These effects vary greatly with the direction, body support, and restraint. Intensity is a measure that correlates sound pressure to loudness. For every 20-decibel increase in loudness, sound pressure increases by a factor of 10. The same sound pressure moving through the air that stimulates the ear to hear may also cause hearing loss under certain conditions. Table 7-1 shows the effects of various sound intensities on listeners.
Duration is the length of time that an individual is exposed to noise or vibrations.
It is a variable factor that may be measured in seconds, minutes, hours, or days or any other selected unit of time. Natural body resonance is the mechanical amplification of vibration by the body occurring at specific frequencies. Table 7-2 shows resonant frequencies for various parts of the human body. Damping is the loss of mechanical energy in a vibrating system. This loss causes the vibration to slow down.