Indoor area after a mold remediation that looked good but was not successfulAirborne Mold Spore Count Number FAQs
Q&A on Acceptable Level of Mold in Buildings

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Airborne mold spore count report or number questions & answers:

Frequently-asked questions about how to interpret the mold test number that is returned by your mold test consultant or mold test lab.

This article series discusses the possible significance of different levels of indoor airborne mold spore counts and mold test reports.

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Building Mold Contamination Levels: What are Acceptable Mold Spore Count Levels in Buildings

Stachybotrys spores (left) and structure (right)

These questions and answers about how to interpret the mold count returned by various mold tests were posted originally at AIRBORNE MOLD COUNT NUMBER GUIDE - topic home.

On 2017-10-29 by (mod) - what is the significance of an air test that found ONE spore of Stachybotrys Chartarum ?


you'll see that although they are wildly poplular (and profitable) an air test for mold is not reliable since the numbers can vary by several orders of magnitude depending on test conditions and test conduct.

Based on your report of one single spore (of any genera species) that was actually captured, extrapolating to 40 spores per meter, the count is in a quantitative sense, means almost nothing.

One single mold spore is certainly not a suitable nor meaningful "pass fail" criteria, nor would we spend a lot of money on its account. Heck it might have come in through a window or on the inspector's foot from a prior job. (Was she swinging her feet about during the air test for mold?)

Stachybotrys chartarum is certainly NOT the only mold, nor even the most important mold you should be looking for in a building mold investigation. For example while exposure to very high levels of S. chartarum can indeed cause serious medical problems, species of Aspergillus or Penicillium in buildings, at high levels, are more likely to cause serious respiratory illness.

S. chartarum's popularity stems from media and sales attention, not mycology nor good building science, except for this: it might be a water indicator mold.

This mold is considered a "water indicator" or "leak indicator" mold since it likes to grow on wet drywall or "sheetrock" or on other materials found in buildings like paper and often, wood. So S. chartarum MIGHT indicate that there have been mold-friendly conditions nearby.

S. chartarum is a big, sticky spore (evolved to spread by growing in straw and sticking to the cow's hoof). These spores are not often found indoors in air except when there has been a mold contamination problem somewhere nearby, or perhaps a mold cleanup job.

So even at low levels a "mold inspector" might warn you that looking further for a mold reservoir might be justified.

Finding even low levels of some molds, even when using an unreliable test method, might still be suggestive that building conditions deserve more investigation.

An actual, true, useful "mold inspection" would never rely just on a "mold test" of some sort or other. It would include

- interviews with building occupants about apparent building-related health complaints and individual vulnerability
- a taking of the history of the building, particularly leaks, sewage backups, and the like
- a thorough visual inspection for clues that suggest possible hidden mold reservoirs
- and a diagnostic report that says a heck of a lot more than

"Yeah there seems to be a mold problem here ... somewhere" - that's maybe diagnostic but not prescriptive: you have no idea what to do next, no idea where the problem might be, no idea what caused it, no idea what cleanup is needed.

So you end up having to hire someone all over again - paying all over again - to find out what to do.

The lab that processes a "mold sample" can't tell you what to do - they have no information about your building and little information about how the test was conducted. ALL the lab can do is tell you what they found in the sample.

If your "mold expert" didn't give you more information than the lab report, well that is, in my OPINION, disappointing and not very helpful.

On 2017-10-29 by Kirsten

I recently had a mold test done at my residence. The report Indicated "Elevated Mold Conditions!!".

I requested the lab data to be provided to me. Results from 6 samples taken at my residence: 5 air samples show NO Stachybotrys found and one indicates 40 spores/ m^3, 6% raw count 1. Based on the lab results, the presence of mold appear to be low, what are the acceptable levels? Is this an acceptable count?

On 2017-10-21 by Daniel

I recently had a mold test done in a home that I'd like to buy and all looks ok except the Aspergillus/Penicillium, which seems a very high count. I'm no expert and need some help to determine if there is a problem or not. Here was the report results:


Guest Bedroom: Raw Count = 182 M3=2,427

Living Room: Raw Count = 344 M3 = 4,587

Master Bedroom: Raw Count = 2,493 M3 = 33,240

Any assistance on this would be greatly appreciated. Also, what might be the cause of such a high reading or count?

On 2017-09-16 by (mod) - counts in your mold test report could certainly indicate an indoor mold problem


Those counts in your mold test report could certainly indicate an indoor mold problem because the absolute count was high.

The comparison with indoor and outdoor mold counts ONLY makes sense and is ONLY useful IF we know for sure that we are looking not just at the same general "type" or "genera" of mold but at the very same mold species.

The underlying theory was that we were going to try to avoid calling out as an indoor mold problem mold that just happened to blow in the window around the time an indoor air test for mold was performed.

Since getting mold identified down to the exact species is often beyond reasonable cost or test scope, we're not sure what to make of such count comparisons, even though everybody loves to obtain them.

On 2017-09-16 by (mod) - air tests for mold have a lot of variability - additional on-site information is needed


I am sorry to say that "air tests" for mold are unreliable: the actual count can vary several orders of magnitude depending on how a test is conducted, so a number of 270 could be 2.7 or 27,000 in actual truth. Worse, an air test does not tell us what needs to be cleaned, nor where the mold reservoir is, if there is one that needs action.

So the number is not very helpful without a competent onsite inspection to find the problem mold reservoir OR to tell you that enough looking in the most-suspect areas means that further action isn't justified.

The next time you hire a "mold inspector" my advice is to withhold payment until you are satisfied that you understand what is meant by the report you receive. An inspector who won't provide that help is ... not helpful.

On 2017-09-16 by Mandy Janicki

This is our second mold testing. Caldosporium came back at 270/m3 and penicillium/aspergillus came in at 1300. We are set to move in a few weeks. They said they will clean the vents to help remove the rest of the count. Not sure if this is a good number or not.

On 2017-09-15 by Eric

My son was away from his apartment for a few months and upon his return he discovered there had been a leak and the unit had mold. The owner of the building repaired the unit and gave us the below information regarding its mold testing. Is it safe for him to return to the unit?

Air samples were taken Friday (9/8/17). The results (reported in total spore count per cubic meter (spores/³cm)) are as follows;

Exterior of the building: 22,350 spores/³cm.
Inside #109: 13,293 spores/³cm (0.5947% of exterior).

On 2017-08-07 by (mod) - culture plates won't detect all mold genera/species but the car company told you to take a walk


I understand why you'd be frustrated and annoyed, as would I with people who more or less blow you off to avoid trouble for themselves - at least that's what it sounds like. Even though the tests you performed, especially if you used culture plates, are innately inaccurate, the worst inaccuracy is when such tests do NOT find evidence of mold - a false negative - when in fact there is a mold problem to be found and removed.

If your car smells like mold, which can happen if interior padding or carpets or headliner etc get wet, the solution is to find and remove those components, clean the surfaces, then air out the car, then restore it. Sometimes those costs are prohibitive.

I'm not aware of a government agency willing to step in to this individual consumer problem, especially with our current government's view of reducing government size, services, and protection. You can complain to your local better business bureau, and you can register what you believe is a health concern that could affect other consumers facing similar car leaks by notifying the US CPSC by reporting that under some situations your car is an unsafe product - - however I think the CPSC would reviewer might think that without a sufficient number of complaints this particular issue may not be an innate design or materials hazard in the car itself.

That leaves applying the lemon law which, depending on where you live, can be effective at demanding a new car if you've asked and failed to have a serious health or safety or other hazard corrected at least three times without success.

Keep me posted.


and be sure to see also CAR MOLD CONTAMINATION
both easily found again (if you lose these links) by searching using our on page search box to find "CAR MOLD"

On 2017-08-07 by denise marcoccia

My vehicle had a faulty evaporator core. It took Infiniti almost a year to determine where the musty mold smell was coming from. They removed the evaporator core but did nothing to remove the mold. The service tech said it was really "bad" I did mold test before and after and it is worse now level are 2600 asper.penicillium, 40 stachybotys, 200 basidiospores, 40 ascospors, 40 ganoderma. I'm allergic to Penicillin, my health over the last year has been horrible barely getting to work 2 days a week.

Car company saying the results are "inconclusive" and there was no mold..they never tested for it. The manufacturer Nissan says it's the dealers responsibility the dealer is saying it's the manufacturer's responsibility. Neither are doing anything. Can you advise a government agency that might get involved? I am just over guidelines for lemon law...

On 2017-07-12 by (mod) - mold testing is not useful in some situations


Unfortunately mold testing is not at all useful for the situation you describe - and its results would not change what action is or is not needed. Furthermore, while elevated levels of Pen/Asp (IF that's what's really there, which is arguable), are a health risk to building occupants,

If I can be frank in my OPINION, everything you were told (or that was reported to you and that you report to us) points to someone who doesn't know mold from molasses.

One can't say based on a "test" that a building needs to be demolished, and nobody in their right mind could to argue that based simply on detecting 31 physical mold spores of Aspergillus indoors that a building needs to be smashed up.

Depending on the test performed and how it was conducted, the data could be wrong by up to 4 orders of magnitude.

One does not "treat" mold - "treatments" like mold killers are the incorrect approach, don't fix the problem, and risk leaving harmful particles in the building.

An inspector whom you hire has a legal duty to report his or her results to you and to NOT report results to others except if s/he thinks that there is an immediate life safety threat to those others (unlikely as they're not living in the home) so your inspector has behaved unprofessionally, improperly, unethically, and possibly illegally as well as incompetently. Just sayin'

What's actually needed is a thorough inspection by someone who knows more than your "mold tester" and who will

- find the mold reservoirs
- define the extent of cleanup needed

and then a handyman (for small areas under 30 sqft of contiguous mold) or a professional cleaner for larger areas who will

- remove it or remove materials that can't be cleaned, like drywall
- clean the remaining surfaces
- fix the cause
- restore everything

On 2017-07-11 by Janet

We are in the process of selling our home and the buyer during a home inspection found signs of dried mold and active mold (moisture barrier was not fully dispersed during remodel).

We immediately stated that we would pay for the mold testing as we had no idea this was an issue or we would have addressed it immediately and felt that we wanted to make sure everything was right. The Air analysis in the Living Space on the main floor was Normal, The basement stated Problem with *Indoor Problem Fungi - Aspergillus 31 Raw Count, 208 Spores/m3, % of Total 25% **Non-Problem Fungi Penicillium/Aspergillus 51 raw, 342 Spores/m3, % of Total 42%

. The inspector will not call us back however spoke to the buyers (who did not pay for the test) and stated that these numbers were extremely dangerous and could never be treated with success. They would be better off tearing down and rebuilding. I am not a brain surgeon but can't help but think something is not right here.

On 2017-07-06 by Bob Kenworthy

We recently moved to our new home and found it had been flooded for several month prior to our arrival. Needless to say, it was a major loss. My question is this: After removing EVERYTHING, to include all insulation, walls, ceilings and floors, the mold remediation team took air samples immediately after completing deconstruction.

There is a LOT of dust and the entire house is open to the outside. The air samples taken show Penicillium/Aspergillus types ranging from 31,000/m3 to 53000/m3 in the room where the last deconstruction was done. The mold team did spray for mold on the rafters, floor joists and wall studs just prior to taking the readings. Is it possible that all of the dust and debris in the air is causing artificially high numbers?

The lab doing the analysis reported Sample Clarity and visibility as Moderate, with all other tests for Cladosporium species spores, Basidiospores, "Marker" spore types, (Chaetomium) and "Other" spore types, (Other brown, Smutes, Periconia, Myxomycetes), returning counts similar to outside samples. I am thinking I should do a better cleanup and spray everything with Total Solutions Lemocide before rebuilding just to be safe. Your thoughts or suggestions would be greatly appreciated!

On 2017-06-23 by BarbB

Daughters bedroom was tested and 150000 per cubic aspergillosis and penicillin air borne spores were found and my daughter has had years of respiratory sickness and asthma diagnosed 2015 I'm at a loss...

On 2017-05-27 by (mod) - what does a total spores per m3 of 1820 mean? Not much.

I'm sorry to say, almost nothing.
"Mold Tests" especially air tests for mold contamination are not reliable in part because the level of airborne particles in a building varies by 1-4 ORDERS OF MAGNITUDE depending on when where and how a test is conducted. So 1820 could be 1.82 or it could be 1,820,000 spores/M3 of air.

What's needed is a visual inspection to find where there is mold, to define what cleaning is needed, and what caused the wetness and thus the mold growth - as that must be fixed or the cleanup won't be effective; and if there is a large area of more than 30 sqft. professional cleaning is needed.

On 2017-05-26 by Anonymous

this basement has been wet, the test result is that the total spores per m3 is 1820, what does it mean

On 2017-03-17 by (mod) - out of context a mold count number doesn't help tell us much at all

Out of context the "number" means absolutely nothing.

We have no idea what inspections were made, what mold is or was present, what sort of test was done, what number or reporting scale is being used.

You are entitled to demand that whomever was paid (probably plenty) give a useful interpretation of what they found. Or get your money back and hire someone useful.

Keep in mind that "counts" particularly airborne mold counts can vary by 4 orders of magnitude ("1" might be "1000") depending on test conditions.

On 2017-03-17 by Barbara

I was told by board member that a report number of. #7 from an inspection was low and wasn't serious. W
This is in a club house at the Complex. What does this mean?

On 2017-03-10 6 by (mod) - the spore number isn't helpful unless we know what spores


The absolute number of spores may be less diagnostic than what is the spore mix; for example if Aspergillus or Penicillium are the dominant particle in an indoor sample I suspect the cleanup may have been incomplete.

An on-site expert should review the work that was done, the success of it, the clearance inspection and test, and then the building history and actual condition for possible mold reservoirs.

On 2017-03-10 by Tam

We had a flood in our basement, there was some mold, then company left wet dry wall which created more mold, asbestos was also found and remediated. They did an air clearance test that passed, said it was safe to go back. I continued to become more unwell as time passed, after remediation/reconstruction.

We had an independent person come into do another air sample and found slightly elevated mold spores upstairs but not downstairs where the house was remediated, in comparison to outside. We know the company did not cover the vents when remediating, left vapour barrier open and turned on the furnace!

So I assume they created airborne spores.
Q -Why would the count be higher upstairs now than down? I recently spent 5 days in hospital with sever asthma complications so trying to problem-solve in anyway I can. Thank you!!

On 2017-01-13 by (mod) - mold counts tossed over the wall are not nice


OPINION: If the people you hired to make "measurements" are not going to explain what the results mean, you should start by asking for your money back.

I do not assume anything about the crawl space from just your brief text. Sure mold spores might be mixed in with dust, but in a crawl space if there's mold contamination it's probably going to be found on organic surfaces (wood, paper, framing, subflooring) and sometimes in insulation. If the crawl area has ever been wet the risk of mold contamination there is greater.

Nobody in their right mind would pretend to give instructions to protect your workers from a brief e-text and a questionable mold report. Sorry.

On 2017-01-12 by Brian Pruden

5 air samples were taken in different locations in a crawlspace under a large building with a dirt floor and came back with readings of 16,000, 2,800, 400, 3,700 and 6030 Count/M3 of Aspergillus/Penicillium.

Visual inspection did not detect any mould reservoirs. The crawl space is dry and dusty and its assumed the spores were part of the dirt dust. Does this represent a hazard to workers and if so what should be done to make sure workers are safe.

On 2016-12-02 by Priscilla Palacio

We found penicillin, aspergillus and cladosporin in our home but most concerning is we found 38 spores stachybotrys and 17 chaetomium in bathroom. mold guy said not to worry, probably blew in window. if that's true why not in whole house? SHOULD we move? REMEDIATE?

On 2016-12-01 by Nicole Smith

My mother passed away and when we moved her belongings we discovered mold on her walls and carpet . We had it tested and came 300,000 particles per..they said it was very high and toxic . The mold was Aspergillus. My mother lived there for 5 years and lost 50 lbs, was in the hospital numerous times for dehydration and once with pneumonia . Could this high level of mold be a cause of some of her health issues ?

On 2016-11-01 by CHRIS


garage mold exposure levels spores/m3 is 290,000. basement is 21,000 and kitchen is 6,900. garage raw count is 508. also has basidiospores180m3 and cladosporium 360m3 raw 4 basement 21,000p/a raw 477 clad. 1,400 raw 16 kitchen/a 6,900 clad. 710 raw8. how bad is this?

On 2016-10-11 by Priscilla

My indoor air mold sample had <1 chaetomium. and a host of other molds 1200 for penicillin and aspergillus. i'm very concerned about my safety and my family. the mold guy said it's not significant number. how serious is it? my apartment was very small 1 bedroom. i got itchy, sneezing, headache, nausea whenever inside apartment>

On 2016-10-10 by (mod) - what kind of mold test do I need if I already know there's mold?


Not in my OPINION, rather it's a waste of money. Such a test, I'll bet dinner at Gusto's in Poughkeepsie, will be accompanied by a disclaimer of any responsibility for its results; the "professional" collects 3 samples, sends them to a lab, the reports come to you and you have no idea what to make of it. Even if the report indicates a problem remains you will have no idea where it is or what needs to be done. Such testing is IMO not worthwhile.

A mold test without an expert inspection of the building as I'll describe further is very unreliable.

Even a trivial event like waving a notebook or walking across a carpet can change the airborne particle level by 1-4 orders of magnitude! So is the count 4 or 4000? and what does "count" mean? Too much depends on circumstances and on how a "sample" is collected. A building can have a significant mold problem that does not show up in an "air test".

Air tests and their reliability are discussed at

Culture tests are 95% "wrong" when you open the kit.

I don't object to a few inexpensive (say $50./ea) screening tests of settled dust or of visible mold when they are supplemental to a thorough inspection by an expert who also reviews the case history, the cleaning and remediation work that was done, the whole building for its conditions that risk leaks or moisture problems, etc.

On 2016-10-10 by Jeanne

We know we had mold. We had drywall and insulation removed on the outside wall of the condo.

The shutters and vent hole were leaking. I'm trying to determine what type of mold test I need and how to choose someone to do it.

We have 'cleaned' the condo and want to make sure the cleaning was "acceptable". The recommendation for the professional is to perform 3 airbone tests (one upstairs, one downstairs and one outside for comparison). Is that reasonable?

On 2016-09-29 by (mod) -

Jessica, Sorry to be less than able to give a confident "yes" or "no" to your question. Air tests alone, without a visual inspection, are not reliable. The article above gives general guidelines. This article series points out that we can see up to four orders of magnitude in "counts" depending on how a "test" is conducted. So "tests" alone are a bit risky. Your 67 spores /M3 could as well be 67,000.

If your mold test professional who examined your home cannot give you any help at all interpreting what the report means to you, If it were my home I'd want my test-money back.

On 2016-09-28 by Jessica

Air sample was taken in 3 rooms of apartment for 5 min (75L of air). No visible leaks or water damage in apartment. Humidity not high. Some shower mold. We moved from a moldy place with our furniture and are scared of cross-contamination.

Cladosporium 67 count/cubic meters
Aspergillus/Penicillum 53 count/cubic meters
Curvalaria 27 count/cubic meter
Pitomyes 27 count/cubic meter
Smuts/Priconia/Myxomycetes 27 count/cubic m
Torula 13

Are any of these molds especially worrisome?

On 2016-09-25 by Theresa

Also, what are the Risks of such Levels?

What is High Concentration Level Mold Mean.

On 2016-06-21 by (mod) - 12,000 Aspergillus spores/meter of air -- IF that is what your "test consultant" measured -- is a high number

I don't know what "on the roof" means. 12,000 Aspergillus spores/meter of air -- IF that is what your "test consultant" measured -- is a high number enough that if that's inside the HVAC system further investigation and cleaning are probably in order.

As I whine constantly about these "grab a sample, get some money, send the sample to a lab, and throw a report over the wall to the cient" mold test people are not being very helpful.

A "mold test" or "mold count" used alone with no other information and no inspection of your building, no occupant interview, no leak history, no assessment of risk of hidden mold reservoirs, in short, no actual diagnostic information, is simply not reliable.

Your case is a good example: someone got paid to "do a mold test" but it's not diagnostic. Even if the number seems "high" it's not telling you what's needed. What did you pay for that "test" Leigh?

On 2016-06-20 by Leigh

We just had testing done in our office which is top floor. There were 12,000 aspergillus on roof, air handling system nearby. Is this number worthy of more investigating?

On 2016-06-18 by (mod) - air tests with no other data? Need more info. But raw counts of "1" are questionable.

Sorry, but a "mold test" or "mold count" used alone with no other information and no inspection of the home, no occupant interview, no leak history, no assessment of risk of hidden mold reservoirs, in short, no actual diagnostic information, is simply not reliable. No one should be risking the health of an occupant nor the decision to face costly expense to investigate and clean a mold hazard indoors on such a paucity of information.

Low spore counts like "1" raise an eyebrow if anyone draws important conclusions from such thin data.

Finally, if the "mold expert" whom you hired has simply collected test samples and then tossed a lab report "over the wall" to you without giving more helpful information, you should ask for your money back.

On 2016-06-18 by Debbie

I would like some input on
Stachybotrys Raw Count 1, Count/m 10, % of total 1.2
could/might mean in a Mold Report

On 2016-06-16 by Anonymous

Aspergillus/Penicillium: Bedroom 720 count/m3 Bathroom 840 Outside 200 These readings came from the home of my elderly father. Is it safe for him to reside in the home? He is in good health.

On 2016-05-23 by Zenzen

Had an ambient air test done. Asp/pen outdoor count (control) was zero but indoor was 200. Same with Myxomycetes. There is some visible mold water leakage noted in bathroom. How concerned shoudl we be?? Is 200 a high count?

On 2016-05-04 by fresh air m.i.a.

This is at my daughters school the portable is about 30'- 20'..They are saying that chaetomium is ok for kindergarten kids to breath. The air sample was a 2 min air test. All the kids in the class have been so sick this year. With upper respiratory problems, ear infections,sinus problems.. The list goes on..I currently have pulled my child from that school.

On 2016-05-04 by (mod) - ask the mold test consultant to explain the significance of her test results

If the person whom you hired is not able or willing to explain the results of their work to you, you should ask for your money back.

In my opinion no simple mold quantity count in an air sample is very helpful without other information. We don't have any idea how the sample was collected, over what what air volums,nor other factors that would help us to understand the number, such as the results of a visual inspection, the building leak history, the occupant complaints, and other things.

However high levels of Chaetomium, if that are a big percentage of the total of all spores found in the air, suggest that there have been leaks and that there is an interior mold problem somewhere in the building.

The mold reservoir needs to be found, its size determined, the cleanup requirements specified and the cause of the leak that cause the most growth needs to be identified and the leak repair made.

On 2016-05-04 by fresh air m.i.a.

I would like some help undestanding what 6,100 m3 of chaetomium means in an average sized class room.?

On 2016-04-10 by (mod) - how harmful is it to find Stachybotrys mold in air?

It's unusual to find the mold you cite in air and typically indicates that there has been demolition or disturbance of moldy materials, but an air test for mold is fundamentally unreliable and incomplete, unlikely to accurately characterize what molds are present in the building nor their extent except to possibly indicate a problem;

if an air test doesn't indicate a problem I have no confidence that it's correct. What's needed is a thorough inspection for visible mold, areas of high risk of hidden mold contamination, and conditions likely to cause a mold problem.

The mold you cite is a water-loving mold that particularly likes drywall; so I'd be looking not just for that mold but for what got wet and what else is present and how much of it is there.

How an air test is conducted changes the results of what it finds, quantitatively, by 1-4 orders of magnitude, so I don't know if the real airborne level was 4, 400, 4000, or 40,000 spores/m3 of air. But I agree that it's unusual to find this mold in indoor air at more than occasional spore level.

No one can assess the level of harm in your building from a brief e-text, but what you describe suggests that a more competent investigation would be warranted.

On 2016-04-10 by e.grant

A mold test was performed in my workplace and it was found that "an unusually elevated level of Stachybotrys mold was found with a result of 400. How harmful is this. There is a daycare right across the hall from the affected area.

On 2016-02-19 0 by (mod) - We find Stachybotrys chartarum in the air after it has been disturbed

We only find Stachybotrys chartarum in the air after it has been disturbed such as during a remediation or during demolition of moldy drywall.

But a more valid test is after 24 hours. I don't know what your remediators did about fresh air, cleaning, scrubbing etc. The important questions would be

- was all of the problem moldy material removed
- was the cleanup complete
- was there improper dust control and thus cross contamination in the building
- was the cause of mold found and fixed

On 2016-02-19 by Joe B.

I have had a mold test done following some remediation (immediately as they were leaving). We have replaced quite a bit of dry wall and trim. The new mold tests tested lower than outside levels, but 53 stachybotrys spores per cubic meter were found.

I've read that stachybotrys is not normally airborne when its alive, so is such a low level a cause for concern? Is that the dead, dried out stachybotrys flaoting around?

On 2016-02-15 by (mod) - how aggressive should we be when conducting an air test for mold?


I really like your question and have to give some different answers.

If you were trying to construct a "worst case" test of airborne particles in a home, turning on a fan or blower to stir up dust will help do that. You cannot assume that the airborne particle counts from a worst-case test are necessarily an accurate representation of the normal exposure of the building occupants unless those fans are often running.

I find several orders of magnitude in indoor particle counts depending on how much disturbance is going on in the test area. Just walking across a carpet or waving a notebook in the air will change particle counts over the test interval.

If you are trying to measure the probable occupant exposure level to airborne particles, conduct the test under the usual building conditions of fans on or off. If you've stirred up indoor air when you didn't want to you'd need to leave air moving equipment off for 24 hours to eliminate most of that effect. Even then some ultra-small particles may remain airborne even longer.

If screening a building for problematic particles, as airborne levels vary so widely, I like to collect settled dust samples.

A quantitative analysis of settled dust is nonsense unless the sample was created under controlled and known conditions. But settled dust will usually represent a longer time interval, possibly weeks or months of settling dust particles. Screening that sample for unusual particles or for dominant particles other than fabric fibers and skin cells can be informative.

During an aggressive test of an HVAC system for contaminants I placed an air sampler right inside the return air plenum and turned it on. An agent who was watching the operation became incensed when I used my flashlight to give a good RAP to the side of the return duct. "That's not 'normal'" she exclaimed.

My reply: "Really? Do you think the kids playing in this basement never toss a ball or throw a toy that bangs into this exposed ductwork?" She slapped me.

More truthfully, I was really looking for contaminants in the system, not characterizing usual exposure.

On 2016-02-15 by charles

Before and air quality inspection within the home, should to interior air be moved around by a low volume blower to stir up the
spores for evaluation by the lab.

Question: Aspergillus/Penicillum has a raw count of 54 and a spore count of 350

(Apr 4, 2014) ida said:
hello, i had an a mold inspection done in my apartment. Aspergillus/Penicillum has a raw count of 54 and a spore count of 350 in my bedroom. Also, in my bedroom was Cladosporium. Outside raw count is 3 and count /M3 was 20. Inside raw count is 8 and count/M3 is 53. Are these counts worth bringing up to the landlord, and are they any cause for concern.


Ida, as you can read in the article above, these are low counts, and the outside comparison is more or less nonsense anyway. But interpreting even low counts of airborne molds requires some intelligence, a building inspection, client interview, case history, building history, because even low counts can sometimes indicate a problem.

A "mold count" alone is *NOT* a reliable indication of building conditions. THerefore if your mold tester did not answer your questions and you have to resort to asking us, who know nothing about your building, it's disappointing and suggests you paid too much for too little. Ask for your money back if your test person can't give intelligent answers to your concern.


(Dec 23, 2014) Kim said:
Hi. We hired a company to come inspect our home. Got lab report back today. Hyphal Fragments 2 26 4 52
Spore Trap Used
raw ct. spores/m3 % raw ct. spores/m3 % raw ct. spores/m3 %
Alternaria 1 13 3
Ascospores 3 39 16 9 117 14
Basidiospores 6 78 32 27 351 77 54 702 82
Bipolaris/Drechslera 1 13 5
Cladosporium 9 117 47 6 78 17 3 39 5
Curvularia 1 13 3
Colorless/Other Brown 2
Background debris (1-5)3 3 3 3
Sample Volume(liters) 75 75 75
TOTAL SPORES/M3 19 247 35 455 66 858

Can you please help? I've read about bipolaris and have questions.



In the article above we give some general guidance about the significance of airborne mold spore counts.

However, the meaning of any mold test is very dependent on building conditions at the time of the test, and no mold test makes any sense without a visual inspection of the building and occupant interviews.

If your mold test company cannot answer basic questions about the meaning of a test they provided, I would ask for a full refund of whatever fee you paid. After all, the test person was there to inspect the home not just to collect a sample, right?

Let me know if you get nowhere with the person who actually inspected your home and we'll take it from there.

Question: I don't know how to read my mold report

17 June 2015 Amber said:
I just received the official mold report from an inspection being done in a house that I rent. I don't know how to read the reports, but I wanted to know if there was a way to find out if this specific mold that was elevated is making my family and our dog sick.

These were the molds that showed up with the top results on the report

Penicillium/Aspergillus: raw ct - 138; Spores - 1790; % - 77
Cladosporium: raw ct - 21; Spores - 273; % - 12
Basidiospores: raw ct - 18; Spores - 234; % - 10
Smuts/Periconia/Myoxmy: raw ct - 1; Spores - 13; % - <1



I would ask for a refund from anyone who inspected and tested my home for mold but who would not or could not give me any meaningful answer to the most basic questions about the home's mold contamination level.

The article above gives some general guidelines about when airborne mold counts are indicative of a water damaged building where significant mold contamination is or is likely to be present, but mere counts with no data about the building and still less data about how and where the tests were performed don't tell me a darn thing.

The counts you give have no meaning to me without knowing something about the building, its leak history, construction, materials, occupant complaints, visible mold contamination, identification of risk areas for hidden mold and results of their exploration.

This article is part of our series: the Mold Action Guide which provides an easy to understand step-by-step guide for dealing with toxic or allergenic indoor mold and other indoor contaminants: what to do about mold "mildew," moisture, in your house or office, building-related illness, involving your physician, treatment, sick building investigators, reduction of irritants, and special products to help clean buildings and air.

Article Series Contents


Continue reading at AIRBORNE MOLD COUNT NUMBER GUIDE or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.




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