Wednesday, April 22, 2009

Evaluation of Portable Mercury Vapor Monitors and Their Response to a Range of Simulated Oil Processing Environments

K.J. Grice, L.D. Van Orman, and L.A. Young, Chevron Energy Technology Company, and C.R. Manning, Assay Technology, Inc.
copyright 2008, Society of Petroleum Engineers

Portable mercury vapor monitors are relied on for quick decision making to determine safe work practice requirements. There is little specific information regarding their use limitations and/or potential interference data, especially in environments of high temperature/humidity and various concentrations of hydrocarbons (HC) and inorganic gases, as are commonly found in oil processing environments. This work was undertaken to objectively assess the accuracy of each monitor under ideal conditions and then assess the effects of potentially interfering conditions or substances on monitor accuracy. This data was used to highlight specific limitations and create field user guides.

A secondary objective was to compare the overall usability and user-friendliness of the monitors evaluated. The paper describes the experimental method used and results provided by several mercury vapor monitors exposed to known concentrations of mercury vapor while other variables such as temperature, relative humidity and the concentration of potentially interfering compounds were varied to simulate field measurement conditions. Two types of detection technology were assessed, Gold Film resistance and Cold Vapor Atomic Absorption, (CVAAS). All monitors were tested against a variety of potential interference compounds, e.g., organics, benzene, toluene, and inorganics, ammonia, sulfur dioxide, nitrogen dioxide and hydrogen sulfide. The testing revealed several strengths and weaknesses for each monitor. Negative interference was found with the Gold Film unit in high relative humidity (RH). All CVAA units showed positive interference with high organic concentrations. Poor repeatability across the entire exposure range is common. Survey technicians need to become familiar with the specific limitations of the survey meter used to accurately assess the work environment where mercury (Hg) vapors are present. READ MORE

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