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Air Monitoring

Air Monitoring. Instructional Goal: Enable participants to recognize the value of direct-reading instruments in providing immediate air concentration results at a hazardous waste site. Sampling Methods. Area sampling

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Air Monitoring

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  1. Air Monitoring Instructional Goal: Enable participants to recognize the value of direct-reading instruments in providing immediate air concentration results at a hazardous waste site.

  2. Sampling Methods • Area sampling • involves placing collection devices within designated areas and operating them over specific periods of time. • Personal sampling • involves collecting samples from within the breathing zone of an individual, sometimes by the individual wearing a sampling device.

  3. Instantaneous Sample • are collected over brief periods of time • grab-type sample • examines stable contaminant concentrations or peak levels of short duration. • require highly sensitive analytical methods due to the small sample volume

  4. Air Monitoring Data is used to • assess health risks • determine location where PPE must be worn and correct PPE to wear • determine actual or potential effects on the environment • select actions to mitigate the hazards • determine the effectiveness of decontamination activities

  5. Sampling System • sampling instrument or system chosen depends on a number of factors: • instrument or system efficiency • operational reliability • ease of use and portability • availability of the instrument and component parts • information or analysis desired • calibration requirements

  6. Air Monitoring Instruments must be • portable and rugged • easy to operate

  7. Air Monitoring Instruments must be Inherently Safe • explosion-proof • intrinsically safe • purged

  8. Air Monitoring Instruments must give Reliable and Useful Results • Response time • is the length of time the monitor takes from when it "senses" a contaminant until it generates data. For direct-reading instruments, response times may range from a few seconds to several minutes.

  9. Air Monitoring Instruments must give Reliable and Useful Results • Sensitivity • defined as the ability of an instrument to accurately measure changes in concentration. Sensitive instruments can detect small changes in concentration. • It is important to use an instrument with an operating range that will measure the ambient concentrations on-site.

  10. Air Monitoring Instruments must give Reliable and Useful Results • Selectivity • the ability of an instrument to detect and measure a specific chemical or group of similar chemicals. • Interferences from other chemicals can affect the accuracy of the instrument reading by producing a similar response.

  11. Air Monitoring Instruments must give Reliable and Useful Results • Accuracy • the relationship between a true value (i.e., the actual concentration of a contaminant) and the instrument reading.

  12. Air Monitoring Instruments must give Reliable and Useful Results • Precision • a statistical measurement of an instrument's ability to reproduce a reading. • When an instrument does not receive routine maintenance the precision of the readings may change (become more random) this can affect the amount of error in the data collected.

  13. BenchCalibration • follow manufacturer’s directions for calibration to ensure accurate field data • use standard sample of known concentration for calibration • adjust the instrument read-out so that it corresponds to the actual concentration

  14. Monitoring Equipment • Direct-Read Instruments • oxygen availability monitor • combustibility monitor • toxic atmosphere monitor • radiation monitor

  15. Oxygen Indicators • 20.8% O2 isnormal air • at and below 19.5% O2 in air, O2 deficient • either displaced by another gas • or consumed by combustion or reaction • > 23% O2 in air, increased risk of combustion (possible oxidizer present)

  16. Combustible Gas Monitor • measures concentration of flammable vapor or gas in air • reads in % Lower Explosion Limit (LEL) • read out is relative to the calibration gas; therefore, may not show actual % of LEL • for use only in normal oxygen atmospheres

  17. Relative Response CGI Meter methane 100% 80% pentane 60% METER READING % LEL 40% xylene 20% 0% 100% 0% 50% ACTUAL % LEL

  18. % LEL Policy • The employer will issue work permits when the % LEL is from 0-10% LEL. • When the LEL exceeds 10%, special approval is required in order for a work permit to be issued. • For all confined space entry permits, a 0% LEL is required.

  19. Toxic Atmosphere Monitors

  20. Colorimetric Indicator Tubes Features glass tube with indicating chemical chemical specific contaminated air pumped in at pre-determined rate Limitations other chemicals may interfere with result poor accuracy and precision affected by temperature and humidity interpretations vary time consuming - 1 to 30 minutes per tube

  21. Photoionization Detector Features Nonspecific gas and vapor detection for organics and some inorganics Sensitivity is related to the ionization potential of compound Portable with remote sensing capabilities Response time of 90% in less than 3 seconds More sensitive to aromatic and unsaturated compounds than the flame ionization detector Limitations Does not monitor for specific gases or vapors Cannot detect Hydrogen cyanide or methane Cannot detect some chlorinated organics High humidity and precipitate will negatively affect meter response Photoionization detectors are calibrated to a single chemical

  22. Flame Ionization Detector Features Nonspecific total hydrocarbon analyzer Most sensitive to saturated hydrocarbons (alkanes), and unsaturated hydrocarbon (alkenes) Portable with remote sensing probe Response time of 90% in 2 seconds Limitations Not suitable for inoganic gases (e.g. chlorine, hydrogen cyanide, ammonia) Less sensitive to unsaturated compounds than PID Can not use in the presence of a flammable gas (ignition source) Substances that contain substituted functional groups (-OH) and (-Cl) reduce the detector's sensitivity

  23. Aerosol Monitors • Solids and liquids can become suspended in air • light scatter detector • piezoelectric crystal mass monitor • beta attenuation • Total particulate amount • Type not determined

  24. Sample Problem Suppose prior analysis has established that the dust at a certain site contains 5 percent lead and 1 percent arsenic. During subsequent monitoring, the concentration of dust is found to be 2mg/m3. (% of each)amount of dust= conc of each 100 present in air X

  25. Answer The concentration of lead and arsenic, therefore, are calculated to be 0.1 mg/m3 and 0.02 mg/m3 respectively: 0.05 x 2 mg/m3 = 0.1 mg/m3 lead 0.01 x 2 mg/m3 = 0.02 mg/m3 arsenic

  26. Combination Instruments • flammable gas and O2 • trimeters • four gas meters

  27. Radiation Monitoring • Alpha • Proportion Counters • Scintillation Counters • Beta and Gamma • Geiger-Mueller Counters

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