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l <br /> Field monitoring instruments are available that combine measuring functions into one <br /> instrument by combining two or more detectors Possible combinations include combustible gas and <br /> Oxygen 2, combustible gas, 02, and carbon dioxide, combustible gas, 02, and H2S hydrogen sulfate), <br /> and combustible gas, 02i H2S, and CO They may be equipped with an audible and/or visual <br /> alarm(s), that can be preset at a selected concentration level of concern The combined detectors use <br /> a common pump, battery, and electronic circuit Normally, each detector operates independently, <br /> thereby allowing one to be used even if the other is not working properly <br /> Combination units afford response personnel several advantages over single units, the chief <br /> among these being portability Additionally, combined instruments may incorporate an adjustable <br /> alarm circuit that alerts the user to potentially hazardous conditions This capacity frees the user of <br /> the need to take frequent meter readings and focuses attention on other hazards <br /> 2.0 OXYGEN-DEFICIENT ATMOSPHERES <br /> The oxygen content in a confined space is of prime concern to anyone about to enter that <br /> -,� space Removal of oxygen by combustion, reduction reactions, or displacement by gases or vapors is <br /> a hazard that hazardous waste on-site workers and emergency response personnel cannot detect <br /> Consequently, remote measurements must be made before anyone enters a confined space <br /> Portable oxygen indicators are invaluable when responding to emergencies at hazardous waste <br /> sites Terrain variations, unventilated rooms or areas, and confined spaces may or may not contain <br /> sufficient oxygen to support life In addition, oxygen measurements are necessary when Combustible <br /> gas indicator CGI measurements are made, since the oxygen level in the ambient air effects the <br /> accuracy of CGI's readout When used properly, the portable oxygen indicator will read the percent <br /> oxygen in the immediate atmosphere The normal ambient oxygen concentration is 20 8 percent by <br /> volume <br /> l <br /> Most indicators have meters that display the oxygen content from 0 to 25 percent There are <br /> also oxygen indicators available that measure concentration from 0 to 25 percent and 0 to 100 <br /> percent The most useful range for response is the 0 to 25 percent oxygen content readout since <br /> decisions involving air-supplying respirators and the use of combustible indicators fall into this range <br /> 1I O - 2 <br /> I <br /> l <br />