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Selecting BSL-3 Supply Air Duct Material and Decontamination

March 6, 2024

When considering the material for BSL-3 supply air ducts, the primary objective of biosafety design is to ensure a continuous duct path from the room’s supply diffusers and exhaust outlets (including biological safety cabinets [BSCs]) to ideally an airtight valve in the supply and exhaust ductwork, respectively. This sealed duct section not only maintains the concentration of decontamination gas or vapor required for efficacy but also prevents any leakage of the decontamination agent into surrounding rooms. We advocate for two options while advising against two other alternatives. Selection should be based upon a risk assessment of your facility’s ductwork design.

Option 1: Welded Stainless Steel Ductwork

In the context of BSL-3 facilities, employing welded stainless steel ductwork for both exhaust and supply systems is recommended. This ductwork extends from the BSL-3 laboratory to the airtight isolation damper of the HEPA caisson inlet and the low leakage shut-off control air valve or isolation valve. These supply and exhaust ductwork sections are referred to as “decon duct sections” to distinguish them from ductwork sections where the decon agent is not held for decontamination efficacy. During the decontamination process, the closure of only these two airtight valves is necessary, aligning with current design practices. This approach provides the necessary airtight duct sections for the supply and exhaust decon duct sections.

In terms of operational ease, the preparation for decontamination is streamlined through a dedicated button on the Building Automation System (BAS) interface. However, even with the implementation of welded stainless steel ductwork, it remains imperative to conduct integrity testing of the duct decon sections during the commissioning phase. This precaution is essential as the risk of potential welding pin holes in the ductwork hinges upon the proficiency of the welder involved.

Option 2: Galvanized Ductwork With Sealed Joints

An alternative to Option 1 is round galvanized steel ductwork with press fit joints, where all duct joints are sealed with duct mastic to ensure airtightness. Rectangular or square ductwork can be flanged with neoprene gaskets. Like Option 1, readiness for decontamination requires closing the two airtight valves. It’s advisable to conduct an integrity testing during commissioning. Additionally, this design entails an annual visual examination of duct connections to detect any breaks or deterioration in the mastic at ductwork joints. The risk of ductwork mastic failure hinges on the meticulousness of the mastic application process.

Option 3: Supply Spiral Galvanized and Welded Stainless Steel Flexible Ductwork (Not Recommended)

We discourage the use of galvanized and welded seam stainless steel spiral flexible ductwork for the decontamination section. Welding may not be feasible due to the gauge of the metal.

Option 4: Non-Metal Flexible (Not Recommended)

This approach is discouraged. While some engineers have devised their own modifications, replicating the custom duct seal raises concerns particularly when dealing with a carcinogenic decontamination agent.

Some material options offer unique benefits and considerations, ensuring the effectiveness and safety of BSL-3 laboratory decontamination operations. Option 3 and Option 4 should be avoided.

Contact World BioHazTec to schedule a free 30-minute consultation or send us an email. You are a conversation away from starting down a successful pathway to meet BSL-3 facility compliance.



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