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' the peak can be made very narrow by varying the instrumental conditions, component concentration is <br /> proportional to peak height, that can be read directly off the chart <br /> 4.2,3 Limitations <br /> 1 <br /> As with the HNU, the use of the OVA in the survey mode is strictly qualitative The OVA is <br /> ' sensitive to many organic and inorganic vapors and gases and cannot be used as a quantitative <br /> measuring instrument in unknown situations It measures total organic vapors and gases in ppm It is <br /> ' strictly qualitative, except when the nature of the contamination is known, and the instrument has <br /> been calibrated to, or a calibration curve has been generated for, the contaminant being measured <br /> t <br /> In addition, the unit requires an individual trained specifically to maintain and operate it For <br /> ' use in the gas chromatography mode, specific experience in gas chromatography is essential Since <br /> the instrument is factory calibrated to methane, all relative responses are given in percent, with <br /> ' methane at 100 <br /> Table at the end of this attachment contains a list, provided by the manufacturer, of the <br /> relative sensitivities of the OVA to some common organic compounds <br /> ' 4.3 OTHER GAS SAMPLERS AND MONITORS <br /> ' There are several other gas samplers and monitors that utilize electrochemical cells for <br /> detection CO, H2S, and hydrogen cyanide (HCN) are three gases of interest The principle is <br /> ' similar to the 02 meter previously described Monitors of this type are typically adjusted to sound an <br /> alarm when a particular contaminant level is reached <br /> Probably the newest detector available is the Mixed Oxide Semi-Conductor (MOS) It can be <br /> ' calibrated to a variety of gases including chlorine, trichloroethene (TCE), NH, nitrogen dioxide <br /> (NO2), freon, and toluene It can be used in multiple detection units incorporating several MOS <br /> ' detectors and an 02 cell <br /> 0 - 14 <br />