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

Abstract

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® threshold limit value (TLV®) the ability of these devices to selectively respond to these new lower 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.

Keywords:

• hydrogen sulfide
• petroleum industry
• portable gas monitors
• sulfur dioxide

ACKNOWLEDGMENTS

The authors would like to thank the American Petroleum Institute Industrial Hygiene Task Force for funding this work and for their work in developing the test protocol, and the instrument manufacturers for kindly lending their monitors for testing.