmental Industrial Hygienists (ACGIH) allows the use of the C Scale for that purpose.
Other factors that impact workers’ hearing include the following:
- EXCHANGE RATE: is the amount of time a noise persistS before it is measured by the instrument. Both 3- and 5-second exchange rates are common. The shorter the exchange rate period, the greater the chance that the noise will be measured.
- NOISE THRESHOLD: is the minimum decibel value that will be measured by the instrument and included in determining the average decibel level.
- CRITERION: is the integrated, allowable level of exposure usually measured in decibels for a given period of time (i.e. 85 dBA for 8 hours of exposure.)
- DOSE: is a linear scale of exposure in percentage that corresponds to the criterion (i.e. 85 dBA for 8 hours corresponds to 100% dose.)
OSHA has the most lenient standards for computing noise exposure. When attempting to protect worker’s hearing, it may be better to consider other available standards. While most rule-making organizations use dBA, the other four factors can vary greatly:
- OSHA has an Action Level, which uses an exchange rate of 5 seconds, threshold of 80 dBA, limit of 140 dBA, and a criterion of 85 dBA for an 8-hour exposure, which corresponds to a 50% dose.
- OSHA also has a Permissible Exposure Limit (PEL), which uses an exchange rate of 5 seconds, threshold of 90 dBA, and a criterion of 85 dBA for an 8-hour exposure.
- The National Institute of Occupational Safety & Health (NIOSH) has a Recommended Exposure Limit (REL) uses an exchange rate of 3 seconds, threshold of 80 dBA and limit of 140 dBA, and a criteria of 85 dBA for an 8-hour exposure, which corresponds to a 100% dose.
- ACGIH has a Threshold Limit Value (TLV) uses an exchange rate of 3 seconds, threshold of 80 dBA and limit of 140 dBA, and a criteria of 85 dBA for an 8-hour exposure, which corresponds to a 100% dose.
- The European Union uses an exchange rate of 3 seconds, threshold of 80 dBA, and a criterion of 80 dBA for an 8-hour exposure.
For more information on this topic and to discuss your company’s safety and industrial hygiene needs call OccuSafe at (214) 662-6005 or contact us at occusafe@occusafeinc.com
OccuSafe Industrial Hygiene & Safety, Inc. provides skills and expertise to recognize, evaluate and control hazards and injuries in the areas of industrial hygiene, occupational safety and health. OccuSafe services companies of all sizes in a range of industries.
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