The NEBB Professional 2024 - Quarter 2

The actual canopy opening elevation, D MAX , should be taken from Figure 6. The associated Q B should be suffi cient to achieve at least 88 fpm inflow at D MAX . To provide a properly designed canopy connection four modifications should be specified. (1) Provide a suspension system and/or adjustable slot to maintain the appropriate slot opening elevation, D. (2) Provide a bi-modal positioning mechanism for uplifting the canopy assembly to allow for HEPA filter integrity scanning and decontamination access. (3) Include a blast gate or other adjustable airflow damper device to allow for site installation assessment during certifi cations. (4) Provide an alarm system to monitor both hi-negative and low-negative (positive) pressure. Figure 7 illustrates a suggested conceptual properly designed canopy connection. By including a mandatory blast gate damper in the throat of the canopy round duct, two incipient issues are rectified. This allows the technician agency to ver ify the alarm operation without affecting other BSCs in the facility. Without the tools to do so, it is unrea sonable for NSF/ANSI 49 to mandate the alarm op eration as a portion of the routine field BSC certifica tion, burdening the certifiers with an impossible task. Incorporation of an integral blast gate, coupled with adjustable height mounts facilitates exhaust HEPA

filter integrity scanning and enables decontamination sealing and taping. The installed alarm is adjusted to alarm at low pressure (highly negative, i.e., ≤ -0.012” H2O) and may incorporate a sail switch to indicate positive canopy duct pressure. At a minimum, the canopy positioning must be bimodal for normal oper ation and for service, certification, and maintenance. While NSF/ANSI – 49 does not have the authority to mandate such a device, it is incumbent upon the man ufacturers who are already providing their own canopy designs to incorporate these suggestions.

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Figure 7: Properly Designed Canopy Connection

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The NEBB Professional | Quarter 2 | 2024

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