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The Leq is the foundation of the composite noise descriptors such as L&and CNEL, as defined above, and
<br /> correlates well with community response to noise.
<br /> Negative Effects of Noise on Humans
<br /> Negative effects of noise exposure include physical damage to the human auditory system, interference, and
<br /> disease. Exposure to noise may result in physical damage to the auditory system,which may lead to gradual or
<br /> traumatic hearing loss. Gradual hearing loss is caused by sustained exposure to moderately high noise levels over
<br /> a period of time;traumatic hearing loss is caused by sudden exposure to extremely high noise levels over a short
<br /> period. Gradual and traumatic hearing loss both may result in permanent hearing damage. In addition,noise may
<br /> interfere with or interrupt sleep,relaxation,recreation, and communication. Although most interference may be
<br /> classified as annoying,the inability to hear a warning signal may be considered dangerous.Noise may also be a
<br /> contributor to diseases associated with stress, such as hypertension, anxiety, and heart disease. The degree to
<br /> which noise contributes to such diseases depends on the frequency,bandwidth, and level of the noise, and the
<br /> exposure time (Caltrans 1998).
<br /> Vibration
<br /> Vibration is the periodic oscillation of a medium or object. The rumbling sound caused by the vibration of room
<br /> surfaces is called structureborne noise. Sources of groundborne vibrations include natural phenomena
<br /> (e.g., earthquakes,volcanic eruptions, sea waves, landslides) or human-made causes (e.g., explosions,machinery,
<br /> traffic,trains, construction equipment). Vibration sources may be continuous, such as factory machinery, or
<br /> transient, such as explosions.As is the case with airborne sound,groundborne vibrations may be described by
<br /> amplitude and frequency.
<br /> Vibration amplitudes are usually expressed in peak particle velocity(PPV)or root mean square(RMS), as in
<br /> RMS vibration velocity. The PPV and RMS velocity are normally described in inches per second. PPV is defined
<br /> as the maximum instantaneous positive or negative peak of a vibration signal. PPV is often used in monitoring of
<br /> blasting vibration because it is related to the stresses that are experienced by buildings(Federal Transit
<br /> Administration [FTA] 2006, Caltrans 2004).
<br /> Although PPV is appropriate for evaluating the potential for building damage, it is not always suitable for
<br /> evaluating human response. It takes some time for the human body to respond to vibration signals. In a sense,the
<br /> human body responds to average vibration amplitude. The RMS of a signal is the average of the squared
<br /> amplitude of the signal,typically calculated over a 1-second period.As with airborne sound,the RMS velocity is
<br /> often expressed in decibel notation as vibration decibels(VdB),which serves to compress the range of numbers
<br /> required to describe vibration(FTA 2006). This is based on a reference value of 1 microinch per second(µin/sec).
<br /> The background vibration-velocity level in residential areas is usually approximately 50 VdB. Groundborne
<br /> vibration is normally perceptible to humans at approximately 65 VdB. For most people, a vibration-velocity level
<br /> of 75 VdB is the approximate dividing line between barely perceptible and distinctly perceptible levels
<br /> (FTA 2006).
<br /> Typical outdoor sources of perceptible groundborne vibration are construction equipment, steel-wheeled trains,
<br /> and traffic on rough roads. If a roadway is smooth,the groundborne vibration is rarely perceptible. The range of
<br /> interest is from approximately 50 VdB,which is the typical background vibration-velocity level,to 100 VdB,
<br /> which is the general threshold where minor damage can occur in fragile buildings. Construction activities can
<br /> generate groundborne vibrations,which can pose a risk to nearby structures. Constant or transient vibrations can
<br /> weaken structures, crack facades, and disturb occupants(FTA 2006).
<br /> Construction vibrations can be transient,random, or continuous. Transient construction vibrations are generated
<br /> by blasting, impact pile driving, and wrecking balls. Continuous vibrations result from vibratory pile drivers,
<br /> Manteca WQCF and Collection System Master Plans EIR EDAW
<br /> City of Manteca 4.4-5 Noise
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