Abatement Work Practices, Containment, and Engineering Controls
Containment construction
Containment isolates the work area and keeps airborne fibers from migrating. Critical barriers seal doors, windows, vents, and other openings. Floors and walls are covered with polyethylene sheeting, commonly 6-mil, with seams sealed. A negative-pressure enclosure uses HEPA-filtered negative air machines to maintain a pressure differential and exhaust filtered air outside. Warning signs, restricted access, and a decontamination unit complete the system. The enclosure must be inspected and repaired before work starts and throughout the job.
Work practices and engineering controls
Wet methods and amended water suppress dust. Glove bags and mini-enclosures allow small removals without a full room containment when used correctly. Wrap-and-cut techniques keep material intact during removal. HEPA vacuums clean surfaces and equipment. Work should proceed from clean to dirty areas, and debris should be bagged as it is generated rather than allowed to accumulate. No visible emissions are permitted, and settled dust must be cleaned, not swept dry.
Worked example
A room measures 20 feet by 30 feet by 10 feet, or 6,000 cubic feet. At a target of 4 air changes per hour, required airflow is 6,000 times 4 divided by 60, or 400 cubic feet per minute. A HEPA machine rated 500 to 600 cubic feet per minute at operating pressure can provide margin for filter loading and duct losses. The supervisor must verify negative pressure with a manometer or smoke test, not just assume the machine is adequate.
Traps that cost marks
- Sizing negative air machines by room floor area instead of volume and air changes.
- Forgetting critical barriers over vents and doors.
- Dry sweeping or shoveling debris.
- Assuming a glove bag is appropriate for a large, damaged removal.