Saturday, March 12, 2016


By Edward R Close, PhD, PE

I am often asked to review laboratory analytical reports as part of consulting for clients using the Close Protocol for Preventing and Eliminating Mold in Buildings. If the sampling and analysis is done properly, lab reports will contain valuable information critical in the design of an effective site-specific protocol to eliminate mold problems in buildings.

Finding someone to do sampling in your area is more cost effective, however, you must also know what to look for when searching for a professional to do sampling. Please review our previously posted article:  FINDING A PROFESSIONAL TO DO MOLD SAMPLING

Having someone take appropriate and proper samples provides the information required to develop an appropriate protocol for a specific site. And good sample information can make thousands of dollars’ worth of difference in remediation costs.

Today, I want to address a very specific point about air sampling for mold spores that has been relevant in a number of recent cases; namely, the question of sample size.

One of the most critical parameters related to the validity of a sample is sample size. The sample size of spore-trap air samples is usually given in liters, while spore counts are reported in spores per cubic meter. One cubic meter (m3) is 1,000 liters. For comparison, a liter is approximately nine-tenths of a quart (0.908 qt.), and a cubic meter is a little more than thirty-five cubic feet (35.31 ft.3).

Occasionally, I receive lab reports from samples taken in buildings that have known mold issues, with suspiciously low spore counts. And in a few cases, the lab reports taken by other samplers have shown zero mold spores. When this happens, I know that the samples are not representative of actual conditions. A zero spore count prior to remediation or use of the Close Protocol is an almost automatic indicator that there is a problem with the samples. Either the equipment malfunctioned, the sample size (volume of air) was too small, or the sample was not collected properly.

If I receive a lab report for samples collected prior to remediation that has zero spore counts for mold, then I have to do some detective work. And because I have never personally seen spore counts at zero in any sample I have ever collected prior to doing the Close Protocol, I usually recommend asking the company that did the sampling to re-sample at no cost. Why? Because, if the sample is not representative of actual conditions due to equipment failure or technical incompetence, the results are worthless, and the client should not have to pay. If the company refuses, they simply are not trustworthy, and it would be better to look for another, more reputable company. Even if you don’t think the company is deliberately dishonest, it is a good idea to get a second evaluation, if the first one is suspect.

Now, it is quite common for samplers to collect samples that are not representative due to the lack of regulations and oversight in the mold remediation industry. I’m not a big fan of over-regulation, but it would be helpful to have some industry standards or best practices guidelines that protect the consumer. The following is how I determined what was the best practices I could follow to protect my clients.

When I started doing mold sampling, in 1995. I did some research and spoke with Microbiologists, Industrial Hygienists, and others who had been doing mold sampling, as well as those who performed laboratory analyses on samples collected. The best information I received was given to me by a Microbiologist working at an EPA approved lab, who reviewed mold samples every day as part of her job, and had done so for many years. I was informed by this individual that many people take samples that are not representative of the space being sampled. There are professionals who teach mold sampling techniques and tell people they only have to collect 25 liters of air. I was told by the Microbiologist, “It’s really just a math problem.” And being a mathematician/physicist and environmental engineer by education, this was easy for me to comprehend.

This person explained to me that they had many samples submitted for analysis that only captured 25 liters of air and this was not sufficient to get a representative sample. I have since seen numerous lab reports, myself, with samples collected by others that were based on this same sample size, 25 liters of air. And I must agree they are not representative.

A sample of this size might be adequate for a small enclosed space, like a small closet or under a kitchen sink, but it is NOT adequate for a normal size room. Why? Tests I’ve done personally, and tests done by others, show that, for the average room (anything up to 1000 square feet), with a ceiling of normal height, with the average recirculation rate of a central HVAC system (which should be running during the sampling) to be representative, the sample size must exceed 100 liters.

Based on room volume and air flow calculations (and this was recommended by the Microbiologist with years of experience in reviewing laboratory data for mold samples),  I determined that collecting 150 liters of air per sample was an appropriate sample size for any room up to 1000 sq. ft. with a normal ceiling height of 8 to 9 feet. Subsequently, I have always recommended collecting a minimum of 150 liters of air per sample. It is also necessary to collect at least one out-door sample for a base-line comparison of mold spores in the ambient air. I also recommend using a high volume pump, with in-date, high quality air sampling equipment, and the pump volume should be set on 15 liters per minute, the mid-range for most sampling pumps. I run the pump at these settings for at least 10 minutes.

And I tested the hypothesis that 150 liters of air is appropriate for spaces less than 1,000 square feet and with normal ceiling height. The difference in the results were astonishing, but only astonishing to someone who doesn’t understand the math. Here’s what I did:

With the help of a certified mold inspector (who was told during his training by another professional that collecting 25 liters of air was sufficient), I designed a controlled test. We collected samples in several rooms in a hotel in Atlanta, Georgia, using identical sampling equipment. We started two pumps at the same time in the same room. One pump was set to collect 25 liters, while the other was set to collect 150 liters of air.
The samples were carefully labeled, sealed, packed and shipped to the exact same environmental lab. The difference in the reported results were striking.

The 150 liter samples had spore counts up to twice the counts of the 25 liter samples, and the 150 liter samples contained one or more species not found at all in the 25 liter samples, including in one case, the species Stachybotrys chartarum, the infamous ‘toxic black mold’.

This underlines the importance of making sure the samples are properly collected as well as representative of actual conditions. A false negative result could cause you to underestimate a mold problem with potentially disastrous results to your health and the health of others.


Since the Close Protocol for dealing with mold infestations was introduced in 2006, we have helped many hundreds of people successfully eliminate mold and mold-related problems from their homes and workplaces. There are now tens of thousands of people using natural, non-toxic essential oils to prevent, eliminate, and/or control mold in their living environments, although a great many of them are doing so without our direct help. While we receive many calls and emails commenting on and asking questions related to mold problems and mold remediation daily, we are only two people, and our time (like everyone else) has many, many demands. Because of the volume of calls and emails, if you have questions, we strongly urge you to look for answers we’ve freely provided on this website, at public presentations we do, and through our publications available for purchase, before attempting to contact us directly.

Here is a link to our PUBLICATIONS page where you can order copies of our publications.
Basic information about the ten-step protocol is presented in Chapter 7 of our book, “Nature’s Mold Rx, The Non-Toxic Solution to Toxic Mold.” The book also discusses twenty case studies in detail, and most of the questions that may arise when the protocol is applied are answered in the book or on this website.

If you have questions about which diffuser to use and how to use it, please visit our

Many discussions of mold remediation options and detailed answers to questions about applying the protocol before and after sampling procedures are freely provided on this website. For those of you who require additional help, please visit our REQUEST HELP page.

You may also find answers to your questions by reviewing questions and comments posted below various articles and on various pages on this website. We do our best to respond in a timely manner to questions posted on this website, however, there are times when it may take a few days or possibly longer for us to respond.

May you be blessed richly and abundantly, and may you always enjoy Vibrant Health!

Very Sincerely,
Dr. Ed and Jacqui Close

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Copyright EJC Advantage LLC and Edward R Close and Jacquelyn A Close, 2016 and continuing.  This information and parts thereof may not be reproduced, copied, pasted, or posted elsewhere through any means whatsoever without written permission from the authors. We invite you to provide a link to this webpage if you wish to share this information with others.

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