This is a brief overview of bubble tight dampers, including their locations relative to the cabinet, their primary functions and proper use.
A bubble tight damper has two main functions. Its primary function is for use when performing gaseous decontamination of a biosafety cabinet. Once a bubble tight damper is closed, it minimizes the probability of gas escaping the targeted area during decontamination.
A secondary function of bubble tight dampers is in the biosafety cabinet certification process. Each biosafety cabinet comes installed with an alarm that will sound when airflow velocity falls below a certain range. According to Annex F of NSF/ANSI Standard 49, these alarms must be tested for proper functioning. A bubble tight damper can be used to simulate a reduction in exhaust flow that should set off the alarm.
A bubble tight damper should be used only during decontamination and certification. Generally, it should not be used as a means of controlling excessive exhaust airflow, which is typically controlled by an automated valve downstream of the bubble tight damper, or by a building’s fan speed. In some cases, minor adjustments to a bubble tight damper can be made to accurately achieve the necessary exhaust airflow without affecting the control valve downstream.
Bubble tight dampers are typically installed directly above a cabinet, connected to a building’s exhaust duct work, but they may also be placed inside a ceiling compartment downstream of the exhaust connection. The latter setup allows for future servicing or adjustment when necessary.
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