National Institute for Occupational Safety and Health

“ The working range is 0.6 to 14 ppm (0.9 to 20 mg/m 3) for a 20-L air sample [1] . The method is applicable to 15-min samples taken at 1 L/min and 10-min samples taken at 1.5 L/min. The upper limit of loading depends on the concentrations of hydrogen sulfide and other substances in the air, including water vapor. High relative humidity (80%) increases the capacity of the sampler four-fold, relative to dry air. Some lots of charcoal have excessively high sulfur backgroun ds and/or poor desorption efficiencies; therefore, screening of each lot should be done before field use. ”

“ Recoveries, based on mass of H 2S found on samples analyzed on day 1, were 97.2% for ambient storage and 98.9% for refrigerated storage. The overall method for H 2S has a limit of detection of 11 μg per sample and a limit of quantitation of 17 μg per sample. A mean bias of -0.17% was determined from the recoveries of six samples generated at each of four concentration levels (0.1, 0.5, 1 and 2 x PEL) with a precision ( Sr) of 0.031. ”

“ Prepare fresh working standards biweekly. b. Analyze together with samples and blanks (steps 14 and 15) . c. Prepare calibration graph (peak height vs. μg SO 24- per sample) . 11. Determine desorption efficiency (DE) at least once for each lot of charcoal used for sampling in the calibration range (step 10) . Prepare four tubes at each of three levels plus three media blanks. a. Generate concentrations of H 2S from a calibration gas mixture or a permeation device. Mix with dilution air as necessary. b. Collect samples at a flow rate of 1 L/min for 30 min. ”