Although the blast site the committee toured was a coal mine, the committee is studying the effects of all types of blasting, both on coal mines and elsewhere. The regulations make some distinctions between frequencies but generally speaking, an airblast of more than 129 decibels is prohibited. In addition to being annoying, air blast can break windows. Ground vibration is measured in inches per second. That is how fast the ground is moving at the point of measurement.
Ground vibration breaks plaster, sinks wells, etc.
There is some dispute over what level of ground vibration is acceptable. When the Office of Surface Mining did regulations in the late 1970's, it commissioned studies, hired experts, etc. More recent research indicates that structures respond differently to vibration depending upon their construction and upon the frequency of the blast vibration. If the goal were to protect each structure, then the blast design would be site specific depending upon the construction of the structures in the vicinity. In one wanted to avoid doing site specific design, then one could limit vibration to .5 inch per second.