Release of lead containing particles from a wall enclosure

The 1995 Department of Housing and Urban Development (HUD) Guidelines for t he Evaluation and Control of Lead-Based Paint Hazards in Housing discusses using interior and exterior wall enclosures for lead hazard control. Leaded dust may be aerosolized inside enclosures and released through gaps and cr acks into a room. The effects of airflow and mechanical disturbances on dus t release were studied using a laboratory wall enclosure model with dust co llected from homes with lead-based paint hazards. Airflows relevant to resi dences were blown down the enclosure and out a 4-, 6-, or 3-mm horizontal g ap at its bottom, simulating potential enclosure failure. Then, low-frequen cy mechanical vibrations also were applied to the enclosure. No significant dust release was found when blowing air down the enclosure even at 37 cm/s ec (representing extremely high flow); release occurred only with this high flow and 3 Hz mechanical disturbances. Dust was released primarily from th e floor area immediately adjacent to the enclosure gap; the release rate fl uctuated over time, Most dust initially settled near the enclosure. Dust re lease for 1 hour at extreme conditions (high airflow with vibration) yields lead loading above the 1995 HUD clearance level of 100 mug/ft(2) only with in 3-4 cm of the wall; for the HUD standard (1 ft(2)) sampling area, the le ad loading does not exceed 30 mug/ft(2). Redistributing dust over the room' s 16 m(2) floor space yields average extreme-condition loading rate of 2 mu g/ft(2)/hour. At less-than-extreme conditions, dust would have to be releas ed for years without cleaning to yield a hazard.