ENFORCE24971 - Laserfiche WebLink

Home Browse Search

0 0 ~~ I PERCEP/ID BLAST PIBRATION EFFECTS f Thus far in this chapter vibration intensities have been referred to, unavoidably, in terms of "particle velocity". Normally, when a member of the wblic hears soneone - mine operator, government official or consultant - speak of vibrations in unintelligible language - "point six five inches per second" - he cannot help but consider that it is just so much "gobbledygook" '~ and that perhaps the "experts" are even trying to hide things from him. Why can't they speak in terms that everyone understands? Unfortunately, no-one has Bret invented terms for this rather ~~ specialized field that everyone does understand. ' What can be done in this chapter, however, that may at least alleviate this problem, is to discuss in simple everyday terms the ~ way that hurian beings feel or perceive blasting vibrations. First, there is no doubt at all that some people can feel 1 vibrations alnost as low as instrwnents can measure them. It is j often commented that human senses are very dull compared to those of animals, [hough it is not often realized how keen in fact some of these human senses are! The sense of touch, for instance. Stretch a human hair across a smooth surface, or overlap two thin sheets of paper, and run a finger across, and few people will have any problem at all in feeling just two or three thouvandths of an J inch! Although many people Chese days -especially the young - have reduced hearing ability, the tnaian body as a whole' is astonishingly sensitive to ground vibrations. Levels can be felt that present absolutely no danger at all to structures. In fact, houses are vibrating much of :the tine to one extent or another. People, particularly heavy ones, or active children, generate motion that J at times approaches - of even exceeds - the limits set by OSMRE. Climbing or descending stairs, jumping, door slamming or even just walking across a floor can cause considerable notion in a structure. The fact is that when people themselves are in motion, l they do not notice any novement in the structure of their homes. So how do most people react to, and actually feel blast vibrations? The most obvious effect is usually the airblast. Since ' it does not always contain frequencies that humans can best hear, jn it is not alwavs a very loud event. It is usually perceived as anything from a dull thu~p to a loud ba:cg. A loud bang is not always a "high" airblast, and conversely, a dull thin may in-fact be one. It might even be inaudible! The house may well react, or ' respond, the structure may creak, the windows may rattle, and, if a person is not expecting it, it may be quite startling. It is most !.l unlikely ever to cause damage. 115 ~~