Where extensive remediation is required and it is anticipated that the air within the containment will undergo significant contamination, air filtration is employed both within and outside of the containment during and after removal of material. 

Air filtration consists of HEPA filtered negative air machines with both the intake and exhaust to the indoors.  The air scrubber machine(s) filter minimum of four air changes per hour within the containment and one air change per hour outside of the containment.  

The air within and outside of the containment is filtered for a minimum of 96 air changes, and a minimum of one day after the gross removal of material is complete.  When space is available, the intake and exhaust of the air scrubber is separated by at least 10 feet to provide good air circulation and mixing.  This can be accomplished with a flexible extension attached to the exhaust of the air scrubber. 

Additional fans, or electric blowers, may also be used to promote good air circulation and mixing during the air-filtration period.  Cleaning (HEPA vacuum and wet wiping) inside or outside of the containment can be conducted during this post-remediation air-filtration period.  During the post-remediation filtration period, the doors and windows of the building are kept closed.