The below information was not provided as final and definitive mold spore level specifications because health responses to mold spore exposures differ from person to person. Also, health responses to mold spores can be affected by the length of time you are exposed to spores, the size or type of spore you are exposed to, the levels of dust mite and roach allergens, individual sensitivity to allergens, emotional stress, general health, as well as other substances and factors that have not yet been discovered by mold inspectors. Thus, as a result mold spore levels alone at your property cannot always be relied on to always answer questions such as "Are molds in my environment making me sick."

The following information is just offered as some general helpful information and should not be relied on as any type of medical advise, see your doctor if you feel sick. 

"Guidelines on Assessment and Remediation of Fungi in Indoor Environments" published in 2000 by the New York City Department of Health."

The most widely accepted guideline by mold inspectors to help determine if indoor mold spore levels are indicative of a possible mold problem is the comparison of indoor and outdoor mold spore levels. Indoor mold spore levels should be similar to or lower than levels found outdoors, and the types of mold spores found indoors should be similar to types found outdoors. Most mold inspectors, certified indoor environmentalist, and industrial hygienists also will generally support the above mentioned comparison method and have determined that indoor mold spore levels should be similar in number and type to outdoor mold spore levels and types. The below listed organizations and governing bodies also support the above view.

ACGIH 1989, Canada M&H CO. 1991,   ACGIH 1993,   OSHA 1994, and Brazil 2000.

 
The American Conference of Government Industrial Hygienists (ACGIH) stated (Harriet Burge et. al) stated in 1987 that indoor mold spore levels are generally less than 1/3 the outdoor level and that when indoor mold is at more than this level remedial action should betaken to find the source of the elevated counts and to clean it up.

Burge 1990

If indoor microbial aerosols qualitatively differ from outdoor, and indoor levels are consistently more than double the outdoor levels and exceed 1000 cfu per cubic meter of air, investigate.  

 

The following are additional helpful general guidelines all from well known and respected industry experts.

They show actual numbers of spores or colony forming units per cubic meter of air.
Remember that> means greater than
so>1,000 contamination means greater than 1,000 spores per cubic meter or air indicates indoor fungal contamination. 
 

OSHA 1992 findings

>1,000 Contamination

ACGIH 1993 Findings

>1,000 High 

American Conference of Governmental Industrial Hygienists

(Air Sampling Instruments for Evaluation of Atmospheric Contaminants 1995)

100 cfu or less per cubic meter of air is low.

100 cfu to 1000 cfu per cubic meter of air is intermediate.

1000 or more cfu per cubic meter of air is high.

Much of the below information is from  Worldwide Mold Exposure Standards for Mold and Bacteria, Robert C. Brandys, PhD, MPH, PE, CIH, CSP, CMR and Gail M. Brandys, MS, CSP, CMR:

Brazil Government Findings 2002

100-500 normal indoor mold spore levels per cubic meter of air, can be higher in summer. 

Norway Government Findings

<750 acceptable.

Czech Republic 2000 Findings

> 2,000 Health complaints.

American Academy of Allergy, Asthma and Immunology/National Allergy Bureau findings 2002
1 - 6,499 Low- Only individuals extremely sensitive to these pollens and molds will experience symptoms.  

6,500 - 12,999 Moderate - Many individuals sensitive to these pollens and molds will experience symptoms.    

13,000-49,999 High Most individuals with any sensitivity to these pollens and molds will experience symptoms.  

50,000 Very High - Almost all individuals with any sensitivity at all to these pollens and molds will experience symptoms. 

Extremely sensitive people could have severe symptoms.

Please note that the above National Allergy Bureau findings are not trying to indicate what are expected spore levels, but what levels may effect various populations if exposed to such levels outdoors.  By no means should you try and use the above findings to determine what moderate indoor spore levels are. They they are not talking about indoor spore levels but outdoor spore levels. Your indoor levels should in most cases be several times lower than outdoor levels.


Caoimhin P. Connell

As a general rule, the normal indoor total fungal spore counts across the central portion of the U.S. (bounded by a latitude of, say, 35° north to 45° north), for healthy buildings (buildings not experiencing fungal problems) is usually less than 500 counts per cubic meter (counts/m3); with indoor concentrations exceeding 900 counts/m3 less than 15% of the time.4
According to my database, the viable fungi concentrations of non-symptomatic, healthy environments is not dissimilar; 383 colony forming units per cubic meter of air (CFU/m3), with a 95% probability that one sample in five (21%) samples will exceed 900 CFU/m3.
The above information is from Caoimhín P. Connell. who is a Colorado area mold expert with over 20 years experience as an industrial hygienist, he is also a law enforcement officer specializing in the identification and processing of clandestine drug labs. 
He has served on three of the ASTM International Standards Committees:  D22 (Indoor Air Quality), E30 (Forensic Sciences) and the E50 (Environmental Assessment, Risk Management and Corrective Action).


Recommended References Materials on Indoor Spore Levels For Mold Inspectors

*Worldwide Mold Exposure Standards for Mold and Bacteria, Robert C. Brandys, PhD, MPH, PE, CIH, CSP, CMR and Gail M. Brandys, MS, CSP, CMR