Informational Articles Referenced in 'References and Abstracts'--Safety and Health Considerations Related to Vacuum Gauging

摘要

Safety or health hazards exist with some common types of vacuum gauging including mercury manometers, thermal conductivity gauges, and ionization gauges. Mercury filled manometers and McLeod gauges have been replaced by other gauging in most applications. The difficulty with thermal conductivity gauges arises because the calibration curves for various gases diverge widely at the upper end of the range, from 10 to 1000 Torr. When they are used to monitor backfilling to atmospheric pressure, dangerous over or under pressure situations may exist if the identity of the gas is not known. The greatest danger with hot cathode ionization gauge systems is electric shock from the high voltages supplied by the control unit. Especially with gauges using electron bombardment degas, proper use of grounds, cables, and connectors is necessary. A concern with many hot cathode ionization gauge sensors is the thorium oxide electron emitting coating on the cathode. Natural thorium is an alpha emitter with a half-life of 1.4 X 1010 years. Yttrium oxide is a safe alternate coating material now available in ionization gauges.