CLASS II, TYPE A2 BIOLOGICAL SAFETY CABINETHEPA FILTER LOADING CAPACITYWILLIAM PETERS - VICE PRESIDENT OF ENGINEERINGHow Long are HEPA Filters supposed to last?and performance of the original Class II, Type 1 (now type A1/A2)The life of a HEPA filter for a Biological Safety Cabinet (BSC)BSC’s. Section 3.5.6 and covered both the fan and motoris an important subject when considering the life cycle cost ofrespectively.any BSC. HEPA filter loading capacity has always been a majorconcern for the design and performance of a BSC. Not only interms of replacement cost, butMetal Frame HEPA FilterFan and motor performance were specified by the followingrequirements:also laboratory safety through3.5.6.3 Total fan delivery shall fall off no more than 10% asthe replacement process, downa result of 50% increase in the pressure drop acrosstime, and associated costs.the filter.With the use of new energy3.5.7.3 The motor shall be sized to operate the fan at aefficient motor technologies,static pressure sufficient to meet the requirementsexpected HEPA filter loadingof paragraph of BSC’s may be reduced but still meet theNSF/ANSI 49 requirements. The discussion below provides ashort explanation as to the requirements, what has changed,why it changed and what information is required frommanufacturers to assure at a minimum the same HEPA filterloading capability. The energy savings obtained by using someof the new energy efficient motor designs of today may beoffset by replacing the HEPA filters more often.HistoryThe first major BSC specification developed by the NationalInstitutes of Health (NIH) dating back to August 1973 includeda specification for filter loading capacity. The NIH-03-112specification scope and objective was to provide procurementspecification for a safety cabinet that included downflow (whichTo satisfy the above requirements, a fan curve provided bythe fan manufacturer along with operational BSC staticpressures and motor torque information provided by themotor manufacturer at the nominal airflow set point was plottedto theoretically calculate the loading capacity of the system.In this case, the system refers to the fan, motor and filters (withthe specific pressure drops) of the individual BSC.The NIH specification remained the only BSC specification untilJune 1976, when the National Sanitation Foundation (NSF)adopted Standard 49 Class II (Laminar Flow) Biohazard Cabinetry.The NSF Standard was based on the NIH specification; so manyparts were nearly identical, if not the same including the fanand motor requirements as stated below.was new back then) along with inflow to provide both4.21.2 Total air delivery shall fall off no more that 10% asproduct and personnel protection. The cabinets would be useda result of 50% increase in the pressure drop acrossin biological research or production as an aid to controlthe filter without readjusting the fan speed control.airborne contaminants, which may represent a low to mediumrisk hazard to scientific personnel and/or be deleterious to4.22.1.2 The motor(s) shall be sized to operate the fan(s) atthe equipment.a static pressure sufficient to meet the requirementsof item 4.21.2. Fan motors shall be UL or CSA listed.The specification provided requirements for design, construction763.553.1270 WWW.NUAIRE.COMCopyright 2016. NuAire, Inc. All Rights Reserved. Process: 20-1204-W-G-EN-2-1115

Class II, Type A2 Biological Safety Cabinet HEPA Filter Loading CapacityAgain to satisfy the above standard requirements, cabinetable to attain 180% increase in pressure drop or static pressuremanufacturers submitted a fan curve with the appropriatedacross the filter with no more than a 10% fall off in total airmotor and static pressure information was provided to NSF asdelivery. The 180% increase in pressure drop then became theevidence of compliance to the standard facto industry standard being used and published by mostIn the late 1980’s an NSF task group was formed to develop atest method to demonstrate compliance to the standard al,governmental, university and private industry BSC specifications.providing theoretical evidence of compliance. The motor blowerThe following statement in some form represents thisperformance task group based the current test method on thespecification used today:Air Movement and Control Association (AMCA) publication 210,laboratory methods of testing fans for rating purposes. Thebasis of the test was to load the cabinet airflow system andmeasure the static pressures of the fan per AMCA, thenmeasure airflow fall off to determine compliance to thestatement above. The test method was officially updated in the1992 revision of the standard and remains the same today perNSF/ANSI 49, Annex A.12, Motor / Blower Performance.Cabinet motor/blower shall be positioned so as to createeven filter loading, thereby prolonging the life of the HEPAfilters, and shall deliver over 50% of the initial HEPA filterstatic pressure with no more than a 10% decrease of totalCFM. Equip each cabinet with a voltage compensating motorspeed controller that automatically compensates for voltagechanges to maintain constant voltage to motor. Speedcontroller will permit manual or automatic adjustment toUnderstanding the basis for the Specification:deliver over 180% of the initial HEPA filter static pressureThe design and performance basis for both of the abovewith no more than a 10% decrease of total CFM.specifications was the use of an AC PSC motor and a forwardcurved fan. The AC PSC motor has an inherent designcharacteristic of increasing motor RPM with more resistance(Torque) or when used in a cabinet with a forward curved fanwill increase RPM of the fan with more static pressure causedby particulate loading on the HEPA filters of the BSC. So, byspecifying that no more than a 10% fall off of total air deliveryfrom a 50% increase in static pressure assured the correct fan,motor and HEPA filters were designed into the BSC. The 50%increase in static pressure is considered the baseline withoutreadjusting the fan speed control knowing that the fan speedcontrol would add additional capacity to the system. Although,not specified by NSF, the additional capacity was virtuallyHEPA Filter Life:Since actual filter loading in the field is based upon thelaboratory environment the BSC is used in, actual life of theHEPA filters will vary for each installation. If the BSC wasinstalled in a clean room, theoretically the filters will lastforever. If the BSC was installed in an environment that has orgenerates a lot of particulates, the filters won’t last as long. Toestablish average filter life in a standard life science laboratory,historical data was reviewed as to when replacement HEPAfilters were ordered. Based on NuAire data and knowing our ACPSC motor design provides a 180% increase in pressure drop,it was found that filters were lasting an average of 7 years.guaranteed using AC PSC motors and forward curved fans.Manufactures, provided what additional capacity they couldoffer that basically indicates how much particulate load can beapplied to the system and still maintain cabinet airflows at alevel to provide containment.Using available AC PSC motors, forward curved fans and HEPAfilters with average pressure drops, most manufacturers wereWood Frame HEPA Filter763.553.1270 WWW.NUAIRE.COMCopyright 2016. NuAire, Inc. All Rights Reserved. Process: 20-1204-W-G-EN-2-1115

Class II, Type A2 Biological Safety Cabinet HEPA Filter Loading CapacityUsing 7 years as a benchmark for 180% increase in pressurespeed control to be changed making sure the AC PSC motordrop, the following chart was then established equaling averagewas sized correctly with the fan using its inherent capability tofilter life to percent increase in pressure drop or filter loadingincrease rpm (torque) with more resistance or filter loading.capacity. As you might note, the chart is not linear, but is similarThe new energy efficient motors require the use of anto that of a fan curve that allows more loading of new filters,integrated control system to increase rpm (speed) tothen tends to trail off as the loading increases.compensate for HEPA filter loading. The NSF standard doesnot restrict usage of a control system or place additionalrequirements with its use. The standard today, still only requiresPercent Increasein Pressure Drop*Average HEPA FilterLife (Years)50%3 Years**result of 50% increase in the pressure drop across the filter.100%5 YearsThe additional capacity of 180% that was virtually guaranteed180%7 Years***with the use of an AC PSC motor may not be present anymore,250%10 Yearsunless the product specifications for the BSC indicate the* Percent increase testing based on NSF/ANSI 49, Annex A.12motor blower performance test methods** Base line NSF requirement assuming more capacity is available*** Industry standard requirement based originally on designedusage of AC PSC motorthat the total air delivery shall fall off no more that 10% as arequirement or manufacturer provides this information withinthe specifications of the BSC.Advantages of DC ECM Motor TechnologyThe DC ECM new motor technology actually increased the filterNEW Energy Efficient Motor TechnologyAC PSC versus New Motor TechnologiesNew motor technologies are being designed into most BSC’stoday primarily as a way to reduce energy consumption. AC3-phase, DC ECM and DC motors are being used into cabinetstoday, these technologies offer increased energy efficiencyranging from 40% to 80%. However, most all of these newmotor technologies don’t provide the older AC PSC motortechnology inherent capabilities to increase rpm (torque) withgreater filter loading [resistance]. Instead, these new motorsmust be used with an airflow feedback loop control systemloading capability. The DC ECM motor was optimally incorporatedand implemented with a specific forward curved fan for eachwidth/volumetric size of cabinet. The DC ECM motor designprovides additional capacity in terms of motor rpm thatprovides a 250% increase in pressure drop or static pressurefilter loading capacity. In addition to the increased filter loadcapacity, energy costs have been reduced by 50 % and thesystem is quieter in terms of noise and vibration. The DC ECMmotor, when properly designed and engineered into the BSC,provides the lowest life cycle cost in terms of energy, filterload capacity and reliability.or a motor feedback control system. Both methods arevalid and provide adequate airflow control to keep the inmentperformance range.Utilizing these new motor technologies with the necessarycontrol capability can reduce the designed filter load capacityof the system and still meet the NSF requirement formotor / blower performance. In other words, the originalrequirement of the NSF standard didn’t allow the fan (motor)Ultra High Efficiency ECM Motor763.553.1270 WWW.NUAIRE.COMCopyright 2016. NuAire, Inc. All Rights Reserved. Process: 20-1204-W-G-EN-2-1115

Class II, Type A2 Biological Safety Cabinet HEPA Filter Loading CapacityOther Considerations: Size and Type of Supplyand Exhaust FiltersCommon airflow plenum means particles generated in theHEPA FiltersHEPA Filters (99.99%) retain or trap onlyparticulates. [To learn more, see NuAireTechnical Bulletin entitled “Use of HEPAFilters in Biological Safety Cabinets”]Metal Frame HEPA FilterFumes, chemicals, gases, and vaporspenetrate through HEPA Filter Media. As with any media-typefilter, the surface area or the size of the filter and the number ofcabinet work zone will be pulled into the blower and dischargedinto the positive pressure common plenum for distribution ofboth supply and exhaust airflow. Particle distribution withinthe common plenum is ideally spread evenly to minimize thegeneration of high/low airflow velocities within the cabinetwork zone. An exhaust choke or damper is provided as a meansto balance the down flow to exhaust flow (inflow).air exchanges through the filter will ultimately determine howEven particle distribution along with balancing down flow toeffective the filter is at retaining particles.inflow will provide maximum cabinet containment performanceFilter Mediaand extend HEPA filter life.Electronic Airflow Control System[Motor Speed Controller]Metal FrameAlong with the many benefits already mentioned of using DCECM motors. The DC ECM has the ability to be programmed toprovide constant air volume even as the HEPA filter loads withGasketparticulates. In addition, the airflow control system can be finetuned to assure maximum containment performance along withULPA Filtersmaximum allowable HEPA filter use.ULPA Filters (99.999%) create more resistance in the airflowdynamics of the cabinet, requiring a larger blower or multipleblowers to maintain proper airflows. ULPAfilters typically cost more, contain highergrade dense fiberglass media and must bereplaced more often than a HEPA filter. Forbiological applications, there is no advantagein using a ULPA filter compared to a HEPAfilter. [See Technical Bulletin]Advantages of NuAireNuAire incorporates our technical knowledge and the best ofthe new DC ECM technology to give you a better Value, Lowerenergy costs, longer filter life, and reduced noise andvibration. NuAire uses the largest HEPA filters with the mostpleats per square inch; an electronic airflow control system;internal exhaust damper; and individually selected, optimallydetermined forward-curved fans for each model size / width.We are the only manufacturer to give these features insuringyou the best performance, quality, reliability, service and costControlling Airflowsaving technologies.Airflow in a Class II, Type A2 BSC consists of both down flowWilliam Petersfor product protection and inflow for personnel protection. TheVice President of Engineeringairflow velocities of both down flow and inflow are designed andbalanced in a common plenum to provide optimal containmentperformance.763.553.1270 WWW.NUAIRE.COMCopyright 2016. NuAire, Inc. All Rights Reserved. Process: 20-1204-W-G-EN-2-1115To learn more or to speak with someone at NuAireplease visit or call 763-553-1270.

4.21.2Total air delivery shall fall off no more that 10% as a result of 50% increase in the pressure drop across the filter without readjusting the fan speed control. The motor(s) shall be sized to operate the fan(s) at a static pressure sufficient to meet the requireme