A gas and vapor generation system with programmed automatic cyclic output.

This paper describes a gas and vapor generation system that can be programmed to produce contaminant concentrations that are variable with time and that are repeatable. The system utilizes an electromechanical programmer designed to vary a potentiometer in accordance with variations in a program curve manually etched in the surface of a special program card. The output of this programmer is interfaced with a linear mass flow controller which will control either the contaminant stream or the dilution air stream to achieve the desired range of contaminant concentrations. The results of some experiments with carbon monoxide and toluene show repeatability of one to three percent for periodically repeated cycles, and demonstrate the flexibility of the system.

On-site screening for benzene in complex environments.

A technique is described for on-site screening of workplace atmospheres for benzene in the presence of many potentially interfering substances. The technique allows benzene monitoring with reasonable specificity at the part per million (ppm) level in confined spaces. A commercially available portable gas chromatograph (GC), shown in the laboratory to be capable of resolving benzene from a complex mixture of hydrocarbons, was compared in the field with other portable GCs, sorbent tube samples, and detector tubes. During three field evaluations samples were collected in Tedlar bags, which allowed replicate, on-site analyses by up to three portable gas chromatographs and three types of detector tubes. Additionally, replicate samples were collected from each bag onto charcoal tubes for subsequent laboratory analysis by capillary column flame ionization gas chromatography and by gas chromatography/mass spectrometry. The portable GCs resolved samples to the extent that an integratable response with the retention time of benzene was seen. In some samples this response was not due solely to the presence of benzene, but such instances would overestimate the concentration and provide a more conservative result. The portable GCs had a total analysis time of less than 10 minutes and detected concentrations of benzene below the Occupational Safety and Health Administration's permissible exposure limit of 1 ppm (in most samples, below 0.1 ppm, although the limit of quantitation was matrix dependent). While benzene concentration measurements using detector tubes were less precise, they agreed in almost every instance with the other techniques regarding whether the space was within the 1 ppm "safe for entry" concentration.

A comparison of four personal sampling methods for the determination of mercury vapor.

Four sampling and analytical methods for mercury vapor were compared to each other in terms of precision and accuracy. The four sampling medias used were the 3M passive Mercury Vapor Monitor, the Los Alamos tandem sampling tube, the hopcalite tube, and the iodine impregnated charcoal tube. Six samples from each method were collected at nominal mercury concentrations of 0.05, 0.1, and 0.2 mg/m3. The hopcalite and 3M monitors gave comparable results at all three concentrations while the Los Alamos method gave similar results at the two highest concentrations. The iodine charcoal tube method was the only one exhibiting poor precision when tube loadings were less than 3 micrograms of mercury.