The NEBB Professional 2024 - Quarter 2

widely varying exhaust and bypass air? Finally, how can the exhaust filter downstream surface be sealed with tape and plastic during planned biological decon tamination efforts without adequate technician access openings and with the disruptive suction pressure and sideways turbulence caused by the canopy bypass? Previously, when the cabinets were directly connected as in Figure 2, these incipient issues were preempted by optionally performing overall penetration testing (rather than scanning) of the exhaust filter, pitot-tra versing the exhaust duct, and closing an airtight duct damper. NSF/ANSI 49 makes various suggestions for canopy installation including typical canopy connec tion duct pressures, flexible duct sections and acces sible manual balancing dampers but does not, nor cannot, mandate these suggestions. The particular site configuration is subject to the whims of the design engineer and site installation contractor. In a recent case study, we encountered a Q.A. labo ratory having four of these Class II, Type A2 Vented cabinets sharing a common exhaust blower and hav

issued a memorandum reading, “NSF Accredited field certifiers shall no longer certify either direct-connected Type A cabinets or canopy-connected Type A cabinets without alarms, even if specifically asked to do so by the customer.” Figure 2 Shows the original configuration of multiple directly connected A2 vented cabinets. Canopy duct connections were thus required on Class II, A2 Vented biological safety cabinets going forward. Prescribing this engineering solution to the problem, however, raises other collateral issues. The first issue is how much bypass air to exhaust. Further, how can the cabinet exhaust filter air, Q I , be integrity tested for downstream challenge concentration when it is being diluted by the inrush of dilution room bypass air? How can the exhaust HEPA filter be integrity tested using a hand-held scanning probe without adequate access for the hand and arm of the technician? How can the work access opening airflow be measured in the duct if it is conjoined with the room bypass air? How is the duct pressure in the canopy transition regulated with

Figure 2: Direct connected A2 cabinets with common exhaust system

The NEBB Professional | Quarter 2 | 2024

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