How do you calculate the cubic feet per minute (cfm) needed for negative air machines?

To determine the appropriate cubic feet per minute (cfm) for negative air machines during asbestos abatement procedures, using the formula for air changes per hour (ACH) is essential. The correct calculation involves taking the ACH (the number of times the air volume in a space is replaced in an hour) and multiplying it by the total volume of the space (measured in cubic feet). This product is then divided by 60 to convert the measurement into a per-minute basis.

This formula effectively ensures that the negative air machines can adequately exchange the air in the space to maintain safe conditions, particularly important in environments where asbestos may be present. This process leads to creating a negative pressure environment, thereby preventing the spread of airborne contaminants.

The other approaches, such as merely multiplying the total square footage by ACH or adding the volume to ACH, do not accurately consider the necessary air volume in cubic feet and do not result in a per-minute figure that is needed for setting up the negative air machines. Using a fixed rate of 500 cfm does not account for the specific requirements of a particular space, which can vary based on its volume and the necessary ACH for effective abatement. Hence, the formula that incorporates both ACH and volume is the most reliable