1: Introduction
Overview
Range of Sound
Sound pressure is measured in decibels, or tenths of a Bel. Sound pressure level is indicated
as dB SPL. Since the human ear can detect sounds with an extensive range of amplitude, a
decibel scale is used to simplify the measurement results. For example, the ratio between the
threshold of hearing and threshold of pain in the human ear if measured in true energy is
10,000,000 times! The same range using the dB scale is 0–140 dB referenced to 20 µPa
(Micropascals).
The quietest sound that humans can hear has an amplitude of approximately 0 dB. Prolonged
exposure to sound pressure levels exceeding 85 dB can cause permanent damage to the ear.
Sound levels in excess of 130 dB are more than the human ear can safely withstand and can
result in serious pain and permanent damage.
What do the Standards Say?
Many organizations have studied and analyzed the effects of high sound exposure on hearing.
As a result, standards were developed to regulate personal noise exposure. In the United
States, the Occupational Safety and Health Administration (OSHA), the Mine and Safety and
Health Administration (MSHA), and the American Conference of Governmental Industrial
Hygienists (ACGIH) have all created regulations and limitations on total permissible noise
exposure. International standards are specified by the health and safety regulations such as
the European Union (EU) Directive 2003/10/EC. Additionally, the International Electrotechnical
Commission (IEC) IEC-61252 has specific guidelines and regulations to monitor noise in the
workplace.
To access these copyrighted standards, please refer to the following:
OSHA—http://www.osha.gov
MSHA—http://www.msha.gov
NIOSH—http://www.cdc.gov/niosh/topics/noise
ACGIH—http://www.acgih.org/
IEC—http://www.iec.ch
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