A Liquid Crystal-Based Passive Badge for Personal Monitoring of Exposure to Hydrogen Sulfide

Abstract

A new liquid crystal (LC)-based passive dosimeter badge for personal monitoring of exposure to hydrogen sulfide (H₂S) gas is reported. When a thin film of LC supported on a surface functionalized with lead perchlorate Pb(ClO₄)₂ (the LC sensor) is exposed to H₂S, the orientation of LC molecules in the film changes from perpendicular to parallel. This reorientation induces a change in the appearance of the LC film when viewed between crossed polarizers. A H₂S dosimeter was fabricated by pairing a LC sensor with a glass substrate forming a headspace between the two surfaces, to control diffusion of H₂S across the LC film. When the dosimeter is exposed to H₂S, a bright front appears as a function of exposure time. An algorithm has been developed to correlate this response length and exposure dose. The dosimeters are functionally stable when subjected to extreme temperature and humidity fluctuations, and are immune to a number of potentially interfering chemicals, except mercaptans. These dosimeters detect H₂S at 0.2 ppm TWA (8 hr) with ±20% overall accuracy. The dosimeters were used to monitor the personal exposure of personnel working in an oil refinery. The TWA concentrations measured by the LC-based dosimeters correlate strongly with the NIOSH 1063 method that uses a sorbent tube and a pump followed by laboratory analysis. Thus, the LC-based dosimeters can provide a sensitive tool for on-site assessment of personal exposure to H₂S in different environments.

Keywords:

• occupational exposure
• TWA
• TLV®
• passive monitoring
• hydrogen sulfide

ACKNOWLEDGMENTS

This work was partially supported by the Department of Defense contract # W911SR-11-C-0025. The authors would like to acknowledge the technical assistance from Darrin Most, Heidi VanTreeck, and Avijit Sen. Authors thank Cindy Kuhlman and Linda S. Coyne of SKC Inc., Eighty Four, Pa, for testing performance of the dosimeters at different face velocities, and Professors Nicholas Abbott (University of Wisconsin-Madison) and Robert Lindquist (University of Alabama-Huntsville) for stimulating discussions.