PubMed Health⌕ Search

Biomedical subjects

D W Underhill

Publications and source records attributed to D W Underhill.

9 recordsLinked to original sources
PubMed1993

Basic theory for the diffusive sampling of radon.

From the closed-form solution of the Fickian equation describing the uptake of radon by a diffusive sampler, the following are calculated: 1) the optimal estimate of the time-weighted average radon concentration; 2) the effect of the geometry of the diffusive sampler on performance; 3) the maximum sampling time consistent with a predetermined maximum error in the estimated time-weighted average concentration of radon; and 4) the effects of temperature and pressure on the performance of the sampler. It is shown that the maximum sampling error can be greatly reduced by dividing the adsorbent bed into two layers placed in series and by using a weighted average of the uptakes on the two layers.

Air Pollutants, Radioactive↗
PubMed1987

Calculation of the performance of activated carbon at high relative humidities.

The Dubinin-Radushkevich potential theory was extended to include a term giving the effect of relative humidity on the uptake of adsorbate. This extended equation permits the adsorptive capacity of the activated charcoal in a respirator cartridge to be estimated for any combination of temperature, relative humidity, and concentration of contaminant. Application of this theory to previously published data of Werner showed a good correlation between theory and experiment. This equation is consistent with the experimental observations that 1) below a certain value, the relative humidity has little effect on the uptake of adsorbate, and 2) the effect of relative humidity, if observed, is more severe for lower than for higher concentrations of contaminant.

Adsorption↗
PubMed1984

Efficiency of passive sampling by adsorbents.

The efficiency of passive samplers can be influenced strongly by the adsorption isotherm. In this study calculations of sampling efficiency were made in terms of dimensionless variables for adsorption controlled by the Langmuir, Freundlich, and Dubinin-Radushkevich isotherms, respectively. Of particular importance is that for the latter isotherm, which is often followed by activated charcoal for the adsorption of solvent vapors, passive sampling may remain highly efficient until a significant fraction of the capacity of the adsorbent has been utilized.

Adsorption↗
PubMed1979

A critique of the U.S. standard for industrial exposure to sodium hydroxide aerosols.

Published studies of the toxicity of sodium hydroxide aerosols are few. These studies were generally marred by inadequate characterization of particle size and chemical compositon and of the ambient humidity. Because NaOH aerosols can readily undergo reaction with carbon dioxide to form sodium carbonate, a much less alkaline (and less hygroscopic) compound, these shortcomings may warrant a reconsideration of the NaOH standard and the consideration of a Na2CO3 standard.

Aerosols↗
PubMed1978

Respiratory response of guinea pigs to ozone alone and with sulfur dioxide.

This study was designed to utilize our guinea pig bioassay method for irritant response to address the question of whether or not ozone and sulfur dioxide appeared to react to form sulfuric acid in the respiratory tract. Animals were exposed to 0.2, 0.4, and 0.8 ppm of each gas alone and to the combination at concentrations of 0.4 and 0.8 ppm. In these experiments sulfur dioxide alone produced no statistically significant alterations in respiration. All concentrations of ozone produced an increase in respiratory frequency. At the two higher concentrations the increase in frequency was accompanied by a decrease in compliance. The response to the combinations was the same as the response to those levels of ozone alone. No sulfuric acid was detected in the chamber atmosphere. The biological data suggest that none was formed in the lung.

Animals↗