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Administrative Draft Environmental Impact Report Gill Medical Center Project 4.15.1.5 Effects of Noise on People Hearing Loss While physical damage to the ear from an intense noise impulse is rare, a degradation of auditory acuity can occur even within a community noise environment. Hearing loss occurs mainly due to chronic exposure to excessive noise but may be due to a single event such as an explosion. Natural hearing loss associated with aging may also be accelerated from chronic exposure to loud noise. The Occupational Safety and Health Administration (OSHA) has a noise exposure standard that is set at the noise threshold where hearing loss may occur from long-term exposures. The maximum allowable level is 90 dBA averaged over eight hours. If the noise is above 90 dBA, the allowable exposure time is correspondingly shorter. Annoyance Attitude surveys are used for measuring the annoyance felt in a community for noises intruding into homes or affecting outdoor activity areas. In these surveys, it was determined that causes for annoyance include interference with speech, radio and television, house vibrations, and interference with sleep and rest.The Ldn as a measure of noise has been found to provide a valid correlation of noise level and the percentage of people annoyed. People have been asked to judge the annoyance caused by aircraft noise and ground transportation noise.There continues to be disagreement about the relative annoyance of these different sources. For ground vehicles, a noise level of about 55 dBA Ldn is the threshold at which a substantial percentage of people begin to report annoyance. 4.15.2 Fundamentals of Environmental Groundborne Vibration 4.15.2.1 Vibration Sources and Characteristics Sources of earthborne vibrations include natural phenomena (e.g., earthquakes,volcanic eruptions, sea waves, landslides) or manmade causes (explosions, machinery, traffic, trains, construction equipment, etc.). Vibration sources may be continuous (e.g., factory machinery) or transient (e.g., explosions). Ground vibration consists of rapidly fluctuating motions or waves with an average motion of zero. Several different methods are typically used to quantify vibration amplitude. One is the peak particle velocity (PPV); another is the root mean square (RMS)velocity. The PPV is defined as the maximum instantaneous positive or negative peak of the vibration wave.The RMS velocity is defined as the average of the squared amplitude of the signal.The PPV and RMS vibration velocity amplitudes are used to evaluate human response to vibration. PPV is generally accepted as the most appropriate descriptor for evaluating the potential for building damage. For human response, however, an average vibration amplitude is more appropriate because it takes time for the human body to respond to the excitation (the human body responds to an average vibration amplitude, not a peak amplitude). Because the average particle velocity over time is zero, the RMS amplitude is typically used to assess human response.The RMS value is the average of the amplitude squared over time, typically a 1- sec. period (FTA 2018). Noise 4.15-6 October 2021