Evaluation of Portable Single-Gas Monitors for the Detection of Low Levels of Hydrogen Sulfide and Sulfur Dioxide in Petroleum Industry Environments

Many portable single-gas monitors are used for the detection of low concentrations of hydrogen sulfide (H2S) and sulfur dioxide (SO2) in the workplace. With the recent lowering of the H2S and SO2 ACGIH (R) threshold limit value (TLV (R)) the ability of these devices to selectively respond to these newlower levels is not well documented in petroleum industry environments, which often have potential interfering gases and vapors present as well as varying environmental conditions. Tests were carried out to measure the ability of various monitors with their respective sensors to correctly quantify and respond to H2S and SO2 in a simulated petroleum industry environment. This included the identification of selected interference effects and estimation of the reliable lower limit of detection for real workplace environments. None of the H2S monitors responded at 0.1 times the new TLV (0.1 ppm), only some of them responded at the new TLV concentration (1 ppm), and all the monitors exposed to five times the new TLV (5 ppm) responded with reasonable accuracy. There was generally little effect of interferent gases and vapors on the H2S monitors. None of the SO2 monitors responded at 0.1 and 1 times the new TLV (0.025 ppm and 0.25 ppm) concentrations, and all but one of them exposed to five times the new TLV (1.25 ppm) responded. There was much greater cross-sensitivity to interferents at the tested concentrations with the SO2 monitors, which responded to six out of eight of the interferents tested. Results demonstrate that these monitors cannot reliably alarm and measure H2S or SO2 concentrations at the new TLVs with an acceptable degree of accuracy. However, these monitors are designed to alarm as a safety device; these results do not change this important function.