How many clearance samples should be taken for mold remediation?

In a recent article written by Dr. Harriet Burge, in The Environmental Reporter for EMLAB P&K, she discussed this question and came up with an interesting answer. As we discuss in our mold remediation classes, clearance sampling is used to document that the mold contamination was successfully removed as part of a well designed written protocol (scope of work).

In preparing the scope of work for the project, the consultant should take pre-abatement air samples to have a picture of the air before the remediation. Air samples should be taken inside the area being remediated, outside the area being remediated, and outside the building. This sampling must be representative of the air in the areas sampled. Using these results and the data created, the consultant (writing the remediation protocols) can pre-determine the percentage change they want to see in the clearance samples and add that information to the protocols.

Based on Dr. Burge's article she suggests that the number of air samples should represent 5% of the air in the room or 2% of the air in the room if the air is thoroughly mixed. (when mixing air the method used should not send so much dust in the air that it will require you to sample for less than 10 minutes). Assuming a 10 minute air-o-cell sample represents slightly more than five (5) cubic feet of air, a 1000 cubic foot room would require four (4) samples to achieve 2% with proper mixing and ten (10) samples without mixing.

It is important to remember no single sample is representative of any environment (as discussed in Dr.Burge's article and supported by various publications by the American Conference of Governmental Industrial Hygienists (ACGIH), the American Industrial Hygiene Association (AIHA), and others). As consultants, we must ensure the remediations we recommend are complete and this can only be accomplished if the interpetations are supported by quality data that is representative of the environment we are sampling. Multiple samples are the only way to ensure the environment is accurately evaluated.