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Acoustical Analysis Report Griffith Energy Storage Project 1.3 Vibration Metrics and Terminology Vibration is an oscillatory motion that is described in terms of displacement,velocity,or acceleration. Velocity is the most common descriptor used when evaluating human perception or structural damage. Velocity represents the instantaneous speed of movement and more accurately describes the response of humans, buildings,and equipment to vibrations. Peak-Particle-Velocity(PPV) and root mean square velocity are typical metrics used to describe vibration levels in units of inches per second in the United States. However,to evaluate annoyance to humans,the vibration dB (VdB) notation is commonly used.The decibel notation acts to compress the range of numbers required to describe vibration. In the United States,the accepted velocity reference for converting to dB is 1x10-6 inches per second.The abbreviation "VdB" is used for vibration dB to reduce the potential for confusion with sound decibels. In contrast to airborne noise,ground-borne vibration is not an everyday occurrence for humans.The background vibration velocity levels within residential areas are usually 50 VdB or lower,which is well below the human perception threshold of approximately 65 VdB. However, human response to vibration is not usually significant unless the vibration exceeds 70 VdB. For a significant impact to occur,vibration levels must exceed 72 VdB during frequent events,75 VdB for occasional events,and 80 VdB during infrequent events(Federal Transit Administration 2006). Outdoor sources that generate perceptible ground-borne vibrations are typically construction equipment,steel-wheeled trains,and traffic on rough roadways.Table 3 provides common vibration sources as well as human and structural response to ground-borne vibrations. Table 3. Typical Levels of Ground-Borne Vibration Human/Structural Response PPV Velocity Level Typical sourcesi feet from source) Threshold,Minor Cosmetic Damage, 0.4 100 Blasting from Construction Projects Fragile Buildings 0.17-0.2 92-94 Heavy Tracked Construction Equipment Difficulty with Tasks,Such as Reading 0.125 90 a Computer Screen 0.074 85 Commuter Rail,Upper Range 0.04 80 Rapid Transit,Upper Range Residential Annoyance,Infrequent 0.013 75 Commuter Rail,Typical Events 0.023 72 Bus or Truck Bump Over Residential Annoyance,Frequent 0.013 70 Rapid Transit,Typical Events 0.007 65 Approximate Threshold of Human 0.005 62 Bus or Truck,Typical Perception 0.0013 50 Typical Background Vibration Levels *RMS Vibration Velocity in VdB reference to 10-6 inches/second Source:FTA(2006) The degree of annoyance cannot always be explained by the magnitude of the vibrations alone. Phenomena,such as ground-borne noise and rattling,visual effects (e.g., movement of hanging objects), and time of day,all influence the response of individuals.The American National Standards Institute (ANSI) and the International Organization for Standardization (ISO) has developed criteria for evaluation of human exposure to vibrations.The recommendations of these standards and other studies evaluating OTETRA TECH 4 August 2023