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d. Breathing zone vapor concentrations that reach or exceed 50 ppm at the drilling area, as detected <br /> by the OVA, requires site activities to be stopped until concentrations decrease. Site manager <br /> should continuously monitor site perimeter. <br /> e. If breathing zone vapor concentrations are detected at the site perimeter, the site manager shall <br /> monitor the perimeter at 30 minute intervals.; ; <br /> f If the vapor concentrations continue to reach or exceed a value of 10 ppm at the site perimeter for <br /> 15 minutes, drilling activities shall be stopped Appropriate regulatory agencies should be <br /> contacted (see contact sheet). Site manager.shall continue to monitor conditions until levels are <br /> reduced to background conditions. <br /> TABLE 5-1 <br /> Benzene Exposure Limits <br /> Compound OSTIA-PEL TLV-TWA TLV-STEL ppm REL ppm Odor threshold it Odor Characteristic Mai iimum Sail <br /> PPm Ppm values,ppm Concentration to date,' <br /> PPM <br /> $enzene! 1 10 5 0.1 4.65 aromatic,sweet NA <br /> (Ca) <br /> Toluene. 100 100 150 100# 1.74 sweet,pungent NA <br /> Xylene l Op 100 150 300✓1 0.27 aromatic,sweet NA <br /> PEI. -OSHA Permissible Exposure Limit. <br /> TLV ACGIR Tluvshold Limit Values. <br /> TWA -Time Weighted Average. <br /> STEL -Short Term Exposure Limit. <br /> REL -NIOSH Recommended Exposure Limit <br /> Ca -Suspected carcinogen,1988-89 ACGM TLV. <br /> ii -60 minute ceiling,10 hour TWA,200 ppm 10 minute ceiling. <br /> r <br /> j <br /> F <br />