E-mails 2003 M. Gilsenan

NYC 9/11 Public Portal Document

WTC Indoor Dust Cleaning Program Exhaust System Cleaning Procedures General

1. It is necessary to ensure that sufficient air velocity and/or negative pressure is maintained in the duct during cleaning, to prevent the dispersion of dust outside of the duct and to ensure that debris dislodged by mechanical cleaning devices is transported to a collection device. A HEPA filtered vacuum collection device shall be used to depressurize the ductwork to be cleaned. The AFD or vacuum collection equipment shall be adequate to collect all dust and debris released by the cleaning process and shall be attached to the existing ductwork with air-tight connections and located to attain maximum collection efficiency.

2. Provisions must be made to prevent the release of dust or debris at access points that are disturbed by the cleaning activities. If the branch ducts are accessible (typically 6’ or less in length from access point) it is not necessary to construct a temporary containment at the access point provided that a) they may be cleaned using HEPA vacuums with brush attachments and wet methods and b) negative pressure within the system is sufficient to provide a face velocity at the grille opening of 500 feet per minute. For larger branches (typically 6’ or greater in length from access point) that require the use of mechanical devices such as whips, brushes, and compressed air, or where it is not possible to establish a face velocity at the grille opening of 500 feet per minute, construct a temporary containment (e.g., a “cube” or “cocoon” with flapped entrance) at the access point to provide protection against the release of dust. Containment is not required for air handling units located outdoors unless located near active air intakes.

3. It is recommended that air filtration devices and vacuum collection equipment be exhausted to the outdoors unless special measures are taken to control the leakage of air contaminants from the exhaust of such equipment (see Procedures item 7).

Procedures

1. Identify the system to be cleaned including exhaust fan (e.g., “mushroom” fans), number and location of risers, and apartments or common spaces affected.

2. Determine how many floors on a riser will be cleaned as part of one continuous cleaning (5-10 floors).

3. Lock out and tag out the exhaust fan.

4. Attach a local capture, HEPA filtered, vacuum collection system to the riser to place the system under negative pressure. Polyethylene sheeting should be used to protect the floor underneath the vacuum collection equipment if located indoors.

5. Exhaust the vacuum collection system or AFD to the outdoors. If no window is available, a stairwell may be appropriate. Alternately, two vacuum collection systems or AFD’s may be connected in series so that a second unit filters the exhaust air from the first. Alternately, the cleaning contractor can have the collection equipment leak tested in-place by an independent third party to ensure that contaminants do not leak through the air cleaning device.

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