While compounding in a horizontal laminar airflow workbench, a technician sets a stack of supplies between the HEPA filter and an open vial. Why is this unsafe?

a.It interrupts first air, so the critical site no longer receives unobstructed HEPA-filtered air and may become contaminated
b.It raises the temperature inside the hood above the permitted range
c.It triggers the hood's pressure differential alarm
d.It blocks the technician's view of the syringe graduations

Explanation

First air is the clean air leaving the HEPA filter before it touches anything, and any object placed upstream of a critical site creates turbulence and a shadow of unfiltered air over that site. Work should be performed at least 6 inches inside the hood with nothing between the filter and the vial or needle. Temperature limits, alarms and sightlines are not the reason the practice is prohibited.

Law Reference: USP <797>

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