A Method for Evaluating Exposure to Nitrous Oxides by Application of Lognormal Distribution
A Method for Evaluating Exposure to Nitrous Oxides by Application of Lognormal Distribution: S.S. Borjanovic, et al. Department of Work Physiology, Institute of Occupational Health “Dr Dragomir Karajovic”—A lognormal distribution adequately describes exposure to nitrous oxides in a work environment. The aim of this paper was to assign to the measured data a certain degree of variability which defines the interval in which real concentrations can be found with a given probability. Exposures may be evaluated by using estimates of the geometric mean (GM) and the geometric standard deviation (GSD), i.e. central value and dispersion index, to calculate the confidence interval (Cl) around the mean exposure and compare this interval to the occupational exposure limit. The concentration of nitrous oxides (114 random temporal measurements covering all three shifts, during 6 consecutive days) on coated electrode welding in a car manufacturing plant, was determined with colourimetric direct reading method. Statistical analysis (chi‐square and Kolmogorov‐Smirnov goodness of fit tests, lognormal and Gaussian distribution fitting and Q‐G plots) was performed. The distribution of the nitrous oxides concentration in the work environment studied closely resembled that of lognormal distribution. The geometric mean was 4.098 mg/m3, median 4.00 mg/m3, geometric standard deviation 1.829 and 95% confidence interval 3.66‐4.58 mg/m3. It is possible to apply the computed GSD for evaluation of exposure limits to nitrous oxides in any other work environment, even with only a few measurements.
Balancing cost and precision in exposure assessment studies.
Because of the cost involved both for personnel and laboratory analyses, it is incumbent that industrial hygiene (IH) sampling plans be both precise and cost effective. The purpose of this paper is to describe a method of balancing two opposing objectives, increasing precision and decreasing the cost by manipulating the number and nature of IH sample collections. Data from a pilot study were used to obtain an optimum sampling scheme for exposure assessment. The design that obtains the highest precision while controlling costs serves as the model of choice. An approach is illustrated with data from an ongoing study examining health effects of workers exposed to solvents. It is shown that there is a large variation in precision for identical IH measurements, depending on the efficiency of the sampling schedule.
Improved culture method for the isolation of Histoplasma capsulatum and Blastomyces dermatitidis form contaminated specimens.
Studies were performed to evaluate a method for selective isolation of Histoplasma capsulatum and Blastomyces dermatitidis from contaminated specimens. Ammonium hydroxide placed on an agar medium surface was found to inhibit the growth of many bacteria, yeasts, and saphrophytic fungi normally found in specimens such as animal tissues and sputum. In one study involving the culture of B. dermatitidis from canine tissues, 24% more isolations were obtained on a medium using NH4OH compared with a similar medium. Increases in the isolation of H. capusulatum from sputum specimens were also obtained, ranging from 20 to 32% compared with four other media without NH4OH.