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6.3 ACTION LEVELS <br /> Action levels for upgrade and d downgrade of respiratory protection/PPE <br /> fiLevel Action Taken <br /> Workers in support zone Level D PPE <br /> Workers within l0 feet of Level D PPE <br /> drill rig <br /> Breathing zone OVA readings Level C_PPE <br /> > .50 ppm. <br /> Perimeter zone OVA readings Respiratory protection required f <br /> >25 ppm <br /> Rationale for upgrade/downgrade m ' <br /> atrix: <br /> The decision to upgrade to Level C protection at 50 m OVA readings is based on PEL for <br /> Pg P PP g <br /> r gasoline vapors. This action level is based on the assumption that total petroleum.hydrocarbons <br /> l.� <br /> potentially located below ground surface would approximate toxicity levels for gasoline. <br /> i <br /> TETRA TECH: HEALTH AND SAFETY PLAN PAGE 12 <br />