DESIGN OF A

ROOM PASS-THROUGH

USING A DUAL ACCESS

BIOLOGICAL SAFETY CABINET

DESIGN OF A

ROOM PASS-THROUGH

USING A DUAL ACCESS

BIOLOGICAL SAFETY CABINET

Traditional Pass-ThroughTraditional Pass-Through

Pass-throughs have been used for many years as a means of moving material from dirty rooms to clean rooms.

Traditional pass-throughs consist of a sealed chamber installed into a common wall between rooms, whose doors are interlocked preventing both doors from being opened at the same time, minimizing the spread of contamination between rooms.

These traditional types of pass-throughs present many limiting factors in terms of size and function.

Typical Facility Design Using aDual Access BSC

Typical Facility Design Using aDual Access BSC

The use of a Dual Access BSC in applications requiring a pass through between rooms presents several unique installation considerations for proper operation. Proper facility design is very important to the success of the installation:

E E

S S

RECEIVING “DIRTY” ROOM CLEAN ROOM

SST SEAL FLANGE

BARRIER WALL

NU-610BSC

Room doors & HVAC supply/exhaust ducts should be located away from dual access BSC to prevent high velocity airflow currents near the cabinet

It is recommended that no other devices requiring venting be installed in the roomsMaterial and personnel movements should be analyzed for efficiency, minimizing

personnel traffic around the dual access BSC is important

The use of a Dual Access BSC, NuAire Model NU-610, as a room pass-through offers many advantages: The Dual Access BSC provides both personnel and

product protection from either side of the cabinet (i.e. clean side or dirty side)

Offers greater flexibility for joint material movement through and around the cabinet

A typical application requires that “dirty” materials be brought into a “clean” room within the barrier facility. The materials are prepared and placed into the NU-610 where they are disinfected before being brought into the clean room. This material movement process is performed more efficiently and under a higher level of quality using a dual access BSC.

NU-610 Dual AccessBiological Safety Cabinet

NU-610 Dual AccessBiological Safety Cabinet

Photograph Courtesy of Baylor University

The NU-610 airflow pattern is similar to a standard Class II, Type A/B3 BSC. The BSC has been functionally divided into two identical and separate recirculation air systems, each responsible for one-half of the airflow. The blowers located in the cabinet base, one on each

end, draws one-half of the inflow air equally through one-half of the access openings.

The inflow air is merged with one-half of the downflow air, which represents one-half of the total flow of the cabinet blower.

The blowers provide air to separate Supply and Exhaust HEPA Filters via a common plenum in each side wall.

The airflow is then divided with approximately 30% being exhausted and 70% re-circulated, becoming downflow air again.

NU-610 AirFlow PatternNU-610 AirFlow Pattern

Electrical requirements for the Dual Access BSC are greater than the typical BSC. Having two (2) motor/blowers, fluorescent lighting, and accessory outlets. The electrical ratings are typically – 115 VAC, 24

amps, single phase A 30 amp service would be required and can be

designed for either cord connected or hard wired application

All electrical services are exposed into the “dirty” side of the installation and can be accessed by front or side service panels

Electrical ConsiderationsElectrical Considerations

HVAC Facility InterfaceHVAC Facility Interface

Starting with both rooms at equal pressure and both blowers synchronized to deliver identical inflows and downflows, the “split line” forms directly down the lengthwise center of the work zone. As the difference in pressure increases both blowers will increase draw through the access opening from the positive pressure room and decrease draw from the negative pressure room, since blowers produce constant CFM. Given enough difference, the positive pressure side will lose product protection while the negative room will lose personnel protection. It should also be stated that biological safety cabinets are constant volume devices also and, in this case for all practical purposes, must be installed into constant volume rooms only.

The Dual Access BSC as previously mentioned, is designed to be installed in the “dirty” room and project through the wall into the “clean” room. As a result, all exhaust air from the cabinet’s two exhaust filters is vented into the dirty room. Regardless if the cabinet is vented into the plant exhaust system or not, the “clean” side will require makeup air to replace the work access inflow volume, and the “dirty” side will require that this same volume of air be removed, or the “dirty” room will be under positive pressure which will cause the “system” (I.e. supply/exhaust/cabinet) to naturally seek self “im” balance as discussed above.

The HVAC facility interface is the most complex installation issue. To gain an understanding, lets look at the following example:

The mechanical attachment of the Dual Access BSC that is placed into the barrier wall typically uses a SST mounting flange. The SST mounting flange is designed in several pieces that are contoured to the shape of the cabinet.

The Dual Access BSC would be placed within the rough opening of the barrier wall so the face of the BSC would extend just into the clean room side. The SST flange would then be place around the cabinet and attach to the wall surface within the clean room. Any small cracks and or crevices would then be caulked and sealed.

Mechanical AttachmentMechanical Attachment

Photograph courtesy of Cornell University

Testing MaterialsTesting Materials

To understand even further the HVAC facility interface and it’s impact on the performance of the dual access BSC. We have conducted testing to evaluate the dual access containment performance under both positive and negative room changes. To Accomplish the evaluation, we performed biological tests to characterize the dual access BSC personnel and product containment performance. The following materials were used:

I. Clean Room

II. NuAire Model NU-610 Dual Access BSCIII. Aerosol challenge of bacillus subtilis used at a concentration level of no less

than 5.0 x 108 for personnel protection and 5.0 x 106 for product protection

IV. Collison CN-31 Nebulizer

V. Mattson-Garvin and New Brunswick Slit Samples

VI. Trypticase Soy Agar

VII. Ace Glass Impingers

VIII. Stainless Steel Cylinder

IX. TSI Model 8355 Thermoanemometer

X. Shortridge Model ADM-870 Flowhood

XI. Pacific Power Source Power Supply

XII. Manometer

XIII. NuAire Model NU-101 Hepa Filtered Blower Module

Testing MaterialsTesting Materials

Test Set-UpTest Set-Up

The NU-610 Dual Access BSC is positioned and sealed in what normally is the clean rooms door way. The NU-101 HEPA filtered blower module is positioned to minimize room air currents and provide supply make up air to control the rooms air pressure.

Air SupplyDuct

NU-101 HEPA FilteredBlower Module

Airflow Directionfrom

Clean RoomEntrance

CLEAN ROOM

Biological Test Setup Area

NU-610 BSC

Clean Room toNU-610 BSCSeal FlangeNU-610 BSC ExhaustingOutside of Clean Room

Clean RoomControl Panel

Protection Test Set-UpProtection Test Set-Up

Personnel ProtectionTest Set-Up

Product ProtectionTest Set-Up

I. Adjust BSC power supply to 115 VAC

II. Adjust airflows on the Dual Access BSC to nominal values of: 105 FPM inflow and 75 FPM downflow

III. Adjust air volume on room supply module to achieve desired room pressurization

IV. Run bacterial aerosol challenge in triplicate

V. Plate out the results and incubate for 24 hours

VI. Record test results

Test Set-UpTest Set-Up

Personnel Protection TestPersonnel Protection Test

Control plate must contain greater than 300 Colony Forming Units (CFUs)Slit sampler totals must not exceed 5 CFUsImpinger totals must not exceed 10 CFUsPass/Fail Criteria per NSF Standard 49

ROOM PRESSURIZATION

+/- CFM

BSC WORKSURFACESPLITLINE MOVEMENT CONTROL L. SLIT R. SLIT IMP. PASS/FAIL

+231 3” N/A

+180 2 ½” N/A

+128 2” N/A

0 Center

>300>300>300

010

030

001 Pass

-274 2”

>300>300>300

030

200

421 Pass

-291 2 ½”

>300>300>300

150

040

463 Fail

-304 3”

>300>300>300

123

112

56710 Fail

Product Protection TestProduct Protection Test

Control plate must contain greater than 300 Colony Forming Units (CFUs)

ROOMPRESSURIZATION

+/-CFM

BSCWORKSURFACE

SPLITLINE MOVEMENTCONTROL PLATES PASS/FAIL

+231 3”>300>300>300

01

46Fail

+180 2 ½”>300>300>300

0240

Fail

+128 2”>300>300>300

000

Pass

0 Center>300>300>300

000

Pass

-274 2” N/A

-291 2 ½” N/A

-304 3” N/A

ConclusionConclusion

1. Both dirty & clean rooms should be designed as a single constant volume system.

2. A constant volume controller(s) should be used for the supply air.

3. If a Dual Access BSC is exhausted, a constant volume controller for the exhaust air should be used.

4. No other devices requiring venting should be installed in the rooms.

5. The “clean” room may be slightly positive, but should not exceed a room differential air volume of greater than 100 CFM. The testing results indicate that this requirement would provide a good safety margin keeping the BSC worksurface splitline movement to within +/- 1 inch of the center.

6. It is recommended to let the system run 24 hours a day, 7 days a week. However, if the system must be shutdown, the clean room side being positively pressurized should always start up first and shut down last.

A Dual Access Biological Safety Cabinet can successfully be used as a room pass-through. The successful integration of the Dual Access BSC has many areas of concern that must be addressed, like facility design, electrical/mechanical attachment and HVAC facility interface. Below are some basic guidelines for successful integration:

Personnel & Product Protection Test Results

Personnel & Product Protection Test Results

The test results indicate a range of acceptable containment performance based on the increase/decrease of room differential pressure. Room differential pressure represented in positive and negative CFM gives an indication of allowable amounts. However, a better indication is the BSC worksurface splitline movement that is easily obtained with a smoke stick. During our testing, we tried to obtain room differential pressure readings using several different types of manometers, but were unable to measure pressure in inches of water. This was most likely due to our clean room test set-up not being pressure tight, and due to the actual pressure differential being very low (around 0.01 inches water gauge).

Based on the testing results and applying a safety factor with respect to room pressure variances, the pressurization should not exceed 100 CFM positive or negative. This would equal approximately a +/- 1 inch BSC worksurface splitline movement and well within the containment performance requirements.

ReferencesReferences

NSF Standard 49, Revision 1992. NSF International – Ann Arbor, Michigan

Kruse, R.H., Puckett, W.H., Richardson, J.H. 1991 – Biological Safety CabinetClinical Microbiology Review 4:204-241

CDC/NIH, 4th Edition, 1999 – Biosafety in Microbiological and Biomedical Laboratories