PHA Guidance for Correlating H2S Concentrations in Process Streams to Severity of Adverse Health Outcomes in the Event of a Leak

Abstract

Process hazard analysis (PHA) teams are responsible for determining and categorizing the potential impact of a loss of containment. For streams containing hydrogen sulfide (H2S), the health and safety consequences of a worker being exposed to H2S are a function of airborne concentration in the breathing zone and duration of exposure. PHA teams often do not have the technical knowledge to link the known concentration of H2S in the process stream to an adverse health outcome. This paper describes the methodology and the assumptions made in developing such guidance. H2S concentration in the stream was correlated to concentration of H2S in the breathing zone. Vapor releases used dispersion modeling, while liquid releases required additional modeling to determine the amount of H2S liberated from the released liquid. Modeling was done on different process streams under a variety of conditions. Concentration in the breathing zone was linked to the most probable health and safety outcome by surveying relevant literature published by private and government sources. This correlated the stream concentration of H2S directly to the consequence categorization used in the PHA. Results were summarized, providing simplified guidance that is valid over a wide range of process conditions and release scenarios.