Airborne Particle Calculations
How to calculate airborne particle concentrations for mold, IAQ, allergens, or other forensic particle studies - Mold Test Laboratory SOPs
AIRBORNE PARTICLE ANALYSIS METHODS - CONTENTS: Detailed procedure for computing the count of particles per cubic meter of air - indoor air quality and mold test lab procedures
POST a QUESTION or READ FAQs about computing the count of particles per cubic meter of air - indoor air quality and mold test lab procedures. Questions & answers about how to calculate airborne mold or other airborne particle levels expressed as n particles per cubic meter of air
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How to calculate airborne mold or other airborne particle levels.
This document describes proper procedures for evaluating mold and other aerobiological samples for purposes of
identification of environmental sample contents and to help in assessing potential exposure of building occupants
to levels of indoor particles, mold, allergens, and other materials. Included are procedures for proper
particle counting from air samples, lab chemistry for sample preparation, and a directory of field sampling
practices and methodology.
References are also given for particle identification.
This is Daniel Friedman's general aerobiology & forensic procedure. Other mold test laboratories & forensic laboratories follow similar procedures but details and policy may vary. For clarity, some topics are
addressed in separate documents listed here.
How A Mold Lab or Forensic Lab Calculates Airborne Particle Concentration Levels
Example % of Trace Calculations for an Olympus CH-2 microscope #5F0837
To form an accurate understanding of the percentage of particle trace that has been examined in the microscope we need to know the physical area of the particle trace and the physical area encompassed by one field of view in the microscope for a given microscope objective (e.g. 40x or 100x objective).
[The actual magnification in the field of view is the product of the microscope objective magnification and the microscope eyepiece magnification. Typically the eyepiece magnification is 10x or 15x.
Typical microscope objective magnifications used for aerobiology, mold particles, pollen, and other small particle identification and counting are 40x, 60x, 100x or 120x.
Indeed while counting is faster and easier at the lower magnifications of 40x or 60x, only by going to 100x oil immersion can we reliably see and count small particles in the 1-5u range, such as Penicillium or Aspergillus spores.
If we are counting less than 100 percent of the particle trace, the dimensions of the trace width and length are required to complete airborne particle
concentration calculations. While we give the standardized particle trace dimensions and the percentage represented by one pass across the trace at different magnifications (below), keep in mind that the true particle trace on an air sampler slide varies due to site conditions and other factors - as you can see in our example photo at left.
@1000x: .173mm field width/14.4mm x 100 = 1.2% of trace per pass
@ 400x:.44mm/14.4mm x 100 = 3.05% of trace per pass
@ 1000x: .173mm/14.0mm x 100 = 1.24% of trace per pass
@ 400x: .44mm/14.0mm x 100 = 3.14% of trace per pass
@ 1000x: .173mm/.145mm x 100 = 1.193% of trace per pass
@ 400x: .44mm/.145mm x 100 = 3.03% of trace per pass (e.g. use .303 as divisor
in formula below)
(WARNING: this data is
calibrated for a particular microscope in our lab. This number must be
calibrated to the microscope, and optics used for the examination of the
A Detailed Example for Airborne Particle Concentration Counting Calculations using the Allergenco Time-Lapse Impaction Sampler
To compute the airborne concentration of any individual particle (or of all particles) in an air test sample we need to know the air sample volume (total liters), for which we need to know the air sampling device flow rate in liters per minute and the number of minutes the sampler was run. We also need to allow for cases in which we count less than 100 percent of the particle trace. The basic formula for calculating the airborne particle concentration in an air sample is
Particles/M3 = [ 1000 liters per cubic meter / liters of air sampled ] x [Raw particle count / % of particle trace examined]
1. Sample Volume in Liters = (Sampler run time in minutes x calibrated sampler flow rate in LPM)One M3 is 1000 cubic liters. So another version of the calculation could use
2. Sample Volume in M3 = [(Flow rate in
LPM)/1000] x [run time in minutes]
(or if you prefer, 15 lpm=.015 M3/m )
To obtain the total volume of air that was processed during an air test for airborne particles we multiply the air flow rate of the sampler (e.g. 15 lpm) by the number of minutes the sampler was operated (e.g. 3 minutes).
E.g. if we ran our Burkard Personal Air Sampler for 7 minutes, knowing that this devices pulls air through its impaction sampler slit at 10 liters per minute, 10 x 7 = 70 liters of air in our sample.
3. Percentage of the total particle trace that was examined. As we explain below, very dense or overloaded samples may have so many particles as to preclude an accurate count of 100 % of the trace sample. If we are counting less than 100% of the sample we need to include that factor in our calculations.
Trace length counted = (Microscope field diam) x (#
4. Particles / M3 = (raw particle count / % portion of trace counted) x
(1000L/M3 / sample volume in L)
Example 1 - Number of particles represented by a 10 minute air test using an Allergenco impaction sampler
Allergenco time-lapse impaction air sampler is run for 10 minutes, 150 L was
sampled (10 minutes x 15 LPM)
For the Allergenco, 1 cross trace pass at 1000x = 1.193% of
For the Allergenco, 10 cross-trace passes = 11.93% of the
trace, or .1193 of the trace.
Example: If Particle "x" was counted at 653 particles in 10
passes of the trace at 1000x.
Example: if 100% of the trace was counted, then the "raw count" will be divided by 1 (100%)
/ (.1193 of
trace/pass )] x [1000 L in 1 M3 of air / 150 L in sample] = 34,490.6 particles/M3
of air in the sample. This number should
be documented in the lab as 34,490.6 but in an interpretation may be described
as 34,500 particles/M3 of air.
Airborne particle concentration is found to be 34,500 particles/M3 of air.
Example 2 - Airborne mold concentration represented by an 8 minute air test using a Burkard Personal Sampler
The Burkard PAS samples air at 10 lpm, so an 8-minute sample represents a test volume of (10 x 8) = 80 liters of air.
We counted 100% of the particle sample trace in this case, identifying the number of occurrences of each particle type found in the sample. Using just one of these particles, Alternaria sp., we found 7 Alternaria spores in the entire trace.
Particles / M3 = (raw particle count / % portion of trace counted) x
(1000L/M3 / sample volume in L)
An Alternative count procedure for Airborne Particle Concentrations
Measure the actual trace length. Divide the trace into equal
segments by 4ths
Count 1 segment completely, selecting a representative
segment after scanning lengthwise the whole trace. Multiply the actual count by
the number of segments (4) to get the "trace total count. ["trace total count"]
x [1000/sample volume] = particles/M3
General Counting Rules for Airborne Mold or Other Particle Concentrations in Air Tests & Samples
Interferences in Reaching the Objective of 100% Trace Counting - handling overloaded air particle samples
For low density particle traces it is easy and reasonable, as well as most accurate, to count 100% of the particle trace area. Where practical, in our lab we count 100% of the particle trace on the sampling slide or cassette.
Our photo (left) illustrates a reasonable-density air particle sample trace on a slide from one of our Burkard Personal Air Sampler devices. By examination using the naked eye the trace density appears not to be overloaded, though final decision on how to process this sample will be made after the initial examination in the microscope. This particle sample was collected inside the return air plenum of a heating & air conditioning air handler, using passive air sampling methods - we just placed the sampler in the space and ran it for a number of minutes, with minimum disturbance to the environment. And of course the equipment was OFF during the test.
But some airborne particle or dust vacuum particle traces are so dense with particles that an accurate particle count can be difficult, impractical, or even impossible. Our second Burkard PAS particle trace (below left) was collected in the same location as the first particle trace above, but we used our standard "aggressive" sampling method intended to dislodge local particles that might otherwise not appear in the test.
We rapped once with a flashlight on the side of the air handler's air plenum chamber. You can see that this approach made an enormous difference in the number of particles collected even though we ran the air sampling device for the same time interval as in the first test. This sample is probably overloaded.
For example, a very dense particle trace suggests that during the latter portion of the air sampling period, late-arriving particles may impact particles already on the trace medium surface rather than contacting the more sticky trace capture media. As a result, the particle bounce rate increases late in the air sampling period - such particles are lost and thus under-represented in the trace result.
For thick, occluded, dense particle traces too, the absolute number or raw particle count could be in the thousands, making accurate manual counting inaccurate or infeasible. For such dense particle traces our minimum objective is to count 25% of the trace. 20% may be used in the most difficult cases.
We first scan the entire particle trace at lower magnification, perhaps 400x, in order to note the presence or absence of anomalies such as voids in the trace capture media or thick clusters of particles or large particles that can substantially affect the accurate particle count number and that might be missed during a 25% random trace area count approach.
Particle or mold spore cluster or spore chain counting & reporting rules
Believe it or not some mold test labs count the four spores seen at left as "one" particle because they occur in a single cluster.
Similarly, and more important, some mold test labs count a chain of connected mold spores such as Aspergillus spores or Penicillium spores as "one" spore.
Inconsistencies in how labs count clusters and chains of particles can make a very large difference in the airborne particle concentration reported.
We count the individual spores in clusters or chains, and we use that number in our airborne particle concentration calculations.
But because the presence of Pen/Asp spores in chains in an indoor air sample screening for building mold contamination is very important, we also report the presence of spores in chains as a separate technical examination.
Airborne Particle Trace Count Stopping Rules
Airborne Particle Trace Count Stopping Rules may be considered. (when 200 particles/M3 are reached continue that pass across the particle trace to completion,
record the total count, calculate the total based on % of trace read, and
express it as a minimum with citation of stopping rule.)
IAQ Investigation and Airborne Mold or Particle Level Reporting
Also see ACCURACY vs PRECISION of MEASUREMENTS where we argue that measurements should be reported to include their percentage of error or a +/- figure to give a realistic understanding of the actual reliability of the data.
Indoor Air Quality Sampling Equipment Calibration Procedures
Also see the following forensic lab & microscopy equipment calibration
and adjustment details in these individual lab equipment procedures notebook or policy documents, including the latest microscope calibration
Procedures Microscopy Count Calibrate ™ directory
including Trace calculations recap.doc (this file in non-html form)
Procedures Field ™ directory @SampMeth.doc (field
method descriptions, comparisons) including bulksamp.htm (client-submitted
tape sample procedure) and IAQMethods.htm (equipment lists) and see LAB & FIELD IAQ EQUIPMENT SOP for notes on air sampling equipment calibration.
Particle Identification ™ directory (disk library
and reference texts in lab)
Review microscope setup, Kohler illumination, objective centering, stage micrometer calibration of eyepiece reticule scale, and other preparation procedures in
the lab notebook dedicated to each microscope.
See LAB PROCEDURES MICROSCOPE TECHNIQUES for a discussion of microscope adjustment, setup, and calibration procedures. For each microscope (or other equipment) the lab maintains a procedures manual that gives these details as well as records of calibration and adjustment dates and results.
Olympus Microscope Operation
Polam Microscope Operation
Stereo Microscope Operation
Projecting Microscope Operation
Review objective/eyepiece field width measurement data at spread sheet dedicated to each microscope
Lab Chemicals for Particle Sample Examination
Review list of chemicals, uses, preparations in the Lab Procedures
™ Chemistry & Slide Preparation notebook.
Review the MSDS for each lab
chemical in the Lab Supplies MSDS notebook. Key files:
Other files in directory Procedures Lab SOP Chemistry
Procedures for Qualitative Building Surface Particle Sample Analysis or Vacuum Sample Analysis for Surfaces, Carpets, Soft Goods
Tape or vacuum cassette
(tape, Air-o-Cell, or filter cassette) samples are prepared using lab SOP
for each sample
type. Qualitative analysis and
characterization is described in each lab report. Quantitative analysis of
surface tape samples is highly questionable since particle density across a
building surface cannot be assumed to be uniform.
For Air-o-Cell or MCE filter
cassettes, scan the entire trace at low magnification, 40x or 100x, for
consistency and for unusual particle clusters to be considered in selecting
areas for cross-scans.
For tape samples, the sample
may be examined using the low-power stereo microscope to evaluate sample
consistency and to select a sample tape segment most-likely to contain
significant particles. A 1 cm segment is selected for analysis. If the tape
appears to contain a variety of particles by texture, color, etc., multiple
1-cm segments may be required for analysis.
Scan across the trace
beginning at one end of the selected area, to and from areas where no particle
are visible while crossing the trace. See separate counting rules and stopping
rules (if any stopping rules are to be applied), obtaining raw counts of
significant or other particles of interest in each pass and totaling for the
trace. See Particle Counts.xls for worksheets used for this purpose. The
worksheet automates particles/M3 of air when the raw counts and volume of the
sample are entered.
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.
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
how do I remove all the bad airborne particles that are making me sick?
2015/10/24 colleen said:
I've tried many different approaches in removing some sort of airborne particles that has invaded my vehicle and has multiplied in every apartment i've lived. this happens to be number three since March 2015 where i was exposed to many fungus spores one is black toxic mold according to experts report. need help with removal. I've seen all kingdoms. now what's next,being the host? Occasionally i feel them up and down my back
You cannot remove all airborne particles unless you live in a building or room similar to a computer "clean room" with very extensive air filtering and positive interior air pressure - particles occur in outdoor air; IF there is a problem with high levels of unsafe indoor air particles one needs to find and remove the source, such as mold contamination on drywall due to building leaks.
About what you feel on your back, start with a consult with your doctor. Ask her if your complaint is likely to have an environmental cause.
Ask a Question or Search InspectApedia
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
 "Particulate Matter Sampling", ATPI 435: Atmospheric Sampling Course, U.S. EPA, retrieved 9/9/12, original source: http://www.epa.gov/apti/Materials/APTI%20435%20student/Student%20Manual/Chapter_4_noTOC-cover_MRpf.pdf [copy on file as Particulate_Matter_Sampling_USEPA.pdf.]
 For most-recent microscope optical measurements: field width data and calibration see: Olympus-CH-2.xls & Polam Optics.xls Calibration is repeated no less than when an objective is removed/replaced or other microscope optical or
stage components are removed/replaced, or if a new technician is employed.
For most-recent calculations of % of trace represented by n cross-scans see: Particle Counts.xls
For automated calculations of particles or spores per cubic meter of air (spores/M3)
from raw airborne particle counts see: @SporeCountWork.xls
For spore count worksheets see: sheet 2 of @SporeCountWork.xls
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Kansas State University, department of plant pathology, extension plant pathology web page on wheat rust fungus: see http://www.oznet.ksu.edu/path-ext/factSheets/Wheat/Wheat%20Leaf%20Rust.asp
"A Brief Guide to Mold, Moisture, and Your Home",
U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
US EPA - Mold Remediation in Schools and Commercial Building [Copy on file at /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
US EPA - Una Breva Guia a Moho - Hongo [Copy on file as /sickhouse/EPA_Moho_Guia_sp.pdf - en Espanol
Allergies, Allergens, Allergy Testing in Buildings - References & Products
Allergen Tests in Buildings advice about how to test, what to look for, in evaluating the level of dog, cat, or other animal allergens in a building
"IgG Food Allergy Testing by ELISA/EIA, What do they really tell us?" Sheryl B. Miller, MT (ASCP), PhD, Clinical Laboratory Director, Bastyr University Natural Health Clinic - ELISA testing accuracy: Here is an example of Miller's critique of ELISA
http://www.betterhealthusa.com/public/282.cfm - Townsend Letter for Doctors and Patients
The critique included in that article raises compelling questions about IgG testing assays, which prompts our interest in actually screening for the presence of high levels of particles that could carry allergens - dog dander or cat dander in the case at hand.
http://www.tldp.com/issue/174/IgG%20Food%20Allergy.html contains similar criticism in another venue but interestingly by the same author, Sheryl Miller. Sheryl Miller, MT (ASCP), PhD, is an Immunologist and Associate Professor of Basic and Medical Sciences at Bastyr University in Bothell, Washington. She is also the Laboratory Director of the Bastyr Natural Health Clinic Laboratory.
Allergens: Testing for the level of exposure to animal allergens is discussed at http://www.animalhealthchannel.com/animalallergy/diagnosis.shtml (lab animal exposure study is interesting because it involves a higher exposure level in some cases
Allergens: WebMD discusses allergy tests for humans at webmd.com/allergies/allergy-tests
Animal Allergens: Dog, Cat, and Other Animal Dander - Cleanup & Prevention Information for Asthmatics and regarding Indoor Air Quality.
Recognizing Allergens: What various indoor allergens look like - identification photos to help identify pollen, dust mites, animal dander, toxic or allergenic mold - Common Mold and other Allergens, Irritants, Remedies & Advice
Rodent control issues, including dander, fecal, and urine contamination of Buildings and Building insulation are discussed at our
Associations: Sick House, Sick Building, SBS - Air Quality, Government, Private Associations and Information Resources
Atlas of Clinical Fungi, 2nd Ed., GS deHoog, J Guarro, J Gene, & MJ Figueras, Centraalbureau voor Schimmelcultures, Universitat Rovira I Virgili, 2000, ISBN 90-70351-43-9 (you can buy this book at Amazon) - The Atlas of Clinical Fungi is also available on CD ROM
"A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
"Disease Prevention in Home Vegetable Gardens,"
Department of Plant Microbiology and Pathology,
Department of Horticulture, University of Missouri Extension - extension.missouri.edu/publications/DisplayPub.aspx?P=G6202
Fifth Kingdom, Bryce Kendrick, ISBN13: 9781585100224, is available from the InspectAPedia online bookstore - we recommend the CD-ROM version of this book. This 3rd/edition is a compact but comprehensive encyclopedia of all things mycological. Every aspect of the fungi, from aflatoxin to zppspores, with an accessible blend of verve and wit. The 24 chapters are filled with up-to-date information of classification, yeast, lichens, spore dispersal, allergies, ecology, genetics, plant pathology, predatory fungi, biological control, mutualistic symbioses with animals and plants, fungi as food, food spoilage and mycotoxins.
Ozone Warnings - Use of Ozone as a "mold" remedy is ineffective and may be dangerous.
Rot concerns in buildings-some building mold such as Meruliporia incrassata "Poria" risks serious rot and hidden structural damage
US EPA: Una Breva Guia a Moho - Hongo [Copy on file as /sickhouse/EPA_Moho_Guia_sp.pdf - en Espanol
OTHER IAQ ISSUES: How To Find and Address Other Indoor Air or Indoor Environment Contaminants Besides Mold
Mold or allergens may not be the only or even the main indoor environmental contaminant. Don't let media attention to mold
cause so much enviro-scare fear that other, possibly more urgent hazards go un-addressed.
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
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Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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