Lesson Learned Statement:Portable HEPA filtered exhausters used for ventilation may be capable of generating air flows higher than the rated flow of the HEPA filters in the exhausters.
Discussion:This bulletin describes two incidents in which exhausters were operating above their rated flows.
ANSI/ASME N509 section 4.3 states:
Size (Installed Capacity) of Air Cleaning Units
- The installed capacity (cfm) of the air cleaning unit shall be no greater than the limiting installed capacity of any bank of components contained in the air cleaning unit through which the airflow must pass.
In December 2000, a HEPA filtered portable exhauster was found to be operating at almost twice the rated flow of the HEPA filter on the unit.
The exhauster, a Bartlett AP-1000 exhauster made by Bartlett Nuclear Services, was purchased as a 1000 cfm exhauster but came with a 500 cfm HEPA filter installed. The manufacturer confirmed that according to their design specifications the unit had the proper filter. The manufacturer's specifications are based on differential pressures across the filters, not air flows. The advertising brochure lists the unit as having a capacity of 1000 cfm with a 500 cfm filter.
The exhauster was aerosol tested. Other than the high airflow, it was functioning properly. After dampering the flow down to the filter's rating, the unit was retested and again proved to be functioning properly.
In January 2001, two "Blue Max" HEPA filtered exhausters were found operating at 1100-1200 cfm. The rating on the filters was 1000 cfm. The units were subsequently aerosol tested and other than the high flow, they were functioning properly. One unit was removed from service and the other unit's flow was dampered down below 1000 cfm and aerosol tested again. The test was completed successfully.
Recommended Actions:Similar exhausters were checked for flow and filter ratings.
A purchase specification was written for the procurement of Bartlett Exhausters to include the installation of a restrictor plate to ensure that the air flow cannot exceed the filter's rated capacity.
Facilities should check all HEPA filtered systems to ensure the air flow ratings of the fan are consistent with the ratings of the HEPA filters.
Originator:CH2M Hill Hanford Group, Inc./D.A. Gilles, (509) 363-1857
Validator:G.A. Skogley, Gloria_A_Skogley@rl.gov
Contact:River Protection Project Lessons Learned Coordinator,
Name Of Authorized Derivative Classifier:Not required
Name Of Reviewing Official:HM Hassell
Priority Descriptor:Blue / Information
Keywords:Vent & Balance; HEPA, exhausters, flow rate
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DOE Function / Work Categories:Inspection & Testing
Maintenance - HVAC
Operations - Facility
ISM Category:Analyze Hazards
Develop / Implement Controls
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