Gas Testing of Secondary Exhaust Systems on Hazardous Gas Enclosures
Ronald L. Tubby - University of Washington (SSA Journal Volume 5 Number 2 - June 1991 pp. 12 - 18 )
Tracer gas testing has many applications in the semiconductor industry, from stack plume characterization to indoor air diagnostics. The use of tracer gas techniques allows existing ventilation systems and potential new systems to be evaluated under simulated worst case conditions. Such testing can indicate how systems will perform in the even of actual equipment failures. This study utilized tracer gas testing to characterize the effectiveness of three different types of secondary exhaust systems on hazardous gas source cabinets typically used in the semiconductor industry. Two different diffusion furnace source cabinets and a gas pad cylinder cabinet were tested. Sulfurhexafluoride was piped in to the source cabinets and released at cylinder pressures matching those of the equipment configurations. Air samples were collected at six points around the cabinet with polyproplylene syringes for sulfurhexafluoride analysis on a gas chromatograph. Experiments demonstrated that significant exhaust reductions (33 percent) could be attained by sealing the access panels and doors airtight and providing baffled make-up air entry points. Experiments conducted on the gas pad cylinder cabinets demonstrated that significant decreases in the tracer gas leakage rate to the surrounding work environment could be achieved by incorporating the use of flow limiting orifices. The experimental results provided valuable information about the actual performance of secondary exhaust systems under worst case conditions and were used to diagnose means of improving existing systems.