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<br />3E?-20-98 SUN 1938 John F P,bel 1r <br />FAK N0. Feu a an e.aoaM, <br />303?7.98163 Gage ;,is <br />P, 06 <br />"D° Seem/boar Cr~~k Impact Page 6 September 21, 1998 <br />• Figure 1. Collapse chimney height above room and pillar workings <br />in the !'ittsburgli Seam (Gray, et al, 1977). <br />100 <br />Cumufatfve percent of chimney collapse height <br />(Gray, Bruhn and Turka, 1977) <br />90 <br />80 <br />.., <br />W <br />g ~o <br />W <br />OG <br />~ 80 <br />Z <br />• ~ 50 <br />a <br />> ~ <br />g <br />= 30 <br />V <br />20 <br />10 <br />0 <br />o so 100 1so zoo <br />HEIGHT OF CHIMNEY COLLAPSE (feet) <br />