Guardian 8TM Gas Protection System Efficiency Study
K.R. Schmerber – Colorado State University; H.J. Beaulieu – Industrial Hygiene Resources, Ltd.; R.M. Buchan – Colorado State University; C.E. Mitchell - Colorado State University (SSA Journal - March 1993 pp. 47 - 52)
Special thanks to MDA Scientific, Inc. for their donation of two MDA Series 7100 Toxic Gas Monitors as well as their enthusiastic technical support throughout the project.
This technical paper is a portion of a Masters Thesis from the Department of Environmental Health at Colorado State University.
Guardian is a trademark of MG Industries, a division of Hoechst Corporation.
The conversion efficiency of waste hydride (dopant) process gases from semiconductor manufacturing by a Guardian 8 Gas Protection System was investigated. Two MDA Series 7100 Toxic Gas Monitors were used to simultaneously monitor the pre and post-combustion waste effluent streams. The process gases of concern were arsine, dichlorosilane, phosphine, and silane.
The Guardian was found to have a waste hydride conversion efficiency of greater than 0.983 for 55.6 percent of deposition time. For the other 44.4 percent of deposition time conversion efficiency was between 0.536 and 0.983. Resolution of the data in percent of deposition time was as follows: 35.3 percent less than 0.899; 23.0 percent less than 0.799; 12.9 percent less than 0.699; and 4.2 percent less than 0.599.
Excellent conversion was observed for the silicon hydrides. This was due to the highly reactive and pyrophoric properties of both silane and dicholorsilane. However the conversion of both arsine and phosphine were not as readily handled by the Guardian system. This was believed to be due to oxygen deficiency within the Guardian's reaction chamber.
Findings of this research indicate the need for further detailed study of air flow patterns within the Guardian system. The following steps can be taken to help improve Guardian performance:
Quantify and distribute inert gas flow to any single system
Separate silicon hydrides from other dopant gases
Limit inert gas flow to minimum required for safe waste gas transport;
Implement a period maintenance program.