In 1975 Tennessee enacted their first Blasting Standards Act. At that time a 2.0 peak particle velocity vibration limit was set. Compliance with this limit allowed blasting contractors to monitor with a seismograph capable of measuring peak particle velocity in 3 mutually perpendicular directions. A blasting contractor could also comply with this limit by loading their blasts in accordance with a standard table of distance, which prescribed the maximum load of any 8 millisecond delay period giving the closest exposure distance to a particular blast.
"In January of 2008 the vibration standard for this law was changed. Since 1975 several administrative changes had been made to the law; however, this was the first time that the vibration standard was changed."
The Tennessee Blasting Standards Act still allows a blaster to comply with the vibration standard portion of the law by utilizing a standard table of distances for all blasts located within 300 feet of a structure; however, now the law utilizes two different formulas for blasting in areas located between 300 – 5,000 feet and for blasts located in areas greater than 5,000 feet from a particular blast. These formulas are shown in the figure below.
The vibration standard is no longer a flat 2.0 inches per second (in/s). The vibration standard has been divided into 2 sections. The first standard is strictly based on distance. If blasting occurs within 300 feet of a structure, the contractor is allowed to blast up to 1.25 in/s. If blasting occurs between 300 and 5,000 feet of a structure, a blasting contractor is allowed to shoot up to 1.00 in/s, and if blasting occurs at distances greater than 5,000 feet a blasting contractor is allowed to shoot 0.75 in/s. Each of this vibrations measurements are made in in/s peak particle velocity. The law also allows an alternate standard. The blasting contractor has the option of using the OSM frequency based curve for compliance. This frequency based curve allows a blasting contractor to shoot up to 2 in/s for those blasts where the vibrations occur in a higher frequency range above 30 hertz. The following graph shows the alternate OSM frequency based vibration limit.
Previously, the Tennessee Blasting Standards Act had not mandated an air blast level for any blasting activity; however the new law enacted on January 1, 2008, specifies that all blasting will be conducted at levels not to exceed 140 decibels. As a result of current changes VCE, Inc. and PMT, Inc. have cooperated in manufacturing a new version of seismograph software. This software allows seismograph users to identify compliance of measured data with the new law. The message of noncompliance will also be displayed on LCD, which will allow fast and effective blasting adjustment throughout the project for the explosive companies.