(1) Operation. The negative air pressure equipment shall operate continuously, 24 hours a day, from startup of negative air pressure equipment, through the cleanup operations and satisfactory clearance air sampling results being obtained, or the asbestos project is complete.

(2) Timing of installation. The negative air ventilation units shall be installed and made operational after the critical barriers and isolation barriers are installed.

(3) Negative air pressure. A negative air pressure, relative to areas outside of the enclosure, shall be maintained at all times in the regulated abatement work area during the asbestos abatement project to ensure that contaminated air in the regulated abatement work area does not escape back to an uncontaminated area.

(4) Manometer. A manometer shall be used to document the pressure differential for all OSHA Class I large and small size asbestos project regulated abatement work areas. A minimum of -0.02 column inch of water pressure differential, relative to pressure outside the regulated abatement work area, shall be maintained within the regulated abatement work area, as evidenced by manometric measurements. Once installed, on a daily basis at least twice per workshift, the asbestos abatement contractor's supervisor shall document the manometer reading within the daily project log. The manometer shall be installed and made operational once the negative air has been established in the regulated abatement work area. Magnahelic manometers shall be at a minimum calibrated semi-annually, and a copy of the current calibration certification shall be posted at the work site during Phase II operations.

(5) Ventilation units. If more than one primary HEPA-filtered ventilation unit is installed, the units shall be turned on one at a time and the integrity of temporary hardwall isolation barriers checked for secure attachment or the need for additional reinforcement shall be checked. A minimum of one additional unit having a capacity of at least equal to that of the primary unit shall be installed, as a backup unit to be used upon primary unit failure, or if necessary during primary unit filter changes. Ventilation unit exhaust ducting shall not exceed 25 feet in length, due to reduction in volumetric flow rates caused by friction.

(6) Power supply. A GFCI protected temporary power supply shall be available to satisfy the requirements of the total of all ventilation units.

(7) Power failure. In the event of electric power supply failure, abatement shall stop immediately and shall not resume until power is restored and exhaust units are operating fully. In the event of extended power failure (longer than one hour), after evacuation of all persons from the regulated abatement work area, the decontamination system enclosure facilities shall be sealed airtight.

(8) Air changes. Negative air pressure ventilation equipment shall be installed and operated continuously to provide at least four air changes in the regulated abatement work area every hour including during clearance air sampling.

(9) Openings in enclosure. Openings made in the enclosure system to accommodate these units shall be made airtight with duct tape or caulking or both. Where possible, the intake side of the negative air ventilation unit shall remain within the regulated abatement work area to permit filter changing, while minimizing equipment contamination and the likelihood of contamination of non-work areas.

(10) Installation and care. Proper installation procedures, including use of appropriate filters and manufacturer's recommended operating procedures shall be followed.

(11) Exhaust location. The exhaust shall be vented to the outside of the building or structure, to a controllable area away from public access. Each negative pressure ventilation unit exhaust duct shall not terminate less than 15 feet from a receptor or adversely affect the air intake of any building or structure. If the exhaust duct termination location for this section cannot be met due to allowable space restrictions or the regulated abatement work area being located above the ground floor, the exhaust shall terminate at the exterior of the building or structure, and all receptors less then 15 feet from the exterior exhaust duct termination location shall be plasticized with two layers of at least six mil polyethylene. Exhaust tubes may be grouped together in banks of no more than five tubes, with each tube exhausting separately and the bank of tubes terminating together at the same controlled area.

(1) The use of negative pressure air equipment is not required for the following:

(2) This exemption does not relieve the asbestos abatement contractor from the negative pressure equipment requirements on other portions of the same project that require the use of negative pressure equipment.