Guidelines for Cleaning Ducts and Unit Ventilators - 6/02
The unit ventilators and related air intake plenums must be cleaned inside a contained enclosure with negative air filtration (similar to asbestos abatement tent procedures). The work should be performed by certified environmental professionals. All porous insulation inside the units and plenums must be removed and replaced with non-porous insulation. If necessary a lock-down encapsulant should be applied inside the plenum to seal any residual dust. Clearance testing must be performed inside the unit ventilator/plenum and the classroom to insure the effectiveness of the cleaning procedure.
The classroom must remain vacated during the abatement procedure. If possible classrooms on either side should also be vacated to create a buffer zone. Although summer school has been scheduled, the cleaning can take place as long as the rooms being cleaned and preferably the adjacent rooms are unoccupied during the cleaning.
All air handling units (AHUs), supply and return air ducts must be cleaned by a certified duct cleaning contractor. Certified NADCA (National Air Duct Cleaners Association) Air Systems Cleaning Specialists (A.S.C.S.) must be on-site for each shift.
All AHU chamber components, such as fans, intake louvers/dampers, coils, pans, filter assemblies, etc. which are within the air stream must be cleaned.
The air conveyance system should be cleaned starting at the return air duct system and/or outdoor air intake, air handling unit, and cleaned to the floor distribution system. Ductwork sections which are being cleaned must be sealed or blocked to insure that contaminants are not spread into areas which have been cleaned, or areas which have not yet been cleaned. Cleaning should progress in the same direction as the system airflow. Material removal will be at the downstream end of the section through an access connection in the bottom of the duct or at ceiling diffuser connection. All other openings are to be sealed except for an upstream opening to supply air to the vacuum and filter system. The portion of the system which is being cleaned must remain under a minimum negative pressure of .25 inches w.g. at all times.
Collectors shall be fan powered, high efficiency dust and particulate collection systems. The collection systems shall be a self-contained unit, with necessary components to adequately prevent dirt and debris from entering the diffuser plenums by capturing this debris within the collection device. The components of the collector that connect the base collection unit to the diffuser plenum shall be air tight and reusable from area to area. The filtration within these collection systems shall be at a minimum of two state filtration 99.97% efficient on 0.3 micron DOP particulate challenge at the rated flow.
Access doors are to be provided at pre-determined locations within each air conveyance system to facilitate inspection program and future maintenance inspections. The quantity, size and locations shall be submitted to the school construction representative for review and approval, prior to the start of cleaning.
For ducts more than 2 square feet in cross-sectional areas, provide and install minimum 20" x 20" access doors every 100 feet apart for worker access. The duct cleaning Contractor shall verify that the ductwork is capable of sustaining the weight of a worker inside the duct. Cleaning can be manual, with a combination of scraping and compressed air blasting.
For ductwork less than 2 square feet in cross-sectional area, insert air powered cleaning tools and contact all interior surfaces of the duct by contact cleaning.
Where the ducted systems have internal porous insulation, an encapsulating paint should be considered (e.g., Portersept 3830 or Fosters 40-20).Using a spraying system with approved resurfacing agent, apply a one (1) mil thickness wet application to the liner surfaces or the maximum as recommended by the manufacturers specifications. Ensure even coating with a broad tip spray.
All workers must wear personal protective equipment (PPE) including HEPA filtered respirators. Clearance testing must be performed inside the ducts to insure the effectiveness of the cleaning procedure.
The AHUs and duct risers must be cleaned while the building is unoccupied. When the branch ducts on a given floor are being cleaned, that entire floor must remain vacated during the cleaning procedure.
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