How many air changes per hour are required when negative air machines are utilized?

The requirement of 4 air changes per hour (ACH) when utilizing negative air machines is based on established safety standards aimed at controlling airborne contaminants, particularly in environments where asbestos abatement is taking place. Negative air machines help create a controlled environment by exhausting air from the work area while filtering and ensuring that no contaminants escape back into the surrounding areas.

Achieving 4 ACH is crucial in maintaining air quality, as it ensures that the air within the space is effectively replaced and that any asbestos fibers or other hazardous materials present are continuously filtered out. This level of air exchange is adequate for minimizing health risks for workers and surrounding occupants by diluting any potential contaminants with fresh, filtered air.

The other options suggest either insufficient or excessive air changes. While lower rates might not effectively control the concentration of airborne contaminants, higher rates could lead to unnecessary energy consumption and may not provide proportional safety benefits in typical asbestos-related scenarios. Thus, 4 ACH strikes an effective balance to ensure safety and efficiency during asbestos abatement operations.