HVAC cleaning procedures technical questions comments, Jan 2003

NYC 9/11 Public Portal Document

Cosiments on Exhaust System Cleaning Procedures.

General 1. Is there a measure for sufficient negative pressure or is sufficient as defined in item 4. Of the procedures?

Some duct cleaners use vacuum collection systems that are not HEPA filtered. Specify HEPA filtered vacuum collection system and loose the commentary about asbestos contractors and duct cleaners.

Is "adequate to collect all dust" a visual observation?

General 2. Containments are not addressed for exhaust fans/mushrooms similar to the A/C units procedures. Is this because they are outdoors? If so we should be consistent. What constitutes a "containment"? Is this similar to a "tent"? Must the containment be exhausted and will it be air tested? Although there are not many horizontal ducts longer than 6 feet, this would apply to any location that we use to access the riser for cleaning (ie: bathrooms and kitchens).

General 3. What are "special measures"? Insert note: Refer to item 5. under procedures.

Procedures 4. Field conditions and stack effect may require that we exhaust from the roof of highest point of the riser, rather than the lowest point. If it is necessary to exhaust from the roof on vertically feeding systems or as mandated by access points, cleaning should start from the grills toward the fan unit. It is more appropriate to specify that cleaning will always start and work toward the vacuum collection system rather than a component of the exhaust system.

Procedure 5. Delete: through a window. This does not apply if exhausting from the roof. I have been told by equipment manufacturers that it is not recommended to run two vacuum collection systems in tandem, as it creates a backpressure that can damage the equipment or cause gasket leaks. DOP testing should be by others (Athenica).

Procedure 8. Removal of mushroom will be out of sequence if exhausting from the roof.

Procedure 10. Sequence may be from bottom up. SSC recommends cleaning the grills and branch ducts before the riser to prevent recontamination of the riser.

Procedure 10. Some toilet vents are fabricated of sheetrock. Nylon brushes should be used. Exhaust ducts should be modified as appropriate.

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