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P f <br /> AIR MONITORING <br /> The Safety Coordinator/Project Manager will conduct periodic air <br /> monitoring using direct reading sampling equipment as required. <br /> At a minimum the following monitoring will be performed. <br /> A) Combustible Gases and Vapors <br /> Potentially explosive concentrations of gases and vapors <br /> will be monitored at least once every 15 minutes during <br /> sampling activities using a combustible gas meter. If at <br /> any time the concentration exceeds 20$ of the lower <br /> explosive limit (LEL), activities will stop and the area <br /> will be evacuated until gas levels have been reduced to less <br /> than 20% of the LEL and the source of combustible gases or <br /> vapors has been determined. <br /> B) Total Organic Vapors <br /> A direct reading photoionization detection ( PID) meter (HNU <br /> PI 101 or equivalent ) will be used to monitor the <br /> concentrations of organic vapors in the work area. <br /> Measurements will be taken at least once every 15 minutes <br /> during surface and subsurface sample collection. The meter <br /> will be calibrated with isobutylene. Total organic vapor <br /> measurements will be used to determine the appropriate <br /> levels of respiratory protection and conditions for site <br /> evacuation. Total organic vapor concentrations in the <br /> workers breathing zone in excess of 10 ppm above background <br /> will trigger sampling for benzene with a direct reading <br /> colormetric tube. Breathing zone concentrations of total <br /> hydrocarbons in excess of 500 ppm will stop the work on-site <br /> until the work zone concentrations are reduced to below 500 <br /> ppm. <br /> C) RESPIRATORY PROTECTION <br /> If total organic vapors exceed 10 ppm additional sampling <br /> for benzene will be performed using direct reading <br /> colormetric tubes. If benzene concentrations exceed 10 ppm, <br /> personal protection will be increased to Level C. <br />