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White Paper: The Use of Negative Air Machines in Clearance Testing for Mold Remediation Projects

For large-scale remediation projects, there is near-unanimous agreement on the need to physically contain the work area and isolate it from adjacent nonwork areas to help prevent the spread of mold to those areas. A majority of the guidelines also recommend the use of HEPA-filtered NAMs to establish a negative pressure differential between the work area and adjacent spaces. One consistent theme on the reasoning for containment is the need for effective removal of mold contamination while maintaining the safety and health both of the remediation workers and of the other building occupants. Additionally, the use of NAMs helps to prevent cross-contamination of previously unaffected adjacent spaces.  This new IAQA white paper provides guidance on the proper use of negative air machines in the remediation process.


One remediation procedure applied inconsistently is the use of blowers and fans called negative air machines (NAMs) to create a pressure differential between the work area and surrounding areas to create a space that is negatively pressurized compared to the uncontaminated or less-contaminated areas. In some instances, NAMs have been turned off before clearance or post-remediation verification (PRV) air sampling. This practice could be considered by some to be inconsistent with other remediation practices designed to protect the nonwork areas from contamination from airborne or settled mold spores. As a result, IAQA formed an ad hoc committee to define the issue and to identify gaps in current knowledge and practice. After reviewing the currently available literature, the committee developed this white paper.

It is the consensus of the committee that mold remediation work, particularly for large areas (greater than 100 ft2 within the same specific area), be conducted where the work area is isolated and maintained under negative pressure throughout the entire remediation process. If required, verification that airborne fungal spore concentrations meet a predetermined acceptance level can proceed with the NAMs either on or off. The determination of whether a NAM is in operation during the collection of PRV samples should be evaluated on a case-by-case basis by a competent person, who should document the decision and the rationale behind it. The committee concludes that current industry guidelines and recommendations do offer the latitude for the coexistence of each position within the industry. However, the committee also believes that further action is necessary to clarify the specifics regarding NAM use as well as PRV and clearance sampling criteria. Both the “NAM on” and the “NAM off” premises lack scientific data supporting them and require further research.

The committee provides specific recommendations regarding further research to be done in this area, and encourages other IAQ industry partners to use this document to foster further discussions on this matter to better understand the latitude of professional judgment in the use of NAMs on mold remediation projects and to adjust their own guidance documents accordingly to be consistent with these findings until additional scientific evidence becomes available.