Vacuum cassette test methods for building dust or mold.

This article explains the advantages and shortcomings of using vacuum cassettes or spore traps to collect mold test samples (or other dust or particle samples) from indoor surfaces such as carpets, couches, or multiple hard surface dust samples:

How to do it & Guide to Good Dust Sampling Practices.

In this article series we discuss the validity of nearly all of the popular mold testing methods currently in use, pointing out the strengths and weakness of each approach to mold sampling in the indoor environment, beginning with air sampling for airborne mold levels indoors.

A Guide to Using Vacuum Samples for Screen Buildings for Toxic Mold

[Click to enlarge any image]

15th Annual North Carolina/South Carolina
Environmental Information Association Technical Conference
Myrtle Beach, SC
Daniel Friedman 23 September 2005, Updated 4/14/2009 & 10/5/2012

A collection canister is connected to an air or vacuum pump which is used to draw particles onto a filter-surface or into a special collection container.

A collection device, slide, cassette, or tape are used with a calibrated air pump to collect surface particles.

The lab prepares a slide from the cassette (of the types below) or if an MCE filter cassette was used to collect particles, the lab clears the filter onto a microscope slide, washes the filter onto a microscope slide, or uses another method to transfer particles for examination by microscope for preparation by culture.

Our MOLD INFORMATION CENTER includes more broad discussions of the overall approach to building investigation, as do many expert references cited at that web.

For a more comprehensive collection information about mold test methods

see INDOOR AIR QUALITY METHODS COMPARED. For more on "mold classes" (Cosmetic mold vs. allergenic mold vs. toxic or pathogenic mold)

see MOLD CLASSES, HAZARD LEVELS and more references such as a Mold Action Guide are at the end of this document.

Using a simple portable pump calibrated to a known flow rate allows rough estimation of particle density per square inch of surface tested if that analysis is needed.

People using this approach may make use of a disposable paper square template that defines a precise surface area to be vacuumed (photo above left). In our opinion a precise quantitative approach to surface vacuuming is silly because there is normally large particle variation over building surfaces for many reasons. But the approach is useful to screen for high levels of particular particles (such as mold spores, animal dander, insect allergens).

Our photo (left) shows five vacuum test areas on a hallway carpet during a study conducted by the author to examine the variation in particle deposition by foot traffic in a residential hallway.

Our hypothesis was that more outside dirt and debris could always be found in the center of the main path of foot traffic even though that area also received more aggressive vacuum cleaning than the hallway sides. We have tested carpeting before and after various types of cleaning and after suffering various types of contamination.

Surface vacuuming for mold

We emphasize that in this article we are discussing surface vacuuming to collect particles from an exposed surface onto which the vacuum device and collector can be placed directly.

This is an effective and useful particle or mold sampling method.

We are not referring building wall or ceiling cavity vacuuming methods that attempt to draw air and particles from the building cavity through a punctured opening and tube into a collecting device - an approach that our test found was ineffective.

We discuss building cavity vacuuming below

at VACCUMING BUILDING CAVITIES

Vacuum samples can be useful for testing soft goods (clothing, bedding, curtains, carpets) for high levels of contaminated spores in a qualitative approach.

We particularly like vacuuming a number of surfaces in an area using a single collection device as a less-costly way to make a more confident inspection of the level of contamination by moldy dust in buildings with a known problem.

We also use this method as part of a mold clearance inspection to evaluate the thoroughness of both the containment system and the general cleaning effort.

For example we may collect a sample of vacuumed surface dust from 10 different surfaces in 5 rooms on a floor of a home, forming a more broad screen for moldy dust than single tape lifts of surface dust.

We've found wide variety in levels of mold found growing in or on carpets, depending on a number of variables including even the level of other dirt present in the carpeting.

Some experts question this measure.

Carpet vacuuming for mold is interesting as a pre and post remediation baseline data source for areas out of the remediation/containment area, but for any carpet this method quickly overloads a particle sampler.

The Burkard personal air sampler (photo above) can also be used to vacuum particles from surfaces provided that a strong air flow is not required to lift the particles from the surface (this device pumps at 10 lpm).

Shortcomings of surface and carpet vacuuming for mold

1. Vacuuming will not collect identifying structural components 
   
   of mold as well as tape and will almost certainly damage or destroy the structures which it collects, imposing some limits on identification


2. Vacuuming will not collect all of the material on a hard surface 
   
   (which tape handles well). Particles which are easily lifted by the airflow into the canister will be over-represented compared with sticky particles which are adhered to the test surface.
   
   This problem is particularly sensitive to the flow rate (LPM) used. A low-flow rate (1LPM) avoids a sample overload problem (too many particles, can't read the sample) but may fail to collect or under-collect certain particles.
   
   A high flow rate improves particle pick-up but then limits the number of sample sites (increasing test cost) in order to avoid sample overload. We suspect that no vacuum method we have tested could reliably pull mold or debris reliably from deep inside a heavy upholstered couch.


3. Carpet vacuums and some furniture or drapery vacuums will either be overloaded 
   
   or restricted to culture (to which we have already objected).

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Need guidance on dust sampling or testing methods

I have looked at several articles, but the answer for me is not that easy.

We live in a 1528 Sqft home. And the dust that gets in our home is just unbelievable. With the new A/C unit we recently put in, the dust has gotten worse, but I kin of expected that as a new unit is probably pulling more air in and out.

I can put a 20" box fan in the middle of a room with a merv 11 filter on the back and within 3 weeks the filter will be dirty.

The 2 rooms left with carpet are the worse and i know the carpet does not help, especially since is really old. The original duct work ( 30 years old ) cannot be accessed in the attic.

My question is where do I start? We have had an environmental company test and seal and the reduction got down to about 28% from 45% loss. I feel from reading a good place to start may be placing the dust capture squares to actually identify what kind of dust is present. Hopefully dust on a piece of furniture will work also, as that is not hard to get.

Thanks so much for any direction you can offer. Jim 2014-08-01 by Jim B.

Reply by (mod) -

Jim

Your question about house dust in our article on dust sampling methods may be confusing to some readers.

Basically to control a dust problem I'd look first for

1. the principal source of the dust - if it's not obvious then collect a couple of settled dust samples for lab analysis to determine the dominant particles.

With the source identified we may understand that source removal or amendment are in order.

I like to clean a horizontal surface, then let dust accumulate for a week or two for sampling. That way I know we're looking at current conditions.

2. Improved air filtration and fan use to reduce indoor dust levels. See

AIR FILTER OPTIMUM INDOOR about cascaded air filters

and see

BLOWER FAN CONTINUOUS OPERATION about continuous blower fan operation.

As you say the dust is worse since installing [central?] air conditioning, I'd look close to the return register to see if there is a particular dust source nearby.

...

Continue reading at VACUUMING BUILDING CAVITIES or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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Recommended Articles

• DUST SAMPLING PROCEDURE
• INDOOR AIR QUALITY METHODS COMPARED
• MOLD TEST PROCEDURES
• TECHNICAL & LAB PROCEDURES
• MOLD / ENVIRONMENTAL EXPERT, HIRE ?
• VACUUMING BUILDING CAVITIES
• VACUUM CASSETTE FILTER SAMPLE TESTS for DUST / MOLD
• VACUUM SAMPLING EQUIPMENT, DIY
• VACUUM TEST INSULATION CONTAMINANTS

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Citations & References

In addition to any citations in the article above, a full list is available on request.

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