Fog Introduction into Positively Pressurized Isolators
Teams often assume a larger fogger will force fog into an enclosure. That can be the wrong diagnosis. The system must overcome pressure, hose loss and entry restrictions without creating a jet that invalidates the airflow observation.
Why fog stalls at the boundary
Positive enclosure pressure opposes inward flow. Long or narrow hose runs add resistance. A splitter, wand or improvised fitting can reduce local delivery further. If the fogger fan or gas-delivery system has high volumetric output but low static-pressure capability, visible fog may accumulate outside while little enters the isolator.
Engineering options to evaluate
- Use an approved upstream introduction port within the enclosure air path.
- Reduce hose length, bends and restrictive fittings.
- Use a larger cross-section where the system permits.
- Coordinate temporary pressure state only if the protocol and process owner allow it.
- Select an outlet or delivery system with adequate static-pressure capability.
- Avoid connecting directly to a process port without contamination and pressure review.
- Run a non-protocol proof test with the exact setup.
Do not “win” by distorting the test
Document pressure differential, port geometry, hose layout, output setting and any temporary operating change. If the method cannot be demonstrated without distortion, redesign the study rather than declaring the generator insufficient.
Build a defensible fogger requirement
Send Applied Physics the room, process, utilities, documentation and safety constraints—not just a model number.