Gary O. Nelson

Respirator cartridge efficiency studies. V. Effect of solvent vapor.

We have determined the service lives of organic vapor respirator cartridges for 121 solvent vapors and gases including aromatics, alcohols, acetates, alkanes, ketones, amines, and chlorinated materials. We passed the vapor and air mixtures through the cartridges and monitored the downstream concentration with a flame ionization detector (FID). Monitoring continues until the cartridge is completely saturated. We compared breakthrough times to values calculated from the adsorption isotherm and Mecklenburg equation and obtained reasonable agreement. In general, the activated carbon has greater affinity for the less volatile materials. Also, the higher the boiling point of the solvent, the greater is the weight of solvent adsorbed. Water vapor, in general, decreases the amount of solvent vapor adsorbed, especially of the more volatile solvents and those soluble in water. The effect of concentration on breakthrough time was briefly investigated and found to conform to the basic Freundlich equation.

Respirator cartridge efficiency studies: VII. effect of relative humidity and temperature

Cartridge service life is not appreciably affected at relative humidities below 50%. However, performance is severely compromised when the humidity exceeds 65%. Experimental values are compared from those calculated from the adsorption isotherm, Mecklenburg and modified Wheeler equations. Calculations indicate that temperature does not play a significant role in service life predictions.

Respirator cartridge efficiency studies: VI. effect of concentration

The service life of organic vapor cartridges was determined for ten vapors at concentrations between 50 and 3000 ppm. The breakthrough time (tb) conformed to the empirical expression tb = aCf, where C is the concentration in ppm and a and be are constants. The average value for b at 10% breakthrough was -0.67 +/- 0.17. The service life is inversely proportional to flow rate for acetone and benzene.

Glove permeation by organic solvents

We have tested and measured the vapor penetration of 29 common laboratory solvents on 28 protective gloves using gas-phase, infrared spectrophotometric techniques to determine the permeation characteristics. Five different types of permeation behavior were identified. No one glove offered complete protection against all the solvents tested. The permeation rate of the solvent was found to be inversely proportional to glove thickness for a given manufacturers material. Of two solvent mixtures tested, one exhibited a large, positive, synergistic rate.

Respirator cartridge efficiency studies: VIII. summary and conclusions

The theory of solvent vapor adsorption on activated carbon is reviewed. Calculated and experimental cartridge service life values are compared using various breathing rates, relative humidities, concentrations and solvent vapors. Cartridge service life (the 10% breakthrough time) can be estimated from the emperical expression: t10% = 2.4 × 106Wc(a + bt)/C2/3MQ Carbon weight (wc), relative solvent volatility (a, b and t) concentration (C), molecular weight (M) and breathing rate (Q) all play a vital role in cartridge performance predictions.

Respirator Cartridge Efficiency Studies

A system for determining the breakthrough characteristics of respirator cartridges has been assembled that continuously produces known concentrations of solvent vapor in humidified air. Concentrations from 1 ppm to several percent can be generated in airflows of 20 to 250 liters/min. The humidity can also be selectively adjusted from 1 to 95%. The contaminant gas concentrations on either side of the respirator cartridge are monitored continuously by two flame ionization detectors. Concentrations of several parts per million are routinely detected. The airflow rate, humidity, and gas concentrations are recorded continuously on strip recorders for easy display and comparison of data.

Respirator Cartridge Efficiency Studies IV. Effects of Steady-State and Pulsating Flow

The service life of organic vapor respirator cartridges has been evaluated for steady-state and pulsating flow rates; a mechanical breathing simulator was used to evaluate the pulsating flow rates. Two types of cartridge have been tested at work rates of 0, 208, 415, 622, 830, and 1107 kg-m/min and their equivalent respective steady-state flow rates of 14.0, 20.6, 29.8, 36.9, 53.3, and 71.4 liters/min. Cartridge break-through characteristics were recorded with both types of flow for several solvents at 1000 ppm and 0%, 50%, and 80% relative humidity. No significant differences were observed between the steady-state and pulsating flows, even at the highest work rate and humidity conditions. The effective service life appears to be inversely proportional to the flow rate at a given concentration.

Enhancement of air filtration using electric fields.

Although polarized electrostatic air filters are efficient air filtrating devices, their main disadvantages are difficulty in collecting conductive particles or in operating at relative humidities above 70%. We describe here a new filter design that eliminates these problems. A nonconductive media, normally a glass fiber mat, is placed between two insulated conductive screens. As the voltage across the screens is increased, the penetration of particles decreases exponentially. Increasing the electric field from 0 to 10 kV/cm will decrease the mass penetration from 60% to less than 10% of a polydispersed 0.8 micrometer ammd(sigma g = 2.0) sodium chloride aerosol. The experimental effects of face velocity, particle charge and size, packing density, fiber size, and screen insulation mirror the theoretical effects of these variables on particle penetration.

Permeation of substituted silanes and siloxanes through selected gloves and protective clothing

Testing of the permeation resistance of eight glove and suit barriers against commercially available substituted silanes and siloxanes was performed using the ASTM F739-96 standard test method. In addition to barrier performance to the pure organosilanes, the permeation rates of the hydrolysis product (usually ethanol or methanol) were investigated. The silanes and siloxanes used as the challenge agents were N-2-(aminoethyl)-3-aminopropyltrimethoxysilane; 3-aminopropyltriethoxysilane; 3-chloropropyltrimethoxysilane; ethyltriacetoxysilane; 3-glycidoxypropyltrimethoxysilane; 1,1,1,3,3,3-hexamethyldisilazane; hexamethyldisiloxane; 3-methacryloxypropyltrimethoxysilane; methyltriacetoxysilane (50%)/ethyltriacetoxysilane (50%); methyltrimethoxysilane; methyltris(methylethylketoxime)silane; phenyltrimethoxysilane; polydimethyl siloxanes (PS 340); octamethylcyclotetrasiloxane (D4); tetraethoxysilane; tetramethoxysilane; 1,1,3,3-tetramethyl disiloxane; triethoxysilane; trimethoxysilane; vinyltrimethoxysilane; and vinyltris(methylethylketoxime)silane. Protective gloves tested were nitrile rubber, neoprene rubber, butyl rubber, 4H laminate, and polyvinyl chloride. Garments tested included Tyvek/Saranex 23P, CPF 2, and Responder, all made by Kappler Safety Group. In all cases the protective suit materials lasted 8 hours or more. The only glove that lasted 8 hours against all chemicals was the 4H laminate. The polyvinyl chloride glove lasted 10 min to 8 hours or more depending on the chemical. The nitrile, neoprene, and butyl rubber gloves lasted from 53 min to 8 hours or more depending on the chemical. The alcohol permeation was similar to the organosilicon compounds. The suit materials and the butyl glove all lasted more than 8 hours for both methanol and ethanol.

A Dynamic Method for Mercury Vapor Detector Calibration

Abstract An apparatus has been designed to facilitate the calibration of mercury vapor detectors. Known volumes of pure air, and air saturated with mercury, are mixed and introduced into a Lucite box which houses the meter under study. Calibration points are then obtained by adjusting the mercury vapor and air dilution ratios. Mercury concentrations are checked chemically by collecting the vapor in acidified potassium permanganate and analyzing by a dithizone extraction method.