How To Perform Clearance Sampling
By Dr. Harriet Burge, EMLab P&K's Director of Aerobiology
I have had several questions lately about clearance or exit sampling. As we have discussed in
the past. This task involves sampling for the negative case, which is always difficult, if not
As usual, how you do clearance sampling depends on exactly what you want to document. Do you
want to prove that the remediation was designed and performed correctly? That the environment
is better than it was before remediation? That the indoor environment is better than that
outdoors? That exposure to occupants is below some predetermined limit? Each of these needs
requires a different approach to sampling.
1) Was the remediation designed and performed correctly?
In this case you can inspect the work that was done, and use some sampling method (dust sampling?)
to document that in the process of remediation you have not contaminated the rest of the space.
2) Is the indoor environment better (with respect to mold) than it was before remediation?
This question might be answered by inspection as above. However, this assumes that the principal
problem with the environment was recognized during the initial inspections and design of
remediation protocols. A series of air samples collected before and after remediation would
provide some indication of the potential for hidden, unremediated mold. Combined with bulk or
surface samples of discovered mold, it might also provide a clue as to whether or not all of
the mold growth has been discovered.
3) Is the indoor environment better (after remediation) than that outdoors?
Here can collect a series of air samples outdoors and in for direct comparison, or for
comparison using a statistical method such as the
4) Is exposure to occupants less than some predetermined limit?
In this case, you have to decide for yourself what the predetermined limit will be, since there
are no reasonable guidelines to assist you. You might make this decision after collecting air
samples to determine what the pre-remediation exposure are, and consider how much lower you want
the exposure to be.
So obviously a single air sample or a few tape samples are not going to tell you much, and
certainly won't be defensible if the occupants continue to have problems. It should also be
clear that clearance protocols must be designed individually for each specific case, although a
structural frame work can be developed and details added.
This article originally appeared in the April 2011 issue of Indoor Environment Connections.
Reprinted by permission.
About Dr. Harriet Burge
Dr. Harriet Burge is EMlab P&K's Director of Aerobiology and Chair of EMLab P&K's
Scientific Advisory Board. Widely considered the leading expert in indoor air quality (IAQ),
Dr. Burge pioneered the field more than 30 years ago. She has served as a member of three
National Academy of Sciences committees for IAQ, including as Vice-Chair of the Committee
on the Health Effects of Indoor Allergens. View Dr. Burge's Curriculum Vitae.
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