When should negative air machines be shut down after barrier construction?

The correct answer focuses on the critical point of safety and compliance with regulatory standards regarding asbestos removal and handling activities. Negative air machines, which are used to create negative pressure and filter potentially contaminated air, should only be shut down after the area has passed clearances.

Passing clearances indicates that air quality tests have confirmed that asbestos fibers are no longer present at harmful levels, making it safe to stop containment measures. Shutting down these machines prematurely, before confirming that the area is free from contaminants, could expose workers and the environment to the risks associated with airborne asbestos.

The importance of waiting for these clearances cannot be overstated, as they ensure that the area is truly safe for re-entry and that proper compliance with safety regulations is being maintained. This practice is vital in preventing exposure and ensuring that all necessary precautions are taken for public health and safety.