Avoiding Exposure to Mercury During Inspection and Maintenance Operations in Oil and Gas Processing
Wilhelm, S. M., "Avoiding Exposure to Mercury During Inspection and Maintenance Operations in Oil and Gas Processing", Process Safety Progress, Fall (1999).
ABSTRACT
Exposure to mercury and its compounds poses a potential health risk to workers involved with inspection and maintenance activities in facilities that process hydrocarbons containing significant amounts. The risks of exposure to mercury are often underestimated for a variety of reasons. Foremost is the fact that the exact amount of mercury present in processed petroleum often is not known with certainty. Secondly, the specific quantities of mercury compounds that may be present in hydrocarbon liquids seldom are known at all. Thirdly, monitoring for mercury vapor in work environments is not a routine procedure for many processing facilities. Lastly, mercury toxicity is gradual and produces no immediately apparent impairment that easily can be associated with occupational exposure. Superimposed on the risk issues are several aspects of the chemistry of mercury that make it illusive both to quantitative analysis and to detection in work environments. The combination of the cited factors increases the likelihood that workers who are inadvertently exposed to occupational environments that contain mercury will be adversely affected.
The discovery of significant quantities of mercury in hydrocarbons is not a recent occurrence and, in spite of the fact that mercury is abundant in some major fields, major health deficiencies have not been documented in large classes of workers in the petroleum industry. This fact is reassuring, however, maintenance workers in some locations are exposed to mercury and mercury compounds during equipment cleaning, tank inspections and during hot work on contaminated equipment and piping. Exposure risks generally are proportional to the concentration (total) of mercury in processed hydrocarbons. Risks can be minimized by understanding the toxicological, chemical and physical properties of mercury, determination of the possible exposure pathways in the work place and adopting policies and procedures that mitigate exposure.
Chronic occupational exposure to mercury is rarely diagnosed unless a specific program is in place to monitor mercury concentrations in the blood or urine of at-risk workers over time. Absent a monitoring program, diagnosis is extremely difficult unless affected individuals exhibit significant and readily apparent symptoms. For most petroleum workers, acutely toxic environments are infrequently encountered and chronic exposures require years to manifest. Also important is the fact that large fields containing high concentrations of mercury are rare in the US and Europe. High mercury concentrations are found in the Gulf of Thailand, Indonesia, China, North Africa (Algeria), parts of South America (Venezuela) and in a few fields in the Middle East. In many of these locations, the risk factors are compounded by logistical impediments to detection of mercury in produced hydrocarbons and to monitoring accumulated mercury levels in at-risk groups.
Avoiding exposure to mercury, in most maintenance and inspection activities, is readily accomplished if some fairly simple steps are taken to identify those situations in which exposure is possible, and by provision of commonly available equipment for detection of mercury vapor and for worker protection from inhalation or dermal absorption. Incidents of inadvertent exposure are more likely in situations that are not routine or that involve unsupervised or contract personnel. With proper procedures and plans, protection of workers can be achieved without tremendous expense or operational impediment.
The perspective on mercury in hydrocarbons has changed in a fundamental fashion over the last ten years as the influences of mercury on processes and equipment have become more apparent and researched and our ability to measure mercury in hydrocarbon matrices has improved. The toxicity of mercury and the mechanisms of mercury's interaction with human physiology likewise are much better understood today. These trends transcend the petroleum industry and are the driving force behind efforts to eliminate anthropogenic sources of mercury discharge to the environment and to reduce the exposure of humans to mercury both occupationally and otherwise.
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