A reliable exhaust system was designed to ventilate gloved enclosures xn an existing building which was modified to provide for the safe handling of kilogram quantities' of alpha-emitting materials. The new exhaust system was designed especially for this purpose, and as a separate system, it relieved the existing overtaxed exhaust systems which could not be economically upgraded to ^perform the same function. The arrangement of components and the features incorporated in the new system provide

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... any improvements in reliability and maintenance not found in other systems of this type. The more significant events experienced during the design, fabrication, and installation of this system, beginning with the design criteria and ending T?ith an objective critique for the benefit of others, are discussed herein. DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED GCr 12th AEC AIR CLEANING CONFERENCE With the present facility personnel as operators, the new alpha enclosure ventilation system will be extended to serve various building areas as the changes planned for different research programs are realized. The criteria established for the design of the new system were developed to attain suitable service provisions of the type and quality foreseen for current and future alpha enclosure ventilation "needs. System Design Criteria The goal of the system design criteria was maximum safety for gloved enclosure operations and for the environment; the key being reliable troublefree system operation. A basic design premise was that reliability is best attained by engineering Simplicity and another was that human error is a greater threat to safety than material or equipment failure. This philosophy underlies the approaches taken to implement the criteria into an integrated system design. Some points of the criteria characterize only this system, while other points reflect the application of long-standing practices. Significant points of the criteria are outlined as follows. 1.-The system shall be designed and sized to operate with an ultimate airflow rate of 3000 cfm. Initial operation.shell be at a rate as low as 600 cfm, with periodic increases as other branch connections are put into service under future programs. 2. A negative pressure of 4 in. H 2 0 shall be maintained with a high degree of service continuity in each branch duct. 3. Protection si-ill be provided to safeguard each branch dues against excessive negative pressure. 4. Two physically separated and separately testable HEPA filter stages shall be provided to filter all effluent before release to the atmosphere. The first stage shall be within the building confinement limits and be applied individually to each branch duct. 5. Fire barriers shall be provided upstream of each of the three secondstage HEPA filter housings to intercept any burning debris that might result from a breakthrough of the first-stage filters. 6. The total system airflow and the flow in each individual branch duct shall be continuously monitored. 7. The system shall be instrumented so that an on-duty operator can quickly determine the status of the system at an existing central station ia the building. 8. The system ducts shall be metal with minimal leakage, and they shall be incapable of collapse by fan suction or exposure to weather. 9. The system shall be tested upon completion of construction to demonstrate performance compliance with J-he design criteria. ... 10. The recommendations given in USAEC Report ORNL-NSIC-65^ ' shall be used as a guide. ; Arrangement of System Components I I Various desirable features, the selection of which was at the option of the designer, were considered for their relative value in adding safety and reliability to the system. These features (in descending order of judged desirability) were (1) ah alternate (electrical) power source, (2) standby tan(s), (3) vacuum relief devices to limit suction in the system, (4) multiple ORNL-DWG 72-7372 -STEM COIl TO AT«O|PNERE-' I ^-MlillNB I VALVED BUEO-IN FILTER CHANCE PERIODS STACK EXISTING CONNECTIONS " STACK 4-ORIFICE STATION (TOTAL SVSTEH FLOS RATE) ONLY utn FILTER mwiNe-i (SECOM STAtE) ^HAMMl DAMPER (LEVER HANDLE) » CLOSURE BLADE MFOR MAINTENANCE ONLT) BACK PRESSURE DAMPER MANUAL SAMPER (BEAR OPEitATOR/tiHAINIHEEl) FUTURE CONKCTIM (ffrieAl) •AIR KST WP imufojmtt iuciisls / REPA FIUTER ORIFICE HATIOH (IRANCN FLM RATE) PPESSUSE SIITCHES FOR FAN OPERAT*SN