Mercury Contamination from McLeod Gauges

There are two mechanisms for contamination from McLeod gauges (1) contamination which is backstreamed into the system from the McLeod gauge and (2) contamination which comes from the McLeod gauge storage bulb during the evacuation process. 

Research by Carstens, Hord, and Martin displayed a relatively high level of mercury being pumped out of a McLeod gauge during the evacuation process. Typical readings (in mg/m3) were 

To make these measurements, a special vacuum system is required. A complete derivation of the formulas and procedures can be found in the book The Design of High Vacuum Systems and the Application of Kinney High Vacuum Pumps by C.M. Van Atta, 1955 by Kinney Manufacturing Division, New York Air Brake Company. 

However, once a layer of low-vapor-pressure oil was added to cover the mercury in the storage bulb, the readings went down by a decade  

The research authors pointed out that because the levels were erratic and low, the actual health dangers were also rather low. 

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Be aware that the old oil from a pump (and any solvent used to clean out the old oil) more than likely contains any toxic materials that may have come from the vacuum system. For example, if the system had a McLeod gauge, it is likely that the old oil is contaminated with mercury. The amount of contamination concentration determines how the oil or solvent can be disposed of. Unfortunately, because of the possibility that specific EPA-established concentration levels will change before you read this book, no disposal procedures are provided. Therefore, contact the EPA, or local regulatory agencies, to verify the various toxicity levels and the proper disposal procedures for materials of those levels. 

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