Document mm2XB99Vzv2N7pGYdkZYG0qVO

nEU) DESICn IDERS Organic vapor concentrations recorded by badge Monitoring device acts as sample container Brian J Hogan, Midwest Editor Worn near breathing zone, organic vapor monitor is first such unit that does not require analyst to handle active medium in multiple-step operation. Carbon layer is never touched during analysis. Patented elutriation cap hermetically seals monitor. Note ports for introducing and removing solvent that desorbs contaminants. St. Paul, MN--Airborne concentrations of organic vapors are recorded by adsorbing their molecules upon a layer of carbon. That active medium rests within a housing made from a proprietary, impermeable, solvent-resistant polymer. A microporous front shield on the housing admits air and organic molecules to the monitor, and creates a layer of placid air and organic molecules between the shield and the active medium. Molecules diffuse from the shield to the 0.015-inch-thick carbon layer. The carbon adsorbs the organics, creating a zone (near the carbon) that's starved of organic molecules. Thus, as more organics enter, they flow down a concentration gradient from the shield to the carbon layer. Molecules inside the sampler travel at approximately one mile/second, but each experiences about 100 billion collisions/second. Thus, a molecule's trip from the front of the monitor to the carbon layer takes about 2 seconds. Mechanical engineers John A. Trine and David L. Braun of 3M's Occupational Health and Safety Products Div. worked together to design that firm's new Model 3500 Organic Vapor Monitor, This diffusion-type device measures the Time-Weighted-Average (TWA) exposure of personnel to organic vapors. Carbon tubes and battery-operated pumps have been used previously to monitor organic vapors. But the 3M unit is small (2.5 inches OD) and can be clipped to a collar near one's breathing zone. Also, when your shift ends, you don't need to remove the carbon for analysis 3M 100535 R-DN AR(90.25)R 1 of adsorbed organics. Instead, you snap over the monitor something called an elutriation cap. This cap hermetically seals the sample. You write the total exposure time on the unit's shell. To measure your exposure to. for example, benzene, analysts at 3M (or vour company lab) inject a premeasured amount of solvent (eluent)--usually car bon disulfide--into the monitor through one of two ports on the cap. After a half hour, eluent is decanted through a second port into a vial, and it's analyzed by using a gas chromatograph. The active medium will adsorb organic molecules until it loads up completely and few or no adsorption sites are available. The capacity of the sampler varies tor different organic compounds, and is specified as the "upper exposure limit" of each compound. That number is related to the weight of contaminant collected when significant deviation from linear adsorption is seen. It's generally 15 mg for strongly adsorbing materials. Some compounds do not adsorb well to carbon or won't desorb. Obviously, the monitor can't be used to measure exposure to such substances. Diffusion-type samplers require a slight air movement across or impinging upon the front shield. In stagnant air, the supply of contaminant is adsorbed from the placid zone beneath the shield, and not renewed. Thus, the concentration of organic recorded is slightly low. On the other hand, the device will function effectively in all normally ventilated indoor environments and also outdoors in moderate winds. Results of Gasoline Exposure Test Components Test 3M NO. 3500 Charcoal Tube of Concentration Concentration Concentration Gasoline (PPM) (PPM + 2o) (PPM 2o) Pentane Heptane Octane Benzene Toluene Xylenes 5.602 0.573 0.294 0.928 1.768 1.153 5.832 + 0.408 0.570 0.045 0.307 0.047 0.892 0.160 1.710 0.119 1.230 + 0.086 5.053 0.500 0.578 0.082 0.329 0.056 0.873 0.180 1.552 0.220 1.034 0.160 Diffusion-type monitor samples complex hydrocarbon mixtures; it traced concentrations of components of gasoline in test. Each vapor is sampled as if it were present individually. Typical Monitorable Compounds Acetone Acrylonitrile Benzene Carbon Tetrachloride Chloroform Heptane Methyl Ethyl Ketone Styrene Toluene Trichlorethane Vinyl Chloride m-xylene Typical Unsuitable Compounds Carbon Monoxide Hydrogen Sulfide Ethylene Oxide Methyl Alcohol Methyl Chloride Sulfur Dioxide Formaldahyde Isocyanates Typical monitorable and typical unsuitable compounds. Reprinted from DESIGN NEWS March 24, 1980 1980 CAHNERS PUBLISHING COMPANY 3M 100536 Litho in U.S.A