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Confined Spaces Exposure Investigations Challenged by Sensor Interferences (AIHce EXP 2023 OnDemand)

Course Description:
Recorded at AIHce EXP 2023

This session will present two confined space case studies to demonstrate the need to understand capabilities and limitations of sensors related to interferences and cross sensitivities. 1) A near fatal confined space accident occurred on a commercial fishing vessel when a refrigeration failure led to the loss of shrimp that had been treated with sodium metabisulfite to slow spoilage. Two workers who entered the affected hold were overcome by sulfur dioxide derived from the treatment. A detectable yet safe exposure to hydrogen sulfide registered on the monitor used. 2) Firefighters evaluated a confined space atmosphere where entry to a manhole to empty a grease trap resulted in death. The multi-gas meter used by responders detected oxygen deficiency, flammable gas, 3.5 ppm hydrogen sulfide, and 9.5 ppm hydrogen cyanide. Atmosphere characterization efforts erroneously focused on the HCN readings, in spite of knowing hydrogen sulfide sensitivity for the HCN sensor used. Post-incident on-scene gas phase Fourier transform infrared measurements confirmed high carbon dioxide and methane in the space and no HCN. The actions and conditions that led to both accidents will be reviewed, and the effects of interfering contaminants will be explained along with strategies to avoid confusion.

Learning Outcomes:
Upon completion of the session, the participant will be able to:

• Use real-time detection tools for detection of dangerous atmospheres.
• Develop strategies to employ monitors and interpret monitoring results.
• Review manufacturers' information and other resources regarding sensor performance and interferences.
• Determine the whole-air composition of unknown samples using Fourier transform infrared spectroscopy, gas chromatography, and gas chromatography-mass spectrometry.
• Discuss the capabilities and limitations of various laboratory procedures available to determine whole-air composition.

Contact Hours:


Presentation Date:

Bonnie Lockhart
Philip Smith, PhD, CIH, FAIHA
Robert Henderson, MBA