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vti <br />~ O <br />Citizen Interests <br />This, amongst other things, at least tells us that the Bureau <br />of Mines research personnel experienced considerable difficulty <br />quantifying and qualifying blast vibration damage! lfiat sort of <br />difficulty caill the layman have when attempting to detetnine if he <br />has suffered blast damage? <br />First, he will have to have been considerably startled or <br />disturbed by the high level of the vibration, if he eras there to <br />observe it. If he was, a*~d he actually observed damage occur, then <br />he trill have no doubts at all,.and will be .able to testify quite <br />confidently. <br />Secondly, he will have to look for srall, almost hairline <br />cracks that are fresh, without dust, spider webs, insect detritus <br />or paint inside [hem. Small fallen flakes of paint or plaster will <br />be an indication, as will be the widening of existing cracks. One <br />problem in determining whether an existing crack has widened, of <br />course, derives from whether its original dimension was either <br />!mown or recorded. Imagination can cause cracks to widen, <br />especially if the observer is distressed. <br />Thirdly, he may observe cracks in the jointing paper covering <br />the separations between gypsum wall and ceiling panels. Again, he <br />should make sure that these are in fact fresh, for many such shall <br />imperfections can pass unnoticed for years until [he householder <br />fears that blasting may be harming his house, and he starts looking <br />for signs of damage. <br />Many of these small cracks will typically run from the corners <br />of openings such as doors or windows, or follow separations between <br />building elements. Outside brickwork cracks, normally in the mortaz. <br />between the bricks, will also follow the same pattern; running fran <br />the corners of openings, and also from lintel tops, or below sills. <br />A "stairstep" crack is quite typical in brickwork, though a <br />stairstep crack Hauling diagonally from ground level neaz a corner <br />to the wall corner above ground level, very often indicates <br />settlement rather than blast damage. <br />Concrete, pazticulazly reinforced concrete, is very resistant <br />to blast vibration damage. Cracks will not nott~ally appear in <br />concrete below perhaps 10.0 inches per second, a velocity that is <br />not only faz higher than OSMRE regulations permit, but that would <br />normally cause undisputed and quite extensive cracks to occur to <br />plaster, gypsum>boazd and brickwork. I>amage to concrete is therefore <br />normally accompanied no[ only by erceptionally high velocities, but <br />also by other, and obvious damage. _ <br />i:henever the citizen stLSpects, therefore, that his home is <br />suffering from the effects of excessive blast vibrations, he should <br />without delay carefully and thoroughly inspect the whole structw:e <br />- or engage an expert to inspect it - or, within the [eras of the <br />OSMRE regulations and the comments on page 10 of this manual, <br />