Work Practices, Engineering Controls, and Decontamination
Work-practice questions test whether you can keep fibers inside the enclosure and move workers and waste out without recontamination.
Core controls
- Critical barriers seal floors, walls, ceilings, doors, and penetrations before the enclosure is built.
- Negative-pressure enclosure with HEPA-filtered exhaust keeps the work area under a slight negative pressure, commonly about 0.02 in. w.g.
- Wet methods with amended water suppress fibers during removal; keep material wet through bagging.
- HEPA vacuuming replaces dry sweeping and compressed air, both of which are prohibited.
- Decontamination unit: dirty room, shower, clean room, with one-way worker flow and equipment decontamination.
Worked example
An enclosure measures 20 ft × 15 ft × 9 ft = 2,700 ft³. At 4 air changes per hour, required flow is 2,700 × 4 ÷ 60 = 180 CFM. A HEPA unit rated 500 CFM at 1 in. w.g. provides ample capacity, but install two units for redundancy and to maintain pressure as filters load. Verify pressure with a manometer and record it.
Traps
- Using box fans or recirculating air into the building.
- Shutting down negative air during breaks or at night.
- Skipping the shower or reversing worker flow.
- Over-pressurizing the enclosure so poly seals fail.