Airborne Particle Trace Calculations Recap - how to calculate airborne particle concentrations for mold, IAQ, allergens, or other forensic particle studies - A Laboratory SOP
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Airborne Particle Trace Count of Particles per Cubic Meter of Air: (particles/M3 of air) Procedure
- How to calculate the level of airborne mold or other particles indoors
- Detailed procedure for computing the count of particles per cubic meter of air - indoor air quality and mold test lab procedures
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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 American Home Service Company - AHS - General Lab Procedure. For clarity, some topics are
addressed in separate documents listed here.
© Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.
Indoor Air Quality Sampling Equipment Calibration Procedures
review equipment calibration
and calibrator details in Equipment Procedures notebook, latest calibration
dates in
- Procedures Microscopy Count Calibrate ™ directory
including |
Trace Calcs recap.doc (this file in non-html form)
- Procedures Lab SOP Chemistry ™ directory Lab SOP - @LAB SOP.doc
- Procedures Field ™ directory @SampMeth.doc (field
method descriptions, comparisons) including bulksamp.htm (client-submitted
tape sample procedure) and IAQMethods.htm (equipment lists)
-
Particle Identification ™ directory (disk library
and reference texts in lab)
Microscope calibration:
review microscope setup, Kohler illumination, objective centering, and other preparation procedures in
the lab notebook dedicated to each microscope.
Quantitative Particle Counting:
review details in Equipment Procedures notebook, writeups
per/sampler to review slide handling and counting procedural details beyond the
example given below.
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:
- @LABChemicals.doc
- @slide preparation.doc
- Meltmount tips.doc
- Other files in directory Procedures Lab SOP Chemistry
Qualitative Surface or Vacuum Sample Analysis:
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.
For documentation and
training purposes some example manual calculations are shown below.
Chemical and mechanical details of slide preparation of
various media are not addressed in this document.
A Detailed Example for Airborne Particle Counting using the Allergenco Time-Lapse Impaction Sampler
Sample Volume in Liters = (Sampler run time in minutes x calibrated sampler flow rate in LPM)
1. 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]
i.e. 15 lpm=.015 M3/m
3. Trace length counted = (Microscope field diam) x (#
cross-width traverses)
4. Particles / M3
= (raw particle count / portion of trace counted) x
(1000L/M3 / sample volume in L)
Example: If an
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
trace
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.
[653particles
/ (.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.
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 Concentrations
Objective is to count 25% of the trace.
20% may be used in difficult cases.
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
requirements
See prototype Field Investigation, Lab Determination,
Clearance report prototypes.
Air Sampling Equipment Trace Dimensions
This information is required to complete airborne particle
concentration calculations.
See www.inspect-ny.com/sickhouse/IAQEquip.htm
to determine airborne particle trace dimensions for various air sampling equipment.
More Information on Building Diagnostic Inspections and Repairs
- Lab procedures: Airborne Particle Trace Calculations Recap - how to calculate airborne particle concentrations for mold, IAQ, allergens, or other forensic particle studies - A Laboratory SOP
- Lab procedures: Calibration and Mold Test Laboratory SOP documents?
- Lab procedures: Cargille meltmountTM slides for rapid field or laboratory use, how to prepare
- Lab procedures: Microscopy - Microscope techniques and laboratory procedures for indoor air quality, toxic mold identification, & bioaerosol investigations
- Lab procedures: Slide preparation - tips on mold lab procedures?
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