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1 <br /> 3.3 CALIBRATION <br /> CGIs are calibrated at the altitude that the testing will be performed using a calibration gas, <br /> usually pentane, methane, or hexane furnished by the manufacturer The instrument is "warmed up" <br /> ' and the zero control is adjusted to read 0 percent LEL on the meter The calibration gas is <br /> introduced into the sensor opening following the manufacturer's instructions The span control for <br /> ' the meter reading is adjusted, if necessary, to indicate the correct percent LEL for the calibration gas <br /> used <br /> 4.0 TOXIC ATMOSPHERES <br /> Airborne toxic contaminants can present a significant threat to worker health and safety <br /> Thus, identification and quantification of these contaminants through air monitoring is an essential <br /> component of a health and safety program at hazardous waste sites Reliable measurements of <br /> ' airborne toxic contaminants are useful for <br /> 0 Selecting personal protective equipment for (PPE) initial site entries <br /> • Delineating areas where personal protective equipment is needed on a continuing basis <br /> t • Making decisions on upgrading or downgrading the personal level of protection as work <br /> conditions change, <br /> • Assessing the potential health effects of exposure, and <br /> • Determining the need for specific medical surveillance tests and procedures <br /> 1 Initial air monitoring for identification of toxic air contaminants is usually qualitative (i e , the <br /> contaminant, or the class to which it belongs, is demonstrated to be present but the determination of <br /> ' its concentration (quantification) must await subsequent testing) Two principal approaches are <br /> available for identifying and/or quantifying airborne toxic contaminants the on-site use of direct- <br /> reading instruments, and laboratory analysis of air samples obtained by air sampling filter, sorbent, <br /> sampling bag, or wet-contaminant collection methods Direct reading instruments are used the most <br /> ' for "routine" work at hazardous waste sites <br /> O - 6 <br />