Passive monitors

Personal monitoring devices (sometimes referred to as "dosimeters") are carried or worn by individuals and are used to measure that individual s exposure to particular chemical(s). Devices that include a pump are called "active" monitors devices that do not include a pump are called "passive" monitors. Such devices are currently used for research purposes. It is possible that sometime in the future they may also be helpful in lAQ investigations in public and commercial buildings. 

An automatic control system is often introduced because it appears to do a job better than the human. However, the human is still asked to monitor its effectiveness. It is difficult to see how the worker can be expected to check in real time that the automatic control system is, for example, using the correct rules when making decisions. It is well known that humans are very poor at passive monitoring tasks where they are required to detect and respond to infrequent signals. These situations, called vigilance tasks, have been studied extensively by applied psychologists (see Warm, 1984). On the basis of this research, it is unlikely that people will be effective in the role of purely monitoring an automated system. 

Human dose comparisons utilizing biomonitoring and passive monitoring of an exposure environment following surface treatment with an insecticide... 

Ambient air may also be collected on adsorbent traps (Krost et al. 1982 Oliver et al. 1996) or in stainless steel canisters (Anlauf et al. 1985 EPA 1988 McLaren et al. 1996). Detection limits, where reported, are in the low ppb to low parts per trillion (ppt) range (Anlauf et al. 1985 McLaren et al. 1996 Oliver et al. 1996). Recovery of 75-98% (for all compounds tested) has been reported for collection on Tenax adsorbent (Krost et al. 1982). Passive monitors are utilized for ambient air and indoor air (Cao and Hewitt 1993 Fellin and Otson 1994 Otson et al. 1994). Detection limits in the low ppb range have been reported (Otson et al. 1994). 

Petty, J.D. and Orazio, C.E. 1996, Application of Semipermeable Membrane Devices (SPMDs) Ay Passive Monitors of the Environment of Antarctica. USGS, Midwest Science Center, Columbia, MO Unpublished report to National Science Foundation Washington, DC. 

All passive monitoring devices operate on the basis of diffusive transfer, regardless of whether they are classified as diffusion, permeation or unclassified (e.g., SPMDs), and the rate-limiting barrier is the step with the greatest resistance to mass transfer (see Figure 3.1). Pick s first law is the fundamental law of diffusion. It states that the flux of a chemical in the x-direction (j , e.g., ng cm d ) is proportional to the concentration gradient (9C/9x)... 

Philip West (4) reviewed the status of passive monitors for toxins such as chlorine, S02, vinyl chloride, alkyl lead, benzene, H2S and HCN. Dr. West predicts a bright future for passive monitors. He points out the disadvantages of active monitors and the merits of passive devices. In my opinion, we need more information on precision and accuracy in sophisticated validation studies before we let our hopes rise too high. 

As we move toward passive monitors, validation protocols must also include extensive examination of such factors as face velocity and variable concentration, especially where short spikes occur. 

West, P. W., "Passive Monitoring of Personal Exposures to Gaseous Toxins," Amer. Lab., July 1980, p. 35. 

These research efforts have resulted in many sampling and analytical methods for determining workplace exposures to toxic substances. However, there are still many substances for which no suitable methods exist. Much of the information and developmental protocols used in this study can be applied to future studies on these and other substances. In addition, some of the sorbents used for sampling may be directly extendable to passive monitor sampling. There is still a great deal to learn in the area of sorption and sample collection. 

Groundwater Relatively passive Monitoring difficulties LNAPL/DNAPL present... 

An automated data collection system (DCS) of approximately 6(XX) channels continuously records the readings of the various sensors on an hourly basis. The DCS scans and records the readings of temperature, humidity, pressure, MPBXs, strain gages, convergence monitors, and current and voltage for heater power. The measurements made by the DCS are referred to as passive monitoring. Other measurements such as ERT, neutron logging, GPR, acoustic emissions, REKA probe, and others are made periodically (every few weeks to few... 

Evans, P. R., Horstman, S. W. Desorption Efficiency Determination Methods for Styrene Using Charcoal Tubes and Passive Monitors, Am. Ind. Hyg. Assoc. J. 42, 471 (1981)... 

Sefton, M. V., Mastracci, E. L., Mann, J. L. Rubber Disc Passive Monitor for Benzene Dosimeter, Anal. Chem. 53, 458 (1981)... 

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